An Investigation On Capillary Water Upward Movement In Sand Soil And The Salt-water Transport In Drip Irrigation Under The Influence Of Water Quality

In recent years,sand planting as a new soil-less culture technology,has been widely used at home and abroad,because of its advantages of easy availability of substrate,low cost,good air permeability and less crop pests and diseases,etc.In the region with higher groundwater salinity and shallow depth,groundwater will rise to the root layer of the crop through capillary action,and provides favorable conditions for crops to absorb and use groundwater,but also can harm to the growth of crops with salt and water upward build there.On the other hand,underground salt water as an unconventional water resources,is widely used in irrigation.However,the characteristics of sand soil capillary upward and salt-water movement of drip irrigation under saline water was different as compared with fresh water.The effect of different water quality on capillary water upward in sand soil,and the salt-water distribution in drip irrigation were researched for provide some theoretical support for salt water drip irrigation of sand planting.The main conclusions of experiments are as follows:(1)A series of laboratory experiment were conducted to quantify the influences of water quality and Sand particle size on capillary water upward movement and salt-water distribution in sand soil column.Four Sand particle size(d<2.36 mm,d<1.4mm,d<0.7mm,d<0.212mm),9 saline levels of groundwater(9 different combinations of SAR=2,20,30 and C=10,40,80meq/L)were used in the experiment.The results showed that: the upward height of capillary water increased with time,however,The capillary water rise rate gradually decreased with time.There is a clear logarithm relationship between capillary rise height and time.Groundwater replenishment under sand soil particle size d<0.212 mm was much larger than that under other particle size treatments.Groundwater replenishment decreased with the increase of SAR.The sand soil salinity in the profile under C<40meq/l decreased gradually with the increase of capillary rise height and then increased sharply when capillary rise height in excess of 30-40 cm.salts were accumulated in the upper part of sand soil profile.The sand soil salinity in the profile dramatic decreased with the increase of capillary rise height under C=80meq/l.Salts were accumulated in the lower part of sand soil profile.The results suggested that the increase of water salt concentration inhibited the rising movement of salt.(2)Laboratory experiments were conduced to investigate the effects of different drip irrigation water quality((1)freshwater,(2)SAR=2,C=10meq/L,(3)SAR=2,C=40meq/L)and emitters discharge rates(q=1?2?4L/h)on the wetted soil column and the wetting front dynamics.The results indicated that the two-dimensional wetting front boundary shape in the sandy soil can be approximately expressed to an semi-ellipse centered on the emitter.Higher discharge rate produced higher horizontal and vertical movement of soil water.Irrigation with higher water salt concentration yielded lower vertical advance distances,and the width-depth ratio of wetted soil body increased when the discharge rates q=1L/h.For every treatments,the average moisture content of the wetted body was very large(almost reached saturated moisture level)at the beginning and with irrigation went on,the average moisture content of the wetted body declined rapidly and tended to be steady at 0.2-0.3.With the increase of the distance between the point of extraction and the point of water supply,soil moisture content tended to decrease,and the salt concentration tended to increase,and the salt accumulated near the edge of the wetting front.