A rapid method for estimating labile carbon and nitrogen pools in Mollisols under no-tillage

The objective of this study was to adapt the partial chemical digestion method for estimation of labile soil organic matter pools by evaluating the effect of different digestion times in Mollisols of the Argentine Pampas. The soils were sampled from nine agricultural fields under no-tillage at the0-20cm depth. A chemical method was performed through partial soil digestion with dilute sulphuric acid at 100 degrees C on the basis of four digestion times: 1 (N-d1), 2 (N-d2), 4 (N-d4) and 6 (N-d6) hours. Soil organic carbon (C) and nitrogen (N) fractions were determined. The extracted organic N (N-d) ranged from 0.076g kg(-1)to 0.273g kg(-1), with a mean of 0.154g kg(-1). Statistically, the means for each digestion time indicated highly significant differences (P=0.008). High correlations were found between N(d)for different times and labile C and N fractions. However, the best fit prediction was observed between N(d2)and soil total carbohydrates (CHt), with a high coefficient of determination (R-2=0.94). Partial chemical digestion for 2h can be used as a rapid indicator to accurately predict CHt. Because of its speed and simplicity, this method may also be useful for rapid soil quality assessments.