Effect of Deep Straw Return under Saline Conditions on Soil Nutrient and Maize Growth in Saline–Alkali Land

To clarify the effect of tillage methods on saline–alkali land improvement and maize growth in cropland salinized to different degrees, we set up two treatments (shallow rotation (15 cm depth; CK) and deep straw return (35 cm depth; DPR)) in land characterized by three different salinization degrees and analyzed the effects of the two treatments on soil nutrient content, salinity index, chlorophyll fluorescence, growth status, and yield at three salinization levels. The results show that (1) compared with CK, alkaline N, total N, Olsen P, exchangeable K, and organic matter in saline soils were all significantly improved, and total salt and pH values were reduced by 34.01–50.79% and 2.56–7.54%, respectively, under deep straw return conditions, representing the largest values in moderately saline–alkali land. (2) Compared with CK, chlorophyll fluorescence was significantly improved, and maximum photochemical efficiency (Fv/Fm), photochemical quenching (qP), and effective quantum yield of PSII (ΦPSII) were significantly increased by 8.09–15.41%, 9.13–17.93%, and 38.79–70.83% following deep straw return treatment; these increases were the largest ones observed in moderately saline–alkali land. (3) Deep straw return promoted the growth of maize and significantly increased the yield of maize. Plant height, leaf area index, and yield increased the most in moderately saline–alkali land and increased by 6.84–21.79%, 0.59–2.28 units, and 12.78–28.07%, respectively. The yield increased by 33.89 %, which was mainly due to the increase in 1000-grain weight. The results provide a theoretical basis for taking straw return measures to improve soil and increase maize yield in saline–alkali land.