Decomposition Of Crop Residues Research Articles

Leaf litter and crop residue decomposition in ginkgo agroforestry systems in eastern China: Soil fauna diversity and abundance, microbial biomass and nutrient release

The response of soil fauna to the litter decomposition process has received considerable attention, but this effect has not been fully examined in agroforestry systems. A 1-year in situ decomposition experiment was carried out in a pure ginkgo plantation and two ginkgo agroforestry systems using a litterbag method (11 different treatments were tested in three systems). We found that the application of different organic materials (crop residues) produced positive effects on the number of soil fauna in the ginkgo planting systems; the mixture of ginkgo leaves and corn leaves was the best performing treatment. Collembola and Acarina were the predominant groups in the litter bags and were mainly responsible for the differences among the treatments. Litter mixing promoted the abundance, richness, and diversity of soil fauna, and significant differences regarding the Shannon–Wiener index of the soil fauna were observed among the 11 treatments in July. Significantly higher soil MBC (microbial biomass carbon) and MBN (microbial biomass nitrogen) were observed in agroforestry systems than in pure ginkgo plantations. These results suggest that the practice of intercrop residue application plays an important role in enhancing soil ecosystem function in ginkgo agroforestry systems and may ultimately contribute to sustainable intercrop production, soil fertility, and local economic diversity.

Integrating Legumes as Cover Crops and Intercrops into Grain Sorghum Production Systems

Core Ideas Intercropping cowpea with grain sorghum dramatically decreased sorghum grain yield. Clover green manure only increased sorghum grain yield 1 out of 3 yr. Fertilizer effects likely masked by mineralized organic matter from plowing of perennial pasture. Crop residue decomposition was mostly unaffected by treatments. Crop residue decomposition was largely driven by residue C/N ratios. Legumes fix N, reduce fertilizer inputs for primary crops, and contribute C to soil organic matter (SOM), which benefits soil productivity and sustainability. Objectives of this study were to (i) maintain grain sorghum [Sorghum bicolor (L.) Moench] yields while decreasing N fertilizer requirements and build SOM using a temperate legume cover crop and tropical legume intercrop; (ii) quantify soil water usage between legume treatments and N fertilizer rates; and (iii) evaluate treatment effects on residue decomposition of each crop. In Overton, TX, crimson clover (Trifolium incarnatum L.) and cowpea [Vigna unguiculata L. (Walp)] were used as green manure and an intercrop, respectively, with grain sorghum. Four N fertilizer rates of 0, 45, 90, and 135 kg ha−1 were randomly assigned within a four replicate split‐split plot design on a Lilbert loamy fine sand. From 2010 through 2012, intercropped cowpea decreased sorghum grain yield between 77 and 93% compared to monocropped sorghum. Clover green manure increased sorghum grain yield 21% over winter fallow in 2012, but not significantly (P = 0.22). After 3 yr, soil organic C (12.4 g kg−1) and soil N (1.1 g kg−1) were 18% (P = 0.01) and 21% (P = 0.01) higher, respectively, for clover green manure compared to fallow at 0 to 15‐cm depth. Crop residue decomposition was relatively stable across years and only intercropping showed small increases in decomposition of grain sorghum residue. Overall, clover green manure proved to be a more sustainable choice than intercropping cowpea from both a yield and soil perspective.

A Web‐Based Model of N Mineralization from Cover Crop Residue Decomposition

Core Ideas The model provided good estimates of N mineralized when linked to climate data. Modifications to rate constants and some parameters led to good model fit. The model predictions in the validation were accurate for incorporated residues. Cover crops can provide substantial quantities of N for subsequent crops, but estimating the amount of N that will be mineralized from residues is challenging. Complex interactions of residue chemistry with soil temperature and soil water content affect N mineralization during residue decomposition. A simulation model can describe these interactions and provide estimates of N mineralized if specific soil water and temperature data are available. Our objectives are (i) to describe a web‐based N mineralization model and its operation, (ii) to calibrate the model with results from published N mineralization studies, and (iii) to validate it using field studies investigating decomposition of surface‐applied or incorporated crimson clover (Trifolium incarnatum L.) or rye (Secale cereale L.) residues over 3 yr. Inputs required by the model include residue N, nonstructural carbohydrates, cellulose + hemi‐cellulose, and lignin contents, as well as 5‐yr average values of daily soil temperature and soil water content from a user‐selected weather station. The model was successfully calibrated with published data from eight laboratory and field studies and was validated with data from field studies that used soil cores with cover crop residues. Simulated values of N mineralized were acceptable for incorporated residues but tended to overpredict N mineralized from surface residues because soil temperature and water content are not good drivers to simulate N mineralization from residues on the soil surface. Additional research is needed to develop algorithms to estimate temperature and water content/water potential of surface residues so they can be used as driver variables for the model.

