Phosphorus Leaching effects of organic and mineral fertilizers on a clay loam soil through in-situ soil columns

The leaching pattern of phosphorus (P) from continuous fertilization is generally neglected in heavy-textured soils. Generally speaking, P is hard to migrate vertically compared with nitrogen (N) and potassium (K) especially in clay loam soils. However, our study has proved that P could be leached to the depth of 1 m below the groundwater under circumstances of heavy rainfalls and large temperature differences. Our research is based on in-situ soil column experiments to estimate the effects of soil P leaching in typical fertilization regimes of Northeastern China. Fertilization treatments include CK (No fertilizer), NPK (900 kg ha^-1 of compound fertilizer), NPKS (NPK + straw return), NPKSM (NPK + straw return + 7.5 ton ha^-1 of dried cattle manure compost), 80% NPKS (720 kg ha^-1 of compound fertilizer + straw return), 80%NPKSM2 (720 kg ha^-1 of compound fertilizer + straw return + 15 ton ha^-1 of dried cattle manure compost). In 2019 and 2020, we collected 10 leachates of each treatment and determined the concentrations of TP (Total P), TDP (Total dissolved P), PP (Particle P), SRP (soluble reactive P), and DOP (dissolved organic P). The results showed that P leaching has obviously occurred after 5-year continuous fertilization, with the leaching ratio accounted for 0.61%-2.2% of total P input, and the ratio of PP to TDP was about 1:1. Furthermore, the leaching loss caused by chemical fertilizer was equivalent to that of straw application and low-dose manure fertilizer, while high-dose manure application significantly caused more P leaching losses than the other treatments. What’s more, manure addition mainly promoted the vertical movement of PP, while straw application chiefly increased the leaching ratio of TDP. 20% reduction of chemical fertilizer significantly reduced the leaching loss of TDP, with a ratio of 16%-17% compared to full-scale chemical fertilizer. Overall, in terms of slightest environment risks from P loss via leaching in this study, the excessive manure application appears to pose a long-term risk of vertical P migration than the inorganic fertilizer and straw amendment.