Effect of sorghum residues on wheat productivity in semi-arid Argentina. I. Stover decomposition and N distribution in the crop

Abstract

Humification and residual effects of 3-month-fallowed sorghum residues on the productivity of winter wheat in a petrocalcic Haplustoll soil in semi-arid Argentina were studied. 15N-labelled urea was applied at sorghum harvesting-mulching (or beginning of fallow, F), wheat seeding (S) and tillering (T). Sorghum residues interacted strongly with N added to the soil. Total aerial plant dry matter (tadm) was lowest (4.94 Mg ha −1) when N was added at the beginning of fallow thus indicating a strong N immobilization, and highest (8.30 Mg ha −1) when N was incorporated at S. The N uptake followed a similar pattern. The percentage of N derived from fertilizer and that of recovery as well as the N content of the tadm increased from F to S to T. These data suggest that the sorghum residues immobilize larger amounts of N when it is applied at the beginning of fallowing than when it is incorporated at a later time such as seeding and tillering.