Crop Residue Soil Research Articles

Effect of Eighteen Years of Continuous Crop Residue Application on Crop Yields, Soil P Fractions, and Crop P Uptake in Conservation Tillage Under Semi-Arid Tropical Rainfed Conditions

The continuous use of crop residue in soil can enhance the crop yield and potential availability and mobility of P fractions to crops in conservation tillage. A field experiment was conducted to assess the long-term effects of surface crop residue applications on soil P fractions and their relationship with P uptake and crop yields. Field experiment was conducted at ICAR-Central Research Institute for Dryland Agriculture, Hyderabad, India during 2005 to 2022. The experimental treatments applied were: T1 - no crop residue application, T2 - application of crop residue @ 2 t ha-1, T3 - application of crop residue @ 4 t ha-1, and T4 - application of crop residue @ 6 t ha-1 in conservation tillage. The test crops viz. sorghum (Sorghum vulgare) and cowpea (Vigna unguiculata) were grown in a yearly rotation every year in the kharif season in conservation tillage. The results of the long-term study revealed that the per cent increase in sorghum (Sorghum vulgare) grain yield with the application of crop residue at the rate of 2, 4 and 6 t crop residue ha-1was to the tune of 7.9, 16.1 and 26.0%, respectively over no crop residue application. Similarly, the per cent increase in the cowpea (Vigna unguiculata) seed yield was to the extent of 25.2, 43.0 and 64.1% in 2, 4 and 6 t ha-1, respectively over no crop residue application. The sorghum and cowpea stover yield also significantly (p=0.05%) increased with the added levels of the crop residue. Significantly higher P uptake by sorghum and cowpea was recorded in 6 t crop residue ha-1 as compared to the other crop residue treatments. Results of the current study also showed the significant positive response of long-term crop residue application on the P fractions viz., water-soluble phosphorus (WS-P), aluminum bound P (Al-P), iron bound P (Fe-P), calcium bound P (Ca-P) and reductant soluble P (RS-P), and on available P and total P in soil as compared to no crop residue application. The average percent contribution of P fractions toward the sum-total of extracted P was in the order: Fe-P (30.8%)>RS-P (30.7%)>Al-P (24.2%)>Ca-P (9.4%)>WS-P (4.8%). The WS-P and Al-P were found to be the P fractions indicating their specificity by cowpea crop, and WS-P and Ca-P were found to be P fractions indicating their specificity by sorghum crop. The results of the present study will be highly useful in understanding the effect of crop residue application in conservation tillage on the P fractions and their contribution toward P uptake and crop yields.

Impact of Crop Residue Incorporation and Incubation Period on DTPA-Extractable Micronutrient Cations

ABSTRACT Micronutrient deficiency is a major problem in sustainable crop production due to the intensive cropping. Excessive application of chemical fertilizers often results in poor soil physical properties and microbial population resulting in adverse effects on soil fertility and productivity. Therefore, crop residue incorporation as organic manure is gaining interest among growers. The assessment of nutrient release from various crop residues in soil at different intervals will help to formulate the rates and frequency of these residue applications. Therefore, a lab study was carried out to evaluate the impact of crop residue incorporated on micronutrient content in soil i.e., zinc (Zn), manganese (Mn), iron (Fe), and copper (Cu) at different incubation periods. In this study, 11 crop residues including biomass of eight field crop residues (Lens culinaris, Avena sativa, Zea mays, Oryza sativa, Saccharum officinarum, Triticum aestivum, Brassica juncea, and Hordeum vulgarae) and leaves of three tree species (Melia azedarach, Azadirachita indica, and Populus alba) were selected to study their effect on diethylene triamine pentaacetic acid (DTPA-extractable) micronutrient cations over a 63 days period in a sandy loam soil. Results of study revealed that DTPA-extractable micronutrient cations substantially enhanced after addition of different crop residues over the control treatment. The DTPA-extractable micronutrients were generally higher at 14th days after incorporation. Among crop residue treatments, the incorporation of M. azedarach residue resulted in higher content for micronutrients.