Long-term fertilization management affects the C utilization from crop residues by the soil micro-food web

Crop residue decomposition is a major component of carbon (C) cycling and provides energy and nutrients to the soil micro-food web. An in-situ field experiment was conducted to examine how exogenous organic C is incorporated into the soil micro-food web and how this is influenced by four different fertilization treatments: organic manure (M), urea fertilizer (U), the combined application of organic and urea fertilizer (MU) and unfertilized control. The amount of 13C-enriched maize remained was traced in microbial phospholipid fatty acids (PLFAs) and in different trophic groups of the soil nematode community after a 183-day decomposition period. The fertilization type influenced the incorporation of residue into the microbial community. Soil bacterial and fungal PLFAs utilized the least 13C-labeled crop residues in the U treatment. Both the nematode bacterial and the fungal pathways utilized more crop residues in the M treatment than in other treatments. Given the ecological services provided by the soil organisms, our results suggest that long-term manure application increases the soil C pool directly. This also leads to more C from crop residues utilized by the soil food web, which in turn, can benefit crop growth or C accumulation in agroecosystems.

Influence of winter crop residue and nitrogen form on greenhouse gas emissions from acidic paddy soil

We conducted an incubation experiment to explore the effect of different crop shoot residues (milk vetch, ryegrass, winter wheat and rape) and nitrogen forms (no fertilizer, CO(NH2)2, (NH4)2SO4 and KNO3) on greenhouse gas CO2, CH4 and N2O emissions from submerged paddy soils. Regardless of nitrogen form, cumulative CO2 and CH4 emissions were in the order of milk vetch > ryegrass > winter wheat > rape. (NH4)2SO4 and KNO3 application decreased CO2 emissions in comparison to treatments without N application. Compared with other N form fertilizer treatments, KNO3 application dramatically stimulated N2O emissions and inhibited CH4 emissions at all crop residue treatments. In the presence of KNO3, N2O emissions of milk vetch and ryegrass residue treatments were significantly higher than those of winter wheat and rape residue treatments. CO(NH2)2 application significantly lowered the N2O emissions from soils with rape residue amendment and increased that from soil with milk vetch residue amendment. We suspected that the differences among these treatments might due to differences of the speed of inorganic N immobilization and N release during crop residue decomposition. Milk vetch + (NH4)2SO4, rape + CO(NH2)2 and ryegrass + (NH4)2SO4 combinations got the relatively low global warming potential, which were recommended to reduce the global warming potentials in paddy soils.

Biochemical stabilization of soil organic matter in straw-amended, anaerobic and aerobic soils

Crop straw incorporation is a useful approach for increasing the quantity and changing the chemical composition of soil organic matter (SOM). This process is influenced by soil aeration. The present study investigated the stability of whole SOM, particulate organic matter (POM) and mineral-associated organic matter (MinOM) fractions with wheat straw amendment under aerobic and anaerobic conditions over a 12-month incubation period. Solid-state nuclear magnetic resonance and Fourier transform infrared spectroscopy were used to analyze the chemical composition of whole SOM, POM and MinOM fractions. The decomposition rate of wheat straw was lower under anaerobic than under aerobic conditions (0.014 vs. 0.020day−1). Wheat straw incorporation increased the original soil organic carbon content (7.4g kg−1) under both aerobic (up to 10.2g·kg−1) and anaerobic (up to 10.3g·kg−1) conditions, but the content of mineral-associated organic carbon (MinOC) under aerobic condition (7.0g·kg−1) was significantly larger than that under anaerobic condition (4.9g·kg−1). The proportion of alkyl carbon (C) in SOM, POM and MinOM fractions was greater under anaerobic than under aerobic conditions, while the opposite was true for the proportion of O-alkyl C of SOM and POM and MinOM fractions. A/O-A indices (i.e., the ratio of alkyl C to O-alkyl C) of whole SOM, POM and MinOM were higher under anaerobic than under aerobic conditions. We conclude that wheat straw incorporation resulted in the enrichment of alkyl C in the POM and MinOM fractions under anaerobic conditions, and thus improved the stability of SOM. In this way, the decomposition of crop residue influenced SOM structural chemistry at the molecular level.

