Performance of maize, beans and ginger as intercrops inPaulownia plantations in China

S. M. NEWMAN 1, *, K. BENNETT2 and Y. WU3

1

Biodiversity International Ltd, Marriotts, 13 Castle St, Buckingham MK18 1BP, UK; 2 Department of Plant Sciences, Oxford University, UK; 3 Chinese Academy of Forestry, Beijing,China (*Author for correspondence: E-mail: 101375.2007@compuserve.com)

Key words: PAR transmission, specific leaf weight, tree proximity, yield depression

Abstract. Yield, morphology and specific leaf weight of summer crops maize, beans and gingerwere studied in relation to tree proximity and PAR transmissivity in a 7-year old plantation ofPaulownia elongata grown at a spacing of 15 m

× 5 m in Eastern China. The yield of beansand maize was significantly reduced, compared to controls, at all positions relative to the trees.This yield depression was particularly marked at positions closest to the trees. Beans grown at2 m from the trees had reduced height and specific leaf weight. These crops would yield moreat wider tree row spacings. Ginger gave high yields when intercropped and is an ideal shadecrop for these systems. Further research is required on optimisation using a bioeconomicapproach. Further agronomic, physiological and biochemical work is required on gingerand other economic members of its family as these appear to have compatibility with denseagroforestry plantings.

Introduction

Paulownia agroforestry is extremely important in China and is estimated tocover over 2 million hectares (Zhu et al., 1991). Research on Paulowniaagroforestry has recently been extensively reviewed (Zhu et al., 1991; Wu andZhu, 1997). Paulownia agroforestry is especially important in the temperateNorth China Plain region which is the main wheat growing area. The mainspecies used is Paulownia elongata. Considerable yield advantages arepossible in Paulownia-wheat systems due temporal partitioning of resourceuse (especially light). Wheat is generally sown in the autumn after Paulownialeaf fall (November) and it normally begins to senesce prior to Paulownia leafdevelopment in the spring (May). It has been claimed, that the presence ofPaulownia protects growing wheat from the hot dry winds that characterisethe region (Zhu et al., 1991; Wu and Zhu, 1997). Little information is avail-able on the effect of Paulownia on summer crops such as maize, beans andcotton. Although these crops are less profitable than the winter crops in China,it is important that data on this part of the cropping cycle are obtained ifPaulownia agroforestry is to be transferred to other countries where summercrops are important. There is also little information in the literature on thespatial variation of yield and form of the understorey crops across the alley,between the tree rows. This can be useful in the elucidation of cropping zones.

Agroforestry Systems 39: 23–30, 1998. 1998 Kluwer Academic Publishers. Printed in the Netherlands.

For instance if studies show that the yield of maize in zones 2 m from thetree rows is depressed due to low light levels, this zone could be reserved forcrops that are less sensitive.

The typical spacing of Paulownia in agroforestry is 5 m within the row.The between-row spacing can vary due to objectives from 5 m to 50 m. Therows are nearly always planted in a North-South orientation. This study isthe first time that the distribution of photosynthetically active radiation (PAR)has been studied under the trees. PAR is thought to be a major determinantof understorey yield as most fields are irrigated and receive adequate fertiliserfor the trees and crop.

The general aim of this study was to make a preliminary investigation ofthe effects of PAR levels and tree proximity on three test crops, maize (Zeamais) beans (Phaseolus spp) and ginger (Zingiber officinale) grown underPaulownia agroforestry at between-row spacings of 15 m. These crops werechosen as typical summer crops for the area based upon consultations withfarmers. Cotton was not chosen due to local problems with pests and disease.Specifically three null hypotheses were to be tested:

1. Vegetative parameters and yield of the crops are not related to tree prox-imity or aspect in a Paulownia intercrop.

2. There is no significant change in light distribution across the alley in aPaulownia intercrop.

3. There is no significant relationship between maize growth and PAR dis-tribution.

Materials and methods

Site details

The two villages of Gou Chun and Chang Qiao in the county of Chengwuwere chosen for the experiment. The county is located on the alluvial plainof the Huanghe (Yellow) and Huaihe rivers in the south west corner ofShandong province at longitude 116° E and latitude 35° N. The soil is alluvial,sandy and alkaline. The climate is generally dry from October to the firsthalf of June followed by a marked wet season between late June andSeptember. Mean annual rainfall averages around 720 mm. Chengwu has afrost free period of 205 days. Natural disasters such as droughts and stormsin the winter, and flooding in the rainy season are common.

Planting of Paulownia in the county began in the 1970s and Paulowniaagroforestry now covers an area of 63000 ha.

