Labile soil organic matter plays an extremely important role in crop nutrient acquisition, but quantifying this pool can be prohibitively expensive to farmers. A better understanding of rapid and inexpensive measures of labile organic matter could lead to new tools for predicting soil N supply and crop performance. Toward this end, we quantified several simple measures of labile C and N over the course of the corn ( Zea mays L.) growing season in a long-term systems trial to determine:(i) the temporal dynamics of these measures, (ii) the long-term response of these measures to management, and (iii) the capacity of these measures to predict corn agronomic performance. We found that all labile soil measures (permanganate oxidizable carbon [POXC], C mineralization, N mineralization, and soil inorganic N) varied temporally and responded to long-term differences in management. Corn grain and vegetative biomass also responded to long-term treatment differences and these differences were strongly related to the measured labile soil C and N fractions. The history of crop rotation had a greater influence than management regime on all soil measures, with the exception of POXC. Of all the measures, C mineralization was the best predictor of agronomic performance both individually ( r=0.61-0.78, depending on corn stage), and when modeled with multiple indicators (six out of nine models). The results presented here demonstrate the strong relationship between crop growth and labile organic matter dynamics, and provide further evidence that C mineralization is an inexpensive, but sensitive predictor of corn agronomic performance.