Green-Cane Harvested Sugarcane Crop Residue Decomposition as a Function of Temperature, Soil Moisture, and Particle Size

Sugarcane, a complex hybrid of Saccharum species, is grown on over 170,000 ha in the state of Louisiana. In 2016, the crop was worth $750 million US. Green-cane harvest, widely used in sugarcane producing countries, deposits up to 20 Mg ha−1 of crop residue annually. Green cane harvesting of sugarcane is recognized to be a more sustainable management opportunity than burning residue, or standing or heaped stalks. In Louisiana, cool, wet winters coupled with the crop residue left on the field reduce ratoon yields by as much as 10% year−1. However, the residue represents an important opportunity to improve degraded, low organic matter soils to facilitate sustainable sugarcane production. Our objective was to evaluate how temperature, soil moisture, and particle size influence sugarcane residue decomposition rates. In laboratory experiments, we observed rapid residue carbon (C) mineralization rates at temperatures of ≥ 23 °C across all soil moisture levels tested, and calculated the residue decomposed by 71–95% over the course of the 155 days experiment. Particle size also increased decomposition, with 61, 72, and 91% decomposition observed for the > 2.0, 0.25–2.0, and < 0.25 mm particle size fractions, respectively. The results indicate that earlier cut cane fields have the best chance to decompose green-cane harvested residue by taking advantage of warmer October temperatures, and that shredding the residue further increases its susceptibility to microbial decomposition. Future experiments will study field decomposition of residue in situ as well as incorporation of residue C into soil organic matter.

Effects of detritivorous invertebrates on the decomposition of rice straw: evidence from a microcosm experiment

Decomposition of crop residues is a key process in agricultural systems that influences nutrient cycling and productivity. To clarify the roles of different groups of invertebrates in decomposition in paddy fields, we conducted a microcosm experiment, testing the effects of soil eluate filtered through a 21 μm mesh (control treatment) against the effects of microfauna (< 0.1 mm) and small gastropods (juvenile golden apple snails (Pomacea canaliculata), ca. 2 mm shell diameter), both separately and in combination, on rice straw decomposition. Rice straw in litterbags was incubated at the soil surface and in the soil together with standardized amounts of the respective detritivores for 10 and 21 days. Compared to the control treatment, snails and microfauna enhanced the reduction in straw mass on the soil surface by 19 and 22%, respectively. Both groups combined increased the reduction in straw biomass by 30%. Below the soil surface, the contribution of detritivores to decomposition was smaller, reducing straw biomass by just 1% (snails), 11% (microfauna) and 14% (snails + microfauna) compared to the control. The effects of microfauna and snails on decomposition were not fully additive, a pattern that could be due to competition or trophic interactions. Model selection using Akaike’s information criterion on nested linear mixed effects models led to a model including the main effects (snails, microfauna, position and time), several two-way interactions and the three-way interaction snails * microfauna * litterbag_position as the most parsimonious description of the data. Keeping straw accessible to aquatic invertebrate detritivores should be a suitable management strategy to enhance decomposition in paddy fields, although trade-offs with other management issues such as pest control need to be considered.

Decomposition of tree leaf litter and crop residues from ginkgo agroforestry systems in Eastern China: an in situ study

Purpose Litter decomposition is a crucial biogeochemical process linking nutrient cycling and carbon (C) storage in ecosystems, but few studies have investigated this process in agroforestry systems, where tree leaf litter is mixed with intercrop residues.

Fungal plant pathogens on inoculated maize leaves in a simulated soil warming experiment

