The Agroecology Of Corn Production In Tlaxcala, México

8/16/2019 The Agroecology Of Corn Production In Tlaxcala, México

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H u m a n E c o l o g y Vo l . 1 5 N o . 2 1 9 8 7

T h e A g r o e c o l o g y o f C o r n P r o d u c t i o n

in T l a x c a la M e x i c o

M i g u e l A A l t i e r i 1 a n d J a v i e r T r u j i l lo 1

The primary components o f Tlaxcalan corn agriculture are described includingcropping patterns employed resource management strategies and interactions ofhuman and biological factors. Tlaxcalan farmers grow corn in an array of poly-culture and agroforestry designs that result in a series of ecological processesimportant fo r insect pest and soil ferti lity management. Measurements der-ived fr om a few selected fie lds show that trees integrated into cropping sys-tems modify the aerial and soil environment of associated understory cornplants influencing their growth and yields. With decreasing distance fr omtrees surface concentrations o f most soil nutrients increase. Certain tree spe-cies affect corn yields more than others. Arthropod abundance also variesdepending on their degree o f association with one or more of the vegetation-al components of the system. Densities of predators and the corn pest M a cr o d a c t y l u s sp. depend greatly on the presence and phenology of adjacentalfalfa strips. Al though the data were derived from nonreplicated fields theynevertheless point out some important trends information that can be usedto design new crop associations that will achieve sustained soil fer til ity andlow pest potentials.

K E Y W O R D S : c o r n a g r o e c o s y s t e m ; a g r o e c o l o g y ; p o l y c u l t u re s ; ag r o f o r e s t ry ; t r ad i t i o n a l f a r m i n g .

I N T R O D U C T I O N

Tr a d i t io n a l f a r m i n g s y s te m s i n t h e T h i r d W o r l d h a v e e m e r g e d o v e r c e nt u r ie s o f c u l tu r a l a n d b i o l o g ic a l e v o l u t i o n a n d r e p r e s e n t a c c u m u l a t e d e x

1 D i v i s io n o f B i o l o g i ca l C o n t r o l , U n i v e r s i t y o f C a l i f o r n i a , B e r k e l e y, C a l i f o r n i a 9 4 7 2 0 .

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0300-7839/87/0600-0189505.00/0 9 1987 Plenu m Pub lishingCorporation


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19 A l t i e r i and Tru j i l l o

per i ences o f in t e rac t ing wi th the env i ronment by f a rmers wi thou t access toexternal inputs , capi ta l , or sc ienti f ic know ledge (Chang , 1977; W ilken, 1977;Egger, 1981). Such exper i ence has gu ided fa rm ers in man y a reas to deve lop

sus ta inab le ag roecosys tems , managed wi th loca l ly ava i l ab le r e sources andw i t h h u m a n / a n i m a l e n e rg y ( H a r w o o d , 1 97 9; K le e , 1 98 0). T h e s eagroeco sys tem s , based o n the cu l t iva t ion o f a d ive r si ty o f c rops in t ime andspace , have a l lowed t r ad i t iona l f a rmers to max im ize ha rves t s ecur i ty wi thl imi ted resources and space (Clawson, 1985) .

As change occurs in the f ace o f inev it ab le ag r icu l tu ra l m odern iza t ion ,gene t ica l ly va r i ab le ind igeneous va r ie t ie s o f c rops a re be ing rep laced by newhigh-yie ld ing ones (H ar lan , 1976), and k now ledg e of the tradi t iona l c ro p-p ing pa t t e rns and m anag em ent p rac t i ces and the eco log ica l r a t iona le beh ind

them are be ing gradual ly los t (Cham bers , 1983). M ode rn agr icul tura l develop-men t , charac ter ized by broad-sca le technologica l recom m enda t ions , has la rge-ly ignored the env i ronm enta l , cu l tu ra l, and soc io econ om ic he te rogene i tytyp ica l o f t r ad i t iona l ag r i cu l tu re (Co nw ay, 1985). La rge - sca le p rom ot io n o fun i fo rm c rop va r i e ti e s, t echno log ies , a nd fa rming sys tems , l a rge ly inacces -s ible to the g rea t ma jo r i ty o f peasan t s , has c rea ted a n inev i t ab le mismatch-ing o f ag r i cu l tu ra l d eve lop m ent and the n eeds and po ten t i a ls o f loca l peop le(deJanvry, 1981) .

A m ore app ropr i a t e ag r i cu l tu ra l s t r a tegy requ ire s a ho l is ti c app roach ,sensi tive to the com plex i ti e s o f ag roeco log ica l and soc ioeco nom ic p rocesses ,which can l ead to the des ign o f f a rming sys tems and t echn iques t a i lo red tothe needs o f specif ic pea sant gro ups and regional agroeco sys tem s (Al tie ri andAn derson , 1986). A cha l lenge o f th i s na tu re r equ i re s an under s t and ing o fthe f ea tu res o f tr ad i t iona l ag r i cu l tu re such as the ab i l i t y to be a r r i sk , l a borcons t r a in t s , d i e t p re fe rences, and the spa t ia l and t emp ora l dy nam ics o f sym-b io t i c c rop mix tu res .

Al tho ugh as sessmen t s o f t r ad i tiona l kno w-h ow and an th ropo log ica l ,geograph ica l , an d e thno bo tan ica l s tud ies o f t r ad i t iona l f a rming pa t t e rns inthe Th i rd W or ld a re numerous (Bye , 1981 ; Denevan , Treacy, Alcorn , Pad och ,Den s low, and F lo res Pa l t a n , 1984; Klee , 1980 ; Brok enshaw , W ar ren , andW erne r, 1980; Po sey , 1983; Ve rme er, 1979; W eins to ck, 1983; Alc orn , 1981,1984; Brush , Carney , and H ua m an , 1981; A lverson , 1984; G rossm an, 1984;Gl ie s sman , G arc ia , and Am ad or, 1981; M ar ten , 1986). Th ey have ma in lyf o c u s e d o n t h e p a t t e r n s o f b e h a v i o r f o l l o w e d b y a n e t h n o g r a p h i c u n i t in t h erea lm o f ag r i cu l tu ra l t echno log y, w h ich r e su lt i n un ique se ts o f l and u t i li za-t ion in t ime and space , s easona l d i s tr ibu t ion o f l abor, n u t r i ti on , and o the rneeds . Rare ly have s tud ies examined the eco log ica l m echan i sm s tha t under-l ie the sus t a inab i l ity o f these ag roecosys tem s . S imi la r ly, ag ronom ic and eco-n o m i c e v a l u a t i o n s o f t r a d i t i o n a l a g r o e c o s y s t e m s a r e r o u t i n e l y c o n d u c t e ddur ing Fa rming Sys tems Resea rch (FSR) p ro jec t s (Byer l ee , Co l l inson ,


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C o r n P r o d u c t i o n i n T l a x c a l a 9

Perrin, Winkelman, and Biggs, 1980; Harwood, 1979; Shaner, Phillip, andSchenhl, 1982; Zandstra, Price, Litsinger, and Morris, 1981). Although FSRsurveys analyze the natural and socioeconomic circumstances affecting small

farms and attempt to involve the farmers themselves in all stages of theresearch and development process, their emphasis on higher yield inevitablystill leads to the continual recommendation of high input technology Oasa,1985), with no apparent understanding of the ecological processes involved.

Although greatly modified, most traditional agroecosystems still utilizeminimal inputs, lack continuous disturbances, and exhibit complex interactionsamong and between people, crops, soils, animals, etc., which makes them uniquesettings from which to extract ecological principles for the design of new, im-proved, and locally adaptable sustainable agroecosystems Altieri, 1983). There-

fore, it is crucial to ecologically analyze traditional farming systems, not onlyto evaluate their properties of stability, equitability, and sustainability, but alsoto determine which elements of resource use and conservation should be re-tained during the course of agricultural modernization.

With this in mind we studied the agriculture of the state of Tlaxcala,Mexico Benitez, 1953; Wilken, 1977). Tlaxcalan farmers have continuouslyfaced problems of low quality natural resources, low soil fertility, and ex-treme climatic limitat ions. They have managed to survive in this fragile en-vironment through a process of ecological modification and adaptation basedon diversified farming, genetic diversity maintenance, and unique land andwater management practices.

As part of a long-term research project begun in 1982, ecology of corn-based traditional farming systems has been studied in order to derive agroeco-logical principles that may serve to guide future agricultural developmentin the region. Corn production is the basis of Tlaxcalan agriculture, and cornfields are diversified at both the species and genetic level. Corn is grown mixedwith annual and perennial plants in polycultural and/or agroforestry pat-terns, and also in genetically complex fields that mainta in numerous geno-types over time and space. These systems provide a unique oppor tunity toexamine the ecological consequences of crop diversity patterns on conserva-tion of soil and water resources, pest regulation, stabilization of production,and on the long-term sustainability of the agroecosystem as a whole. Wequalitatively describe here the general structure and management o f tradi-tional corn production systems. With da ta derived from a few selected fields,we also attempt to illustrate the ecological dynamics of the agroecosystems,with some quantitative descriptions of the influence of vegetational diversi-ty on plant-soil relationships and on the populat ion levels of insect pests andassociated natural enemies. We focused on these processes because they seemto be important indicators of the dynamics of most mixed farming systemsAltieri, 1983, Altieri and Letourneau, 1982).


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9 2 A l t i e r i a n d T r u j i il o

Fig. 1. A descriptive map of Tlaxcala, M exico.

R E G I O N A L S E T T I N G O F T H E S T U D Y

T l a x c a l a is l o c a t e d i n e a s t c e n t r a l M e x i c o i n th e h i g h l a n d s o f t h eNe ovo lcan i c ax i s on t he M esa Cen t r a l F ig . 1 ). Th e s t a t e, s i t ua t ed abo ve 2300m e l e v a t i o n , is b i s e c t e d f r o m t h e n o r t h w e s t t o t h e s o u t h e a s t b y a w i d e f l a ta l lu v i a l c o r r i d o r b o r d e r e d b y lo w - l y i n g hi ll s a n d m e s a s . T h e c l i m a t e o f T l a x -c a la is c h a r a c te r i st i c a ll y t e m p e r a t e s u b h u m i d ) . R a i n f a l l o c c u rs f r o m M a y -O c t o b e r , r a n g i n g f r o m 5 00 m m p e r y e a r e a st o f H u a m a n t l a t o 8 0 0 -1 0 0 0 m mi n t h e s o u t h w e s t . R a i n f a ll v a r i a ti o n s i n t h e m i d - s u m m e r m o n t h s c a n l e a d toe x t e n d e d d r o u g h t s . Av e r a g e m o n t h l y t e m p e r a t u r e s f l u c t u a t e w i t h in a n a r -r o w r a n g e , w i t h J a n u a r y b e i n g t h e c o l d e st m o n t h 0 - 9 ~ a n d A p r i l o r M a yg e n e r a l ly t h e w a r m e s t 1 9 - 2 7 ~ F r o s t s a r e f r e q u e n t a n d a r e p a r t i c u la r l yt h r e a t e n i n g f r o m N o v e m b e r - F e b r u a r y . I n a b o u t 40~ o f t h e s ta t e, it h a il sa n av e r a g e o f 2 - 4 d a y s p e r y e a r A n o n y m o u s , 1 98 1).

