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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]

Organic growers use a wide range of organic fertilizers and materials to supply nutrients and meet plant demand of N. These products range from commercially processed animal and plant byproducts to composts and poultry litters. To better synchronize N release with plant demand, we investigated the rate and pool of potentially mineralizable N from 22 commercial, organic fertilizers; 15 poultry litters; and 11 composts. Fertilizers and organic materials were mixed with soil and inorganic N was measured over 99 days under optimal conditions (50% estimated water holding capacity and 30◦C). Net N mineralized from the organic fertilizer or material was determined and fit to first-order kinetics to determine the rate of mineralization (k) and the pool of mineralizable nitrogen (N0). Net N mineralized ranged from 25–93%, 10–55%, and 1–5% of the organic N applied for the fertilizers, poultry litters, and composts that mineralized, respectively. The pool of mineralizable N was accurately predicted from the initial total N of the materials, but no characteristics predicted the rate constant, k. Using a grouped approach based on product type and the percentage of N mineralized to determine k, we were able to predict net mineralized for fertilizers (R² = 0.84) and poultry litters (R² = 0.62). [ABSTRACT FROM AUTHOR]

Previous studies have indicated that soil properties and texture could lead to differences in N mineralization from applied organic materials. We conducted a 100-day (d) incubation study to measure net N mineralized from feather meal (14–0.1–0.1) and pellet mix (10–1–6) at 150 mg N kg soil −1 (approximately 72 kg N ha−1) incorporated into four common southeastern soils: Cecil 1, Cecil 2, Greenville, and Tifton. A second 23-d study was conducted to determine pH dynamics and the potential for ammonia volatilization from the same soils and materials. There were no differences in net N mineralized from pellet mix among soils, but net N mineralized from feather meal was lower in Greenville soil, which had the greatest clay content. Analysis of the first-order dynamics of N mineralization indicated that even in soils that differ in clay content it may be possible to describe N mineralization from feather meal and pellet mix with a single model. Our results also suggest that the effect of pH on the N mineralization dynamics of these fertilizers may be more important than the effect of clay content. No ammonia loss was observed regardless of soil texture, soil pH buffering capacity, or initial soil pH. [ABSTRACT FROM AUTHOR]

A sound prediction of soil organic phosphorus (P o ) mineralization would be helpful to improve fertilizer recommendations. However, in most mineral soils expensive and time consuming isotopic dilution experiments are required to assess P o mineralization. A proposed method to estimate P o mineralization is the quantification of P in the coarse fraction (CF, >53 μm) of the soil. The aim of this study was to evaluate if P in the CF can effectively predict P o mineralization. Soil samples from three North American long-term arable field experiments (>10 years) with different textures (sand content 15–82%) and different fertilization treatments (non-P-fertilized, mineral P fertilizer, poultry litter) were analyzed. Soil samples were physically fractioned into CF and fine fraction (FF, <53 μm). Total P (P t ), P o , and total carbon (C t ) were determined in each fraction. Gross and net P o mineralization rates as well as soil respiration were determined in a 13-day-incubation experiment. The cumulative gross P o mineralization over 13 days ranged from 8.3 to 38.6 mg P kg −1 , while P t in CF varied between 9.7 and 90.7 mg P kg −1 and P o in CF between 6.1 and 17.7 mg kg −1 . No association between P t in CF and gross or net mineralized P o was observed. However, a significant linear relationship between P o in CF and net (R 2 :0.68, p < 0.01) and gross mineralized P o (R 2 :0.72, p < 0.01) was observed after 6 days and 13 days of incubation. Additionally, gross and net mineralized P o could also be predicted from C respiration, and these models were significantly improved by incorporating the C t :P o ratio of the CF. Our results suggest that the quantification of P o in the CF as well as the measurement of respiration corrected by the C t :P o ratio of the CF are promising non-isotopic indicators of P o mineralization rates. [ABSTRACT FROM AUTHOR]

Composts and soil conditioners may be useful soil amendments to provide organic matter as well as nutrients such as N and P, but net N mineralized and P released can vary greatly among materials. Consequently, it is important to identify the material characteristics that control these processes. Furthermore, the magnitude of these processes may be affected by particle size. We conducted two laboratory studies at 30°C to: (i) identify variables that can be used to estimate N mineralized and Mehlich-1 P released from 14 composts and soil conditioners; and (ii) evaluate net N mineralized from three size fractions (<1.0 mm, 1.0-2.0, and 2.0-4.0 mm) of five different composts. Organic N content and C/N ratio explained 83% of the variability in the amount of net N mineralized or immobilized per unit of material from the 14 composts or conditioners in 214 d. Similarly, organic N content and total P content explained 99% of the variability in the amount of Mehlich-1 P released per unit of material. In the study with size fractions, we found that larger size fractions (1-4 mm) mineralized more N (4% of applied N) than the 0- to 1-mm size fraction (0.5%). These results indicate that sieving composts to obtain specific size fractions may affect the rate of 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]

Culturing and using effective microorganisms from locally derived microorganisms has become a common practice employed by farmers throughout Central America as well as parts of South America and Southeast Asia to control foul odors and flies around compost piles and livestock facilities. These local, effective microorganisms (LEM) are applied in a concentrated solution fermented from carbohydrate-rich substrates inoculated with locally-sourced, actively decomposing leaf litter. Despite its growing prevalence among small-scale farmers in some parts of the world, there is little published research that explores the beneficial or detrimental effects of changing the biome of animal-based nutrients and the soils to which LEM are applied. The objectives of this study were to evaluate the effect of combining LEM with swine effluent to fertilize annual ryegrass ( Lolium multiflorum ) on plant-available nitrogen, nematode community structure, and forage productivity. Forage performance was good across all of the treatments – with relative feed quality (RFQ) values above 200 and 100 in the March and May harvests respectively. In the first, second and third sampling dates, soils from 0 to 5 cm depth showed more nitrogen mineralized in LEM-treated soils than in control soils (p = 0.178, p < 0.0001 and p = 0.027) respectively. After nutrient applications, soil-nematode community structure (0–10 cm) at the trophic group level changed over time. Most changes were similar between treatments, however, plant parasitic nematode populations were found to be significantly higher in LEM-treated plots in all but one of the sampling dates. LEM is gaining popularity as a natural amendment and although we have shown that it does increase N availability and changes trophic-level nematode community structure, more research is needed to optimize the potential of these benefits. [ABSTRACT FROM AUTHOR]