CARBON AND NITROGEN MINERALIZED FROM LEAVES AND STEMS OF 4 COVER CROPS

Increased understanding of surface residue decomposition may improve c over crop management in no-till systems. Most decomposition studies of cover crop residues have been conducted with samples composed of a mi xture of leaves and stems. Because leaves and stems have different com position, however, they would be expected to show different mineraliza tion kinetics. The objective of this work was to study C and N mineral ization from isolated stems, isolated leaves, and a mix of leaves and stems of wheat (Triticum aestivum L.), rye (Secale cereale L.) oat (Av ena sativa L.), and crimson clover (Trifolium incarnatum L.). Cecil lo amy sand soil (clayey, kaolinitic, thermic Typic Kanhapludult) was pac ked into acrylic plastic cylinders, adjusted to 55% water-filled poros ity, treated with either leaves, stems, or a mix of both (1-cm pieces) on the surface, and incubated at 35-degrees-C for 160 d. Air samples for CO2 and N2O determinations were taken periodically and NH3 evolved was trapped during the first 16 d. Soil columns were leached periodic ally and leachates were analyzed for N (total and inorganic) and total C. The dynamics of C and N mineralization of a mix of leaves and stem s was different from the patterns predicted from isolated leaves and i solated stems. These results indicate a strong interaction between ste ms and leaves during early stages of decomposition, which may be relev ant for predicting N mineralization from cover crop residues. The best predictors for N mineralization were residue C/N ratio and the recipr ocal of residue N concentration.