提高冬油菜播种量和施氮量抑制杂草生长的机理研究

【目的】草害是影响油菜产量主要因素之一，研究大田条件下直播油菜播种量和施氮量对油菜和杂草生物量的调控作用，揭示其氮素竞争规律，为提高直播油菜产量提供种植管理依据。【方法】于2014年10月至2015年4月在华中农业大学校内试验基地开展田间试验，试验设置三个播种量为1.5、4.5、7.5 kg/hm2和五个氮梯度为0、60、120、180、240 kg/hm2，在油菜地上部生物量最大时，调查了杂草和油菜的生物量、氮素含量和氮素积累量，运用Shannon指数分析杂草均匀度，计算不同处理油菜与杂草在生物量和氮素积累上的竞争关系。【结果】增加油菜播种量和施氮量可以提高油菜生物量和氮素积累量，与播种量1.5 kg/hm2相比，播种量为4.5和7.5 kg/hm2的所有氮用量处理油菜平均生物量分别提高了23.3%和45.2%，平均氮素积累量分别提高了21.2%和39.2%；与不施氮相比，用量从低到高各施氮处理油菜生物量平均分别增加了0.9、1.7、2.2和2.7倍，氮素积累量平均分别增加了1.0、2.0、3.5和4.4倍。杂草的生物量和氮素积累量随油菜播种量的增加而降低，播种量4.5和7.5 kg/hm2的各氮肥处理平均生物量比播种量1.5 kg/hm2的杂草平均生物量分别降低了16.8%和25.8%，杂草氮素积累量分别降低了17.3%和29.4%；而杂草生物量和氮素积累量随氮肥用量的增加而提高，但提高的幅度远低于油菜。相同处理的杂草氮含量高于油菜，且二者的氮含量均随施氮水平提高而增加，但油菜对氮肥的响应大于杂草，最高施氮处理油菜平均含氮量比对照增加了46.2%，相应的杂草氮含量增幅只有24.1%。油菜与杂草的氮素积累量比值在播种量为1.5 kg/hm2时均小于1，增加播种量，比值增大，在7.5 kg/hm2处理中施氮处理比值均大于1，施氮240 kg/hm2处理高达2.2，说明高密高氮可以提高油菜的氮素竞争力。施氮会改变杂草种群结构，杂草群落的均匀度随氮肥用量增加而降低。【结论】油菜生物量和氮素积累量对施氮量和播种量的敏感度大于杂草，通过增施氮肥和提高播种量可以提高油菜的氮素竞争力，抑制杂草的生长。

Mechanism of controlling weed biomass through increasing winter rapeseed seeding amount and nitrogen application rate

[Objectives] Weed is one of the main factors affecting yield of rapeseed.Controlling its growth cost effectively plays key role for improving the production efficiency of direct seeding rapeseed.[Methods] A field trial was carried out in Wuhan during October 2014-April 2015.Three seeding amounts of rapeseed (1.5,4.5 and 7.5 kg/hm2) and five nitrogen application rates (0,60,120,180 and 240 kg/hm2) were designed in the experiment.The biomass,N content and N accumulation of weed and rapeseed were analyzed when the shoot biomass reached maximum.The Pielou evenness of weed community was analyzed with the Shannon index.[Results] The biomass and N accumulation of rapeseed were increased with the increases of seeding rate and nitrogen rate.The average rapeseed biomass of all N treatments with 4.5 and 7.5 kg/hm2 seeding rates were increased by 23.3％ and 45.2％ than those with 1.5 kg/hm2 seeding rate,and the N accumulation was increased by 21.2％ and 39.2％,respectively.Compared with no nitrogen treatment,the rapeseed biomass were increased by 0.9,1.7,2.2 and 2.7 times from N application 60 kg/hm2 to 240kg/hm2,respectively,and the N accumulation was increased by 1.0,2.0,3.5 and 4.4 times,respectively.The biomass and N accumulation of weeds were decreased with the increase of the seeding amount.The average weed biomass of all N treatments with 4.5 and 7.5 kg/hm2 seeding rates were decreased by 16.8％ and 25.8％ than those with 1.5 kg/hm2 seeding rate,and similarly the N accumulation was decreased by 17.3％ and 29.4％,respectively.However nitrogen supply improved weed biomass and N accumulation,but the increases were much lower than those of rapeseed.The N content in weeds was higher than rapeseed at the same treatment,and both of them were improved with the increasing of N supply.However the rapeseed was more sensitive to N fertilizer.Under N 240 kg/hm2,the average N concentration of rapeseed was increased by 46.2％,while that of weeds was increased by 24.1％,compared with the control.The ratios of N accumulation of rapeseed to weeds were less than 1 under the seeding rate of 1.5 kg/hm2,and were increased with the increase of seeding rate.The ratio in the 7.5 kg/hm2 sowing quantity and 240 kg/hm2 N rate was up to 2.2,which suggested that nitrogen competition of direct seeding winter rapeseed could be improved by high density and high N application.However,the increase of N rate could change the structure of weed population,and decrease the evenness of weed community.[Conclusions] The sensitivity of rapeseed in response to the N fertilizer and sowing amount is greater than that of weeds.The nitrogen competition ability of rapeseed can be improved by increasing the amount of N fertilizer and seeding amount.