Quality Of Crop Residues Research Articles

Soil nitrous oxide emissions following crop residue addition: a meta‐analysis

Annual production of crop residues has reached nearly 4 billion metric tons globally. Retention of this large amount of residues on agricultural land can be beneficial to soil C sequestration. Such potential impacts, however, may be offset if residue retention substantially increases soil emissions of N(2)O, a potent greenhouse gas and ozone depletion substance. Residue effects on soil N(2)O emissions have gained considerable attention since early 1990s; yet, it is still a great challenge to predict the magnitude and direction of soil N(2)O emissions following residue amendment. Here, we used a meta-analysis to assess residue impacts on soil N(2)O emissions in relation to soil and residue attributes, i.e., soil pH, soil texture, soil water content, residue C and N input, and residue C : N ratio. Residue effects were negatively associated with C : N ratios, but generally residue amendment could not reduce soil N(2)O emissions, even for C : N ratios well above ca. 30, the threshold for net N immobilization. Residue effects were also comparable to, if not greater than, those of synthetic N fertilizers. In addition, residue effects on soil N(2)O emissions were positively related to the amounts of residue C input as well as residue effects on soil CO(2) respiration. Furthermore, most significant and stimulatory effects occurred at 60-90% soil water-filled pore space and soil pH 7.1-7.8. Stimulatory effects were also present for all soil textures except sand or clay content ≤10%. However, inhibitory effects were found for soils with >90% water-filled pore space. Altogether, our meta-analysis suggests that crop residues played roles beyond N supply for N(2)O production. Perhaps, by stimulating microbial respiration, crop residues enhanced oxygen depletion and therefore promoted anaerobic conditions for denitrification and N(2)O production. Our meta-analysis highlights the necessity to connect the quantity and quality of crop residues with soil properties for predicting soil N(2)O emissions.

Winter Cover Crop Seeding Rate and Variety Effects during Eight Years of Organic Vegetables: III. Cover Crop Residue Quality and Nitrogen Mineralization

Winter cover crops (CCs) can improve nutrient‐use efficiency in tillage‐intensive cropping systems. Shoot residue quality and soil mineral N following incorporation of rye (Secale cereale L.), legume–rye, and mustard CCs was determined in December to February or March during the first 8 yr of the Salinas Organic Cropping Systems trial in Salinas, CA. Legume–rye included Vicia faba L., V. sativa L., V. benghalensis L., Pisum sativum L., and rye; mustard included Sinapis alba L. and Brassica juncea Czern. Cover crops were planted in the fall at standard and three times higher seeding rates (SRs) before vegetables annually. Significant CC × year interactions occurred for C and N concentrations and C/N ratios of CC shoots. In general, C concentrations were higher in rye and legume–rye, N concentrations were higher in mustard and legume–rye, and C/N ratios were higher in rye. During the season, C concentrations and C/N ratios tended to increase, whereas N concentrations decreased. Compared with rye and mustard, legume–rye residue quality changed least during each season. Increasing the SR reduced N concentrations and increased C/N ratios; however, the effect varied with time and by residue. Following CC incorporation, soil mineral N varied between years and CC and was typically highest following legume–rye or mustard and lowest without CC. Rainfall after CC incorporation reduced soil N one year, suggesting that leaching occurred. We conclude that mustard and legume–rye produce higher quality residue that will decompose more rapidly and minimize tillage challenges for subsequent vegetables but may be more prone to post‐incorporation N leaching.

