JWSS - Journal of Water and Soil Science

Infiltration is the most crucial process affecting surface irrigation uniformity and efficiency as it is the mechanism that transfers and distributes water from the surface to the soil profile. As a direct method of infiltration measurement, the volume balance method requires time, accuracy and high costs. Moreover, before the land preparation and at the research phase the use of this method is not feasible. The revised USDA- NRCS method is used to convert the infiltration parameters to different hydraulic conditions. In this study, the accuracy of the original and revised USDA-NRCS method in the estimation of furrow irrigation infiltration parameters in Amir Kabir Agro Industrial sugarcane fields of Ahvaz was evaluated. For this purpose, infiltration parameters and the cumulative 6 hour infiltration for furrow irrigation systems of this region were estimated using four methods of original USDA- NRCS, revised USDA- NRCS for border irrigation, revised USDA- NRCS for furrow irrigation and field measurement (inflow-outflow). For evaluation of the results, four indices including average prediction error of model (Er), distribution into 45° line (λ), determination coefficient (R2) and average relative error of model (Ea) were used. According to the results, the revised USDA- NRCS method for border irrigation with average values of λ, R2, Er and Ea equal to 0.95, 97, 6.5 and 7.6 percent, respectively was the best estimate of cumulative infiltration.

Simulation of water and solute transport in soil is very useful for optimum management of water and fertilizer use. In this study, the HYDRUS-1D model was used to simulate water and nitrate transport in furrow irrigation of sugarcane. For this putpose, a large-scale experiment was performed as a split plot design based on the randomized complete blocks with 3 replications in a 25-hectare piece of land in the Dehkhoda Sugarcane Agro-Industry Company from March 2012 to October 2013. The main factor was split application of fertilizer at three levels: two, three and four splits. The sub-main factor was fertilizer amount, applied at three levels (i.e. 350, 280 and 210 kg urea corresponding to 100%, 80% and 60% fertilizer requirements, respectively). Soil hydraulic parameters were estimated through inverse modeling using moisture data collected during more than 4 months of the sugarcane growing season. Solute transport parameters were then estimated using the hydraulic parameters and nitrate concentration data. In this study, statistical criteria including R², RMSE, ME and SSQ were used to compare the observed and simulated values of moisture content and nitrate concentration. The results indicated that R² for simulated moisture content and nitrate concentration in four splits and 60% fertilizer requirement treatment (i.e. calibrated treatment) were 62.7 and 91.2 percent, respectively. Cumulative infiltration depths were about 46 and 58 mm for calibration and validation treatments, respectively. For these treatments, the cumulative evapotranspiration rates were 50 and 60 mm, respectively. Soil moisture content in the surface layer varied from 21 to 45 and 21 to 42 percent, for calibration and validation treatments, respectively while the changes in the deep layer moisture content were 33 to 38 percent, for both treatments.