黄土高原旱作农田土壤水分对苜蓿种植年限和后茬春小麦的响应

Response of soil moisture to the age of alfalfa standing and subsequent spring wheat in the rainfed Loess Plateau

春小麦(Triticum aestivum)是黄土高原雨养农业区主要的禾谷类作物,该区紫花苜蓿(Medicago sativa)的种植也较为广泛。针对黄土高原半干旱雨养区连续种植多年苜蓿会形成土壤干层,并对后茬粮食作物生长产生严重影响的问题,以黄土高原半干旱区生长9年的苜蓿草地为研究对象,通过连续8年(2012–2019年)的定位试验,研究探讨黄土高原半干旱区不同种植年限苜蓿地和生长9年的苜蓿地翻耕轮作不同年限春小麦后0–300 cm土层土壤水分演变特征,明确旱作农田土壤水分对苜蓿种植年限和后茬春小麦轮作的响应。结果表明,苜蓿种植1年后50–110 cm土层水分为14.17%,开始呈现出轻度干燥化现象,110–200 cm土层在连续种植3年苜蓿后土壤水分变为12.39%,表现出轻度干燥化现象,200–300 cm土层在连续种植3年苜蓿后土壤水分为13.50%,低于凋萎湿度,土壤表现为重度干燥化。生长9年的苜蓿地翻耕轮作春小麦后,随着轮作年限的延长,土壤干层水分明显恢复,其中50–110 cm土层土壤水分在轮作第5年完全恢复,110–200 cm土层水分在轮作第6年完全恢复,而200–300 cm土层经过连续7年的春小麦轮作后,土壤水分仅为15.11%,依然不能完全恢复。因此,在陇中黄土高原半干旱区连续种植多年苜蓿后,应适时与一年生作物轮作以维持雨养农业系统的可持续发展。

Spring wheat(Triticum aestivum)is the main cereal crop in the rainfed agricultural area of the Loess Plateau.Alfalfa(Medicago sativa)is also widely cultivated in this area.Cropping systems are dominated by continuous spring wheat in the north-western Loess Plateau of China,and the inclusion of alfalfa in cereal-based cropping systems is a traditional practice as well.Continuous production of alfalfa can form a dry soil layer and have a serious impact on the growth of subsequent crops.The aim of this study was to discuss the soil moisture characteristics of the 0–300 cm soil layer on land with different standing years of alfalfa and the alfalfa-spring wheat rotation system on the western Loess Plateau and to determine the soil moisture response to alfalfa standing years and succession spring wheat over an 8-year(2012–2019)field experiment on a 9-year-old alfalfa pasture.The results showed that the soil water content in the 50–110 cm soil layer was 14.17%in 1-year-old alfalfa and began to present light desiccation.The soil moisture in the 110–200 cm soil layer was 12.39%after 3-year-old alfalfa and showed light desiccation.Furthermore,the soil moisture in the 200–300 cm soil layer was 13.50%in the third year of alfalfa planting,which was lower than that under withering humidity and was severely desiccated.After the 9-year-old alfalfa was removed,the moisture of the desiccated soil layers recharged significantly over the rotation year.The soil moisture in the 50–110 cm soil layer fully recharged after five years of rotation,and the soil moisture in the 110–200 cm soil layer was fully recovered after six years of rotation.The soil moisture in the 200–300 cm soil layer after seven years of spring wheat rotation was only 15.11%,which could not be fully recovered.In conclusion,the soil profile was very dry after long-term continuous alfalfa production,especially the soil layer below 200 cm which was severely desiccated.Therefore,to maintain high land productivity and improve soil water storage conditions,crop rotation is needed after long-term continuous alfalfa production in the semiarid Loess Plateau of China.