Above-ground Residues Research Articles

Low N2O emissions induced by root-derived residues compared to aboveground residues of red clover or grass mixed into soil

The default The Intergovernmental Panel on Climate Change (IPCC) guidelines assume a constant N2O emission factor (EFN2O) for both belowground crop residues (BGR) and aboveground residues (AGR), and that ∼70 % of total N2O emissions following renewal of temporary grasslands come from BGR. However, empirical evidence is lacking, which motivated this study. BGR-free and BGR-rich clay loam collected in grass or red clover leys were incubated alone or mixed with AGR and different doses of nitrate over 107 days. The average EFN2O of BGR was around 18 % of that of AGR, and remained low even when soil nitrate concentration was very high, whereas EFN2O of AGR varied largely and rocketed even with a small increase in soil nitrate. The decomposition of the carbon present in crop residues was critical for N2O emissions. Lower EFN2O of BGR relative to AGR were related to slower C decomposition, which was not predicted by the biochemical characteristics. It is also likely that BGR were less conducive than AGR to develop into hotspots for N2O emission because of the roots’ finer distribution and closer contact with soil particles. Differences in EFN2O among AGR were mostly linked to the availability of N, either derived from residue mineralization or present in the soil. In conclusion, N2O accountings based on present IPCC default methodology likely overestimate the contribution by crops’ BGR.

Synergetic management of the water-energy-food nexus for cropland ecosystems under climate change: Toward a multistakeholder-based systematic optimization approach

The optimal management of the water-energy-food (WEF) nexus in cropland ecosystems (CEs) can help promote food security and resource sustainability. However, the intrinsic interactions among multisource energy, water, the yield-formation process, and the economic-environmental effect have not been systematically quantified and determined. This paper constructs a WEF-based cooperative optimization model in CEs under climate-change conditions, which is capable of reflecting the reciprocal transformations and coordinated interactions among light energy, thermal energy and biomass energy in CEs and of balancing the energy/water use efficiency, economy and environmental factors considering the biomass residue potential. The method is tested and implemented on the Sanjiang Plain, Northeast China. The results show that (1) a cooperative relationship between energy utilization efficiencies and economic benefits was identified. For example, if the utilization efficiencies of light and heat energy increase by 1%, the economic benefits increase by 13.59%, and the biomass energy production potential increases by 10.82%. (2) The aboveground residue can be reused in power generation, carbonization, anaerobic fermentation, feed preparation and sales applications to increase the economic benefits by 3.38%–20.70%. This study contributes to a deeper understanding of multiple renewable energy management and the bound with water and food production, promoting the sustainable development of agroecosystems.

Roots are the key for soil C restoration: A comparison of land management in the semiarid Argentinean Pampa

The objective of the study was to elucidate the relationship between soil management and carbon (C) stocks, and to identify the factors that intervene in the processes that favor C sequestration. The study was carried out on a farm in the Argentinean semiarid pampas with four land management practices (2019–2021): natural grassland (NG), crop-pasture rotation (RO), soybean monoculture (S-S) and with cover crop (S-CC). Aerial and root biomass were quantified at cover crop termination and soybean flowering. In addition, residues on soil surface were determined two times a year. In all cases, C and N contents were quantified. On composite soil samples, soil organic C (SOC), particulate C (POC), microbial biomass C and N (MBC, MBN), and soluble C and N were determined at 0–0.1 m depth. Results showed that NG had the highest and the most stable aboveground (3807.1 kg residue-C ha-1) and belowground inputs between years (4965.8 kg root-C ha-1). Similar results were observed in RO treatment during the first year (4221.0 kg root-C ha-1) diminishing by 67% after plowing for the annual crop in the second year reaching similar root-C values than S-CC and S-S (721.7 kg ha-1). S-S presented the lowest aboveground (49%) and belowground inputs (77%) compared to NG. Cover crops (S-CC) contributed with 31% and 14% of extra residue-C and root-C, respectively, compared to S-S. MBC showed a non-linear response with increases in root-C, reaching maximum carrying capacity of 110.6 ± 4.3 kg MBC ha-1 with root-C inputs ≥ 2200 kg ha-1. Our results showed significant relationships between root-C and POC and SOC, while no relationships were found for aboveground residues. Increases in soluble N explained 86% of SOC variability. Both RO and S-CC reached the “4 per Mille” goal with an average annual SOC storage rate (ΔC) of 0.24 and 0.16 Mg ha-1 y-1, respectively, while S-S had SOC losses of 0.04 Mg ha-1yr-1.

