March 26, 2008
Effect of Vegetable, Fruit And Garden (VFG) Waste Compost on Soil Physical Properties
By Leroy, Ben L M Herath, Herath M S K; De Neve, Stefaan; Gabriels, Donald; Bommele, Lydia; Reheul, Dirk; Moens, Maurice
Compost and other organic amendments have been proven to improve the soil physical quality. In Flanders, vegetable, fruit and garden (VFG) wastes are collected selectively and composted. We studied the effects of the combined application of three different doses of VFG compost and cattle slurry and one treatment with only mineral N applied, during 9 years on a range of soil physical properties: aggregate stability, saturated hydraulic conductivity, bulk density, total pore volume and soil moisture retention. The organic amendments had a significantly beneficial impact (p
Compost was shown to (i) protect the soil against erosion (Bazzoffi et al. 1998; Faucette et al 2004) (ii) to decrease soil acidity (Van den Berghe and Hue 1999) and soil bulk density (Celik et al. 2004), and (iii) to increase soil organic matter content (Celik et al. 2004). Additionally, composts have the potential to protect crops against pathogens (De Brito Alvarez et al. 1995; Epstein 1997; Stratton and Rechcigl 1998; Hoitink et al. 2001). This has been attributed to different mechanisms, such as increased parasitism and antibiosis and induced resistance (Hoitink et al. 1993). There is evidence too that immature compost can be used for weed control, due to the presence of phytotoxins like acetic and propionic acid (Ozores-Hampton et al. 2001). The use of compost has a significant impact on the soil fauna and flora. Pfotzer and Schuler (1997) and Forge et al. (2003) proved that the application of compost enhanced the biological activity of the soil (higher microbial activity and higher numbers of protozoa and bacterivorous nematodes), resulting in enhanced turnover of organic matter and release of plant available nutrients.
Compost from organic wastes was also shown to increase soil organic matter content and to have beneficial effects on soil physical properties in croplands such as total porosity, saturated hydraulic conductivity, available water content, bulk density, aggregate stability and resistance to water and wind erosion (Zebarth et al. 1999; Edwards et al. 2000; Celik et al. 2004). This results in the improvement of the root environment and stimulates the plant growth (Darwish et al. 1995).
Currently, very few field studies exist on the specific effects of VFG compost application to soil. To our knowledge, no studies examined the combined effect of VFG compost and cattle slurry on soil physical properties. The combined application of compost and cattle slurry is relevant under Flemish conditions owing to the huge amounts of animal slurries being produced. The objective of this research was to investigate the effects of separate and combined applications of VFG compost and cattle slurry over a 9-year period on the following soil physical properties: aggregate stability, saturated hydraulic conductivity, bulk density, total pore volume and soil moisture retention.
Materials and Methods
The experiment was located in Melle (experimental site of Ghent University, Belgium, 50[degrees]59' N, 03[degrees]49' E, 11 m above sea level). The sou type is a sandy loam soil with the following granulometrie composition: 10.4 % 0-2 'm, 42.0 % 2-50 [mu]m and 47.6 % > 50 [mu]m. The experimental field was monocropped with maize from 1982 on. From 1997 on, the field was used in a long term experiment with different types of organic and inorganic fertilizers. Some soil chemical parameters at the start of the experiment are summarized in Table 1.
Soil chemical properties of the top soil (0-30 cm) before the start of the experiment
The experimental design is a block design with three replicates; plot size is 9 m x 9 m. The following treatments and their combinations were applied (Figure 1):
FIGURE 1. Experimental design of the field trial: S- = no slurry, S+ = slurry, CO = no compost, C1 = 22.5 ton ha^sup -1^ compost yearly, C2 = 45 ton ha^sup -1^ compost every other year till 2003, from 2004 on 22.5 ton ha^sup -1^ compost three yearly, ON = 0 kg N ha^sup -1^ yearly, 100N = 100 kg N ha^sup -1^ yearly, 200N = 200 kg N ha^sup -1^ yearly.
C: spring application of vegetable, fruit and garden waste (VFG) compost at a rate of 0, 22.5 or 45 ton compost ha^sup -1^ (C0, C1 and C2 respectively), applied after ploughing and incorporated with a rotary harrow.
S: spring application of dairy cattle slurry (S+) or no slurry application (S-) (the amount slightly differed form year to year); the surface application was immediately followed by incorporation with a cultivator and a few days later the soil was ploughed.
N: mineral nitrogen fertilization (ammonium nitrate 27%) of 0,100 and 200 kg N ha^sup -1^ year^sup -1^ (0N, 100N and 200N, respectively), applied just before sowing (after ploughing) and incorporated with a rotary harrow.
