Interaction of Applied Water Volume and Irrigation Water Salinity on Wheat Yield in Arid Regions (Case study: Yazd)

Farmers, who are faced with the problem of irrigation water salinity, sometimes ask questions about the yield forecast under the effect of irrigation water salinity (ECiw) and the volume of applied water (Viw). The answer to this question requires knowledge of the crop production function. The aim of this study was to investigate the interaction between ECiw and Viw on wheat grain yield (Narin cultivar) in the Yazd region. For this purpose, the response of wheat yield under the effects of irrigation water salinity (including 3, 5, and 8 dS.m-1) and volume of applied water (from 4500 to 11600 m3.ha-1) was analyzed during 2017-2018, 2018-2019, and 2019-2020 cropping seasons. The results showed that the effectiveness of applied water on wheat yield has increased in saline conditions than in non-saline conditions. Therefore, wheat growers in saline areas should be confident about the adequacy of available water to meet the field water requirements (both ET and leaching requirements) and also follow the irrigation scheduling more carefully and obsessively compared to none-saline conditions. In this case study, a wheat yield function was presented and evaluated, as well. This function works based on the salinity and the volume of irrigation water (ECiw and Viw). With a coefficient of determination (R2) of 0.67, this function is expected to estimate the wheat yield with an approximate error of ±524 kg.ha-1. This equation can be used to estimate the production decline due to increasing salinity of irrigation water or decreasing the volume of applied water, to predict the yield before the harvest time as well as to meet the field water required to produce a certain amount of grains in the studied region