Contributions of plant breeding to soil carbon storage: Retrospect and prospects

AbstractThere is interest in harnessing cropland C storage potential at a large scale to mitigate climate change and improve land productivity. While the effects of soil management practices on C storage have been studied extensively, opportunities to select for C sequestration traits in crop plants remain largely unexplored. This review describes how genetic improvement of major US crops may have altered soil C stocks historically and identifies potential opportunities for plant breeding to increase cropland C stocks. Through quantitative literature review, we find that breeding has led to an increase in aboveground residue C inputs to the soil for corn (Zea maysL.) and soybeans (Glycine max(L.) Merr) and a decrease in aboveground residue C inputs for wheat (Triticum aestivumL. andTriticum turgidumL.). Breeding has largely not altered the root:shoot ratio of these crops. Given that there is limited potential for further major improvements in harvest index, breeding for high grain yields may necessitate increasing aboveground biomass and residue production in the future. Crop root traits and residue quality may influence the stabilization of crop‐derived C in soil, but there is uncertainty regarding historical changes in these traits due to breeding, the magnitude of their effect on soil organic C stocks, and tradeoffs or synergies with breeding for high yield. Nevertheless, root traits such as suberin content, rhizodeposition, mycorrhizal association, and depth emerge as potential targets for more efficient C stabilization. There is also a large opportunity for plant breeding to enhance the performance of cover crops, double crops, perennial grains, and perennial groundcovers, which can increase annual C inputs to the soil by occupying fallow periods. Our review reveals that there are many opportunities for plant genetic improvement to fix more C in cropping systems and enhance its stabilization in the soil to meet the goals of sustainable intensification and cropland C capture.

Soil organic carbon dynamics in multipurpose cropping systems

Diversification of conventional food-based cropping system with multipurpose lignocellulosic crops could increase biodiversity, farmer’s market opportunities, feedstock for biorefineries, though can also imply soil organic carbon (SOC) stock changes, without competing with food production. Sunnhemp ( Crotalaria juncea L.), biomass sorghum ( Sorghum bicolor L.), kenaf ( Hibiscus cannabinus L.), and industrial hemp ( Cannabis sativa L.) are annual high yielding lignocellulosic crops with great potential for their multiple applications. The objective of the present study was to identify the SOC changes when the aforementioned crops are grown during the fallow periods of a conventional maize ( Zea mays L.)-wheat ( Triticum aestivum L.) rotation over five years. For this purpose, the SOC, carbon inputs (i.e. above and belowground residues), soil respiration , and cumulative CO 2 emissions were evaluated. The experiment was carried out in northern Italy (44°30′ N, 11°21′ E) from 2016 to 2021 in a randomized complete block design (n = 4) by adopting conventional field and harvest management practices (i.e. straw removal with hay machineries and alternating conventional with minimum tillage). The SOC stock increased by 7% from 2016 (56 Mg ha −1 ) to 2021 (60 Mg ha −1 ), regardless of the rotation system. Despite one of the highest CO 2 cumulative soil emissions (11 Mg ha −1 , two and three times higher than sunnhemp, kenaf, and industrial hemp, respectively) the rotation including biomass sorghum ended with higher SOC concentration (7.6 g kg −1 ) compared with industrial hemp (7 g kg −1 ) and kenaf (6.9 g kg −1 ), whereas fallow (7.2 g kg −1 ) and sunnhemp (7.1 g kg −1 ) showed intermediate values. The combination of high aboveground residues and high nitrogen fertilizations are deemed to act primarily on SOC level compared with belowground residues. In summary, the crop intensification did not deplete SOC, moreover biomass sorghum cropping system outperformed kenaf and industrial hemp through the decomposition into SOC of higher released residues. The rotation including sunnhemp coupled high SOC levels with low CO 2 emissions, raising interest in the light of its nitrogen fixing ability which can further help reducing the system’s carbon footprint. • Cropping systems with wheat and maize including lignocellulosic crops during the fallow period are presented. • Over five years, the SOC carbon stock increased by 7%, regardless of rotation. • The rotation resulting with the highest SOC concentration included biomass sorghum (7.6 g kg −1 ). • The rotation resulting with the lowest SOC concentration included industrial hemp (7 g kg −1 ), and kenaf (6.9 g kg −1 ). • Aboveground crop residues, reduced tillage and nitrogen fertilization are likely the main drivers influencing SOC.

