Organic Fertilization Improves the Availability and Adsorptive Capacity of Phosphorus in Saline-Alkaline Soils

Organic fertilizer could improve soil phosphorus (P) availability and retention capacity, and the intensive management of P nutrition in saline alkaline paddy soil is of great significance to the sustainable development of rice planting. The P fractions and adsorption-desorption characteristic in saline-alkaline soils were evaluated in a 5-year field experiment. Four treatments were designed: (1) NK (255 kg N ha(-1) year(-1) and 229 kg K ha(-1) year(-1)), (2) NPK (128 kg P2O5 ha(-1) year(-1) plus NK), (3) NPKC1 (450 kg C ha(-1) year(-1) plus NPK), and (4) NPKC2 (900 kg C ha(-1) year(-1) plus NPK). The results showed that, compared with NPK treatment, soil available P (AP) concentration was significantly increased in NPKC1 and NPKC2 treatments. Especially, soil NaHCO3-P-i concentration was increased by 112.4% and 94.6% in NPKC1 and NPKC2 treatments, respectively. And soil organic carbon (SOC) showed similar trend. However, soil pH and electrical conductivity (EC) were decreased in two organic fertilization treatments. The isothermal adsorption experiment showed that the X-m values of all treatments were in the order of NPKC1 > NPKC2 > NK > NPK. Correlation analysis showed that X-m was positively correlated with SOC and negatively correlated with soil pH. Under the same initial P concentration, the desorption rates in NPKC1 treatment was the lowest, which indicated that low organic fertilizer was more conducive to the soil P retention capacity. Therefore, organic fertilizer application could increase soil P availability and retention capacity, and lower organic fertilizer addition (NPKC1) was better to improve soil P availability and retention capacity in saline-alkaline soils.