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The irregularity in monsoon has severely affected the water availability at surface and sub-surface systems. Diminishing surface and sub-surface availability has not only decreased the water availability, but it additionally affected the ecosystem and increased disastrous situations like floods and droughts, resulting problems of stress on groundwater recharge. Groundwater recharge is a technique by which infiltrated water passes through the unsaturated region of groundwater and joins the water table. It is based upon soil type, land use land cover, geomorphology, geophysical and climate (viz. rainfall, temperature, humidity etc.) characteristics of a region. Over the years, due to variations in weather pattern and overexploitation of aquifers groundwater recharge has decreased and groundwater level has reduced in the most parts of the country. This has led to severe water deficit problems in several parts of the country. This can be solved by different direct and indirect methods of groundwater recharge technology. This technology can reduce the wastage of water and enhance groundwater availability for uses in different sector like irrigation, domestic and industrial uses.

To achieve effective water allocation and planning, the information about Lentil crop water requirements, irrigation withdrawals, soil types and climate conditions were gathered from the study area i.e. Anantapur district of Andhra Pradesh (A.P). The main objectives of the study area wereto estimate the Lentil crop water requirement (i.e., evapotranspiration) and deciding the proper sowing time in semi-arid agro-climatic conditions.The CROPWAT 8.0 was used to estimate the climatic water deficit, net irrigation requirement (NIR) and gross irrigation requirement (GIR) under different rainfed and irrigated conditions with six different growing dates with aninterval of 10 days.The results showed that the best sowing dates were last week of September to 1st week of October, which gives thebest utilization of rainfall as effective rainfall. The net and gross irrigation requirement(NIR and GIR) varied from a minimum to maximum as 69.7 mm, 110.3 mm, 78.2 mm, 119.4 mm, 114 mm and 165.9 mm; respectively for all sowing dates. Thus by adopting a proper sowing date and irrigation scheduling criteria, it is possible to save 49.7 mm of water as NIR for theearly sown crop.

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SUMMARY :Groundwater exploration for irrigation is a costly and scare input in agriculture and plays an important role in increasing food production. Due to over use of groundwater resources, it has become very important to estimate the Crop Water Requirement for different crops. Unscientific and injudicious application of groundwater in the Anantapur region resulted in depletion of the groundwater table. Anantapur region was chosen as the study area as its sever water problem. To achieve effective utilization of the groundwater resources, there is a need to estimate the crop water requirement for different crops at different management levels to accomplish effective irrigation management in the Ananthapur region. It is important that the water requirements of the crops are known. This study was carried out using CROPWAT 8.0 model. The information about climatic conditions, soil types and cropping pattern were obtained in the study area to estimate the crop water requirement under rainfed condition. The crop water requirement for the different crops of Anantapur region is very essential for effective utilization of the groundwater and also to be increase the crop yield. The maximum quantity of effective rainfall observed during the month of September as 79.5 per cent of the monthly rainfall i.e. 101.7 mm and average annual effective rainfall was estimated over the period 1985 to 2012 as 85.5 % of the average annual rainfall i.e. 526 mm out of 615.4 mm of average annual rainfall. The crop water requirement for the groundnut Kharif and Rabi crops in the Anantapur region was estimated as 591.3 mm and 443.3mm, respectively and for the vegetables, cotton, rice, grains and maize in the Anantapur region are to be 594.1 mm, 878.6 mm, 1110.6 mm, 699.9 mm and 679.3 mm, respectively. Efficient water management becomes crucial and critical in normal or deficit rainfall years.HOW TO CITE THIS ARTICLE : Babu, R. Ganesh, Veeranna, J., Kumar, K.N. Raja and Rao, I. Bhaskara (2014). Estimation of water requirement for different crops using CROPWAT model in Anantapur region. Asian J. Environ. Sci., 9(2): 75-79.