宁南半干旱与半干旱偏旱区苜蓿草地土壤水分与养分特征

Soil water and nutrient characteristics of alfalfa grasslands at semi-arid and semi-arid prone to drought areas in southern Ningxia

通过对宁夏南部半干旱区(固原)和半干旱偏旱区(海原)不同生长年限紫花苜蓿(Medicago sativa L.)草地深层土壤水分与养分含量的测定,分析和比较了2种干旱类型区苜蓿草地土壤水分与养分差异及其土层剖面的分布特征。结果表明:(1)2个类型旱区苜蓿草地0—1000 cm土层平均土壤湿度随生长年限的延长逐渐降低,但草地衰败后对水分的消耗减少。(2)随土层深度的增加,2个类型旱区苜蓿草地土壤湿度表现出先减少后增加的变化趋势;有机质、全氮、碱解氮和速效磷含量不断减少。(3)随生长年限的延长,2个类型旱区苜蓿根系对土壤水分和养分的消耗不断加深,6 a苜蓿草地土壤含水量、碱解氮和速效磷发生了不同程度的亏缺;10 a苜蓿草地均已进入衰败期,土壤有机质、全氮和碱解氮自上而下逐渐恢复,且半干旱偏旱区恢复的较快;速效磷含量随生长年限的延长不断减少,苜蓿草地衰败后消耗速率减小。(4)半干旱偏旱区相同生长年限苜蓿草地0—400 cm土层土壤养分含量均高于半干旱区。(5)土壤水分亏缺与养分不均衡导致苜蓿草地衰败。因此,在实际生产中对旱地苜蓿草地应进行合理灌溉与施肥,平衡土壤养分并延缓草地衰败。

In order to explore the relationship of alfalfa grassland among soil water,soil nutrient and grassland degradation,and provide theoretical basis and practical guidences for fertilizater application and soil water management of alfalfa grassland in southern Ningxia,soil water and nutrient contents in deep soil layers on alfalfa grasslands with different growth years at semi-arid area-Guyuan and semi-arid prone to drought area-Haiyuan of southern Ningxia were determined,the differences of soil moistures,nutrient contents and distribution characteristics were analyzed and compared.The results showed as follows：（1） Alfalfa yields of semi-arid area were generally higher than that of semi-arid prone to drought area,but there were normal distribution patterns between alfalfa yields and growth year at both of 2 rainfall areas,1―6 year-old alfalfa grasslands were in vigorous growth period,after that time it entered into degradation.（2） The mean soil moistures decreased with the increasing of alfalfa growth age in 0—1000 cm soil layers at 2 varied rainfall areas before alfalfa entering into wane,but the comsumption of soil water descended when alfalfa grasslands entered into wane.Soil water of 10 year-old alfalfa grassland began to recover from upper to deep soil layers at Haiyuan,but 12 year-old alfalfa grassland showed no signs of recovery at Guyuan,since alfalfa growth of Guyuan was better than that of Haiyuan,12 year-old alfalfa grassland was still in soil water comsumption period.（3） The influences of rainfall and soil water comsumption made soil moistures decreased firstly then increased with the increasing of soil depth;The root and residue of alfalfa could return nutrients to upper soil layers,so soil organic matter,total N,available N and available P contents in 0—30 cm soil layers were highest at 2 different rainfall areas.（4） Soil water and nutrient consumption depths deepened in soil profile with the increasing of alfalfa growth age at 2 different rainfall areas,the contents of soil available N and available P decreased with different extent on 6 year-old alfalfa grasslands;Since 10 year-old alfalfa grasslands had entered into wane,soil organic matter,total N and available N contents restored from the upper to deep soil layer,but the soil nutrients of semi-arid prone to drought area restored faster than that of semi-arid area.Soil available P content reduced with the increasing of alfalfa growth age,but the consumption rate decreased after 6 years.（5） Comparing alfalfa grasslands with the same growth age,soil nutrient contents of semi-arid prone to drought area were generally higher than that of semi-arid area in 0—400 cm soil layers.（6） The changing trends of alfalfa yields,soil water and nutrient of both 2 different rainfall areas showed that the imbalance of nutrients and deficit of soil water led to grassland degradation.So feasible irrigation and fertilization measures should be taken in arid alfalfa grasslands to balance soil nutrient and delay degradation,suitable alfalfa growth year of semi-arid and semi-arid prone to drought areas was 6—7 and 5—6 years respectively in southern Ningxia.