The Effect Of N Fertilizer And Its Residual Influence On Spring Wheat In Dry Land

By field located experiment in semi-aired areas of loess plateau for successive 4 years with spring wheat, effects of N fertilizer and residual effect of N fertilizer on spring wheat was studied .The results showed as following:1) With the increasing of N application in loess plateau, yield of sping wheat increased first and decreased then in huangmian soil. With pure nitrogen application of 52.5～210㎏/hm² for successive 4 years, yield of the four years increased 25.1～40.3%. Yield increased 2.0～5.6㎏ per kilograme N, and 3.7㎏ on average, which was lower than the average data (12.7㎏/㎏ N) of Food and Agriculture Organization. Effect of N on crop yield decreased with successive application of N for years. When successive application of N exceeded 105㎏/hm², yield increasing rate decreased. By magrginal utility analysed, when pure nitrogen application was 148.48㎏/hm², economic benefit was highest.2) Residual effects of N fertilizers on yield, water using efficiency and dry matter of spring wheat was obvious. Under the circumstance of successively applying N fertilizer at the first two years and not applying any N fertilizer in other years, the current crop did only take a part of N from the fertilizer, and a large portion of unused N had significant effects on the yield of following crops. Yield of spring wheat was increased 7.5%～41.6% in the third year and increased 12.1%～25.7% in the fourth year; Dry matter was increased at the five leaves and the following dates; Water use efficiency was increased 0.15～1.49㎏/hm².㎜ in the third year and increased 0.31～0.82㎏/hm².㎜ in the fourth year(except the treatment N2s). Residual effect of N fertilizers had some effect on the economic characteristics of spring wheat, but not obviously compared with the other characters such as yield, dry matter et al. Residual effects of N fertilizers had no effect on the economic characteristics of spring wheat in 2005, but had obvious effect in 2006. The magnitude and durative of residual effect of N fertilizer were increased with the increase of N application, but declined along the prolonging of the year.3) Different quatity of applying N fertilizer influenced distribution of NO₃^--N content of 0～200㎝ soil profile significantly. Average content of NO₃^--N of 0～200㎝ soil profile was 3.9～16.7㎎/㎏ with successive application of N for 3 years, and the peak was in 80～110㎝ or 110～140㎝. Average content of NO₃^--N of 0～200㎝ soil profile was 3.0～7.5㎎/㎏ with successive application of N for 2 years and no N application in the third year, the peak was in 50～80㎝ or 80～110㎝. The tread was the same below 140㎝ under the two circumstances.4) Under the circumstance of successively applying N fertilizer at the first two years and not applying any N fertilizer in other years, the yield of spring wheat in the third year was linearly correlated to the NO₃^--N content of 0～200㎝ soil profile at sowing and the relativity was significant.The yield of spring wheat in the fourth year was linearly correlated to the NO₃^--N content of 0～110㎝ soil profile at sowing and the relativity was mighty significant. Under the circumstance of successively applying N fertilizer at the first two years and not applying any N fertilizer in other years, increasing per㎏ nitrogen of last season, the residual NO₃^--N in the soil can increase the yield of spring wheat 5.1313㎏ in the third year and increase 6.6074㎏ in the fourth year, and residual effect of N fertilizers was increased with the the increas of residual NO₃^--N in the soil.5) When successively apply pure nitrogen 52.5㎏/hm²,105㎏/hm²,157.5㎏/hm²,210㎏/hm² for four years ,the current using rates of nitrogen by the each treatment were 24.2%,26.3%,14.5%,17.4% respectively on average. Under the circumstance of successively applying N fertilizer at the first two years and not applying any N fertilizer in other years with pure N of 52.5㎏/hm²,105㎏/hm²,157.5㎏/hm²,210㎏/hm², the accumulative using rates of nitrogen by the each treatment were 35.3%,31.6%,20.9%,24.7% respectively, increased from 7.8 to 12.9 hundred cents comparing with the treatments of successively applying N fertilizer for four years.