Optimization of manure allocation in view of crop requirements and environmental impacts in Chinese agriculture

The average manure recycling ratio in China is lower than 40%, implying that over half of the nutrients in manure are lost to the environment. Enhanced manure recycling by recoupling crop and livestock production is an important option to reduce soil acidification and environmental pollution caused by nitrogen (N) and phosphorus (P) losses to air and water in China. However, the optimal amount of manure to reduce soil acidification differs considering the need to stay below an acceptable P input depending on the soil P status and an acceptable N surplus in view of water quality. This study aims to identify optimal manure recycling strategies for six counties in the Chinese city Quzhou, by calculating the required nitrogen (N), phosphorus (P), sulphur (S), potassium (K), calcium (Ca) and magnesium (Mg) input to fulfil their crop demand using current crop yields, while accounting for the need to minimize soil nutrient surpluses and soil acidification. The current nutrient balance in Quzhou city indicated that under current manure and straw recycling rates, extra mineral fertilizer is needed in view of remaining nutrient demands of N (-11630 tonnes), K (-3800 tonnes), P (-550 tonnes), and S (-380 tonnes). However, at full manure and straw recycling, nutrients from livestock manure can meet crop demands at city level except for N (-6300 tonnes), with some counties having a deficit in N and also K, and other counties having an excess implying the need for manure transport out of the county.