Dry Matter Decomposition Research Articles

Phytomass decomposition of cover crops subjected to mechanical management and soybean yield

The research had as objective to evaluate the crops residues decomposition of cover crops mechanically managed and its effect on the soybean yield cultivated in succession. The design used was randomized blocks in a factorial arrangement (5 x 2), subdivided over time, with four replications, consisting of five soil covers (black oats, turnip, turnip + oats, common vetch and fallow) and two forms of species management (knife-roller and shredder). The six collection times (0, 20, 40, 60, 80 and 110 days after management- DAM) were the subplots. The straw decomposition time was evaluated using the litter bags method. At 110 DAM, the covers that showed the greatest decomposition were vetch and fallow (91 and 90%) as well as the shortest half-life-T½ (31 and 33), evidencing their low soil protection. The cover that remained the most was black oats (35%) being a good option to keep the soil covered. In the first 60 DAM, the shredder accelerated the dry matter decomposition by 40% and presented a lower T½ (45). The cover crops cultivation and its management before soybean cultivation did not influence grain yield.

Spatial and Temporal Distribution of Cattle Dung and Nutrient Cycling in Integrated Crop–Livestock Systems

Residue decomposition from cattle dung is crucial in the nutrient cycling process in Integrated Crop–Livestock Systems (ICLS). It also involves the impact of the presence of trees exerted on excreta distribution, as well as nutrient cycling. The objectives of this research included (i) mapping the distribution of cattle dung in two ICLS, i.e., with and without trees, CLT and CL, respectively, and (ii) quantification of dry matter decomposition and nutrient release (nitrogen—N, phosphorus—P, potassium—K, and sulphur—S) from cattle dung in both systems. The cattle dung excluded boxes were set out from July 2018 to October 2018 (pasture phase), and retrieved after 1, 7, 14, 21, 28, 56 and 84 days (during the grazing period). The initial concentrations of N (~19 g kg−1), P (~9 g kg−1), K (~16 g kg−1), and S (~8 g kg−1) in the cattle dung showed no differences. The total N, P, K and S released from the cattle dung residues were less in the CLT system (2.2 kg ha−1 of N; 0.7 kg ha−1 of P; 2.2 kg ha−1 of K and 0.6 kg ha−1 of S), compared to the CL (4.2 kg ha−1 of N; 1.4 kg ha−1 of P; 3.6 kg ha−1 of K and 1.1 kg ha−1 of S). Lesser quantities of cattle dung were observed in the CLT (1810) compared to the CL (2652), caused by the lower stocking rate, on average, in this system (721 in the CL vs. 393 kg ha−1 in the CLT) because of the reduced amount of pasture in the CLT systems (−41%), probably due to light reduction (−42%). The density of the excreta was determined using the Thiessen polygon area. The CL system revealed a higher concentration of faeces at locations near the water points, gate and fences. The CLT affects the spatial distribution of the dung, causing uniformity. Therefore, these results strengthen the need to understand the nutrient release patterns from cattle dung to progress fertilisation management.

Dry matter decomposition and potassium cycling in no-till integrated crop-livestock systems: the effects of tree shading and nitrogen fertilization

In integrated crop-livestock systems (ICLS), understanding residue dynamics is crucial to synchronize nutrient release from pasture litter to cash-crop nutrient demands and overcome potential deficiencies using suitable fertilization strategies. The present study evaluated how the inclusion of trees and N availability affected the release rates of K from pasture (black oat + ryegrass) residues to the subsequent maize crop in a no-till ICLS. The experimental design was randomized blocks with treatments set up in split-plots with three replications. Main plots were systems (crop-livestock only and crop-livestock with trees) and sub-plots N levels (90 and 180 kg N ha-1). Litter decomposition and K release from pasture residues were assessed using litterbags, which were installed at maize sowing, for retrieval at 8, 15, 30, 60, 90, 120, 150, and 165 days of incubation. Regardless of N level, shade of 7-year-old trees reduced pasture residue (-30%). Tree residues were unable to offset the shading effect on pasture growth. A faster dry matter decomposition was observed in treeless treatment and with 180 kg N ha-1, with a half-life ranging from 14 to 38 days. Despite no changes in K-release dynamics among treatments, total K released was significantly higher for treeless system (61 kg K ha-1) than in system with trees (40 kg K ha-1), due to changes in the initial amount of residue. These results must be taken into account in fertilization practices. Therefore, a few feasible silvicultural interventions should be considered to avoid losses in soil cover, maximizing nutrient cycling benefits.

