Effects Of Reducing N Input With Increased Seeding Rate On Grain Yield,N Uptake And Utilization Of Winter Wheat

The field experiment was carried out in 2014^-2015 at the experimental station of Dongwu Village, in Dawenkou Town, Daiyue District, Tai'an Shandong, P.R. China. With a large-spike winter wheat cultivar Tainong 18, field experiments including four nitrogen ?N? application rates (0 kg ha^-1, NO; 180 kg ha^-1, N180; 240 kg ha^-1, N240; 300 kg ha^-1, N300) and three seeding rates (270 plants m^-2, D270; 405 plants m^-2, D405; 540 plants m^-2, D540) were conducted. The field experiment was established as a spilt-plot designed of three replicates with nitrogen as the main plot and seeding rate as the subplot.15N-microplot experiment was also included in each plot. The field experiments investigate the effects of reducing N input with increased seeding rate on dry matter accumulation, grain yield, N uptake efficiency ?UPE?, N utilization efficiency ?UTE? and N use efficiency ?NUE? of winter wheat. The main results are shown as follows:1 Effects of different nitrogen levels and seeding rates on grain yield of winter wheat1.1 Effects of different nitrogen levels and seeding rates on dry matter accumulation and harvest index of winter wheatUnder the same nitrogen level, the dry matter accumulations at maturity increased with the increased seeding rate. Under the same seeding rate, the dry matter accumulations at maturity also increased with the increased nitrogen level, the dry matter accumulations at maturity significantly increased with nitrogen input. Harvest index increased significantly with the increased seeding rate at the nitrogen level of 0 kg ha^-1. Harvest index decreased with the increased seeding rate at the nitrogen level of 180 kg ha^-1, with no significant difference between the medium density and high density. Harvest index decreased with the increased seeding rate at the nitrogen level of 240 kg ha^-1, with no significant difference between the low density and medium density. Harvest index decreased significant with the increased seeding rate at the nitrogen level of 300 kg ha^-1.1.2 Effects of different nitrogen levels and seeding rates on grain yield of winter wheatGrain yields increased with the increased seeding rate at the nitrogen level of 0 kg ha^-1. Grain yields increased firstly and then reduced with the increased seeding rate at the nitrogen level of 180 and 240 kg ha^-1. Grain yields decreased with the increased seeding rate at the nitrogen level of 300 kg ha^-1, no significant difference between the low density and medium density. Grain yields increased with the increased N application rate at the seeding rate of 270 plants m^-2. Grain yields increased firstly and then reduced with the increased N application rate at both 405 and 540 plants m'2. Additionally, the highest grain yields of the two higher seeding rates were both observed at the N application rates of 180 and 240 kg N ha^-1. High seeding rates (both 405 and 540 plants m^-2) could also achieve high grain yield levels as the N application rate decreased from 240 to 180 kg ha^-1, and the highest grain yield were observed at the seeding rate of 405 plants m^-2.2 Effects of different nitrogen levels and seeding rates on nitrogen use efficiency of winter wheat2.1 Effects of different nitrogen levels and seeding rates on nitrogen uptake efficiency of winter wheatCompared with no N treatment, N uptake efficiency decreased significantly with the N input. N uptake efficiency increased firstly and then reduced significantly with the increased seeding rate at the nitrogen level of 0 kg ha^-1. N uptake efficiency increased with the increased seeding rate at the nitrogen level of 180,240 and 300 kg ha^-1, with no significant difference between the medium density and high density. 2.2 Effects of different nitrogen levels and seeding rates on nitrogen utilization efficiency of winter wheatCompared with the NO treatment, N utilization efficiency decreased significantly with the N input. N utilization efficiency increased with the increased seeding rate at the nitrogen level of 0 kg ha^-1, with no significant difference between the low density and medium density. N utilization efficiency decreased significantly with the increased seeding rate at the nitrogen level of 180 and 300 kg ha^-1. N utilization efficiency decreased with the increased seeding rate at the nitrogen level of 240 kg ha^-1, no significant difference between the medium density and high density, but both significantly lower than the low density treatment.2.3 Effects of different nitrogen levels and seeding rates on nitrogen use efficiency of winter wheatUnder the same seeding rate, N use efficiency decreased with the increased nitrogen input. N use efficiency increased with the increased seeding rate at the nitrogen level of 0 kg ha^-1 with significant difference among treatments. N use efficiency increased firstly and then reduced with the increased seeding rate at the nitrogen level of 180 and 240 kg ha^-1. N use efficiency of medium density treatment was the largest, significantly higher than that of high density and low density treatment. N use efficiency decreased with the increased seeding rate at the nitrogen level of 300 kg ha^-1, no significant difference between the low density and medium density, but both significantly higher than the high density treatment.