Impacts of Long-Term Rice Cultivation on Phosphorus Transformations in Saline-Sodic Soils of the Songnen Plain, China

Abstract

The perpetual cultivation of rice within saline-sodic wastelands can enhance soil nutrient availability and promote microbial growth. Nevertheless, the impacts of reclamation process on the fractions of inorganic phosphorus (Pi) in saline and sodic soils remain elusive. To study the transformations of Pi in the soil of saline wasteland with long-term rice cultivation and in the plow layer (0-20 cm) in different years of cultivation, we collected saline-sodic wasteland soil and soils that had undergone 1, 5, 10, 20, 29, and 51 years of rice cultivation. Along with a continuous decrease in electrical conductivity (EC), the soil organic matter attained its peak after 20 years of rice cultivation and sustained stability subsequently. An escalating trend was discerned in available phosphorus and microbial biomass phosphorus during the protracted cultivation period within the saline-sodic soil. In the nascent phases of cultivation (0, 1, 5, and 10 years), the Ca-P ratio constituted 64%, 71%, 57%, and 61% of the Pi pool within the soil, respectively. However, at the intermediate (20 and 29 years) and advanced stages (51 years), Al-P and Fe–P emerged as the predominant phosphorus fractions across all samples, accounting for 40%, 57%, and 53% of the Pi pool, respectively. Long-term rice cultivation of the saline-sodic soil bolstered the poorly crystalline Fe/Al oxide content and fostered accumulation of the Fe-P pool with the increasing years of rice cultivation. Partial Least Squares Path Modeling (PLS-PM) elucidated that while the salinity and sodicity exhibited an indirect influence on Pi fractions, nutrients (SOM, STN, STP, Po and Fe/Al oxides) played a vital role in the transformation of Pi fractions. This research illuminates that the mitigation of saline-sodic parameters enhances the accumulation of Pi and bolsters the growth of microorganisms within the saline-sodic soils subjected to long-term rice cultivation.

Keywords: saline sodic soils, soil reclamation, phosphorus fraction, Salinity, sodicity, phospholipid fatty acids