Changes during winter in water‐stable aggregation due to crop residue quality

AbstractThere is a need to develop practices that contribute to increased water‐stable aggregation (WSA) during winter in a humid temperate climate when soil is particularly prone to water erosion. Our objectives were to determine the effects of crop residue quality on WSA during winter and to relate these effects to biochemical indicators of fungal and bacterial biomass. Three graminae crop residues were selected for their different C/N ratios and biochemical characteristics (green oat residues, C/N = 18.8; wheat straw, C/N = 125.6; and mature miscanthus residues, C/N = 311.3). In October 2009, crop residues were added with an equivalent amount of C in the 0–10 cm layer to a Luvisol in north‐west France. WSA, expressed as mean weight diameter (MWD), amino sugar, soil mineral N and water contents were measured at regular intervals during 5 months. Aggregate MWD of the control soil decreased rapidly and remained low until the last sampling date in March which illustrates the structural vulnerability of bare soils in winter in this pedo‐climatic area. The incorporation of all three crop residues had significant positive impacts on aggregate MWD. Despite widely different C/N ratios, the maximum MWD under each treatment was similar (three times greater than the control soil). Maximum MWD occurred at times that clearly depended on residue quality. Maximum values occurred early for green oat (29 day), but were delayed to 50 day for wheat straw and to 154 day for miscanthus. Results from correlation analysis suggest that variations in WSA were partly mediated by microbial agents with a dominant effect of bacteria for green oat and a combined role of fungal and bacterial biomass for wheat straw. We suggest that the maximum MWD associated with the miscanthus late in the experiment is related to changes in the composition of the fungal community. Overall, our study shows that autumn application of crop residues increases WSA during winter with its effect being microbially mediated and determined by residue quality.

N Mineralization from Residues of Crops Grown with Varying Supply of 15N Concentrations

A laboratory study was conducted to evaluate the effects of varying 15N concentrations on crop residue quality (rice straw=RS and soybean=SY) and N mineralization. Two crops (rice and soybean) were grown in a glass-house under four 15N concentrations, i.e., 0 mM (N0), 0.625 mM (N1), 2.5 mM (N2) , and 10 mM (N3) supplied as CO(15NH2)2, in 30 cm diameter plastic pots containing 5 kg of quartz sand. Eight weeks after planting the above-ground biomass was pruned and oven dried at 60o C for 48 hours and analyzed for polyphenol, lignin, N, C, C/N, organic matter and % 15N-abundance. Each of the eight crop residues produced from this experiment was then incorporated into 10 g of soil in a 50 ml plastic bottle. Mineralization of N from the residues was measured over a 14-week period under controlled non-leaching conditions.The results showed that increasing N concentration in the nutrient solution (0 to 10 mM) increased total N but decreased C, lignin and polyphenol content in the crop residues. The results suggested that N supply may increase the quality of the crop residues, as indicated by decreasing of C/N, lignin/N, polyphenol/N ratios. SY residue released N about 2x faster than RS residue, and the amount N released increased with increasing supply of the N concentration. At the 10 mM N supply, RS and SY residues released respectively 3734,857 mg kg-1 and 4352.34 mg kg-1 cumulative amount of mineral N with the mineralization rate about 7x faster than without 15N in the solution. Differences in the %N mineralized were determined by the quality of the crop residues. Regression analyses showed that the N, lignin and polyphenol contents were the residues quality factors which could be used to predict N mineralization of the crop residues, and the relationship was best described by a linear regression.

Soil microbial biomass, functional microbial diversity, and nematode community structure as affected by cover crops and compost in an organic vegetable production system

Soil microorganisms play a crucial role in mineralization and breakdown of complex organic compounds in soil. Microbial populations and functional diversity are greatly influenced by quantity and quality of crop residue and other incorporate organic amendments. This study investigated the effect of cover crops (rye or a mixture of rye-vetch) and compost on soil microflora and microfauna under an organic tomato production system. Each cover crop treatment was used in conjunction with or without compost in a split-plot experimental design. Data on soil respiration, microbial biomass, metabolic quotient, and nematode populations were measured at the end of the growing season. Metabolic characteristics of the soil microbial community were determined using 31 C substrates on Biolog-EcoPlate™. Community level physiological profile (CLPP) was assessed by calculating average well color development (AWCD), richness (S), Shannon–Wiener diversity index (H), and evenness (E). Effect of compost was more pronounced on soil respiration than cover crop treatment. Highest microbial biomass was found in the soils amended with rye and compost (195–210μggdrysoil−1). Regression analysis between microbial biomass and soil organic matter (SOM) showed strong correlation (R2 value of 0.68–0.56) in two out of the three growing seasons. Calcium, magnesium, and potassium concentrations in soil also positively correlated with microbial biomass. There were significant differences among soils in numbers of plant parasitic, bacterial, and fungal feeding nematodes during the initial years of the study but the differences were not evident later. Shannon–Wiener diversity index was significantly affected by cover crop treatment with rye treatments generally exhibiting higher degree of soil microbial functional diversity. Biolog-EcoPlate™ assay was sensitive to changes in the short-term. Principal component analysis of the Biolog data allowed differentiation of treatments but distribution patterns varied from year to year. We conclude that both rye and rye-vetch mixture can affect the functional diversity of soil microbial community but differences between them are marginal when compared to compost and no-compost treatments. Microbial communities were more responsive to compost applications than cover crop effects.

