Bioresource Technology 37 ( 1991) 223-228

Effect of Pig Slurry Additions on the Organic Carbon of Calcareous Soils M. R Bernal, A. Roig* & J. Cegarra

Department of Organic Resources, Centro de Edafolog/a y Biologfa Aplicada del Segura, CSIC, Box 4195, Murcia, Spain

(Received 28 June 1990; revised version received 2 November 1990; accepted 7 November 1990)

Abstract

The effect of pig slurry additions at various rates over two years on the organic carbon in two calcareous soils with silt-loam and sandy-loam textures was studied in a greenhouse experiment. The organic carbon content in fresh pig slurries was very low, most of it being in a water-soluble form. There was, in general a predominance of the fulvic-like fraction as opposed to the humic-like fraction.

Because of the low level of organic carbon in the fresh slurry, the increases found in the soil were detected only with the highest doses, the equivalent of 800 and 1000 m 3 ha -t year -t, and after 14 months of additions. With a longer period of treat- ment there were significant increases using low rates. Thus, after two years, increases were detected with additions from 200 to 400 m 3 ha -t year -t, depending on the soil characteristics. In order to reach the same addition of organic carbon, a higher level of slurry was required in the sandy- loam soil than in the silt-loam soil because in the former the organic matter mineralization was quicker and also the losses through leaching of water-soluble carbon were higher.

Key words: Pig slurry, organic carbon, organic wastes, calcareous soil, fertilization, fulvic acids, humic acids.

INTRODUCTION

The presence of organic matter in the soil is of well known importance and is a factor with great influence over nearly all soil properties. There are

*To whom correspondence should be addressed.

abundant references in the literature which associate the characteristics of organic matter (chemical composition, structure, etc.) with the soil properties (C/N ratio, cation exchange capacity, pH, chemical fractions, nutrient assimilation, etc.).

By the mineralization processes induced by microorganisms, nutrients are gradually released from organic amendments. The addition of organic matter also stimulates the growth and activity of the microorganisms, which helps the decomposition processes. Also, the organic matter and its decomposition products have a great chelating capacity, which significantly improves the available level of the microelements in the soil. The decomposition processes are associated with carbon material losses, and with the creation of new microbial tissue, which can lead to solubilization of mineral nutrients, such as nitrogen and phosphorus, by the incorporation of their barely-soluble forms into the microflora tissues produced.

From an agricultural point of view, slurry is considered, in general terms, as a liquid fertilizer. The most relevant characteristic is its mineral content, about which there are many references in the literature (Boschi et al., 1976; Tunney, 1979; Collins, 1980; Duthion et al., 1980; Destain & Raimond, 1983; Westerman et al., 1985). Not much attention has been paid to the slurry organic matter, mainly because its level has not been high and also because the soils to which slurry has been added usually have had quite high values of organic matter, and it has been difficult to detect any increase unless there has been long-term treatment (Lecomte, 1980; Stadelmann & Furrer, 1985). However, there is a large number of cal- careous soils which do not exceed 1-5% organic

223 Bioresource Technology 0960-8524/91/S03.50 © 1991 Elsevier Science Publishers Ltd, England. Printed in Great Britain

224 M. P. Bernal, A. Roig, J. Cegarra

matter, and for them any organic matter addition is very important, small as it may be.

The aim of this paper is to assess the influence of pig slurry addition at various rates during a period of two years on the organic carbon in calcareous soils. The organic carbon of the slurry and its different fractions are also quantified.

METHODS

Two calcareous soils with low levels of organic matter were used, both of them being classified as Typic Calciorthids according to the American Soil Taxonomy. Their main differences were in the amount and type of clay (Table 1).

