Evaluation of the effect of soil salinity on the crop coefficient (Kc) for cotton (Gossypium hirsutum L.) under mulched drip irrigation in arid regions

Soil salinity and associated problems are the major challenge for the arid region of Northwest China. Strategies to cope with salinity, including a better understanding of the impacts of soil salinity on the crop coefficient (Kc), are essential for precision irrigation in arid regions. In this study, two years of non-weighing lysimeter (NWL) experiments were conducted to investigate the Kc of cotton (Gossypium hirsutum L.) under different degrees of soil salinization. The stress coefficient (Ks) model was modified and validated based on the NWL and field experiments. Three irrigation water qualities (GW, groundwater, 1.27 g l−1; BW, brackish water, 3.03 g l−1; SW, saline water, 4.90 g l−1) were applied to mulched-drip irrigated cotton. Both NWL and field experiments revealed that BW and SW irrigation increased the soil salt content which reached the moderately saline soil level. Adjusted for local weather, the Kc-Local of cotton for the initial, middle and end seasons was 0.29, 1.10 and 0.52 under slightly saline soil (GW irrigation) and 0.24, 0.98 and 0.46 under moderately saline soil (BW and SW irrigation). In addition, the linear negative correlation relationships of soil ECe with yield response factor (Ky) and slope b (reduction in yield per increase in ECe beyond the ECe threshold) were developed. Furthermore, the Ks model was modified under salt stress conditions, which provided an acceptable Ks estimation under field conditions. These findings could be helpful for efficient water management in cotton cropping systems under mulched drip irrigation in arid regions.