Assessing soil system changes under climate-smart agriculture via farmers' observations and conventional soil testing.

Soil degradation remains a challenge in African highlands, where land management lacks a strong context‐specific evidence base. We investigated the impacts of recently implemented soil and water conservation (SWC) practices—farmyard manure addition, incorporation of crop residues in soil and fanya juu terracing under an agroforestry system on soil health indicators in the East Usambara Mountains of Tanzania. Farmers' observations of soil changes were combined with conventional soil testing to assess the initial impacts of SWC practices relative to conventional non‐SWC practice. Majority of farmers (66%–83%) reported that combining fanya juu terracing with organic amendments led to soil colour change from red to black and an increase in crop yield. Despite the observed darkening of the soil, there was no significant increase in soil organic carbon stock and the contents of N, P, K. There were important changes in soil physical properties, including greater aggregate stability (mean weight diameter of 1.51–1.71 mm) in the SWC plots, a greater volume of transmission pores (>60 μm) and coarse storage pores (10–60 μm) in the surface soil layer (0–15 cm), and greater volume of fine storage pores (0.2–10 μm) and residual pores (0.2 μm) in the sub‐surface layer (15–30 cm) of the SWC plots compared with the conventional plots. These changes indicate that SWC rapidly enhances infiltration and retention of water within the root zone, which are important for increasing crop yields and improving the resilience of the agro‐ecosystem to environmental stress. Combining SWC with effective soil fertility management is needed for sustainable highland agriculture.

The Role of Cover Crop Types and Residue Incorporation in Improving Soil Chemical Properties

Soil chemical properties can be improved by incorporating crop residues in soil and letting it decompose. This study explored the use of incorporating residues of cover crops for improvements in soil chemical properties including soil organic matter (SOM), soil pH, and the selected soil macro- and micronutrients in greenhouse and field trials. Factors of interest included (i) cover crops and their combinations and (ii) methods of crop termination and incorporation in soil (disc, mow + disc, glyphosate, roller crimper). The greenhouse trial showed up to a 20% higher amount of SOM accumulated in soils incorporated with crop residues. Buckwheat (3.12%) and phacelia (3.12%) produced significantly different and larger SOM than that of the control treatment that received no crop residues (p ≤ 0.05). The soil pH of the brown mustard treatment was also significantly affected by the experimental treatments (p ≤ 0.05). The incorporation of crop residues did not affect soil phosphorous (P) or potassium (K) concentrations, except for brown mustard, with significantly higher values of P and K than the control treatment. Calcium (Ca) was significantly higher in the soil of phacelia + pea treatment (p ≤ 0.05). Buckwheat + pea produced a higher concentration of Ca (1028 mg/kg) followed by buckwheat alone (1006 mg/kg). Analysis of variance (ANOVA) calculated on the results of the field trial showed that the mix treatment that had a mixture of four cover crops significantly increased the SOM content. Buckwheat produced the highest (2.95%) SOM, then brown mustard and timothy. This study concludes that, irrespective of the tillage incorporation methods, the residues from cover crops are a potential source of improvement in soil health, and this practice may promote sustainable agriculture in conditions similar to those in this study.

Survival of Fusarium oxysporum f. sp. lactucae on Crop Residue in Soil.

Fusarium oxysporum f. sp. lactucae, the cause of Fusarium wilt of lettuce, can survive on crop residue in soil. Persistence of the pathogen over time will be influenced by the rate at which residue decomposes. We evaluated the effect of drying and fragmenting crop residue on the rate of decomposition and survival of F. oxysporum f. sp. lactucae. In a controlled experiment that represented optimal drying conditions, fragmenting and oven drying infested lettuce taproots at 30°C significantly reduced the frequency of recovery of the pathogen, compared with untreated tissue. However, in a field experiment, drying infested crop residue on the soil surface prior to incorporation did not significantly reduce survival of F. oxysporum f. sp. lactucae after 1 year. Regardless of treatment, there was not a significant decrease in soil inoculum density between 1 and 12 months after residue was incorporated. In a greenhouse experiment, fragmenting crop residue prior to incorporation in pathogen-free soil resulted in significantly higher inoculum densities of F. oxysporum f. sp. lactucae after 1 year. The increase in inoculum levels was associated with a faster rate of residue decomposition, which may be beneficial in the long run but not where lettuce will be replanted within the next year.

