Implementation of FAO-CROPWAT 8.0 model for estimation of crop water requirement and planning of irrigation for Angul district, Orrisa, India

Introduction

Water for agriculture is becoming more and more limited, and severe water shortages are emerging in several countries, especially in India, as a result of the expanding demands for water from various sectors (IWMI 2010) [6] . More effective use of water in agriculture should be the main concern because it uses the most water in India (81%). An important input for the cultivation of crops is water. The area is experiencing a growing scarcity of crop water during the season, despite Orrisa State's average annual rainfall of 1401.9 mm. The scarcity's main natural causes are drought and aridity. The severe situation has recently been made worse by man-induced desertification and water shortages, while the population is growing and competition for water among various water consumer sectors has intensified. Furthermore, the extensive use of pesticides and fertilizers has lowered the quality of the available water. As a result, there are now fewer resources of pure water available. To guarantee appropriate use and distribution of the water among consumers as well as to the agricultural sector, better planning and management of the water resources are therefore required. Water conservation may be achieved by precisely planning and delivering the required amount of water in the given period of time and space. A scarce water resources and growing competitions for water will reduce its availability for irrigation. Achieving greater efficiency of water use will be a primary challenge for the near future and will include the employment of techniques and practices that deliver a more accurate supply of water to crops. Prediction of the crop water requirement is of vital importance in water resources management. Crop water requirements are normally expressed by the rate of evapotranspiration (ET) in mm day -1 or mm period -1 . One of the major practices adopted by the researchers for water requirement of crops is modelling. For determination of crop evapotranspiration and yield responses to water, CROPWAT 8.0 model is used which was developed by the FAO Land and Water Development Division (FAO 1992) [5] . It includes a simple water balance model that allows the simulation of crop water stress conditions and estimation of yield reductions based on well-established methodologies. Several researchers have used the CROPWAT 8.0 model for analyzing crop water and requirements in different parts of the world (Kar and Verma, 2005; Martyniak et al., 2006; Dechmi et al., 2003, Vikash et. Al., 2019) [7,8,3,11] . For different crops, the recommended irrigation schedule should be location-specific, taking into account the agro-ecological conditions and soil types. For effective irrigation scheduling, water balancing, canal design capacity, regional drainage, water resources planning, reservoir operation studies, and crop production potential assessment, scientific crop water needs are necessary.

Materials and Methods

Study area

Angul district is located in the centre of the state of Orrisa and lies between 20 0 49´N to 52°00´ N latitude and 85°05´E to 50°00´ E longitude. The altitude is between 564 to 1187 metres. The district has an area of about 150 kilometres. The normal annual rainfall of this area is about 1401.9 mm. It is the one of the hottest district in India where the maximum temperature goes up to 40.2 0 C during summer.

Soil data

There are mainly five types of soil available in the study area as: red loam, clay and heavy clay, medium textured red loam, black soil and river valley alluvial. The percentage variation and areal distribution of the different types of the soil texture are presented in Table 2. The model carries out calculations for reference evapotranspiration, crop water requirements and irrigation requirements in order to develop irrigation schedules under various management conditions. It allows the development of recommendations for improved irrigation practices, the planning of irrigation schedules and the assessment of production under rain-fed conditions or deficit irrigation (Adriana and Cuculeanu, 1999) [1] . The sequence of the applied methods in this study, using the model is as follow: 1. Computation of reference evapotranspiration, 2. Estimation of Crop evapotranspiration and 3. Effective rainfall computation.

Reference Evapotranspiration:

This parameter is calculated in the model, which uses the FAO Penman-Monteith method (Allen et al., 1998) [2] . In this model, most of the equation parameters are directly measured and can be readily calculated from weather data using the Equation 1.

where, ET o is reference evapo-transpiration (mm day -1 ), R n is net radiation at the crop surface (MJ m -2 day -1 ), G is soil heat flux density (MJ m -2 day -1 ), T is air temperature at 2 m height (°C), u 2 is wind speed at 2 m height (m s -1 ), e s is saturation vapour pressure (kPa), e a is actual vapour pressure (kPa), e s -e a is saturation vapour pressure deficit (kPa), Δ is slope vapour pressure curve (kPa °C-1 ), Υ is psychrometric constant (kPa °C-1 ).

