Extensive land area in arid and semiarid regions of India has gone out of cultivation due to rise in water table and accumulation of salts leading to unfavourable soil-water-air relationships and decrease in crop productivity. Irrigation aspects of problem soil, waterlogged soils and use of poor quality irrigation water for crop production are briefly discussed.
1. Practices for Salt Affected Soils and Brackish Water:
Unfavourable soil-air relations and accumulation of certain elements in toxic proportions in plants limit crop growth on alkali soils. Alkali soils have low infiltration rates, reduced water availability and poor water transmission to growing roots. These constraints warrant controlled water management practices.
On coastal saline soils, 3-4 cm water at CPE of 50 mm resulted in wheat yield advantage over two normal irrigations. At Ludhiana, light and frequent irrigation with 5 cm depth was advantageous than less frequent irrigations.
Accumulation of salts is closely associated with soil texture. In general, accumulation of salts in a soil under normal drainage increase from coarse to fine textured soils by about two times. Thus, waters with EC of 12 to 16 dS m-1 could be used for tolerant and semitolerant crops like wheat, barley and mustard in coarse textured soils with an annual rainfall above 400 mm.
However, water with EC of more than 2 dS m-1 often create salinity problem in fine textured soils. Saline waters up to 6 dS m-1 for pearlmillet and cotton and up to 12 dS m-1 for wheat, barley and mustard can be used through sprinklers on undulating light textured soils, provided sprinklers are run during cool hours in summer.
These are situations where limited quantities of good waters are available in addition to saline water resources. These two supplies should either be mixed to bring the EC within permissible limits or used in alternate irrigations. The former option requires mechanism of mixing and several issues relating to decision on the mixing ratios. Potato yields did not differ considerably due to alternate irrigation with canal water and well-water with EC of 6 dS m-1.
Wheat and rice yields did not differ significantly due to one irrigation with brackish water after two irrigations with canal water of good quality. Seeding on conserved soil moisture or irrigation with good quality water during seed establishment and poor quality water at later crop growth stages is a good strategy under conditions of limited canal water availability. In areas with brackish groundwater, a reduction in canal water supply by at least 20 per cent would go a long way in reducing harmful effects of high water table, besides saving fresh water for needy areas.
2. Practices for High Water Table, Waterlogged and Flood Affected Areas:
Adequate drainage and efficient on-farm water management assume significance to sustain crop production on long term basis. Good quality groundwater at shallow depth considerably minimise supplemental irrigation, provided groundwater table is about 50 cm. Under such situations, one irrigation at crown root initiation is adequate for wheat. If the water table is medium (100-150 cm) two to three irrigations are adequate for wheat. There was significant reduction in irrigation needs of rice at Pantanagar when the water table was 50-100 cm.
Choice of crops for flood prone areas is closely related to depth and duration of water stagnation, receding duration of floodwaters, soil type, salt tolerance of crops, quality and quantity of irrigation water and other management practices. Rice and sugarcane crops perform better than other crops in flood prone areas. If the recession time of water is relatively longer, rice is ideal than sugarcane. All the crops need reduced depth and frequency of irrigation depending on duration of flooding. Sprinkler and drip irrigation systems can reduce excessive irrigation relative to flood irrigation.