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Corn and weed residue decomposition in northeast Ohio organic and conventional dairy farms
Agriculture, Ecosystems and Environment 95 (2003) 559–565
Corn and weed residue decomposition in northeast Ohio organic and conventional dairy farms R.I. Vazquez a,∗ , B.R. Stinner b,c , D.A. McCartney c a
b
Institute for Agriculture and Trade Policy, 2105 First Avenue South, Minneapolis, MN 55404-2505, USA Environmental Science Graduate Program, The Ohio State University, OARDC, Wooster, OH 44691-4096, USA c Department of Entomology and Agroecosystems Management Program, The Ohio State University, OARDC, Wooster, OH 44691-4096, USA Received 20 July 2001; received in revised form 27 September 2002; accepted 30 September 2002
Abstract Increasingly, farmers claim that management practices can significantly influence soil quality. For instance, it is common practice for dairy farms in their rotation cycle to harvest grain and then leave stubble and weeds over winter on the soil surface before ploughing in spring ahead of planting crops. Corn stubble and weeds protect soil in winter, decompose through the seasons, and release nutrients that are utilized by crops and microorganisms. Also, plant residues may harbor increased soil decomposing organisms that feed up on them. Both conventional and organic farmers tend to follow these practices with the major difference that in the conventional systems, inorganic fertilizers and pesticides are applied. Organic matter breakdown in soils under different management (organic versus conventional as in this case) may be different because some inorganic chemicals are known to affect soil decomposers and also these might be less abundant in soils with less food resources, since the organic farmers rely totally on soil fertility derived from organic source. This hypothesis was tested in an on-farm decomposition study conducted in an organic and a conventional farm that grew corn (Zea mays L.) for dairy cattle feed, in Wayne County, OH. Mesh bags containing crop and weed residues were laid on the soil surface at the onset of winter and sampled thereafter to determine decomposition. Mass loss was significantly different among substrates, with crop residues decomposing faster than weeds. Mass and nitrogen (N) loss varied among substrates and variations were greater in summer. Between farms mass and N loss were significantly higher in the organic farm in summer. Earthworm population density was significantly higher in the organic farm. In summary, corn residues decomposed faster than weed residues, and differences in decomposition among substrates increased in summer. Decomposition was faster in summer at both farms, however, it was higher at the organic one, where more soil decomposers were found. The higher metabolic activity in the soil of the organic farm in warmer weather suggests a more active soil biota, which may be crucial for farms whose main or sole source of nutrients derives from organic matter decomposition. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Organic matter; Organic and conventional farms; Mesh bags; Decomposers; Soil metabolic activity; Wayne County (Ohio)
1. Introduction
∗ Corresponding author. Tel.: +1-612-870-3441; fax: +1-612-870-4846. E-mail address: [email protected] (R.I. Vazquez).
There is a broad range of soil management practices aimed at maintaining soil fertility, among them is the application of organic amendments to the soil, such as animal manure, crop residues, etc. (Wander
0167-8809/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 8 8 0 9 ( 0 2 ) 0 0 1 7 6 - 7
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R.I. Vazquez et al. / Agriculture, Ecosystems and Environment 95 (2003) 559–565
et al., 1994; Magdoff, 1995; Karlen and Cambardella, 1996) as well as inorganic fertilizers. The organic substrates eventually decompose and release nutrients that can be used by plants and microorganisms (Hendrix et al., 1986). Soils managed, primarily, with synthetic fertilizers and pesticides may differ in both numbers and species composition of decomposers compared with soils not receiving inorganic chemicals (Edwards and Thompson, 1973; Hendrix et al., 1990), although the impacts of chemicals would be expected to vary depending upon specific products and their time and mode of application (Edwards, 1989; Edwards and Bohlen, 1994). Differences in richness or abundance of soil biota may affect organic matter decomposition rates (Parker, 1990), a process crucial for soils whose fertility is dependent upon nutrient release from organic matter breakdown. Another factor that influences organic matter decomposition is litter quality (Berg and Staaf, 1980; Melillo et al., 1982). For example, high nitrogen (N) content and low lignin concentration of plant residue are typically associated with high biological activity (Berendse et al., 1987), because decomposers (e.g. microorganisms and invertebrates) that need N for reproduction (and carbon (C) as an energy source) attack N-rich substrates first (Smith et al., 1993). Soil metabolic activity may serve as an indicator of soil quality because it is an expression of the activity of soil biota and therefore, represents an indirect measure of its richness and/or abundance. However, differences in soil quality might not be evident under harsh environmental conditions, similar to what is experienced during winter in the northcentral US. Climatic variables affect decomposition rates of organic matter (Meentemeyer, 1978; Swift et al., 1979), because the biological activity of decomposers, i.e. microorganisms, overall is regulated by moisture and temperature (Elliott and Stott, 1997). In this study, an on-farm decomposition experiment was conducted at two Ohio dairy farms under different soil management practices: the organic farm applied organic amendments to sustain soil fertility and the conventional farm added inorganic fertilizers. The conventional one also applied herbicides and insecticides to control for weeds and insects. The research objectives were: (1) to compare decomposition among crop and weed residues that are left atop the soil after harvest; (2) to compare decomposition of crop and weed residues through the seasons; (3) to
compare decomposition of crop and weed residues between an organic and a conventional farm.
