Paddy soil is the main arable land resource in China, but due to factors such as different soil properties and unreasonable development by mankind, 75 percent of paddy soils in China suffer from potassium (K) deficiency, especially in southern areas, which significantly limits the potential of crop yield. Iron (Fe) and aluminum (AI) oxides are common inorganic cementing substances in paddy soils, and they have important regulatory effects on carbon, nitrogen, and phosphorus in the soil. However, the effects of Fe and AI oxides on the response of soil K in different soil types remain unclear.

Based on long-term fertilization experiments at sites in red (Ferralsols) and purple (Cambisols) paddy soils, the study reveals the relationship between Fe and AI oxides and the exchangeable (EK) and non-exchangeable potassium (NEK) contents in soil profiles under different long-term fertilization treatments.

The results show that the application of combined NPK and manure (NPKM) significantly increased the contents of EK, NEK, and amorphous and chelated Fe and AI oxides. With potassium balance (KB) increasing, the EK increase in Ferralsols was higher than that in Cambisols. Amorphous oxides were important for soil K change in surface (0−20 cm) layers of red soil. The free oxides and chelated oxides were important for Ferralsol K change in 20−40 cm and for Cambisol K change in 20−40 cm, respectively (Figure 1).

The above results provide new in-depth understanding of the effectiveness of Fe and AI oxides on potassium regulation in paddy soils, and are of great significance in guiding the rational application of K fertilizers in southern paddy soils.

These findings were published in Soil and Tillage Research (IF=5.374), with the title Soil potassium regulation by changes in potassium balance and iron and aluminum oxides in paddy soils subjected to long-term fertilization regimes.

Han Tianfu from the Institute of Agricultural Resources and Regional Planning(IARRP) of the Chinese Academy of Agricultural Sciences is the first author, and research fellow Zhang Huimin is the corresponding author.

The research was funded by the National Natural Science Foundation of China, the National Key Research and Development Program of China and a national public welfare project.

https://www.sciencedirect.com/science/article/pii/S0167198721002415?dgcid=coauthor

Figure 1 A conceptual framework of soil potassium regulation by changes in potassium balance and iron and aluminum oxides subjected to long-term fertilization

Note: Left and right are purple and red soil, respectively. ①: free Fe and AI oxides, ②:amorphous Fe and Ai oxides, ③: chelated Fe and AI oxides. Red and blue indicate surface (0-20cm) and subsurface (20-40cm), respectively. Percentage means relative importance. Decimals indicate increase rate.