Effects of water quality and nitrogen on wheat productivity: Experimental and modelling study using the SALTMED model

The effects of different water qualities and nitrogen doses need to be investigated for wheat growth to determine the optimal management strategy for sustaining wheat production potential to ensure human food security. Therefore, a 2-year study (2020–2021 to 2021–2022) was conducted on wheat irrigated with different water qualities, including canal water (Ca), tubewell water (Tu) and mixed Ca-Tu water (Mx), each fertilized with two nitrogen doses, that is, N75 = 75 kgN.ha⁻¹ and N100 = 100 kgN.ha⁻¹. Ca⨯N100 performed best, with 5.12 t.ha⁻¹ grain yield, 11.60 t.ha⁻¹ biomass, 102.83 cm plant height and 1.32 kg.m⁻³ water productivity. The best values of the root mean square error (RMSE), normalized root mean square error (NRMSE), coefficient of determination (R²) and coefficient of residual mass (CRM) were 0.11, 0.12, 0.93 and −0.004, respectively, for calibration and 0.13, 0.15, 0.87 and ±0.01, respectively, for validation of the SALTMED model. The scenario simulation was performed for additional levels of water salinity (electrical conductivity [EC] = 8 and 12 dS.m⁻¹) and nitrogen doses (50, 125, 150 and 175 kgN.ha⁻¹). The results revealed improvements in wheat grain yield of 107%, 16% and −6% at EC = 8 dS.m⁻¹ and 125%, 31% and 5% at EC = 12 dS.m⁻¹, while the improvements in biomass were 113%, 22% and −2% at EC = 8 dS.m⁻¹ and 137%, 29% and 8% at EC = 12 dS.m⁻¹ with increasing nitrogen doses from 50–125 kg.ha⁻¹, 125–150 kg.ha⁻¹ and 150–175 kg.ha⁻¹, respectively. It is recommended that high-quality water with the lowest possible EC and nitrogen applications of up to 150 kgN.ha⁻¹ be adopted for wheat production in semi-arid areas of Punjab, Pakistan.