Short communication
Short-term compost effect on macroaggregation in a sandy soil
under low rainfall in the valley of Mexico
F. de LeoÂn-GonzaÂlez
a,*, M.M. HernaÂndez-Serrano
a, J.D. Etchevers
b,
F. PayaÂn-Zelaya
a, V. Ordaz-Chaparro
baDepartamento de ProduccioÂn AgrõÂcola y Animal, Universidad AutoÂnoma Metropolitana-Xochimilco,
Calzada del Hueso 1100, 04969 D.F. Col. Villa Quietud, Mexico
bInstituto de Recursos Naturales, Colegio de Postgraduados, 56230 Montecillo, Estado de MeÂxico, Mexico Received 15 September 1998; received in revised form 30 August 1999; accepted 2 May 2000
Abstract
Several studies have shown the importance of organic material in the formation and stability of soil aggregates. The organic matter of soil (SOM) is affected among other factors by the application of farmyard waste and compost, as well as tillage and crop rotation. This paper examines the aggregation and stability of a sandy soil (Haplic Fluvisol) in the valley of Mexico when treated with either 40 Mg haÿ1of compost or urea (80 kg haÿ1of N) and sown to amaranth (Amaranthus hypochondriacusL.)
under dryland conditions. The application of compost resulted in a signi®cantly larger proportion of aggregates in the fractions >1 mm (1.0±2.0, 2.0±2.3, 2.3±4.7 mm) than in the smaller fraction (<1 mm). However the stability of the macroaggregates >1 mm in the compost treatment was not higher than in contrasting treatments which did not include organic matter. Compost, which was applied under drought conditions, did not increase the aggregate stability of the soil probably because of the restricted transformation of the compost and microorganism activity.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Macroaggregates; Compost; Sandy soil;Amaranthus hypochondriacusL.; Valley of Mexico
1. Introduction
Several authors have shown the importance of organic matter in the formation of soil aggregates (Edwards and Bremner, 1967; Tisdall and Oades, 1982; Hamblin, 1991). The aggregates formed with the in¯uence of organic material offer greater poten-tial for soil conservation if they remain stable in water (Singh and Singh, 1996). Aggregate stability seems to be closely correlated to polysaccharides, roots and fungi, and long-chain aliphatic compounds (Tisdall
and Oades, 1982; Tisdall et al., 1997). Soil organic matter (SOM) is affected by tillage and crop rotation (Monreal et al., 1995) and by compost and farmyard manure applications, among other factors.
It has been suggested that soil structure responses to soil amendment are soil-site speci®c (Toogood, 1978). Soils in Mexico's high valleys are mostly derived from recent volcanic materials (with a high concentration of sand and silt) and show high susceptibility to erosion. Under these conditions, the addition of compost can be bene®cial for soil conservation (Pinamonti and Zorzi, 1996). Most studies of the effects of compost on soil aggregation have mainly been conducted under con-ditions of controlled incubation (Fortun and Fortun, 1996; Roldan et al., 1996). Literature concerning the *Corresponding author. Tel.:1-52-54837504;
fax:1-52-54837238.
E-mail address: dlgf2220@cueyatl.uam.mx (F. de LeoÂn-GonzaÂlez).
aggregation process on sandy soils in the ®eld is scarce. This work tests the hypothesis of whether large quantities of compost (prepared from urban market waste) when applied to sandy soils under conditions of fairly low rainfall can increase the formation of macroaggregates and their stability.