INVESTIGATING COMPONENT SPECIES PROPORTIONS IN A CEREAL-LEGUME COVER CROP MIXTURE UNDER ORGANIC MANAGEMENT

ISHS XXVIII International Horticultural Congress on Science and Horticulture for People (IHC2010): International Symposium on Organic Horticulture: Productivity and Sustainability INVESTIGATING COMPONENT SPECIES PROPORTIONS IN A CEREAL-LEGUME COVER CROP MIXTURE UNDER ORGANIC MANAGEMENT

Impact of plant cell wall network on biodegradation in soil: Role of lignin composition and phenolic acids in roots from 16 maize genotypes

Residue quality is a key factor governing biodegradation and the fate of C in soil. Most investigations of relationships existing between crop residue quality and soil decomposition have been based on determining the relative proportions of soluble, cellulose, hemicellulose and lignin components. However, cell wall cohesion is increased by tight interconnections between polysaccharides and lignin that involve cross-linking agents (phenolic acids). The aim of this study was to determine the role of lignin composition and phenolic acids on short- to medium-term decomposition of maize roots in soil. Sixteen maize genotypes, presenting a range of chemical characteristics related to root lignin and phenolic acids, were used. The main components were characterized by Van Soest (VS) extraction and cell wall acid hydrolysis, and the non-condensed Syringyl and Guaicyl lignin monomers, esterified phenolic acids and etherified phenolic acids were determined. Maize roots were then incubated in soil under controlled conditions (15 °C, −80 kPa moisture) for 796 days. Results showed that VS extraction over-estimated the structural hemicellulose content and that VS lignin was more recalcitrant than Klason lignin. The tremendous effect of cell wall chemical characteristics was shown by marked variations (almost two-fold differences in C mineralization), between the 16 maize roots. Decomposition was controlled by soluble residue components in the short term whereas lignin and the interconnections between cell wall polymers were important in the long-term. Notably the cell wall domain rich in non-condensed lignin and esterified phenolic acids was prone to decomposition whereas the presence of etherified ferulic acids seemed to hamper cell wall decomposition.

Fermentation quality and nutritive value of rice crop residue based silage ensiled with addition of epiphytic lactic acid bacteria.

Silage is the feedstuff resulted from the preservation of forages through lactic acid fermentation. The aim of this study was to evaluate nutritive value, fermentation characteristics and nutrients digestibility of rice crop residue based silage ensiled with epiphytic lactic acid bacteria (LAB). The mixture of rice crop residue (RC), soybean curd residue (SC) and cassava waste (CW) in a 90: 5: 5 (on dry matter basis) ratio was used as silage material. Three treatments silage were (A) RC + SC + CW as a control; (B) RC + SC + CW + LAB inoculums from rice crop residue; (C) RC + SC + CW + LAB inoculums from king grass. Silage materials were packed into plastic silo (1.5 kg capacity) and stored for 30 days. The results showed that crude protein content in B and C silage was higher than that of silage A, but NDF content in silages B and C was lower than that of silage A. Lactic acid concentration was higher (P < 0.01) in silage C compared to silage B and A, thus pH value of silage C was lower (P < 0.01) than silage B and A. Silage C had the highest Fleigh point than that of other silages. Dry matter and organic matter digestibilities were higher in silages B and C (P < 0.01) than that of control silage. It was concluded that the addition of LAB inoculums from king grass to rice crop residue based silage resulted a better fermentation quality compared to LAB inoculums from rice crop residue. Key Words : Silage, Rice Crop Residue, Lactic Acid, In Vitro

In Situ Dynamics of Microbial Communities during Decomposition of Wheat, Rape, and Alfalfa Residues

