EFFECTS OF STRAW RETURN AND BIOCHAR APPLICATION ON SOIL NUTRIENTS AND OSMOTIC REGULATION IN COTTON UNDER DIFFERENT SOIL SALINITY LEVELS

. To clarify the effects of straw return and biochar application on the amelioration of soils with different salinity levels and cotton growth, in this soil column simulation test, straw and biochar were applied to soils with different salinity levels (1.5 (S1), 5 (S2) and 10 (S3) g/kg), with application rates equal to the same amount of carbon (two carbon levels: 6 t/hm 2 of straw (C1) = 2.25 t/hm 2 of biochar (B1); 12 t/hm 2 of straw (C2) = 4.5 t/hm 2 of biochar (B2)). Then, changes in soil physicochemical properties and cotton physiology were determined. The results showed that straw return and biochar application reduced soil salinity at S1, S2, and S3 levels. Besides, both of them increased soil water, total nitrogen, organic matter, available phosphorus, and available potassium contents, but there was no difference between S3 soil and S1 soil and between S3 soil and S2 soil ( p > 0.05). Straw return and biochar application also increased chlorophyll and soluble sugar contents in cotton leaves ( p < 0.05), and decreased the relative conductivity and malondialdehyde content in S1 and S2 soils ( p < 0.05). However, in S3 soil, there was no difference between C1 treatments and CK and between B1 treatments and CK ( p > 0.05). Thus, straw return and biochar application can improve the physicochemical properties of saline soil and regulate osmolytes in cotton, but the amelioration effect of low application rates on high-salinity soils is insignificant ( p > 0.05).