The Effects Of Weeds On The Winter Wheat Yield And The Nitrogen Use Efficiency

In semi-humid wheat farmland ecosystem, there are both C₃ plants and C₄ plants, in which crops are C₃ plants and most weeds are C₄ plants,and the C₄ plants will absorb some nutrient. Therefore, weeds of farmland may affect residual minal nitrogen accumation in soil, crop yield, nitrogen utilization, nitrogen loss and nitrogen uptake by plant. This field experiments will answer for the question. In this thesis, crop density, weed treatments and nitrogen were arranged in a split-plot design with three replications. Fertilization was set up no fertilization, only executing nitrogen, only executing phosphorus, and different level of nitrogen and phosphorus matching. Different weed treatments are imposed, including removing weeds before winter, removing weeds at reviving stage, removing weeds at jointing stage and without removing weeds at all. Density of sowing crop was set up normal density and low-density. For the normal density of sowing, six levels of nitrogen P₀N₀, PN₀, PN₄₅, PN₉₀, PN₁₃₅ and PN₁₈₀ are applied to provide nitrogen fertilizer while for lower density, four levels of fertilizer P₀N₀, PN₀, PN₁₃₅ and P₀N₁₃₅ were applied. This experiment is carried out in Eum-Orthic Anthrosol in the semi-humid winter wheat(Triticum aestivum)field ecological system. By using the treatments of field experiments, this thesis systematically investigates the effect of nitrogen uptake by weed on nitrogen loss and nitrogen utilization efficiency at different levels of nitrogen fertilizer usage, tries to explain the effect of sowing density on nitrogen loss and nitrogen utilization efficiency, also carries on a discussion about the effect of nitrogen uptake by weed in different life periods of winter wheat.Following conclusions were obtained:1 The results reveals that with an increase of nitrogen fertilizer usage, the cumulative volatilization loss increases, the peak of volatilization comes early, and the time span of ammonia volatilization is prolonged. Ammonia volatilization with nitrogen fertilizer level of 180kg N·ha^-1 peaks on the 2nd and the 4th, and barely finishes on the 15th. Ammonia volatilization of 135kg N·ha^-1 peaks on the 3rd, and barely finishes on the 15th. Ammonia volatilization of 90kg N·ha^-1 and 45kg N·ha^-1 peaks on the 4th, and barely finishes on the 12th. Ammonia volatilization with only phosphorus treatment peaks on the 3rd, and basically finished on the 8th. Generally, ammonia volatilization is maximized with amount of 5.62 kg N·ha^-1 on the 4th, then reduces gradually. After 9 days the ammonia volatilization amount tends low and stable. The ammonia volatilization amount of the first 9 days is 8.98 kg N·ha^-1, weighs 77.4% of the amount of totally 29 days. The phosphorus fertilization usage can reduce 9.9% of the NH3 volatilization. There is remarkable relationship between cumulative NH3 volatilization and temperature from10℃to 15℃.2. This experiment made clear the change law of mineral nitrogen in different winter wheat growth stages, especially NO₃^--N and relationship between fertilization and sowing density, which is in semid-humid farmland ecosystem winter wheat. The results show that NO₃^--N accumulation in soil layer increased remarkably with the N fertilizer usage, and NO₃^--N accumulation in 0¹00 cm soil layer is linear correlated with N fertilizer usage. Increasing crop density and phosphorus(P) fertilizer usage can reduce the residual NO₃^--N accumulation in soil layer. After harvest, NO₃^--N accumulation of soil layer come down to a fairly low level as N is uptake by wheat. However, if the nitrogen usage level is higher than 135 kg N·ha^-1, there is still redundancy residual nitrogen in 0 100 cm soil layer. By analysis of NH₄⁺-N accumulation, there is no significantly relationship between residual NH₄⁺-N accumulation and nitrogen fertilizer usage. There is also no remarkably difference between different nitrogen fertilizer usage levels on NH₄⁺-N accumulation in over-wintering stage. But from reviving stage to jointing stage, there is tremendous difference between N fertilizer usage and CK. Increasing the phosphate fertilizer reduces residual NH₄⁺-N accumulation in soil layer, but the effect of sowing density is not remarkably. Generally speaking, mineral nitrogen accumulation in soil is mainly NO₃^--N accumulation in the