effects of split application and nitrogen fertilizer levels on n-use efficiency in rice (oryza sativa l. cv. khazar)

effects of nitrogen fertilizer levels on agronomic efficiency (ea), physiological efficiency (ep), and recovery efficiency (er), in rice (oryza sativa l.) cv. khazar was investigated in a rcbd of three replications in a sandy soil in guilan province, iran in 2003. this study compared the effects of six n rates, namely: control (no n fertilizer), 40 (basal), 40+40 (basal + midtillering), 40+20+20 (basal + midtillering + panicle initiation), 60+60 (basal + midtillering) and 60+30+30 (basal + midtillering + panicle initiation) kg/ha in the form of urea. nitrogen contents in shoot and in rice grain were determined at the end of plant growth and physiological maturity. results indicated that grain yield in triple split application treatments sixth and fourth (4832, 4668 kg/ha) were significantly higher than those in the rest of the treatments. the highest n uptake was observed in sixth treatment (146.9 kg/ha), which was significantly higher than in the others. the highest ea, ep and er were observed in the fourth treatment (20.1, 30.1 and 66.9% respectively). ea and er were significantly higher in the fourth treatment than in the others, but ep significantly differed only in the second treatment. there were no significant differences observed among treatments in nitrogen harvest index (nhi), the highest nhi being related to the forth treatment (0.44). grain yield was not significant in the fourth treatment in comparison with that in the sixth one, but the higher ea, ep and er may lead to an economization of n fertilizer application and as well to its less leaching in the sandy soil. the fourth treatment was finally decided as the best treatment for rice, cv. khazar throughout the whole experiment.