Analysis of nutrient resources in livestock manure excretion and its potential of fertilizers substitution in Beijing suburbs

Abstract: With the rapid development of urban intensive livestock farms, large amounts of organic waste (feces and urine) discharge obviously led to high environmental pressure in the peri-urban regions with inadequate arable land. However, the N, P, K nutrients in feces and urine could equally contribute to increase crop production as chemical fertilizer. Therefore, sustainable development of urban agriculture is closely dependent on how to recycle these organic wastes as nutrient resources. In this study, considering the current status of livestock farming and arable land area in Beijing suburbs, the current situation of organic waste resources in livestock farming and its substituting potential for chemical fertilizer in Beijing were estimated through livestock farm surveys, the collection of livestock excretion coefficients and crop nutrients demand through literature and related Beijing statistical data. The results indicated that the total amount of N, P, K contained in solid manure and liquid manure production was 58.7×103 t N, 21.3×103 t P, 29.8×103 t K, which included 43.1×103 t N, 20.3×103 t P and 19.7×103 t K in solid manure, respectively. The total amount of N, P, K contained in solid manure and liquid manure could be satisfied with 99.3%, 185.2% and 62.7% of the total crop requirement of N, P, K in Beijing in 2011, especially since the amount of generated manure P has exceeded total crop P requirement in most districts of Beijing. Moreover, cereal crop residue returned to soil could bring equivalent to 11.0×103 t N, 1.6×103 t P, and 15.0×103 t K to arable land. In the scenario analysis, the allowable amount of N, P, K nutrients in livestock manure to be applied to arable land were only 18.3×103 t N, 9.9×103 t P, and 10.3×103 t K, respectively, based on the P balance method, if considering cereal crop residue incorporation. Additional 29.8×103 t N and 22.2×103 t K were needed to be supplied with chemical fertilizers to meet crop nutrient demand. P surplus sourced from organic waste obligated the solid manure to be composted and transported to the neighbor regions with inadequate P supply. Total N, P, K nutrients contained in composted solid manure decreased by 23%, 11% and 12% after aerobic composting, and the transportation of commercial composted solid manure exported out of Beijing will further reduce N and P loads in arable land and consequently reduce the risk of environmental pollution.