earlier stage, but later is NH₄⁺-N accumulation. The difference of mineral nitrogen accumulation with different fertilizer level is obvious in earlier growth stage, but not obvious after jointing stage. Mineral nitrogen accumulation in soil decreases from over-wintering stage to jointing stage. But comparing harvest stage with jointing stage, mineral nitrogen accumulation increased. The possible reason is that NO₃^--N accumulation by organic nitrogen mineralized is still carrying on while the uptake by plant roots at the harvesting stage has already ceased.3 There further studied effect of various nitrogen efficiency on nitrogen application. Fertilizer plays an important role to increase the yields of corps. Yields with P and N fertilizer usage(5237.5 kg·hm^-2)are much higher than only N fertilizer usage(4406.2 kg·hm^-2)or only P fertilizer usage(3808.2 kg·hm^-2). Yields with P fertilizer are also higher than without any P fertilizer. The yield increases obviously with N and P fertilizer from 0～180 kg N·hm^-2 and it peaks with fertilizer usage of 135 kg N·ha^-1, amounting to maximum 5.65 T·ha^-1. N uptake by crops increases with increasing usage of N fertilizer. However, there is no notable increase for the nitrogen amount uptake by plant once the nitrogen usage level is higher than 135 kg N·ha^-1. Nitrogen utilization rate, nitrogen use efficiency and nitrogen agronomy efficiency decreased with increase of N fertilizer usage during whole growth stage of winter wheat. Apparent N fertilizer loss is linear correlated with N fertilizer usage, and the correlation coefficient R2 is 0.980, weeds are considered. The average value of N fertilizer loss maintains between 59.9 and 96.1 kg N. ha^-1 at different weed treatments. The average value of N fertilizer loss is from 32.9 to 128.0 kg N.ha^-1 under different fertilizer treatments.4 This experiment made clear effect of NO₃^--N accumulation on different time to removing weeds, the effect of yield nitrogen efficiency, and the relationship between nitrogen balance and fertilization. In farmland ecosystem, the difference in time to remove weeds affects differently. Weeds apparently decrease the NO₃^--N accumulation in soil profile, but they have no significant effect on NH₄⁺-N accumulation. Different weed treatments affect notably on the yields. Taking yields with over-wintering weeds removed as criterion, reviving stage, jointing stage, and without removing weeds in whole stage, the yields of lower nitrogen fertilizer (PN₄₅ and PN₉₀) treatment increases with the increasing of nitrogen usage and the yield of higher nitrogen fertilizer (PN₁₃₅ and PN₁₈₀) treatments increases with the increasing of nitrogen usage, and then decreases. By removing weeds advanced, yields with lower N fertilizer usage increases and decreases with higher N fertilizer usage. With no weeds removal and lower N fertilizer usage, yields decreases. In jointing stage, after removing weeds, the more fertilizer usage the lower yields. Yields with P and N fertilizer usage are higher than only N fertilizer usage or only P fertilizer usage. There is remarkable difference between P fertilizer usage and no P fertilizer. The yields increase when only P fertilizer is used and decrease when both N and P fertilizer are used. However, the yields of only N fertilizer used decrease in normal density and increase in lower density. The highest nitrogen utilization rate is 43.8% for the fields without weeds removing treatment at whole growth stage and the lowest is 26.3% for the fields with weeds removing treatment at reviving stage. The highest nitrogen utilization efficiency is 42.8 kg·kg^-1N for fields with removing weeds treatment at over-winter stage and the lowest is 40.6 kg·kg^-1N for fields with removing weeds treatment at jointing stage. The highest nitrogen physiology efficiency is 57.5 kg·kg^-1 N for fields with removing weeds treatment at reviving. All in all, there was notable effect for different weed treatments on nitrogen utilization efficiency and nitrogen loss, especially when removing weeds in over-winter stage. In this experiment, there is no significant effect of weed on N balance. Analysis of the nitrogen efficiency and the yields efficiency, usage of 135 kg N·ha^-1 was the best fertilization amount and the time to remove weeds should be earlier for winter wheat, the best time are over-winter and reviving stage.