T l a x c a l a n s o i ls a re g e n e r a ll y s an d y a n d h i g h ly d r a i n e d , t h o u g h s o m es o il s a r e g r a v e l ly o r r o c k y. D e p t h v a r i es f r o m 1 0 c m i n t h e L i t h o s o l s o f th ew e s t a n d n o r t h c e n t r a l r eg i o n s t o d e e p F l u v is o ls o n t h e p l a in s o f H u a m a n t -l a . M o s t s o i l s a r e i n f e r t i l e d u e t o l a c k o f o rg a n i c m a t t e r. S o i l p H t e n d s t ob e sl ig h t l y a c i d A n o n y m o u s , 1 9 81 ). M u c h o f t h e s lo p i n g l a n d u n d e r a g ri c u l-t u r e i s a f f e c t e d b y e r o s i o n i n d i f f e r e n t d e g r e e s . T l a x c a l a h a s o n l y t w o s u p e r -f ic ia l w a t e r w a y s o f im p o r t a n c e : t h e R i o Z a h u a p a n a n d R i o A t o y a c .s u b t e r r a n e a l w a t e r i s t h e p r i n c i p a l s o u r c e o f s u p p l y f o r a ll t y p e s o f u s e .


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C o r n P r o d u c t i o n i n T l a x c a l a 9 3

More than 70 of the total land area of the state (nearly 2900 km 2)is dedicated to the production of corn, barley, wheat, beans, fava beans.potatoes, and some vegetables (Anonymous, 1984). Less than 4 is irrigat-

ed. Most of the land (71 ) is government owned as part o f the land reformprogram and farmed by e j i d i t a r i o s(Anonymous, 1984). Average farm sizein the state is 4.83 ha, where only a few families are able to produce suffi-cient harvests to both feed themselves and to sell in local markets for addi-tional income. Most must look for off-farm work, many as day laborersO o r n a l e r o s)on other farms, or as workers in nearby cities such as Pueblaor Mexico, D.F. during the off-season. Farm labor is generally supplied byall family members. Many farmers do exchange work with neighbors or otherextended family, especially during peak demand periods such as harvesting.

Rarely is labor hired except by some of the largest landowners.

M E T H O D S

The information presented here was obtained through 3 years of fieldsurveys, biological data collections, reviews of published materials , and in-terviews with farmers, agricultural technicians, and extensionists. Fif ty farm-ers were interviewed throughout the state to ga ther information descriptive

of farm designs, crop patterns, use of local resources, and farmers' prac-tices, as well as to understand why, in light of their particular circumstances,farmers adopt such cropping systems and production methods. The inter-views were also designed to assess the factors affecting farmers' decisionswith respect to the use of crop technologies, and how they avoid risk andadapt to natura l and socioeconomic constraints. Direct interviews and ob-servations provided detailed information about crop management practices,i.e., land preparation, planting, weeding, pest control, fertilization, harvest,etc., their timing, and amount of inputs utilized in farm operations (Byerleee t a l . , 1980).

Field surveys included the general description of the landscape, iden-tification of existing crop patterns, description of cropping systems' deter-minants, and the actual and potential interactions between the variousbiological components in the various polycultures and agroforestry systems(Shaner e t a l . , 1982). Field measurements were conducted in a few selectedfields to quanti fy the effects of trees on chemical and physical soild proper-ties and corn yields, and to elucidate the population trends of pest insectsand associated natural enemies, and the resulting degree of pest damage incorn systems grown under various levels of vegetational diversity.

Since all fields utilized were comprised of simple, nonreplicated ex-perimental units, an inherent complication associated with research in farm-


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94 A l t i e r i and Tru j i l l o

e r s f ie l d s, i n f e r e n t i a l s t at i st ic s w e r e n o t a p p l i e d t o t h e d a t a . H o w e v e r,b i o l o g i c a l k n o w l e d g e a n d i n t u i t i o n w e r e u s e d t o a p p r a i s e w h e t h e r t h e o b -s e rv e d d i f f e re n c e s in m e a s u r e d p a r a m e t e r s b e t w e e n f ie ld s w e r e d u e t o t h e

e f f e c t s o f d i f f e r e n t i a l d i v e r s i f i c a t i o n .

T r e e I n f l u e n c e s o n S o i l P r o p e r t i e s a n d o r n Yi e l d s

I n 1 9 83 , f o u r r a i n f e d c o r n f i e l d s i n s o u t h e a s t e r n T l a x c a l a w i t h s c a tt e r e dc a p u l i n Prunus capuli) a n d s a b i n o Juniperus deppeana) r ee s we re s e l ec t edfo r t he s t ud y (Fa r r e l l , 1984 ).

F o u r s i m i l ar - si z e ( 8 - 1 0 m ) t r e e s o f e a c h s p e ci e s w e r e s e le c t ed i n e a c h

f i e l d . F i v e z o n e s w e r e c h o s e n a r o u n d e a c h t r e e r e p r e s e n t i n g v a r i o u s a r e a so f t re e i n f l u e n c e w i t h i n w h i c h s a m p l i n g w a s c a r r i e d o u t . T h e s e i n c l u d e d t h ec a n o p y z o n e ( C ), m o r n i n g s h a d e z o n e ( S -W ) , a f t e r n o o n s h a d e z o n e ( S -E ) ,r o o t z o n e ( R ) , a n d z o n e o f n o t r e e i n f l u e n c e (N I ; Z i n k e , 1 9 62 ).

Su r f ac e so il s am p le s t o a d ep th o f 15 cm w ere co l l ec t ed a t 2 , 6 , 10 , 14,18, a n d 2 2 m f r o m t h e b a s e o f e ac h t re e a l o n g f o u r r a n d o m l y c h o s e n t r a n -s ec ts . S o i l p r o p e r t i e s m e a s u r e d w e r e : t o t a l n i t ro g e n ( b y m a c r o p k j e l d a h l ) ,w a t e r s o l u b le p h o s p h o r u s ( d e t e rm i n e d c o l o ri m e t r ic a l ly ) , t o t a l c a r b o n ( b y d r yc o m b u s t i o n ) , h y d r o g e n io n a c t i v i t y ( w i t h a g la ss e l e c t r o d e u s i n g a s a t u r a t e d

s o il p a s t e ) , a n d c a t i o n e x c h a n g e c a p a c i t y. E x c h a n g e a b l e p o t a s s i u m , c a l -c i u m , a n d m a g n e s i u m w e r e d i s p l a c e d w i t h a m m o n i u m a c e t a t e s o l u t i o n a n de s t i m a t e d b y a t o m i c a b s o r p t i o n s p e c t r o p h o t o m e t r y (B l a ck , 1 96 5). S oi lm o i s t u r e c o n t e n t w a s d e t e r m i n e d g r a v i m e t r i c a ll y o n s a m p l e s b r o u g h t t oe q u i l i b r i u m o n a s e m i - p e r m e a b l e c e r a m i c p l a t e m a i n t a i n e d a t a p r e s s u r ed i f f e r e n t i a l o f 1 / 3 a n d 1 5 b a r s .

M e a s u r e m e n t s o f d e n s i ty, h e i g h t , a n d g r a i n y ie l d o f c o r n p l a n t s w e r et a k e n w i t h i n t h re e , f o u r , a n d f iv e 4 - m t r an s e c t s r a n d o m l y p l a c e d a l o n g r o w sw i t h i n th e c a n o p y , s h a d e , r o o t , a n d n o n - i n f l u e n c e z o n e s i n m i d - O c t o b e r

a f t e r t h e m a i z e h a d f u l ly m a t u r e d . G r a i n y i el d w a s e s t i m a t e d b y d e t e r m i n i n gt h e l e n g t h a n d b a s a l d i a m e t e r o f e a c h e a r a l o n g t h e t r a n s e c t s u s i n g a r u l e ra n d c a l ip e r s . A g r a i n y i e l d p e r e a r i n d e x w a s o b t a i n e d b y m u l t i p l y i n g l e n g t hb y d i a m e t e r o f e a rs . T h i s m e t h o d w a s e x t e n s iv e l y u s e d d u r i n g t h e P u e b l aP r o j e c t t o e s t i m a t e y i e ld s o f t a rg e t m a i z e f ie ld s ( C I M M Y T, 1 97 4).

T h r e e m a i z e f i e l d s l o c a t e d 1 . 5 - 2 k m e a s t o f C u a p i a x t l a w e r e c h o s e nt o s t u d y t h e p o t e n t i a l e f fe c t s t h a t t y p i c a l m a g u e yAgave s p .) b o r d e r p l a n t -i n g s h a v e o n a d j a c e n t m a i z e c r o p s . T h e fi e ld s w e r e 1 5 0 m x 5 0 m a n d b o r -d e r e d o n b o t h s id es b y a r o w o f 1 . 5 - 2 m h i g h m a g u e y p l a n ts r u n n i n g t h e

l e n g th o f th e f ie ld . T h e o u t e r m a i z e ro w s w e r e p l a n t e d w i t h i n a d i s ta n c e o f1 . 5- 2 m f r o m t h e b o r d e r r o w s o f m a g u e y. A f t e r t h e m a iz e h a d m a t u r e d ,p l a n t d e n s i t y a n d y i el d w e r e m e a s u r e d a l o n g f iv e r a n d o m 4 - m t r a n s e c ts i nt h e o u t e r t w o r o w s o n b o t h s id e s a n d c e n t e r t w o r o w s o f e a c h f ie ld . I n a d d i -


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Corn Prod uction in Tlaxcala 95

t i o n , g r o w t h a n d y ie ld m e a s u r e m e n t s w e r e t a k e n i n v a r i o u s o t h e r t r e e - c r o passoc ia t ions , i nc lud ing co rn f i e lds c l ea red wi th in bo th a sab ino and a i l i t e(Alnusfirrnifotia)woodland and co rn in t e rp lan ted wi th in app le and pea r-

app le o rcha rds .

T h e I n f l u e n c e o f Ve g e t a t i o n a l D i v e r s it yo n I n s e c t P o p u l a t i o n s

Soi l dwe l l ing and fo l i age insec t communi t i e s were moni to red dur ing1982 and 1983 ( f rom M ay -A ug us t ) i n f ive co rn f ie lds o f va ry ing degrees o fvegeta t ional d ivers i ty : corn m ono cul ture , corn s t r ip-cropped wi th a l fa l fa , cornmixed wi th f ava beans , co rn in t e rc ropped wi th app le t r ees , and co rn g row-ing in an ag ro fo res t ry sys t em composed o f sab ino , a l i t e , and capu l in t r ees .