Long-term crop rotation and different tillage practices alter soil organic matter composition and degradation

Conservation agriculture such as conservation tillage and crop rotation can alter soil organic matter (OM) storage and cycling. However, little is known about how these methods alter the molecular-level soil OM composition and turnover. We collected soil samples (0−10 cm) from a 37-year experiment with contrasting diversity crop rotations under conventional tillage and conservation tillage. Soil organic carbon concentrations, molecular-level OM composition and microbial biomass and community structure were measured. Soil organic carbon concentrations were similar between the two tillage practices, likely due to the balance between carbon loss via degradation and carbon gains through incorporation of crop residues in soil. We observed significant changes in soil OM composition between conventional tillage and conservation tillage despite similar soil organic carbon concentrations. Under long-term conservation tillage practice, lower suberin-derived compounds and higher lignin-derived compounds were observed. The degradation of cutin-, lignin-derived compounds and soil OM were lower under conservation tillage among most rotations. The changes in lignin-derived compounds and degradation were microbially driven and likely controlled by substrate utilization. In contrast, the differences in suberin-derived compounds were likely associated with crop residue-induced OM inputs and/or the differential introduction of OM (e.g. root materials) to the upper layer of soil due to conventional tillage vs. conservation tillage managements. These findings reveal that microbial degradation, OM inputs from crop residues and management-induced OM distribution in soil layers may alter agricultural soil OM composition. Additionally, we found that the differences in some specific groups of compounds between conventional tillage and conservation tillage were lower in crop rotations with higher diversity, highlighting the benefits of the interaction between diverse rotations and conservation tillage.

Environmental Factors Affecting the Mineralization of Crop Residues

The aim of this article is to present the issues related to the significance of microorganisms in the mineralization of crop residues and the influence of environmental factors on the rate of this process. Crop residues play a very important role in agriculture because they can be used both as an environment-friendly waste management strategy and as a means of improving soil organic matter. The inclusion of crop residues in the soil requires appropriate management strategies that support crop production and protect the quality of surface water and groundwater. Crops need nutrients for high yields; however, they can only absorb ionic forms of elements. At this point, the microorganisms that convert organically bound nitrogen, phosphorus, and sulfur into soluble NH4+, NO3−, H2PO4−, HPO42−, and SO42− ions are helpful. Mineralization is the transformation of organic compounds into inorganic ones, which is a biological process that depends on temperature, rainfall, soil properties, the chemical composition of crop residues, the structure and composition of microbial communities, and the C:N ratio in soil after the application of plant matter. An adjustment of the values of these factors enables us to determine the rate and direction of the mineralization of crop residues in soil.

Robustness of visible near‐infrared and mid‐infrared spectroscopic models to changes in the quantity and quality of crop residues in soil

AbstractThe robustness of soil organic carbon (SOC) and total nitrogen (TN) content prediction accuracy by visible near‐infrared spectroscopy (visNIRS) and mid‐infrared spectroscopy (MIRS) models after a change in the quantity or quality of crop residues requires investigation. Arable soils (0–20 cm) from 20 locations across Germany were collected, and 0, 2, 4, or 8 g C kg soil−1 of wheat straw (C/N ratio, 54) or clover (C/N ratio, 13) were added. Before and after a 56‐d incubation, dried and ground samples were measured for SOC and TN content and by visNIRS and MIRS. The complete dataset (n = 280) was subdivided into calibration and validation datasets to test the robustness of partial least squares regression models to changes in crop residue quantity and quality in soil. Noise‐reducing data pretreatments included region selection, moving averages, resampling every second data point, and the Savitzky‐Golay algorithm. The MIRS estimates for SOC (7.4–33 g kg−1) had lower root mean squared error of validation (RMSEV = 0.9–2.9 g kg−1) compared with visNIRS (RMSEV = 1.6–7.1 g kg−1). Total N estimates (0.7–2.8 g kg−1) were more comparable for MIRS (RMSEV = 0.1–0.3 g kg−1) and visNIRS (RMSEV = 0.1–1.0 g kg−1). Loadings of partial least squares regression components suggested the predictive mechanisms for SOC and TN were more similar for visNIRS than for MIRS. Differing crop residue quantity or quality in calibration versus validation resulted in biased SOC and TN estimates by visNIRS and MIRS models. However, calibration with a global residue model containing all soils and crop residue quantities and qualities lowered RMSEV for SOC and TN prediction with visNIRS and MIRS, demonstrating the usefulness of this approach.

