SORGHUM STOVER REMOVAL EFFECTS ON SOIL ORGANIC-MATTER CONTENT, EXTRACTABLE NUTRIENTS, AND CROP YIELD

Crop residues play an important role in sustaining the productivity of many agroecosystems. A four year field study was conducted to determine the effects of sorghum [Sorghum bicolor (L.) Moench] cultivar, differential stover removal, and added fertilizer N on soil properties and crop yields in a continuous sorghum cropping system. The soil used was Ships clay (very-fine, mixed, thermic Udic Chromustert). Neither sorghum cultivar nor fertilizer N addition influenced soil pH, microaggregation, organic C, or extractable nutrients in this fine-textured Vertisol. Removing all stover significantly decreased soil organic matter (SOM) content and extractable P and K by 5.2, 10.0, and 4.0%, respectively, but did not affect soil microaggregation. In plots where all stover was removed annually and no fertilizer N was added, sorghum yields increased over time. Stover removal possibly disrupted SOM equilibrium, causing an estimated additional annual net release of 14 to 35 kg N and 1.7 to 4.1 kg P ha-1.