Acidification Rate From Chemical N Fertilization and Alleviation By Manure in An 18–Year Field Experiment in a Ferralic Cambisol, South China.

Soil acidification from chemical N fertilization has worsened and is a major yield-limiting factor in the red soils of southern China. Assessment of the acidification process under field conditions over a long term is essential to develop strategies for maintaining soil productivity. The objective of this study was to quantify soil acidification rates from chemical fertilizers and determine the annual amount of manure needed to alleviate the acidification process from long-term (1990-2008) field applications in a wheat-corn cropping system. Treatments included non-fertilized control, chemical N only (N), chemical N and P (NP), chemical N, P and K (NPK), pig manure only (M), and NPK plus M (NPKM; 70% total N from M). Annual soil sampling and analysis were carried out. Soil pH decreased sharply from an initial pH of 5.7 and then stabilized after 8 to 12 years of fertilization in N, NP, and NPK treatments with a final pH of 4.2, 4.5, and 4.5, respectively. These three treatments significantly increased soil exchangeable acidity dominated by Al, decreased soil exchangeable Ca2+ and Mg2+, and elevated acidification rates (from 3.2 to 3.9 kmol (H+) ha-1 yr-1). In contrast, the manure applications (M or NPKM) showed either an increase or no change in soil pH and increases in soil exchangeable base cations. This research concluded that as 70% total N source, continuous manure application can fully prevent or reverse red soil acidification process. As an effective animal waste management tool, manure incorporation into acidic soil promotes the overall agricultural sustainability.