Assessment of crop residue and palm shell biochar incorporation on greenhouse gas emissions during the fallow and crop growing seasons of broccoli (Brassica oleracea var. italica)

The impact of broccoli crop residues on greenhouse gas (GHG) emissions may vary with post-harvest management. The incorporation of biochar together with broccoli residues could have a GHG mitigation potential in soil. A field experiment was conducted to evaluate the combined effect of broccoli crop residues and palm shell biochar (PSB) incorporation on GHG emissions during the fallow (post-harvest) and crop growing seasons of broccoli. We also evaluated the plant biomass, N uptake, and soil chemical properties after harvest. The treatments included; No-residues (NR), Residues (R), Residues + 10 t ha−1 PSB (R10), Residues + 20 t ha−1 PSB (R20) and Residues + 40 t ha−1 PSB (R40), arranged in a completely randomized block design. The fallow season had significantly higher GHG emissions than the crop growing season. Incorporation of crop residues in soil significantly increased N2O and CO2 emissions but did not significantly affect CH4 emissions when compared to those of the NR treatment. PSB amendment did not significantly affect N2O, CO2 and CH4 emissions from crop residues and also the biomass and N uptake of the crop residues remaining after broccoli harvest. The application of PSB at 40 t ha−1 significantly increased the total N, total C, C/N ratio and exchangeable K but did not significantly affect soil pH, EC, available P, exchangeable Ca and Mg, and CEC. The large amounts of N2O and CO2 emissions emitted from broccoli crop residues during the fallow season may necessitate higher biochar application rates to achieve the GHG mitigation potential of biochar while maintaining a high soil nutrient status. The combined incorporation of broccoli crop residues with biochar requires further evaluation in terms of GHG emissions, soil nutrient status and broccoli crop yield in different soil types and tillage systems.

Effect of Green Manuring Crops on Carbon Mineralization, Dehydrogenase and β-Glucosidase Activities in Inceptisols

Pot culture and incubation studies were conducted to assess the carbon mineralization and soil enzyme activities with green manure crop residue in Inceptisols. The studies were undertaken with six green manure crop residues viz., sunhemp (Crotolaria juncea), cluster bean (Cymopsis tetragonaloba), cow pea (Vigna unguiculata), mutant dhaincha (Sesbania rostrata), green gram (Vigna mungo) and soybean (Glycine max L. Merrill) which were grown up to 50 per cent flowering in the pot along with control at Division of Soil Science and Agricultural Chemistry, College of Agriculture, Pune during 2020-21 in completely randomized design with three replications. Carbon mineralization and soil enzyme activities i.e. dehydrogenase and β- glucosidase were studied by incorporating green manure crop residues in soil. In the incubation study, the mutant dhaincha recorded significantly higher release of CO2-C throughout the incubation period than othertreatments. The rate of release of CO2-C was slow at 0 and 15 days after incubation but increased at 45 days after incubation and thereafter, gradual decline in all green manures incorporated treatments was observed. Higher dehydrogenase and β- glucosidase activity were recorded in sun hemp treated pots.

