أثر استخدام المياه الجوفية على التربة و إنتاجية بعض المحاصيل الزراعية بمنطقة تبراك

Abstract EN

Tebrak area, locating within the Manjour outcrop approximately 100 km west of Riyadh, is one of the main agricultural areas in Saudi Arabia especially after the large expansion of cultivated area during the eighties.

Salt accumulation within soil as well as sodicity of irrigation water constitute a potential threat to soil as a media for crop production in such an arid area where groundwater is used for irrigation and evapotranspiration rates are very high.

This paper aimed to evaluate the effects of groundwater use on soil and some crops yield in Tebrak area by determining: (1) the magnitude of yield reduction for some crops (wheat, maize, barseem, pepper, okra, cucumber and tomato) due to salt accumulation in the root zone and (2) the likelihood of permeability hazard and soil surface crusting due to sodicity of irrigation water.

To accomplish this, 54 samples of groundwater were obtained from obstruction wells in the area and analyzed for total salinity and major cations.

This data set was used to estimate average root zone salinity which in turn used to calculate crops relative yield.

Also, calculated sodium adsorption ratio (SAR) were plotted against total salinity to determine the likelihood of permeability hazard and soil surface crusting.

The results indicate that groundwater salinity in the area falls within the class of slightly saline waters with average total salinity of 2.6 mS cm*' and minimum and maximum of 1.48 and 5.69 mS cm'1, respectively.

SAR averaged 5.5 .

The plots of SAR against total salinity falls within the area of unlikely permeability hazard which means that groundwater in Tebrak area is safe for irrigation in terms of soil permeability reduction and soil surface crusting.

Estimated root zone salinity averaged 6.6 and 5.2 mS cm'1 at leaching fractions of 0.1 and 0.2, respectively.

Calculated relative yield of the crops based on estimated average root zone salinity indicate that wheat yield is high averaging 96% and 99% at leaching fractions of 0.1 and 0.2, respectively.

Barseem relative yield averaged 71% and 79% at leaching fractions of 0.1 and 0.2, respectively.

The relative yield of the rest of the crops ( maize, pepper, okra, cucumber and tomato) is low even at high leaching fractions which means that it is not economical to cultivate these crops in Tebrak area.