Water Use Strategies Of Plant On Shallow Purple Soil

Purple soil is the most important agriculture resource in upper-middle reaches of Yangtze River.Because of shallow soil layer,this region is prone to influenced by soil erosion and draught.That's why water is the mainly restrictive factor in this region.The purple soil in Sichuan basin accounts for51.53%of the nation purple soil area,agricultural and forestry composite ecosystem is a common land utilization type in purple soil region.Water use strategies of plants in this ecosystem can affect the ecosystem function,crop yield,hydrological cycle in sloping farmland and many other biochemical processes.Therefore,a better understanding about water use strategies of different plants has an important implication for vegetation restoration,management and agricultural drought control.This study takes crops?wheat,maize?,herb?thatch?,shrub?vitex?,arbor?cypress?as research objects,adopts isotope technology as research method,combined with soil water content.,Our analysis provided get the following main results and conclusions:?1?The local meteoric water line of Yanting was:?D=7.15?¹⁸O+12.70?R2=0.97,n=37?.There is no“temperature effect”¹⁸O from precipitation,but there do exist a significant“precipitation effect”,with obvious seasonal characteristics such as ¹⁸O value was low in summer and autumn whereas it remained high during winter and spring;?2?It is found that the soil isotopes in the shallow layer of sloping farmland have the enrichment effect.From the characteristics variation of ¹⁸O value in different seasons,all the year round,the isotope content are higher in 0-20cm of soil layer in forest,because the shallow soil layer is easy to be influenced,while 40 cm is relatively stable.Soil water isotope value decreases with the increase of depth.Compared with the water equation,the slope and intercept are obviously small.?3?The water content in the 0-10cm of the soil layer is most important water source for maize as it consumes more than 70%of the water content in its growing period.The soil water utilization rate of 0-10cm in the seedling stage was up to 85.3%.Due to the high monthly precipitation,the soil water utilization of 0-10cm reached its maximum value of 86.4%at the jointing stage.The maize roots in the heading stage,filling stage and mature stage are more developed,so the whole soil layer water is used by maize.Wheat mainly use soil water of 0-10cm,with a use ratio as high as 95.5%.During the jointing stage soil water utilization increased as a whole.During the heading stage use of soil water decreased in 0-10cm of the soil layer,whereas increased in 10-20cm of the soil layer.During the filling and mature stage,wheat utilizes major proportion of soil water in 0-30cm of the soil layer.From March to October,the utilization rate for thatch was high in 0-10cm soil layer,and reached to 90.2%during July,while little difference was found in all the layers for utilization rate during November to January.In different months,the utilization ratio in 0-10cm soil water for vitex was the largest?except December and January?,reaching the maximum utilization rate of 87.6%in July.The proportion of soil water utilization was large in 10-30cm of the soil layer during January to June.During November to February,vitex had a greater utilization of groundwater,bu t it also had a stable utilization of water sources from other soil layer.Cypress roots are mainly distributed in the topsoil,in case of more rainfall the soil water utilization rate is therefore higher in 0-10cm of the soil layer and the utilization rate can reach from 60%to 80%.From November to April,the use of all water sources vary greatly,but it is mostly sourced from soil layer below 30cm and groundwater.?4?No matter crops,grasses,shrubs or trees,they have a higher utilization of soil water from 0-10cm of the soil layer.In maize and wheat,due to limitation of roots during seedling stage soil water is largely utilized from0-10cm of the soil layer.During the growing stages wheat utilizes more than40%of its water requirement from 0-10cm of the soil layer,whereas maize utilizes this layer more than wheat.In the rainy season,the cypress,vitex,and thatch mostly utilize water from 0-10cm of the soil layer.Soil water utilization ratio in 40-50cm layer of the soil followed a pattern of thatch>wheat>maize.Generally,cypress trees have higher utilization ratio of groundwater than vitex.Therefore,there is a competition for water source from shallow soil layer during rainy season,whereas during the dry season these plants approach deep soil water sources.