The trees in the experiment were seven years old and had a mean heightof 16 m, a diameter at breast height of 35 cm and canopy diameter of 7 m.

24

Crop measurements

The term crop form, used below, denotes morphological variables such asheight, stem diameter, leaf and internode length and a structural variable,leaf specific weight. Crop form was measured in order to generate hypotheseson the biological basis of any yield variation. This approach has proved usefulin previous PAR agroforestry studies in the UK (Newman, 1984, and Newman,1989) and is particularly powerful when linked to discriminant analysis(Newman, 1986). These studies have shown that increased height, leaf lengthand reduced specific leaf weight are good indicators of situations where lightis a limiting factor on yield

The yield and form of the crops was measured on a per plant basis alongtransects from tree to tree in the intercropped plots. Ploughing was carried outusing animal draught power.

In order to test for any systematic effects of soil variation due to ploughing,control plots were established in areas away from the influence of the treesand transects taken to give corresponding positions. That is the tree lines wereprojected into the control area.

Details of the crop form measurement protocol are given in Table 1. Yieldwas measured in all crops at harvest using 1m quadrats.

PAR measurements

Daily PAR transmissivity measurements were carried out in the Maize plotsusing standard integrating energy sensor based instruments (Newman, 1984b;Newman, 1985 and Newman, 1989b) at the transect points with two sensorsin the control. The instruments measure radiation between 400–700 nm witha flat spectral response and can be calibrated in energy units by using standard

25

Table 1. Crop form measurement details Form variables were Plant height in cm (ph), stemdiameter at 5 cm above ground in cm (sd), Leaf length in cm (ll), Internode length in cm (il)and Specific leaf weight in g (sl). Chengwu county, Shandong province China 1993.

Crop Location Tree Sampling points Number Dates in Measurementsspacing along transect of 1993between (m from transect (dd/mm)row (m) west row) replicates

Maize Goun Chun 15 3, 7.5, 12 8 17, 22, 27/07, ph, sd, ll, il, sl01/08

Beans Chan Qiao 15 2, 3.75, 7.5, 5 18, 23, 28/07, ph, sd, ll, il, sl11.25, 13.25 02/08

Ginger Chan Qiao 15 –2, 0, 2* 6 19, 24, 29, ph, sd, ll, il, sl03/08

* In the case of Ginger measurements were taken of plants within the tree row and at 3 m westand east of it.

Kipp Zonen solarimeters. In this case where relative values are required themeasure is without units. PAR measurements were taken during July andAugust and an average taken.

Results

A T-Test was carried out to compare intercrop with sole crop yield for thethree crops. The results are shown in Table 2.

One way analysis of variance, SED determination for pairs of means andthe fitting of a quadratic value (with distance) was then carried out to assessthe effects of tree proximity on the different intercrops. The results are pre-sented in Tables 3, 4 and 5.

26

Table 2. T Test of intercrop vs sole crop yield under Paulownia. Chengwu county, Shandongprovince China 1993.

Crop Intercrop yield Sole crop P-value Relative yield valueg m–2 dry wt yield g m–2 (intercrop/sole crop)

Maize 439 646 < 0.05 0.68Beans 50 79 < 0.001 0.63Ginger 1327 992 < 0.001 1.34

Table 3. Percentage PAR and form variable means at different distances from the tree row inmaize (Paulownia at 5 × 15 spacing) Control transect values are given in bold. Means within arow and with the same letter do not differ significantly. Quadratic functions were fitted to thedata. Chengwu county, Shandong province, China 1993.

Variable 3m 7.5m 12m Quadratic significance value

% PAR measured using single representative sensor 050 055 035

Height cm 105.2 a 132.8 b 076.6 c 0.000154.9 a 138.7 a 152.2 a 0.254

Stem diameter cm 001.9 a 002.9 b 001.3 c 0.000003.0 a 003.1 a 003.3 a 0.187

Leaf specific weight g 0.011 a 0.012 b 0.009 c 0.0000.015 a 0.015 a 0.015 a 0.762

Leaf length cm 074.2 a 074.4 a 065.0 b 0.187065.5 a 055.9 a 057.7 a 0.309

Internode distance cm 006.6 a 007.5 ab 007.7 b 0.968007.0 a 006.3 a 006.2 a 0.593

Discussion

Intercropping significantly affected the yield of all summer crops tested. Theworst case was maize with only 63% of sole crop yield. Beans were margin-

27

Table 4. Mean yield and form variation in beans at different distances from the WesternPaulownia tree row at 5 × 15 spacing. Control transect values are given in bold. Means withina row and with the same letter do not differ significantly. Quadratic functions were fitted to thedata. Chengwu county, Shandong province, China 1993.

