Assessment of apparent N mineralization at field scale

Abstract

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.

Short‐term corn yield response associated with nitrogen dynamics from fall‐seeded cover crops under no‐till dryland conditions

“…These types of estimates inherently ignore mineralization of soil organic N, the stimulation of soil N mineralization activities by cover crops via direct (plant exudates, residues) and indirect (e.g., soil structure) mechanisms, and the contribution of soil N fixed by legumes but not assimilated into legume biomass. Estimates of ANM based on soil N, fertilizer N, and N uptake (Schepers & Meisinger, 1994; Zubillaga et al., 2021) were also low, ranging from 16 to 57 kg N ha −1 across all treatments and site‐years, but consistent with expectations based on cover crop biomass and C:N ratios. Low estimates of PAN from cover crops using easily measured quantities would encourage over‐application of fertilizer N by producers.…”

“…These estimates (Equations and ) are based upon cover crop biomass and/or N content and can be approximated prior to the following cash crop growing season. Another approach requires in‐season measurements to estimate N mineralization, the apparent N mineralized (ANM), which uses soil nitrate samples collected prior to corn planting (Nsoil planting ) and samples collected following harvest (Nsoil harvest ), corn N uptake (Nuptake), and in‐season fertilizer N application (Nfert; Schepers & Meisinger, 1994; Zubillaga et al., 2021). Apparent N mineralization is calculated as follows (Equation ): $$\begin{eqnarray}{\rm{ANM }}\left( {{\rm{kg\, ha}}^{{\rm{-1}}}} \right) &=& \left( {{\rm{Nsoil}}_{{\rm{harvest}}} + {\rm{Nuptake}}} \right){\rm{ }}\nonumber\\ && - {\rm{ }}\left( {{\rm{Nsoil}}_{{\rm{planting}}} + {\rm{Nfert}}} \right)\end{eqnarray}$$…”

“…(4) These estimates (Equations 3 and 4) are based upon cover crop biomass and/or N content and can be approximated prior to the following cash crop growing season. Another approach requires in-season measurements to estimate N mineralization, the apparent N mineralized (ANM), which uses soil nitrate samples collected prior to corn planting (Nsoil planting ) and samples collected following harvest (Nsoil harvest ), corn N uptake (Nuptake), and in-season fertilizer N application (Nfert; Schepers & Meisinger, 1994;Zubillaga et al, 2021). Apparent N mineralization is calculated as follows (Equation 5):…”