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Crop residues are important inputs of carbon (C) and nitrogen (N) to soils and thus directly and indirectly affect nitrous oxide (N2O) emissions. As the current inventory methodology considers N inputs by crop residues as the sole determining factor for N2O emissions, it fails to consider other underlying factors and processes. There is compelling evidence that emissions vary greatly between residues with different biochemical and physical characteristics, with the concentrations of mineralizable N and decomposable C in the residue biomass both enhancing the soil N2O production potential. High concentrations of these components are associated with immature residues (e.g., cover crops, grass, legumes, and vegetables) as opposed to mature residues (e.g., straw). A more accurate estimation of the short‐term (months) effects of the crop residues on N2O could involve distinguishing mature and immature crop residues with distinctly different emission factors. The medium‐term (years) and long‐term (decades) effects relate to the effects of residue management on soil N fertility and soil physical and chemical properties, considering that these are affected by local climatic and soil conditions as well as land use and management. More targeted mitigation efforts for N2O emissions, after addition of crop residues to the soil, are urgently needed and require an improved methodology for emission accounting. This work needs to be underpinned by research to (1) develop and validate N2O emission factors for mature and immature crop residues, (2) assess emissions from belowground residues of terminated crops, (3) improve activity data on management of different residue types, in particular immature residues, and (4) evaluate long‐term effects of residue addition on N2O emissions. [ABSTRACT FROM AUTHOR]

Using organic fertilizers on sugarcane mulches is a potentially interesting substitute for mineral fertilization in terms of economic and environmental impacts. However, no general agreement exists regarding the short-term effect of combining mulching and organic fertilization on greenhouse gas (GHG) emissions. Therefore, we studied different mixtures in the field by combining two amounts of sugarcane mulch (5 and 10 Mg ha−1) with different N fertilizers (urea, pig slurry, and digested sewage sludge). We measured CO2 and N2O emissions shortly after application of the mixtures (0–14 days) and the mulch decomposition dynamics from 0 to 120 days after application. We hypothesized that the relative amount of N to C modifies the decomposition dynamics and GHG fluxes. The emitted N2O-N and CO2-C were measured using static chambers. Mulch-C decomposition was measured using litterbags. Our results showed that the proportion of mulch-C remaining on the soil on day 120 was not altered by either the type of N fertilizer or the mulch amount. On a shorter time scale (0–49 days), the different N treatments affected the mulch-C and mulch-N losses and the C:N ratios, indicating a transient interaction between the dynamics of the mulch and the added N. The intensity of N2O-N emission was ranked as pig slurry > urea > digested sewage sludge, underscoring the effect of the physical form of N fertilizer. This work highlights the need to jointly study carbon and nitrogen dynamics and consider both soil carbon and gas emissions to assess the GHG balances of sugarcane farming practices. [ABSTRACT FROM AUTHOR]

• The vertical decomposition gradient was characterized in mulches of various thicknesses. • Top mulch layers decomposed similarly, regardless of the thickness of the underlying mulch. • Low mulch layers decomposed faster as the thickness of the overlying mulch increased. • The decomposition gradient within the mulch was closely correlated with the moisture gradient. Crop residues left on the soil surface as mulch influence many services provided in agrosystems, particularly soil protection, water dynamics and nutrient fluxes. For a given crop, the residue mass influences the mulch thickness, but the effect of thickness on decomposition is not well understood, and decomposition gradients within mulches in the field have not been described. This study aimed to quantify the decomposition of sugarcane straw mulches by varying their mass and thickness and determine the decomposition gradient within the mulches. The experiment was conducted on a first-ratoon sugarcane crop for one year, with 4, 8 and 12 Mg straw dry matter ha−1. Mulches were displayed in 0.16-m2 litter boxes and formed by straw layers of equivalent mass, i.e., 4 Mg ha-1, stacked either as a single layer (Low/Top layer), 2 layers (Low and Top layers) or 3 layers (Low, Middle and Top layers) to reconstitute the 3 mulch quantities. We quantified the carbon (C) and nitrogen (N) contents, the chemical composition and the water content of the remaining mulch particles in each layer 10 times within the 360 days. The mulch degradation rates were proportional to the initial amount of straw, the mulch losses representing 75% of its initial C and 46% of its initial N after one year, regardless of the initial mass. Fertilizer-N addition did not change the k decomposition rate, with k = 0.0044 d−1. However the decomposition rate differed according to the layer position in the mulch, e.g., in the 12 Mg ha−1 treatment k = 0.0064 d−1, 0.0046 d−1 and 0.0033 d−1 for the low, middle and top layers, respectively, indicating that the low layers in contact with the soil decomposed faster than the top layers in contact with the atmosphere, while the medium layers demonstrated intermediate behaviour. The top layers evolved similarly, regardless of mulch thickness, while the lower layers in contact with the soil decomposed more quickly as the overlying straw thickness increased. Regardless of the thickness and position of a given layer within mulch, the one-year layer C loss was linearly correlated with the average water content of that layer over the year (y = 52.79 - 0694x, R2 = 0.991, P < 0.05). Here, we demonstrate that the dynamics of mulch decomposition is primarily driven by the dynamics of water, which is itself driven by mulch characteristics, rain regime and evaporation. [ABSTRACT FROM AUTHOR]