Effects of trees and nitrogen supply on macronutrient cycling in integrated crop–livestock systems

AbstractResidue decomposition from pastures and crops plays an important role in nutrient cycling in integrated crop–livestock systems (ICLS). The objective of this research was to quantify dry matter decomposition and nutrient release—nitrogen, phosphorus, and potassium (N, P, and K, respectively), the most commonly required nutrients in tropical and subtropical agriculture—from pasture and soybean (Glycine max) residues of stocking and crop seasons in two ICLS (with and without trees, CLT and CL, respectively) and two N fertilization levels (90 vs. 180 kg N ha−1, N90 and N180, respectively, applied during the pasture phase). Litter bag incubations were set out in the December 2014 (soybean phase) and May 2015 (pasture phase), and retrieved after 7, 15, 30, 60, 90, and 120 d in each season. The total N, P, and K released from the pasture or soybean residues were related to the initial quantity of plant residues, which was reduced in the CLT systems, mostly for pasture residue (−60%), probably due to light reduction (−55%), rather than changes in litter quality and dynamics. Significant amounts of N (∼57 kg ha−1), P (∼11 kg ha−1), and K (∼58 kg ha−1) were cycled, particularly in CL and N180 treatments. The quantities of K released from pasture residues were enough to restore the quantity of K exported by soybean grains. Therefore, results reinforce the need to understand nutrient release patterns from residues to improve fertilization management.

