Changes in soil mineral N content and abundances of bacterial communities involved in N reactions under laboratory conditions as predictors of soil N availability to maize under field conditions

Proper management of soil fertility requires specific tools for predicting N availability for crops as a consequence of different fertilization strategies. More information is required, especially for organic fertilizers, depending on their mineralization rate, composition, and processing (i.e., fresh or composted manure), as well as their effects on soil properties. Laboratory soil incubations were used as a proxy for understanding plant–soil N dynamics under field conditions. Chemical and microbiological measurements as contents of mineral N, potentially mineralizable N and the abundance of key genes regulating the overall N cycle were used as predictors of mineral N availability to maize in two contrasting pedoclimatic conditions. Our results showed that there was a good correlation between chemical and microbiological measurements from laboratory soil incubation experiments and soil–plant N dynamics of maize cropping systems. Mineralization patterns from soil incubation proved to be useful for optimizing fertilization management of maize under field conditions as long as incubation time is normalized over maize growth cycle, according to the simplified model of growth degree days. Average cumulative soil mineral N values calculated over a short incubation period (42 days) showed a significant correlation (R2 = 0.72, p < 0.05) with maize N uptake. The shape and kinetic parameters of net N mineralization from medium-term (112 days) soil incubation provided consistent information on the interaction between fertilizers and native fertility. The abundance of N fixation, nitrification, and denitrification genes (nifH, amoA, nirK, and nirS) was sensitive to soil characteristics and N fertilization. This work provides a suitable starting point for developing a crop-based approach for using incubation data to optimize maize fertilization. However, more studies with different maize cultivars and pedoclimatic conditions are needed to generalize this approach.