O n a w eek ly bas i s , 20 co rn p lan t s were r and om ly se l ected in the cen te rand bord e r rows o f each co rn f i e ld , and a ll a r th ropo d species p resen t on thesep l a n ts a n d t h e le v el o f p e s t d a m a g e w e r e re c o r d e d . S o il a r t h r o p o d p o p u l a -t ions were m oni to red by rand om ly p lac ing f ive p i t f a ll tr aps in the cen te r o fa l l f i e lds . In the co rn f i e lds , ad jacen t to wood lands and a l f a l f a , f ive add i -t iona l p i t fa l l tr aps w ere r andom ly p laced a long the borde r s . The p i tf a ll s weref i l l ed wi th a mix tu re o f 250 ml wa te r and 100 ml an t i f r eeze , and rep laced

w e e k l y. Tr a p s w e r e t a k e n i n to t h e l a b o r a t o r y w h e r e a r t h r o p o d s w e r e so r t e dand counted (Baars , 1979) .

R E S U LT S A N D D I S C U S S I O N

T h e C o r n A g r o e c o s y s t e m s

The ag r i cu l tu ra l sys t ems o f T laxca la a re c lose ly r e la t ed to the Tequex -

q u i n a h u a c s y s te m , w h i c h i s b a s e d o n t h e p r o d u c t i o n o f a v a r ie t y o f c r o p sand an ima l s a s sembled in seve ra l subsys tems : (1 ) r a in fed annua l c ropp ingsys tem s (parce la de tem pora l ) , (2) k i tchen ga rden (hue r to fam i l ia r ), (3)agostadero, which inc ludes fa l low fie lds , secon dary fores ts , and o ther a reas

for ga ther ing , (4) fores t p lo ts in gull ies an d h i ll sides for f i rew oo d and c har-coa l p rodu c t ion , (5 ) conf ined m anag em ent o f pigs, pou l t ry, r abb i t s , e t c . ,and (6 ) f r ee-g raz ing m anag em ent o f ho r ses , mules , cows , oxen , and goa t s .O u r s t u d y f o c u e s o n t h e d y n a m i c s o f c o rn p i 'o d u c t i o n in p a r c el a s d e t e m -p o r a l , w h e r e c o r n is g r o w n a ss o c i a t e d w i t h a n u m b e r o f a n n u a l, s em i -

pe renn ia l, a nd pe renn ia l p lan t s in po lycu l tu ra l an d / o r ag ro fo res t ry pa t t e rns(Fig. 2).

A c o m m o n c o m p o n e n t o f th e b o r d e r s o f c o r n fi e ld s o n h i ll si de s is t h em aguey , a mu l t ipu rpo se p lan t o f the cen t ra l va l l ey, s ac red to the ea r ly Ind i -


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96 Altieri and Trujillo

Fig. 2. A multiple-use agroecosystem,comprisedby capulin Prunus capulh), tejocote Cratae-

gus mexieana), pear-apple Pyrus communis), and maguey Agave spp.).

ans (Beni tez , 1953) . About 130,000 ha of agr icul tural land in the s ta te havemag uey p l an t ed i n con to u r on s lop ing l and o r a s pa r t o f a t er r ac ing sys tem,a practice that ca n subs tantially l imit soil ero sion (Cr uz, 1949; Do nk in, 1979).Mag uey i s mos t va lued fo r i ts r o le i n t he p rod uc t ionofpulque, a t rad i t iona ldr ink of the reg ion .

Fa rme r s a lso u se mag uey l eaves a s a ri ch o rgan i c am end me n t fo r t he

so i l , to make a s t rong f iber fo r making ropes , l assos , and co l la r s fo r muleteams , as a ho t -b urn in g , low-s mo ke f i re source , and as fo rage for p igs . Th es t rong sp ines have been used as need les , an d the ou te r sk in of the leaves canbe pee led o ff and u sed in cook ing . Magueys a r e a lso a sou rce o f the m uchcove ted gusano de mag uey Hypopta agavis and Aegiale hesperiaris), wormscons ide red to be a de l icacy by m an y M exicans ; in 1983, the va lue of one kgo f worms ma tched t he p r i ce o f 10 kg o f bee f .

Tree s a r e a l so consp i cuous com pone n t s o f t he ag r i cu l tu r a l l andscape .A number of d i ffe ren t spec ies , i . e . , capul in Prunus sp . ) , sab ino Juniperus

spp . ) , t e j oco t e Crataegus mexicana), peach Prunus persica), a n d t e p o z a nBuddleja americana), are integrated w ith corn in a var ie ty of pat terns resem-

bl ing a ver i table cro p sava nnah (Fig. 3) . These t rees are not c om m only plantedby fa rmers bu t a re main ta ined a long f ie ld borders o r l e f t sca t te red wi th in


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Corn Produc t ion in Tlaxcala 197

Fig 3 Corn planted within a woodland of sab noJuniperus deppeana) and capulin Prunus

capuh), conforming a typical agroforestry pattern.

f i elds wi th co rn p lan ted r igh t up to the i r bas e . S t il l h igher t r ee densi t ie s ca nh e f o u n d w h e r e n a r r o w f ie l ds h a v e b e en c l e a re d a n d p l a n t e d t o c r o p s w i t h i ndense sab ino and a il it e woodlands . Trees and c orn a re a l so mixed in o rchards ,a n d i n f r u it - g r o w i n g a r e a s s u c h a s C u a x o m u l c o , r o w s o f t re e s in c l u di n g

a p p l e , p e a c h , p l u m , p e a r- a p p l e , a p r i c o t , a n d w a l n u t a r e c o m m o n l y i n t er -p l a n t e d w i t h c o r n a n d a l f a l f a .O u r i n t e r v i e w s r e v e a l e d t h a t f a r m e r s a p p r e c i a t e t h e m u l t i p l e u s e s o f

t r ee s . T h e y v a l u e t h e y e a r- r o u n d v e g e t a t iv e c o ~e r p r o v i d e d b y tr e es f o r e r o -s ion con t ro l , the add i t ion o r o rgan ic ma t te r ( l ea f l i tt e r) f rom semi-dec iduoust rees , and the f ru i t o f noncrop t rees such as capu l in , t e joco te , and peach .Roas ted seeds o f capu l in a re a de l i cacy and a re so ld on many s t ree t cornersin towns and c i t i e s fo r add i t iona l income. Trees a re a l so a source o f fue lwo od an d p ro tec t ive shade dur ing the summ er. In the case o f o rchards , f a rm-

ers fee l tha t by in te rc ropp ing they u t i l i ze l imi ted l and and resources moreeff i c ien t ly. W oo de d a reas a re a lso va luab le sources o f l ives tock food , e spe-c i al ly t h e l o w e r s t r a t a o f g r a ss e s a n d h e r b s g r o w i n g u n d e r t r ee s b o r d e r i n gcornf ie lds .


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98 Altieri and Tru jillo

T r a d i ti o n a l C o r n M a n a g e m e n t P r a ct ic e s

C r o p p i n g P a t t e r n s

O u r s u r v e y r e v e al e d t h a t f a r m e r s c h o o s e t h ei r c r o p p i n g p a t t e r n s b a s e do n l a n d r e s o u r c e s a v a il a b le , t h e p r o d u c t i v e c a p a c i t y o f t h e l a n d , t r a d i t io n a lc u s t o m s , c a s h c o n s t r a i n t s , f a m i l y l a b o r, a n d t h e i r p e r c e p t i o n o f o v e r a l l r is k sa r is i ng f r o m n a t u r a l a n d e c o n o m i c c i r c u m s t a n c e s . I n m o s t a r e as , t h e m a j o rc a u s e o f c r o p f a i l u r e is u n p r e d i c t a b l e r a i n f a l l; t h u s , f a r m e r s s t a g g e r p l a n t -i n g a n d / o r d i v e r s if y c r o p p i n g s y s te m s t o r e d u c e t h e e f f e c ts o f r ai n f a ll u n -re l iab i l i ty.

C o r n i n t e r c r o p p i n g s y s te m s a re n o t c o m m o n l y f o u n d i n T l a x c a l a as i no t h e r a r e a s o f M e x i c o . T h e t ra d i t i o n a l c o r n - b e a n - s q u a s h p o l y c u l t u r e is co n -f i n e d t o s e l e ct e d a r e a s i n h a b i t e d b y in d e g e n o u s p o p u l a t i o n s , p a r t i c u l a r l y int h e B e l e n a r e a a n d t h e d r a i n e d - f i e l d z o n e o f s o u t h w e s t e r n T l a x c a l a w h e r es o il m o i s t u r e i s n o t s o l im i t i n g ( Wi l k e n , 1 9 69 ). M o r e c o m m o n , h o w e v e r, a r em i x t u r e s o f c o r n a n d f r ij o lP h a s e o l u ss p p . ) o r c o r n a n d f a v a b e a n sViciaf a v a ) . T h e p l a n t in g o f c o r n w i t h f r i jo l is d o n e i n th e t r a d i t i o n a l w a y o f s o w -i n g b o t h c o r n a n d b e a n s e ed s in t h e s a m e h o l e ; h o w e v e r , p l a n t in g d e si g n sv a r y d e p e n d i n g o n t h e b e a n v a r i e t y u s e d . U s u a l l y, b u s h b e a n sFri jo l ayo-

cote) a re p l an t ed a t l ower densi ti e s ( abo u t 8000 p l a n t s /h a ) , t ha n m os t c l imb ingb e a n v a r ie t ie s ( m a t e a d o , v e n t u r e r o , g u i a la r g a) , w h i c h a r e u s u a ll y p l a n t e da t v e r y h ig h d e n s it ie s ( 1 0 -1 0 0 , 0 0 0 p l a n t s / h a ) . F a v a b e a n s a r e n o r m a l l y p l a n t e db e t w e e n m o u n d s o f c o r n w i t h i n a g i v en r o w. B o t h t y p e s o f b e an s a r e im p o r -t a n t f o o d s o u r c e s a n d a r e a ls o r e c o g n i z e d f o r t h e i r s o i l - i m p r o v i n g q u a l it i e s( b u e n r a st r o j o ) . T h e c o r n - f a v a b e a n c o m b i n a t i o n p r o v i d e s t h e a d d i ti o n a lb e n e f i t o f ri s k a v e r s i o n i n a re a s t o f r o s t d a m a g e s i n ce f a v a b e a n s a r e f a i r l yt o l e r a n t o f f r o s t c o n d i t i o n s .