坡度和埋深对橡胶林凋落叶分解及红外光谱特征的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 坡度和埋深对橡胶林凋落叶分解及红外光谱特征的影响 DOI: 10.5846/stxb201804070781 作者: 作者单位: 中国热带农业科学院橡胶研究所/土壤肥料研究中心,中国热带农业科学院橡胶研究所/土壤肥料研究中心,中国热带农业科学院橡胶研究所/土壤肥料研究中心,中国热带农业科学院橡胶研究所/土壤肥料研究中心,中国热带农业科学院橡胶研究所/土壤肥料研究中心,中国热带农业科学院橡胶研究所/土壤肥料研究中心,中国热带农业科学院橡胶研究所/土壤肥料研究中心,中国热带农业科学院橡胶研究所/土壤肥料研究中心 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点研发计划（2018YFD0201100）；中央级公益性科研院所基本科研业务费专项资金项目（1630022017029） Effects of varying slopes and depths on decomposition and infrared spectrum characteristics of leaf litter in a rubber forest Author: Affiliation: Rubber Research Institute/Soil and Fertilizer Center, Chinese Academy of Tropical Agriculture Science,Rubber Research Institute/Soil and Fertilizer Center, Chinese Academy of Tropical Agriculture Science,,,,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:橡胶树凋落叶在橡胶林生态系统养分循环中起着重要的作用，研究凋落叶的分解和养分释放特性及其影响因素，对资源的循环利用及指导高效施肥具有重要意义。在海南省天然橡胶主产区选取橡胶林地进行凋落叶原位分解试验，研究坡度和埋深对橡胶树凋落叶干物质分解特性、养分元素释放规律及其物质成分红外光谱特征的影响。结果表明，凋落叶分解速率明显受到坡度和深度的影响；分解9个月后，干物质残留率高低顺序为坡地覆盖（39.6%） > 平地覆盖（26.8%） > 平地埋深（11.2%） > 坡地埋深（6.9%）；凋落叶的损失符合Olsen指数衰减模型（P < 0.01），各处理凋落叶干物质分解95%所需要的时间分别为29.3、20.5、12.8和13.2个月；各处理C/N比从最初的25.1下降到12.7、14.4、16.2和16.9。分解期间各处理养分残留率差异显著（P < 0.05）；分解9个月后，坡地覆盖处理S-I养分元素C、N、P、K、Ca、Mg的残留率最高，分别为10.9%、21.6%、10.7%、9.7%、10.4%、7.9%，而坡地埋深处理S-Ⅱ最低，分别为3.8%、6.5%、3.4%、2.3%、0.8%、2.1%。傅里叶红外光谱（FTIR）分析显示，凋落叶分解前后在3387 cm-1、1734 cm-1处的吸收峰强度明显减弱，表明纤维素、半纤维素、木质素、多糖、脂肪族等碳水化合物遭到分解；1050 cm-1处的吸收峰向低频方向位移了17 cm后变为1033 cm-1，表明分解破坏了凋落叶原有的可溶性糖和纤维素C-C键和C-O键伸缩振动。综上所述，埋深处理有利于加速凋落叶物质分解和养分元素释放速率；建议橡胶树生产中将凋落叶与表土混合或压青处理，提高橡胶林养分循环效率。 Abstract:Leaf litter plays an important role in nutrient recycling in rubber ecological systems. Studying the decomposition characteristics of dry matter and nutrient release and their effects has important significance for resource utilization and the management of high efficiency fertilization. A decomposing-bag experiment was conducted in a rubber forest at the main production areas of natural rubber trees in Hainan Province, China. The objectives were to study the effects of slope and depth on the characteristics of dry matter decomposition, nutrient release, and FTIR (fourier transform infrared spectroscopy) of leaf litter. The results showed that the decomposition rates were significantly affected by varying degrees of slope and depth. The dry matter remaining rates between different treatments were in the following order:covered slopes (39.6%) > covered flatland (26.8%) > buried flatland (11.2%) > buried slopes (6.9%). Leaf litter loss agreed with an Olsen exponential attenuation model (P < 0.01). The time required for 95% leaf litter decomposition was 29.3, 20.5, 12.8, and 13.2 months, and the C/N ratios decreased from the initial 25.1 to 12.7, 14.4, 16.2, and 16.9 after 9 months, for the above treatments, respectively. The nutrient remaining rates were significantly different (P < 0.05) among different treatments during the decomposition stage. After 9 months, the nutrient remaining rate for C, N, P, K, Ca, and Mg on the covered slope was higher than that in other treatments, at 10.9%, 21.6%, 10.7%, 9.7%, 10.4%, and 7.9%, respectively; but that in the buried slopes was lower than that in the other treatments, at 3.8%, 6.5%, 3.4%, 2.3%, 0.8% and 2.1%, respectively. Analysis of the FTIR spectroscopy characteristics of leaf litter showed the absorption peak strength at waves of 3387 cm-1 and 1734 cm-1, which obviously became weak after 9 months of decomposition, thus proving the decomposition and transformation of carbohydrates, i.e. cellulose, hemicellulose, lignin, polysaccharide, and fatty acid group compounds. The absorption peak at 1050 cm-1 shifted to 17 cm at low frequency and then changed to 1033 cm-1, suggesting that decomposition destroyed the original soluble sugar and cellulose C-C and C-O bond stretching vibration. In conclusion, buried leaf litter could contribute to mass loss and nutrient release. Therefore, we suggest that the litter of rubber forests should be mixed with soil or buried in green manuring pits to improve the recycling efficiency of rubber plantation systems. 参考文献 相似文献 引证文献

DRY MATTER DECOMPOSITION OF COVER CROPS IN A NO-TILLAGE COTTON SYSTEM

ABSTRACT No-tillage cotton systems require soil coverage with cover crop residue for a longer time due to the late cycle of cotton. However, decomposition rates may vary between cover crops, and the adjustment of models to describe it is critical to no-tillage cotton management. Two non-linear regression models, exponential (EM) and Michaelis-Menten (MM), were adjusted to dry matter decomposition of cover crops in a cotton no-tillage system, in Brazil. Three field trials were performed in 2012 for the cover crops Urochloa ruziziensis (brachiaria), Pennisetum glaucum (pearl millet), and Cajanus cajan (pigeon pea). Samples of cover crop were collected at 20, 50, 70, 110, 140, and 170 days after sowing upland cotton to measure dry matter decomposition. MM showed better adjustment than EM for all cover crops. The estimations of half-life parameters were different between the cover crops, suggesting that each cover crop has its own rate of decomposition. For pearl millet, brachiaria, and pigeon pea, the half-life estimation by exponential model was over the MM in 9, 12, and 12 days.

