Study On The Coordination Mechanism Of Increasing Yield Under Combined Application Of Optimal Density And Nitrogen Fertilizer On Direct-Seeding Winter Rapeseed

As the force of rural labor famine and booming development of oilseed rape light and simple cultivation technique which focuses on direct-seeding rapeseed, optimal planting density and nitrogen fertilizer application is more and more important to ensure increasing the seed yield. It is not good for increasing yield if development between population and individual is discordant, but combined application of optimal density and nitrogen fertilizer can improve growth of population and individual to add the yield. For ascertaining the coordination mechanism of increasing yield under combined application of optimal density and nitrogen fertilizer on direct-seeding rapeseed, the field experiments are conducted in two years and two sites. According to the experiments, we evaluate the difference of yield and yield components, dry matter production, nitrogen uptake and utilization and morphological characteristics under different planting density and nitrogen treatment, explain the interaction between density and nitrogen fertilizer application through perspective of shoot collective competition and build scale of the population including reasonable seeding rate and Nitrogen application rate. The main results are summarized below.1. Adding the planting density and nitrogen application rate increased grain yield of rape. When the seeding rate was increased(3.0, 4.5 and 7.5 kg/hm2), seed yield increased by 5.8~128.5%; when the nitrogen application rate was increased(60, 120, 180 and 240 kg/hm2), seed yield will increase by 59.8~879.6%. The yield would be reduced with both high seeding rate and nitrogen application rate. Comparing with the treatment seeding rate 4.5 kg/hm2, the yield at seeding rate 7.5 kg/hm2 decreased by 486 kg/hm2 at most. Pod number per plant gave the greatest contribution to yield among yield components. Adding seeding rate promoted the harvesting density to achieve yield increasing effect by population, however, it restrained increasing of pod number per plant. As seeding rate was raised, harvesting density increased by 451.7% at most and pod number per plant decreased by 5.0~128.0%. Applying nitrogen fertilizer(60, 120, 180 and 240 kg/hm2) developed pod number per plant and it increased by 27.6~418.6%.2. Increasing density and nitrogen application significantly contributed to dry matter and nitrogen accumulation and distribution, nitrogen uptake and utilization at harvesting stage. With seeding rate increasing(3.0, 4.5 and 7.5 kg/hm2), dry matter and nitrogen accumulation of population increased by 4.3~121.3% and 0.8~134.7% respectively, but those of individual decreased by 356.1% and 361.3% at most. Through adding the rate of nitrogen(60, 120, 180 and 240 kg/hm2), dry matter and nitrogen accumulation of population increased by 39.1~928.3% and 62.5~1086.6% respectively, those of individual increased by 9.7~616.3% and 32.2~925.9%. Harvesting index(HI) changed little with increasing seeding rate, but it first rose and then dropped with adding nitrogen application rate; nitrogen harvesting index(DHI) went down as seeding rate and nitrogen application rate decreased. Nitrogen content at harvesting stage presented trend that dropped with adding seeding rate, and if the Nitrogen application rate sent up, the trend turned to rise along gradually. Apparent recovery efficiency of applied nitrogen was increased by 2.0~90.7% with adding seeding rate, and the largest descend range is 66.0% with nitrogen application rate increased. In the every growth period, nitrogen content presented a go-down development trend and dry matter and nitrogen accumulation first rose and then remained stable. Increasing seeding rate and nitrogen application rate enhanced dry matter and nitrogen accumulation.3. Increasing sowing rate and nitrogen fertilizer application promoted the growth of oilseed rape population, while the amount of nitrogen fertilizer was limited, high sowing rate raised the amount of suppression of individual growth. Increasing seeding rate significantly inhibited the growth of mean plant height, leaf area per plant and of the plant crown breadth at the seedling stage, over-winter stage and bud stage. Improving the nitrogen application rate promoted the growth of mean plant height, leaf area per plant and of the plant crown breadth at each growth period. For group morphological characteristics, increasing seeding rate promoted leaf area index and group the crown of population. Leaf area index(LAI) and plant crown breadth of population with applying nitrogen was higher than these without applying nitrogen and as time went by, these characteristic gradually increase. The performance of total dry matter was consistent with leaf area index and group the crown at each growth period. 4. The different seeding rate and nitrogen fertilizer application produced diverse intensity of shoot competition which affected the yield. The relation between area of ecological field and seed yield was expressed in a quadratic equation at seeding stage, over winter stage and bud stage. When the area of ecological field reached 107.5, 433.3 and 567.5, the maximum theoretical seed yield is 2425, 2537 and 3116 kg/hm2 respectively. It indicated that high density and high nitrogen application rate led to intense shoot competition by population and decreased seed yield. The scale of density and nitrogen application rate should be optimized to coordinate effect of density and nitrogen application rate and avoided intense shoot competition by population for increasing yield. The appropriate population under target yield was established by concept nitrogen application per plant. If target yield was between 1000~2500 kg/hm2, 3100~9918×104/hm2 pod number, 5115~8563 kg/hm2 total dry matter and 45.4~125.5 kg/hm2 nitrogen accumulation should be supplied. For meeting the nitrogen requirement, the nitrogen application rate should be between 180~240 kg/hm2. As harvesting density reached 21.0~116.1×104 plant/hm2, nitrogen fertilizer should be 180 kg/hm2 and harvesting density reached 15.3~92.7×104 plant/hm2, nitrogen fertilizer should be 240 kg/hm2. Seeding rate changed when the specific target yield range was different.