Microbial communities are of major importance in the decomposition of soil organic matter. However, the identities and dynamics of the populations involved are still poorly documented. We investigated, in an 11-month field experiment, how the initial biochemical quality of crop residues could lead to specific decomposition patterns, linking biochemical changes undergone by the crop residues to the respiration, biomass, and genetic structure of the soil microbial communities. Wheat, alfalfa, and rape residues were incorporated into the 0-15 cm layer of the soil of field plots by tilling. Biochemical changes in the residues occurring during degradation were assessed by near-infrared spectroscopy. Qualitative modifications in the genetic structure of the bacterial communities were determined by bacterial-automated ribosomal intergenic spacer analysis. Bacterial diversity in the three crop residues at early and late stages of decomposition process was further analyzed from a molecular inventory of the 16S rDNA. The decomposition of plant residues in croplands was shown to involve specific biochemical characteristics and microbial community dynamics which were clearly related to the quality of the organic inputs. Decay stage and seasonal shifts occurred by replacement of copiotrophic bacterial groups such as proteobacteria successful on younger residues with those successful on more extensively decayed material such as Actinobacteria. However, relative abundance of proteobacteria depended greatly on the composition of the residues, with a gradient observed from alfalfa to wheat, suggesting that this bacterial group may represent a good indicator of crop residues degradability and modifications during the decomposition process.

Bt plants and effects on soil micro-organisms.

Abstract The continued and increasing adoption of genetically modified plants (GMPs) in agriculture has raised both perspectives on increasing the productivity and some concern over their potential effects on the environment, especially on soil. These effects include unintentional changes in the chemical compositions of root exudates, and the direct or indirect effects of transgenic plants on non-target species of soil micro-organisms that have a key role in the maintenance of soil quality and environmental sustainability. Therefore any change to the quality of crop residues and rhizosphere inputs could modify the dynamics of the composition and activity of organisms in soil. One of the most common transgenic traits in commercial GMPs is insect resistance based on the expression of Cry toxin derived from Bacillus thuringiensis ( Bt ), and it is crucial that risk assessment studies on the use of Bt crops consider the impacts on micro-organisms in soil. This review summarizes the results of most of the studies that have been conducted to specifically test the effects of Bt plants on soil microbial communities, and examines the role of soil properties as one of the most important factors to be considered to study the interactions between micro-organisms and Bt plants. Most studies suggest that the Bt plants that have been released for commercial purposes could cause small changes in microbial communities and these are often transient in duration. However, experimental results are often contrasting and, given our limited knowledge of the soil system and the linkage with the soil microbial community's diversity and function, more work needs to be done on a case-by-case basis to further evaluate the effects of Bt plants on soil micro-organisms and soil ecosystem functions.

Effect of different crop rotation systems and continuous fallow on soil microbial biomass carbon and nitrogen under different fertilizer treatments

以黄土高原南部半湿润易旱区已进行17年的田间定位试验为研究对象, 研究了不同培肥措施(不施肥、施用氮磷钾及氮磷钾与有机肥配合施用)下两种种植制度(一年1熟及一年两熟)和撂荒对土壤微生物量碳、氮(SMBC、SMBN)及可溶性有机碳、氮(SOC、SON)等含量的影响。结果表明, 与一年1熟的小麦-休闲种植制度相比, 一年两熟小麦-玉米轮作提高了0~10 cm土层SMBC、SMBN、有机碳(TOC)、全氮(TN)和土壤SOC、SON的含量, 而对10~20 cm土层上述测定指标影响不大。与不施肥(CK)或单施化肥处理(NPK)下小麦-休闲和小麦－玉米轮作方式相比, 撂荒处理显著提高了0~10 cm土层各测定指标的含量。不同培肥措施相比, 氮磷钾配施有机肥显著提高了0~10 cm、10~20 cm土层SMBC、SMBN含量; NPK处理0~10 cm土层SMBN含量显著增加, 10~20 cm土层SMBN和0~10 cm、10~20 cm土层SMBC含量增加但未达显著水平。不同培肥措施和种植制度对SMBC/TOC和SMBN/TN的比例无明显影响。