T h e r o t a t i o n o f c o r n a n d a l f a l f a is v e r y c o m m o n i n ar e as w i th a v a il a -

b l e i r r i g a t i o n o r w i t h d e e p s o il s c h a r a c t e r i z e d b y s u f f i c i e n t l y h i g h m o i s t u r e -h o l d i n g c a p a c i t y. A l f a l f a i s g r o w n a s a n i m a l f o d d e r a n d p l a n t e d w i t h c o r ni n a s t r ip - c r o p p i n g a r r a n g e m e n t , c r e a ti n g a m o s a i c p a t t e r n i n t h e l a n d s c a p et h a t c h a n g e s e v e r y y e a r , a s c o r n i s g r o w n w h e r e a l f a l f a g r ew t h e p r e v i o u sy e a r a n d vice versa( se e F i g . 2 ). B a s e d o n r e l i a b l e a g r o n o m i c d a t a f r o m s im i -l a r ar e a s , w e e s t im a t e d t h a t , u n d e r T l a x c a l a c o n d i t io n s , a l f a l fa c o u l d f ix u pto 150 k g / N h a , a l m o s t s u f f i c ie n t t o m e e t m o s t o f t h e N r e q u i r e m e n t o f ap r e c e d i n g c o r n c r o p ( S p r a g u e a n d T r i p l e tt , 1 98 6) . O t h e r c r o p s o f t e n g r o w ni n r o t a t i o n w i t h c o r n a r e w h e a t a n d b a r l e y, w h i c h a r e v a l u e d f o r t h e i r su p -

p r e s s iv e e f f e c t o n c e r t a i n w e e d s p e c ie s . T h e r e a r e n u m e r o u s v a r i a t i o n s i n r o -t a t i o n p a t t e r n s , i n c lu d i n g c o r n - b a r l e y (o r w h e a t ) - c o r n , c o r n - f a v a b e a n ( o rf r i j o l ) - c o r n a n d c o r n - f a v a b e a n - b a r l e y - c o r n .


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C o r n P r o d u c t i o n i n T l a x c a la 9 9

Soil Preparation

Farmers usually prepare the soil for planting around December. In slop-

ing lands or very sandy soils susceptible to erosion, the soil is not workedafter harvesting but rather just before planting. Thus, crop residue from theprevious crop is left standing to protect the soil against early spring windsand rain.

Soil preparation generally involves breaking up the larger soil clods,the barbecho and the mixing and leveling of the soil, the rastreo. There arevariations in the practice depending on soil type and availability of equip-ment, but the end result of loosening and leveling the upper 20-30 cm ofsoil is the same. The equipment used includes discs, ploughs, harrows, or

a combination of these. I f a team of animals is used, a plough is generallyused to loosen the soil while a railroad tie is often dragged for leveling.

Planting

The most commonly planted corn variety is the criollo blanco (whiteseeds), which matures in about 6-7 months and gives the highest yield de-pending on environmental conditions. Many farmers, however, prefer to mix

several corn varieties in their fields, especially several types of early-maturingvarieties (violentos) including criollo amarillo and toluqueno (yellow seeds),criollo negro morado or azul (blue-purple seeds), and another white-seededvariety, monte alto de ocho carreras. These mature within about 4-5 monthsafter planting. The high genetic diversity resulting from such mixtures ap-parently provides some degree of risk aversion from diseases, pests, frosts,etc. Farmers normally obtain their seeds by selecting the best grains (xinast-li) from the previous year s harvest, but when the harvest is poor, farmersbuy seeds in the market or borrow from relatives and friends. A few farmers

have recently switched to hybrid seeds, but most recognize the low ecologi-cal amplitude and the high input requirements of these varieties.Considering the unpredictable nature of the weather in Tlaxcala, the

decision of when to plant often represents a big gamble for the farmer. Theobject is to begin early enough to take advantage of a long growing seasonand to harvest before the early fall frosts. Thus, the average planting dateusually occurs in April, although many farmers choose to plant in March.In particularly dry years, the first seeds may not be sown till June. Frostand rainfall risks may be avoided by planting later with an early maturing

variety, although yields may be significantly lower. In years of late rains,farmers often choose to plant barley or wheat rather than corn. In the caseof partial crop failure early in the season, most farmers will replant with


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2 A l t i e r i and Tru j i l i o

the same type of seed or with early-maturing varieties in affected parts ofthe field.

Because the app ropri ate planting time is so dependent on the weather,

farmers have developed unique and elaborate methods for predicting weatherconditions passed from generation to generation. The cabanuelas are oneof these predictive guides and apply to longer-term weather patterns. Thismethod consists of the interpretation of weather conditions during the ini-tial or final 12 days of a given year, including fractions of certain of thesedays. It is believed that the climatic conditions experienced on these daysor factions thereof represent the conditions to be expected during their cor-responding months of the upcoming year.

Farmers have also developed effective ways to predict short-termweather conditions. One of these is the observation of cow milk produc-tion, which according to farmers, changes with weather. The second involvesthe observation of maguey plants. Sometimes referred to as vacas verdes(green cows), they are said to produce more juice than normal with thecoming of rain. When the quantity of juice is less than normal and the in-terior of the bowl takes on a white color, dry days may be expected.

Planting is most often carried out manually with a shovel, althoughmore farmers are now using mechanical planting equipment. Furrows aremade with a plow and seeds generally planted at the bottom of the furrowto a depth of 10-15 cm, depending on soil moisture. Many farmers affirmthat the depth the shovel penetrates depends on the amount of moisture inthe soil, suggesting that they use this method to indicate how deep to plantat that particular time. Seeds are usually planted at a greater depth underdrier soil conditions, especially in sandy soils.Spacing between plants within a given row is variable and depends on whetherseeds are planted in clumps matas) or evenly spaced, on the availability ofwater and nutrients, and, in some cases, whether the corn is grown for fod-der or grain. Matas tend to be spaced about 80 cm apart with 2-4 seeds usuallyplanted together. Plants sown individually are normally 50-60 cm apart. Cornplanted for fodder is sown at much higher densities, with spacings of 25-30cm within the row. Average distance between rows, depending on the sizeof the plow, ranges between 50-90 cm.

Cultivation and Management of Weeds

Three cultivation practices are carried out after initial planting: the es-carda, the labra, and the segunda. The escarda is done when the young plantshave reached a height of about 10-15 cm and transfers soil from the adjacentmound to the furrow, building up soil around the plants for support. The


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o r n P r o d u c t i o n i n T l a x c a l a 2 1

f u r r o w s a l so c o l l e c t w a t e r i n t h e a r e a o f r o o t e x t e n s i o n . T h elabra u s u a l l yoccu r s wh en t he p l an t s have r each ed a he igh t o r abo u t 25 cm. A s l i gh t ly w ide ra n d d e e p e r p l o w i s u s e d t o b u i l d a d d i t i o n a l s o il a r o u n d t h e p l a n ts . T h esegun-

da is t h e l a st p a s s , w h e n c o r n is a b o u t 1 0 0 - cm t al l , w h i c h d e e p e n s t h ef u r r o w a n d b u i l d s u p t h e m o u n d h i g h e r a n d s t e e p e r t o h e l p g u a r d a g a in s tl o d g i n g .

T h e segunda i s a l s o t h e l a s t c u l t u r a l m e a s u r e t a k e n t o s u p p r e s s t h eg r o w t h o f a v a r ie t y o f w e e d s t h a t c o m m o n l y i n v a d e c o r n f ie l d s , i .e . ,Simsiafoetida, Lopezia racemosa, Brassica campestris, Bidensspp . , Cyperuss p p . ,Chenopodium graveolens, Raphanus raphanistrum,a n d Lupinus elegans.A f t e r t h i s p o i n t , f a r m e r s r e c o g n i z e t h a t t h e s e p l a n t s h a v e l i tt le n e g a t iv e e f -f e c t o n c o r n g r o w t h ( M o r e n o , T r u j i l l o , a n d R u i z , 1 9 8 1 ).

F a r m e r s d o n o t r e f e r to t h e s e p l a n t s a s w e e d s ( m a l e z a s ) b u t r a t h e r a sh i e r b a s , a r v e n s e s , o r q u e l i t e s ( w i ld p l a n t s ) ; t h e r e f o r e , m a n y o f t h e s e

p l a n t s a r e d e l i b e r a t e l y l e f t i n t h e f i el d s as a s e c o n d c r o p . M a n y o f t h e s e q u e -l i t e s a r e i m p o r t a n t s o u r c e s o f m i n e r a l s a n d v i t a m i n s s u c h a s c a l c i u m , t h i a -m i n e , r i b o f l a v i n , v i t a m i n A , a n d v i t a m i n C , t h u s i m p r o v i n g t h e n u t ri t i o n a lqua l i t y o f t he d i e t (Bye , 1981). I n f ac t , t he r e is ev idence t ha t T l axca l an f a rm er sa c t u a l l y s p o n s e r w i l d p l a n t s in t h e i r f ie l d s t h r o u g h s e le c ti v e w e e d i n g( Wi l l ia m s , 1 9 85 ). M a n y s p e c ie s o fSolanum, Jaltomata,a n d Physalis a re soa d a p t e d t o t h e t r a d i t i o n a l p a t t e r n s , p e r f e c t l y m i m i c k i n g t h e b i o l o g ic a l cy c leo f c r o p s , t o t h e p o i n t t h a t t h e i r fr u it s m a t u r e w h e n c r o p s a r e r e a d y f o r h a r-ves t i ng (F ig . 4 ) . I n a T l axc a l a ba r l ey f i e ld , Wi l l i ams (1985 ) e s t im a ted a y i e ldo f 1 32 5 k g o f f r u i ts f r o m 4 7 0 0Solanum mozin ianump l a n t s / h a , w i t h n o a p -p a r e n t s i g n if ic a n t i m p a c t o n b a r l e y p r o d u c t i o n . I n t h a t a r e a , f r u i t g a th e r i n ga f f o r d e d a m e a n i n g f u l i n p u t t o a g r i c u l t u r a l s u b s i s t e n c e , s i n c e t h e f r u i t s o ft h e s e a r v e n s e s a r e u s e d f o r d o m e s t i c c o n s u m p t i o n , re s t r ic t e d c o m m e r c i a l i-z a t i o n , a n d f o r c e r e m o n i a l p u r p o s e s ( W i l k e n s , 1 9 70 ). I n t h e ar e a s o f T l a x -ca l a, Con t l a , an d Ap izaco , tw o spec ie sofA m ar an thu s A. Hypochondriacus,a n d A. cruentus)a r e st il l g r o w n a s s o c i a t e d o r i n r o t a t i o n w i t h c o r n , a s f a r m -e rs s ti ll r e c o g n i z e th e r i t u a l a s w e l l a s n u t r i t i o u s ( 1 3 - 1 8 % p r o t e i n ) i m p o r -t a n c e o f a l e g r ia .

