Transient soil salinity under the combined effect of reclaimed water and regulated deficit drip irrigation of Mandarin trees

Abstract

Regulated deficit irrigation (RDI) strategy using saline reclaimed water is becoming a frequent practice under semiarid Mediterranean climatic conditions in the southeastern region of Spain. There is a concern that the long-term use of this strategy will affect the production sustainability of the agricultural soils. This paper evaluates the field consequences of this strategy on the accumulation of salts within the plant root zone. Full and regulated deficit surface drip deficit irrigation was combined with fresh water (EC 1dSm−1) and saline (EC 3dSm−1) tertiary reclaimed water to irrigate adult mandarin trees over a 3-year period. The control treatment received 100% of the crop evapotranspiration “ETc” and the RDI treatment received 50% of ETc during the 2nd stage of fruit growth. Soil water content was monitored every other week within the soil wetted volume under the emitter. Gravimetric soil samples were collected from 3 depths and at 3 distances to the emitter, twice a year: at the end of irrigation season and at the conclusion of RDI period. Soluble salts, electrical conductivity and sodium adsorption ratio were determined in the saturated paste extract. The results show how the RDI strategy intensifies the development of salinity gradient away from the emitter even when using good quality water. The combination of RDI with saline reclaimed water produced transient saline-sodic conditions at the outer superficial limits of the wetted bulb under the emitter. The appearance of such adverse conditions is alarming and would threaten the sustainability of agricultural soils. Therefore soil water deficit should be avoided whenever saline reclaimed water is in use for irrigation.