Relationships between livestock density and soil phosphorus contents – County and farm level analyses

Soil fertility of cropland depended partly on the local availability of livestock manure in history. The relationship between soil fertility and livestock density became entangled through spatial decoupling of livestock and crop farms. Understanding this relationship is important for spatial planning of livestock farms and for manure management. This paper addresses the relationships between livestock density and soil phosphorus content at farm and regional levels in Hebei (CN), which experienced a very rapid livestock revolution. County-level relationships were explored using existing databases with livestock density and Olsen-P contents. Farm level relationships were explored with a farm survey among 80 livestock farms and 480 crop farms, and with analyses of total phosphorus (TP) and oxalate-extractable phosphorus (Pox) in topsoil (0–15 cm) and subsoil (15–30 cm) of 562 fields. Results indicate that mean Olsen-P (9–41 mg/kg) did not have clear relationship with mean livestock density (0.4–16.0 LSU/ha) in the 167 counties. There was also no clear relationship between livestock density and TP and Pox contents at farm level. However, livestock farms with cropland had higher TP and Pox contents than crop farms without livestock. Most livestock farms applied excessive amounts of manure to on-farm cropland and exported manure to crop farms within a distance of 5 km. Manure application on crop farms depended on crop types; 21 % of cereal fields, 31 % of cotton fields, 58 % of the orchards fields, and 65 % of the vegetable fields received manure regularly. The TP content of the subsoil was as high as or higher than the TP content of the topsoil in 21 % of the fields from livestock farms and 41 % of the fields from crop farms, which suggests P leaching. Our results indicate that livestock manures are not well utilized. There is a need for manure application limits, especially on livestock farms, and incentives for improving manure distribution and utilization.