Fertilizer and organic matter amendments were applied every year, except the 45 ton ha^sup -1^ VFG compost, which was applied every other year. In 2004, it was decided to slightly change the experimental design. On the C2 plots the application of 45 ton ha^sup -1^ VFG compost every other year was changed in an application of 22.5 ton ha^sup -1^ every three years, starting in 2004 with the first application. The precise amounts and application dates of compost and manure are shown in Table 2. The amounts applied (22.5 ton ha^sup -1^ VFG compost and ca. 40 - 50 ton ha^sup - 1^ cattle slurry yearly) are similar to what is used in conventional agriculture. The combined application of compost and slurry results in a rather high amount of nutrients added. Table 3 gives the average composition (1997-2005) of the applied cattle slurry and VFG compost. On the plots receiving no slurry, an additional amount of 300 kg ha^sup -1^ K^sub 2^O (muriate of potash, 40%) and 75 kg ha^sup -1^ P^sub 2^O^sub 5^ (triple super phosphate) was applied yearly. Every year the mineral fertilizer was applied the day following the compost application.
Quantities of compost and slurry applied in the period 1997-2005
Average composition (standard deviation between brackets) of the cattle slurry and VFG compost (1997-2005)
Soil samples were taken on August 31, 2005 for the determination of aggregate stability and hydraulic conductivity. For the aggregate stability, on each plot 15 cores were taken to a depth of 10 cm, using an auger with a diameter of 1.8 cm, and bulked. Three undisturbed ring samples (volume of 98 cm^sup 3^) were taken per plot for the determination of the saturated hydraulic conductivity (Ks). Two additional undisturbed ring samples (volume of 98 cm^sup 3^) were taken per plot on March 17,2006 to measure the soil moisture retention, the total pore volume (TPV) and the bulk density (BD).
Samples were taken exclusively on plots amended with all possible combinations of compost (C0, C1 and C2) and cattle slurry (S- and S+), but without mineral N application. The plots fertilized with 200 kg mineral N ha^sup -1^ year^sup -1^ (200N) but without organic amendments (CO and S-) were also sampled.
Soil Physical Properties
Two methodologies were used to measure the aggregate stability: the procedure of De Leenheer and De Boodt (1959), adjusted by Hofman (1973) and the method of Le Bissonnais (1996). For the methodology of De Leenheer and De Boodt (1959), 300 g of the air dried soil samples sieved over an 8 mm sieve were sieved again over a set of sieves with the following apertures: 8,4.76,2.83 and 2 mm. The set of sieves was gently shaken by hand to obtain several aggregate fractions (8 - 4.76 mm, 4.76 - 2.83 mm and 2.83 - 2 mm), which were weighed in nickel cups. The fraction
The procedure of Le Bissonnais (1996) encompasses 3 different methods which represent different wetting conditions: fast wetting (Method I), slow wetting (Method II) and mechanical breakdown by shaking after pre-wetting (Method III). Air dried samples were forced through a 4.76 mm sieve and the 3 - 4.76 mm aggregates were selected. These aggregates were put in the oven at 40[degrees]C for 24h in order to obtain a constant marrie potential. The 3 methods differ in the way the aggregates are wetted. Method I simulates the field conditions of wetting by a heavy rain storm in the summer. The slow wetting with controlled tension in Method II corresponds to a field condition of wetting under a gentle rainfall. It is less destructive than fast wetting and may allow a better discrimination between unstable soils. In Method III, the objective of pre-wetting is to test the wet mechanical cohesion of aggregates independently of slaking. Therefore, the air must be removed from the aggregates before the energy is applied. This can be done by rewetting with a nonpolar liquid such as ethanol. At the end of all three procedures, the aggregates were oven dried and sieved on a set of 6 sieves: 2000, 1000, 500, 200, 100 and 50 centsm.
Le Bissonnais also classified the aggregate stability of the soils depending on the MWD.
During the 9 years of the experiment, the evolution of the soil organic carbon content in the 0-30 cm layer was monitored. Soil was sampled in 1997, 2000 and 2003 (bulk sample consisting of 3 samples per plot to a depth of 30 cm) and the soil organic carbon (SOC) content was measured following Walkley and Black (1934) and Walkley (1947). In spring 2004 (March 17) bulk samples were taken on plots amended with compost and/or slurry to analyze the soil chemical properties of the top soil layer (0-30 cm) (Table 4).