2. Materials and methods 2.1. The study site This study was conducted at two dairy farms in Wayne County, OH, in the Winter, Spring and early Summer of 1993. Soils at the study sites were Luvisols (fine-loamy, mixed, mesic Ultic Hapludalf Alfisols from the Mechanicsburg series). Both farms produced corn for grain and silage, and hay, i.e. alfalfa (Medicago sativa), orchard grass (Dactylis glomerata), and small grains (wheat (Triticale), oat (Avena)). The organic farm followed a 5-year rotation system, in which 2 consecutive years were planted with corn and the remaining 3 years with forage crops. Cow manure composted with oats straw from the stable bedding was spread and incorporated into the soil during the early spring before planting corn. During the 1st year of corn production, the whole above ground portions of the plant—stalk and grain—were harvested for silage, so the ground was left nearly bare. Only grain was harvested from the 2nd-year corn, so relatively large quantities of corn residues (leaves, stalks, and roots) and weeds were left on the ground throughout winter. In early spring of the 3rd year, the corn and weed residues were turned under the soil when the land was ploughed in preparation for planting alfalfa, orchard grass, and oats. Forage crops remained during the next 3 years and were harvested 2–3 times a year to feed the cows. In early spring of the 6th year cow manure was spread and then ploughed under, together with hay residues and the 5-year cycle began. Weeds were controlled using a rotary hoe and a cultivator. Gypsum was applied to corn and hay crops. The conventional farm had a shorter crop rotation, in which corn was planted for 3–4 years, and after that forage crops were planted for about 3 years. Liquid cow manure was applied in Spring before ploughing in preparation for planting crops, and nitrogen phosphorus, and potassium (NPK) fertilizer was applied after planting as a starter, with additional N as a side dress treatment. Corn plants were harvested for silage, so little residue was left on the soil over winter. Insecticides were used at the standard rate to control
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corn rootworm (1.45 kg/ha phorate: 0,0-diethyl S[(ethylthio) methyl], phosphorodithioate) and as a seed treatment (0.3 g/kg seed diazinon: diethyl 0-(2isopropyl-6-methyl-4-pyrimidinyl), phosphorothioate). Herbicides were applied at standard rates 1–2 weeks after planting, 1.12 kg/ha cyanazine (2[[4chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile), 0.28 kg/ha potassium salt of dicamba (3.6-dichloro-o-anisic acid), and 1.12 kg/ha atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine). Crop rotations may vary at each farm, depending on weather and needs, sometimes orchard grass may be planted with alfalfa at the organic farm, and wheat may be planted after corn at the conventional farm in certain years. The experiment began after the grain harvest of the 2-year corn at the organic farm and silage harvest at the conventional farm. 2.2. Experimental design and sampling Treatments were arranged in a randomized complete block at each farm. On each farm two sets of six consecutive plots each, opposite from one another and separated by 17 rows of corn, were established. Plots dimensions were 25 corn rows by 11 paces wide. A pace was 0.5 m long. Plot size was determined by counting corn rows and paces whose numbers were drawn from a random table. Mesh bags made of fibreglass, 10 cm × 10 cm, 1 mm × 1 mm mesh size, were filled with oven-dried (60 ◦ C) samples of corn residues (leaves and stalks), four common weeds, and a mixture of the four weeds (referred to as mixed weeds) for a total of six treatments. The weeds used were giant foxtail (Setaria faberi), Pennsylvania smartweed (Polygonum pensylvanicum), smooth pigweed (Amaranthus hybridus), and common lambsquarters (Chenopodium album). Initially, one mesh bag per substrate type was filled with substrate, weighed, and the substrate weight calculated. All subsequent mesh bags for each type were weighed with about the same oven-dried weight as the initial one. On 15 December 1992, on each of the 12 plots at both farms mesh bags were laid on the ground surface: three bags of corn residue and of mixed weeds; plus one bag of each of the four weed species. Bag location was determined drawing digits from a random table, which were then counted as paces from the beginning
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of the plot. On 11 March, 9 April, and 22 July 1993 one mesh bag each of corn residue and mixed weeds, were collected from every other plot. Four mesh bags, one of each weed species, were collected on the second and third collection dates from every other plot. The mesh bags collected on 22 July were out of the field for 55 days (from 9 April to 3 June), in a cold room, because the land was ploughed for the spring crops, oats and alfalfa, and rains made it difficult to till on time. The mesh bags were buried in a vertical position under the soil surface on 3 June (to simulate conditions of ploughed crop residues) where they remained until 22 July. Early rain was followed by a drought and as a consequence, mesh bags containing corn residue and mixed weeds were sampled on three dates only, and not on six dates as originally planned because the experiment was forced to end when the field at the organic farm was ploughed and replanted again due to a crop failure (not part of this study). Also, on 9 April earthworms (Lumbricus rubellus) were collected and counted from the surface using a 0.25 m square frame on all plots at both farms. Roots and large pieces of contaminant soil were removed from the mesh bags before they were ovendried at 60 ◦ C. Oven-dried mesh bag content was weighed, ground and subsamples ashed at 500 ◦ C in a muffle furnace to determine percentage ash free dry mass (% AFDM). Similarly, soil samples from each plot were ground, dried at 60 ◦ C, weighed, and ashed at 500 ◦ C to determine percentage of soil organic matter. 2.3. Calculations and statistical analysis Litter mass was corrected for soil contamination before determining mass loss using the following equation (Blair, 1988) Fli =
SaAFDM − S1AFDM , LiAFDM − S1AFDM
where Fli is the fraction of mesh bag content that is actually the litter, SaAFDM the % AFDM of the entire mesh bag sample, S1AFDM the average % AFDM of the soil at the site, and LiAFDM is the initial % AFDM of the litter substrate. There are three underlying assumptions in this equation: (1) the proportion of organic matter is the same in the soil contaminating the mesh bags; (2) the proportion of organic matter is constant in litter as it
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decomposes; (3) the only contaminant of the mesh bags is soil. Proportion of remaining litter at time t was calculated as the product of remaining litter and the sample fraction that is litter (Fli), divided by the initial oven-dry weight. One sample of each substrate per farm from each collection date was ground in a Brinkmann centrifugal mill, then dried at 60 ◦ C for 48 h and analyzed for N and C concentration using a Carlo-Erba NA 1500 Series II C/N analyzer. Similarly, soil samples from each plot underwent the same procedure as the mesh bags to determine N and C concentrations present in the soil. Soil N and C contamination of substrates in the mesh bags was corrected using the following equation (Blair, 1988) LiNt =
[SaNt − (FSl × SlNt)] , Fli
where LiNt is the nutrient concentration in the residual litter, SaNt the nutrient concentration of the entire sample, SlNt the average nutrient concentration in the soil, FSl the fraction of the sample that is soil (1 − Fli from the soil correction equation), and Fli is the fraction of the sample that is litter. Proportion of nutrient remaining at time t was calculated as the product of proportion mass remaining and nutrient concentration in the residual material (LiNt) at time t divided by the initial nutrient concentration of that litter type. On the data of the proportion of remaining litter two ANOVAs were run in Minitab using the general linear model (GLM), one for corn residue and mixed weeds sampled on 11 March, 9 April, and 22 July, and another for corn residue, mixed weeds, and the four weed species collected on 9 April and 22 July.