Nitrogen fertilization on palisadegrass: phytomass decomposition and nutrients release

ABSTRACT Topdressing or pre-seeding nitrogen (N) application increases phytomass production, providing a higher nutrients accumulation and indirectly favoring the subsequent crop. However, N fertilization can alter the dry matter decomposition and nutrients release dynamics. This study aimed at evaluating the decomposition rate, cellulose, lignin and nutrients release speed from palisadegrass as a function of N fertilization. The experimental design was randomized blocks with four replications, in a factorial scheme constituted by two N fertilization levels and six sampling times after desiccation [0, 14, 34, 41, 51 and 68 days after management (DAM)]. The topdressing N fertilization on palisadegrass increases the dry matter production and N accumulation, but does not alter the decomposition and release speed. N fertilization reduces the C/N ratio, but it does not change the contents of cellulose and lignin and the decomposition and release of N, K, Ca, Mg, C and Si. The amounts of P and S accumulated in the plant and released into the soil increase with N fertilization. The maximum release rates occur within 0-14 DAM, being more intensive for P and S when N is applied. These results demonstrate the high potential of this species for crop-livestock integration systems, with some advantages that can be potentialized with higher N doses.

Decomposição e liberação de nutrientes da palhada de braquiária, sorgo e soja em áreas de plantio direto no cerrado goiano

The evaluation of plant litter decomposition added to the soil by cover crops provides a better understanding of nutrient supply to crops of commercial interest. The objective of this study was to evaluate the decomposition rate and dynamics of release of N, P and K in crop residues from crop of soybeans grown in Oxisol under no tillage. The residues used were Congo grass (Brachiaria ruziziensis) and sorghum (Sorghum bicolor L. Moench). The average production of Congo grass biomass + soybean was 6.1 Mg ha-1 and soybean + sorghum was 3.8 Mg ha-1. The dry matter decomposition and nutrient release were monitored at 15, 30, 60, 90, 120 days using bags containing residues deposited on the soil surface. A mathematical model was used to describe the litter decomposition and N, P, K release and the decomposition constant (k) and half-life (T1/2) were calculated. The values of T1/2 for dry matter were 154 and 258 days for Brachiaria + soybean and soybean + sorghum, respectively, in the dry season and 99 and 119 days in the rainy season. The nutrient with the lowest T1/2 was P, followed by K and N in both litters and evaluated at different times.

Adubação verde e nitrogenada na cultura do trigo em plantio direto

Pouco se sabe sobre os benefícios do cultivo de adubos verdes sobre o desempenho da cultura do trigo, cultivada em sucessão e, até que ponto, pode substituir ou reduzir a adubação nitrogenada mineral. Objetivou-se com o presente trabalho avaliar a produção e decomposição de matéria seca bem como o acúmulo e liberação de nutrientes de plantas de cobertura de solo (nabo forrageiro, ervilhaca comum, ervilha forrageira, tremoço e feijoeiro) e quantificar seus efeitos sobre o desempenho da cultura do trigo, cultivada em sucessão, sob diferentes doses de adubação nitrogenada (sem adição de nitrogênio, 40, 80 e 120 kg ha-1). O experimento foi desenvolvido no município de Pato Branco (PR), em duas safras agrícolas, em sistema de plantio direto. O nabo forrageiro e o tremoço acumularam as maiores quantidades de cálcio e potássio. A ervilha forrageira e o nabo forrageiro destacam-se pela produção de matéria seca, acúmulo de nitrogênio, fósforo, potássio, bem como pela decomposição e liberação de nitrogênio para a cultura do trigo em estádios fenológicos de maior demanda deste nutriente. A relação C/N (superior a 40) dos restos culturais do milho e feijoeiro não possibilitou equilíbrio entre os processos de mineralização e imobilização. Os adubos verdes promoveram acréscimos significativos na produtividade de grãos em comparação ao pousio. Houve resposta do trigo à aplicação de nitrogênio mineral, e esta foi dependente da planta de cobertura antecessora.