Bioremediation of Agricultural Wastes through Vermicomposting

ABSTRACT The post-harvest residues of some local crops, e.g., wheat (Triticum aestivum), millets (Penniseum typhoides and Sorghum vulgare), and a pulse (Vigna radiata) were subjected to recycle through vermicomposting. The crop residues were amended with animal dung, and three types of vermibeds were prepared: (i) millet straw (S. vulgare + P. typhoides in equal quantity) + sheep manure (1: 2 ratio) (MS); (ii) pulse bran (V. radiata) + wheat straw (T. aestivum) + cow dung (1: 1: 2 ratio) (PWC); and (iii) mixed crop residues (mixing of all types crop residues, used in this study) + cow dung in 1:1 ratio (MCR + CD). The fourth treatment was cattle shed manure (CSM). Vermicomposting resulted in a significant increase in total N (97.3% to 155%), available P (67.5% to 123.5%), exchangeable K (38.3% to 112.9%), and exchangeable Ca (23.3% to 53.2%), and decrease in organic C content (20.4% to 29.0%) in the different vermibeds. The earthworm showed the higher biomass gain, growth rate (mg wt. worm−1 day−1) and cocoon numbers in the CSM vermibed. The quality of crop residues was directly related to the rate of organic matter mineralization during the vermicomposting. This study suggests that agriculture wastes could be converted into some value-added products, e.g., vermicompost and worm biomass through vermicomposting technology. The higher concentrations of plant nutrients in end products indicate a potential for using agriculture wastes in sustainable crop production.

Opportunities and limitations of food - feed crops for livestock feeding and implications for livestock - water productivity

The paper discusses the contribution of crop residues (CR) to feed resources in the context of the water productivity of CR in livestock feeding, using India as an example. It is argued that crop residues are already the single most important feed resource in many livestock production systems in developing countries and that increasing their contribution to livestock feeding needs to be linked to improving their fodder quality. Using examples from multi-dimensional crop improvement, it is shown that CR fodder quality of key crops such as sorghum, rice and groundnut can be improved by genetic enhancement without detriment to grain and pod yields. Improving crop residue quality through genetic enhancement, agronomic and management interventions and strategic supplementation could improve water productivity of farms and systems considerably. The draw-backs of CR based feeding regimes are also pointed out, namely that they result in only moderate levels of livestock productivity and produce higher greenhouse gas emissions than are observed under feeding regimes that are based on high quality forages and concentrates. It is argued that feed metabolisable energy (ME) content should be used as an important determinant of livestock productivity; water requirement for feed and fodder production should be related to a unit of feed ME rather than feed bulk. The paper also revisits data from the International Water Management Institute (IWMI) work on livestock–water productivity in the Indian state of Gujarat, showing that water input per unit ME can vary several-fold in the same feed depending on where the feed is produced. Thus, the production of one mega joule of ME from alfalfa required 12.9 L of irrigation-derived water in south Gujarat but 50.7 L of irrigation-derived water in north Gujarat. Wheat straw in south Gujarat required 20.9 L of irrigation-derived water for 1 MJ ME and was in this instance less water use efficient than alfalfa. We conclude that water use efficiency across feed and fodder classes (for example crop residue v. planted forages) and within a feed is highly variable. Feeding recommendations should be made according to specific water use requirement per unit ME in a defined production system.

Utilização do nitrogênio da palha de milho e de adubos verdes pela cultura do milho