Ranking of substrates and of farms was made by means of the least significant difference (LSD) of the means. The data was arranged in two tables to emphasize differences between residues of corn and mixed weeds on three collection dates as compared to two dates for individual weeds.
3. Results and discussion Crop and weed residues had different initial nutrient content characterized by low N (Table 1). Corn with higher initial N concentration decomposed faster than weeds (P < 0.025) (Tables 2 and 3). However, among weeds, lambsquarters with the highest initial N lost less biomass (P < 0.025) (Tables 1 and 3). There were differences in organic matter decay among farms, with substrates decomposing significantly faster at the organic farm in the warmer season (P < 0.025) (Tables 2 and 3). Earthworm counts were significantly higher at the organic farm (P < 0.001). The two-way interaction between substrates and field days (P < 0.01) and between farms and field days (P < 0.05), indicate that differences in decomposition among substrates and between farms varied with sampling date (Tables 2 and 3). Thus, weather conditions seemed to have affected soil biological activity. 3.1. Litter quality Litter quality is known to influence decomposition rates (Melillo et al., 1982). Initial N concentration may have influenced decomposition rates. Thus, corn residues with the highest N content decayed faster
Table 1 Initial and final N concentrations and C:N ratios for corn and weed residues in the organic and conventional farms Residue
Initial N (%)
Corn Mixed weeds Foxtail Lambsquarters Smartweed Pigweed
1.51 1.12 0.97 1.46 0.73 1.32
Final C:N
33.1 42.8 46.7 31.1 60.7 32.6
N (%)
C:N
Organic
Conversion
Organic
Conversion
1.91 1.62 1.36 0.70 1.50 1.07
3.53 1.40 1.22 1.02 1.44 1.65
25.6 28.9 34.2 66.3 31.6 43.2
16.3 33.1 40.2 45.8 31.9 28.2
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Table 2 Ranking of means of the proportions of remaining litter and N for corn and mixed weeds residues, and for the organic and conventional farms on three collection dates (LSD) (P < 0.025)a Residue
Field days 86 (11 march 1993)
115 (9 April 1993)
164 (22 July 1993)
Proportion of remaining litter (means) Corn 0.71a (±0.04) Mixed weeds 0.89b (±0.03)
0.71a (±0.07) 0.81b (±0.05)
0.2a (±0.06) 0.44b (±0.07)
Both substrates Organic Conventional
0.8a (±0.03) 0.81a (±0.04)
0.74a (±0.07) 0.77a (±0.05)
0.27a (±0.06) 0.37b (±0.06)
Proportion of remaining nitrogen (means) Corn 0.66a (±0.1) Mixed weed 0.53a (±0.75)
0.65a (±0.07) 0.48a (±0.04)
0.42a (±12) 0.35a (±0.06)
Both substrates Organic Conventional
0.59a (±0.06) 0.56a (±0.05)
0.27a (±0.08) 0.49b (±0.1)
0.59a (±0.07) 0.55a (±0.1)
a For remaining litter units are grams dry matter remaining per grams dry matter initial. For remaining N units are grams of N in dry matter remaining per grams of N in dry matter initial.
than the rest (Tables 1–3). Pigweed with high N content, by spring proportionally lost as much mass as corn residue (Tables 1 and 3). However, lambsquarters residue, with the highest initial N concentration among weeds, decomposed relatively fast by spring but became the slowest decomposing substrate with the least N concentration by summer (Tables 1 and 3). It may be that lambsquarters released its more degradable compounds first and contained mostly recalcitrant material by summer. Also, smartweed (with least N) was the slowest decomposing substrate by the spring but its decay increased by summer, proportionally losing the least N. Possibly N in smartweed was protected in a recalcitrant fraction and mostly degradable compounds were released. Substrates were analyzed only for N, not for soluble compounds (i.e. sugars), or for polysaccharides (i.e. starch) or recalcitrant compounds (i.e. lignin), therefore its presence is deduced from previous research (Swift et al., 1979; Melillo et al., 1982). Most substrates increased their N concentration by summer (Table 1). Nitrogen concentration tends to increase during decomposition due to a faster loss of C (Swift et al., 1979; Blair, 1988).
one in summer (Tables 2 and 3). Litter ingestors, i.e. earthworms, were significantly more numerous at the organic farm (mean = 55.6 m−2 ) in early spring than at the conventional one (mean = 0.34 m−2 ), a factor which may have contributed to increase organic matter decomposition. N concentration was greater for most substrates at the end of the study (Table 1). Some substrates had higher N concentration at the conventional than at the organic farm. The proportion of remaining N in substrates was greater at the conventional farm than at the organic one at the end of the study (Tables 2 and 3). N increase can occur due to fungal translocation (Beare et al., 1992) which might have taken place at both farms. If translocation occurred, presumably earthworms at the organic farm ate the enriched N residues, which might explain the lower N concentration levels of some substrates and the lower proportion of remaining N compared to the conventional farm. Also, N levels might have been higher at the conventional farm because of N fertilizer and higher inputs of cow manure.
