Phosphorus Leaching Risk Assessment with Manure Fertilizer Application in South China

To investigate the phosphorus (P) leaching risk caused by applying manure fertilizer, six different manure fertilizers, namely, 0 (CK), 3,000 (F200), 4,500 (F300), 7,500 (F500), 10,500 (F700), and 15,000 kg ha−2 (F1000), were applied to the surface soil (0–20 cm) prior to vegetable planting. The maximum Olsen P decreased with increasing amounts of the manure fertilizer. Total P did not change with treatments below 7,500, but decreased in the higher manure treatments. Water dissolved P (WDP) was highest in the upper (0–20 cm soil) layer, intermediate in the middle (20–40 cm soil) layer, and lowest in the lower (40–60 cm soil) layer. The 7,500, 10,500, and 15,000 treatments increased the WDPs in both the middle and lower soil layers and enhanced the degree of P saturation in the lower layer. This indicates that vertical leachate movement of P accumulation in the middle soil layer may be underestimated and the P leaching risk is enhanced using manure fertilizer levels >7,500 kg ha−2.