Rotation increases soil phosphorous bioavailability and improves phosphorous nutrition of the latter crop in rotation

Objectives We assessed the bioavailability of soil P to crops in a rotational system using a biological P fractionation method (BBP). The aim was to provide a reference for choosing a suitable crop rotation with the highest nutrient use efficiency and crop output potential.

Methods  A pot experiment was used for the research, no planting crops as control, and the preceding crops planted in the rotation were faba bean (Vicia faba), wheat (Triticum aestivum), ryegrass (Lolium perenne), and hairy vetch (Vicia villosa Roth). For all the treatments, the latter crop planted in the roration was maize (Zea mays). All the treatments were either not fertilized or received 60 mg/kg P₂O₅ while planting the preceding crops. Soil samples were taken for Olsen-P and biological P fractionation (CaCl₂-P, Citrate-P, Enzyme-P and HCl-P) to evaluate available soil P when the crops were harvested. Yield and P content and accumulation in aboveground biomass were measured after harvesting maize.

Results Crop rotation (P < 0.05) increased maize aboveground biomass. The biomass increase under no P application was higher than that under P application, with the highest increase (185.7%) recorded for the faba bean plant. With P application, there was no significant difference in the aboveground biomass of maize rotated with fababean or ryegrass, but it was significantly higher than that rotated with wheat and hairy vetch. Without P application, rotation (P < 0.05) increased the aboveground P content of maize. Among the preceding crops, ryegrass had the highest P content (66.7%). There was no significant increase in the aboveground P content of maize with the P application compared with the control. However, ryegrass recorded (P < 0.05) higher P content than the other rotation crops. Without P fertilization, planting faba bean, wheat, ryegrass, and hairy vetch increased soil enzyme-P by 20%, 19%, 29% and 15% compared with no planting crops control. In contrast, P application only enhanced soil enzyme-P in faba bean and ryegrass, consistent with their growth-promoting effect. Without P application, planting faba bean, wheat, ryegrass, and hairy vetch decreased citrate-P by 20.99%, 13.30%, 5.05%, and 10.66%, respectively. With P application, the Citrate-P reduction was 32.56%, 22.86%, 20.33% and 27.62%, respectively. Irrespective of applying P or not, planting faba bean and hairy vetch (P < 0.05) decreased soil HCl-P content, but not wheat.

Conclusions Whether P fertilizer was applied or not , crop rotation reduces soil Olsen-P but promotes subsequent maize growth planted in the rotation. According to the biological P fractionation method, rotation reduced Citrate-P, HCl-P and increased Enzyme-P in soil to some extent, thereby improving the bioavailability of P and the subsequent uptake of P by maize. Ryegrass has the greatest potential to excavate soil P supply capacity among the four preceding crops in the rotation.