[Effects of corn-based cropping systems on phosphorus fractions and availability in red soil]

To clarify the effects of corn-based cropping systems on phosphorus (P) fractions and availability in red soil, we measured P fractions and availability of topsoil (0-20 cm) and subsoil (20-40 cm) in abandoned farmland (control) and three corn-based cropping systems (corn continuous cropping, zucchini-corn rotation and pea-corn rotation), respectively. The results showed that total P, available P contents and P activation coefficient in topsoil were higher than those in subsoil. The value of relative P parameters in topsoil of pea-corn rotation was the highest among all cropping systems. Organic P was the main P fraction in red soil, accounting for 57.8%-81.1% (topsoil) and 74.3%-85.5% (subsoil) of total P. Except for pea-corn rotation soil, sodium hydroxide extractable P (NaOH-P) was the main P fraction in other cropping systems. The contents of water-soluble P (H₂O-P) and sodium bicarbonate extractable P (NaHCO₃-P) with high availability were lower than other P fractions, only accounting for 0.3%-2.1% (topsoil) and 1.7%-10.0% (subsoil) of total P. The pea-corn rotation soil had the highest hydrochloric acid extractable P (HCl-P) content in topsoil and subsoil, and significantly differed from other cropping systems. The contents of available P, sodium bicarbonate extractable organic P (NaHCO₃-P_o), sodium hydroxide extractable organic P (NaOH-P_o) and hydrochloric acid extractable inorganic P (HCl-P_i) were significantly correlated with pH, cation exchange capacity, iron-aluminum oxides and soil texture. In conclusion, pea-corn rotation was the most suitable system to improve P availability of red soil in Panxi area.