Differences of soil nutrient distribution in profiles under long-term fertilization in upland red soil

Objectives Different fertilization measurements affect the moving down behaviors of soil nutrients in upland red soil. Clarifying the fertilization effects on improving soil fertility and possible environmental risk is necessary for formulating reasonable nutrient management and promoting the utilization of livestock and poultry manure.

Methods Based on a 28-years' long-term fertilization field experiment in upland red soil since 1986, soil samples were collected from five treatments, including no fertilizer (CK), nitrogen, phosphorus and potassium fertilization (NPK), double usage amount of NPK fertilizers (2NPK), piggery manure (OM), and NPK plus manure (NPKM). Soil pH, the contents of organic matter, the total and available N, P and K were analyzed for every 20 cm depth of soil till 100 cm.

Results The contents of soil organic matter, total N, alkali hydrolysable N, total P, available P and readily available K decreased gradually with the increase of soil depth. The soil pH showed the trend of increase first and then decrease with the increase of soil depth. Manure significantly increased soil pH of 0–40 cm depth. The contents of total K remained stable in 0–100 cm soil layers. In NKP and 2NPK treatments, the soil total N, alkali hydrolyzable N, total P and available P were mainly concentrated in the 0–20 cm soil layers, the readily available K reached 40 cm soil layers. Compared to NPK and 2NPK, soil nutrient contents moved deeper in treatments of NPKM and OM, the soil total N and alkali hydrolyzable N reached 40 cm in depth, while the soil total P and available P reached 60 cm. Pig manure increased the P accumulation in the depth of 0–60 cm, and there was no accumulation below 80 cm.

Conclusions The long-term chemical fertilization mainly causes soil nutrients accumulation in the topsoil of 0–20 cm, while pig manure (with or without chemical fertilizer) causes nutrients accumulation in the 0–40 cm soil depth, promotes down-movement of phosphorus even to the 60 cm soil depth. Comprehensively, application of manure could alleviate soil acidification, improve soil fertility and cultivate fertile deep soil. Although the downward leakage depth of N and P caused by long-term application of pig manure has not reached 80 cm, more attention should be paid to its potential environmental risk.