Agro-farming systems determine phosphorus budget characteristics at the farm and catchment scales in subtropical China

Agricultural and economic activities may profoundly determine phosphorus (P) budget characteristics that affect environmental quality; therefore, P budget characteristics were investigated at the farm and catchment scales, and the total-phosphorus (TP) concentrations in stream water were observed to examine their relationships in eight Chinese subtropical catchments. The results showed that chemical fertilizer accounted for 67–76% of the total P input and cereal grain comprised of 60–62% of the output in the planting farms, while animal feed and animal product accounted for 62–95 and 48–71% in the planting–livestock farms and livestock farms, respectively, indicating that agro-farming systems determined the P budget characteristics at the farm scale. The P input, output, and surplus intensities linearly increased with agricultural incomes in the agro-farming systems, suggesting that economic activities greatly affected the P budget characteristics at the farm scale. The catchment P budget characteristics were largely shaped by the characteristics at the farm scale; the planting–livestock farm proportion was negatively correlated (R 2 > 0.55) while the livestock farm proportion was positively correlated (R 2 > 0.59) with catchment P budget items. These effects on catchment P budget characteristics greatly deteriorated stream water quality; both the TP concentrations and loadings in stream water were significantly correlated to catchment P input, output, and surplus intensities. Considering the higher economic benefits and lower P input and surplus intensities due to the closed P cycle loop between cropping and husbandry, planting–livestock system should be promoted at the farm scale to protect catchment water environmental quality in subtropical China.