Soil chemical properties of the top soil (0-30 cm) as sampled on March 17,2004
Data were subjected to analyses of variance (ANOVA) tests using S- Plus software and significant differences between means were determined by Tukey's test.
Nine years of different organic fertilizer treatments had a significant effect on soil physical properties. Compost and cattle slurry applications significantly influenced the soil aggregate stability (p
FIGURE 2. Aggregate stability expressed as the stability index following De Leenheer and De Boodt (1959). Different letters indicate significant (p
FIGURE 3. Aggregate stability expressed as the mean weight diameter following the Le Bissonnais methods (1996) (BI = method 1, BII = method 2 and BIII = method 3). Different letters indicate significant (p
VFG compost and cattle slurry, increased Ks significantly (p
FIGURE 4. Saturated hydraulic conductivity. Different letters indicate significant (p
The soil moisture retention curves of the 7 different treatments in the top soil were quite similar. Therefore, in Table 5 only the moisture content values at -10, -30, -50, -70, -100 (field capacity), -345, -1033, and -15495 cm (permanent wilting point) are presented. Since the addition of organic matter to the soil usually has the highest influence on the lower tension range (matric potential) of the soil moisture retention curve, only this range (saturation to field capacity) of the curves was compared. Statistical analysis showed that there was no significant difference (p
Soil moisture content, expressed as volume/volume (v/v), at different suction heads (S- = no slurry; S+ = slurry; C0 = no compost; C1 = 22.5 ton ha-1 compost yearly; C2 = 45 ton ha^sup -1^ compost every other year till 2003, from 2004 on 22.5 ton ha^sup - 1^ compost three yearly; 200N = 200 kg N ha^sup -1^ yearly)
The inverse relationship between BD and TPV with respect to the different fertilizer treatments is shown in Figure 5. The application of compost and slurry significantly affected (p
In Figure 6 the evolution of the soil organic carbon (SOC) content during the first seven years of the experiment is presented. On plots without organic amendments (C0S- and C0S-200N) there was a clear downward trend, while on all organically amended plots, the SOC content increased. The combined application of the two organic amendments resulted in the highest SOC content.
FIGURE 5. Bulk density and total pore volume. Different letters indicate significant (p
FIGURE 6. Evolution of the soil organic carbon content between 1997 and 2003
The results for the SI obtained by the method of De Leenheer and De Boodt (1959) were similar to these of the MWD of the Le Bissonnais (1996) method. Organical treatments had a significantly positive influence on aggregate stability. Similar findings in other studies involving organic amendments to soils were reported by Aggelides and Londra (2000) who found that the improvement of the aggregate stability was proportional to the compost application rate after a one time addition of compost (made of town wastes, sewage sludge and sawdust) ranging from 0, 39,78 to 156 ton ha^sup -1^. Guerrero et al. (2000) found that a single application of as little as 10 ton ha^sup -1^ of municipal solid waste compost had a beneficial effect on aggregate stability. Aggregate stability is strongly correlated with SOC content (Hofman 1973; Chaney and Swift 1984; Elliot 1986). Figure 6 shows a steadily increase of SOC on organically amended plots with time. SOM is assumed to stabilize aggregates and to protect them against disruptive soil processes like slaking, mechanical and physico-chemical dispersal and differential swelling of clays (Le Bissonnais 1996) by two major actions. On the one hand, OM increases the cohesion of aggregates through the binding of mineral particles by organic polymers, or through the physical enmeshment of particles by fine roots or fungi (Tisdall and Oades 1982). On the other hand, OM may decrease the wettability of aggregates, slowing their rates of wetting and thus the extent of slaking (Sullivan 1990). Therefore, increase of SI or MWD can be related to the increased SOM content of the organically fertilized plots.
When comparing Figure 2 and 3, it is clear that the method described by De Leenheer and De Boodt (1959) was superior to the method of Le Bissonnais (1996) in discriminating between the different treatments. Indeed the differences within the values of the SI for the different treatments as measured by the De Leenheer and De Boodt method (Figure 2) were much more pronounced (SI of the C2S+ plots was 4 to 5 times higher than the Si of the C0S- plots) compared to the values of the MWD of the three methods of Le Bissonnais (Figure 3). Casamitjana i Causa (2005) also concluded that the most sensitive procedure to assess management related changes in aggregate stability was the one described by De Leenheer and De Boodt. The increase of Ks can be related to the formation of larger and more stable aggregates due to the OM application. Addition of OM will result in an increase of the SOM content (Figure 6) and hence of the total pore volume (TPV), which can be clearly seen in Figure 5. As soil permeability is a function of TPV, increased pore volume or porosity has a direct influence on the Ks of the soil (Flowers and Lal 1998). Celik et al. (2004) found in a 5- year field experiment that the application of 25 ton ha^sup -1^ compost (made of a mixture of grasses, stubbles and leaves) and 25 ton ha^sup -1^ farm manure among other fertilizer treatments, significantly affected the saturated hydraulic conductivity. Comparable results have been found by Aggelides and Londra (2000) and many others. The lower level of SOM on plots receiving no exogenous OM (Figure 6) weakened the OM effect on aggregation and hence on saturated hydraulic conductivity.