Climate change will affect the survival of plant pathogens and the decomposition of crop residues on temperate arable soils. Information on the survival of fungal plant pathogens is important for assessing the subsequent infection risk of susceptible agricultural crops. Therefore, a soil warming experiment was performed to examine the effects of rising winter soil temperatures on the inoculum load of fungal plant pathogens (Fusarium culmorum, F. graminearum, Rhizoctonia solani) and the decomposition of infested maize leaves under field conditions. Using heating cables, an arable soil was subjected to temperature treatments simulating medium (+1.3°C up to the year 2050) and long-term (+2.7°C up to the year 2100) climate warming scenarios. Litterbags filled with pathogen-inoculated and non-inoculated maize leaves were placed on top of the soil. Soil microbial biomass below the litterbags, maize leaf decomposition as well as microbial colonisation of leaves were measured after 152days. Pathogen load was estimated by DNA, total saprotrophic biomass by fungal glucosamine and bacterial muramic acid. Rising soil temperatures increased decomposition of pathogen-infested, but not that of non-inoculated maize leaves, without correlation to fungal and bacterial biomass. F. culmorum DNA produced the largest increase in DNA on maize leaves, but did not significantly respond to soil temperatures. In contrast, the increase in F. graminearum DNA was considerably lower, but revealed a significant positive response to rising soil temperatures. DNA from mycelia and sclerotia of R. solani strongly decreased. Rising winter soil temperatures will most likely cause shifts within the plant residue colonizing fungal community, especially between different Fusarium species.

SOIL SICKNESS AND NEGATIVE PLANT-SOIL FEEDBACK: A REAPPRAISAL OF HYPOTHESES

Soil sickness (SS) is the rise of negative conditions for plant vegetative and reproductive performances induced into the soil by the plant itself. In natural ecosystems, plant ecologists refer to SS as negative plant-soil feedback (NPSF). Scope of this review is to provide an updated picture of the current SS understanding by an explicit comparison between agroecosystems and natural plant communities. By an extensive analysis of literature we found that SS is pervasive in agro-ecosystems, occurring in 111 cultivated plants belonging to 41 taxonomic families. Concerning NPSF in natural plant communities, we found evidence of this phenomenon for a total of 411 vascular plants belonging to 72 plant families. NPSF occur in most of the terrestrial ecosystems, including tropical and temperate forests, coastal sand dunes, old fields and grassland, deserts, as well as heathland and tundra. Three main hypotheses have been proposed to explain SS: (i) soil nutrient depletion or imbalance; (ii) build-up of soilborne pathogen and parasite populations, coupled with a shift in soil microbial community composition; (iii) release of phytotoxic and autotoxic compounds during decomposition of crop residues. Evidences from both agro-ecosystems and natural plant communities undoubtedly ruled-out the nutrient deficiency as a primary causal factor. Moreover, the massive use of mineral fertilizers, especially under intensive cultivation systems, appears an incorrect strategy that only exacerbates the decline of soil quality by inducing acidification and salinization. Soilborne pathogens are often isolated from symptomatic plants and many autotoxic compounds have been identified and quantified from sick soil. However, both the pathogenic and autotoxicity hypotheses are still unable to fully explain the species-specificity, as well as the long durability of SS observed in field conditions. The recent discovery that extracellular DNA (exDNA) has self-inhibitory effects, support the autotoxicity hypothesis, nevertheless this is a totally new topic, and more solid and systematic field investigations are needed. A better understanding of the causes of SS is a necessary step to develop eco-friendly solutions to overcome this problem.

Application of different cover crops and mineral fertilizer doses for no-till cultivation of broccoli, cauliflower and cabbage

No-till practices have not been widely adopted by vegetable producers due to the necessity of seedbed preparation to incorporate organic fertilizers and plant residues of the preceding crops. This study evaluated biomass yield and residue decomposition of different cover crops, and their influence on agronomic performance of Brassica crops cultivated under no-till system. The experiment was laid out in randomized complete blocks with 4 x 3 factorial treatment combinations of four cover crops: Sunn hemp (SH), Signal grass (SG), Pearl millet (PM), and SH + PM mixture, and three doses of mineral fertilizer-0, 50, and 100% of the recommended fertilizer doses for broccoli. The same design and treatments were used for cauliflower and then for cabbage, separately.. The experiment was carried out with 4 repetitions on parcels of 20 m2. No beds were raised, for the planting of seedlings was done in pits. The following agronomic traits were evaluated: Dry biomass (DB) and decomposition of cover crop residues (DR), and the number of leaves (NL), height (H), fresh head weight (FHW) and dry head weight (DHW), and yield (Y) of Brassica crops. The highest DB occurred in treatments with SH (Give value). SG presented the highest DR constant and the shortest half-life of residues in this study.; Broccoli presented better agronomic performance when cultivated on residues containing SH.; Fertilizer doses influenced broccoli and cabbage productivity, which were the highest for the treatment with 100% dose of mineral fertilizer.

