Soil salinization is a problem that arouses the world’s attention. Soil salinity is an important limitation for agriculture production in coastal area. Phosphorus is a very important nutrient element in the process of plant growth, and its effectiveness affects plant growth to a great extent. In this study, soil available phosphorus and its component in Hedley phosphorus classification were found to be affected by soil salinity in coastal areas of Jiangsu Province. Several key environmental factors changed under the saline environment of the coastal areas, such as soil salinity, soil pH, and soil alkaline phosphatase activity. These environmental factors were significantly correlated with soil available phosphorus. Results showed that there were significant correlations between soil salinity and other environmental factors, and soil salinity and alkaline phosphatase activity were the main influencing factors of soil available phosphorus in this study. Significant positive correlation was found between alkaline phosphatase activity and soil salt content, and soil salinity was considered as the most important impact factor for soil available phosphorus as it affected the surrounding environment, and the soil alkaline phosphatase could be considered as the direct influencing factor for soil available phosphorus. Analysis between the soil alkaline phosphatase activity and phosphorus component showed that soil alkaline phosphatase activity could increase the proportion of active inorganic phosphorus and medium active inorganic phosphorus in soil phosphorus pool, which explained the effect of soil alkaline phosphatase activity on soil available phosphorus.

China with large area of land planted with crops are suffering secondary salinization in coastal area for the lack of fresh water and saltwater intrusion to the groundwater. The purpose of this study was to investigate the effects of biochar (BC) and fulvic acid (FA) on the amelioration of coastal saline soil and their impact on crop yields under maize-barley rotation system. A three year field experiment was conducted in a saline soil on a farm in coastal area of east Jiangsu Province, China. A maize-barley rotation system had been carried out for ten years with local conventional management before the experiment. The saline soil was amended with BC at rates of 0, 7.5 t ha⁻¹ (BC1), 15 t ha⁻¹ (BC2) and 30 t ha⁻¹ (BC3) alone or combined with fulvic acid (1.5 t ha⁻¹) compared with control. Fertilizers were applied under normal planting strategies. The BC was added only once during the four growing seasons, and the FA was applied before each sowing. Soil salinity changed significantly during the three year field experiment. This was mainly due to the great quantity of rain during the period of maize cultivation. Although Na⁺, Cl⁻ and SO₄²⁻ in BC and /or FA treatments significantly decreased, the pH value increased up to 9.0 as the CO₃²⁻ + HCO₃⁻content increased. Total organic carbon (TOC) and phosphorus (TP) responded positively to biochar addition rate. BC applied with appropriate rate at 15 t ha⁻¹ (BC2) in combination with FA showed optimal effects on soil salinity amelioration, soil physics properties regulation, soil nutrition improvement and crop yields increase. The TOC and TP was 5.2 g kg⁻¹ and 507 mg kg⁻¹ in BC2 + FA treatment, which were lower than BC3 and BC3 + FA treatments. However, the highest total grain yield was obtained in the BC2 + FA treatment, and the total yield was increased by 62.9% over the CK. This study emphasizes that using combined organic amendment of BC with FA for profitable and sustainable use of salt-affected soils would be practicable.