Six different proportions of fresh pig slurry (200, 400, 500, 600, 800 and 1000 m 3 ha -~ year -a) were poured over the soils; after a week the upper 5 cm of the soil was plowed. A control without any fertilization was also run. Each treat- ment had three replicates, and the soils were in containers of 0.209 m 2 area and 0"30 m height, perforated with a few holes at the bottom to allow water to drain out. They were situated in a green- house according to a randomized complete block design. The temperature in the greenhouse was controlled, and kept below 28°C by cooling during the summer when there was a high ambient temperature.

The annual slurry dose was divided into four equal portions, which meant eight additions of

Table 1. Characteristics of the soils

Soil B Soil C

pH (H20) 7'8 7.6 pH (KCI) 7.0 7.1 EC (S ml- 1) a 0"036 0"031 Organic matter (%) 0"76 0"67 Total-N (g kg- 1) 0.41 0.54 C/N 11.22 7.41 Total-P (g kg- 1) 0.21 0' 15 Exchangeable-K (cmol kg- 1) 0"13 0'50 CEC b 12"3 6'7 CaCO 3 (%) 46 63 Clay (%) 17.6 7'6 Silt (%) 52.1 37.2 Sand (%) 30.3 55.5 Texture Silt-loam Sandy-loam Dominant clay types ' I I-M (int) WHC (g kg- l)d 213 146

aEC = Electrical conductivity. bCEC = Cation exchange capacity (cmol (Ba + 2) kg- J soil). ' I = Illite, M = montmorillonite, int = interstratified. dWHC = Water holding capacity.

slurry during the two years of the experiment. Fresh pig slurry was collected each time from a pit from which the slurry was removed every two months. During the period in which the experi- ment was conducted, the most common horti- cultural crops of the Murcia Region were grown, according to the season: green pepper, lettuce, and tomato, with 2, 2, and 1 plants per container, respectively. The soils were watered according to the crop necessities; the soils were also plowed before planting, and after harvesting each crop. Between each plant growth the soil lay fallow for two months, and in that period it was not watered. The plants were harvested after fruit production, and the roots were removed from the soil to avoid any increase of soil organic matter apart from that caused by the slurry treatment.

The soil samples, formed by a mixture of five subsamples, were taken with a core from the full 30 cm depth of each container after harvesting of each crop, which meant at the 8th, 14th and 24th months, and after 2, 5, and 8 slurry additions respectively.

Both the organic carbon of the soil and the freeze-dried slurry (Corg) were determined by an automatic elementary microanalyzer. The follow- ing fractions were extracted from the freeze-dried sample of the slurry: water-soluble carbon (Cw) in the ratio 1:20; extractable carbon (Cext) in 0.1 M sodium pyrophosphate at the same 1:20 ratio (Cegarra et al., 1974); the fulvic acid carbon (Cfa) was removed by precipitation with sulfuric acid at pH 2 from the pyrophosphate extract (Cegarra, 1978). These three fractions of organic carbon were determined in an automatic elementary microanalyzer. The humic acid carbon (Cha) was calculated as the difference between extractable and fulvic fractions.

RESULTS AND DISCUSSION

Organic carbon in the pig slurry In general, the content of organic carbon in the pig slurries was low and varied from 0.1 to 6.0% of the fresh matter, depending on the proportion of feces/urine and on the amount of cleaning water added. However, for soils with such a low level of organic carbon as those employed here, any addition of organic matter can be important.

The content of organic carbon of the slurries actually applied was within the range 0.20-2.45% of the fresh weight (Table 2).