Potential for the adoption of measures to reduce N2O emissions from crop residues in Denmark

Crop residues represent a climate change dilemma: they can promote carbon (C) sequestration, but they may also stimulate emissions of the powerful greenhouse gas nitrous oxide (N2O). Although there are crop residue management measures to reduce N2O emissions, N2O reductions achieved at national scale with these measures have been seldom studied, and how farmers' willingness to accept the measures constrains their potential remains largely unknown. Using Denmark as a case study, we combined a survey (completed by 592 farmers) and national data to assess the practical potential and obstacles for the successful implementation of management strategies to reduce N2O emissions from crop residues. Crop residue removal (particularly from vegetables and cover crops) and nitrification inhibitors were identified as effective in reducing N2O emissions from a biophysical perspective. If all aboveground crop residues from vegetables and cover crops were removed, N2O emissions could be reduced by 0.181 Gg N2ON, corresponding to 11% of the total N2O emissions from crop residues nationally. However, a low percentage of farmers would be willing to remove crop residues from the field, especially for vegetables and cover crops (25%), in connection to the possible short- to medium-term reduction in C sequestration. Similarly, use of nitrification inhibitors would reduce emissions by 0.247 Gg N2ON, corresponding to 15% of the total residue N2O emissions, and only 37% of all farmers would accept their use. Our results highlight that farmer’ preferences for the adoption of measures can constrain the use of the few available effective mitigation options. Better knowledge dissemination and advisory services are crucial to address this challenge; farmers may be motivated to remove aboveground crop residues by highlighting the proportionally more important contribution of belowground residues to C sequestration, and that aboveground residues may have commercial value (biorefining, biogas, biofuel), although these options need further development.

Roots and other residues from leys with or without red clover: Quality and effects on N2O emission factors in a partly frozen soil following autumn ploughing

Revised IPCC guidelines assume that a constant share of N in decomposing crop residues is directly emitted as N2O (emission factor: EFN2O), and calculate the amount of nitrogen (N) in non-removable residues of temporary grasslands proportionally to the average annual herbage yield. However, EFN2O depends on the intrinsic quality of the residues and their interactions with environmental conditions. Only a few field studies on N2O emissions from grassland renewal are available, and none have simultaneously quantified the N amount and quality of non-removable residues (roots and stubble).To gain insight into the effect of non-removable residue quality on EFN2O, we studied the amount and quality of roots and stubble and their effect on EFN2O following the ploughing of three-year-old swards.The measured amount of N in non-removable residues was approximately 20, 25, and 31 kg N per 1 Mg average annual dry matter yield in grass, red clover-grass, and red clover, and 70–83% of it was below ground. However, the EFN2O of non-removable residues measured over 252 days was lower (0.24%, SE = 14% for grass and red clover-grass) than the IPCC default value (0.6%, CV: 50%) for wet regions, although within the uncertainty margin, and was significantly lower than the EFN2O of incorporated herbage, which was related to differences in EFCO2. We advocate for more specific studies that separate the effects of belowground and aboveground residues (AGR), considering the possibility of simplifying the accounting of N2O emissions from belowground residues while improving that of non-removable AGR from temporary grasslands and other green crops.We observed the accumulation of N2O in the frozen soil under snow, which was released during diurnal percolation of meltwater. N2O emissions from frozen soil accounted for 30% or more of the total emissions.

