黄土高原半湿润区苜蓿草地土壤氮素消耗特征研究

Soil nitrogen consumption characteristics of alfalfa grassland in the semi-humid areas of the Loess Plateau

本文研究了黄土高原地区生长年限分别为4 a、6 a、10 a、12 a、18 a及26 a苜蓿草地土壤氮素的变化特征。结果表明,在0—1000 cm土层,不同生长年限苜蓿草地土壤全氮与碱解氮含量均呈现规律性的变化,即随土层深度的增加,全氮及碱解氮含量下降,350 cm土层以下,变化趋势平缓。在0—200 cm土层,26 a苜蓿草地全氮、碱解氮含量低于4 a、6 a苜蓿草地,高于10 a、12 a苜蓿草地;在200—1000 cm土层,土壤全氮、碱解氮含量在不同生长年限之间差异不大,表明苜蓿生长超过一定年限,土壤氮素有一定恢复,但受土壤氮素累计消耗的影响,只能使土壤上层的氮素逐步得到恢复,而深层土壤氮素难以恢复;苜蓿草地有机碳与全氮、碱解氮及C∶N之间均为正相关关系。苜蓿生长6 a以后,应对苜蓿草地进行合理施肥,以维持苜蓿草地的氮素平衡。

This paper presents a study about soil nitrogen （N） variations in the grasslands with alfalfas growing for four years, six years, ten years, twelve years, eighteen years and twenty-six years. The study showed that there were consistent change of total N and available N contents with alfalfas growing for different lengths of time in 0-1000 cm soil. Soil total N and available N contents decreased with soil depth, and tended to remain relatively constant in soils deeper than 350 cm below soil surface. In 0-200 cm soil, total N and available N contents in 26a was lower than 4a and 6a, but higher than 10a and 12a. In 200-1000 cm soil, there were little difference among different treatments in total N and available N content, which further illustrated that the recovery of soil nitrogen began in upper soil and high consumption of deep-soil nitrogen in the early alfalfa growth made it difficult to recover soil nitrogen in deep soil. There were positive correlation between SOC and total N, available N and C：N. After six years of alfalfa growth, fertilization should be applied to maintain nitrogen balance in alfalfa grassland.