Pig slurry and organic-C in calcareous soils 225

Table 2. Carbon contents in water-soluble fractions, pyrophosphate extractable fraction, humic and fulvic acids, and total carbon in the pig slurries

Slurries

l" 2 ~ 3 ~ 4" 5" 6 a 7 b 8 b

Corg (% fresh matter) 1.03 0"99 0.42 0.20 1.78 1.68 0.77 2.45 Corg (% dry matter) 29.3 33'6 30.3 25.0 34.5 35'0 31"3 34.6 Cw (% dry matter) 8"05 6.74 11.78 12.10 6.52 9.84 5.34 2.19 Cext (% dry matter) 8.77 8.94 14.27 12"81 8.48 13.42 13"99 4.58 Cfa (% dry matter) 5"00 6.56 8.74 5.76 6'31 10" 11 3" 10 2.73 Cha (% dry matter) 3"77 2.38 5"49 7"05 2"17 3'31 10.89 1'85 Cha/Cfa 0.75 0.36 0.63 1.22 0.34 0.33 3.51 0.68 Cw (% Corg) 27.5 20.1 38"9 48.5 18.9 28.1 17.1 6'30 Cext (% Corg) 29"9 26.6 47'2 51"3 24.6 38"4 44"7 13"3 Cfa (% Corg) 17.1 19.5 29.0 23.1 18.3 28.9 9-9 7.9 Cha (% Corg) 12.9 7.1 18.1 28.3 6.4 9.5 34.8 5.4 Cfa (% Cext) 57.0 73.4 61.5 45.0 74-4 75.3 22.2 59.6

Corg = Total organic carbon; Cw = water-soluble carbon; Cext = carbon extractable in sodium pyrophosphate; Cfa = fulvic acid carbon; Cha = humic acid carbon. ~Freeze-dried slurry. bSlurry dried at 40°C. Slurry number refers to time of addition to soil (see Methods section).

The fraction extractable by sodium pyro- phosphate accounted for 13.3-51.3% of the total organic carbon. The predominant fraction was made up of a water and sodium pyrophosphate insoluble residue (Fig. 1) which was also propor- tional to the dry matter content (correlation coef- ficient 0.941 ).

In most of the samples there was a lower pro- portion of humic than fulvic acid-like carbon (Table 2) and the percentage of fulvic acid carbon with respect to the extractable carbon was very high in all cases, rising to 75% in slurry number 6. This shows the poor humification of the material and confirms the presence of very little trans- formed material in the insoluble residue.

The water-soluble carbon was rather high in all the slurries, and represented in one of the samples more than 48% of the total organic carbon. Nevertheless, it never reached the value of the extractable carbon, since the latter fraction includes the humic-like substances. The high proportion of water-soluble organic carbon con- firmed the presence of poorly humificated simple substances.

Evolution of the organic carbon in the soils The analysis of variance of the organic carbon in the soils (Table 3) showed that both the soils and doses were highly significant for the three sampl- ings. The slurry produced increases in the level of organic carbon in both soils in each sampling.

% Cor8

100[. I ctn,ol ~ Cha ~ cto

I 80

60

40

20

0 1 2 3 4 5 6 7 8

Slurries

Fig. 1. Carbon distribution of the pig slurry in the insoluble fraction, and humic and fulvic acids.

Tracing the evolution of organic carbon in each soil during the treatment period, both the doses of slurry added and the number of additions, as well as the interaction of the two factors, determined the level of carbon in the soil to a high probability level (P< 0"01)(Table 4).

Figures 2 and 3 show the evolution of the organic carbon in each soil throughout the experi- ment. In the first sampling no significant dif- ferences were detected in both soils. In soil B the Duncan's test differentiated the control from the dose of 800 m 3 ha- 1 year- 1, after five additions of slurry in 14 months (P<0.01); in soil C the Duncan's test only differentiated at the level of 1000 m 3 ha- l year-1, although there were slight

226 M. P. Bernal, A. Roig, J. Cegarra

Table 3. Analysis of variance: effects of soils and doses in each sampling

Source df SS MS F Fcrit

First sampling Soils 1 0.28 Doses 6 0"06 S x D 6 0'05 Error 28 0'05

Total 41 0.44

Second sampling Softs 1 0'20 Doses 6 0"36 S × D 6 0'06 Error 28 0.14

Total 41 0.76

Third sampling Softs 1 0.71 Doses 6 1.66 S x D 6 0.05 Error 28 0.45

Total 41 2.87

0"28 155'77 7"64 (P = 0"01) 0-01 5'88 3"53 (P = 0"01)