Important constraints on soil organic carbon formation efficiency in subtropical and tropical grasslands.

More than 10% of Australia's 49Mha of grassland is considered degraded, prompting widespread interest in the management of these ecosystems to increase soil carbon (C) sequestration-with an emphasis on long-lived C storage. We know that management practices that increase plant biomass also increase C inputs to the soil, but we lack a quantitative understanding of the fate of soil C inputs into different soil organic carbon (SOC) fractions that have fundamentally different formation pathways and persistence in the soil. Our understanding of the factors that constrain SOC formation in these fractions is also limited, particularly within tropical climates. We used isotopically labelled residue (13 C) to determine the fate of residue C inputs into short-lived particulate organic matter (POM) and more persistent mineral-associated organic matter (MAOM) across a broad climatic gradient (ΔMAT 10°C) with varying soil properties. Climate was the primary driver of aboveground residue mass loss which corresponded to higher residue-derived POM formation. In contrast, MAOM formation efficiency was constrained by soil properties. The differential controls on POM and MAOM formation highlight that a targeted approach to grassland restoration is required; we must identify priority regions for improved grazing management in soils that have a relatively high silt+clay content and cation exchange capacity, with a low C saturation in the silt+clay fraction to deliver long-term SOC sequestration.

Towards integrated cover crop management: N, P and S release from aboveground and belowground residues

Ecological intensification is crucial for arable organic farmers, in order to partly close the yield gap to conventional yields. One strategy for this is improved management of cover crops, to increase availability of both nitrogen (N), phosphorus (P) and sulfur (S) for the subsequent main crop. However, the potential of cover crops to take up and release nutrients has primarily been determined for aboveground biomass and mostly for N. There have been fewer studies on belowground biomass, and these have focused on recoverable roots. Thus, unrecoverable residues from rhizodeposits and nodules, have been overlooked. The aim of this incubation study was therefore to assess the release of N, P and S from aboveground residues and from intact soil with belowground residues of different cover crop species at low temperature. Shoots and intact soil with roots from seven different cover crops were incubated for 80 days at a temperature of 5 °C.A comparison of the cover crop species revealed a wide variation in nutrient uptake, chemical composition and release of N, P and S, that also varied between shoot and intact soil with roots. Release of N from shoots showed a marked non-stoichiometric behavior, in contrast to the release of P and S, that correlated well with C:P and C:S ratios. N release (from Vicia villosa) and especially P mobilization (from legumes) in intact soil was much greater than the amounts determined in recoverable roots. This shows that unrecoverable pools such as rhizodeposits and fine roots contributed to nutrient release. Garden sorrel (Rumex acetosa) is a promising cover crop regarding uptake and mobilization of P, but also as a multifunctional cover crop for supplying N, K, S and Mg. Hairy vetch (Vicia villosa) is a promising cover crop for N, oilseed radish (Raphanus sativus) for S, P and K, and white lupin (Lupinus albus) for N, P and Mn supply.Based on our results, we propose the use of mixtures of cover crops with different N, P and S uptake and release having the potential to supply a more complete suite of nutrients to the subsequent crop.

