微咸水灌溉下盐碱和冻融交替对土壤碳氮循环的影响机理及模拟

Agricultural use of brackish water has become an effective way to solve the fresh water resource shortages in Yellow River irrigation districts. However, higher salinity in brackish water, soil saline-alkali and freeze-thaw cycles in Yellow River irrigation districts could alter the microbial communities, enzymes activities, carbon and nitrogen cycling and their conversion processes. Therefore, in accordance with the irrigation water use problem in Yellow River irrigation districts, based on successive field experiments, the aims of this project are to study the characteristics of greenhouse gases emissions and dynamic changes of soil carbon and nitrogen during crop growth period and freeze-thaw period, which irrigation with Yellow River water and brackish water with different degrees of mineralization. The isotopic tracer, nitrification inhibitor, molecular biology test and other techniques are selected to explore the mechanism of different salinity and alkalinity, freeze-thaw cycles on soil microbial communities, enzymes activities, carbon and nitrogen mineralization, nitrification and denitrification processes. A kinetic model is established for describing carbon and nitrogen cycling affected by three factors including brackish water irrigation, soil saline-alkali, and freeze-thaw cycles. Then modelling and analyzing the effects of long-term brackish water irrigation on greenhouse gases emissions and soil salinization and alkalization. Finally, the rational brackish water irrigation mode for reducing greenhouse gases and preserving soil health is proposed, which provides the theoretical and technical support for the long-term safe use of brackish water and improve the construction of ecological irrigation district.

微咸水农业利用成为解决引黄灌区水资源紧缺的有效途径，而引黄灌区矿化度较高的微咸水灌溉、土壤盐碱化及冻融交替都可能影响土壤微生物群落、酶活性以及碳氮循环转化过程，进而影响土壤温室气体的排放。本项目针对引黄灌区灌溉用水中存在的问题，通过连续的田间试验，摸清黄河水及不同矿化度微咸水灌溉下作物生育期和土壤冻融交替期田间温室气体的排放特征和土壤碳氮的动态变化规律。通过同位素示踪、硝化抑制剂和分子生物学测试等技术，结合室内试验研究不同盐度和碱度、以及冻融交替对土壤微生物和酶、碳氮矿化、硝化和反硝化过程的影响机理，建立能够描述微咸水灌溉、土壤盐碱性、土壤冻融交替3种因素影响的碳氮循环转化动力学模型，利用构建的模型分析长期微咸水灌溉下土壤盐碱性和温室气体排放效应，提出面向温室气体减排和土壤健康的微咸水合理灌溉模式，为微咸水长期安全利用和完善生态型灌区的建设提供理论基础和技术支撑。

微咸水的农业利用已成为解决引黄灌区水资源紧缺的有效途径，而引黄灌区矿化度较高的微咸水灌溉、土壤盐碱化及冻融交替都可能影响土壤微生物群落、酶活性以及碳氮循环转化过程，进而影响土壤温室气体的排放。本项目以内蒙古河套灌区为代表区，于2017–2020年间在灌区开展了连续的春玉米生育期及冻融期土壤温室气体排放特性田间试验，并在室内开展了碳氮矿化、不同盐碱度土壤温室气体排放特性培养试验，系统研究了不同灌溉水盐分条件下灌溉方式、咸淡水轮灌比例、灌水量对土壤理化性质、温室气体排放及春玉米生长的影响，提出了面向减少温室气体排放、土壤可持续利用和保证产量的微咸水高效灌溉模式。研究结果表明，土壤为CO2与N2O的排放源，生育期土壤CO2与N2O排放量分别占到了周年排放量的83.93%和52.48%以上。膜下滴灌较地面灌溉能显著减少土壤CO2与N2O排放，灌水量增加一定程度上促进了土壤CO2与N2O排放，灌溉水盐分通过促进土壤的硝化作用进而提高了土壤N2O排放，温度、水分与土壤无机氮含量均为影响土壤CO2与N2O排放的重要因素；在冻融期，灌溉方式与灌溉水盐分均未对土壤CO2与N2O排放产生显著影响。土壤盐碱化程度越重，土壤氨挥发量与N2O排放量越大。在微咸水灌溉与冻融交替条件下，盐分不是土壤碳氮矿化过程中的主要影响因素，碳氮矿化过程主要受到土壤碳氮比的影响。微咸水灌溉增加了土壤盐分含量，抑制了春玉米生长，根系主要吸水深度的平均贡献率减小，进而抑制作物吸水，土壤含水率增加，但对春玉米籽粒品质并未产生显著影响。“地下水–微咸水”交替方式的农业可持续性更高。在综合考虑节约农业灌溉水资源，减轻土壤盐碱化程度，减少温室气体排放，避免春玉米减产等因素的基础上，利用2.0g/L微咸水滴灌（灌水量为255mm）或采用较高矿化度微咸水与地下水轮灌可作为适宜于河套灌区春玉米种植的微咸水灌溉方式。本研究提出的微咸水高效合理利用模式，能促进微咸水在引黄灌区的科学利用。本项目的预期目标全面达成。