Soil Properties for Predicting Soil Mineral Nitrogen Dynamics Throughout a Wheat Growing Cycle in Calcareous Soils

A better understanding of the capacity of soils to supply nitrogen (N) to wheat can enhance fertilizer recommendations. The aim of this study was to assess the soil mineral N (N-min) dynamics throughout the wheat growing season in crucial stages for the plant yield and grain protein content (GPC). To this aim, we evaluated the utility of different soil properties analyzed before sowing: (i) commonly used soil physicochemical properties, (ii) potentially mineralizable N or N-o (aerobic incubation), and (iii) different extraction methods for estimating N-o. A greenhouse experiment was established using samples from 16 field soils from northern Spain. Wheat N uptake and soil N-min concentrations were determined at following growing stages (GS): sowing, GS30, GS37, GS60, harvest, post-harvest, and pre-sowing. Pearson's correlation analysis of the soil properties, aerobic incubations and chemical extractions with the soil N-min dynamics and N uptake, yield and GPC was performed. In addition, correlations were performed between N-min and the N uptake, yield, and GPC. The dynamics of soil N-min throughout the cropping season were variable, and thus, the crop N necessities were variable. The soil N-min values in the early wheat growth stages were well correlated with the yield, and in the late stages, they were well correlated with GPC. N-0 was correlated with the late N uptake and GPC. However, the chemical methods that avoid the long periods required for N-0 determinations were not correlated with the N uptake in the late wheat growth stages or GPC. Conversely, clay was positively correlated with the late N-min values and GPC. Chemical methods were unable to estimate the available soil N in the later stages of the growing cycle. Consequently, as incubation methods are too laborious for their widespread use, further research must be conducted.