Incorporation of Municipal Biosolids Affects Organic Nitrogen Mineralization and Elephantgrass Biomass Production

Municipal biosolids (MBS) represents an alternative source of nutrients for the production of bioenergy crops like elephantgrass (Pennisetum purpureum Schum.). Two experiments were conducted during 2 yr in Florida to evaluate the effect of soil incorporation vs. surface application of MBS on: (i) elephantgrass dry matter (DM) yield, tissue N and P concentration and removal, and soil C and P (Exp. 1); and (ii) organic N mineralization and DM decomposition rates of MBS measured in the field using a litter bag incubation technique (Exp. 2). In Exp. 1, three treatments supplied 350 kg total N ha−1 yr−1 from surface‐applied municipal biosolids (MBS‐SA), soil‐incorporated municipal biosolids (MBS‐INC), and surface‐applied ammonium nitrate (NH4NO3). A fourth treatment provided 700 kg total N ha−1 yr−1 from MBS‐SA (double rate of municipal biosolids, 2x‐MBS). In Exp. 2, MBS was field incubated in litter bags placed on the soil surface or at a 5‐cm soil depth. Elephantgrass DM yield, and N and P removal were greater for MBS‐INC than MBS‐SA. Dry matter yield for MBS‐INC was not different than for NH4NO3 fertilizer (22.5 vs. 24.3 Mg ha−1). Removal of N and P increased 39 and 10 kg ha−1 yr−1, respectively, for MBS‐INC and MBS‐SA. Total organic N mineralized was greater for MBS‐INC (386 g kg−1) than MBS‐SA (308 g kg−1). Incorporation of MBS increases elephantgrass DM yield and nutrient removal compared to surface application and allows MBS to replace a greater proportion of inorganic N fertilizer.

Municipal Biosolids as an Alternative Nutrient Source for Bioenergy Crops: II. Decomposition and Organic Nitrogen Mineralization

High‐yielding biomass crops remove significant quantities of soil nutrients, and nutrient replacement using inorganic fertilizers may not be sustainable. Municipal biosolids (MBS) are an alternative nutrient source. Organic N is the primary N form in MBS, and patterns of N mineralization can determine the effectiveness of MBS as an N source. The objectives of this experiment were to: (i) determine the effect of season of application on organic N mineralization rate and dry matter (DM) decomposition of Class A MBS measured in the field with litter bags and (ii) compare N mineralization measured using a field‐based technique with that predicted from the DECOMPOSITION model. Treatments were season of MBS application (spring and summer) during 2 yr. Organic N mineralization measured using litter bags followed the same pattern and arrived at a similar endpoint as predicted by the DECOMPOSITION model in three of four seasons. Lower spring temperatures and rainfall were associated with lower rates of N mineralization and DM decomposition during the 50 d following spring vs. summer application of MBS. When MBS were applied in summer, organic N mineralization leveled off approximately 50 d after application compared with 150 to 250 d following spring application. Seasonal weather conditions and N mineralization patterns should be considered when determining whether to apply MBS as the source of N, the timing of MBS application, and if single or split applications are best.