Crop Evapotranspiration:

For calculation of crop evapotranspiration CROPWAT 8.0 model uses crop coefficient approach and crop water requirements of different crops have been estimated by summing up the crop evapotranspiration for all growth stages using the Equation 2.

where, ET c represents crop evapotranspiration, K c represents crop coefficient and ET o represents reference evapotranspiration.

Effective Rainfall:

It is the part of rainfall which is stored in the soil profile and helps in the growing of crops. Rainfall of Angul District in Orrisa is given in Table 3. The model applied USDA Soil Conservation Service method to calculate the effective rainfall (Smith, 1991) [9] using Equation 3 and Equation 4. Where, P eff represents effective rainfall (mm) and P tot represents total rainfall (mm)

Results and Discussion

Reference Evapotranspiration:

The simulated values of reference evapotranspiration (ETo) through CROPWAT 8.0 model using Penman-Monteith equation, for the Angul district along with the meteorological parameters is presented in the Table 4 and monthly distribution of reference evapotranspiration is shown in the Figure 2. From the result, it is revealed that the maximum ET 0 was found in May month (6.66 mm/day), which is mainly due to high temperature and wind velocity, whereas it is minimum in December (2.78 mm/day). The reference evapotranspiration is the function of temperature and is also affected by the relative humidity (RH).

Effective Rainfall:

The effective rainfall has been calculated for the study area with the help of USDA SCS method which is presented in Table 5 and Figure 3. This will provide help for the estimation of irrigation water requirement of rice crops for the research area. From the analysis, it was found that the effective rainfall was maximum in August month (157.

Crop Water Requirement:

The difference in the evapotranspiration and evaporation is considered as the water consumed by the crop and termed as crop water requirement. Estimated crop water requirement of major crops for Angul district has been presented in Table 6 and the water demand of crops presented in the Figure 4. The results show that the crop water requirement of rice crop is more in the month of January followed by April month within the study area. This is due to nearly high reference evapotranspiration in the same months. This is also due to the fact that, large quantity of water is needed during the growing and developing period of crops for various physiological functions. The crop water requirement is calculated for Angul district of Orissa State and it has been found to be maximum for Rice crop (844.6mm) followed by Mango (768.6mm), Citrus (464.1mm), Onion (388.5mm), Cowpea (326.8mm) and so on, whereas minimum is for Maize crop (3.4 mm). From the result, it is revealed that most of the crops have the average water requirement is in the range of 200mm to 300mm. A crop grown in a sunny and hot climate needs more water per day in comparison to a crop grown in a cool and cloudy climate.

Apart from sunshine and temperature, other climatic factors like wind velocity and humidity also influence the crop water need.

Based on the crop water requirement of major crops, irrigation water demand has been calculated for Angul district of Orissa State, which is shown in Figure 5 and Table 7. The water demand for crop will help in water management as well as in the irrigation scheduling in the study area. The areal variation of the net scheme of irrigation required has been shown in Figure 7 and Table 8.

Conclusion

This study will assist in determining the net irrigation water need and comprehending how meteorological parameters behave in relation to reference evapotranspiration. The findings unequivocally demonstrate that, in comparison to other times, crop water requirements are significantly higher during the summer. The findings of this study may aid in the creation of effective water management strategies, which will eventually aid in the effective use of the water resources that are now accessible.

Acknowledgement

AcknowledgmentsThe authors wish to acknowledge the technical and data support by the staff of the ICAR-Indian Institute of Soil & Water Conservation (Uttarakhand), India. Authors also put into record the deep appreciation to Dr. Anand Gupta, Scientist, ICAR-IISWC, Dehradun for their immense support during the preparation of the present manuscript.

References

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