Effects of Combined Application of Biochar with Chemical Fertilizers and Organic Fertilizers on Nutrients and Phosphorus Forms in Purple Soils

This study investigated the changes in purple soil nutrient content and different forms of phosphorus content under the treatment of biochar combined with chemical fertilizers and organic fertilizers and explored the effects of different fertilization methods on purple soil nutrients and phosphorus forms to provide a scientific basis for the rationality of using biochar in the purple soil area. Using the pot experiment method, we established the following treatments: control (CK), traditional fertilization (F), chemical fertilizer +20 t•hm-2 rice husk biochar (FP), chemical fertilizer +10 t•hm-2 rice husk biochar +10 t•hm-2 corn biochar (FPM), organic fertilizer +20 t•hm-2 rice husk biochar (PP), and fresh organic fertilizer +20 t•hm-2 rice husk biochar (NPP). The change in soil nutrient content and the conversion between different forms of phosphorus were analyzed to identify the effects of chemical fertilizer and organic fertilizer combined with biochar on purple soil nutrients and phosphorus forms. The results showed that: ① The application of biochar can increase the pH value of the soil. Among the treatments, PP and NPP had the greatest effect on pH. The pH of the rhizosphere soil increased by 1.78 and 1.87 units, respectively, compared with that under the F treatment. ② Compared with the F treatment, the combined application of biochar (FP, FPM, PP, and NPP) significantly increased the content of soil organic matter, total nitrogen, total phosphorus, and available phosphorus, showing an obvious rhizosphere effect and significantly reducing the content of available potassium. ③ Compared with the F treatment, the PP and NPP treatments significantly increased plant biomass, plant total phosphorus, and total potassium content and significantly reduced plant total nitrogen content. ④ The most important phosphorus occurrence form in the soil was moderately active phosphorus, which accounted for 46.64% to 57.46%. The application of biochar can promote the conversion of soil insoluble phosphorus to available phosphorus, increase the ratio of active phosphorus to moderately active phosphorus, and show obvious rhizosphere effects. ⑤ The application of biochar is beneficial to the mineralization of soil organic phosphorus and can promote the conversion of NaHCO3-Po to NaHCO3-Pi, with the mineralization under the PP treatment being the most apparent. The combined application of biochar can improve the soil phosphorus status and promote the conversion of soil insoluble phosphorus to available phosphorus and the mineralization of organic phosphorus; among treatments, the PP treatment had the greatest such effects. Therefore, biochar combined with decomposed pig manure is the most effective nutrient management strategy in purple soil areas. © 2021, Science Press. All right reserved.