Effects of cover crop in an apple orchard on microbial community composition, networks, and potential genes involved with degradation of crop residues in soil

Changes in the soil microbial communities and networks were monitored after planting the cover crop for 9 years. The field experiment included plots with a cover crop and without a cover crop but with weed control, and two subplots with or without chemical fertilizer (192 kg N ha−1, 108 kg P2O5 ha−1, and 168 kg K2O ha−1 each year). After applying the cover crop and chemical fertilizer for 9 years, the composition and activity of bacterial and fungal communities changed significantly (p < 0.05), with the cover crop had greater effects than the chemical fertilizer on the composition of the soil microbial community. The relative abundances of 22 selected genera (in Firmicutes and Bacteroidetes) and two selected classes (Ascomycota) related to cover crop residue degradation increased significantly in the presence of the cover crop (p < 0.05). Network analysis showed that the cover crop decreased the number of positive links between bacterial and fungal taxa by 25.33%, and increased the negative links by 22.89%. The positive links among bacterial taxa increased by 16.63% with the cover crop, mainly among Proteobacteria (increase of 39), Firmicutes (16), Actinobacteria (five), and Bacteroidetes (10). The links among fungal taxa were less than among bacterial taxa and were not significantly affected by cover crop. Taxa such as Thaumarchaeota, unidentified_Nitrospiraceae, unidentified_Nitrosomonadaceae, Faecalibacterium, Coprococcus_3, and Ruminococcaceae_NK4A214_group dominated the network without the cover crop but they were not dominant with the cover crop. The relative abundances of potential genes involved with the degradation of cellulose, hemicellulose, and cello-oligosaccharides increased significantly with the cover crop. Therefore, the SOC and TN contents were enhanced by the cover crop with the increase of the soil enzyme activities. Thus, the apple yield was improved by the cover crop.

Multi-Seasonal Nitrogen Recoveries from Crop Residue in Soil and Crop in a Temperate Agro-Ecosystem.

In conservation tillage systems, at least 30% of the soil surface was covered by crop residues which generally contain significant amounts of nitrogen (N). However, little is known about the multi-seasonal recoveries of the N derived from these crop residues in soil-crop systems, notably in northeastern China. In a temperate agro-ecosystem, 15N-labeled maize residue was applied to field surfaces in the 1st year (2009). From the 2nd to 4th year (2010-2012), one treatment halted the application of maize residue, whereas the soil in the second treatment was re-applied with unlabeled maize residue. Crop and soil samples were collected after each harvest, and their 15N enrichments were determined on an isotope ratio mass spectrometer to trace the allocation of N derived from the initially applied maize residue in the soil-crop systems. On average, 8.4% of the maize residue N was recovered in the soil-crop in the 1st year, and the vast majority (61.9%-91.9%) was recovered during subsequent years. Throughout the experiment, the cumulative recovery of the residue N in the crop increased gradually (18.2%-20.9%), but most of the residue N was retained in the soil, notably in the 0-10 cm soil layer. Compared to the single application, the sequential residue application significantly increased the recovery of the residue N in the soil profile (73.8% vs. 40.9%) and remarkably decreased the total and the initially applied residue derived mineral N along the soil profile. Our results suggested that the residue N was actively involved in N cycling, and its release and recovery in crop and soil profile were controlled by the decomposition process. Sequential residue application significantly enhanced the retention and stabilization of the initially applied residue N in the soil and retarded its translocation along the soil profile.

Effect of fertilization on decomposition of 14C labelled plant residues and their incorporation into soil aggregates