3.2. Litter and N changes between farms
Warmer weather increases biological activity as well as organic matter breakdown (Meentemeyer, 1978). The later indeed increased during summer at both farms, however it was significantly faster in the
Substrates decomposed significantly faster (P < 0.025) at the organic farm than at the conventional
3.3. Weather effect
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Table 3 Ranking of means of the proportions of remaining litter and N for residues of corn, mixed weeds, individual weeds, and for the organic and conventional farms on two collection dates (LSD, P < 0.025)a Residue
Field days 115 (9 April 1993)
164 (22 July 1993)
Proportion of remaining litter (means) Corn 0.71a (±0.04) Mixed weeds 0.81b (±0.05) Foxtail 0.85cb (±0.06) Pigweed 0.68a (±0.09) Lambsquarters 0.82b (±0.03) Smartweed 0.91c (±0.02)
0.2a (±0.06) 0.44bc (±0.07) 0.42bc (±0.03) 0.37b (±0.05) 0.58d (±0.08) 0.47c (±0.07)
All substrates Organic Conventional
0.37a (±0.06) 0.45b (±0.06)
0.78a (±0.06) 0.81a (±0.04)
Proportion of remaining nitrogen (means) Corn 0.65ab (±0.07) Mixed weeds 0.5a (±0.04) Foxtail 0.73bc (±0.3) Pigweed 0.50a (±0.05) Lambsquarters 0.47a (±0.05) Smartweed 0.89c (±0.09)
0.42a 0.35a 0.53a 0.41a 0.35a 0.92b
All substrates Organic Conventional
0.42a (±0.06) 0.57b (±0.08)
0.61a (±0.07) 0.64a (±0.07)
(±0.12) (±0.06) (±0.06) (±0.08) (±0.05) (±0.06)
a For remaining litter units are grams dry matter remaining per grams dry matter initial. For remaining N units are grams of N in dry matter remaining per grams of N in dry matter initial.
soil of the organic farm (P < 0.05) (Tables 2 and 3). Variation in decomposition was greater in summer (P < 0.025) (Tables 2 and 3). Also, the interaction between farms and field days (P < 0.05), as well as between substrates and field days (P < 0.01) indicate that differences in decomposition (between farms and among substrates) varied significantly with sampling date. It should be noted that the mesh bags collected on 22 July were under the soil surface for 49 days, previously they were atop the surface during winter and early spring (before they were removed for land preparation). Because they were buried, the mesh bags sampled in summer were in closer contact with decomposers, such as soil microorganisms and invertebrates. Buried substrates by being in closer contact with soil organisms would be more affected by an increase of biological activity than substrates laying on the soil surface (Beare et al., 1992).
4. Conclusions Higher metabolic activity may be an indicator of soil biological quality. It seems that litter, soil biology, and weather are all interconnected in soil ecological processes. Crop and weed residues because of their wide C:N ratios contribute more C than N to soils (Melillo et al., 1982; Berendse et al., 1987; Smith et al., 1993). Also, because of their slow decomposition some C may be sequestered for a longer period in the organic matter pool. Faster decomposition in organic soils may not translate into all C being released into the atmosphere, but in more long-term soil C sequestration (Wander et al., 1994). In summary, residue quality influenced organic matter decay. Residues with high initial N concentration experienced faster decomposition, with corn residues being the fastest. Organic matter decay was higher in the soil of the organic farm. Soil metabolic activity increased with warmer weather at both farms. However, wider differences in decomposition among residues and faster metabolic activity in the organic farm were observed in summer. Weather appeared to play a significant role in stressing differences in substrate and soil quality.
Acknowledgements We thank Drs. Deborah Stinner, John Cardina, John Vimmerstedt, and David Ferree for their suggestions. Special thanks to Bert Bishop from Computing and Statistical Services at OARDC/OSU for his statistical advice. The help of Rossana Fravetto, Dorothy Brazis, and Donald Beam from the Soil Ecology Lab in Entomology at OARDC/OSU is much appreciated. References Beare, M.H., Parmelee, R.W., Hendrix, P., Cheng, W., Coleman, D.C., Crossley Jr., D.A., 1992. Microbial and faunal interactions and effects on litter nitrogen and decomposition in agroecosystems. Ecol. Monogr. 62, 569–591. Berendse, F., Berg, B., Bosatta, E., 1987. The effects of lignin and nitrogen on the decomposition of litter in nutrient-poor ecosystems: a theoretical approach. Can. J. Bot. 65, 1116–1120. Berg, B., Staaf, H., 1980. Decomposition rate and chemical changes of Scots pine litter. II. The influence of chemical composition. In: Persson, T. (Ed.), Structure and Function of
R.I. Vazquez et al. / Agriculture, Ecosystems and Environment 95 (2003) 559–565 Northern Coniferous Forests—An Ecosystem Study, vol. 32. Ecological Bulletin, Stockholm, pp. 373–390. Blair, J.M., 1988. Nitrogen, sulfur and phosphorus dynamics in decomposing deciduous leaf litter in the southern Appalachians. Soil Biol. Biochem. 20, 693–701. Edwards, C.A., 1989. Impact of herbicides on soil ecosystems. Crit. Rev. Plant Sci. 8 (3), 221–257. Edwards, C.A., Bohlen, P.J., 1994. The effects of contaminants on the structure and function of soil communities. Acta Zool. Fenn. 194, 1–6. Edwards, C.A., Thompson, A.R., 1973. Pesticides and the soil fauna. Residue Rev. 45, 1–79. Elliott, L.F., Stott, D.E., 1997. Influence of no-till cropping systems on microbial relationships. Adv. Agron. 60, 121–147. Hendrix, P.F., Parmelee, R.W., Crossley Jr., D.A., Coleman, D.C., Odum, E.P., Groffman, P.M., 1986. Detritus food webs in conventional and no-tillage agroecosystems. Bioscience 36 (6), 374–380. Hendrix, P.F., Crossley Jr., D.A., Blair, J.M., Coleman, D.C., 1990. Soil biota as components of sustainable agroecosystems. In: Edwards, C.A., Lal, R., Madden, P., Miller, R.H., House, G. (Eds.), Sustainable Agricultural Systems. Soil and Water Conservation Society, Ankeny, IW, pp. 637–654. Karlen, D.L., Cambardella, C.A., 1996. Conservation strategies for improving soil quality and organic matter storage. In: Carter, M.R., Stewart, B.A. (Eds.), Structure and Organic Matter