Soil Physico-Chemical Properties and Crop Yield Improvement Following Lantana Mulching and Reduced Tillage in Rainfed Croplands in the Indian Himalayan Mountains

In the rainfed crop fields of the Central Himalayan Mountains in India, low soil moisture and low soil fertility are the two major constraints on crop yield. Therefore, an experiment was conducted to test the hypothesis of whether mixing a high-quality (high foliar N, P, and K and low lignin) organic residue (Lantana camara leaves) with the relatively low-quality leaf litter of oak (Quercus leucotrichophora) and pine (Pinus roxburghii) forests, and then mulching the organic residue, would enhance the rate of organic residue decomposition and nutrient release to contribute to the soil fertility and crop yield of wheat and paddy in rainfed crop fields. To achieve the study objectives, Lantana residue was mixed with oak and pine leaf litter in four different proportions and applied under three tillage frequencies in 36 experimental plots in a completely randomized block design. These four mulch combinations were also studied for dry matter decomposition and nutrient release pattern. Results showed that both the decomposition rate (k = 1.86 yr−1) and rate of nutrient release from decomposing litter (N = 0.208 mg d −1 and P = 0.042 mg d −1) for Lantana residue were much higher than the other litter combinations. Mixing Lantana with other mulch materials positively influenced the decomposition and nutrient release of otherwise slow decomposing oak and pine leaf litter. The 100% Lantana mulched plots recorded substantially higher soil moisture among the four mulching treatments. The 100% Lantana mulched plots also recorded significantly higher soil nutrients (NO3 +-N and PO4 −-P under wheat and NH4 +-N under rice crops) and rate of N-mineralization, and produced significantly higher wheat grain (920 to 1309 kg ha−1) and wheat and rice straw yield than the conventional practice of crop cultivation. Lantana residue thus proved to be a potential mulch to achieve soil moisture conservation, soil fertility enhancement, and higher crop yields in the region.

Chemical composition and decomposition rate of plants used as green manure

Productive systems in which green manure is the source of nutrients must develop more efficient ways to improve soil nutrient dynamics. A well-synchronized balance must be established between specific crop demands and supply of nutrients from decomposition. However, scientific data and information to help improve green manure management in Brazil is still insufficient. For that reason, a number of arboreal species was first chemically characterized and then subjected to decomposition analysis in order to establish a correlation between some parameters. Species were grouped together based on the similarity of chemical composition and decomposition rate. The lignin:N and (lignin+polyphenol):N ratios were found to have the greatest correlation coefficient with the dry matter decomposition rate and nitrogen release.

A Model for Phosphorus Transformation and Runoff Loss for Surface‐Applied Manures

Agricultural P transport in runoff is an environmental concern. An important source of P runoff is surface-applied, unincorporated manures, but computer models used to assess P transport do not adequately simulate P release and transport from surface manures. We developed a model to address this limitation. The model operates on a daily basis and simulates manure application to the soil surface, letting 60% of manure P infiltrate into soil if manure slurry with less than 15% solids is applied. The model divides manure P into four pools, water-extractable inorganic and organic P, and stable inorganic and organic P. The model simulates manure dry matter decomposition, and manure stable P transformation to water-extractable P. Manure dry matter and P are assimilated into soil to simulate bioturbation. Water-extractable P is leached from manure when it rains, and a portion of leached P can be transferred to surface runoff. Eighty percent of manure P leached into soil by rain remains in the top 2 cm, while 20% leaches deeper. This 2-cm soil layer contributes P to runoff via desorption. We used data from field studies in Texas, Pennsylvania, Georgia, and Arkansas to build and validate the model. Validation results show the model accurately predicted cumulative P loads in runoff, reflecting successful simulation of the dynamics of manure dry matter, manure and soil P pools, and storm-event runoff P concentrations. Predicted runoff P concentrations were significantly related to (r2=0.57) but slightly less than measured concentrations. Our model thus represents an important modification for field or watershed scale models that assess P loss from manured soils.

Decomposição e liberação de nutrientes acumulados em leguminosas herbáceas perenes consorciadas com bananeira