Returning crop residues to soil helps to maintain soil C stocks. Organic C stocks and microbial biomass are important factors controlling the decomposition or retention of crop residues in soil and the formation of aggregates. Little is known about the specific contribution of crop residues to soil aggregate size fractions in the framework of long-term fertilization. This study investigated the effects of long-term fertilization on the decomposition of 14C-labelled plant residues and their incorporation into soil organic matter (SOM) of different aggregate size fractions. Soils were collected from 0–10 cm in the Ap horizon of a long-term (since 1988) field experiment at Grossbeeren (Germany). The following four fertilization treatments were used: 1) without fertilization or manuring (Control), 2) nitrogen applied by mineral fertilizer (N), and 3) manure with low (M) and 4) high (2 M) application doses. Soils were incubated for 100 days at 20 °C, with or without 14C-labelled plant residue. The incorporation of 14C into three aggregate size fractions–large macroaggregates (2–1 mm), small macroaggregates (1–0.25) and microaggregates (<0.25 mm)–was analyzed. After 15 days of incubation, 44–57% of plant residue was mineralized in the order: M > N > control soil > 2 M. Adding plant residues increased soil β-glucosidase activity and microbial biomass C. On day 16 of incubation, more residue 14C was retained in small and large macroaggregates than in microaggregates in the control soil. In contrast, in fertilized soils the reverse was measured. Additionally, N, M and 2 M soils showed significant differences by incorporation of 14C in microbial biomass and β-glucosidase activity in different aggregate size fractions. The results imply that long-term fertilization significantly increased the residue 14C retention in microaggregate size fractions and its decomposition in soils.

Interactions between residue placement and earthworm ecological strategy affect aggregate turnover and N 2O dynamics in agricultural soil

Previous laboratory studies using epigeic and anecic earthworms have shown that earthworm activity can considerably increase nitrous oxide (N 2O) emissions from crop residues in soils. However, the universality of this effect across earthworm functional groups and its underlying mechanisms remain unclear. The aims of this study were (i) to determine whether earthworms with an endogeic strategy also affect N 2O emissions; (ii) to quantify possible interactions with epigeic earthworms; and (iii) to link these effects to earthworm-induced differences in selected soil properties. We initiated a 90-day 15N-tracer mesocosm study with the endogeic earthworm species Aporrectodea caliginosa (Savigny) and the epigeic species Lumbricus rubellus (Hoffmeister). 15N-labeled radish ( Raphanus sativus cv. Adagio L.) residue was placed on top or incorporated into the loamy (Fluvaquent) soil. When residue was incorporated, only A. caliginosa significantly ( p < 0.01) increased cumulative N 2O emissions from 1350 to 2223 μg N 2O–N kg −1 soil, with a corresponding increase in the turnover rate of macroaggregates. When residue was applied on top, L. rubellus significantly ( p < 0.001) increased emissions from 524 to 929 μg N 2O–N kg −1, and a significant ( p < 0.05) interaction between the two earthworm species increased emissions to 1397 μg N 2O–N kg −1. These effects coincided with an 84% increase in incorporation of residue 15N into the microaggregate fraction by A. caliginosa ( p = 0.003) and an 85% increase in incorporation into the macroaggregate fraction by L. rubellus ( p = 0.018). Cumulative CO 2 fluxes were only significantly increased by earthworm activity (from 473.9 to 593.6 mg CO 2–C kg −1 soil; p = 0.037) in the presence of L. rubellus when residue was applied on top. We conclude that earthworm-induced N 2O emissions reflect earthworm feeding strategies: epigeic earthworms can increase N 2O emissions when residue is applied on top; endogeic earthworms when residue is incorporated into the soil by humans (tillage) or by other earthworm species. The effects of residue placement and earthworm addition are accompanied by changes in aggregate and SOM turnover, possibly controlling carbon, nitrogen and oxygen availability and therefore denitrification. Our results contribute to understanding the important but intricate relations between (functional) soil biodiversity and the soil greenhouse gas balance. Further research should focus on elucidating the links between the observed changes in soil aggregation and controls on denitrification, including the microbial community.

Environmental risk assessments for transgenic crops producing output trait enzymes

The environmental risks from cultivating crops producing output trait enzymes can be rigorously assessed by testing conservative risk hypotheses of no harm to endpoints such as the abundance of wildlife, crop yield and the rate of degradation of crop residues in soil. These hypotheses can be tested with data from many sources, including evaluations of the agronomic performance and nutritional quality of the crop made during product development, and information from the scientific literature on the mode-of-action, taxonomic distribution and environmental fate of the enzyme. Few, if any, specific ecotoxicology or environmental fate studies are needed. The effective use of existing data means that regulatory decision-making, to which an environmental risk assessment provides essential information, is not unnecessarily complicated by evaluation of large amounts of new data that provide negligible improvement in the characterization of risk, and that may delay environmental benefits offered by transgenic crops containing output trait enzymes.

