不同施氮水平和杂草清除时间对氮肥利用及平衡的影响

Effects of different nitrogen fertilizer levels and time of removing weeds on nitrogen utilization and nitrogen balance

以半湿润区中等肥力土垫旱耕人为土为供试土壤，在冬小麦不同生育期采集0～100cm土层土壤样品、作物及杂草的样品，研究不同施肥及杂草处理对半湿润农田生态系统氮肥损失及氮素平衡的影响。试验结果表明，土壤中残留NO3^--N累积量均随施氮量增加而增加；NH4^＋-N累积量随施氮量变化不显著，总矿质氮随施氮量的变化趋势与硝态氮基本一致；农田系统中杂草的存在，能在一定程度上增加土体残留矿质氮（Nmin）累积量，且在高施氮处理下影响较大；在全生育期不清除杂草（A）、越冬前清除杂草（B）、返青期清除杂草（C）和拔节期清除杂草（D）等杂草处理下，杂草吸氮量平均值分别为2．38、1．60、4．72和4．54kgN／hm^2，占农田植物地上部分（作物＋杂草）总吸氮量的1．97％、1．38％、3．98％和3．76％，返青期杂草吸氮量最高，其值是越冬期杂草吸氮量的2．94倍；氮肥损失随施氮量增加而呈线性相关，考虑杂草时，相关系数R^2=0．9802。不同杂草处理间氮素表观损失量为59．9～96．1kg／hm^2，不同施氮处理间表观损失量为32．9～128．0kg／hm^2；不同时期清除杂草对氮损失和氮肥利用率影响显著，而越冬期清除杂草的影响效果最大；本试验条件下，杂草的存在对氮素平衡影响不显著。

Application of nitrogen （N） fertilizer is one of the most important measures that increase grain yield and improve grain quality of winter wheat. However, it is common that excessive N fertilizer is applied on fertility field, which not only causes the decline of N use efficiency and economic effects, but also results in larger amount of nitrate-N accumulated in soil, and so it is concerned to bring potential risk environment. Nitrogen （N） was manipulated through fertilizer application, to determine the extent to which these treatments alleviated a competition, and that this would be related to levels of resource availability, particularly available N. However, application of N fertilizer not only helped control weed but also increased mineralization of the residues. Therefore, the experiment was a randomized complete block design consisting of two different factors. Nitrogen and weed treatments were arranged in a split - plot design with three replicates. Within normal density treatments, five levels of nitrogen, 0, 45, 90, 135 and 180 kg N/hm^2 were applied. Within each of these treatment combinations, different weed treatments were imposed. This experiment was carried out in Eum-Orthic An- throsol located in the semi-humid farmland ecological system. Soil sample was collected from 0- 100 cm layer. Sample of crops and weed were collected from the winter wheat in different growth stage. The research was concerned to effects of different fertilizer and weed treatment on N fertilizer loses and N balance in semi-humid farmland ecosystem. This experiment showed that residual nitrogen accumulation in soil increased with addition of N fertilizer application, but the ammonium nitrogen accumulation was stable. The total N mineralization increased with addition of N fertilizer application. The average value of Nitrogen uptake by weed in treatment A, B, C and D was respectively 2.38, 160, 4.72 and 4.54 kg N/hm^2. Meanwhile, nitrogen uptake by weed accounted forl. 97 % 、 1.38 % 、3.98 % and 3.76 % of N uptake by aerial parts plant. N uptake of weed in the overwinter was the lowest. The N uptake of weed in the reviving stage is higher, which was the time 2.94 of N uptake by weed in over-winter. Nitrogen utilization rate decreased and apparent N fertilizer loss increased along with the increase of N fertilizer application. Apparent N fertilizer loss was the linear correlation with N fertilizer application, and the correlation coefficient R2 was 0. 9802, considering weed. The average of N fertilizer loss maintained between 59.9 and 96.1 kg N/hm^2 at different weed treatments. The average of N fertilizer loss was in the range of 32.9 to 128.0 kg/hm^2 at different fertilizer treatments. There was obvious effect of removing weeds on N utilization rate and apparent N fertilizer loss at different time, especial before over-winter. There was no significant effect of weed on N balance.