C h i c l e Asclepiass p p . ) is t r a d i t io n a l l y u s e d f o r m a k i n g c h e w i n g g u ma n d a s a h e m o r r h o i d a l cu r e a n d ca n b e c o m m o n l y se en s p o n s o r e d w i t hi nm a n y f i e l d s . N o p a l Opuntia s p p .) i s p r o b a b l y t h e m o s t w i d e ly u se d o f t h e

w i l d p l a n t s , a l t h o u g h i t is p l a n t e d a s a c r o p i n s o m e a r e a s . T h e l e a v e sa r e p e e l e d a n d c o o k e d a s a v e g e t a b l e a n d t h e f r u i t s ( t u n a ) a r e e a t e n r a w.T h e y a r e a l s o u s e d a s s o il s t a b il i ze r s a n d h a v e b e e n p l a n t e d e x t e n s i v e ly o nt e r r a c e r is e rs e a s t o f T l a x c a l a C i t y. I n c e r t a i n a r e a s s u c h a s Te q u i x q u i t l a a n dA l t a m i r a , a v a r i e t y o f g r as s s p e c ie s a re u s e d f o r r o o f i n g m a t e r i a l in h o m e sand s to r age f ac i l i t i e s . Tab l e I l i s t s s eve ra l w i ld p l an t s and t he i r co r r e spond-i n g u s e s b y T l a x c a I a n f a r m e r s .


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202 l t i e r i a n d Trujillo

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J ] F I M ] A I M I J I J I A I S ] 1 N I D I

Fig. 4. Agricultural and phenological cycle of corn, barley, and wild Solanaceae (Solanumspp .) in Tlaxco , Tlaxcala (Williams, 1985). (1 = sow ing, 2-4 = culti vatio n practices, 5 =corn piling, 6 = harvest, 7 = barbech o (fallow), 8 = mulchi ng,/x = sponta neous emer-gence, O = flowering, [] = fruiting, and 9 = fruit matur ation ).

F a r m e r s d e r iv e o t h e r b e n ef it s f r o m t h e p r e s e n c e o f t o l e r a b l e le v el s o fw i l d p l a n t s i n t h e i r f i e l d s . F o r e x a m p l e , f r i j o l i l l oLupinus s p p . a n d c o l z aBrassica cam pestris)a r e a t t im e s i n t e n t i o n a l l y l e f t w i t h i n c o r n f i e l d s, p l a y -

i n g a b e n e f i c i a l r o l e o n t h e d y n a m i c s o f t h e c o r n p e s t f r a i l ec i l loMacrodac-tyluss p . O u r o b s e r v a t i o n s r v e a l e d t h a t f r a i le c il lo c o n s i s t e n t ly f e d m o r e o f t e no n t h e f l o w e r s o f c o lz a a n d l u p i n e t h a n o n c o r n f l o w e r s, i n d i c at i n g th e p o t e n -t i a l i m p o r t a n c e o f th e s e p l a n t s a s t r a p c r o p s . M a n y p l a n t s a r e a ls o c o l l ec t e da f t e r c r o p h a r v e s t , t o b e w o r k e d i n t o t h e s o i l l a t e r d u r i n g p o s t s e a s o n c u l t i -v a t i o n , t o e n h a n c e o r g a n i c m a t t e r c o n t e n t i n t h e f i e l d s .

Fertilization

T h e u s e o f c h e m i c a l f e rt i li z e r s h a s i n c r e a s e d o v e r t h e l a s t 15 y e a r s d u et o a v a i l ab l e cr e d it . C o m m o n f e rt il iz e rs u s e d in c l u d e s u p e r p h o s p h a t e o f c a p


15/32


Table I. Non-Cultivated (Wild) Plants Utilized by Farmers in Tlaxcala, Mexico

Scientific nam e Com mo n nam e Uses

Amaranthus hypopondriacus ~ AlegriaAmaranthus hybridus QueliteArgemone mexicana ChicaloteAristida divaricata Hierba (Pasto)

de la virgenArtemisa absinthius Ajen joBidens pilosa RosillaBrassica campestris ColzaCedronella mexicana Toronj i lChenopodium ambrosioides Epazote

Chenopodium graveolansCyperus sp.

Epazote de zori l loTule and Coquillo

Encelia mexicana AcahualHedeoma piperita Yerbabuena

Heterotheca inuloides Arnica

Ipomoea starts Cacaxtlapa

Marrubium vulgare Marrubia

Matricaria parthenium Manzanil laOpuntia spp. NopalOriganum vulgare OreganoRuta graveolens Ruda

Solanum mozinianum Tlanochtle

Thymus vulgaris Tomil lo

Ingredient for making candiesForageRemedy for eye and skin infectionsmedicinal

Digestive; kills intestinal parasitesForageBird food, industrial oil sourceAp petizer, digestiveFlavoring, remedy fo r intest inal

parasitesIntestinal parasites, diureticW eaving of petates (bed mats)

and basketsForageIntestinal disorders and bronchitis,

ant ispasmodicHelps blood circulation, recovers

muscles from contusive damagesRelieves stomach and menstrual

pains, sedantAppetizer, remedy for diarrhea,

bronchitis, and live inflamationsAppetizer, ant ispasmodicEdible fruit and leavesCo ndim ent, antisepticFor hepat ic and intest inal pains;

used to control skin liceBerries used for human consump-

tion and ceremonial purposesCures gastroenteritis, antiseptic

This plan t is cultivated in some areas, althou gh p lantings rarely exceed 0.1 h a.

c i u m o r a m m o n i u m , u r e a , a n d a n 1 8 -4 6- 0 m i x t u r e . I f a f f o r d a b l e , f a r m e r sa p p l y f e r t il i z e r t w i c e d u r i n g t h e s e a s o n . T h e f i r st a p p l i c a t i o n c a n b e e i th e ra t th e t i m e o f p l a n t i n g o r d u r i n g t h eescarda T h e s e c o n d a p p l i c a t i o n i s c o m -m o n l y d o n e d u r i n g t h esegunda T h e f e r t i l i z e r is d i s t r i b u t e d b y l a n d , w i t ha g i v e n p o r t i o n d r o p p e d e i th e r a t t h e b a s e o f e a c h p l a n t o r g r o u p o f p l a n t s( m a t e a d o ) , o r in s t r ip s a l o n g t h e f u r r o w ( en b a n d a ) . M a n y f a r m e r s f ee l t h a tc h e m i c a l f e r t i l iz e r s a r e e a s y t o u s e , a n d a r e e f f e c t i v e e v e n w i t h l i t t l e r a i n f a l l .H o w e v e r , o t h e r s c o m p l a i n t h a t f e r t i l i z e rs a r e c o s t l y a n d l a st f o r o n l y 1 y e a r ,

m u s t b e a p p l i e d e a c h y e a r , a n d , i n t h e lo n g te r m , i m p o v e r i s h a n d w e a k e nt h e s oi l b e c a u s e o f t h e la c k o f o r g a n i c m a t t e r i m p o r t . I n a d d i t i o n , m a n y f a r m -e r s i n d i c a t e t h a t e x c e s s iv e u s e o f f e r t il i z e r s b u r n t h e s o i l a n d c r e a t e p r o b l e m sw i t h s a l i n i z a t i o n ; h o w e v e r , w e d i d n o t o b t a i n s c ie n t if i c e v i d e n c e to s u p p o r tt h e s e c la i m s . B a s e d o n o f f i c i a l d a t a , i t s e e m s t h a t f a r m e r s w e r e b e t t e r o f f


16/32

2 4 Al t i e r i and Tru j i l i o

Table II. Production Costs and Y ields of C orn under D ifferent TechnologicalLeveJs in T laxcala, M exico

Co st Yield Net gain(pesos/ha) (kg/ha) (pesos/ha)

Imp roved seed, w ith fertilizer 3495 2534 960Imp roved seed, withou t fertilizer 2074 1537 990Criollo seed, w ith fertilizer 3130 1932 720Cr iollo seed , with ou t fertilizer 2045 1284 740

aUnder rainfed ( temporal )conditions, averag eof 3-yeardata 1973-1976. Ban-rural (1976), Co stos de p roduc ci6n de on ce cultivos bfisicos, Fideicom iso parala realizaci6n de Estudios d e Desarrollo Agropecuario.

e c o n o m i c a l l y b y n o t u s i n g s y n t h e ti c f e r ti li ze r s r e g a rd l e s s o f t h e t y p e o f c o r nv a r i e t y u s e d . A s Ta b l e I I s u g g e s t s, a l t h o u g h , i n t h e s h o r t t e r m , f e r ti li z e rsi n c r e a s e y i e ld s , th e i r u s e d o e s n o t c o m p e n s a t e f o r t h e h i g h e r c o s ts o f p r o d u c -t i o n t h a t t h e s e i n p u t s i m p l y.

L o w i n c o m e f a r m e r s w h o c a n n o t p u r c h a s e c o m m e r c i a l f e r t i l i z e r s s u s -t a i n s o il f e r ti li t y b y c o l le c t i n g n u t r i e n t m a t e r i a l s f r o m o u t s i d e t h e f a r m , s u c ha s m a n u r e c o l l e c t e d f r o m p a s t u r e s o r e n c l o s u r e s i n w h i c h a n i m a l s a r e k e p ta t n i g h t. T h i s o r g a n i c m a t e r i a l is s u p p l e m e n t e d w i t h le a v e s a n d o t h e r p l a n tm a t e r i a ls c o l le c t e d f r o m n e a r b y f o r e s t s a n d f a l lo w f i el d s. O t h e r f a r m e r s re c y -

c l e n u t r i e n t s a m o n g t h e v a r i o u s e n t e r p r i s e s o n t h e s i n g l e f a r m , c o m p o s t i n gw a s t e p la n t m a t e r i a l s w i t h h o u s e h o l d w a s t e s a n d m a n u r e f r o m l iv e s to c k . O l d e rl e av e s f r o m t h e m a g u e y p l a n t a r e es p e c ia l ly f a v o r e d , a n d , i n t h e p r i m a r yp u l q u e - p r o d u c i n g a r e a s , l a rg e q u a n t i t i e s o f le a v e s a r e c o l le c t e d i n p i le s w i t ho t h e r d e b r is a n d s o il a n d a l l o w e d t o d e c o m p o s e b e f o r e b e i n g u s e d as a r ic ha m e n d m e n t . A s th e m a n u r e e f f e c ti v e ly p r o v i d e s n u tr i e n ts f o r a b o u t 3 - 4 y e a rs ,f a r m e r s h a v e d e v e l o p e d y e a r l y ro t a t i o n s , a p p l y i n g a v a i l a b l e o r g a n i c m a t e r i -a l t o l o w - f e r t i l i t y a r e a s o f t h e i r f i e l d s . A f a m i l i a r s i g h t a t t h e b e g i n n i n g o ft h e g r o w i n g s e a s o n i s m o u n d s o f m a n u r e e v e n l y d i s t ri b u t e d o v e r f ie ld s b e-

f o r e b e i n g s p r e a d a n d i n c o r p o r a t e d i n t o th e s o i l ( F ig . 5 ).O n e m e t h o d u s e d t o ta k e a d v a n t a g e o f so il e n r i c h m e n t b y d e c o m p o s -

i n g p l a n t r e m a i n s is t h e p r a c t i c e o f r o t a t i n g t h e p l a c e m e n t o f m a g u e y b o r d -e rs . O n c e t h e m a g u e y s t o p p r o d u c i n g a n d b e g i n d y i n g b a c k , t h e y a r e r e m o v e da n d a n e w r o w p l a n t e d w h e r e t h e c e n t e r o f th e f i e ld u s e d to b e . T h e f o l lo w -i ng y e a r , c o r n is p l a n t e d o v e r th e a r e a o f t h e p r e v i o u s m a g u e y b o r d e r , t h u st a k i n g a d v a n t a g e o f th e o r g a n i c m a t t e r a c c u m u l a t e d o v e r t he y e a rs .

