Links between potassium of soil aggregates and pH levels in acidic soils under long-term fertilization regimes

Abstract

Soil pH adjusted by the application of lime can improve soil potassium (K) availability to meet crop K uptake in acidic red soil. However, the response of aggregated K to pH changes is poorly understood. Objectives of this study was to quantify the relationships between aggregate K content and pH levels in soil with different fertilization patterns from a long-term field experiment Then, an incubation experiment of pH adjustment was conducted over 90 days at different pH levels where HCl and Ca(OH)2 were added to nitrogen and phosphorus fertilizers (NP); NP and K fertilizers (NPK); and NPK with manure (NPKM) soils. Our results showed that double linear equations can fit the relationships between aggregate exchangeable K (EK) with pH levels. However, the slopes and other parameters of fitted equations varied among different fertilization soils. Linear equations indicated that increasing pH value could improve non-exchangeable K (NEK) contents of soil aggregates, especially in NP soil with lower initial pH. However, the proportions of EK and NEK stocks in soil aggregates were significantly changed by soil pH adjustment only in NPKM soil. Additionally, redundancy analysis and partial least squares path mode also suggested that soil pH only affected the NEK contents in soil aggregates, although fertilization had direct effects on the EK and NEK contents in soil aggregates. Therefore, this study demonstrated that the aggregate K distribution of adjusting pH varied among soils with different fertilization regimes, then, improved soil pH could maintain high EK and NEK content of soil aggregates in red soil.