A avaliação da decomposição dos resíduos vegetais adicionados ao solo pelas plantas de cobertura permite melhor compreensão do fornecimento de nutrientes para as culturas de interesse comercial. O presente estudo foi realizado no campo com o objetivo de avaliar a decomposição e a liberação de nutrientes pela parte aérea de leguminosas herbáceas perenes. Os tratamentos consistiram de diferentes plantas de cobertura do solo consorciadas com bananeira: amendoim forrageiro (Arachis pintoi Krapov. &amp; W.C. Gregory), cudzu tropical (Pueraria phaseoloides (Roxb.) Benth.), siratro (Macroptilium atropurpureum (Sessé &amp; Moc. ex DC.) Urb.) e vegetação espontânea com predomínio de capim-colonião (Panicum maximum Jacq.). Essas espécies foram cortadas na estação seca (abril de 1997) e na estação chuvosa (janeiro de 1998). Após cada corte, amostras da parte aérea foram acondicionadas em sacos de tela ("litterbags") distribuídos na superfície das parcelas. A decomposição da matéria seca e a liberação de nutrientes foram monitoradas por meio de coletas dos resíduos contidos nos sacos de tela, realizadas 5, 10, 15, 30, 60, 90, 120 e 150 dias após o corte das plantas de cobertura. Os resíduos de amendoim forrageiro apresentaram maior velocidade de decomposição, enquanto a vegetação espontânea mostrou um comportamento mais lento. As constantes de decomposição diminuíram e os tempos de meia-vida aumentaram na estação seca. Houve rápida liberação de N, Ca e Mg pelas leguminosas, enquanto a vegetação espontânea apresentou o mesmo comportamento para P. Com relação à composição química dos resíduos, os teores de celulose e hemicelulose mostraram-se correlacionados com as perdas de matéria seca. As liberações de N foram correlacionadas com os teores de C e hemicelulose. Os dados indicam o potencial das leguminosas herbáceas perenes na liberação de nutrientes, com destaque para cudzu tropical e siratro.

Decomposition of crop residues under conventional and zero tillage

Field experiments were conducted to determine decomposition patterns of red clover (Trifolium pratense), field pea (Pisum sativum), canola (Brassica rapa) and wheat (Triticum aestivum) residues under zero and conventional tillage. Crop residue amounts produced in 2 trial years ranged from 1.6 t ha-1 for monoculture wheat to 6.05 t ha-1 for peas, and tillage had no effect. The extent of dry matter (DM) decomposition was usually less under zero than under conventional tillage, e.g., 31 to 41% of canola DM decomposed under zero tillage while 41 to 50% decomposed under conventional tillage in 12 mo. Corresponding percentages for other residues under zero and conventional tillage, respectively, were: 65 and 75% for clover, 43 and 45 to 55% for pea, and 27 and 40% for wheat. The rate and extent of DM decomposition were positively correlated with N and P concentrations, and negatively correlated with C/N, C/P, lignin/P and lignin/K ratios. These decomposition patterns have implications for nutrient release and soil cover. Rapid decomposition is not necessarily desirable because the nutrients released are subject to losses in soil. Key words: Biological soil quality, crop residue quality, crop rotation

Residue Decomposition and Nutrient Release Dynamics from Two Tropical Forage Legumes in a Kenyan Environment

Soil fertility decline is one of the factors limiting food production on the east coast of Africa. Increased awareness by smallholder farmers of the role of legumes as sources of food and fodder and for soil fertility improvement has stimulated research on the influence of herbaceous legumes in various cropping systems. Decomposition and nutrient release from foliage of legume species clitoria (Clitoria ternatea L.) and dolichos (Lablab purpureus L.) planted in monoculture and as an intercrop with tropical food crops cassava (Manihot esculenta Crantz) and maize (Zea mays L.) were evaluated under field conditions in fine‐loamy, kaolinitic, isohyperthermic, arenic Paleustalfs. The nylon mesh bag technique was used to obtain data to calculate the residue decomposition and nutrient release rates of the clitoria foliage cut every 6 or 10 wk and dolichos foliage cut at 2 or 4 mo. Asymptotic models provided the best fit for both dry matter decomposition and nutrient release. Legume residue decomposition rates (k) were unaffected by cropping system, with values of 0.2 and 0.5 wk−1 for clitoria and dolichos, respectively. Across cutting management strategies, the general order of nutrient release for clitoria at 6 or 10 wk was K &gt; P &gt; Mg &gt; N; while that of dolichos was K &gt; Mg &gt; P &gt; N and K &gt; P &gt; Mg &gt; N for cuts at 2 and 4 mo, respectively. Overall, the residue N, P, and Mg release curves became asymptotic shortly after 60% of the nutrients had been released. Clitoria and dolichos showed their potential to become sources of nutrients for associated crops while protecting the soil surface.