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Storage in Agricultural Soils. Lewis Publishers, Boca Raton, FL, pp. 395–420. Magdoff, F., 1995. Soil quality and management. In: Altieri, M. (Ed.), Agroecology, the Science of Sustainable Agriculture. Westview Press, Boulder, CO, pp. 349–364. Meentemeyer, V., 1978. Macroclimatic and lignin control of litter decomposition rates. Ecology 59, 465–472. Melillo, J.M., Aber, J.D., Muratore, J.F., 1982. Nitrogen and lignin control of hardwood leaf litter decomposition dynamics. Ecology 63, 621–626. Parker, C.F., 1990. Role of animals in sustainable agriculture. In: Edwards, C.A., Lal, R., Madden, P., Miller, R.H., House, G. (Eds.), Sustainable Agricultural Systems. Soil and Water Conservation Society, Ankeny, IW, pp. 238–245. Smith, J.L., Papendick, R.I., Bezdicek, D.F., Lynch, J.M., 1993. Soil organic matter dynamics and crop residue management. In: Metting Jr., F.B. (Ed.), Soil Microbial Ecology: Applications in Agricultural and Environmental Management. Marcel Dekker, New York, pp. 65–94. Swift, M.J., Heal, O.W., Anderson, J.M., 1979. Decomposition in Terrestrial Ecosystems. University of California Press, Berkeley, CA. Wander, M., Traina, S.J., Stinner, B.R., Peters, S.E., 1994. Organic and conventional management effects on biologically active soil organic matter pools. Soil Sci. Soc. Am. J. 58, 1130–1139.
Corn and weed residue decomposition in northeast Ohio organic and conventional dairy farms R.I. Vazquez a,∗ , B.R. Stinner b,c , D.A. McCartney c a
b
Institute for Agriculture and Trade Policy, 2105 First Avenue South, Minneapolis, MN 55404-2505, USA Environmental Science Graduate Program, The Ohio State University, OARDC, Wooster, OH 44691-4096, USA c Department of Entomology and Agroecosystems Management Program, The Ohio State University, OARDC, Wooster, OH 44691-4096, USA Received 20 July 2001; received in revised form 27 September 2002; accepted 30 September 2002
Abstract Increasingly, farmers claim that management practices can significantly influence soil quality. For instance, it is common practice for dairy farms in their rotation cycle to harvest grain and then leave stubble and weeds over winter on the soil surface before ploughing in spring ahead of planting crops. Corn stubble and weeds protect soil in winter, decompose through the seasons, and release nutrients that are utilized by crops and microorganisms. Also, plant residues may harbor increased soil decomposing organisms that feed up on them. Both conventional and organic farmers tend to follow these practices with the major difference that in the conventional systems, inorganic fertilizers and pesticides are applied. Organic matter breakdown in soils under different management (organic versus conventional as in this case) may be different because some inorganic chemicals are known to affect soil decomposers and also these might be less abundant in soils with less food resources, since the organic farmers rely totally on soil fertility derived from organic source. This hypothesis was tested in an on-farm decomposition study conducted in an organic and a conventional farm that grew corn (Zea mays L.) for dairy cattle feed, in Wayne County, OH. Mesh bags containing crop and weed residues were laid on the soil surface at the onset of winter and sampled thereafter to determine decomposition. Mass loss was significantly different among substrates, with crop residues decomposing faster than weeds. Mass and nitrogen (N) loss varied among substrates and variations were greater in summer. Between farms mass and N loss were significantly higher in the organic farm in summer. Earthworm population density was significantly higher in the organic farm. In summary, corn residues decomposed faster than weed residues, and differences in decomposition among substrates increased in summer. Decomposition was faster in summer at both farms, however, it was higher at the organic one, where more soil decomposers were found. The higher metabolic activity in the soil of the organic farm in warmer weather suggests a more active soil biota, which may be crucial for farms whose main or sole source of nutrients derives from organic matter decomposition. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Organic matter; Organic and conventional farms; Mesh bags; Decomposers; Soil metabolic activity; Wayne County (Ohio)
1. Introduction
∗ Corresponding author. Tel.: +1-612-870-3441; fax: +1-612-870-4846. E-mail address: [email protected] (R.I. Vazquez).
There is a broad range of soil management practices aimed at maintaining soil fertility, among them is the application of organic amendments to the soil, such as animal manure, crop residues, etc. (Wander
0167-8809/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 8 8 0 9 ( 0 2 ) 0 0 1 7 6 - 7
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et al., 1994; Magdoff, 1995; Karlen and Cambardella, 1996) as well as inorganic fertilizers. The organic substrates eventually decompose and release nutrients that can be used by plants and microorganisms (Hendrix et al., 1986). Soils managed, primarily, with synthetic fertilizers and pesticides may differ in both numbers and species composition of decomposers compared with soils not receiving inorganic chemicals (Edwards and Thompson, 1973; Hendrix et al., 1990), although the impacts of chemicals would be expected to vary depending upon specific products and their time and mode of application (Edwards, 1989; Edwards and Bohlen, 1994). Differences in richness or abundance of soil biota may affect organic matter decomposition rates (Parker, 1990), a process crucial for soils whose fertility is dependent upon nutrient release from organic matter breakdown. Another factor that influences organic matter decomposition is litter quality (Berg and Staaf, 1980; Melillo et al., 1982). For example, high nitrogen (N) content and low lignin concentration of plant residue are typically associated with high biological activity (Berendse et al., 1987), because decomposers (e.g. microorganisms and invertebrates) that need N for reproduction (and carbon (C) as an energy source) attack N-rich substrates first (Smith et al., 1993). Soil metabolic activity may serve as an indicator of soil quality because it is an expression of the activity of soil biota and therefore, represents an indirect measure of its richness and/or abundance. However, differences in soil quality might not be evident under harsh environmental conditions, similar to what is experienced during winter in the northcentral US. Climatic variables affect decomposition rates of organic matter (Meentemeyer, 1978; Swift et al., 1979), because the biological activity of decomposers, i.e. microorganisms, overall is regulated by moisture and temperature (Elliott and Stott, 1997). In this study, an on-farm decomposition experiment was conducted at two Ohio dairy farms under different soil management practices: the organic farm applied organic amendments to sustain soil fertility and the conventional farm added inorganic fertilizers. The conventional one also applied herbicides and insecticides to control for weeds and insects. The research objectives were: (1) to compare decomposition among crop and weed residues that are left atop the soil after harvest; (2) to compare decomposition of crop and weed residues through the seasons; (3) to
compare decomposition of crop and weed residues between an organic and a conventional farm.
