Better nutrient management strategy for rice-wheat, rice-rapeseed and rice-rice cropping systems

Rice-wheat, rice-rapeseed, and rice-rice cropping systems are dominant in central China (Yangtze River Valley region). This region is one of the main grain crop production areas in China, with large amounts of commercial fertilizer consumption, but also fairly low fertilizer use efficiency. Therefore, to increase fertilization efficiency and improve farm soil fertility, under the support of the Chinese Ministry of Agriculture and IPNI China Program, the project cooperators from the Wuhan Botanical Garden of the Chinese Academy of Science established this five-year research project in Hubei, Hunan and Anhui provinces.

In this first year, results from the field experiments are not yet available. Preliminary results indicate that rice soil showed moderate fertility with 29 g/kg soil organic matter, 82 g/kg total N, 146 mg/kg available N, 17 mg/kg available P, and 101 mg/kg available K. The primary fertilization issue is consistent overuse of N, but with low use of P and K, especially in the rice-wheat rotation. On average, total N fertilizer use efficiency (FUE) is 30 to 35%, FUE for P is 10 to 20%, and FUE for K is 35 to 50%. Usually, recommended fertilizer application in rice and wheat is 180-76-121 kg N-P₂O₅-K₂O/ha for respective grain yields of 7,500 and 5,250 kg/ha. In rapeseed, application is 180-90-121 kg/ha for a seed yield of 2,700 kg/ha.

In the three cropping systems, rice-rapeseed has the highest fertilization rate, but obtained the lowest economic benefit. The main commercial fertilizer sources include urea, superphosphate, potassium chloride, and compound fertilizer, very few bulk blend or controlled-release fertilizers are available for the major crops of rice, wheat, maize, rapeseed, and cotton. About 40% of rice and wheat straw is being returned to farmland soil annually.