Biochar and phosphorus fertilization improved soil quality and inorganic phosphorus fractions in saline-alkaline soils

The establishment of high-yielding agricultural production systems is severely restricted by low soil organic carbon (SOC) and high Na+ concentration in saline-alkaline soils. In order to confirm the effects of biochar and phosphorus (P) fertilization on SOC sequestration, soil physical structure and inorganic P (Pi) fractions, as well as optimize the amount of P fertilizer, a field experiment was designed with two factors: with biochar at 0 (C0), 1% (C1) and 3% (C2); with P at 0 (P0), 64 (P1) and 128 kg ha−1 (P2). The results indicated that biochar input enhanced SOC, however, the effect of P application on SOC and soil physical structure were negligible. Compared to C0, SOC was increased by 98–113% for C1 and 180–195% for C2. Due to the SOC enhancement and reduction of soil Na+ concentration, biochar input decreased ρb, increased MWD and WSMA. For Pi fractions, soil Olsen-P, Ca2-P, Ca8-P, Fe-P and Al-P were increased, mainly due to the direct supply, retention and the improvement of biological availability. Overall, C2P1 was the most efficiency treatment to enhance SOC, improve soil physical structure, and C2P2 avail to increase the supply capacity of soil P, but had no significant difference with that in C2P1.