2. Materials and methods 2.1. The study site This study was conducted at two dairy farms in Wayne County, OH, in the Winter, Spring and early Summer of 1993. Soils at the study sites were Luvisols (fine-loamy, mixed, mesic Ultic Hapludalf Alfisols from the Mechanicsburg series). Both farms produced corn for grain and silage, and hay, i.e. alfalfa (Medicago sativa), orchard grass (Dactylis glomerata), and small grains (wheat (Triticale), oat (Avena)). The organic farm followed a 5-year rotation system, in which 2 consecutive years were planted with corn and the remaining 3 years with forage crops. Cow manure composted with oats straw from the stable bedding was spread and incorporated into the soil during the early spring before planting corn. During the 1st year of corn production, the whole above ground portions of the plant—stalk and grain—were harvested for silage, so the ground was left nearly bare. Only grain was harvested from the 2nd-year corn, so relatively large quantities of corn residues (leaves, stalks, and roots) and weeds were left on the ground throughout winter. In early spring of the 3rd year, the corn and weed residues were turned under the soil when the land was ploughed in preparation for planting alfalfa, orchard grass, and oats. Forage crops remained during the next 3 years and were harvested 2–3 times a year to feed the cows. In early spring of the 6th year cow manure was spread and then ploughed under, together with hay residues and the 5-year cycle began. Weeds were controlled using a rotary hoe and a cultivator. Gypsum was applied to corn and hay crops. The conventional farm had a shorter crop rotation, in which corn was planted for 3–4 years, and after that forage crops were planted for about 3 years. Liquid cow manure was applied in Spring before ploughing in preparation for planting crops, and nitrogen phosphorus, and potassium (NPK) fertilizer was applied after planting as a starter, with additional N as a side dress treatment. Corn plants were harvested for silage, so little residue was left on the soil over winter. Insecticides were used at the standard rate to control
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corn rootworm (1.45 kg/ha phorate: 0,0-diethyl S[(ethylthio) methyl], phosphorodithioate) and as a seed treatment (0.3 g/kg seed diazinon: diethyl 0-(2isopropyl-6-methyl-4-pyrimidinyl), phosphorothioate). Herbicides were applied at standard rates 1–2 weeks after planting, 1.12 kg/ha cyanazine (2[[4chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile), 0.28 kg/ha potassium salt of dicamba (3.6-dichloro-o-anisic acid), and 1.12 kg/ha atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine). Crop rotations may vary at each farm, depending on weather and needs, sometimes orchard grass may be planted with alfalfa at the organic farm, and wheat may be planted after corn at the conventional farm in certain years. The experiment began after the grain harvest of the 2-year corn at the organic farm and silage harvest at the conventional farm. 2.2. Experimental design and sampling Treatments were arranged in a randomized complete block at each farm. On each farm two sets of six consecutive plots each, opposite from one another and separated by 17 rows of corn, were established. Plots dimensions were 25 corn rows by 11 paces wide. A pace was 0.5 m long. Plot size was determined by counting corn rows and paces whose numbers were drawn from a random table. Mesh bags made of fibreglass, 10 cm × 10 cm, 1 mm × 1 mm mesh size, were filled with oven-dried (60 ◦ C) samples of corn residues (leaves and stalks), four common weeds, and a mixture of the four weeds (referred to as mixed weeds) for a total of six treatments. The weeds used were giant foxtail (Setaria faberi), Pennsylvania smartweed (Polygonum pensylvanicum), smooth pigweed (Amaranthus hybridus), and common lambsquarters (Chenopodium album). Initially, one mesh bag per substrate type was filled with substrate, weighed, and the substrate weight calculated. All subsequent mesh bags for each type were weighed with about the same oven-dried weight as the initial one. On 15 December 1992, on each of the 12 plots at both farms mesh bags were laid on the ground surface: three bags of corn residue and of mixed weeds; plus one bag of each of the four weed species. Bag location was determined drawing digits from a random table, which were then counted as paces from the beginning
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of the plot. On 11 March, 9 April, and 22 July 1993 one mesh bag each of corn residue and mixed weeds, were collected from every other plot. Four mesh bags, one of each weed species, were collected on the second and third collection dates from every other plot. The mesh bags collected on 22 July were out of the field for 55 days (from 9 April to 3 June), in a cold room, because the land was ploughed for the spring crops, oats and alfalfa, and rains made it difficult to till on time. The mesh bags were buried in a vertical position under the soil surface on 3 June (to simulate conditions of ploughed crop residues) where they remained until 22 July. Early rain was followed by a drought and as a consequence, mesh bags containing corn residue and mixed weeds were sampled on three dates only, and not on six dates as originally planned because the experiment was forced to end when the field at the organic farm was ploughed and replanted again due to a crop failure (not part of this study). Also, on 9 April earthworms (Lumbricus rubellus) were collected and counted from the surface using a 0.25 m square frame on all plots at both farms. Roots and large pieces of contaminant soil were removed from the mesh bags before they were ovendried at 60 ◦ C. Oven-dried mesh bag content was weighed, ground and subsamples ashed at 500 ◦ C in a muffle furnace to determine percentage ash free dry mass (% AFDM). Similarly, soil samples from each plot were ground, dried at 60 ◦ C, weighed, and ashed at 500 ◦ C to determine percentage of soil organic matter. 2.3. Calculations and statistical analysis Litter mass was corrected for soil contamination before determining mass loss using the following equation (Blair, 1988) Fli =