Association Analysis among Fungi Colonizing Wheat Crop Residues During Decomposition for Sustainable and Environment-Friendly Management of Renewable Natural Resources

The interspecific associations between selected fungal species were calculated based on assumption; the species occurring together in Petri dishes during isolation from litter might be associated as well. Each Petridis was considered as a quadrate for association analysis. The presence and absence of different species in Petri dishes at different sampling dates were recorded as done in grasslands by the quadrate method. In the present study, the interspecific association between 16 fungal species was evaluated, which was isolated during the decomposition of above-ground residues of wheat crop. A sum of 136 combinations was analyzed. The chi-square (χ2) values were calculated to assess the significance of association (positive or negative), and the coefficient of association (V) was also enumerated to find out the extent of association between species in nature. Any organism was influenced by abiotic and biotic factors constituting its environment. The fungi are no exception; the colonization of a substrate by a fungus and its survival and multiplication depends upon the environment it gets. Therefore, before using any fungus as a bioinoculant, we must make sure that other microbes, especially the fungi already present on the substrate, do not negatively impact it. An analysis of the association between species colonizing the substrate would help determine the bioinoculant to be used for the degradation of organic waste in the interest of the environment to make it safe for everyone.

Bridging mapping and simulation modelling in the ecosystem service assessments of boreal forests: effects of bioenergy production on carbon dynamics

BackgroundIncreasing the use of forest harvest residues for bioenergy production reduces greenhouse emissions from the use of fossil fuels. However, it may also reduce carbon stocks and habitats for deadwood dependent species. Consequently, simple tools for assessing the trade-offs of alternative management practices on forest dynamics and their services to people are needed. The objectives of this study were to combine mapping and simulation modelling to investigate the effects of forest management on ecosystem services related to carbon cycle in the case of bioenergy production; and to evaluate the suitability of this approach for assessing ecosystem services at the landscape level. Stand level simulations of forest growth and carbon budget were combined with extensive multi-source forest inventory data across a southern boreal landscape in Finland. Stochastic changes in the stand age class distribution over the study region were simulated to mimic variation in management regimes.ResultsThe mapping framework produced reasonable estimates of the effects of forest management on a set of key ecosystem service indicators: the annual carbon stocks and fluxes of forest biomass and soil, timber and energy-wood production and the coarse woody litter production over a simulation period 2012–2100. Regular harvesting, affecting the stand age class distribution, was a key driver of the carbon stock changes at a landscape level. Extracting forest harvest residues in the final felling caused carbon loss from litter and soil, particularly with combined aboveground residue and stump harvesting. It also reduced the annual coarse woody litter production, demonstrating negative impacts on deadwood abundance and, consequently, forest biodiversity.ConclusionsThe refined mapping framework was suitable for assessing ecosystem services at the landscape level. The procedure contributes to bridging the gap between ecosystem service mapping and detailed simulation modelling in boreal forests. It allows for visualizing ecosystem services as fine resolution maps to support sustainable land use planning. In the future, more detailed models and a wider variety of ecosystem service indicators could be added to develop the method.

Allelopathy of Sorghum Residues on Weed Establishment Is Affected by Hybrid, Phenolic Acid Contents and Environment

Sorghum species are well known for allelopathic potential toward weeds and other crops. Sorghum above-ground residues mediate allelopathic activity through production and release of many allelochemicals including phenolic acids. Information is limited on selection of grain sorghum hybrids with high allelopathic potential and assessment of sorghum residue phenolic activity in soil under field conditions. This study was carried out to investigate several grain sorghum hybrids for allelopathic potential for suppressing weed growth in the field in the subsequent growing season; and to investigate the involvement of phenolic substances released into soil on the establishment of weeds. The weed seedbank was affected by environmental conditions that led to different weed densities subjected to suppression by residues in soil. Differential allelopathy was identified among the sorghum hybrids suggesting that improved selection may increase production and release of allelochemicals in new hybrids to control weeds inexpensively, easily, and environmentally friendly. Tillage type (till vs no-till) had variable effects on weed suppression. Soil type, environment, sorghum hybrid traits and cultural practices complicate the use of allelopathy in weed control and benefits gained from this potentially environment friendly weed control practice. Well-planned management will be required to successfully integrate allelopathic crops into sustainable crop production.