Variable 2 m 3.75 7.5 m 11.2 m 13 m Quadratic significance value

Yield g per m 25.4 a 43.0 b 68.8 c 57.8 d 23.4 a 0.00077.0 a 73.4 a 80.0 a 77.6 a 79.4 a 0.948

Height cm 23.7 a 29.3 ab 35.8 b 27.0 ab 24.7 a 0.01130.4 a 32.1 a 30.4 a 32.9 a 30.3 a 0.409

Stem diameter 0.09 a 0.11 b 0.14 c 0.11 b 0.08 a 0.000cm 0.13 a 0.13 a 0.13 a 0.14 a 0.13 a 0.276

Specific leaf 0.010 a 0.013 bc 0.015 b 0.011 ac 0.011 a 0.002weight g 0.018 a 0.019 a 0.019 a 0.018 a 0.018 a 0.609

Leaf length cm 5.1 a 5.0 a 5.8 a 5.2 a 5.3 a 0.4954.8 a 4.6 ab 4.8 a 5.0 a 4.1 b 0.778

Internode distance 4.7 a 4.5 a 5.2 a 4.4 a 4.9 a 0.987cm 4.0 a 4.0 a 4.0 a 4.1 a 3.8 a 0.622

Table 5. Variable means at different distances from the West Paulownia tree row in gingerunder Paulownia at 5 × 15 spacing. Control transect values are given in bold. Means within arow and with the same letter do not differ significantly. Chengwu county, Shandong province,China 1993.

Variable 3 m west 0 m 3 m east

Yield g per m .1387 a .1415 a .1178 a0.977 a 0.972 a .1027a

Height cm 049.6 a 044.0 b 040.4 c029.2 a 043.3 a 032.2 a

Stem diameter cm 00.35 a 00.29 a 00.30 a00.32 a 00.30 a 00.29 a

Leaf specific weight g 0.014 a 0.014 a 0.013 a0.015 a 0.015 a 0.015 a

Leaf length cm 020.9 b 018.2 a 016.4 a016.0 a 018.1 a 018.4 a

Internode distance cm 002.2 a 002.9 b 002.1 a002.1 a 002.0 a 002.4 a

ally better at 68%. Ginger actually gave 34% higher yields when intercroppedas compared to the sole crop control.

There were no ‘false proximity’ effects in the maize control plots sointercrop proximity effects on maize plant form are due to the presence oftrees and not due to ploughing. In terms of PAR transmissivity, three distinctzones were present. A ‘high’ central zone of 55%. An ‘intermediate’ zone 3m from the west row of 50%, and a ‘low’ zone 3 m from the East row of 35%.This pattern was markedly reflected in height (133 cm, 105 cm, 77 cm), stemdiameter (2.9 cm, 1.9 cm, 1.3 cm) and leaf specific weight (11 mg, 12 mg,9 mg). Effects on leaf length and internode distance were less marked withshortest leaves in the low zone (65 cm compared to 74 cm elsewhere), andshortest selected internode in the intermediate zone (6.6 cm compared to amean of 7.6 cm elsewhere).

For bean leaf length, there was a false proximity effect, so this was notanalysed further. Yield was suppressed at all positions relative to the trees.In the centre of the alley 68.8 g m–2 represented 87% of control, whereas thepositions closest to the trees gave a mean yield of 24.4 g m–2 which repre-sented only 31%. The question arises; is it sensible to intercrop so close tothe trees? This parabolic yield effect across the alley is reflected in height,stem diameter and leaf specific weight (see Table 4). Internode distance wasnot affected by proximity.

The highest ginger yields occurred in the zone spreading from directlyunder the trees to 3 m West. The reasons behind this are not fully under-stood. The respective values were 1414 g m–2 and 1387 g m–2 with a mean of1401 g m–2. This is more than double the control value of 646 g m–2. The valuefor 3 m East was 1178 g m–2. Leaf specific weight and Stem diameter werenot affected by proximity showing the resilience of the crop to low light levels.Height was lowest with 40 cm at 3 m East and highest at 3 m West (50 cm).Height was intermediate directly under the trees at 44 cm. This pattern wasreflected for leaf length in that 3 m west gave highest values. For internodedistance the highest was obtained directly beneath the trees.

