Salt accumulation in soils under furrow and drip irrigation using modified waters in Central Iran

Abstract

The objectives of this study were i) to characterize the water and soils under different managements, ii) to evaluate the sustainability of using hypersaline soils and water, and iii) to assess possible solutions to prevent more degradation of soil and water resources. Field and laboratory analysis of the samples using eight pedons and 128 surface samples taken from grid in four pre-determined land uses; pistachio orchard abandoned, pistachio orchard with furrow irrigation, wheat and maize cropping with furrow irrigation, pistachio orchard with drip irrigation. The study area, 170 ha, comprised two distinct soil parent materials including marls (max. ECe >100 dS/m) and alluviums (max. ECe >60 dS/m). Abandoning lands caused salinity increasing due to lack of leaching by irrigation water. The maximum increase of soil salinity was in the abandoned land use (EC e =98 dS/m), where trees had been removed and there is no irrigation, followed by pistachio plantation land use (EC=11 to 34 dS/m), and wheat and maize cropping land use (EC=11-19 dS/m). The minimum rise in soil salinity was in the drip irrigation due to mixing freshwater with saline water and therefore better water quality (EC=3 dS/m at surface layer and 17 dS/m in next layer). Land use change to agriculture increased the need for irrigation and because of arid climate it mainly supplied by groundwater from deep wells. Using deep groundwater due to rock-water reaction and increasing salinity, decreased water quality in furrow irrigation and therefore it had more significant effect on soil salinity compare to drip. Comparison of the mean values of soil salinity indicators in 2018 showed that salinity has increased by 3-6 times in the furrow irrigation and at least two-fold in the drip irrigation, compared to 2002. The calculated salinity indicators also proved the soil and water resources had been degraded and present land use types are not sustainable. Possible solutions could be to minimize land use change to agriculture, to use drip irrigation with mixed saline and freshwater, and to remove salt crusts from the soil surface.