Contribution of above- versus belowground C inputs of maize to soil organic carbon: Conclusions from a 13C/12C-resolved resampling campaign of Belgian croplands after two decades

The few available studies on maize biomass in soil of field experiments have shown that belowground maize biomass resides more than twice as long as aboveground residues. Our principal objective was to investigate the effect of maize crop residue incorporation on the long-term dynamics of soil organic carbon (SOC) for a selection of croplands with sandy to sandy loam texture in Flanders, Belgium. After a period of more than 20 years, we resampled 31 and 29 parcels that had either silage maize (MS, only belowground biomass input) or grain maize (MG, both above- and belowground biomass input) dominated crop rotations. Changes in maize-derived SOC (Cmaize) of MS and MG systems between 1993 and 2018 were evaluated by detecting SOC content and its δ13C value. In addition, a 140-day incubation experiment (at 20.5 °C) was carried out to compare the stability of Cmaize and the related nitrogen (N) mineralization between the MG and MS fields. After two decades, δ13C raised 2.4 and 2.6‰, while Cmaize increased 1.6 and 2.2 g kg−1 in MS and MG systems, respectively. The estimated average humification coefficient over this period of maize-C was 0.11 for the MS system, about twice as that of the MG system (0.06). This reconfirms findings of stronger contribution of belowground biomass versus aboveground residues to stabilized SOC pools over the medium to long term. By the end of the incubation, on average 10.4% and 11.6% of Cmaize had been decomposed in the MS and MG soils, respectively. These Cmaize mineralization rates were statistically equal for the two systems, which indicates that mainly belowground biomass remained in the soils. Also, net N mineralization was indifferent to the crop rotations (MS: 58.8 mg N kg−1 and MG: 52.6 mg N kg−1). To reconcile the two main observations in this study, we hypothesize that the lower preservation of shoot-C could be manifested on a shorter term. Detailed research is needed to determine the time scale of increased stabilization of root-C versus shoot-C under field conditions.

Assimilation of Aboveground Litter Carbon Versus Soil Carbon by Collembola and Lumbricidae in Spruce Forest: A Litter Replacement Experiment

In a small-scale field experiment, we estimated the contribution of aboveground litter to the energy budget of different collembolan and earthworm species. In a 50-year-old spruce plantation, the natural spruce litter was replaced by an equivalent amount of maize litter. The natural difference in the isotopic composition of carbon (C) between the spruce and maize allowed us to estimate the proportions of different carbon sources in the tissues of soil animals. The dependence on litter-derived C was least pronounced in Collembola having low δ15N values, indicating the feeding on non-vascular plants. In contrast, collembolans having high δ15N values belonged to the food chains based on fresh plant residuals. These results suggest that different species of litter-dwelling collembolans may regulate substantially different energy channels. Some species of endogeic earthworms (Aporrectodea rosea and A. caliginosa) utilize aboveground plant residues, though soil organic matter and other belowground sources of carbon prevail in the energy budget of their populations.

Tracing crop residue N into subsequent crops: Insight from long-term crop rotations that vary in diversity