Soil organic phosphorus transformations during 2000 years of paddy-rice and non-paddy management in the Yangtze River Delta, China

The contents and properties of soil organic phosphorus (Po) largely drive ecosystem productivity with increasing development of natural soil. We hypothesized that soil Po would initially increase with paddy management and then would persist under steady-state conditions. We analyzed soils from a 2000-year chronosequence of a rice-wheat rotation and an adjacent non-paddy 700-year chronosequence in Bay of Hangzhou (China) for their Po composition using solution 31P-NMR after NaOH-EDTA extraction. Land reclamation promoted Po accumulation in both paddy and non-paddy topsoils (depths ≤ 18 cm) until steady-state equilibria were reached within 200 years of land use. Greater Po concentrations were found, however, in the non-paddy subsoils than in those under paddy management. Apparently, the formation of a dense paddy plough pan hindered long-term Po accumulation in the paddy subsoil. The surface soils showed higher proportions of orthophosphate diesters under paddy than under non-paddy management, likely reflecting suppressed decomposition of crop residues despite elevated microbial P compounds stocks under anaerobic paddy-rice management. Intriguingly, the composition of Po was remarkably stable after 194-years of paddy management and 144-years of non-paddy management, suggesting novel steady-state equilibria of P dynamics had been reached in these man-made ecosystems after less than two centuries.

Estimating Nitrogen Mineralization from Cover Crop Mixtures Using the Precision Nitrogen Management Model

Core Ideas The precision N management model performed reasonably well for estimating cover crop N mineralization. Model performance was sufficient to justify incorporation into an N decision support tool. Cover crops as a best management practice can be assessed with the calibrated model. Cover crops influence soil N dynamics and N availability to a subsequent crop. Dynamic simulation models, if properly calibrated and tested, can simulate C and N dynamics of a terminated cover crop and estimate crop‐available N over diverse production environments. We calibrated and tested a dynamic simulation model modified to simulate C and N cover crop residue dynamics in maize (Zea mays L.) production systems. Data from a 2‐yr field study of different cover crop residue mixtures, fertilizer rates, and tillage practices were used in model calibration and testing. First order rate constants governing cover crop residue decomposition were calibrated so that statistical measures of model best fit were optimized. Calibration resulted in a good fit between measured and modeled N release from the terminated cover crop mixtures (root mean square error [RMSE] = 14 kg N ha−1; Willmott's index of agreement (IA) = 0.92). The calibrated model performed reasonably well in the testing phase (RMSE = 25; IA = 0.88) with significantly better performance for the no‐till (NT) treatments compared to the incorporated treatment. Accounting for cover crop components (leaf, stem proportions), calibration of the temperature and moisture response functions that modify the calibrated rate constants, and testing over a wider range of soils, management practices and climates are potential areas for model improvement. The revised, calibrated model will be used in a decision support tool for N management in maize production and in studies of N dynamics in maize agro‐ecosystems that include cover crops.

Effect of in-situ recycling of sugarcane crop residues and its industrial wastes on different soil carbon pools under soybean (Glycine max) - maize (Zea mays) system

A field experiment was conducted during summer 2011-12 at MPKV Farm, Rahuri to evaluate the effect of in-situ recycling of sugarcane crop residues and its industrial wastes on soil organic C fractions like labile carbon, microbial biomass C, particulate organic C, KMnO4 extractable C, physically protected particulate organic matter carbon (POMC) and significantly improved water stable aggregates in the cultivated soil under maize (Zea mays L.)-soybean [Glycine max (L.) Merr.] system. The active carbon pools like soil microbial biomass carbon (SMBC), water soluble carbohydrates (WHC) and acid hydrolysable carbon (AHC) was significantly improved in the treatment receiving 100% recommended dose of fertilizer along with in-situ compost of crop residues, press mud cake and methanated spent wash compost compared to burning of residues. Application of in-situ sugarcane residues with pressmud incorporation retainedabout19.6%, 38.8% and 33% more amount of total organic carbon (TOC), SMBC, AHC respectively, over burning of sugarcane crop residues and removal of stubbles after harvest of maize. The mean values of WSC (43 mg/kg) and the physically protected carbon, i.e. POMC (2014 mg/kg) were greater by 47% and 6.6% respectively, in the treatment (T7) receiving in-situ residue decomposition of sugarcane crop residues in combination with equal proportion (50%) of press mud cake and biomethanated spent wash over the burning of sugarcane crop residues and removal of stubbles after harvest of maize. After harvest of maize the maximum recalcitrant fraction (humic acid) of carbon was observed in the treatment T7 (in-situ decomposition of sugarcane crop residues + 50% press-mud cake + 50% biomethenated spent wash). This study clearly indicated that resistant fraction of carbon might be accumulated more where decomposed organic matter was applied regularly. It clearly indicated that application of in-situ decomposed residues and by-products of industrial waste in combination with NPK enhanced the below and above ground biomass production, SOC stock and carbon pools.