As for the results of the aggregate stability, the highest values of the Ks are found on the plots with a combined application of slurry and VFG compost. It is however striking that the highest values for SI, MWD, Ks and TPV were found consistently on the C2S+ plots and that these values are in all cases much higher (sometimes even significantly, p
The increase of the Ks and the aggregate stability on organically amended plots can also be linked with the abundance of the soil biota. Addition of OM to the soil is believed to be one of the major management variables affecting soil biota, e.g. earthworms. Moreover, earthworms are believed to play a crucial role in aggregate formation and soil structure (Bardgett 2005). Leroy et al. (2007) observed on the same field experiment that on plots amended with VFG compost and slurry the earthworm abundance outnumbered the earthworm population on the C0S-plots and that the effect of the compost was much more pronounced than that of slurry.
Only small differences in soil moisture retention were observed (Table 4). The C2S+ plots tended to have the largest water content at pF 1 (-10 cm), while it was the lowest for plots without slurry or compost application. While the TPV was significantly (p
The soil physical parameters tended to be similar or even worse on the plots receiving only mineral fertilizer (C0S-200N) compared to the C0S- plots. For some parameters as Ks or TPV these differences were large, however not significant (p
Application of moderate amounts of exogenous organic matter seems to improve the soil physical conditions significantly through better aggregation, increased saturated hydraulic conductivity and reduced bulk density. Better soil physical quality is expected to result in more favourable crop growing conditions and hence better yields and yield stability, which was proved by Nevens and Reheul (2003) and Leroy et al. (2007) on the same experimental field. Better crop and root growth, also due to the fertilization, will in turn result in a further improvement of the soil physical properties.
Along with organic amendments' potential benefits to a soil's physical properties, there may be environmental consequences due to long-term applications which certainly have to be taken into account. Long term application of large amounts of OM to the soil may induce environmental risks such as a (higher) nitrate leaching to the ground water. Nitrate leaching as a result of agricultural practices is responsible for much of the environmental damage caused to terrestrial and marine ecosystems (Flores et al. 2005). Much research has focused on nitrate leaching because of increasing concentrations in ground and drinking waters (Hansen et al. 2001; Follett and Delgado 2002). In order to minimize the risk of nitrate leaching upon application of large amounts of exogenous OM, attention should be paid to select these types of OM which maximize the addition of stable organic carbon to the soil combined with a limited nutrient content and a low nutrient release during the period of leaching risk, especially on coarse textured soils. Not only nitrate leaching, but also P movement can result in water quality problems. As most soils possess a strong capacity to sorb phosphates, in contrast to nitrates, the excess of applied phosphate through organic and mineral fertilizers is accumulated in the top soil (Beek and Van Riemsdijk 1982). However, this sorption capacity is limited. Therefore, repeated excessive applications can result in P saturation and significant P leaching to the ground water in acid, light textured soils (De Smet et al. 1996). Moreover, runoff, carrying soil particles to which phosphates are sorbed, may occur and result in eutrophication of surface waters (Withers et al. 2003, Elliott et al. 2007). In this experiment the application of slurry and/or compost did not result in considerably higher P levels in 2004 (Table 4) compared to the initial situation in 1997 (Table 1). However, following Hendrickx et al. (1992) the initial P level should be considered as being rather high, so every amendment may increase the risk of phosphate losses.
The authors wish to thank Franky Van Peteghem and Jean-Pierre Van Maerke for their assistance with the field work and Jan Restiaen for help in the determination of the soil physical properties.
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Ben L. M. Leroy1, Herath M. S. K. Herath1, Stefaan De Neve1, Donald Gabriels1,
Lydia Bommele2, Dirk Reheul2 and Maurice Moens3
1. Ghent University, Department of Soil Management and Soil Care, Gent, Belgium
2. Ghent University, Department of Plant Production, Gent, Belgium
3. Institute for Agricultural and fisheries Research, Merelbeke and
Ghent University, Department of Crop Protection, Gent, Belgium
Copyright J.G. Press Inc. Winter 2008
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