Maize straw and its biochar affect phosphorus distribution in soil aggregates and are beneficial for improving phosphorus availability along the soil profile

Abstract

Abstract Return of crop straw and its biochar to the agricultural field decreases pressure on phosphorus (P) resources and reduces leaching and P runoff. We conducted a 5‐year field trial from 2013 to 2017 to study the capability of maize straw and its biochar to retain soil P, which was quantified by investigating the distribution of P fractions in the soil profile (0–100 cm) and soil aggregates of different grain sizes. The impact of soil treatments with nitrogen‐phosphorus‐potassium (NPK) fertiliser alone or combined with biochar or maize straw were examined. We found that maize straw and its biochar increased soil aggregate stability, which showed an increase in mean weight diameter, geometric mean diameter, and aggregates with diameter > 250 μm. Maize straw and its biochar promoted both inorganic (dicalcium phosphate dehydrate [Ca 2 ‐P], octocalcium phosphate [Ca 8 ‐P], aluminium phosphate [Al‐P], iron phosphate [Fe‐P], hydroxyapatite [Ca 10 ‐P], and occluded phosphate [O‐P]) and organic (labile organic phosphorus, LOP, and moderately labile organic phosphorus, MLOP) P accumulation and stabilization in soil aggregates, especially in small macroaggregates of 250–2000 μm. Total phosphorus (TP), Ca 8 ‐P, Fe‐P, LOP, MLOP, moderately resistant organic phosphorus (MROP) and highly resistant organic phosphorus (HROP) were enhanced by maize straw and its biochar, whereas Ca 2 ‐P and O‐P were decreased in the 0–20‐cm topsoil. We measured decreased TP, Fe‐P, O‐P and Ca 10 ‐P in the 40–100‐cm soil layer following maize straw and biochar deposition, whereas higher Ca 2 ‐P, Al‐P, MROP and HROP were obtained in maize straw‐supplemented soil relative to NPK fertiliser treatment in the 20–100‐cm soil layer. Thus, maize straw and its biochar can be used to effectively improve soil structure to support P retention and biochar has the potential to reduce P leaching from the soil profile. Highlights Maize straw and its biochar effectively improved soil structure to support P retention Inorganic and organic P fractions mainly accumulated in the small macroaggregate fraction Biochar has the potential to reduce P leaching in the soil profile