Diversified grain crop rotations have shown yield advantages, but it is unclear if this is related to improved N supply. Crop residue-N supply could be an important driver of differences observed in contrasting crop rotations. To address this, we focused on a long-term field trial near Guelph Ontario that compares different grain crop rotations and tillage practices. We hypothesized that diversified crop rotations increase the transfer of residue-derived N to subsequent crops. From 2017 to 2018, we used a 15N technique to measure N turnover in a simple corn and soybean rotation compared to a diversified rotation where winter wheat and red clover were included. Although crop yields were greater in the diverse vs. simple rotation, the long-term rotation had no impact on crop residue N turnover to the subsequent crop—a finding that did not support our hypothesis. The recovery of above- plus below-ground residual-N by the subsequent crops varied by crop type and sequence: 9.7–13.5% of corn residue-N was recovered in the soybean seed, 26 % of soybean residue-N was recovered in the corn grain, and 30 % of winter wheat/red clover residue-N was recovered in the corn grain. Below-ground residue-N recoveries in subsequent grain or seed were 4- to 10-times greater than above-ground residues; in terms of the total contribution, below-ground residue-N supplied 8- to 18-times more N than above-ground residues. Indigenous soil N or fixed N were principal contributors to crop N uptake; more so than the crop residues or fertilizer combined. At this site, an accumulated legacy of N fertilizer applications is likely responsible for building a soil N reservoir for crop production, explaining yield benefits observed by diversifying the rotation—but also masking any effect that diversification may have on residue-N turnover and subsequent crop N uptake. To improve N use efficiency, diversifying crop rotations should be accompanied with reduced N fertilizer applications, and better account for below-ground residual N pools as well as legume N inputs.

Growth and yield parameters of white oat and wheat as affected by canola residues

ABSTRACT Despite being an important crop option for Brazilian agriculture, canola has some characteristics that may limit its insertion in some cropping systems, such as its allelopathic effects. Thus, the present work aimed to study the effect of canola crop residues on the seed germination, growth and grain yield of white oat and wheat plants. In laboratory conditions, white oat (Milton) and wheat (Tbio Pioneiro) seeds were germinated in the presence of aqueous extracts of (i) aboveground part, (ii) root system, (iii) whole plant and (iv) twice the concentration of the whole plant extract, besides a control. In green house conditions, the same oat and wheat cultivars were grown until harvest, on soil mixed with fresh canola crop residues (whole plant residues, aboveground residues and root residues) and a control. Aqueous extract of the whole canola plant reduced the germination and increased abnormal seedlings of white oat and wheat, mainly in high concentration. For soil crop, the presence of canola residues did not affect the white oat emergence, growth and grain yield. For wheat, plant emergence was lower in the presence of canola residues, but growth and yield were not affected.

Effect of earthworm and loach on Typha augustifolia aboveground and root litter residue in an integrated vertical subsurface flow constructed wetland

A litterbag experiment was undertaken over 299 days (January to November, 2015) to investigate how earthworm and loaches affect aboveground and root litter residues of Typha augustifolia. An integrated vertical subsurface flow constructed wetland (IVFCW), for use in the experiment, was designed and built in a screen house at Nanjing University of Information Science and Technology. Results showed that the addition of earthworms and loaches into IVFCW significantly increased T. augustifolia aboveground and root litter N content in the influent chamber and effluent chamber at decomposition 299 days (p < 0.05). Similarly, addition of earthworms into IVFCW significantly increased P content of aboveground litter of T. augustifolia in the influent chamber at decomposition 213 days, and in root litter in influent chamber at decomposition 120 days (p < 0.05). With the addition of both earthworms and loaches, the T. augustifolia aboveground litter residual rate was negatively correlated with litter N and P content (p < 0.01), but a significant positive correlation between aboveground litter and C/N and C/P was evident (p < 0.01). Results suggest that earthworms and loaches in IVFCW may stimulate T. augustifolia aboveground and root litter decomposition, and decrease the accumulation T. augustifolia litter.

Phosphorus uptake benefit for wheat following legume break crops in semi-arid Australian farming systems

