宁南旱地草粮轮作田土壤水可持续利用模拟研究

A simulation study on the sustainable use of soil water in dry land for alfalfa-crop rotation systems in the semiarid region of southern Ningxia

采用野外调查和计算机模拟相结合的方法对宁夏南部旱地草粮轮作田土壤水分恢复问题进行了模拟研究。结果表明,模拟土壤湿度和观测土壤湿度剖面分布自上而下的变化趋势一致,土壤湿度模拟值基本能够反映苜蓿地土壤湿度等级在不同土层的分布。苜蓿地土壤干燥化进程和土壤湿度恢复进程均表现为前期快后期慢。在宁夏南部丘陵半干旱区,8～10 m土层土壤湿度恢复较困难,种植苜蓿期间应尽量避免该土层土壤湿度等级降低到D以下,即土壤湿度不应低于8.5%。在宁夏南部丘陵半干旱区苜蓿适宜种植年限为6～8年,翻耕后适宜采用PPW轮作模式（马铃薯→马铃薯→春小麦）进行土壤水分恢复,种植16～20年粮食作物后可以再次种植苜蓿。

Restoration of soil water in alfalfa-crop land was simulated in the hilly-arid region of southern Ningxia by a combination of survey and simulation methods.Simulated vertical distribution of soil water in different soil layers was consistent with observations and a good agreement was found between the simulated and observed soil moisture grades in different soil layers.A similar trend（higher speed at the earlier stage and lower speed at the later stage） was found in the process of forming and eliminating the soil desiccation layer.It was difficult for the restoration of soil water in 8-10 m soil.Therefore,soil moisture in this soil layer should not be lower than D grade,i.e.soil water content should not be less than 8.5% during the cultivation process of alfalfa.For the sustainable development of agricultural production,the appropriate alfalfa stand age was 6-8 years;the optimum subsequent cropping system to recover soil water was potato/potato/spring-wheat;and the appropriate cultivation years of this subsequent copping system was 16-20 years before alfalfa was replanted again.