Estimation of field soil nitrogen mineralization and nitrification rates using soil N transformation parameters obtained through laboratory incubation

We tested the potential of estimating in-field (in situ) nitrogen (N) transformation rates based on soil temperature data and N transformation parameters (Q₁₀ and N transformation rates at standard temperature) obtained through laboratory incubations at three constant temperatures for 4 weeks. This test was conducted based on a comparison between in situ measurements and estimates using soils from 16 sites across 9 regions within the Japanese archipelago. The actual in situ N mineralization and nitrification rates measured using the buried-bag method at 0–50-cm-soil depth were 111 ± 34 and 106 ± 45 kg N ha⁻¹ year⁻¹, respectively, and estimates of both the rate and the amount were largely accurate. For rate alone, estimates were accurate in the 0–10-cm soil layer for annual and seasonal averages (except for spring–summer) whereas for amount alone, estimates were accurate to depths of 50 and 30 cm for N mineralization and nitrification, respectively. Thus, estimates of the rates and amounts were approximately equal to the actual in situ rate/amount, given the wide range of prediction intervals of the field measurement data. The differences between the estimates of N transformation rates derived from hourly measured and monthly average soil temperatures were negligible. Therefore, in situ soil N transformations, which are laborious to measure in the field, have the potential to be estimated from a combination of monthly average soil temperatures and N transformation parameters, which are relatively straightforward to obtain through laboratory incubation.