Soil salinity in a drip and furrow irrigated cotton field under influence of different deficit irrigation techniques

Abstract

We investigated the influence of conventional deficit irrigation (CDI) and partial root zone irrigation (PRI) on soil salinity in a drip- and furrow-irrigated cotton field. Under PRI, one half of the rooting zone is wetted while the other half is maintained partially dry, and thus reduced amount of water is applied. The wetted half of the root zone is alternately changed either every or every other subsequent irrigations. Effects of time length during which one side of the root zone stays wet or partially dry on soil salinity were investigated for only furrow irrigated cotton. We had compared proportional soil salinity developed under CDI and PRI under drip irrigation. Thus we had two field experiments consisting separately drip- and furrow-irrigated cotton. The treatments under furrow irrigated cotton were (1) FULL, control treatment where rooting zone soil water content was increased to field capacity at each irrigation; (2) 1PRI and (3) 2PRI, 50% deficit irrigation compared to FULL treatment was applied while interchanging wetted and partially dry sides every and every other irrigations, respectively. The drip-irrigated cotton had similarly three treatments: (1) FULL, the control treatment where full amount of irrigation water (100% Class-A pan evaporation) was applied to both sides of the plant rows; (2) 1PRI and (3) CDI, where the both treatments had 50% deficit irrigation compared to FULL treatment. Under CDI treatment, the deficit amount of water was uniformly applied to both sides of the cotton rows. Soil salinity was assessed utilizing root zone soil salinity profiles developed at planting and following harvest. Additionally we had isosalinity maps constructed with grid soil sampling of plant root zone at harvest. The results showed that soil salinity increase was significant (P<0.05) only within soil surface layer of 0-20 cm. The highest increase in soil salinity was noted under the treatment of 2PRI with furrow irrigation. The drip irrigated cotton data showed that the salinity increase under PRI was in the same range as the FULL treatment whereas the increase under CDI was the highest. However, any likely soil salinity increase, resulting from deficit irrigation either with CDI or PRI practices, was at levels which could easily be leached with winter rains.