Long-term Cyclic Irrigation in Subsurface Drained Lands: Simulation Studies with SWAP

  •  A.K. Verma    
  •  S.K. Gupta    
  •  R.K. Isaac    


SWAP (Soil-Water-Atmosphere-Plant) version 2.0 was evaluated for its capability to simulate the crop growth and salinity profile for cyclic irrigation of saline waters at Sampla (India) having shallow water table provided with a subsurface drainage system. Cyclic mode with canal water (EC=0.4 dS m-1) and saline drainage water (EC=12.5-15.5 dS m-1) were used to calibrate and validate the model for the years 1989-91. Canal water was used for pre-sowing irrigation and thereafter, canal and saline drainage waters were used as per pre-decided irrigation modes like all CW, CW:DW, 2CW:2DW, DW:CW, and 1CW:3DW. Absolute deviations and standard error between the SWAP simulated and observed relative yields during calibration ranged from 1.3 to 1.8% and 1.7 to 2.2% respectively. A close agreement was observed between the measured and simulated soil salinity profile. It established the validity of SWAP model under the experimental conditions prevalent at the site. It could also be concluded that the crops could be grown very well under subsurface drainage conditions; but, in dry rainfall years, salinity build-up might occur. To achieve a yield potential exceeding 80%, it could be suggested that cyclic use of saline waters such as 1CW:1DW and 2CW:2DW could be used in such years. A pre-sowing irrigation with canal water could be helpful to overcome the build-up of salts and salt amount washing depends upon the rainfall. Thus, there seems to be no fear of use of cyclic irrigation under drained conditions. The same fact was established through the use of model SWAP.

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