Studies Of The Yield Formation Of Various Cultivars And Under Different Planting Densities And Nitrogen Applications Of Oilseed Rape

Rapeseed is the most important oil crop in China. With the decrease of arable land and rapid development of mechanized farming, it is important to study the mechanism of the seed yield formation and to find a way to increase the yield of oilseed rape per unit area, for keeping the supply of edible oil in China. In this dissertation, we studied the effects on oilseed rape yield of different cultivars, planting densities and nitrogen management modes, highlighting the roles of dry matter accumulation and partition and nitrogen nutrient in yield formation. The main objective of this study is to provide experimental data for exploring techniques to increase the seed yield of oilseed rape. The main results are as follows:1. There were significant differences in seed yield among12cultivars that are widely used in the Yangtze River basin. Based on the biomass yield and harvest index, the12cultivars were divided into4types, i.e., high biomass and high harvest index (HH) type, high biomass and low harvest index (HL) type, low biomass and high harvest index (LH) type, low biomass and low harvest index (LL) type. The HH-type cultivars had the highest seed yield, which was21.67%higher on average than LL-type cultivars. In all cultivars, HH-type had the most effective primary branches, pods and the highest biomass yield and nitrogen harvest index. While, LH-type had the highest nitrogen utilization efficiency (NUE). Therefore, the HH-type cultivars had a high yield potential. The main morphological traits for a high yield cultivar were dwarf and lower branching height and more branches numbers.2. The effects on seed yield of planting densities were tested, using the cultivar of "Huayouza62" as material, by controlling the space between plants under mechanical sowing. The results showed that, effective primary branches and pods number per unit area were increased and NUE heightened with increasing planting density in a certain range, which resulted in high biomass and seed yields, and oil content in seed as well, at the harvest. But the seed yield decreased resulting from lower pods number due to drastic competition among individuals, when planting density increased to300,000plants/hm2and more. 3. The vegetative growth of oilseed rape was improved with increasing the proportion of basal nitrogen fertilizer, under the same amount of nitrogen application in the whole growth duration and30%of nitrogen applied at bolting stage. However, the pod number per plant decreased resulting from nitrogen shortage at late vegetative period, when the basal nitrogen fertilizer increased to70%of the total. Under the condition of this experiment, the seed yield and NUE were the highest when60%of nitrogen was applied as basal fertilizer,5%as over-wintering fertilizer, and5%top-dressed at bolting stage. It was determined as the reasonable nitrogen management’s mode in this study.4. Nitrogen had a significant impact on the growth and yield formation of winter oilseed rape, but there were obvious differences for the effects of nitrogen fertilizers applied at different periods. Base fertilizer not only improved the plant growth, but increased the dry matter accumulation and the numbers of branches and pods, therefore, it had the greatest impact on seed yield. Nitrogen application at bolting stage could increase the numbers of secondary branches and pods on branches and have a relatively high impact on seed yield. The effects of nitrogen fertilizer at seeding and over-winter stage were small, but fertilization at seeding stage could improve the nitrogen absorption and utilization of oilseed rape. We suggested that more base fertilizer, relatively high seedling fertilizer, appropriate bolting and less over-winter fertilizer should be applied in the nitrogen management for increasing seed yield and reducing fertilizer loss in winter oilseed rape production.5. The economic yield of oilseed rape was mainly affected by the biomass yield, but little affected by the harvest index. The biomass yield was mainly determined by the dry matter accumulations at vegetative growth and pod developmental stages. The dry matter accumulation at vegetative stage significantly affected the main inflorescence pod and primary branch numbers, while, the dry matter increase at pod developmental stage affected the pod number of branches. Meanwhile, the developments of the main inflorescence pods and primary branches were also affected to a certain degree by the dry matter increase at pod developmental stage. The harvest index was mainly related to the partition of dry matter and nitrogen in various organs. Higher partition in stem and lower partition in leaves at the late vegetative stage, and higher transfer of them from stem to seed at the reproductive stage resulted in higher harvest index.