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Salt and water balance studies using SALTMOD for Tungabhadra command, peninsular India
Abstract
Long-term field experiments are required to develop suitable salt and water balance strategies, but are expensive, site-specific and time consuming. Simulation models, once calibrated using experimental information, could aid as management and decision tools to obtain quantitative guidance in developing and evaluating drainage and irrigation strategies. SALTMOD, a computer programme has been found to be useful for prediction of the salinity of soil water and water table depth in irrigated agricultural lands using different (geo) hydrologic conditions. Field experiments on subsurface drainage (drain spacing, 150 m and drain depth, 0.75 m) were conducted during 1998-2006 near Sindhanur, Karnataka, India in an area of 62 ha. Data collected from the pilot area, where rice-rice cropping sequence was followed, have been used to develop various scenarios of salt build-up and status of the water table. The SALTMOD model predicts that due to existence of subsurface drainage system, root zone soil salinity may be reduced to about 2.5 dS m-1 (from an initial value of 8.5 dS m-1) within two years. Controlled drainage during rabi (dry winter season) only and during the critical crop growth stages in both the cropping seasons (rabi and kharif, the wet summer season) had little effect on the build-up in root zone soil salinity; the root zone soil salinity was maintained within a safe limit (< 4.0 dS m-1). Complete blocking of the drainage system during both the cropping seasons had adverse effect and led to be build-up of soil salinity.
... To prolong the period of salt moderation for as long as possible during crop growth and development, we recommend using layers of over-irrigation, the use of municipal treated wastewater should be a viable option [10]. The leaching process should be accompanied by the application of chemical enhancers to improve the natural soil drainage to evacuate salts, as well as the construction of artificial salt-containment [39]. ...
The aim of this study was to evaluate the initial salinity and the type and amount of salt evacuated from soils of palomas, san luispotosí in a leaching process. These soils present primary and secondary salinization problems, induced by irrigation which affects their productive capacity. The study was conducted in a greenhouse and in the soils laboratory of the graduate college, from april to august 2010. Leaching of salts was done in soil columns that were applied with three soil-water extraction ratios, namely, 1≈0.2-0.6, 1:5 and 1:10, and the normal rates of leaching = 0 , 1.5 AND3.0, where: q a is the volume of water at which a soil reaches its saturation capacity, plus another equal volume, and so on. Q π is the volume of water needed to make the soil reach its saturation capacity. This rate corresponds to volumes of water applied under field conditions of 1971.72 m 3 ha-1 , 2,957.58m 3 ha-1 , and 5915.16m 3 ha-1 , respectively. The initial salinity of each ratio was 4203 69.03 mgha-1 , 153.59mg ha-1 and 201.37mg ha-1. The higher extraction ratio and rate of leaching applied, the higher the amount of soluble salts leached, and the lower the average residual salinity of 0-50 cm soil layer. At zero leaching level no leachate was obtained. The extraction ratio 1:10 and the rate of leaching = 3.0, was significantly (p=0.05) outstanding. Under these conditions appreciable amount of salts were leached off the topsoil, especially nacl and na 2 so 4. The residual salinity of the 30 cm soil layer was 1.68 g salt 100 g-1 of soil (109.48 mg ha-1). This indicates desalination.
The salt and water balances at Konanki pilot area in Nagarjunasagar project right canal command in Andhra Pradesh State of India were analysed using SALTMOD. The model was calibrated by using two-year data collected in the pilot area. From the calibration, the leaching efficiencies of the root and transition zone were estimated as 65% and the out going natural sub-surface drainage was determined as 50 mm per year. The model predicts that the root zone soil water salinity will be reduced to 4, 3 and 2.5 dS/m (from an initial value of 11.5 dS/m) during the first, second and third seasons within six years after installation of the drainage system. Next, the situation prior to the installation of the drainage system was reconstructed using the model. Finally, sensitivity analyses were made to study the effects of varying drain depth, spacing and amount of irrigation water applied on root zone salinity and depth to water table. Here, the model predicted that closer than the present spacing or further deepening of the drains from the present depth of 1 m to 1.4 m will not have any better influence on the reduction of the root zone salinity than in the present situation. These simulations also suggested that by applying 80% of the present amount of irrigation water, the root zone salinity can be brought down to 5 and 4 dS/m by second and fourth years, respectively and this will in turn reduce the problem of water logging and salinity to some extent.
Utility of subsurface drainageas an intervention to reclaim waterloggedsaline lands and to ensure sustainabilityof irrigated agriculture in India has beenestablished through experiments and pilotresearch conducted for over a century.While tracing the history of subsurfacedrainage in the 20th century, thispaper lists several pilots conducted in preand post independence periods. An attempthas been made to critically review thefindings emerging out of such a largenumber of pilots. Salient findings thatcould serve as design guidelines or tooperationalize the systems in an effectiveand eco-friendly manner have been puttogether for their application in future.It is believed that large scale drainageprojects would increasingly be implementedin India and many other developingcountries. In the opinion of the author,the knowledge generated in this centurywould help to design and plan subsurfacedrainage activities on which rests the foodand nutritional security of India and manyother developing nations.
With the introduction of irrigation in areas with rolling topography, low-lying areas are prone to water logging and soil salinization. The problems also occurred in the valley bottoms of the Tungabhadra Irrigation Project (TBP). Subsurface drainage was applied to reclaim the waterlogged saline land in an area of 62 ha (1 ha = 10,000 m2). The drainage system consisted of three pipe drains laid parallel to the valley brook at a spacing of 150 m. The monitoring and evaluation of the system revealed that the water table was lowered; electrical conductivity (EC) of the soil decreased and crop yield and cropping intensity increased in the drained area. Hence, the intervention effectively reclaimed the land, even though the spacing was unusually wide. The cultivation of submerged lowland rice aided in the leaching of salts within a period of one year. Originally the drains were thought to function as interceptor drains and their main effect would stem from intercepting the underground seepage water from the canals in the upland. On the other hand, while assessing the performance of the system, it was observed that drainage discharge and EC of the drainage effluent in all three drains were of the same magnitude. It emerges, therefore, that the system was rather working as a normal subsurface drainage system than as an interceptor system.