Adequate nitrogen (N) fertilisation is an important component of sustainable management in agricultural systems because it reduces the environmental impacts of agriculture. However, taking into account the varied sources of soil N remains a challenge, and farmers require robust decision-making tools to manage increasingly diverse growing conditions. To address these issues, we present the AzoFert® decision support system for farmers and extension services. This tool is capable of providing N recommendations at the field scale for 40 main field crops. It is based on a full inorganic N balance sheet and integrates the dynamic modelling of N supply from soil and various organic sources. Because of the choice of formalisms and parameters and the structure and modularity of the computer design, the tool is easily adaptable to new crops and cropping systems. We illustrate the application of Azofert® through a range of N fertilisation experiments conducted on cereals, sugar beet and vegetables in France. [ABSTRACT FROM AUTHOR]

Energy crops are currently promoted as potential sources of alternative energy that can help mitigate the climate change caused by greenhouse gases ( GHGs). The perennial crop Miscanthus × giganteus is considered promising due to its high potential for biomass production under conditions of low input. However, to assess its potential for GHG mitigation, a better quantification of the crop's contribution to soil organic matter recycling under various management systems is needed. The aim of this work was to study the effect of abscised leaves on carbon (C) and nitrogen (N) recycling in a Miscanthus plantation. The dynamics of senescent leaf fall, the rate of leaf decomposition (using a litter bag approach) and the leaf accumulation at the soil surface were tracked over two 1-year periods under field conditions in Northern France. The fallen leaves represented an average yearly input of 1.40 Mg C ha−1 and 16 kg N ha−1. The abscised leaves lost approximately 54% of their initial mass in 1 year due to decomposition; the remaining mass, accumulated as a mulch layer at the soil surface, was equivalent to 7 Mg dry matter ( DM) ha−1 5 years after planting. Based on the estimated annual leaf-C recycling rate and a stabilization rate of 35% of the added C, the annual contribution of the senescent leaves to the soil C was estimated to be approximately 0.50 Mg C ha−1yr−1 or 10 Mg C ha−1 total over the 20-year lifespan of a Miscanthus crop. This finding suggested that for Miscanthus, the abscised leaves contribute more to the soil C accumulation than do the rhizomes or roots. In contrast, the recycling of the leaf N to the soil was less than for the other N fluxes, particularly for those involving the transfer of N from the tops of the plant to the rhizome. [ABSTRACT FROM AUTHOR]

Characterizes the response of maize (Zea mays L.) to fertilization. Quantification of the N balance during and after the crop cycle; Methodology used in study; Dynamics of soil and fertilizer N (NO3-transport and N balance during cropping and intercropping periods; What results showed about the traditional fertilizer input; Discussion on findings of study; Concluding remarks.

• Management of crop residues influences residue-derived N 2 O emissions. • Major environmental drivers of N 2 O emissions are affected by mulch mass and quality. • Vetch mulch increased soil available C and N and N 2 O emitted compare to wheat mulch. • Crop residue emission factors should consider the effects of mulch on soil functions. Crop residue affects nitrous oxide (N 2 O) emissions in no-tillage systems, but the magnitude of the emissions depends on soil drivers that are directly influenced by crop residue quality and quantity. We conducted a one-year study to investigate how mulch chemical characteristics and mass affect N 2 O emissions during their decomposition in the field under subtropical conditions. The mulch treatments consisted of vetch and wheat crop residues applied to the soil at quantities of 0, 3, 6 and 9 Mg ha−1 dry matter. We followed the kinetics of mulch carbon (C) and nitrogen (N), soil temperature, moisture and inorganic N, the denitrification end-product ratio [N 2 O/(N 2 O + N 2)] at days 15 and 30, and N 2 O and carbon dioxide (CO 2) emissions with a static chamber method. Mulch decomposition and C and N dynamics were very rapid for vetch and much more gradual for wheat, reflecting the differences in their initial chemical compositions, but for both residues, the initial mulch mass had no effect on the decomposition rate. The presence of mulches increased soil moisture in the 0–10 cm soil layer, with the results for water-filled pore space by treatment as 0 = 3 < 6 = 9 Mg ha−1. Vetch also significantly increased the inorganic N content in the soil, unlike wheat, which caused net N immobilization. The daily N 2 O fluxes were strongly and positively correlated with CO 2 fluxes (r = 0.83). The highest N 2 O fluxes were observed in the first 60 days with the vetch residues, and the results increased by treatment as 0 < 3 < 6 = 9 Mg ha−1; for wheat, the mean N 2 O emitted was 50% lower than that for vetch and was not affected by mulch mass. Although the cumulative N 2 O emitted was higher in vetch than in wheat, the N 2 O emission factor was higher for the wheat than for the vetch residues (EF = 4.64% vs 1.75% of N applied). We conclude that while mulch mass and quality strongly influenced soil drivers of N 2 O emissions, not only the N input but also the nature of residue C and the residue location must be taken into account to understand and predict N 2 O emissions associated to crop residue management. [ABSTRACT FROM AUTHOR]