This field study assessed phosphorus dynamics (crop-P uptake, resin-extractable P in the root-zone, P mobilisation and microbial-P) in break crop-cereal rotation sequences at four Australian semi-arid field sites differing in soil P fertility. Phosphorus mobilisation (9–30 kg P ha−1) was apparent under break crops, consistently under canola and peas at three sites with low soil P fertility (i.e. pre-sowing soil resin-extractable P < 20 mg P kg−1). Enhanced biological cycling of P (i.e. increased microbial-P) was limited to a low P site in the break crop phase. Phosphorus content of break crop aboveground residues following grain removal was 1–7 kg P ha−1; P input was greater (12–18 kg P ha−1) where legumes were green/brown manured. Varied residue P input did not result in differences in resin-extractable or microbial-P in soil prior to sowing wheat. Phosphorus uptake was greater for wheat after legume break crops compared to continuous wheat (2.0–4.7 kg P ha−1) at all sites, especially where crops were green/brown-manured (3.9–5.9 kg P ha−1). Greater P uptake by wheat was associated with increased grain yield at three sites but was not significantly correlated with the quantity of P input from break crop residues at all four sites or with soil mineral nitrogen pre-sowing of wheat at three sites. Break crops can directly contribute to P resource-use efficiency by mobilising residual P from soil but the agronomic significance of P supply from break crop residues to a P uptake benefit for following wheat remains to be elucidated.

Pathways of soil organic matter formation from above and belowground inputs in a Sorghum bicolor bioenergy crop

AbstractWhen aboveground materials are harvested for fuel production, such as with Sorghum bicolor, the sustainability of annual bioenergy feedstocks is influenced by the ability of root inputs to contribute to the formation and persistence of soil organic matter (SOM), and to soil fertility through nutrient recycling. Using 13C and 15N labeling, we traced sorghum root and leaf litter‐derived C and N for 19 months in the field as they were mineralized or formed SOM. Our in situ litter incubation experiment confirms that sorghum roots and leaves significantly differ in their inherent chemical recalcitrance. This resulted in different contributions to C and N storage and recycling. Overall root residues had higher biochemical recalcitrance which led to more C retention in soil (27%) than leaf residues (19%). However, sorghum root residues resulted in higher particulate organic matter (POM) and lower mineral associated organic matter (MAOM), deemed to be the most persistent fraction in soil, than leaf residues. Additionally, the overall higher root‐derived C retention in soil led to higher N retention, reducing the immediate recycling of fertility from root as compared to leaf decomposition. Our study, conducted in a highly aggregated clay‐loam soil, emphasized the important role of aggregates in new SOM formation, particularly the efficient formation of MAOM in microaggregate structures occluded within macroaggregates. Given the known role of roots in promoting aggregation, efficient formation of MAOM within aggregates can be a major mechanism to increase persistent SOM storage belowground when aboveground residues are removed. We conclude that promoting root inputs in S. bicolor bioenergy production systems through plant breeding efforts may be an effective means to counterbalance the aboveground residue removal. However, management strategies need to consider the quantity of inputs involved and may need to support SOM storage and fertility with additional organic matter additions.

Эмиссия углекислого газа и азотминерализующая составляющая чернозема выщелоченного в лесостепи Приобья, Западная Сибирь

In model incubation experiment the effect of various agrocenoses on CO2 production and nitrogen-mineralizing ability of the soil to accumulate nitrate nitrogen (N-NO3) was investigated. It was shown that the rates of mineralization of soil organic matter decreased from the first record taken to the last in the following order (in percent): 57 → 63 → 68, further observation of CO2 emissions led to a smoothing of redox reactions. The use of mineral fertilizers in comparison with agrocenoses without fertilizers increased CO2 emissions by 15–24%, depending on the studied variant. It was noted that the agrocenosis with the alienation of aboveground biomass of straw exerted the least load on the total mineralization of soil organic matter – on average, in two levels of fertility, it was 489 mg C / kg. The use of analysis of variance in the experiment did not reveal significant differences in the interaction of signs on the accumulation of N-NO3, however, the solution of correlation and regression dependences contributed to finding a close relationship. It was determined by the capabilities of leached chernozem to compensate losses and restore the carbon-nitrogen potential of the soil. A similar consequence increased in the agrocenosis with mineral fertilizers and with a greater flow of aboveground and underground plant residues into the soil, the maximum CO2 emission was registered in the variant 634 mg C / kg, and high statistical indicators of the studied signs were established.