Managing drainage water at farm level

Irrigated agriculture has contributed to the development of many countries, especially in semi arid and arid regions, and to the food security around the world. One of the negative impacts of irrigated agriculture is salinization due to concentration of salts following evaporation of irrigation water, and water logging due to inappropriate irrigation methods. Drainage of irrigated lands mitigates these two concerns. However, disposal of drainage itself has become a major issue, which threatens long-term productivity of irrigated lands. Consequently, a dire need arises to promote and adopt strategies and practices to reduce drainable surplus and to use generated drainage effluent safely for environmentally sustainable irrigated agriculture. This paper reviews the strategies and measures being developed and practiced around the world as well as in Pakistan to manage agricultural drainage waters at farm level and to extract recommendations most appropriate in the local context of Pakistan. Available options to minimize and reuse drainage effluent include: (i) source control, which covers on- farm water management measures, agro-forestry, biological drainage, design of drainage system, and deficit irrigation practice; and (ii) reuse of drainage effluent, which covers direct and conjunctive use (blending or cyclic use). The main conclusions and recommendations derived from the review are: (1) for water table depth of 0-1 m, wheat on bed planting (95 cm wide bed) could result in 30-35 percent yield increase and 30-40 percent water saving with high water use efficiency (WUE) of 2 kg/m3 compared to flat basin planting (1.5 kg/m ). Cotton can give highest WUE of 3.5 kg/m3 on bed and furrow planting compared to flat planting (1.4 kg/m3). Adoption of bed (95 cm width) planting of wheat and cotton in high water table areas would result in reduced irrigation requirements and consequently reduced drainable surplus; (2) Direct use of saline sodic drainage water cannot be made for crop production without proper soil, water and crop management. Under these conditions, frequent light irrigations, use of gypsum and H2SO4 alongwith adequate leaching, growing salt tolerant crops in proper sequence are required to use saline sodic drainage water for irrigation on sustainable long-term basis; (3) cyclic water management strategy has great value in dual crop rotation, which includes salt sensitive and salt tolerant crops. In cyclic use, salt sensitive crops in rotation are irrigated with low salinity water and salt tolerant crops like cotton, sugar beets and wheat are irrigated with saline drainage water. For salt tolerant crops, switch to saline water is usually made after seedling establishment, pre-plant irrigation and initial irrigation being made with low salinity irrigation water; (4) cyclic strategy is more beneficial as compared to blending strategy, for sustained use of saline drainage water as part of a drainage water reduction scheme provided sufficient rainfall or low salinity water is applied to maintain a salt balance in the soil; and (5) for optimum growth of wheat, tubewell water should be mixed with canal water in 1:1. Under scarce surface supplies, the saline groundwater should be used alternately with canal water.