Molecular characterization of soil bacterial communities in contrasting zero tillage systems

It is well known that agricultural practices change the physical and chemical characteristics of soil. As a result, microbial populations can also be affected. The aim of this study was to analyze the effect on soil bacterial communities of zero tillage (ZT) under maize monoculture (MM) with crop residue removal (-R) (MM/-R treatment), compared to a ZT system under wheat monoculture (WW) with crop retention (+R) (WW/+R treatment). Phylogenetic analysis was used to characterize soil bacterial communities. Phylogenetic groups found exclusively in MM/-R were Caldilineales, Chromatiales, Oscillatoriales, Legionellales, Nitroso- monadales and unclassified ∂-Proteobacteria, while Bacillales, Burkholderiales, Pseudomonadales and Rubrobacteriales were found only in WW/+R. Sequen- ces of bacteria related to fluorescent Pseudomonas sp. were detected only in WW/+R. Acidobacteria, a largely unknown group of bacteria, were the dominant group in both treatments with a relative proportion of 0.703 and 0.517 for MM/+R and WW/-R respectively. It was found that zero tillage with removal of crop residue in soil cultivated with a monoculture of maize strongly reduced microbial diversity (H=3.30; D= 0.9040) compared to soil where crop residue was retained in a wheat zero tillage situation (H=4.15; D= 0.9848).

Decomposition and mineralization of energy crop residues governed by earthworms

Energy crops are increasingly cultivated in agricultural management systems world-wide. A substitution of food crops (e.g. cereals) by energy crops may generally alter the biological activity and litter decomposition in soil due to their varying structural and chemical composition and subsequently modify soil functioning. A soil microcosm experiment was performed to assess the decomposition and microbial mineralization of different energy crop residues in soil compared to a food crop, with or without earthworms. Residues of the energy crops winter rape ( Brassica napus), maize ( Zea mays), miscanthus ( Miscanthus giganteus) and the food crop oat ( Avena sativa) were each provided as food source for a mixed earthworm population, each consisting of one individual of Lumbricus terrestris, Aporrectodea caliginosa, and Octolasion tyrtaeum. After 6 weeks, the rate of litter loss from the soil surface, earthworm biomass, microbial biomass-C and -N, microbial activity, and enzyme activities were determined. The results emphasized, that litter loss and microbial parameters were predominantly promoted by earthworms and were additionally influenced by the varying structural and chemical composition of the different litter. Litter decay by earthworms was highest in N-rich maize litter treatment (C–N ratio 34.8) and lowest in the case of miscanthus litter (C–N ratio 134.4). As a consequence, the microbial biomass and basal respiration in soils with maize litter were higher, relative to other litter types. MBC–MBN ratio in soil increased when earthworms were present, indicating N competition between earthworms and microorganisms. Furthermore, enzyme activities responded in different ways on the varying types of litter and earthworm activity. Enzymes involved in the N-cycle decreased and those involved in the C-cycle tended to increase in the presence of earthworms, when litter with high C–N ratio was provided as a food source. Especially in the miscanthus treatments, less N might remain for enzymatic degradation, indicating that N competition between earthworms and microorganisms may vary between different litter types. Especially, an expansion of miscanthus in agricultural management systems might result in a reduced microbial activity and a higher N deficit for microorganisms in soil.

Quantifying and modelling C and N mineralization kinetics of catch crop residues in soil: parameterization of the residue decomposition module of STICS model for mature and non mature residues

