Direct-sowing establishment method has great significance in improving winter oilseed rape (Brassica napus L.) production and guaranteeing edible oil security in China. However, nutrient responses on direct sown winter oilseed rape (DOR) performance and population development dynamic are still not well understood. Therefore, five on-farm experiments were conducted in the reaches of the Yangtze River (RYR) to determine the effects of nitrogen (N), phosphorus (P), and potassium (K) deficiencies on population density, dry matter production, nutrient uptake, seed yield, and yield components of DOR plants. Four fertilization treatments included the balanced NPK application treatment (NPK, 180 kg N, 39.3 kg P, 100 kg K, and 1.8 kg borax ha–1) and three nutrient deficiency treatments based on the NPK treatment, i.e., –N, –P, and –K. The results indicated that DOR population density declined gradually throughout the growing season, especially at over-wintering and pod-development stages. Nutrient deficiency decreased nutrient concentration in DOR plants, limited dry matter production and nutrient uptake, and thereby exacerbated density reduction during plants growth. The poor individual growth and reduced population density together decreased seed yield in the nutrient deficiency treatment. Averaged across all the experiments, seed yield reduced 61% by N deficiency, 38.3% by P deficiency, and 14.4% by K deficiency. The negative effects of nutrient deficiency on DOR performances followed the order of –N>–P>–K, and the effects were various among different nutrient deficiencies. Although N deficiency improved DOR emergence, but it seriously limited dry matter production and nutrient uptake, which in turn led to substantial plants death and therefore resulted in a very low harvested density. The P deficiency significantly reduced initial density, limited plants growth, and exacerbated density reduction. The K deficiency mainly decreased individual growth and yield, but did not affect density dynamic. Our results highlighted the importance of balanced NPK application in DOR production, suggesting that management strategy of these nutrients should be comprehensively considered with an aim to build an appropriate population structure with balanced plant density and individual growth.

Overestimation of nitrogen (N) uptake requirement is one of the driving forces of the overuse of N fertilization and the low efficiency of N use in China. In this study, we collected data from 1 844 site-years of rice (Oryza sativa L.) under various rotation cropping systems across the Yangtze River Valley. Selected treatments included without (N0 treatment) and with N application (N treatment) which were recommended by local technicians, with a wide grain range of 1.5–11.9 t ha–1. Across the 1 844 site-years, over 96% of the sites showed yield increase (relative yield>105%) with N fertilization, and the increase rates decreased from 78.9 to 16.2% within the lowest range <4.0 to the highest >6.5 t ha–1. To produce one ton of grain, the rice absorbed approximately 17.8 kg N in the N0 treatment and 20.4 kg N in the N treatment. The value of partial factor productivity by N (PFPN) reached a range of 35.2–51.4 kg grain kg–1 with N application under the current recommended N rate. Averaged recovery rate of N (REN) was above 36.0% in yields below 6.0 t ha–1 and lower than 31.7% in those above 6.0 t ha–1. Soil properties only affected yield increments within low rice yield levels (<5.5 t ha–1). There is a poor relationship between N application rates and indigenous nitrogen supply (INS). From these observations and considering the local INS, we concluded there was a great potential for improvement in regional grain yield and N efficiency.

The investigation was carried out to study the response of winter rapeseed to potassium (K) feritlization and the critical soil available K level for current winter rapeseed production in the Yangtze River Valley (YRV) of China. A total of 132 field experiments were conducted in fields of farmers in the major winter rapeseed growing areas in YRV in 2000/2001 and 2004/2005 to 2006/2007 during growing season. Results of these field experiments showed that the average rapeseed yield increment resulting from 100 kg K ha^-1 application was 358 kg ha^-1, an increase over the control CK (no K) of 18.0% in 2005/2006 and 2006/2007. The average internal use efficiency (IE) of K was higher in the CK treatment (21.9 kg grain, kg-1 K uptake) than in the +K (100 kg K ha^-1) treatment (17.7 kg grain, kg^-1 K uptake). Winter rapeseed required 68.1 kg of K to produce 1 000 kg seed. The recovery efficiency of K fertilizer in rapeseed production averaged 39.3%. The K balance was negative, with an average net removal of 117.6 kg K ha^-1 in the CK treatment annually, and 56.8 kg K ha^-1 in the +K treatment. The results indicated that there was a significant negative relationship between yield increments by K application and soil available K content. Based on the relative yield of CK/+K at 90% level, the critical level of soil available K(NH₄OA_c-extractable K) was 135 mg kg^-1.