Effects of straw interlayer on soil water and salt movement and sunflower photosynthetic characteristics in saline-alkali soils

Abstract

Insufficient drainage and over irrigation make salinity still a remaining problem in the Hetao Irrigation District of Inner Mongolia. In view of the occurrence characteristics of saline-alkali soils in this area, controlling invalid soil water evaporation and increasing water use efficiency are very important. It has been demonstrated that surface mulching with straw and film and placing a straw interlayer in soil are effective measures for soil salinity control. In this paper, we investigated the influences of integrated application of mulching and straw interlayer on the movement of soil and water and photosynthetic characteristic of sunflower on a typical saline-alkali soil. Micro-plot experiment was established with four treatments: straw interlayer only (S), straw interlayer plus surface straw mulching (S+S), straw interlayer plus surface plastic film mulching (P+S), and surface plastic film mulching (CK). Water and salt contents in the 0-40 cmm soil layer and crop photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), and intercellular CO2 concentration (Ci) were measured during sunflower growing season. Mulching and straw interlayer significantly modified soil water and salt processes. Compared with the other treatments, the P+S treatment showed lower salt contents and solute concentration in the 0-40 cm soil layer. The S+S treatment increased soil water content and reduced salt content at the seedling stage, but the degree of changes were less than that of the P +S treatment. At later growth stages, the S+S treatment had lower soil water content and higher salt content, suggesting that a straw interlayer plus surface straw mulching was not very effective in soil salinization control. The S treatment had the highest salt content in the whole growing season, an indication that placing a straw interlayer in the soil has limited effect on reducing soil salinity. Although the CK treatment had a higher and table water content in the 0-40 cm soil layer, its salt content remained higher in sunflower growing season. In terms of crop photosynthetic characteristics, compared to the CK, S, and S+S treatments, the P+S treatment significantly increased sunflower Pn, Tr, and Gs, and reduced Ci at seedling stage, bud stage, and flowering stage. In addition, the P +S treatment promoted crop growth, reduced the growth period, and accelerated dry matter accumulation of sunflower plants. We concluded that the P+S treatment was an optimal measure on amelioration of saline- alkali soil in the Hetao Irrigation District.