On Conversion Relation between Surface and Deep Soil Water of Apple Orchard

The soil water within 0-180cm was determined with Trime system from April to October in 2005.Curve between soil water and soil depth,and models using surface soil water to forecast deep soil water.were founded The results showed that the variance of 0-50cm soil water was strong,with increasing of soil depth,the variance of more than 50cm soil water became middling.Furthermore the corresponding effects of 0-10cm and 0-30cm and deep soil water were worse,and the relative error of results more than 10% accounted for 55.56% and 50.00% respectively.The forecasting precision of 0-50cm layer was higher obviously than other layers,and the relative error of results less than 10% accounted for 88.89% and the biggest relative error was 12.98%,furthermore the forecasting effect of experience relation was best.As a result,the best surface depth of soil layer to forecast deep soil water was 0-50cm layer in this region.