Contribution of nitrogen mineralization indices, labile organic matter and soil properties in predicting nitrogen mineralization

The objectives of this study were i) to measure the nitrogen (N) mineralization potential; ii) to evaluate N mineralization indices and labile soil organic matter (SOM) fractions, and iii) to analyze their interrelationship with soil properties for predicting the potential N mineralization in Mollisols under no-tillage of the Argentine Pampas. Potential N mineralization pool was determined by aerobic incubation of soil samples from 0-20 cm depth at 25 degrees C for six drying and rewetting cycles over 21-24 weeks. The data were fitted to a first-order exponential equation to determine the potentially mineralizable N at a variable (N-0) and at a fixed constant rate (N-0kf). Several N mineralization indices, labile organic fractions and soil properties were determined. A broad range of values were found for N-0 (29.9-220.7 mg kg(-1)) and N-0kf (26.9-172.4 mg kg(-1)). A close relationship (P<0.001) was found between N-0 and N-0kf with a high coefficient of determination (R (2)=0.94). High R-2 values were found for predicting N-0 and N-0kf using the principal component as regress variable. Total and labile organic fractions and sand content, explained the majority of the variance. No single N mineralization index, labile organic fraction or soil property can accurately predict the potential N mineralization at a variable and at a fixed constant rate. The potential N mineralization pool may be controlled mainly by the variables related to the size of SOM and some labile fractions, i.e. soil organic C (SOC) and N (SON), soluble carbohydrates (CHs) and fine particulate organic N (fPOM-N) in these Mollisols.