Nutrient Management Strategies for Yunnan

This project was established to monitor the impact of different fertilizer treatments on crop yields under two typical farming systems in Yunnan (i.e., rice-broad bean in Songmin County and wheat-tobacco or wheat-maize in Qunjing County). The goal was to track soil nutrient variability induced by fertilization and to develop rational fertilizer nutrient management systems. At the project initiation in 2001, soil nutrient deficiencies were determined by soil testing and village maps of nutrient variability were formed between 2002 and 2004. In 2005, the proper fertilizer rates were verified and nutrient balances were determined for two major cropping systems. In 2006/07, the object was to continue verifying the fertilizer rates and to analyze the long-term effect of the fertilizer treatments on crop yields.

In Qujing, treatments omitting N, P, and K were compared to a balanced (BF) application of 135-135-135 kg N-P₂O₅-K₂O/ha for wheat and 300-135-135 kg/ha for maize. The BF treatment produced 1,063 kg/ha (+31%), 1,010 kg/ha (+30%), and 938 kg/ha (+27%) more yield than the - N, - P, and - K treatments for wheat, respectively. In maize, BF produced 1,562 kg/ha (+20%), 697 kg/ha (+9%), and 916 kg/ha (+12%) more grain than the - N, - P, and - K treatments, respectively. The best treatments at Songming after several years of trials were adjusted to 120-120-180 kg/ha for rice and 60-135-135 kg/ha for broad bean. Rice yields were 1,757 kg/ha (+20%), 1,870 kg/ha (+21%) and 1,870 kg/ha (+21%) higher than those produced without N, P, or K, respectively. Similarly, broad bean yields were 1,722 kg/ha (+38%) and 2,009 kg/ha (+45%) higher than yields produced without P or K. Fertilizer use efficiency was also significantly improved under the BF regime.

Based on the last 6 years of experiments, the authors wanted to see what would happen if they omitted N, P, or K from the OPT treatment that had been continued for 6 years, and similarly, what would happen if they added N to the OPT-N, P to the OPT-P, and K to the OPT-K treatments. In the first case, if nutrients were omitted from the BF treatment, the yield reduction ranged between 6 to 12%. In the second case, crop yields fell by 2 to 6% when the omitted nutrients were added compared to its BF counterpart. These results imply that the residual effect from fertilization in the previous years is minor and the soil nutrient supply gap can be minimized by proper fertilization. Yunnan-NMS01