Effects of nitrogen stress at different growth stages and weed control on the yield and yield components of rice (cv. Tarom-Mahalli)

Effects of nitrogen stress on different growth stages, as well as, weed control on yield and yield components of rice (Oryza sativa L.) cv. Tarom
Mahalli were investigated. The experiment was carried out as split-plot based on randomized complete block design with three replications at Sari region in 2009. Main factors were weed control at two levels (intact and weed control) and sub factors were allocated to nitrogen stresses including nitrogen stress at the beginning of seedling transplanting, tillering, initial panicle stage, panicle completion and control (without nitrogen stress). Characteristics such as yield and its components were measured. Plant height and panicle length were not significantly affected by treatments. Indeed, significant interaction effects of weed control and nitrogen stress were not found for any traits evaluated. Regarding to weed free treatment, the grain yield was decreased comparing to weed control by 21.6%, because of the lower tiller number per plant and less filled spikelet per panicle competing weed. Nitrogen stresses at the beginning of transplanting and the start of tillering significantly decreased the grain yield by 37.7 and 33.7%, respectively comparing to non-stress treatment. The lowest tiller number per plant and panicle number per m2 were obtained when nitrogen stresses applied at these stages. The highest growth of weeds was obtained under nitrogen stress at the stage of transplanting, which increased weed dry weight by 44.3% copmaring to the control (no nitrogen stress).