Abstract: In order to determine improvements of alfalfa (Medicago sativa) root growth in immature soil of loess parent material, a soil column culture experiment in the tube was conducted with immature soil of loess parent material. Growth characteristics of alfalfa root grown 2~4 years, vertical distributions of rhizospheric soil microbes, enzymes activity, and nutrition from 0 to 300 cm depth were investigated. Results indicated that root weight, root volume, and root diameter of alfalfa from 0 to 300 cm depth fit the decline model of Y=A·e^-BX with soil depth increase. Immature soil structure was effectively improved by the perforating, incising, and squeezing effects of alfalfa roots. Developed roots of alfalfa significantly improved the number of rhizospheric microbes and increased rhizospheric enzyme activities, the contents of rhizospheric nitrogen and organic matter. Alfalfa roots grown four years had the best rhizospheric effect. This study supplied a theoretical basis for improving immature soil of loess parent material by planting alfalfa.

Key words: Immature soil of loess parent material, Alfalfa, Root growth characteristic, Soil microbe, Soil enzyme activity, Soil nutrition

摘要： 为明确苜蓿根系生长对黄土母质生土的改良效应,以黄土母质生土为供试土壤,采用根管土柱栽培方法,研究了2~4年生紫花苜蓿(Medicago sativa L.) 0~300 cm土层根系生长特点及其根际土壤微生物、酶活性以及土壤营养的垂直分布。结果表明:黄土母质生土0~300 cm土层的苜蓿根重、根体积、根直径随土层的加深皆符合Y=A·e^-BX锥形负指数递减模型;苜蓿根系对土壤的穿孔、切割、挤压作用有利于改善生土的结构;苜蓿发达的根系明显促进了生土根际微生物的繁衍、酶活性的提高及土壤氮素营养与有机质含量的提高。试验年限内,以4年生苜蓿根际效应更好。本研究结果为苜蓿应用于黄土母质生土地的改良沃化提供了理论参考。

关键词: 黄土母质生土, 苜蓿, 根系生长特征, 土壤微生物, 土壤酶活性, 土壤营养