The field experiment was conducted at Agricultural Research Station, Kasbe Digraj, Dist. Sangli during Adsali sugarcane season of 2012-13 to 2013-14. The experiment was conducted by installing subsurface drainage system with 10, 20, 30 and 40 m drain spacing and 1 m drain depth. In view of different costs and effectiveness of subsurface drainage associated with the varying depths and spacings, field evaluation of unsteady drain spacing equations was important for finding out the optimal drain spacing equation among various equations. The field evaluation of unsteady drain spacing equations revealed that the van Schilfgaarde, Hammad, Modified Glover, Guyon and Integrated Hooghoudt’s equation performed satisfactory for estimation of water table depths among seven unsteady drain spacing equations. The Glover-Dumm and Modified Glover-Dumm’s equations were not performed satisfactory for estimation of water table depths. Among unsteady drain spacing equations, van Schilfgaarde’s equation performed better and hence recommended for water table depth estimation and in turn for optimal design of subsurface drainage system under waterlogged Vertisols of Maharashtra.
An estimation of optimal design parameters of subsurface drainage system through monitoring of water table depths and drain discharges are expensive in terms of time and money. The simulation modeling is an effective tool for estimation of drainage design parameters at less cost and short time. In view to this, calibration of DRAINMOD model for prediction of water table depths and drain discharges were conducted by installing subsurface drainage system with 40 m drain spacing and 1.0 m drain depth at Agricultural Research Station, Kasbe Digraj, Dist. Sangli (Maharashtra) during 2012-13 to 2013-14. The field data on water table depth and drain discharge were used for calibration of DRAINMOD model. The input data files on climatic, soil, crop and drainage design system parameters were attached to DRAINMOD model and calibrated successfully. It is found that both observed and simulated water table depths and drain discharges showed a fluctuating trend and predicted both water table depths and drain discharges closely with the observed values during frequent rainy days and following the rainy days. The DRAINMOD model reliably predicted water table depths with a goodness of fit (R2 = 0.97), MAE (12.23 cm), RMSE (15.49 cm) and CRM (0.05); drain discharges with R2 of 0.93, MAE of 0.095 mm day-1, RMSE of 0.1876 mm day-1and CRM of 0.04. Thus, the calibrated DRAINMOD model can be used to simulate the water table depths and drain discharges in semi-arid climatic conditions of Maharashtra and in turn to estimate and evaluate drain spacing and depth.
:The field investigation entitled "Physical properties of waterlogged Vertisols under subsurface drainage system with different drain spacings and depths" was conducted on farmer's field at village Mouje Digraj which was located 3 km away from Agricultural Research Station, Kasbe Digraj, district Sangli (Maharashtra), India during Adsali sugarcane season (16-18 months crop duration) of 2012-13 to 2013-14. In order to fulfill the objective of the study, the bulk density, particle density, total porosity and basic infiltration rate of soil were determined at initial and 18 months after drainage with respect to twelve treatment combinations consisting of four drain spacings of (10, 20, 30 and 40 m) and three drain depths (0.75, 1.0 and 1.25 m). It was found that the subsurface drainage system with drain spacing of 10 m and drain depth of 1.25 m recorded highest per cent improvements in bulk density (20.99%), particle density (6.10%), total porosity (13.74%) and basic infiltration rate of soil (13.75%) following 18 months of drainage. However, these per cent improvements in physical properties of soil under different treatment combinations of drain spacings and drain depths were followed decreasing trends from the closer to wider spaced drains under fixed drain depth i.e. 10 m > 20 m > 30 m > 40 m and from deeper to shallower drain depth under fixed drain spacing i.e., 1.25 m > 1.0 m > 0.75 m. Further, the difference between maximum and minimum values of per cent improvement of these physical properties of soil among 12 different treatments combinations were not too large (3.05 to 8.41%) which was within the 10 per cent variation. Considering the economics of twelve different combinations of drain spacings and drain depths, the drain spacing of 40 m and drain depth of 1.25 m were found optimal for economically feasible production of sugarcane and optimum physical properties of waterlogged Vertisols of Maharashtra.
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