Modeling nitrogen mineralization at surface and deep layers of sandy soils

We evaluated potential soil nitrogen mineralization of 46 sandy fields of the Pampas for determining the contribution of deep layers to mineralization and modeling its trend in depth as a possible tool for improving current existing mineralization models based on surface data. Mineralization, total and mineral nitrogen decreased with depth. A potential model fitted well to these variables (R² = 0.95–0.99), but mineralization showed a more stratified profile. Consequently, the fraction of total nitrogen mineralized decreased with depth despite soils had constant texture across the profile. Potential mineralization to 1 m depth could be estimated using data from the 0–0.2-m soil layer and the average curvature of the potential model (R² = 0.60) or linear regression methods (R² = 0.71). Another estimation of potential mineralization could be performed by developing a pedotransfer function which used as predictors total nitrogen and depth (R² = 0.62), without the need of laboratory incubations. Our results showed that for sandy soils, deep nitrogen mineralization account for 40% of soil mineralization and can be assessed using surface data or the total nitrogen content of the soils. Because surface soil mineralization and whole profile mineralization were highly correlated, it is improbable that field mineralization modeling may be improved using deep data in these soils.