SaAFDM − S1AFDM , LiAFDM − S1AFDM
where Fli is the fraction of mesh bag content that is actually the litter, SaAFDM the % AFDM of the entire mesh bag sample, S1AFDM the average % AFDM of the soil at the site, and LiAFDM is the initial % AFDM of the litter substrate. There are three underlying assumptions in this equation: (1) the proportion of organic matter is the same in the soil contaminating the mesh bags; (2) the proportion of organic matter is constant in litter as it
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decomposes; (3) the only contaminant of the mesh bags is soil. Proportion of remaining litter at time t was calculated as the product of remaining litter and the sample fraction that is litter (Fli), divided by the initial oven-dry weight. One sample of each substrate per farm from each collection date was ground in a Brinkmann centrifugal mill, then dried at 60 ◦ C for 48 h and analyzed for N and C concentration using a Carlo-Erba NA 1500 Series II C/N analyzer. Similarly, soil samples from each plot underwent the same procedure as the mesh bags to determine N and C concentrations present in the soil. Soil N and C contamination of substrates in the mesh bags was corrected using the following equation (Blair, 1988) LiNt =
[SaNt − (FSl × SlNt)] , Fli
where LiNt is the nutrient concentration in the residual litter, SaNt the nutrient concentration of the entire sample, SlNt the average nutrient concentration in the soil, FSl the fraction of the sample that is soil (1 − Fli from the soil correction equation), and Fli is the fraction of the sample that is litter. Proportion of nutrient remaining at time t was calculated as the product of proportion mass remaining and nutrient concentration in the residual material (LiNt) at time t divided by the initial nutrient concentration of that litter type. On the data of the proportion of remaining litter two ANOVAs were run in Minitab using the general linear model (GLM), one for corn residue and mixed weeds sampled on 11 March, 9 April, and 22 July, and another for corn residue, mixed weeds, and the four weed species collected on 9 April and 22 July.
Ranking of substrates and of farms was made by means of the least significant difference (LSD) of the means. The data was arranged in two tables to emphasize differences between residues of corn and mixed weeds on three collection dates as compared to two dates for individual weeds.
3. Results and discussion Crop and weed residues had different initial nutrient content characterized by low N (Table 1). Corn with higher initial N concentration decomposed faster than weeds (P < 0.025) (Tables 2 and 3). However, among weeds, lambsquarters with the highest initial N lost less biomass (P < 0.025) (Tables 1 and 3). There were differences in organic matter decay among farms, with substrates decomposing significantly faster at the organic farm in the warmer season (P < 0.025) (Tables 2 and 3). Earthworm counts were significantly higher at the organic farm (P < 0.001). The two-way interaction between substrates and field days (P < 0.01) and between farms and field days (P < 0.05), indicate that differences in decomposition among substrates and between farms varied with sampling date (Tables 2 and 3). Thus, weather conditions seemed to have affected soil biological activity. 3.1. Litter quality Litter quality is known to influence decomposition rates (Melillo et al., 1982). Initial N concentration may have influenced decomposition rates. Thus, corn residues with the highest N content decayed faster
Table 1 Initial and final N concentrations and C:N ratios for corn and weed residues in the organic and conventional farms Residue
Initial N (%)
Corn Mixed weeds Foxtail Lambsquarters Smartweed Pigweed
1.51 1.12 0.97 1.46 0.73 1.32
Final C:N
33.1 42.8 46.7 31.1 60.7 32.6
N (%)
C:N
Organic
Conversion
Organic
Conversion
1.91 1.62 1.36 0.70 1.50 1.07
3.53 1.40 1.22 1.02 1.44 1.65
25.6 28.9 34.2 66.3 31.6 43.2
16.3 33.1 40.2 45.8 31.9 28.2
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Table 2 Ranking of means of the proportions of remaining litter and N for corn and mixed weeds residues, and for the organic and conventional farms on three collection dates (LSD) (P < 0.025)a Residue
Field days 86 (11 march 1993)
115 (9 April 1993)
164 (22 July 1993)
Proportion of remaining litter (means) Corn 0.71a (±0.04) Mixed weeds 0.89b (±0.03)
0.71a (±0.07) 0.81b (±0.05)
0.2a (±0.06) 0.44b (±0.07)
Both substrates Organic Conventional
0.8a (±0.03) 0.81a (±0.04)
0.74a (±0.07) 0.77a (±0.05)
0.27a (±0.06) 0.37b (±0.06)
Proportion of remaining nitrogen (means) Corn 0.66a (±0.1) Mixed weed 0.53a (±0.75)
0.65a (±0.07) 0.48a (±0.04)
0.42a (±12) 0.35a (±0.06)
Both substrates Organic Conventional
0.59a (±0.06) 0.56a (±0.05)
0.27a (±0.08) 0.49b (±0.1)
0.59a (±0.07) 0.55a (±0.1)
a For remaining litter units are grams dry matter remaining per grams dry matter initial. For remaining N units are grams of N in dry matter remaining per grams of N in dry matter initial.
than the rest (Tables 1–3). Pigweed with high N content, by spring proportionally lost as much mass as corn residue (Tables 1 and 3). However, lambsquarters residue, with the highest initial N concentration among weeds, decomposed relatively fast by spring but became the slowest decomposing substrate with the least N concentration by summer (Tables 1 and 3). It may be that lambsquarters released its more degradable compounds first and contained mostly recalcitrant material by summer. Also, smartweed (with least N) was the slowest decomposing substrate by the spring but its decay increased by summer, proportionally losing the least N. Possibly N in smartweed was protected in a recalcitrant fraction and mostly degradable compounds were released. Substrates were analyzed only for N, not for soluble compounds (i.e. sugars), or for polysaccharides (i.e. starch) or recalcitrant compounds (i.e. lignin), therefore its presence is deduced from previous research (Swift et al., 1979; Melillo et al., 1982). Most substrates increased their N concentration by summer (Table 1). Nitrogen concentration tends to increase during decomposition due to a faster loss of C (Swift et al., 1979; Blair, 1988).
