Response differences in growth and yield formation of direct-sown and transplanted winter oilseed rape to N, P and K fertilization

【Objectives】 Direct-sowing (DOR) and transplanting (TOR) are the two dominated planting methods of winter oilseed rape (Brassica napus L.) in the Yangtze River Basin, China. The establishment processes and planting density are contrasting between the two types of oilseed rape, which might lead to their differences in the individual morphology, growth process, and yield formation, as well as the fertilization responses. In this study, a field experiment was conducted to evaluate effects of fertilizers' application and establishment methods on growth and yield formation of winter oilseed rape, and to compare characters and differences of the establishment methods.【Methods】 The field experiment included four treatments: balanced NPK fertilizers (NPK), no N (-N), no P (-P) and no K (-K). The plant height, rootstock diameter and leaf number of oilseed rapes at different growth stages were investigated. When low temperature and drought occurred at the over-wintering stage, physiological and biochemical properties were measured by sampling the top four leaves, including the activities of nitrate reductase (NR), peroxidase (POD) and catalase (CAT), and the concentrations of soluble protein, soluble sugar, proline and malondialdehyde (MDA). The incidences of sclerotinia were investigated at the pod-development stage. The seed yield was weighed at maturity and the yield components were investigated.【Results】 Compared with tran splanting, the individual plant height of direct-sowing oilseed rape is higher at the early stages and obviously decreased after the bolting stage, and the rootstock diameter and leaf number are significantly lower throughout the growing seasons. The physiological and biochemical index levels of DOR are lower than that of TOR, while the MDA concentration is significantly higher. At the pod-development stage, the incidence of sclerotinia is 21.8% for DOR, which is significantly higher than that of TOR (8.5%). The yield components of DOR and TOR at maturity are different. Compared with TOR, the DOR planting density is significantly higher, but its individual plant produces significantly fewer branches, pods/plant, and seeds/pod. Furthermore, the proportion of pod number on main racemes of DOR is higher than that of TOR. The seed yields in the NPK treatment are equal between DOR and TOR, which are 2019 and 2081 kg/ha. However, under the nutrient deficiency condition, DOR shows significantly low seed yields compared with TOR. The growth and yield formation are limited by the deficiency of any kind of nutrients, and the N deficiency shows the most comprehensive and strongest negative effects, and followed by P deficiency, while the negative effect is relatively lower for K deficiency. Contrary to TOR performance, DOR planting density is reduced in the nutrient deficiency treatments. The density reductions are 53.6% and 18.7% in the -N and -P treatments, respectively. The limited individual growth and reduced population density together result in the higher yield decreases for direct sowing oilseed rape under the nutrient deficiency condition.【Conclusion】 The growth and yield formation of winter oilseed rape are more sensitive to nutrient deficiency when they are established by direct-sowing, due to the weaker individual growth at the initial stage under the current cultivation pattern. Compared with transplanting, nutrient management for direct sowing oilseed rape should pay more attention on the balanced N, P and K fertilizers application to enhance individual growth and obtain stable population density for high seed yield at maturity. The direct sowing oilseed rape nutrient management strategy should be further explored, especially for fertilization regulating practices to environmental stress.