SIMULATION OF SALINITY BUILDUP AND CORN (ZEA MAIZE) RESPONSE UNDER IRRIGATION MANAGEMENT PRACTICES USING SALTMED MODEL

Abstract

A field study was conducted to simulate salt buildup and corn (Zea maize) response under different irrigation management practices using SALTMED model. The experiment was carried out at Water Management Research Station, University of Agriculture, Jhang Road Faisalabad. Crop responses and salt variations were investigated under three treatments; firstly irrigation system (bed-furrow irrigation and drip irrigation systems), secondly water quality (good, marginal and poor quality waters), and thirdly irrigation frequency/interval (2, 4 and 6 days). The experiment was laid out in a completely randomized design (CRD) arrangement with three replications of all levels of different treatments in the experiment. SALTMED model was used to estimate soil moisture profile, soil salinity profile and yield comparison for corn (Zea maize). Calibration and validation of SALTMED model was also carried out using field data of different irrigation water qualities and frequencies under drip and bed-furrow irrigation systems. Field observations suggest that plant height, dry matter weight, grain yield and harvest index were all quadratically related with irrigation frequency since the variables performed better in 2 and 6 day frequency plots compared with those of 4-day plots. This is, perhaps, due to the fact that soil solution remains in dilute form in 2-day as against 4-day frequency plots, whereas in 6-day plots, the applied water leached salts out of root zone. Good quality water improved plant dry matter weight by 11.7% and grain yield by 7%. Salinity build up was again a quadratic function of irrigation frequency where the salt level was again maximum in 4-day irrigation frequency plots with 10.3 and 17.5% higher EC values compared with those of 2 and 6-day frequency plots respectively. This partly explains the poor crop responses in the 4-day frequency plots discussed above. As a matter of fact the total quantity of salts is obviously same under all the three frequency plots but the distribution of salts in the soil profile varies. Crop parameters registered better performance for bed-furrow irrigated plots compared with drip irrigated ones in respect of plant height (1.0%), dry matter weight (5.8%) and corn yield (21.9%). The reason being the drift of salts away from the root zone of the plants explains the healthy plants in the bed-furrow xivirrigated plots. However the bed-furrow irrigation cannot be preferred as it consumes more water for crop maturity. SALTMED model version 2013 was calibrated for dry matter weight, grain yield, soil moisture and soil salinity under 2-day frequency and poor quality irrigation water. All the required meteorological data were acquired from University Weather Station, Irrigation File for the model was prepared using data from the field experiments, plant parameters required by the model either measured or acquired from other sources, crop coefficients (K c , K cb , fc) and other data like matric and osmotic potentials were generated using the model. After successful calibrations of model, it was validated for other sets of treatments. For validation, one of the treatments (good quality water with 2-day irrigation frequency) was discussed and the model results for other treatments are appended. The model has successfully handled different hydro-dynamic processes acting simultaneously in soil and its performance to predict total dry matter weight, grain yield, soil moisture and soil salinity profiles under different soil types, climatic conditions and irrigation management practices was acceptable. The percentage relative error calculated for observed and simulated corn yield was about 3.69%. Both Percent relative error and Pearson values were calculated and found strongly supporting the validity of model.