Estimation of crop water requirement of TS channel (Tungabhadra side channel) command of Krishna Western Delta using CROPWAT Model

Introduction

Efficient use of water in the state of Andhra Pradesh is becoming an important issue due to increasing irrigation water requirements as well as environmental sustainability. Since 1850s, the Krishna basin has seen an increasing mobilization of its water resources and dramatic development of irrigation, with little regard to limits of available water resources. This progressively lead to closure of basin (zero or minimal discharge to ocean) during 2001-2004 and surface water resources were almost entirely committed to human consumption uses, increasing ground water abstraction contributed to the decrease in surface water base flows and discharge to the ocean was almost zero. Total annual water requirement for agricultural use is exceedingly large especially for rice. Water required by a rice crop in a given period of time need to be considering for normal growth under field conditions. The amount of water required for a given crop depends on state of development of soil, quantity and type of fertilizer given, quality of water used and the climatic conditions. Measurement or estimation of the rate of crop water use is required for determination of irrigation water requirement. The available water for irrigation, however, is becoming increasingly scarce due to decreasing resources and quality, and increased competition from nonagricultural water users. Recently, the demand of water for industrial, municipal, and other use has been increasingly as less water will be available for agriculture. The estimation of crop water requirement through computer simulation and its comparison with actual application of irrigation water in Ponnur channel command of Krishna Western Delta. The farmers have applied 56.9% and 46.9% excess quantities of irrigation water than required in the years 2000-01, 2001-2002 while in the year 2002-03,15.3% less water than the required. In spite of applying more quantities of irrigation water in the years 2000-2001 and 2001-2002, the average yield of paddy crop in those years was less indicating that applying excess water is not at all advantageous and instead it is wastage of valuable resources Srinivasulu et al. (2003) [3] . The crop water requirement and irrigation scheduling of spring maize using GIS and CROPWAT model in Beijing-Tianjin-Hebei region were capable of extending the crop models to a regional level to estimate the spatial distribution of the evapotranspiration of spring maize, climatic water deficit and the yield reduction of spring maize under different rain fed and irrigated conditions Zhiming et al. (2007) [4] . Based on the water deficit analysis, supplemental irrigation schedule was developed using CROPWAT model.

Materials and Methods

The study area, Tungabhadra side channel, originating from Kommamur branch of Krishna Western Delta in Guntur district of Andhra Pradesh and is located at 16 0 04' N latitude and 80 0 34' E longitudes (Fig. 1). The details of the hydraulic particulars of Tungabhadra side command were given in Table 1. The cropping pattern followed was paddy-maize-fallow. The average rainfall from 2000 to 2012 was estimated to be 932 mm. As part of the research, conjunctive use planning of surface and ground water resources, the crop water requirement for rice and maize both kharif and rabi seasons respectively were estimated using windows based CROPWAT simulation programme model and is reported in this research article. The model is fed with meteorological data collected from Lam farm, Guntur. The weather data contains the average value of 12 years of data. The soil data corresponding to the study area was also incorporated. The cropping pattern is separately fed for rice and maize. The standard crop coefficient values were fed for arriving at crop evapo-transpiration at various stages of crop growth. The results obtained after running the model separately for kharif and rabi is reported and discussed in the next section.

Results and Discussion

The model calculated the effective rainfall in mm for each month taking the average monthly rainfall values for the study area. The weather data fed in the model was used to calculate the effective rainfall duly deducting the evapotranspiration and infiltration and deep percolation losses. The values of effective rainfall (mm) are given in Table 2. The same values are represented through Fig. 3. In the study area, the average monthly rainfall is found to be 932.3mm. Lowest rainfall is found in April and May months, highest average rainfall being in August month. As there is no source of irrigation either through rainfall or through canal releases, farmers keep their lands fallow during summer season. The summary of various input parameters which were incorporated in CROPWAT window are briefly summarized in Table 4. In the table, no. of days each crop growth stage, nursery area, critical depletion etc., were summarized and was read as the output of the model. The corresponding cropping pattern file options widow is also shown in Fig. 4. The summary of various input parameters which were incorporated in CROPWAT window for maize crop in rabi season are briefly summarized in Table 5. In the table, no. of days each crop growth stage, nursery area, critical depletion etc., were summarized and was read as the output of the model. The crop coefficients for various growth periods for paddy and maize crops (FAO-56) were drawn in Fig. 5. The same values were incorporated in the model for the two crops for Kharif and Rabi seasons respectively for arriving at irrigation water requirements on decade basis. It could be observed from the above tables that during kharif season, the effective rainfall is concentrated relatively higher than in rabi season. Hence the irrigation requirement is more in rabi season though maize is less water requiring crop than paddy.

Conclusion

The computer simulation model CROPWAT was applied to estimate crop water requirements of rice and maize crops grown in both the seasons. The decennial meteorological data for years 2000 to 2012 is averaged and given as input to the model. The study showed that a total of 275mm and 344 mm of water is required to be supplemented through irrigation for paddy and maize crops respectively. The area under cultivation is also lower than the actual potential especially during rabi season (3500 ha) as against kharif (4165 ha). Because of non-advisory services regarding crop selection, the effective utilization of ground and surface water is not followed in the command as against the recommendations of the Ground Water Board. This type of analysis would give the planners to recommend for any crop shifts for better income for the farming community.

References

1. Bhandarkar DM, Dhakad SS, Reddy KS, Singh R. Estimation of crop water requirement for important field and vegetable crops in Bhopal region. In: Proceedings of XXXVI ISAE Annual Convention & Symposium, Dr. BSKKV, Dapoli; 16-18 January 2004. p. 61.
2. George BA, Shende SA, Raghuwanshi NS. Development and testing of an irrigation scheduling model. J Agric Water Manag. 2000;46:121-136. http://www.gisdevelopement.com
3. Srinivasulu A, Satyanarayana TV, Ravi Kumar M, Sai Sudha JLN. Crop water requirement in comparison to actual applied in some canal commands of Krishna Western Delta. J Agric Eng. 2003;40(4):43-50.
4. Zhiming F, Dengwei L, Zang Y. Water requirements and irrigation scheduling of spring maize using GIS and Crop Water model in Beijing-Tianjin-Hebei region. Chin Geogr Sci. 2007;17:56-63.