Predicting net N mineralized from soil organic matter under fluctuating environmental conditions

Abstract

Nitrogen mineralization from soil organic matter can provide substantial amounts of N for growing crops. However, it is often overlooked or poorly estimated due to the limited availability of rapid soil tests. We conducted a study to (1) fit first- and zero-order N kinetics models to long-term N mineralization data from 29 US soils, (2) evaluate rapid soil tests to estimate model-fit parameters, and (3) use the estimated model-fit parameters to predict net N mineralized from six different soils under fluctuating environmental conditions. Soils collected from 10 USA states were incubated for 115 days at 29°C and 50% water-filled pore space (WFPS) to determine first- and zero-order rates of N Mineralization. The rapid soil tests evaluated included N hydrolyzed by hot KCl and organic C and N released by hot water. Nitrogen hydrolyzed by hot KCl and soil clay content explained 86% of the variability in the zero-order rate of N mineralization. The zero-order rates of six soils, estimated from hot KCl and clay content, were modulated by hourly temperature and WFPS to predict net N mineralized over 30 days under diurnal cycles of temperature and relative humidity. Measured versus predicted net N mineralized had an r² of 0.90, although measured values were overpredicted at very low levels of net N mineralized and underpredicted by 12%–23% at high levels. While our results are promising, more research should be conducted with additional soils under different environmental conditions to determine whether hot KCl and clay content can be used to predict net N mineralized from soil organic matter.