Effects of a 10-year irrigation with saline water on soil physico-chemical properties and cotton production

Abstract

Saline water irrigation has been widely used for crop production where agriculture is short of freshwater. To reveal the responses of soil environment and cotton (Gossypium hirsutum L.) growth to long-term irrigation with saline water, a 10-year (2006 to 2015) experiment was carried out to study the effects of saline water irrigation on soil physico-chemical properties, as well as the yield and fiber quality of cotton in the low plain around the Bohai Sea (BHLP), China. Five salinity levels of irrigation water were tested (3.4 [T1], 7.1 [T2], 10.6 [T3], 14.1 [T4], and 17.7 dS m⁻¹ [T5]), and freshwater (1.3 dS m⁻¹) was used as control (CK). The results showed that from 2006 to 2015, the electrical conductivity of a saturated soil extract (EC_e) in 0 to 100 cm soil depth did not accumulate linearly with years for all treatments but positively correlated with the ratio of irrigation to precipitation. Cotton yield decreased significantly when salinity of irrigation water exceeded 10.6 dS m⁻¹. Fiber quality tended to get worse when salinity of irrigation water reached 17.7 dS m⁻¹. In the tenth year, EC_e, sodium adsorption ratio (SAR), the content of silt and clay equivalent size particles, and bulk density of soil plow layer increased with increasing salinity of irrigation water, while soil porosity and the content of macroaggregate in plow layer decreased. Compared with the initial chemical properties of soil plow layer in 2006, pH and SAR for saline water treatments increased at the late stage of cotton growth in 2015. The assessment results of soil quality index (SQI) showed that, in comparison with CK treatment, SQI decreased by 3.7%, 11.1%, 16.9%, 21.0%, and 21.7% in T1, T2, T3, T4, and T5, respectively. Therefore, from the aspect of the soil quality of plow layer in the BHLP, long-term use of irrigation with saline water above 3.4 dS m⁻¹ will decrease soil quality, and this agricultural management should be paid more attention.