C and N mineralization kinetics of 25 catch crop (CC) residues, whose organic C:N ratio varied from 9.5 to 34.0, were studied during soil incubations under controlled conditions. Decomposition rates were rather similar for the different CC residues, 59% to 68% residue-C being mineralized after 168 days incubation. C mineralized during the first weeks was mainly correlated to the soluble C content of the residue. N mineralized from CC residues was much more variable (−4.9 to +38.0 mg N g−1 added C at day 168), and was mainly related to the organic N content in residues. C and N mineralization kinetics were simulated with STICS residue decomposition model, using the previous parameterization mostly based on mature crop residues (Nicolardot et al. Plant Soil 228:83–103, 2001). A reasonable agreement was found between measured and simulated C kinetics but N mineralization was underestimated by the model. A new parameterization was carried out to improve N predictions. The fitting procedure was first applied independently to each CC residue in order to optimise the five parameters of the model. The relationships found between each optimised parameter and the C:N ratio of CC residues were similar to those obtained previously, indicating that the same model was applicable to all residues. The parameters of these relationships were fitted on a combined dataset including CC and mature residues. The new parameterisation lead to better simulations for CC residues, the errors of prediction (RMSE) for C and N mineralization being 32 and 1.8 mg g−1 added C, respectively. For the whole dataset (68 residues), the RMSE were 50 and 3.3 mg g−1 added C. The prediction quality is satisfactory with respect to the model simplicity and the single criterion of residue quality (C:N ratio).

Temporal and spatial variability of soil organic matter and total nitrogen in an agricultural ecosystem as affected by farming practices

In agricultural ecosystem, soil organic matter (SOM) and soil total nitrogen (STN) are important indexes in estimating the soil carbon stock, soil fertility and soil quality. This paper examines the temporal and spatial variation of SOM and STN in Rugao city, Jiangsu Province, an agricultural area in Yangtze River Delta region, China, as affected by farming practices using the data from 1982 through 1997 to 2002. Spatially, loamy Stagnic Anthrosols (Baipu) in the eastern area and clay Aquic Cambosols (Changqingsha) in the southern area had high contents of SOM and STN, whereas sandy Ustic Cambosols (Guoyuan) and Aquic Cambosols (Motou) in the mid-western areas had low SOM and STN contents, and loamy Aquic Cambosols (Banjing, Dongchen, etc.) in the northern or southern areas had medium SOM and STN contents. Temporally, SOM had shown a tendency to constantly increase in the past 20 years. During the period 1982–1997, the SOM and STN in the mid-western areas rapidly increased due to the effect of farming practices such as incorporating crop residues in soils and shifting from corn–wheat rotation to rice–wheat rotation. From 1997 to 2002, the soils in the eastern and southern areas had a rapid increase in SOM owing to the adjustment of agricultural and cropping structures and/or application of more organic fertilizers, whereas those in the mid-western areas increased slowly or even decreased because of reduced incorporation of crop residues in soils. Accordingly, STN content in the eastern and southern areas increased slightly, but soil STN content in the mid-western areas did not change or decreased in some areas. In conclusion, the incorporation of crop residues in soils and the application of organic fertilizers were effective in increasing SOM, whereas the application of organic fertilizers in combining with chemical fertilizers were effective for accumulating STN. As regards to the implementation of these sustainable measures under rapid economic development, the government must be liable for guiding or supporting farmers so that the sparse soil resources in the densely populated area can be appropriately utilized.

Influence of crop residues on trifluralin mineralization in a silty clay loam soil

Trifluralin is typically applied onto crop residues (trash, stubble) at the soil surface, or onto the bare soil surface after the incorporation of crop residues into the soil. The objective of this study was to quantify the effect of the type and amount of crop residues in soil on trifluralin mineralization in a Wellwood silty clay loam soil. Leaves and stubble of Potato (Solanum tuberosum) (P); Canola (Brassica napus) (C), Wheat (Triticum aestivum) (W), Oats (Avena sativa), (O), and Alfalfa (Medicago sativa) (A) were added to soil microcosms at rates of 2%, 4%, 8% and 16% of the total soil weight (25 g). The type and amount of crop residues in soil had little influence on the trifluralin first-order mineralization rate constant, which ranged from 3.57E-03 day−1 in soil with 16% A to 2.89E-02 day−1 in soil with 8% W. The cumulative trifluralin mineralization at 113 days ranged from 1.15% in soil with 16% P to 3.21% in soil with 4% C, again demonstrating that the observed differences across the treatments are not of agronomic or environmental importance.