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

Abstract

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°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 (N0) and at a fixed constant rate (N0kf). Several N mineralization indices, labile organic fractions and soil properties were determined. A broad range of values were found for N0 (29.9-220.7 mg kg-1) and N0kf (26.9-172.4 mg kg-1). A close relationship (P<0.001) was found between N0 and N0kf with a high coefficient of determination (R2=0.94). High R2 values were found for predicting N0 and N0kf 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.