Amending Saline-Alkali Soils with Biochar or Fluvial Sand to Improve Bioavailable Nitrogen and Yield of Summer Maize

【Objective】 Soil salinity and alkalinity is a common abiotic stress affecting crop growth worldwide. The objective of this paper is to investigate the efficacy of amending the soil with biochar or fluvial sand to improve nitrogen bioavailability and yield of summer maize. 【Method】 A three-year plot experiment was conducted at a field in the Yellow River delta. There were three biochar treatments: 5 t/(hm2·a) (C1), 10 t/(hm2·a) (C2), 20 t/(hm2·a) (C3), and three sand amendment treatments (w/w): 5%(S1), 10% (S2) and 15% (S3); the control (CK) was no amendment. In each treatment, we measured the changes in soil water content, soil salinity, nitrate and ammonium, as well as the final maize yield. 【Result】 ①Amending the soil with biochar, especially C3, was more effective than with sand to improve the 0~20 cm soil water content; compared with CK, it increased the soil content by 2.20%~7.34% in the first year and 5.08%~16.38% in the third year. ②Amendment with sand, especially S2 and S3, was more effective than with biochar to desalinize the soils; compared with CK, it increased soil desalination by up to 15.52% three years after the amendment. ③Compared with CK, amendment with biochar increased nitrate content in 0~40 cm soil by 10.34%~60.60% in the first year and 14.24%~41.92% in the third year, while in the meantime increased ammonium content by 0.96%~16.96% and -4.56%~7.37% in the first and third year respectively. Overall, C3 was most effective in improving mineral nitrogen content. In contrast, amendment with sand increased mineral nitrogen in 20~40 cm soil but at the expense of mineral nitrogen in the top 0~20 cm soil. ④Amendment with biochar was more effective in improving maize yield, with the yield in the third year increasing by 2.40%~19.86% compared with that in the first year. It was found that the yield increase was proportional to the biochar application. 【Conclusion】 Amending the saline-alkali soil with biochar improved mineral nitrogen and its bioavailability to crop, and the improvement increased as time elapsed. For the experiments conducted at the field in the Yellow River delta, the most effective amendment was adding 20 t/(hm2·a) of biochar to the soil.