Decomposition of and nutrient release from ruminant manure on acid sandy soils in the Sahelian zone of Niger, West Africa

In ago-pastoral systems of the semi-arid West African Sahel, targeted applications of ruminant manure to the cropland is a widespread practice to maintain soil productivity. However, studies exploring the decomposition and mineralisation processes of manure under farmers’ conditions are scarce. The present research in south-west Niger was undertaken to examine the role of micro-organisms and meso-fauna on in situ release rates of nitrogen (N), phosphorus (P) and potassium (K) from cattle and sheep–goat manure collected from village corrals during the rainy season. The results show that (1) macro-organisms played a dominant role in the initial phase of manure decomposition; (2) manure decomposition was faster on crusted than on sandy soils; (3) throughout the study N and P release rates closely followed the dry matter decomposition; (4) during the first 6 weeks after application the K concentration in the manure declined much faster than N or P. At the applied dry matter rate of 18.8 Mg ha −1, the quantities of N, P and K released from the manure during the rainy season were up to 10-fold larger than the annual nutrient uptake of pearl millet ( Pennisetum glaucum L.), the dominant crop in the traditional agro-pastoral systems. The results indicate considerable nutrient losses with the scarce but heavy rainfalls which could be alleviated by smaller rates of manure application. Those, however, would require a more labour intensive system of corralling or manure distribution.

Leucaena hedgerow intercropping and cattle manure application in the Ethiopian highlands I. Decomposition and nutrient release

A litter bag technique was used to study the decomposition and release of N, P, K, Ca, and Mg from Leucaena leucocephala and L. pallida prunings and cattle manure in a hedgerow intercropping trial conducted in the Ethiopian highlands. Hedgerow intercropping (also called alley cropping or alley farming) is an agroforestry system in which trees are grown in dense hedges between alleys where short-cycle crops are grown. The hedges are pruned periodically during the cropping period and the prunings are added to the soil as green manure. Manure was the most resistant to decomposition, losing only 15% of its dry matter (DM) in 15 weeks, compared to 41–57% lost by leucaena prunings. Large quantities of K (up to 104 kg ha–1) were mineralized from prunings and manure, but Ca and Mg were mostly immobilized. More N and P were released from prunings than from manure, which resulted in net immobilization of these nutrients in the initial stages of decomposition and net mineralization in later stages. Between the leucaenas more N was mineralized and less Ca and Mg were immobilized when L. leucocephala prunings were applied than when L. pallida prunings were applied. Fertilizer N increased DM decomposition and N mineralization. Mineralization of the nutrients was constrained by lignin and polyphenol contents. It is concluded that leucaena mulch and cattle manure may be significant sources of N and K for crop growth, but external sources of P, Ca and Mg may be required, particularly in acid soils which have low contents of these nutrients. However, this fertility effect has to be evaluated against the competition effect of trees to predict crop response.

Incremental Cost of Overdrying Farmers’ Stock Peanuts

A study was conducted to determine the incremental costs of drying farmers stock peanuts below the current practice of 10% moisture content wet basis. Three loads of peanuts from the same field were dried using air heated no more than 11 C (20 F) above ambient and no higher than 35 C (95 F) from 10% wet basis to a nominal 9, 7, and 5 1/2% wet basis. The cost, including additional propane, electricity and labor, increased from $2.36/Mg of peanuts dried to 9% to $47.51/Mg of peanuts dried to 5 1/2%. The value of the peanuts dried from 10 to 9% moisture content decreased $8.95/Mg. A reduction in value of $40.97/Mg occurred when the peanuts were dried from 10 to 7%. Peanuts dried from 10 to 5 1/2% were reduced $96.92/Mg in value. Shelling outturns from each trailer indicated that milling losses in terms of dry matter decomposition, split kernels and bald kernels increased as the final moisture content decreased.