Effects of different long-term cropping systems on phosphorus adsorption and desorption characteristics in red soils

PURPOSE: Phosphorus (P) fertilizer has been applied in regions with red soils to ensure high crop yield. However, the supply of bioavailable P for crop plants is insufficient due to the strong adsorption and fixing behaviors in red soils. In this study, we explored P adsorption and desorption characteristics in red soils under different long-term cropping systems. We also analyzed how the cropping systems affect P adsorption and desorption through changing soil physicochemical properties under the experimental conditions. MATERIALS AND METHODS: Eighteen red soil samples were collected at depths of 0–20 cm from six cropping systems (abandoned farmland, corn continuous cropping, taro continuous cropping, pea–corn rotation, canola–tobacco rotation, and walnut–tobacco intercropping for at least 10 years) in Miyi County, Sichuan Province, China. Soil physicochemical properties, zeta potentials, and P adsorption and desorption characteristics were evaluated. RESULTS AND DISCUSSION: The P adsorption capacity of soils increased at a decreasing rate with increasing exogenous P concentration, while the P desorption capacity increased constantly; however, the change in the percentage of desorbed P had no clear trend. The soils under pea–corn rotation and taro continuous cropping had lower P adsorption capacities and higher P desorption capacities compared to those under the other cropping systems. The maximum P adsorption capacities (Qₘ) of pea–corn rotation and taro continuous cropping soils were 16.1% and 32.4% of abandoned farmland soil, while the corresponding desorption coefficients were 6.93 and 1.62 times higher than that of abandoned farmland soil, respectively. Soil available P (AP), cation exchange capacity (CEC), and clay content were positively correlated with a and readily desorbable P (RDP), while they were negatively correlated with Qₘ (P < 0.05); opposite trends were found in the sand content. In addition, the zeta potential of soil colloids decreased with increasing soil pH. Among the cropping systems, the absolute value of zeta potential was lowest for tobacco–walnut intercropping, while its isoelectric point was the highest, resulting in the highest P adsorption capacity. CONCLUSIONS: The long-term cropping systems affect P adsorption and desorption characteristics and P availability in red soils by influencing soil physicochemical properties. The main factors driving the changes in P adsorption behavior were AP, CEC, free Fe oxides, and sand content, while AP, sand, and clay contents were the major factors for the P desorption.