one in summer (Tables 2 and 3). Litter ingestors, i.e. earthworms, were significantly more numerous at the organic farm (mean = 55.6 m−2 ) in early spring than at the conventional one (mean = 0.34 m−2 ), a factor which may have contributed to increase organic matter decomposition. N concentration was greater for most substrates at the end of the study (Table 1). Some substrates had higher N concentration at the conventional than at the organic farm. The proportion of remaining N in substrates was greater at the conventional farm than at the organic one at the end of the study (Tables 2 and 3). N increase can occur due to fungal translocation (Beare et al., 1992) which might have taken place at both farms. If translocation occurred, presumably earthworms at the organic farm ate the enriched N residues, which might explain the lower N concentration levels of some substrates and the lower proportion of remaining N compared to the conventional farm. Also, N levels might have been higher at the conventional farm because of N fertilizer and higher inputs of cow manure.
3.2. Litter and N changes between farms
Warmer weather increases biological activity as well as organic matter breakdown (Meentemeyer, 1978). The later indeed increased during summer at both farms, however it was significantly faster in the
Substrates decomposed significantly faster (P < 0.025) at the organic farm than at the conventional
3.3. Weather effect
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Table 3 Ranking of means of the proportions of remaining litter and N for residues of corn, mixed weeds, individual weeds, and for the organic and conventional farms on two collection dates (LSD, P < 0.025)a Residue
Field days 115 (9 April 1993)
164 (22 July 1993)
Proportion of remaining litter (means) Corn 0.71a (±0.04) Mixed weeds 0.81b (±0.05) Foxtail 0.85cb (±0.06) Pigweed 0.68a (±0.09) Lambsquarters 0.82b (±0.03) Smartweed 0.91c (±0.02)
0.2a (±0.06) 0.44bc (±0.07) 0.42bc (±0.03) 0.37b (±0.05) 0.58d (±0.08) 0.47c (±0.07)
All substrates Organic Conventional
0.37a (±0.06) 0.45b (±0.06)
0.78a (±0.06) 0.81a (±0.04)
Proportion of remaining nitrogen (means) Corn 0.65ab (±0.07) Mixed weeds 0.5a (±0.04) Foxtail 0.73bc (±0.3) Pigweed 0.50a (±0.05) Lambsquarters 0.47a (±0.05) Smartweed 0.89c (±0.09)
0.42a 0.35a 0.53a 0.41a 0.35a 0.92b
All substrates Organic Conventional
0.42a (±0.06) 0.57b (±0.08)
0.61a (±0.07) 0.64a (±0.07)
(±0.12) (±0.06) (±0.06) (±0.08) (±0.05) (±0.06)
a For remaining litter units are grams dry matter remaining per grams dry matter initial. For remaining N units are grams of N in dry matter remaining per grams of N in dry matter initial.
soil of the organic farm (P < 0.05) (Tables 2 and 3). Variation in decomposition was greater in summer (P < 0.025) (Tables 2 and 3). Also, the interaction between farms and field days (P < 0.05), as well as between substrates and field days (P < 0.01) indicate that differences in decomposition (between farms and among substrates) varied significantly with sampling date. It should be noted that the mesh bags collected on 22 July were under the soil surface for 49 days, previously they were atop the surface during winter and early spring (before they were removed for land preparation). Because they were buried, the mesh bags sampled in summer were in closer contact with decomposers, such as soil microorganisms and invertebrates. Buried substrates by being in closer contact with soil organisms would be more affected by an increase of biological activity than substrates laying on the soil surface (Beare et al., 1992).
4. Conclusions Higher metabolic activity may be an indicator of soil biological quality. It seems that litter, soil biology, and weather are all interconnected in soil ecological processes. Crop and weed residues because of their wide C:N ratios contribute more C than N to soils (Melillo et al., 1982; Berendse et al., 1987; Smith et al., 1993). Also, because of their slow decomposition some C may be sequestered for a longer period in the organic matter pool. Faster decomposition in organic soils may not translate into all C being released into the atmosphere, but in more long-term soil C sequestration (Wander et al., 1994). In summary, residue quality influenced organic matter decay. Residues with high initial N concentration experienced faster decomposition, with corn residues being the fastest. Organic matter decay was higher in the soil of the organic farm. Soil metabolic activity increased with warmer weather at both farms. However, wider differences in decomposition among residues and faster metabolic activity in the organic farm were observed in summer. Weather appeared to play a significant role in stressing differences in substrate and soil quality.
Acknowledgements We thank Drs. Deborah Stinner, John Cardina, John Vimmerstedt, and David Ferree for their suggestions. Special thanks to Bert Bishop from Computing and Statistical Services at OARDC/OSU for his statistical advice. The help of Rossana Fravetto, Dorothy Brazis, and Donald Beam from the Soil Ecology Lab in Entomology at OARDC/OSU is much appreciated. References Beare, M.H., Parmelee, R.W., Hendrix, P., Cheng, W., Coleman, D.C., Crossley Jr., D.A., 1992. Microbial and faunal interactions and effects on litter nitrogen and decomposition in agroecosystems. Ecol. Monogr. 62, 569–591. Berendse, F., Berg, B., Bosatta, E., 1987. The effects of lignin and nitrogen on the decomposition of litter in nutrient-poor ecosystems: a theoretical approach. Can. J. Bot. 65, 1116–1120. Berg, B., Staaf, H., 1980. Decomposition rate and chemical changes of Scots pine litter. II. The influence of chemical composition. In: Persson, T. (Ed.), Structure and Function of
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