Responses of plant development, biomass and seed production of direct sown oilseed rape (Brassica napus) to nitrogen application at different stages in Yangtze River Basin

Abstract

Direct sown oilseed rape has been rapidly developed in recent years due to increasing shortage of labor force in the winter oilseed rape (Brassica napus L.) region of Yangtze River Basin. However, the appropriate nitrogen management of the crop has not yet been established, resulting in poor seed yield. Two experiments were conducted, including a pot trial to elucidate the N utilization in different growth periods under sufficient supplies of N and other nutrients, and a field experiment to study the effects of N application rates at different stages on plant development, biomass production, seed yield and N use efficiency of direct sown oilseed rape. The results showed that N applications at different stages extended the growth period of the crop. The vegetative growth was extended more than the reproductive growth by N applied at early stages. Nitrogen application promoted the plant growth center/s leading to high biomass accumulations in different periods. Higher pre-sowing N rates prolonged the fast biomass accumulation period and increased the fastest accumulation speed. The seed yield and NUE of the crop were improved by N applied prior to sowing and at the initiation of stem elongation. The results suggest that, relatively high N rate but not exceeding 135kgNha−1 applied at pre-sowing, 67.5–90kgNha−1 at the initiation of stem elongation, and appropriate rates depending on the seedling growth at 5-leaf stage were optimum N fertilizer strategies to achieve high production for the direct sown winter oilseed rape in Yangtze River Basin.