A n o t h e r v e r y o l d m e t h o d o f s oi l e n r i c h m e n t i s t h e u se o f c a t c h m e n td i t ch e s ( c a je t e s) a m o n g f i e l d b o r d e r s a t th e b o t t o m o f t h e s lo p e s . T h e s e d it c h e s

c o l le c t r u n o f f a n d d e b r i s , w h i c h is p e r i o d i c a l l y r e t u r n e d t o t h e f ie l d t o r e p l a c el o s t n u t r i e n t s a n d o r g a n i c m a t e r i a l .

T h e m o s t v a l u a b l e c h a ra c t er i st ic s o f o rg a n i c m a n u r e r e c o g n iz e d b y f a r m -e r s a r e i t s r o l e i n b u i l d i n g u p t h e s o i l , r e t a i n i n g s o i l m o i s t u r e , a n d t h e f a c t


17/32


Fig. 5. Piles of manure (abono) ready to be spread over a field before corn planting in lateMarch.

that i t s effect iven ess las ts fo r abo ut 3-5 ye ars , a l l cr i t ical prop er t ies in sandyso i l s o f low organic mat te r and low CEC. Farmers a l so ind ica te someprob l ems wi th t he u se o f manu re , such a s t he p rod uc t ion o f h i e rbas t hef i r s t year due to the num ber of weed seeds bro ugh t in wi th it and the favor-ing of gal l ina c iega Phyllophaga spp.) , a saprophagus larval pest that is har-bored in o rgan ic was te .

An oth er s t ra tegy used by fa rm ers to sus ta in so il fe r t i li ty is to ex-ploit the ability o f the cropp ing system to reuse its ow n stored nutrients. Based oncurrent info rm at ion o n nutr ient dynamics in agro fores t ry systems (Nair, 1984),i t is reasonable to exp ec t tha t minera l s los t by annua l c rops in T laxca la a rerap id ly taken up by perennia l c rop p lan ts . In addi t ion , the nu t r ien t - robb ingp ropens i t y o f co rn can appa ren t l y be coun te r ac t ed by t he en r i ch ing add i t ionof o rgan ic mat te r to the so i l by assoc ia ted t rees . So i l n i t rogen i s increasedby incorpora t ing legumes ( fava beans or a l fa lfa ) in the corn-cropping sys tem.

Pest Control

The mos t impor tan t insec t pes t o f corn i s the scarab bee t leMacrodac-tylus sp . o r f ra i l ec iUo, which feeds on newly formed female f lowers , thusimpeding g ra in fo rma t ion . A rmyw orms Spodoptera spp.) , cutworms Prode-


18/32

2 6 Al t i e r i and Tru j i l l o

nia sp., Agrotis spp., and Fenia spp.), aphids Ropalosiphum spp.), and gal-lina ciega sporadically cause damage.

Farmers believe that insect pest outbreaks are instrinsically related to

climatic conditions. This is particularly true for frailecillo, armyworms, andred spider mites which tend to be more abundant during drier periods. Farm-ers also feel that the excessive use of chemical fertilizers and not preparingthe soil in time leads to increased numbers o f pests. Some farmers associatethe phase of the mo on at the time of planting with the occurrence of pests,while still others believe tha t the presence of pests is a consequence of theirbad personal behavior, accepting them as a divine punishment.

Some explanations given decreases in pest numbers include climatic con-ditions such as low temperatures and strong an d/ or continuous rain, increas-

ing plant maturity, the coming of a full moon, and certain religious days.Despite credit support and technical assistance from agricultural ex-

tension, pesticide use in corn is still minimal, mostly limited to control se-vere outbreaks of frailecillo, armyworms, and rodents. Tlaxcalan farmerspractice a number of cultural control methods, such as the manual collec-tion of frailecillo from plants, and the direct application of lime onto frailecil-Io in the morning when dew is still present. Most farmers cult ivate after theharvest or before planting to effectively destroy soil-borne insects. Other farm-ers use measures based on religious beliefs. For example, they collect a num-ber o f frailecillo and take them to the local where they are exorcized by oneof the priests and later released back into the fields where they were collected.

In the valley areas, farmers have problems with mice and rats, whereasin the slopes of hill, they tend to have more problems with gophers and squir-rels. Mechanical traps are oft en used to reduce roden t populations. Farmersalso state that the planting of ayacote Phaseolus coecineus) within fieldsis effective in preventing the establishment o f gophers, apparen tly becausethese plants exude toxic substances from their roots. Many farmers recog-nize the importance of birds and snakes in the control of rodents. However,they do not seem to recognize the importance o f insect predators and para-sites in the maintenance of arthropod balance in their fields.

Harvesting

The most common harvesting method is the amogo tad o, which in-volves cutting the corn plant at the base with a machete after the ears havematured. Plants are then collected and piled together in the form of small

teepees (mogotes) and left to dry for 1-2 months, after which time the earsare picked and put in large burlap bags and the plant remains collected forforage. Some farmers, however, let the corn ears dry on the plant in the field


19/32

Corn Production in Tlaxcala 2 7

and later pick them directly. This method is referred to as dobla : the plantis broken toward the middle, doubled over, and left to dry.

Most farmers prefer the amogotado method, because by cutting and

stacking the corn before it has dried completely, they are able to plow theirfields sooner than they could otherwise. This enables them to incorporatethe remaining noncrop plants into the soil when they are still green. Cuttingthe plants early also conserves the leaves, which otherwise might fall off whenharvesting if the plants were dry. However, corn stacked in piles is most sus-ceptible to disease after late rains as well as to damage by mice and rats.

Corn grain is usually stored still attached to the cob in specially builtstorage facilities (cuexcomates) or in one o f the rooms of the house. To pro-tect the grain against potential pest damage, farmers find that temperature

and humidity are the two critical factors to control. In the cooler regionsof higher elevations there are few problems with storage pests, but in warm-er areas, some farmers must resort to chemical insecticides, e.g., Malathion,Lindane, etc., for control of weevils (Circulionidae) and Pyralid moths.

E c o l o g i c a l I n t e r a c t i o n s

The ffec ts of Individual Trees on Soiland Microclimatic Properties

In the soil study plots, a decreasing gradient in all soil properties meas-ured was observed with increasing distance from the trees (Table III). Soilnitrogen, phosphorus, CEC, and calcium gradients were especiallypronounced in the corn-capulin systems, suggesting that capulin had a greaterdegree of influence on soil properties than sabino. Available phosphorus in-creased 4- to 7-fold and nitrogen 1.5- to 3-fold under the trees (Fig. 6). Total

carbon, calcium, magnesium fold, and CEC increased. Potassium levelsdecreased with distance from the trees, although its concentration was higherunder sabino canopies, soil pH and percent moisture were also slightly greaterunder tree canopies. Both trees appeared to influence surface soil propertieswithin a radius of 6-10 m from their base (Farrell, 1984).

The redistribution o f nutrients with litterfall and the resulting accumu-lation of organic matter under the trees are probably the only significant fac-tors determining the observed trends of soil chemical properties (Zinke, 1962).The higher concentration of carbon beneath capulin and sabino followed

an expected trend due to the accumulation of litter by the trees, and a gener-al lack of organic matter used in the management of these agricultural soils.The dis tribution of nitrogen under the trees also seemed correlated with car-


20/32

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21/32


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F i g . 6. C h a n g e i n m a j o r s u r f a c e so i l n u t r i e n ts i n a c o r n - w o o d l a n d a g r o f o r e s t r y s y s te m , w i t h i n -c r e a si n g d i st a n c e f r o m i n d i v i d u a lcapulin Prunus capuh)a n d s a b in o Juniperusspp . ) t r ee s : a ) n i t rog en ,a n d b ) p h o s p h o r u s O Va rr ell , 1 9 8 4 ).


22/32

2 1 A l t i e r i a n d ru j i l lo

b o n a c c u m u l a t i o n . A c c u m u l a t i o n o f e x c h an g e a b l e c a ti o n s a ls o a p p e a r t o b ec l o s e l y a s s o c i a t e d w i t h o rg a n i c m a t t e r.

P h o s p o r u s m a r k e d l y a c c u m u l a t e d b e n e a t h t h e ca p u l i n t re e s, c o r r e s p o n d -

i n g w i t h p h o s p h o r u s a m o u n t s d e p o s i t e d w i th l e a f l it te r. I n a d d i t i o n , t h e h i g h e rp H f o u n d b e n e a t h t h e tr ee s c o m p a r e d t o in th e o p e n s e e m e d to a c c o u n t f o rt h e i n c r e a s e i n p h o s p h o r u s a v a i l a b i l i t y i n t h a t a r e a .

S o il m o i s t u r e d i f f er e n c e s a t t h e 0 - t o 1 5 -c m d e p t h w e r e m o s t p r o n o u n c e da r o u n d c a p u l i n w h e r e m o i s t u r e w a s g r e a t e s t u n d e r t h e t r e e c a n o p y, s o m e -wh a t l es s i n the shade -wes t zone , a nd l owes t in the r em a in ing zones . N o d i f f e r-e n c es w e r e o b s e r v e d b e t w e e n t h e s h a d e - e a s t, r o o t , a n d n o n - i n f l u e n c e z o n e s .A r o u n d s a b i n o t r e e s , s u r f a c e s o i l w a s w e t t e s t u n d e r t h e c a n o p y, s l i g h t l yd r i e r i n th e t w o - s h a d e a n d r o o t z o n e s a n d d r ie s t in t h e n o n - i n f l u e n c e z o n e .

I n a ll z o n e s e x c e p t u n d e r t h e c a p u l i n c a n o p y , s o i l a t 1 5 - 3 0 c m w a s w e t t e rt h a n s u r f a c e so il s. N o d i f f e re n c e s w e r e o b s e r v e d b e t w e e n a n y o f th e z o n e sa t t h i s d e p t h , i n d i c a t i n g t h a t t r e e i n f l u e n c e s d i m i n i s h w i t h d e p t h .