A qualidade dos resíduos vegetais de culturas comerciais e adubos verdes influencia a taxa de mineralização/imobilização de N e o respectivo aproveitamento desse nutriente pelas subseqüentes culturas. Com o objetivo de avaliar a utilização do N mineralizado da parte aérea e do sistema radicular da crotalária (Crotalaria juncea) e milheto (Pennisetum americanum) e da palha de milho, marcados com 15N, realizou-se um estudo, em casa de vegetação, no Centro de Energia Nuclear na Agricultura - CENA/USP, Piracicaba (SP), em vasos com 5 kg de solo de um Latossolo Vermelho distroférrico. Foram utilizados seis tratamentos e quatro repetições, dispostos num delineamento inteiramente casualizado, compreendendo: T1 = palha de milho-15N (parte aérea, exceto os grãos) (80 mg kg-1 de N no solo); T2 = raiz de milheto-15N (30 mg kg-1 de N no solo); T3 = parte aérea de milheto-15N (80 mg kg-1 de N no solo); T4 = raiz de crotalária-15N (30 mg kg-1 de N no solo); T5 = parte aérea de crotalária-15N (80 mg kg-1 de N no solo) e T6 = tratamento sem adição de fonte orgânica de N. Para os tratamentos que receberam raiz marcada com 15N, adicionou-se parte aérea sem marcação isotópica na mesma quantidade que naqueles que receberam parte aérea marcada, e vice-versa. As raízes foram incorporadas ao solo e a parte aérea adicionada sobre a superfície. Para avaliar absorção de N da palha de milho-15N (7,35 Mg ha-1, equivalente a 56 kg ha-1 de N) pela cultura do milho, realizou-se também um experimento de campo, na mesma área em que foi coletado solo para o experimento de casa de vegetação. A quantidade de N no milho proveniente da crotalária (111,80 mg vaso-1 N ) foi superior à do milheto (30,98 mg vaso-1 N ), que foi superior à da palha de milho (11,80 mg vaso-1N ). A crotalária proporcionou maior absorção de N e produtividade de matéria seca ao milho. O aproveitamento pelo milho do N da parte aérea da crotalária foi superior ao do N do sistema radicular, mas não houve diferença para o N do milheto. A absorção do N dos restos culturais de milho pela cultura do milho, no campo, foi de 4,1 % da quantidade inicial.

Fate and effects of insect-resistant Bt crops in soil ecosystems

Recent applications of biotechnology, especially genetic engineering, have revolutionized crop improvement and increased the availability of valuable new traits. A current example is the use of the insecticidal Cry proteins from the bacterium, Bacillus thuringiensis ( Bt), to improve crops, known as Bt crops, by reducing injury from various crop pests. The adoption of genetically modified (GM) crops has increased dramatically in the last 11 years. However, the introduction of GM plants into agricultural ecosystems has raised a number of questions, including the ecological impact of these plants on soil ecosystems. Crop residues are the primary source of carbon in soil, and root exudates govern which organisms reside in the rhizosphere. Therefore, any change to the quality of crop residues and rhizosphere inputs could modify the dynamics of the composition and activity of organisms in soil. Insect-resistant Bt crops have the potential to change the microbial dynamics, biodiversity, and essential ecosystem functions in soil, because they usually produce insecticidal Cry proteins through all parts of the plant. It is crucial that risk assessment studies on the commercial use of Bt crops consider the impacts on organisms in soil. In general, few or no toxic effects of Cry proteins on woodlice, collembolans, mites, earthworms, nematodes, protozoa, and the activity of various enzymes in soil have been reported. Although some effects, ranging from no effect to minor and significant effects, of Bt plants on microbial communities in soil have been reported, using both culturing and molecular techniques, they were mostly the result of differences in geography, temperature, plant variety, and soil type and, in general, were transient and not related to the presence of the Cry proteins. The respiration (i.e., CO 2 evolution) of soils cultivated with Bt maize or amended with biomass of Bt maize and other Bt crops was generally lower than from soils cultivated with or amended with biomass of the respective non- Bt isolines, which may have been a result of differences in chemical composition (e.g., the content of starch, soluble N, proteins, carbohydrates, lignin) between Bt plants and their near-isogenic counterparts. Laboratory and field studies have shown differences in the persistence of the Cry proteins in soil, which appear to be the result primarily of differences in microbial activity, which, in turn, is dependent on soil type (e.g., pH, clay mineral composition, other physicochemical characteristics), season (e.g., temperature, water tension), crop species (e.g., chemical composition, C:N ratio, plant part), crop management practices (e.g., till vs. no-till), and other environmental factors that vary with location and climate zones. This review discusses the available data on the effects of Cry proteins on below-ground organisms, the fate of these proteins in soil, the techniques and indicators that are available to study these aspects, and future directions.

