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Quantification of nitrogen mineralization at the field scale is necessary to improve current N fertilizer recommendations. The objective of this study was to identify a suitable set of explanatory variables and an appropriate modelling framework to estimate the average daily amount of N mineralized (DANM) during a corn (Zea mays L.) growing season. In six field experiments in Flat Inland Pampas, Argentina, DANM was evaluated in three different homogeneous zones (HZ), which were defined based on terrain elevation. Mixed‐effect generalized linear models were developed that included growing season as random effect as well as HZ, sand, clay, silt, soil organic carbon, and normalized difference vegetation index (NDVI) as fixed effects. Results showed that DANM ranged from 0.19 to 1.25 kg N ha−1 day−1 with a mean of 0.64 kg N ha−1 day−1, which is equivalent to 110 kg N ha−1 for the corn growing season. The best model included HZ, sand, and early NDVI measurements, and predicted DANM with an RMSE of 0.19 kg N ha−1 day−1. Thus, the model should be improved and tested in the Inland Flat Pampas before it could be used to assess N fertilizer application rates. [ABSTRACT FROM AUTHOR]

Cover crop (CC) decomposition and subsequent release of nitrogen (N) are highly influenced by residue water potential (ψ) and temperature (T). To evaluate how carbon (C) and N mineralization from surface-applied CC residues responds to changes in ψ and T, a controlled microcosm experiment was conducted for 150 days with three CC residues (early-killed cereal rye (Secale cereale L.), late-killed cereal rye, late-killed crimson clover (Trifolium incarnatum L.), and a soil-alone control) under different ψ (−0.03, −1.5, −5, and −10 MPa) and T (15, 25, and 35 °C) conditions. Headspace gas was sampled periodically to determine carbon dioxide (CO2) and nitrous oxide (N2O) emissions. Soil inorganic N was determined by destructive sampling at 15, 30, 60, 100, and 150 days. Temporal dynamics in C and N mineralization from surface-applied CC residues were adequately described by first-order rate kinetic models. Early-killed rye and crimson clover (low C:N) residues decomposed quickly and mineralized N, whereas, late-killed rye residue (high fiber content and C:N) immobilized N. The normalized values of C and N mineralized from surface-applied CC residues increased exponentially with increasing ψ from −10.0 to −0.03 MPa. Increasing T from 15 to 35 °C further amplified the effect of ψ, suggesting a strong interactive effect of ψ and T on C and N mineralization from CC residues. Mathematical equations were developed to describe these interactive effects. Existing computer simulation models (e.g., CERES-N) could be improved by integrating these equations to simulate the effect of environmental conditions on surface-applied CC residue decomposition and N mineralization. [ABSTRACT FROM AUTHOR]

Broiler litter is commonly surface applied to grasslands as fertilizer in the southeastern United States. Surface application may lead to losses of P in surface runoff and to losses of N through NH3 volatilization. Adding gypsum to broiler litter can reduce water-soluble P and, therefore, the potential for surface water contamination, but no information is currently available on the effect of gypsum on NH3 volatilization when broiler litter is applied to soil. We conducted three laboratory studies to evaluate the effect of adding flue-gas desulfurization (FGD) gypsum to broiler litter or soil on NH3 volatilized and N mineralized. In two studies, soil with or without 0.01 g FGD gypsum g-1 soil was packed into acrylic columns and broiler litter with or without 0.25 g FGD gypsum g-1 litter was applied on the soil surface and incubated at 25°C for 15 d. In a third study, litter with or without 0.25 g FGD gypsum g-1 litter was mixed with soil and incubated at 25°C for 63 d. Our results showed that the addition of FGD gypsum to broiler litter or soil did not affect net N mineralized or NH3 volatilized when litter was surface applied. Similarly, the addition of FGD gypsum to broiler litter did not affect net N mineralized when broiler litter was incorporated into soil. Thus, the addition of FGD gypsum at these rates does not change NH3 loss or N mineralized from broiler litter. [ABSTRACT FROM AUTHOR]