Further economic assessments are required in order to precisely determinewhich crops can be economically grown in which zones of this configura-tion, for China and other countries. Unless gross margins are found to behigh enough to tolerate yield losses of 37% and 32% for maize and beansrespectively one would not recommend planting these summer crops in anyof the proximity zones. It may be more profitable to use wider between rowspacings and tolerate a reduction in Paulownia tree density. At shade levelsgreater than 45% found in this experiment, one is forced to search for inter-crop species that show shade tolerant characteristics. Ginger is a primecandidate as are many other members of the family Zingiberaceae. Work inIndia (Sankar and Swamy, 1988) on ginger intercropped under arecanut (Arecacatechu) also supports this assertion. Table 6 shows yield increases of 3.5and 5 times the control values in two and seven year old plantations respec-tively at PAR transmissivities of only 30% and 15%.

28

Further work on the shade response and photosynthesis of ginger and othereconomically important members of the Zingiberaceae such as turmeric andcardamom is required. Some of these crops appear to have enormous poten-tial for agroforestry systems where shade is a significant limiting factor.

Conclusions

Crop yield was affected by intercropping. Understorey crop form and yieldwere related to tree proximity and aspect in a complex way.

There was a major change in light distribution across the alley in thePaulownia intercrop. There was a significant relationship between understoreycrop form and PAR distribution in maize.

Both maize and beans suffered as intercrops in the seven year old Paulowniaplantation planted at 15 × 5m spacing. Yield was 63% and 68% of sole cropsrespectively. The form responses supported the idea that shade was a keylimiting factor. (The plantation was irrigated and fertilised). Generally theyield depression and shade response was more marked with tree proximity.Pruning and or increasing between row distances may improve the understoreyyields.

Ginger yields increased when intercropped and were highest when grownin a zone within the tree row and out to a distance of 3 m to the west of therow.

Further work is required on bioeconomic modelling for optimisation.Further work is also required on the intercropping of ginger and other membersof the Zingiberaceae where shade becomes a problem in agroforestry con-figurations.

Acknowledgements

The workers would like to thank the Chinese Academy of Forestry for tech-nical support during the course of this work. Special thanks to the farmersand extension workers of the villages of Gou Chun and Chang Qiao for helpwith the tree and crop management. We are grateful for financial assistance

29

Table 6. Ginger yields and leaf area as when intercropped under different ages of arecanut inIndia. PAR transmissivity and temperature values are also given (data adapted from (Sankarand Swamy 1988)).

Ginger crop Average day PAR transmissivity Leaf area Yield kg/hatemperature °C (%) index (%)

Control 30.0 100 Lowest 02666 (100)2 year old arecanut 28.3 030 Middle 09191 (350)6 year old arecanut 27.9 015 Highest 13487 (500)

provided by the UK Overseas Development Administration and BiodiversityInternational Ltd.

References

Newman SM (1984) The use of vegetable phytometers in the evaluation of the potential responseto understorey crops to the aerial environment in an interculture system. Agroforestry Systems2: 49–56

Newman SM (1984b) The design and testing of a system for monitoring the availability ofsolar radiation for interculture Agroforestry Systems 2: 43–47

Newman SM (1985) Low cost sensor integrators for measuring the transmissivity of complexcanopies to photosynthetically active radiation. Agricultural and Forest Meteorology 35:243–254

Newman SM (1986) Locating the source of interference in agroforestry systems by multivariateanalysis of crop response. International Tree Crops Journal 4(2): 67–76

Newman SM (1989) Ecological methods for agroforestry research. In: Reifsnyder WS andDarnhofer TO. (eds) Meteorology and Agroforestry, pp 347–365. Proceedings of anInternational Workshop on the application of meteorology to agroforestry systems planningand management, Nairobi 1987, ICRAF Nairobi

Newman SM (1989b) Inexpensive instrumentation for measuring PAR in AgroforestryMeteorology and Agroforestry. In Reifsnyder WS and Darnhofer TO. (eds) Meteorology andAgroforestry, pp 297–304. Proceedings of an International Workshop on the application ofmeteorology to agroforestry systems planning and management, Nairobi 1987, ICRAFNairobi

Sankar CR and Swamy SM (1988) Influence of light and temperature on leaf area index,chlorophyll content, and yield of ginger. Journal of Mahrashtra Universities 13(2): 216–217

Wu Y and Zhu Z (1997) Temperate agroforestry in China:149–179. In: Gordon AM and NewmanSM (eds) Temperate Agroforestry, UK: CABI, 1997, pp 269

Zhu Z, Mantang C, Shiji W and Jiang Y (eds) (1991) Agroforestry Systems in China. Publishedjointly by IDRC and Chinese Academy of Forestry, pp 216, ISBN-T-5038-0857-8/S.0441

30