Study On The Different Responses To Nitrogen, Phosphorus, And Potassium Fertilizers And The Mechanism Between Direct Sown And Transplanted Winter Oilseed Rape

Oilseed rape is a dominant oil crop in China. Yangtze River Basin (YRB) is the largest winter oilseed rape planting area in China, oilseed rape development in this region plays an important role in agricultural production and edible oil supply of China. Direct sowing and transplantation are major methods to establish winter oilseed rape in the current YRB. The contrasting growth duration, plant density, individual morphology, and population structure might cause different fertilization responses and nutrient management strategies between direct sown winter oilseed rape (DOR) and transplanted winter oilseed rape (TOR). For a long time, the study on fertilization response and nutrient management of oilseed rape in China had focused on TOR, but the relevant study on DOR was relatively lagged. In this study, field experiments were conducted in multiple years and sites in the middle and lower reaches of Yangtze River by combining large scale study and contrastive-tested study, aiming to evaluate the responses of DOR and TOR plants to N, P, and K fertilization in terms of plant growth, yield and yield components, dry matter production, nutrient uptake and utilization, to compare their nutrient requirement and recommended fertilizer rates, and to provide suggestions to the nutrient management strategy of DOR under the current production condition. The main results are summarized below.(1) Seed yield level was lower for DOR plants than TOR plants, especially in the non-fertilized and P deficiency conditions. Compared with the balanced NPK fertilization treatment, yield reductions of DOR plants was1115kg/hm2(52.8%) under N deficiency,655kg/hm2(65.6%) under P deficiency, and257kg/hm2(17.6%) under K deficiency. The corresponding yield reductions of TOR plants were1097kg/hm2(47.3%),469kg/hm2(38.4%), and269kg/hm2(14.5%), respectively. Both DOR and TOR yields showed significant increases with the increasing rates of N, P, and K fertilizers, and yield responses to N and P fertilizers were larger for DOR plants. The results indicated that DOR plant was more sensitive to N and P, suggesting that its nutrient management should focus on the application of N and P fertilizers on the basis of balanced fertilization.(2) The moderate N, P, and K fertilizers application improved significantly yield components and therefore increased rapeseed yields. Nitrogen fertilizer showed the most comprehensive and strongest effects on all the yield components, followed by P fertilizer, and the effects of K fertilizer were relatively less. Compared with TOR plants, DOR plants had significantly higher density, but its individual yield components were considerably poor. The pods contribution of main raceme was higher for DOR plants than TOR plants. The results of correlation and path analysis indicated that improving TOR yields requires to breed strong seedlings to increase pod number plant-1. For DOR plants, to improve seed yield needs to increase pod number plant-1based on the high plant density.(3) Both dry matter and harvest index were lower for DOR plants than TOR plants. The differences in individual growth and population density had resulted in the contrasting dry matter production processes between DOR and TOR plants. The DOR density showed continuous decrease throughout the growing season. Density reductions were38.5%,73.3%,44.6%, and44.1%in the NPK,-N,-P, and-K treatments, respectively, indicating that nutrient deficiency aggravated DOR density reduction, especially under N deficiency. The application of N, P, and K fertilizers improved significantly plant growth, physiology and biochemical levels, and dry matter production of DOR and TOR during the growing season. The larger fertilization responses of DOR plants were attributed to the reduced plant death with improved individual growth. The results indicated that the nutrient management of DOR plants should focus on the balanced fertilization to improve individual growth and obtain high plant density for increasing dry matter production.(4) The DOR plants showed significantly lower nutrient concentrations at the seedling stage, and the nutrient uptake process also was affected by environment conditions. At maturity, the nutrient uptake of N, P, and K in DOR plants were lower than those in TOR plants, but its P and K harvest indexes were significantly higher. The application of N, P, and K fertilizers improved significantly corresponding nutrient concentration and nutrient uptake in DOR and TOR plants, and the fertilization responses were larger for DOR plants. Under current production condition, the recovery efficiencies of N, P, and K fertilizers for DOR plants were36.2%,21.8%, and42.9%, respectively, and they were36.3%,18.0%,45.0%for TOR plants, respectively. Furthermore, compared with TOR plants, DOR plants showed higher agronomic efficiency of P fertilizer, higher fertilizer contribution rate of N and P fertilizers, and higher N, P, and K nutrient required for producing100kg rapeseed. The results indicated that the nutrient management of DOR plants should be different with that of TOR plants, which should focus on the nutrient supply at the seedling stage to improve individual growth at early the stage and population dominance at the late stage.(5) The parameters of the QUEFTS (Quantitative Evaluation of the Fertility of Tropical Soils) model for seed yield and nutrient uptake of DOR plants were aN=13.2, dN=33.4, aP=57.0, dP=184.0, aK=8.8, dK=25.0, and they were aN=13.4, dN=30.1, aP=74.6, dP=196.7, aK=10.0, dK=25.4for TOR plants. When the yield target was3000kg/hm2, nutrient required for producing100kg seeds were4.67kg N,0.96kg P, and6.61kg K for DOR plants, respectively, and they were4.68kg N,0.78kg P, and5.89kg K for TOR plants, respectively. Under current production condition, the mean recommended N, P, and K fertilizer rates were228.1kg N/hm2,97.3kg P2O5/hm2, and127.6kg K2O/hm2for DOR plants, respectively, and they were232.6kg N/hm2,90.2kg P2O5/hm2,111.8kg K2O/hm2for TOR plants, respectively. The results indicated that DOR plants need more P and K uptake to achieve the same yield target, and the recommended P and K fertilizer rates were also higher for DOR plants. The N requirement amount and recommended N fertilizer rate were equal between DOR and TOR plants.