Changes in soil pH and phosphorus availability during decomposition of cover crop residues

ABSTRACTThe aim of this study was to determine the effect of winter cover crop (CC) residues on soil pH and phosphorus (P) availability. Three incubation assays were performed in pots using two CC: vetch (V) (Vicia villosa Roth.) and oats (Oa) (Avena sativa L.). Soil samples were taken from 10 sites at 0–20-cm depth. The rate of residues were 0 (D0), 10 (D1), 20 (D2), 30 (D3), and 40 (D4) g dry matter kg−1 soil and the soil sampling was after 10, 20, 30, 60, 90, and 120 days of incubation. Soil pH, extractable P (Pe), and soil organic matter (SOM) and its fractions were determined. The pH increase was correlated with the rate applied (D1 < D2 < D3 < D4). No differences were found for pH comparing V and Oa residues with low residue rates. Soil pH changes were dependent from initial pH and SOM fractions in different soils across the incubation period. The multiple regression models showed that the pH changes were dependent on initial pH level and SOM fractions with a high R2 (0.81). CC residues and its quantities produced different changes on pH – especially at the beginning of the incubation – which influenced the P availability.

Long-term stabilization of crop residues and soil organic carbon affected by residue quality and initial soil pH

Residues differing in quality and carbon (C) chemistry are presumed to contribute differently to soil pH change and long-term soil organic carbon (SOC) pools. This study examined the liming effect of different crop residues (canola, chickpea and wheat) down the soil profile (0–30cm) in two sandy soils differing in initial pH as well as the long-term stability of SOC at the amended layer (0–10cm) using mid-infrared (MIR) and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. A field column experiment was conducted for 48months. Chickpea- and canola-residue amendments increased soil pH at 0–10cm in the Podzol by up to 0.47 and 0.36units, and in the Cambisol by 0.31 and 0.18units, respectively, at 48months when compared with the non-residue-amended control. The decomposition of crop residues was greatly retarded in the Podzol with lower initial soil pH during the first 9months. The MIR-predicted particulate organic C (POC) acted as the major C sink for residue-derived C in the Podzol. In contrast, depletion of POC and recovery of residue C in MIR-predicted humic organic C (HOC) were detected in the Cambisol within 3months. Residue types showed little impact on total SOC and its chemical composition in the Cambisol at 48months, in contrast to the Podzol. The final HOC and resistant organic C (ROC) pools in the Podzol amended with canola and chickpea residues were about 25% lower than the control. This apparent priming effect might be related to the greater liming effect of these two residues in the Podzol.

Estimating crop residue cover using SPOT 5 data

Remote sensing of percentage residue cover (PRC) is required to manage crop residue and to provide a key parameter for several biogeochemistry models. However, the growth of the next crop, crop residue decomposition, and precipitation or irrigation can affect the spectral features of crop residue and decrease the spectral difference between crop residue and soil. These factors limit the time window of image acquisition for estimating PRC, especially for double cropping systems (two crops harvested in one year). Remote sensing sensors with a short revisit interval allow imagery to be captured for a specific period (e.g., soon after harvest) when these effects are minimal. SPOT imagery has a short revisit interval of two to three days because of its oblique viewing capacity, and provides balance between high resolution and wide-area coverage. The study aimed to investigate the potential of SPOT 5 imagery for predicting PRC in a typical area of China with a wheat (Triticum aestivum)–corn (Zea mays L.) double cropping system. A SPOT 5 image was acquired with three visible and near infrared bands and one shortwave infrared (SWIR) band, from which six normalized difference indices (NDI) were built. Wheat PRC values (n = 94) were measured immediately after wheat harvest using ground vertical photographs and divided into a calibration set (n = 62) and a validation set (n = 32). To estimate PRC, linear spectral analysis and three regression methods were used. Simple linear regression (SLR) was used for its simplicity, and stepwise regression (SR) and principal component regression (PCR) were used because they could exploit the spectral information from all available image bands. Besides, the bootstrap was used to assess the prediction uncertainty of the regression methods. The results demonstrated that the NDI41 index (derived from SWIR and green bands) performed the best among the four bands and the six indices for estimating PRC when using the SLR method, with a coefficient of determination (R2) of 0.588 and a root mean square error (RMSE) of 0.114 for the validation set. This estimation accuracy was similar to that observed for the SR and PCR models and much better than that for the linear spectral analysis (R2 and RMSE were 0.326 and 0.208, respectively). However, NDI41 accompanied by SLR was the optimal choice for estimating PRC because of its simplicity. These results indicate that SPOT 5 imagery could be used to estimate PRC. Therefore, this study should contribute to crop residue management.