2. Materials and methods
2.1. Study site
A sandy soil (Haplic Fluvisol), located in the south-ern region of the Valley of Mexico (198150N,
998130W; at 2280 m of altitude), was selected for this
experiment. The site was sown with amaranth. Long term and annual rainfall and temperature data in the area are presented in Table 1. Actual rainfall during 1996 was 358 mm of which 329 mm occurred during the amaranth growing-season (June±December). The experimental plots (25 m2) were sown manually on June 16 in rows 0.85 m apart at a distance of 0.90 m each. Three treatments were tested: 40 Mg haÿ1 of compost prepared from urban market organic wastes (Table 2), nitrogen fertilisation (80 kg haÿ1
N was
applied as urea) and a control (without compost or fertiliser). The design of the experiment was a randomised block. Each treatment was replicated four times. The compost and the fertiliser were applied manually, buried in the mounds of earth, at the base of the stem of each plant in July 1996, in order to create adequate conditions for the growth of the adventitious roots of the amaranth (De LeoÂn et al., 1997).
2.2. Soil sampling and analysis
Soil samples (0±0.2 m depth) were collected in December 1996 after the amaranth was harvested. Five samples were obtained with a small spade at the base of ®ve plant stems in each replicate and kept separate. At sampling time, the water content of the soil was lower than permanent wilting point. Samples were carried to the laboratory in plastic bags and the organic residues larger than 1 cm were removed before the soil was sieved. Dry soil samples (approxi-mately 1 kg) were placed each in a four-sieve column and manually shaken for 3 min (at approximately 60 strokes per minute with horizontal movements). The mass of each of ®ve aggregate fractions (<1.0, 1.0±2.0, 2.0±2.3, 2.3±4.7 and >4.7 mm) was recorded and the relative percentage was calculated (Kemper and Rose-nau, 1986).
Table 1
Long-term and 1996 rainfall (mm) and temperature (8C) in Tulyehualco, Mexico
Month Rainfall Temperature
Long-term 1996 Long-term 1996
January 6.6 0 12.2 12.0
February 2.2 0 13.7 14.5
March 8.3 0 16.1 15.6
April 20.5 19.1 17.4 17.3
May 38.0 9.9 17.9 19.7
June 103.5 50.2 17.5 17.3
July 109.7 75.4 16.3 16.6
August 106.1 82.3 16.5 16.8
September 95.4 82.1 16.2 17.6
October 38.7 19.3 15.3 16.3
November 10.1 0 13.7 13.1
December 8.6 19.3 12.2 13.4
Annual rainfall 547.7 357.6
Selected soil (depth, 0±0.20 m) and compost properties
Property Value
Soil
Clay concentration (g kgÿ1) 70 Silt concentration (g kgÿ1) 140 Sand concentration (g kgÿ1) 790
pH (1:2, soil:water) 6.8
Electric conductivity (1:5, soil:water; dS mÿ1) 1.1 Organic matter concentration (g kgÿ1) 12.0
Compost
The four larger macroaggregate fractions obtained by dry sieving were combined in one sample, weighed and subjected to a wet stability test (Kemper and Rosenau, 1986). The combined sample was immersed directly in distilled water and shaken for 15 min with a Yoder apparatus with a two-sieve column (0.15 and 3.25 mm) at 30 cycles minÿ1
. The two aggregate frac-tions separated in the previous operation were oven-dried at 1058C, weighed and their relative quantity calculated and expressed as a percentage of the com-bined macroaggregate sample mass.
Dry and wet sieving results were subjected to an ANOVA test. If the overall F test was signi®cantly different, a Tukey test was performed (Cody and Smith, 1991).
3. Results and discussion
3.1. Dry sieving
Soil mass in the aggregate size fractions 1.0±2.0. 2.0±2.3, 2.3±4.7 mm was signi®cantly higher (Table 3) in the treatment with compost as compared to the control and urea treatment, and decreased in the
smallest size fraction (<1 mm). The compost did not have an effect on the largest macroaggregate fraction (>4.7 mm). The sum of the percentage soil mass in the four largest macroaggregate fractions was signi®cantly higher in the compost-treated soil (Table 3). In summary, compost added to the soil in large quantities and close to the plant stem had a positive effect on macroaggregate formation, even under conditions of low rainfall during the experi-mental period. Other authors (Roldan et al., 1996) had reported similar compost effect working with labora-tory soil incubations.
