Effect of water-fertilizer optimization on rice population quality in cold area of northeastern China

A field experiment with 2 water and fertilizer management methods under 2 plant densities(25 and 30 plants.m-2),optimal fertilization practice under controlled irrigation(OPT) and farmer's fertilization practice under traditional irrigation(FFP),was conducted to study their effects on rice population quality.Yield of FFP-25 was 8.95 t.hm-2,FFP-30 increased grain weight/leaf area by 11.4%(P0.01) by increasing density at heading,but decreased the earbearing tiller rate,therefore,the increase of yield was not significant.Compared with FFP-25,OPT-25 increased earbearing tiller rate,grain weight/leaf area and yield by 4.8%,14.8(P0.01) and 8.5%(P0.05),respectively;OPT-30 improved LAI and grain-leaf ratio at heading by 10.8% and 15.7%(P0.01),therefore,yield was increased by 15.5%(P0.01) compared with FFP-25.The results indicated that the increase of the density could not improve yield,but OPT,decreased total N rate and applied N at later growth under controlled irrigation,significantly enhanced rice yield under higher density because of improving rice population quality and grain-leaf ratio at heading.