Crop residue degradation by fungi isolated from conservation agriculture fields under rice–wheat system of North-West India

In North West-Indo Gangetic Plains (NW-IGP) of India in situ burning of crop residues is practiced by majority of farmers’ which deteriorates soil and environmental quality. Fungi have the potential for lignocellulose degradation and can be used for the in situ decomposition of crop residues. Lignocellulose degrading fungal spp. were isolated and evaluated for the activity of lignocellulolytic enzymes. The lignocellulose degrading fungi were isolated by appearance of zone on carboxy methyl cellulose (CMC) agar media and tannic acid (TA) media. Carboxy methyl cellulase, filter paperase, cellobiase, xylanase and laccase activity were estimated in submerged, as well as solid state fermentation using a mixture of rice and wheat straw in the ratio of 4:1. rice–wheat straw as substrate. The residue left after solid state fermentation was evaluated for carbon/nitrogen ratio, dry mass loss, and loss of cellulose, hemicellulose and lignin. Selected potential isolates were further tested in pot experiment for their effect on wheat plants. The interaction among isolates was also studied. After primary screening, 19 out of a total of 72 fungal isolates were selected based on their enzymatic activity profile and potential to degrade lignocellulosic residues in submerged fermentation. Out of these 19 isolates, 11 were further selected based on their enzymatic secretions in solid state fermentation. All the 11 strains were identified morphologically. Four fungal isolates (RPW 1/3, RPW 1/6, RPWM 2/2 and RZWM 3/2) showed higher enzymatic activities and more loss of dry mass and cell wall constituents over the other isolates. These isolates were identified by ITS region sequencing as Aspergillus flavus, Aspergillus terreus, Penicillium pinophilum and Alternaria alternata. This study revealed that fungal isolates may be used for managing crop residues in conservation agriculture based rice–wheat system of NW-IGP to eliminate ill effects of residue burning.

English

There is increasing global concern with environmental food production and sustainability to maintain high carbon stocks in soil biomass. The biomass produced in crop-livestock integration system increases soil organic matter, acts in nutrient cycling, improves the physical, chemical and biological characteristics of soil and increases grain production. Moreover, this soil management system mitigates greenhouse effect and preserves the environment. However, in the Savannah of Central Brazil region, an efficient mulching production of biomass is one of the factors limit sustainability of direct seeding of soybean, mainly due to accelerated decomposition of crop residues. Thus, this study aimed to evaluate biomass dynamics of pearl millet and Paiaguas palisadegrass in different forage systems and sowing periods on soybean yield. The experiment followed a randomized block design with a 5 x 2 factorial arrangement and three replications, under five forage systems (monocropped pearl millet, monocropped Paiaguas palisadegrass, pearl millet intercropped in rows with Paiaguas palisadegrass, pearl millet intercropped between rows of Paiaguas palisadegrass and pearl millet oversown and intercropped with Paiaguas palisadegrass) at two sowing periods (February and March). The results showed that Paiaguas palisadegrass in a monocropped system generated the highest biomass production and lowest carbon/nitrogen ratio. The highest carbon/nitrogen ratio and cumulative biomass loss occurred with millet in monocropped and intercropped with oversown Paiaguas palisadegrass in which biomass production was reduced by plant competition. Paiaguas forage systems in palisadegrass monocropped and intercropping on and between rows supported higher yield of soybean. The second sowing periods resulted in higher production of remaining biomass and grain yield, in all forage systems. Intercropping in crop-livestock integration systems showed a promising cultivation technique to maintain a sustainable stock of soil carbon. Key words: Carbon/nitrogen ratio, half-lives, [Pennisetum glaucum (L.) R. Br.], Urochloa brizantha cv. BRS Paiaguas.