Rice yield and nitrogen utilization efficiency under alternative straw management practices

Nitrogen fertility is an important component of rice (Oryza sativa L.) cult ivation systems, especially where air and soil quality issues have prompted a search for alternatives to rice straw burning. This study examined the e ffects of different rice straw management practices and winter flooding on yield, N uptake, and N use efficiency. The experiment, established on two s ites in California, was initiated in 1993 on a Sodic Endoaquert near Maxwel l and in 1994 on a Xeric Duraquert near Biggs. Main plot treatments were wi nter flooding and no winter flooding, and four straw management practices-s traw burned, incorporated, relied, and baled/removed-were subplot treatment s. Zero N fertilizer microplots were established yearly in each plot. At cu rrently recommended N fertilization levels, where other nutrients were suff icient, grain yield was unaffected by alternative straw management or winte r flooding. However, in the third year after experiment initiation, the gra in yield in zero N fertilizer plots was greater where straw was retained, i .e., incorporated and rolled. La Years 3 through 5 at Maxwell, straw retent ion increased N uptake by rice by an average of 19 kg N ha(-1) where no N f ertilizer was applied and by It kg N ha(-1) at recommended rate of N fertil izer application. Winter flooding further increased crop N uptake when stra w. was retained. The additional available soil N from straw Led to increase d N uptake without corresponding increased grain yield, which decreased N u se efficiency and necessitates the re-evaluation of N fertilizer applicatio n rates.