| In order to solve the probelms of deep dried soil layers and grass growth decline in artificial alfalfa field of mountain areas in southern Ningxia,12 years and 18 years old rainfed alfalfa were selected as the research object and slope tillage farmland as the control to explore the vertical distribution characteristics of soil moisture(0-1000 cm),nutrients(0-1000 cm)and roots(0-720 cm).The relationship between deep soil water,roots and soil nutrients were further discussed.The following conclusions were obtained through correlation analysis:(1)The vertical soil water content of alfalfa field in the study area was in the order of famland>12 a alfalfa field>18 a alfalfa field.The vertical soil water content in alfalfa field decreased first and then increased.Dried soil layers occurred in 200-880 cm for 12 a alfalfa field and 200-1000 cm for 18 a Alfalfa field.The amount of water consumption for 12 a and 18 a alfalfa field was 42.73 mm and 49.73 mm more than that in the control farmland,which was the main reason for causing dried soil layers in alfalfa field.(2)There was no desiccation in the farmland in 200-1000 cm soil layer with an average desiccation index of 177%;12 a alfalfa field was in severe desiccation stiuation with an average desiccation index of 45.56%;18 a alfalfa field was in extreme desiccation stiuation,with an average desiccation index of-0.34%.No dried layer was found in the farmland.The thickness of severe dried layer was 680 cm and light dried layer was 120 cm in 12 a alfalfa field.The thickness of extreme dried layer was 520 cm and severe dried layer was 280 cm for 18 a alfalfa field.(3)In 200-1000 cm soil layer,the soil water availability grades of 12 years old alfalfa were classified as difficulty-use water,and the soil water availability grades of 18 years old alfalfa in 200-720 cm layer was invalid water,and the rest were difficulty-use water.The water supply coefficient for 18a alfalfa field in 200-720 cm was 0,and alfalfa in this field faced soil water shortage.The degree of soil moisture deficit in 200-720 cm layer is severe and moderate deficit.(4)The spatial distribution of soil total nitrogen,total phosphorus and available potassium decreased in the 0-1000 cm vertical profile for 12 a and 18 a alfalfa field.Soil total nitrogen was mainly concentrated in the 0-120 cm soil layers,which was 152.94%of farmland.Total P was mainly enriched in 0-200 cm soil layer,which was 98.52%of farmland.Available potassium was mainly focused on 0-80 cm soil layer,and the content of available potassium in 0-80 cm soil layer is 81.74%higher than farmland.The contents of soil nutrients in the deep layer were lower than those in the control farmland.With the increase of soil depth,the soil nutrient content of 18 a alfalfa field showed an increasing trend,which was caused by the fact that with the growth of alfalfa,part of the roots of aging alfalfa died and the ability of soil nutrients consumption was decreased and the root nutrients returned to the soil.(5)Soil roots mainly concentrated in 0-120 cm soil layer in 12 a and 18 a alfalfa field and the root amount decreased with the increase of soil depths.The total root amount for 12 a alfalfa was larger than that for 18 a alfalfa,indicating that part of the roots died and nutrients returned to the soil.There was a significant positive correlation between root indexes and nutrient parameters of 12 a and 18 a alfalfa(P<0.01).Soil depth and root nutrient for 12 a alfalfa showed a significant negative correlation.Soil depth and root,total nitrogen and total phosphorus for 18 a alfalfa field showed a significant negative correlation,while soil depths and soil water for 18 a alfalfa field showed a significant positive correlation(P<0.05). |
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