黄土高原半湿润区苜蓿草地土壤干层形成及氮素消耗研究

Dry Soil Layer Forming and Soil Nitrogen Consumption Characteristic of Alfalfa Grassland in the Semi-humid Region of the Loess Plateau

为掌握苜蓿连续种植多年土壤干层的形成规律及氮素的消耗规律,促进黄土高原地区苜蓿草地合理施肥及草田轮作,论文系统研究了3年、4年、6年、12年、14年、18年及26年生紫花苜蓿草地土壤干层及氮素的消耗。结果表明：黄土高原地区土壤干层可分为轻度干层（9-11%）、中度干层（7-9%）、重度干层（〈7%）三级。荒地在80-100 cm土层,出现轻度干层;苜蓿草地土壤干层出现的区域为140-600 cm土层,随生长年限的延长,土壤干层厚度向下延伸,干化程度加剧,苜蓿生长至12年,出现中度干层,干层范围达到500 cm土层。不同生长年限苜蓿草地土壤碱解氮含量呈现规律性的变化,即随土层深度的增加,碱解氮含量下降,300 cm土层以下,变化趋势平缓;苜蓿生长至26年,0-200 cm土壤上层的氮素有一定恢复,而200-1 000 cm深层土壤氮素难以恢复。研究表明,在黄土高原半湿润区紫花苜蓿生长6年以后,应对苜蓿草地进行合理施肥,实施粮草轮作,以维持土壤氮素平衡,持续提高土地生产力水平。

In order to study dry soil layer forming and soil nitrogen consumption characteristic,promote fertilizing and grass-crop rotation in alfalfa grassland,the paper investigated the dry soil layer and soil nitrogen consumption in the grasslands with alfalfa growing for three years,four years,six years,12 years,14 years,18 years and 26 years.The results showed that dry soil layer was divided into three types： slightly dry soil layer（9%-11%）,moderately dry soil layer（7%-9%）and highly dry soil layer（〈7%）.Slightly dry soil layer occurred in 80-100cm soil of wild land and dry soil layer appeared in 140-600cm soil in alfalfa land.With the prolonged period of alfalfa growth,dry soil layer extended its lower boundary downward and became intensified,moderately dry soil layer appeared in the grasslands with alfalfa growing for 12 years and expanded beyond 500 cm deep below ground.There are regular changes in the available N contents in the alfalfa grassland with different number of growth years.The soil available N contents decreased with the deepening of soil depth,and tended to keep a stable state in soil deeper than 300cm below soil surface;after 26 years of alfalfa growth,the soil N content began to rebound to a certain degree in the upper soil of 0-200cm,but it was difficult to rebound at depths of 200-1000cm.The study showed that reasonable fertilization and grass-crop rotation should be practiced to maintain N balance and continue to increase land productivity after alfalfa growing for more than six years in semi-arid areas of the Loess Plateau.