Town-based spatial heterogeneity of nutrient balance and potential pollution risk of land application of animal manure and fertilizer in Shanghai, China

Abstract

Land application of animal manure has been proven to be an efficient and convenient approach for animal manure treatment and resource recycling that has been encouraged in Shanghai suburbs in recent years. Based on livestock and poultry inventories, the available cropland base, and the application amounts of chemical fertilizer in each town of Shanghai, the nutrient supplies from animal manure, nutrient demands of croplands, and the nutrient inputs from chemical fertilizer were calculated. The nutrient balance and potential pollution risk of land application of animal manure and chemical fertilizer were evaluated by a calculated nutrient balance index (NBI) and nutrient pollution index (NPI). The results show that the annual total nitrogen (TN) demand of croplands was about 46,833 tons while the annual total phosphorus (TP) demand was around 11,373 tons. The annual TN supply from animal manure was 23,341 tons while the annual TP supply was 9,581 tons. The annual TN input from chemical fertilizer was 112,550 tons while the TP input was 14,782 tons. For land application of animal manure, more than 10% of all the towns had a NBI > 1 for TN, while more than 20% had a NBI > 1 for TP. For land application of chemical fertilizer, more than 80% of all the towns had a NBI > 1 for TN, while more than 60% had a NBI > 1 for TP. For the pollution risk of land application of animal manure and chemical fertilizer, there were more than 90% of all the towns with NPI > 1 for TN, while more than 80% with NPI > 1 for TP. For the entire city, the local croplands could agronomically use all the animal manure if it were properly distributed and applied reducing the need for large quantities of chemical fertilizer application.