3.2. Wet stability of macroaggregates
Wet stability of 0.15±3.25 and >3.25 mm macro-aggregate-sized fractions was not affected by compost treatment (Table 4). Degens et al. (1994) suggested that sand >0.25 mm in a sandy-loam soil limited macroaggregate stability. Our experimental soil con-tained 790 g kgÿ1
of sand. Such a high value could explain the low stability of the above fractions. In addition, low rainfall during the experimental period might have affected the soil microbial activity, parti-cularly hyphae length (Tisdall et al., 1997), and the Table 3
Effect of the treatments on the mass of aggregates,aexpressed as percentage of the whole-soil mass, after dry sieving test
Aggregate size fraction (mm) Control Urea (80 kg haÿ1N) Compost (40 Mg haÿ1)
<1 85.75.2 ab 82.25.4 a 77.86.6 b
1±2 2.91.0 b 3.00.8 b 5.41.8 a
2±2.3 1.20.4 b 1.70.5 b 2.61.0 a
2.3±4.7 3.41.2 b 4.01.6 b 6.52.2 a
>4.7 6.83.6 a 9.03.6 a 7.83.7 a
1 to >4.7 14.35.2 b 17.85.4 b 22.26.6 a
aMeanS.D.
bBy row comparison of means where different letter indicates signi®cant difference atp<0.05.
Table 4
Effect of the treatments on the mass of aggregates,aexpressed as percentage of total mass of aggregates subjected to wet-stability test (1.0±2.0, 2.0±2.3, 2.3±4.7 and >4.7 mm)
Aggregate size fraction (mm) Control Urea (80 kg haÿ1N) Compost (40 Mg haÿ1)
0.15±3.25 26.75.8 ab 24.66.6 a 28.88.5 a
>3.25 23.213.4 a 24.610.8 a 23.09.2 a
aMeanS.D.
production of some organic substances, both of them being linked to soil aggregation (Puget et al., 1999). The non-stable macroaggregates that were formed by the effect of the compost application are at risk of disintegrating with the effect of rain and tillage. BartheÁs et al. (1996) found that macroaggregates in the ®rst 0.10 m of a clayey Oxisol pro®le decreased within 5 months due to the effect of manual or mechanised tillage. The non-stable macroaggregates formed in the sandy soil after compost application in zones with low rainfall must be considered as a short-term protection against wind erosion. Short-short-term pro-tection could help reduce small air-borne particles, a serious problem during the dry season in the urban concentration of the Valley of Mexico.
Although results reported in this paper correspond to only one year of observation, previous studies have suggested that long-term compost application increased the water stability of aggregates. However, clay concentration appears to be crucial to achieve water stability of newly formed macroaggregates. Guidi and Poggio (1987) found that compost addition (40 Mg haÿ1per year) for three consecutive years had a positive effect on aggregate stability in a soil con-taining 210 g kgÿ1 of clay. Roldan et al. (1996) obtained similar results with a silt-loam soil (Lithic Haploxeroll), but under laboratory conditions. Clay concentration in our experimental soil was only 70 g kgÿ1
. In soils with a higher clay concentra-tion and in wetter climates, the addiconcentra-tion of organic matter in the form of compost could result in higher macroaggregate stability, especially with repeated compost applications over several years (Guidi and Poggio, 1987). The response to the application of compost, in terms of soil aggregation, will probably be greater for areas sown to grasses that have higher root density (Tisdall and Oades, 1982; Degens et al., 1994).
4. Conclusions
The application of large quantities (40 Mg haÿ1
) of market waste compost to a sandy soil under conditions of low rainfall favoured the formation of macroag-gregates in the short term. However, the short-term action of compost was not enough to increase the quantity of stable macroaggregates. Low rainfall
dur-ing the experimental period could have negatively affected compost transformation in the soil and there-fore macroaggregate stability.
Acknowledgements
The authors would like to thank Dr. D. Angers for critically reviewing the manuscript.
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