Decomposition of mulched versus incorporated crop residues: Modelling with PASTIS clarifies interactions between residue quality and location

Crop residue management has been shown to significantly affect the decomposition process of plant debris in soil. In previous studies examining this influence, the extrapolation of laboratory data of carbon and/or nitrogen mineralization to field conditions was often limited by a number of interactions that could not be taken into account by a mere experimental approach. Therefore, we demonstrated the interactive effect between crop residue location in soil (mulch vs. incorporation) and its biochemical and physical quality, in repacked soil columns under artificial rain. Decomposition of 13C and 15N labelled rape and rye residues, with associated C and N fluxes, was analysed using the mechanistic model PASTIS, which turned out to be necessary to understand the interacting factors on the C and N fluxes. The influence of soil and residue water content on decomposition and nitrification was evaluated by the moisture limitation factor of PASTIS. This factor strongly depended on residue location and to a smaller extent on physical residue properties, resulting in a lower decomposition rate of about 35% for surface placed compared to incorporated residues. Irrespective of its placement, the biochemical residue quality (e.g. N availability for decomposition, amount of soluble compounds and lignin) was responsible for a faster and more advanced decomposition of about 15% in favour of rye compared to rape, suggesting only a limited interaction between residue quality and its location. Net N mineralization after nine weeks was larger for rye than for rape, equivalent to 59 and 10 kg NO 3 −–N ha −1 with incorporation, and 71 and 34 kg NO 3 −–N ha −1 with mulch, respectively. This net N mineralization in soil resulted from the interaction between soil water content, depending on residue placement, and N availability, which was determined by the biochemical residue quality. Moisture limitation appeared more important than N limitation in the decomposition of mulched residues. Modelling of gross N mineralization and immobilization also revealed that leaving crop residues at the soil surface may increase the risk of nitrate leaching compared to residue incorporation, if (i) soil water content under mulch is larger than with residue incorporation (more gross N mineralization), and (ii) availability to the applied C-source is limited (less gross N immobilization). Scenario analyses with PASTIS confirmed the importance of moisture conditions on the decomposition of mulched residues and the small interaction between biochemical crop residue quality and its location in soil.

Earthworm activity affects soil aggregation and organic matter dynamics according to the quality and localization of crop residues—An experimental study (Madagascar)

Soil organic matter (SOM) plays a central role in the functioning of ecosystems, and is beneficial from agronomic and from environmental point of view. Alternative cultural systems, like direct seeding mulch-based cropping (DMC) systems, enhance carbon (C) sequestration in agricultural soils and lead to an increase in soil macrofauna. This study aimed at evaluating in field mesocosms the effects of earthworms on SOM dynamics and aggregation, as influenced by residue quality and management. In the highlands of Madagascar, buckets were filled with 2 mm-sieved clayey Inceptisol. The effects of earthworm addition ( Pontoscolex corethrurus), residue addition (rice, soybean, and no addition), and localization of the residues (mulched or buried) were studied. After 5 months, soil from mesocosms with earthworms had significantly lower C concentration and higher proportion of large water-stable macroaggregates (>2000 μm) than those without earthworms, because of the production of large macroaggregates by earthworms. Earthworm effect on soil aggregation was greater with rice than with soybean residues. Casts (extracted from mesocosms with earthworms) were slightly enriched in C and showed significantly higher mineralization than the non-ingested soil (NIS), showing that at the time scale of our study, the carbon contained in the casts was not protected against mineralization. No difference in microbial biomass was found between casts and NIS. Complementary investigations are necessary to assess long-term effects of earthworm addition on SOM dynamics, the conditions of occurrence of physical protection, and the impact of earthworms on the structure of the microbial community.

Review: The composition and availability of straw and chaff from small grain cereals for beef cattle in western Canada

Small cereal grain residues are heterogeneous feeds consisting of several botanical fractions: chaff, grain, leaf blade, leaf sheath, internode and node. These parts vary in composition, digestibility, resistance to comminution, intake potential and energy availability. Large differences in the nutritional quality of straw and chaff may occur from year to year and between locations due to effects of environmental conditions on botanical composition and cell anatomy. Stage of maturity, harvest method and weathering will influence composition and quality of the most nutritious parts of cereal residues, the leaf and chaff. In addition, cultivars and species differ in the proportion, anatomy and digestibility of botanical fractions. As a result, the quality of crop residues is highly variable with an economic value that is difficult to accurately assess. Cereal straw and chaff are of low economic value as they are low in nutritive value, where nutritive value is the product of nutrient intake, digestibility, and efficiency of use. However, due to availability, cereal crop residues have the potential to be a substantial feed resource for beef cows. Previous reviews have not focused on straw and chaff nutrition research relevant to use by beef cattle in western Canada. This review includes discussions on yield and nutritive value with a focus on identifying information deficiencies, including the lack of detailed production statistics for determining residue yields on a regional bases and the need for more detailed nutrient composition to update regional feed data bases for western Canada. Key words: Straw, chaff, nutrient quality, beef cattle

