Effect of solute type and salinity on soil water availability in orchards in saline semiarid regions

Soil water availability is a key factor that restricts land productivity in saline soils. Scientific studies of the effects of solutions with different solute types and salinity degrees have been used to evaluate the application of brackish water on soil salinity and productivity. In this study, the effects of different solute types (NaCl and Na₂SO₄) and salinity degrees (0, 1 g·L^-1, 3 g·L^-1, 5 g·L^-1, 10 g·L^-1) on soil water availability in orchard soils in semiarid saline regions were determined using the dehydration centrifugal method. Soil pore was determined during "conception pore" dehydration instead of "inter-granular pore" and "texture pore" dehydration. This was because soil water loss for the same base membrane properties and structural arrangement was different under different solute types during dehydration. The results showed that compared with the control (CK), treating soils with different degrees of salinity of NaCl and Na₂SO₄ solutes decreased soil field capacity, temporal wilting coefficient, permanent wilting coefficient, slow available water and unavailable water. The contents of total available water and available water of treatments with different salinity degrees of NaCl and 1 g·L^-1 of Na₂SO₄ increased compared with CK. However, the contents of total available water and available water of treatments with 3 g·L^-1, 5 g·L^-1 and 10 g·L^-1 of Na₂SO₄ decreased. Soil aerated porosity and capillary porosity of treatments with different salinity degrees of NaCl and Na₂SO₄ decreased, while inactive porosity increased. Treatments with 5 g·L^-1 of NaCl and Na₂SO₄ decreased aeration porosity by 16.8% and 14.8%, decreased capillary porosity by 5.2% and 6.5%, increased inactive porosity by 15.7% and 14.4%, respectively, compared with CK. The effects of treatments with NaCl on soil specific water capacity and lagging capillary rupture were more significant than treatments with Na₂SO₄. With increasing concentration of salts solution, soil drought resistance and soil water-holding capacity decreased while soil water supply improved.