EFFECT OF LATERALS DRAIN SPACING AND GROUNDWATER DEPTH ON SOIL WATER RELATIONS AND RICE PRODUCTIVITY IN THE NORTH NILE DELTA

A field experiment was conducted in alluvial clay soil located at the north Nile Delta (Motobus District, Kafr El-Shiekh Governorate, Egypt). The soil was cultivated with rice crop (Oryza sativa L.) during two summer seasons 2018 and 2019. The impact of lateral drain spacing at 20m and 40m between laterals (main plots) with controlled drainage (CD) at 0.4, 0.8m depth and uncontrolled drainage at 1.2m below soil surface (sub plots) was studied to evaluate soil-water properties, Nitrate losses, water saving, rice productivity and economic return under rice crop cultivation. Results showed that the relative groundwater depth values (RGWD) are inversely proportional to the drain spacing treatments. The highest values of drainable porosity (0.145 and 0.141%) were achieved in the plots subjected to 20 m drain spacing with uncontrolled treatment, while the lowest values ( 0.1 and 0.101%)  were obtained at 40m drain spacing with 0.4m controlled drainage in both seasons, respectively. It's clear that narrow drain spacing of 20m and water table depth at 0.4m was more efficient than the wider drain spacing at 40m in reducing values of soil salinity, SAR and bulk density compared with its values before installation of drainage system. On the other, hand it gave the highest values for water saving, nitrate saving, productivity of irrigation water, rice yields, net return, net income from water unit, economic efficiency compared to wider drain spacing (40 m) with 1.2 m ground water depth. The controlled drainage reduced drainage outflow compared to conventional drainage. It can be concluded that the treatment of controlled drainage gave more profit than the uncontrolled one.