Determination of Crop Coefficient and Water Requirement of Okra Crop by using Lysimeter for Parbhani District, Maharashtra

Okra (Abelmoschus esculentus L. Moench) is a highly valued crop, particularly for its mucilaginous pods that, due to their soluble fiber content, impart a distinctive slimy texture when cooked. The pods are versatile, consumed in various forms such as cooked, pickled, raw, or added to salads. In developing nations, okra plays a significant role in addressing malnutrition and food insecurity. Nutritionally, raw okra comprises approximately 90% water, 7% carbohydrates, 2% protein, and is a rich source of dietary fiber, vitamin C, and vitamin K (Gemede, 2015). While okra exhibits relative tolerance to water stress, it performs optimally when soil moisture is well-maintained, especially during germination and for achieving high yields. Varughese et al. (2014) emphasize the importance of fertigation with 100% of the recommended fertilizer dose delivered through drip irrigation for optimizing water use and crop yield. Thokal et al. (2020) recommend specific agronomic practices, including a crop spacing of 1200-450 x 150 mm, 100% RDF fertigation, 80% ETₓ drip irrigation, and the use of silver-black mulch to enhance productivity and water efficiency, particularly in the lateritic soils of the Konkan region. Crop water requirements vary throughout the growing season, influenced by changes in canopy structure, climatic conditions, cropping practices, and irrigation methods (Hamdy and Lacirignola, 1999; Katerji and Rana, 2008). Evapotranspiration (ET), encompassing both soil evaporation and plant transpiration, constitutes approximately 99% of the water uptake by plants. Therefore, measuring daily crop evapotranspiration (ETc) throughout the growth cycle is crucial for determining precise water requirements. Accurate estimation of ETc is essential for effective water management, as misestimating water needs can adversely affect economic, social, and environmental outcomes (Shideed et al., 1995; Katerji and Rana, 2008).

The crop coefficient (Kc), a critical factor in irrigation management, represents the ratio of ETc to reference evapotranspiration (ET₀). Kcvalues fluctuate during different growth stages and must be calibrated locally to ensure precise irrigation scheduling (Doorenbos and Pruitt, 1977; Milla et al., 2016). While generalized Kcvalues are available, region-specific data is imperative for effective irrigation planning at the local level.

In Maharashtra, characterized by arid and semi-arid climatic conditions, erratic rainfall patterns present significant challenges to agricultural productivity. The Marathwada region typically cultivates okra during June-July, September-October, and February-March, with the winter-sown crop demanding the highest water input. Given the increasing importance of okra cultivation in the region, afield experiment is proposed to quantify the water requirements and crop coefficients of okra. This research aims to facilitate improved irrigation planning and water resource management in the Marathwada region. With rising global water demand, irrigation is becoming an increasingly significant cost factor in agriculture. Effective irrigation scheduling, which is key to maximizing yields and enhancing water productivity, requires a solid understanding of crop water needs (Dabhi et al., 2020). One of the most commonly used methods to estimate crop water requirements is the FAO-56 Penman-Monteith (PM) method. This method calculates reference crop evapotranspiration (ETo) and multiplies it by crop coefficients (Kc) to determine crop evapotranspiration (ETc), with Kcvalues adjusted to account for the specific characteristics of different crops and their growing environments (Allen et al., 1998). Studies by Gul et al. (2018) highlighted the influence of water table depths on okra’swater usage and overall productivity, while Nyatuame et al. (2019) emphasized the importance of applying the right amount of water to maximize the efficiency of limited freshwater resources. Similarly, James et al. (2017) used a mini-lysimeter to measure water use in okra, further demonstrating the importance of developing irrigation systems that are specifically tailored to the needs of different crops.

Due to the highly site-specific nature of Kcvalues, determining them locally is crucial for optimizing irrigation management (Ramachandran et al., 2021). Although generalized Kcvalues, such as those found in FAO’s Irrigation and Drainage Paper No. 24 (Doorenbos and Pruitt, 1977), are widely applied, they can lead to substantial inaccuracies if not calibrated to local conditions. For instance, Vu et al. (2005) discovered a 17% error when using standard Kcvalues in paddy fields, which highlighted the need for local calibration. Awari et al. (2023) conducted a key study that determined Kcvalues for okra in the semi-arid Marathwada region of Maharashtra using a weighing-type lysimeter. Additionally, Awari and Khodke (2018) developed modified Kcvalues for gram in the Parbhani district, which differed significantly from FAO recommendations due to regional climate and farming practices.

Kcvalues are central to precision irrigation scheduling, as they are derived by dividing ETc by ETo. In a study by Hawari et al. (2023) in the Marathwada region, Kcvalues for okra ranged between 0.61 and 1.41, with the highest values observed around the 10th week. Their research provided Kcvalues of 0.64, 1.07, 1.33, and 0.86 for the initial, developmental, mid-season, and late stages of okra growth. These data are essential for developing more efficient irrigation strategies in similar climates. In sub-humid regions, Patil et al. (2018) examined how subsurface drip irrigation, both with and without plastic mulch, affected okra’swater use. Their research showed that plastic mulch reduced total evapotranspiration from 403 mm to 363 mm, as opposed to 512 mm and 468 mm without mulch. Furthermore, Kcvalues were found to be lower when using plastic mulch (ranging from 0.31 to 0.77) compared to without mulch (0.51 to 0.93). This illustrates how plastic mulch can reduce irrigation demands, lower evaporation losses, and improve crop yields.

Several studies have highlighted the variability of Kcvalues across different crops and climates. For example, Sagar et al. (2022) used a smart weighing lysimeter to calculate Kcvalues for Chrysanthemum grown in a greenhouse, with Kcvalues ranging from 0.43 to 1.27 depending on the crop’sgrowth stage. Similarly, Nigusi Abebe et al. (2021) developed Kcvalues for onions in Ethiopia using non-weighing lysimeters and found significant differences between local Kcvalues and FAO-56 recommendations. These findings underline the importance of site-specific calibration in water management. Environmental factors, such as elevated temperatures and vapor pressure deficits, can influence regional Kcvalues, as noted by Piccinni et al. (2009), reinforcing the need to account for local conditions when determining Kc. This study aims to determine the water requirements and crop coefficients for okra in Maharashtra’ssemi-arid Parbhani district using a weighing-type lysimeter. The results will provide more accurate crop water requirement estimates, aiding in reliable crop production and promoting sustainable water use practices in similar regions.