T h e i n c r e a se d c a p a c i t y o f t h e s oi ls u n d e r c a p u l i n a n d s a b i n o t o r e t a inw a t e r c o m p a r e d t o s o i l i n t h e o p e n i s d u e , i n p a r t , t o t h e h i g h e r l e v e l s o fo r g a n i c m a t t e r b e n e a t h t h e t r e e s . M o r e i m p o r t a n t t o t h e u n d e r s t o r y c o r n i st h e a m o u n t o f w a t e r a v a i la b l e f o r u se ( m e a s u r a b l e d i f f e r e n c e i n m o i s t u r eb e t w e e n 1 / 3 a n d 1 5 b a r s ) , w h i c h w a s s o m e w h a t h i g h e r b e n e a t h t h e tr e e s t h a na w a y f r o m t h e m .

C o r n G r o w t h a n d Yi e l d in g r o f o r e s t r y s y s t e m s

C o r n y i e l d s v a r i e d c o n s i d e r a b l y a m o n g t h e s a m p l e d a g r o f o r e s t r y s y s -t e m s ( Ta b l e I V ); h o w e v e r , s in c e t h e d a t a p r o c e e d f r o m n o n r e p l i c a t e d f a r m -e r s f ie l d s , th e e f f e c t s o f t r ee s o n c o r n y i e ld s c a n n o t b e s t a ti s t ic a l ly s e p a r a t e df r o m o t h e r s o u r c es o f v a r i a ti o n , s u c h a s s o il , m i c r o c l i m a t e , a n d m a n a g e m e n td i f f e r e n c e s b e t w e e n a g r o f o e s t r y s y s te m s , w h i c h c a n a l s o d e t e r m i n e s ig n i fi -

c a n t e f f e c t s o n y i el d s . N e v e r t h e l e s s , t h e d a t a p r o v i d e a te n t a t i v e d e s c r i p t i o no f t h e y ie l d p o t e n t i a l s o f e a c h s y s t e m . N o s i g n i f i c a n t d i f f e r e n c e s (p = . 05 )w e r e f o u n d i n e it h e r p l a n t h e i g h t , d e n s i ty, o r g r a in y i e l d b e t w e e n c o r n g r o w -ing a lon g the edg e (y ie ld ind ex = 729 _+ 102) o r in the ce n te r (734 +_ 279)o f o u r s t u d y f i el d s b o r d e r e d b y r o w s o f m a g u e y. T h e c h a r a c t er i s ti c a l ly w i deb o r d e r s tr i p s a l o n g w h i c h t h e m a g u e y a r e p l a n t e d ( u s u a l l y 4 m ) e n s u r e a 1 . 5-t o 2 - m d i s ta n c e b e t w e e n t h e la st r o w o f c o r n a n d t h e m a g u e y b o r d e r. T h u s ,a l t h o u g h m a g u e y p l a n ts h a v e r a t h e r e x t e n s iv e su p e r fi c ia l r o o t s , t h e y d o n o tr e a c h f a r e n o u g h i n t o t h e f i el d t o h a v e a s u b s t a n t i a l e f f e c t o n c o r n p r o d u c -

t i o n w i t h i n t h e b o r d e r e d f i e l d s .D e v e l o p m e n t a n d y i el d s o f e a r l y ( M a r c h ) a n d l a te ( M a y ) p l a n t e d c o r n

w e r e m e a s u r e d i n t h r e e z o n e s i n t w o s a b i n o w o o d l a n d f ie ld s . Z o n e 1 w a sl o c a t e d a l o n g t h e f i e l d b o r d e r s , w h i l e z o n e s 2 a n d 3 w e r e p r o g r e s s i v e l y f a r -


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C o r n P r o d u c t i o n i n T l a x c a l a 2

Ta b l e IV. Average Yield, Height, and Density of Maize Grow-ing in Association with Various Perennial Plants in Agrofores-

try Systems

Height Density numberSystem Yiel& (cm) of plants/ha)

Apple orchard 597 201 34,515Pear-apple orchard 912 245 33,638Sabino woodland

Early-planted 1127 212 51,772Late-planted 573 173 40,950

Ailite woodland 617 247 32,175Maguey 734 162 45,922NI (capulin) b 1005 192 57,623NI (sabino) 1073 191 40,950

Yield expressed as a relative index per 4-m transect (CIMMYT,1974).bYields from the non-influence (NI) zone around capulin and sabi-no are included for comparison and are regarded as equivalentto monoculture yields.

ther from the trees into the center of the fields. In the early planted field,the rate of maize growth was staggered between the zones with maize in zone3 matu ring first, followed by zone 2 and z one 1. There were no differencesin final grain yield between zones 2 and 3, while maize in zone 1 producedabo ut 33% less (750 _+ 95.1) and cente r (573 + 90.9)zones in the late-plantedfields. Throughout the season, corn growth was slowest along the easternfield borders. Corn along the western borders matured sooner than in theother sectors of the field. Grain yield was lower in the eastern border thanin the other two zones. N o differences in yield were foun d a mon g corn plantsgro wn next to a bor de r o f ailite trees (491 +_ 88.3) and c orn plant s gr ow nin the center rows (554 + 116) of the same field. How eve r, the re were sig-nificant differences in plant height; maize along the center row away fromthe trees was 12% shorter than maize near the trees (237 cm).

Yield and height o f cor n plants g rowi ng near a pple trees (516 _+ 59.3)or 5 m aw ay in the center (597 + 191) o f the int err ow strips were similar.Yields of corn intercropped within pear-apple/peach orchards comparedfavorably to yields in other sampled agroforestry systems (Table IV).

Ar thr op od D ynam ics in the Vario~ts Cropping System s

Foliage Arthrop ods.Dependin g on the degree of vegetational diversityand the mana gem ent intensity of the fields, po pulati ons o f beneficial insectsvaried in species numbers and in relative abundance. Dominant predatorsincluded lady beetles Hippodamia convergens, H . K oe be li, Coccinellanugatoria, and Scymnussp.), malachiid beetle Collops sp.), several species


24/32

212 l t i e r i a n d Trujillo

30

28

26

24

22

20

1 8

16

1 4

12

1 0 -

8 -

6 -

4 -

2 -

0

I

,~ ~ u i I i i i

9 10 11 12 13 14 15

W e e k s after planting

70

60

50

o;~ 40

E 3o

20

10

//

i i i i i i i

9 1 1 1 1 2 1 3 1 4 1 5

W e e k s o f f e r planting

Fig. 7. Cumul ati ve mean densiti es per 200 corn plants of: a) the pestiferous scarab beetle Mac-rodactylus sp., and b) the lady beetles Hippodamia convergens and Coccinella nugatoria ina range of corn-cropping systems. [] = corn monoculture, + = corn-l ava bean intercrop-ping, Lk = corn- alfa lfa strip croppi ng, ~, = agrof ores try system of corn under a tree layerof sabino and aili te trees, and • = corn intercropp ed within an apple orchard).


25/32

C o r n P r o d u c t i o n in T la x c a la 2 1 3

o f Carabidae, Staphylinidae, predaceous Hem iptera such as Orious sp.,N a b i s sp . , p redaceous Dip te ra of the fami l ies Syrphidae and Dol ichopodi -dae , and the comm on ea rwig D o r u sp.) . Spiders of the famil ies Lycosidae,

Arg iopid ae, Tethragnatidae, Salticidae, and Th om isidae were also co m m on lyfound on the p lan ts .

Th e var ious vegetat ional arrangements under wh ich corn was fou ndaffected the arthropod fauna in various ways. Some systems exhibited par-t icular ly high populat ions of corn-feeding insects . For example, in our sam-pled fields, the scarab pest, M a cr o d a ct yl u s sp . , was predominant ly moreabund ant in the corn-a lfalfa s t r ip-cropping system , w hereas in the corn sys-tem g rowing adjacent to a i li te woo dlan ds i t reached the lowest densi ties Fig.7 .

The only system that exhibi ted high densi t ies of several entomopha-gous insects was the corn-fava bean-squash polycul ture . Populat ions of coc-cinellid beetles an d o f a cra b spider species Thom isidae) were higher in thispolycul ture system than in corresp ond ing m ono cul tures Fig. 7b) . Th e pre-dator O r i o u s sp . Hem iptera : Antho cor idae) was no t iceably mo re abundantin the corn-orchard and corn-alfalfa systems than in any other system.

The proximi ty of a l fa l fa s t r ips to corn had a fundamenta l e ffec t onthe occurrence of a l l ar thropods. As observed in Fig. 8 , coccinel l ids

18O

170

160

150

140

I 3 0

120

110

1 0 9

90

80

70

60

50

4 0

50

20

10

0

n t e r

Weeks Af te r P lan t ing

A B C D

F i g . 8 . S e a s o n a l a b u n d a n c e s o f a ) p r e d a c e o u s :Orius , b) C o c c i n e U i d a e , c ) , C o l l o p s m a l a c h i i db e e t l e s , a n d d ) t h e p e s t ,M acrodactyluso n c o r n p l a n t s l o c a t e d i n r o w s i m m e d i a t e l y a d j a c e n tt o a l f a l fa s t r i p s a n d i n r o w s l o c a t e d i n t h e c e n t e r o f t h e fi e ld a w a y f r o m t h e a l f a lf a . T h e li n eg r a p h i n t h e u p p e r r i gh t c o r n e r i ll u st r a te s t h e s e a s o n a l a b u n d a n c e p a t te r n s o f C o c c i n e l l i d a ei n t h e b o r d e r a n d c e n t e r r o w s o f c o r n .


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2 4 A l t i e r i and Tru j i l l o

Collops and Orius) were seasonally more abundant (about 30~ on cornplants located in the row adjacent to alfalfa than in the center of the field,away from the alfalfa strip. Macrodactylus,however, showed the opposite

trend. In systems where alfa lfa was periodically cut, we did not observe theseabundance gradients. Apparently, cutting forces arthropods to disperse, andthrough redistribution they attain similar densities throughout the cornfield.

Soil-Dwelling Arthropods.Pitfall catches yielded significantly highernumbers of lycosid spiders in the corn-alfalfa system than in any of the othercorn systems (Fig. 9a). Spider catches remained at similar low levels in allother systems, although at particular times spiders were caught more frequent-ly in the corn-orchard system and in monocultures. Similarly, as in the case offoliage predators, substantially more lycosid spiders were caught in pitfalls

placed in corn rows adjacent to alfa lfa than in the center rows of the corn-field (Fig. 9b). Ground beetles reached highest densities in the corn-fava bean-squash polyculture, apparently encouraged by the shelter provided by thesquash leaves.