88 × 10 -4 5'01 3"53 (P= 0-01) 17×10 -4

0"20 39"14 7"64 (P = 0"01) 0"06 11'67 3"53 (P-- 0"01 )

99 x 10 .4 1'94 2"00 (P= 0"1) 51x10 -4

0"71 43'75 7"64 (P = 0"01) 0"28 17'18 3.53 (P= 0-01)

86 x 10 -4 0'54 2"00 (P-- 0"1) 0"02

Table 4. Analysis of variance: effects of doses and number of additions in each soil

Source df SS MS F F ,~i t

Soil B Doses 6 0-70 0-12 18.22 3.26(P=0.01) Additions 2 1-92 0.96 149.27 5.15(P--0.01) DxA 12 0-34 0-03 4.38 2.64(P=0.01) Error 42 0.27 64 × 1 0 - 4

Total 62 3.22

Soil C Doses 6 0.68 0.11 15.70 3.26(P=0.01) Additions 2 1.04 0.52 72.04 5.15(P=0.01) DxA 12 0.42 0.04 5.64 2.64(P=0.01) Error 42 0"30 72 × 1 0 - 4

Total 62 2.52

increments in the organic matter from the dose of 500 m 3 ha- 1 year- 1.

Finally, with eight additions in 24 months there were significant increases with the lower doses. To produce significant increases only 400 m 3 ha- year- 1 of slurry in soil C, and 200 m 3 ha- 1 year- in soil B were needed. However, in soil C a high increment with any dose was not detected, since the increases were slow and gradual (Fig. 3). In soil B the most important increase was with 400 m 3 ha-1 year-1, although the increase continued until the dose of 600 m 3 ha -1 year-1, but from there on the values were practically constant.

The great influence of the texture in the varia- tion or evolution of the organic carbon in the soil was reflected by the higher amount of slurry needed in soil C than in soil B to induce sig- nificant differences from the controls.

Spallacci and Boschi (1985) also found dif- ferent patterns in the increments of soil organic carbon, but after four years of pig slurry applica- tions all the different textural soils were enriched in organic carbon, the greatest increase being in the sandy-clay soil.

One of the determining factors for these dif- ferences was the mineralization process, since the organic material added was the same for both soils. The water-soluble carbon would soon be lost by leaching in a coarser texture soil; likewise, the compounds of low molecular weight would be easily degraded by the microorganisms. Con- sequently, in soil C these phenomena were produced with all the doses, whereas in soil B they were produced only with large doses added over a long period of time. The former soil had a lower clay content, and therefore, allowed a better aera- tion, and a quicker mineralization of the organic matter. It also had a higher capacity of percola- tion, which led to higher losses of the water- soluble carbon.

These results suggest that the predominant fraction of organic carbon in the pig slurries was made up of a water- and sodium pyrophosphate- insoluble residue. The poor humification of the

1.30

1.10

1 2

0 . 9 0 "

0 . 7 O -

0.50

0.30

Pig slurry and organic-C in calcareous soils 227

o 200 , 0 0 6 0 0 6 0 0 1ooo

Slurry doses (m3haaycar "~)

Fig. 2. Evolution of the organic carbon contents in soil B, after 8 months (D), 14 months (A), and 24 months (e) of treatment.

ha-~ year-1 to B were needed to produce sig- nificant increments in the soil organic carbon. The pattern for each soil was different; in the sandy- loam soil increases with different doses were slow and gradual, but in silt-loam soil the organic carbon levels were similar with applications of 600, 800, and 1000 m 3 ha -~ year -~ of slurry. Consequently in the first soil organic carbon losses by mineralization and leaching were produced with all the doses, whereas in the sec- ond they were produced only with the larger doses added.