Potassium release during decomposition of crop residues under conventional and zero tillage

Nutrient cycling is an important part of integrated nutrient management. The litterbag method was used in field experiments to determine potassium (K) release patterns from red clover (Trifolium pratense) green manure (GM), field pea (Pisum sativum), canola (Brassica rapa) and monoculture wheat (Triticum aestivum) residues under conventional and zero tillage from 1998 to 1999 and from 1999 to 2000. Potassium contained in crop residues ranged from 25 kg ha-1 in wheat to 121 kg ha-1 in pea residues, both under zero tillage. The percentage of K released over a 52-wk period ranged from 65% of pea K under zero tillage to 99% of clover K under conventional tillage, and the amounts released were 20–32 kg ha-1 from wheat, 31–52 kg ha-1 from canola, 28–79 kg ha-1 from pea, and 31–118 kg ha-1 from legume GM residues. In both trial periods, K from wheat residues was released at a faster rate under conventional tillage than under zero tillage during the first 10 wk of residue decomposition. In contrast, K from pea and canola residues was released more quickly under zero tillage than under conventional tillage. The effect of tillage on K release from GM residues was similar to that on pea and canola residues in 1998–1999, but similar to that on wheat residues in 1999–2000. Correlations between K release and residue quality were inconsistent, presumably because K is not a structural component of plant tissue, and therefore its release is probably related more to leaching than to residue decomposition. These results show that crop residues recycle substantial amounts of K for use by subsequent crops in rotation. Key words: Conservation tillage, crop residue quality, crop rotation, organic soil amendments

Can the Biochemical Features and Histology of Wheat Residues Explain their Decomposition in Soil?

The biochemical characteristics or quality of crop residues is an important factor governing soil residue decomposition. To improve C and N biotransformation models the process underlying this decomposition needs to be better understood and new quality criteria found to describe it. The aims of this explorative study were to (i) improve our understanding of residue decomposition from detailed studies of cell wall biochemical compositions and tissue architecture (ii) find new ways of exploring generic indicators of organic matter quality. To do this, the cell wall composition and tissue architecture of wheat leaves, internodes and roots, before and after their incorporation into soil were determined. Results showed that leaves which were poorly lignified decomposed faster in soil than internodes and roots. Cellulose was the most degraded polysaccharide irrespective of wheat residue. However, cellulose was much more degraded in the case of leaves as compared to internodes and roots. Leaves also presented a highly condensed lignin structure and the extent to which uncondensed leaf lignin was affected by soil decomposition suggests that the contribution of leaf lignin to C mineralization during incubation was very low. Roots which contained similar amounts of lignin than the internodes decomposed more slowly. Roots were enriched in phenolic acids, and more particularly p-coumaric acid (pCA) and presented a more condensed lignin structure than internodes. Phenolic acids are involved in the formation of lignin–polysaccharide complexes known to be recalcitrant to enzymatic attack. Microscopic investigations confirmed that the vessels were the most resistant tissues to decomposition in soil and this could be related either to their lignin content or to the quality of this lignin (condensed-like type lignin). Therefore, cell wall biochemical analyses have revealed that phenolic acids, which in their esterified form represent only 0.1–1% of plant dry matter, have cross link functions within the cell walls that could be of major interest in estimating soil residue degradability. Lignin quality (monomers, level of condensation) was another crucial criterion that could explain why residues with similar amounts of lignin decomposed at different rates in soil (roots vs. aerial parts). Visualization of residue cell walls before and after decomposition in soil underlined the interest of a microscopic approach coupled with image analysis. This study, corroborated by the extensive literature on forage digestibility, confirmed that the proportions of vascular tissue and sclerenchyma cells in plant material are determinant factors affecting plant degradability. In the future, classification of plant material based on these criteria could lead to the definition of new quality parameters for models of C and N biotransformation in soil.