DISCUSSION AND CONCLUSIONS

Many of the agricultural systems and practices currently used by Tlax-calan farmers have evolved over many. years of adapting to a fragile environ-ment with soil, climatic, and biological limitations to food production(Williams, 1985). Other practices, however, have been more recently adopt-ed as a result of increasing exposure to modern agricultural technologies.Thus small farmers in Tlaxcala are in a state of transition from the tradi-tional to the modern. Our surveys indicate that the rationales behind tradi-tional farming practices are often rooted in a sophisticated understandingof local environmental conditions and are closely associated with the persis-tence of a strong cultural tradition. Given the available resources and theproduction constraints, these systems and practices often represent extreme-ly appropriate forms of land use (Toledo, Carablas, mapes, and Toledo,1985).

Although the described systems may bear close resemblance to systemsemployed by other peasants in Mexico (Gliessman et al., 198 I; Wilken, 1970),they differ from some traditional models in a number of ways. Notably, cornis grown under a number of temporal (rotations) and /o r spatial arrangements(intercropping, strip-cropping, and agroforestry) instead of in a cyclic poly-culture or agroforestry pattern characteristically used by farmers in thelowland tropics (Beets, 1982). Tlaxcalan systems are genetically diverse, andthis diversity results from interactions far more complex than the randomplanting of numerous corn varieties. Genetic diversity is also enhanced inthe fields as a result of the protection and encourgement of wild plants


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o r n P r o d u c t i o n i n T l a x e a l a

280

2 1 5

2 6 0

2 4 0

2 2 0

2 0 0

1 8 0

;E 160

1 4 0

E 1 2 0

1O 0

8 0

6 0

2 0 + - - - ~ - 49~

0 ~ - - - - - - 7 , , , , ,1 2 3 4 5 6 7 8

We e k

F i g . 9 . a ) N u m b e r s o f l y c o s i d s p i d e r s c a u g h t in p it f a l l t r a p s p l a c e d i n c o r n s t r i p - c r o p p e d w i t halfalfa (A) , intercropped with fava bean (+ ), intercropped with apples (@ ), and grow n in

mon oculture ([]), and (b) numbers of lycosid spiders caught in p itfall traps placed in corn row sbordering alfalfa strips and in row s located in the center of the field.

t h a t , i n a d d i t i o n t o f i r e w o o d a n d m e d i c i n e s , p r o v i d e d i e t a r y d i v e r s i t y. T h u s ,t h e s y s t e m s se r v e a s s o u r c e s f o r l o c a l h o u s e h o l d n e e d s a n d a l so p r o v i d e c a s hr e t u r n s f r o m t h e s al e o f t h e v a r io u s p r o d u c t s .

T h e d a t a p r e s e n t e d a b o v e o u t l in e s o m e o f t h e in t e r a c ti o n s o f h u m a n ,m a n a g e m e n t , a n d b i o l o g i c a l f a c t o r s c o n t r i b u t i n g t o t h e e c o lo g i c a l d y n a m i c so f c o r n - c r o p p i n g s y s t e m s in th e a r e a . A p p a r e n t l y, g r o w i n g c o r n i n a m u l t i -p l e a r r a y o f v e g e t a t i o n a l d e si g n s is a s tr a t e g y w e l l a d a p t e d t o t h e p l e t h o r ao f m i c r o e n v i r o n m e n t s t o w h ic h c o r n p r o d u c t i o n is s u b je c t ed a n d a ne f f e c t i v e w a y t o c o p e w i t h s e a s o n a l i t y a n d v a r i a b i l i t y.

A l t h o u g h t h e f a r m e r s m a y n o t b e a w a r e o f it, w e f o u n d t h a t t he p r o d u c -t i o n o f c o r n i n p o l y c u l t u r e s a n d a g r o f o r e s t r y p a t t e r n s t r ig g e r s a se ri es o f e c o -l o g ic a l i n te r a c ti o n s w i th i m p o r t a n t c o n s e q u e n c e s f o r in s e ct p e st m a n a g e m e n ta n d s o il f e r ti li ty r e l a t io n s . W e r e c o g n i z e , h o w e ~ e r, t h a t o u r d a t a p r o c e e d f r o mw h a t m a y b e c o n s id e r e d a h a n d f u l o f m a i z e fi el d s, a n d t h e r e f o r e w e d on o t p r e t e n d t o m a k e b r o a d g e n e r a l i z a t i o n s a b o u t t h e e c o l o g i c a l d y n a m i c so f c o r n a g r o e c o s y s t e m s . T h i s w o u l d r e q u i r e m o r e r e f i n e d a n d w e l l - c o n t r o l l e dc o m p a r a t i v e e x p e r i m e n t s u n d e r a r a n g e o f s i te - sp e c if ic c o n d i t io n s . O u r s p e c if -ic q u a n t i t a t i v e a n a l y s e s w e r e i n t e n d e d t o i l lu s t r a te s o m e k e y b i o l o g i c a l i n t e r -a c t io n s t h a t r e su l t w h e n T l a x c a l a n f a r m e r s a s s e m b l e th e i r f ie ld s in v a r i o u s


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2 6 A l t i e r i and Tru j i l l o

R A I N~ . S O L A R

R A D I A T I O N

W I N D . - ~ - - - - ~ . ~ I .T C A r N O : :T, n ~ . . ~ E F F E C TS N ~',1. O d p,n go .A S S O C IAT E D | l e e w a r ds i d e

~ R a d i a n te n e rg y S l o w e r d e v e l o p m e n tA S S O C IAT E D ; A i r m o v e m e n t I n m

M i C R O C L I M AT I CvapotransldrCON DITIONS I ,~ M SX ,a lr te m p . . I I I ~ ~

I N U m l I ~ I T

I t C a t io n e x c h a n g ec a p a c i t y / t [ ~ / ~ \ VA~S OC IA'I--cD ~J *~N u t r ie n t c o n c e n t r a ti o n s i

- f p + l1 S o l . . . . t . r ./ ~ M o i s t u r e r e t e n t io n| ~ S u r fa c a te m p e r a t u re

S o l l a t l b l l l z l l t l o n

Fig. 10. A conceptual mo del of the potential influenceof trees on the growing environmentof corn in agroforestry systems of Tlaxcala Farrell, 1984).

p a t t e r n s . O u r d a t a s u g g e s t t h a t , a t le a s t i n o u r s t u d y f ie l d s, tr e e s i n t e g r a t e di n t o c r o p p i n g s y s t e m s m o d i f i e d t h e g r o w i n g e n v i r o n m e n t o f a s s o c i a t e d u n -d e r s t o r y c o r n p l a n t s , i n f l u e n c i n g t h e i r g r o w t h a n d y i e l d s . F i g u r e 1 0 d e p i c t sv a r i o u s w a y s i n w h i c h w e a s s u m e s e l e c te d t r ee s m o d i f y s o il a n d m i c r o c li -m a t i c f a c t o r s . T h e g r e a t e s t m o d i f i c a t i o n a p p a r e n t l y r e s u l t s f r o m t h e i n t e r -c e p t i o n o f s o l a r r a d i a t i o n b y t r e e c an o p i e s a n d d e p o s i t i o n o f l e a f l it te r , b u tt h e a b o v e - g r o u n d t r e e s t r u c t u r e a l s o p l a y s a s ig n i f i c a n t r o l e i n i n t e rc e p t i n g ,co l l ec ti ng , and r ed i s t r i bu t i ng p r ec ip i t a t i on , r educ in g w ind ve loc i ti e s , and con -t r i b u t in g c h e m i c a l e le m e n t s t o t h r o u g h f a l l p r e c i p i t a t io n . B e l o w - g r o u n d , e x -t e n s i v e r o o t s y s t e m s h e l p t o s t a b i l iz e t h e s o il , d r a w n u t r i e n t s t o b e d e p o s i t e dl a t e r o n t h e s o i l s u r f a c e w i t h l i t t e r f a l l , a n d c o n t r i b u t e o rg a n i c m a t t e r t o t h es o i l a s a r e s u l t o f r o o t d e c o m p o s i t i o n .

Wi t h d e c r e a s i n g d i s t a n c e f r o m t r e e s , w e o b s e r v e d a n i n c r e a s e i n s o i lo r g a n i c m a t t e r , t o t a l n i t r o g e n , a v a i l a b le p h o s p h o r u s , e x c h a n g e a b l e p o ta s s i-u m , c a l c iu m , a n d m a g n e s i u m , c a t i o n e x c h a n g e c a p a ci t y, a n d w a t e r h o l d i n gc a p a c i t y. S o i l m o i s t u r e w a s a l s o g r e a t e r b e n e a t h t h e t r e e c a n o p i e s . T h er e d u c e d a m o u n t o f s o l a r r a d i a t io n r e a c h i n g t h e g r o u n d b e n e a t h t h e t re e c a n o -p ie s re s u l te d i n lo w e r e v a p o t r a n s p i r a t i o n a n d a m a r k e d r e d u c t i o n i n s u r f a c es o i l t e m p e r a t u r e s c o m p a r e d t o t h e o p e n c o r n f i e l d . T h e t r e e s a l s o a c t e d a s


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o r n P r o d u c t i o n i n T l a x c a l a 2 7

a b u f f e r a g a i n s t a i r t e m p e r a t u r e f l u c t u a t i o n s a n d , a s a r e s u l t , l o w e r m a x i -m u m a n d h i g h e r m i n i m u m t e m p e r a t u r e s w e r e f o u n d b e n e a t h t h e t re e ca n o -p i e s t h an i n t he o pe n (Fa r r e l l , 1984 ).

C e r t a i n t r e e sp e c ie s a f f e c t e d m a i z e y i e ld s m o r e t h a n o t h e r s . S u c h t r e e sa s a p p l e , p e a r - a p p l e , a n d p e a c h , w i t h s m a l l e r c r o w n s a n d l o w e r s t a t u r e , a p -p e a r e d t o h a v e a m i n i m a l i n f l u e n c e o n y i e ld s ; t h u s , s u b s t a n t i a l h a r v e s ts w e r eo b t a i n e d f r o m m a i z e i n t e rc r o p p e d i n fr u i t o r c h a r d s . G e r m i n a t i o n w a s r e d u c e dn e a r c a p u l i n a n d s a b i n o t r e e s i n c e r t a i n c i r c u m s t a n c e s , a n d a r e d u c t i o n i ny i e ld s w a s o b s e r v e d o n l y d i r e c t l y b e n e a c h t h e c a n o p i e s o f th e s e t r ee s d e s p i t et h e f a c t t h a t t h e s o il n e a r t h e s e tr e e s w a s n u t r i e n t - r i c h . W e f e e l t h a t t h e s ed i f fe r e n c e s m a y b e d u e t o s u n li g h t a n d / o r w a t e r d i f f e re n t i al s , a n a s p e c t t h a tn e e d s t o b e e x p e r i m e n t a l l y a n a l y

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