ACKNOWLEDGEMENTS

The authors wish to thank 'The Instituto de fomento de la Region de Murcia' for the financial support awarded to Dr M. P. Bernal.

REFERENCES

1.30

1.10

0.90

g 0.70

0.50

0 . 3 0

o , o o , ~ o 60° 600 1o'oo Slurry doses (m3ha'Xyear :)

Fig. 3. Evolution of the organic carbon contents in soil C, after 8 months (o), 14 months (A), and 24 months (e) of treatment.

slurry was shown by the HA/FA ratio of < 1, and the high content of water-soluble carbon. These confirmed the presence of very tittle transformed materials in the insoluble residue.

The pig slurry applications to the soils increased the organic carbon level in both soils, and the longer the period of treatment the higher the content of organic carbon in soil.

After the two years of treatment, addition of 400 m 3 ha- 1 year- 1 of slurry to soil C and 200 m 3

Boschi, V., Spallacci, P. & Montorsi, M. (1976). The agronomic utilization of pig slurry: effect on forage crops and on soil fertility. Anu. 1st. Sper. Agron., 7, 151-67.

Cegarra, J. (1978). Fraccionamiento de fertilizantes orgfinicos y de sus productos de humificaci6n. Tesis doctoral Universidad Aut6noma de Madrid. Ed: CEBAS Murcia.

Cegarra, J., Reverte, L., Lax, A. & Costa, E (1974). Factores que infiuyen en la extracci6n y fraeeionamiento de la materia orgfinica del suelo. Anal. Edafol. Agrobiol., 33, 575-90.

Collins, D. P. (1980). The use of animal manures on pasture for grazing. In Effluents from Livestock, ed. J. K. R. Gasser. Applied Science Publishers, London, pp. 344-59.

Destain, J. P. & Raimond, Y. (1983). La composition chimique du lisier, ses facteurs de variation et ses con- s6quenees agronomiques. Revue de l'Agriculture, 36, 39-49.

Duthion, C., Catroux, G. & German, J. C. (1980). Land- spreading of liquid pig manure. II Nutrient balance and effects on drainage water. In Effluents from Livestock, ed. J. K. R. Grasser. Applied Science Publishers, London, pp. 59-79.

Lecomte, R. (1980). The influence of agronomic application of slurry on the yield and composition of arable crops grassland and on changes in soil properties. In Effluents from Livestock, ed. J. K. R. Gasser. Applied Science Publishers, London, pp. 139-83.

Spallacci, P. & Bosehi, V. (1985). Long-term effects of the landspreading of pig and cattle slurries on the accumula- tion and availability of soil nutrients. In Long-term Effects of Sewage Sludge and Farm Slurries Applications, ed. J. H. Williams, G. Guidi & P. L'Hermite. Elsevier Applied Science Publishers, London, pp. 33-45.

Stadelmann, E X. & Furrer, O. J. (1985). Long-term effects of sewage sludge and pig slurry applications on micro- biological and chemical soil properties on field experi- ments. In Long-term Effects of Sewage Sludge and Farm Slurries Applications, ed. J. H. Williams, G. Guidi & P. L'Hermite. Elsevier Applied Science Publishers, London, pp. 136-45.

228 M. P, Bernal, A. Roig, J. Cegarra

Tunney, H. (1979). Dry matter, specific gravity and nutrient relationships of cattle and pig slurry. In Engineering Pro- blems with Effluents from Livestock, ed. J. C. Hawkins. In Proc. EEC Seminar, Hawkins Publ. CEC Luxembourg, pp. 430-45.

Westerman, P. W., Safley, L. M., Barker, J. C. & Chcscheir, G. M. (1985). Available nutrients in livestock waste. In

Agricultural Waste Utilization and Management. Proc. 5th Int. Sym. on Agricultural Wastes, ed. American Society of Agricultural Engineers (ASAE), Michigan, USA, pp. 295-307.