Formulate empirical models to optimize mustard irrigation level by using energy balance residual and benefit-cost analysis
Abstract
A two-year research study (2020-2022) titled "Formulating Empirical Models to Optimize Mustard Irrigation Levels Using Energy Balance Residual and Benefit-Cost Analysis" was conducted at the IRS Farm of Sam Higginbottom University of Agriculture, Technology and Science, Prayagraj, Uttar Pradesh, India. The study focused on irrigation scheduling based on the Energy Balance Residual for the mustard crop, specifically the Varuna (T-59) variety. The experiment followed a randomized block design (RBD) with five irrigation treatments: I1: λET = 1.75, total irrigation depth = 180 mm, I2: λET = 1.5, total irrigation depth = 240 mm, I3: λET = 1.0, total irrigation depth = 300 mm, I4: λET = 0.755, total irrigation depth = 360 mm, I5: λET = 0.5, total irrigation depth = 420 mm. Among these treatments, the highest yield (2.23 t/ha), 1000-seed weight (5.4 g), and harvest index (24.3%) were observed when irrigation was scheduled at λET = 1.5 with a total water depth of 240 mm (Treatment I2). Additionally, the maximum benefit-cost ratio (BCR) of 3.43 was recorded under this treatment. Furthermore, the residual method of energy balance demonstrated a satisfactory correlation between the benefit-cost ratio and irrigation depth, with a coefficient of determination (R² = 0.6808).
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Introduction
The Indian economy is based primarily on agriculture, and one of the best strategies to save water and energy is to time irrigation plays a crucial role in global agriculture, significantly enhancing crop productivity and ensuring food security. Approximately 80% of the water supply is currently used for irrigation. It is anticipated that this will decrease by up to 73%. Droughts have occurred in India recently. Drought-stricken areas were identified for the 2015-16 school year in Andhra Pradesh, Telangana, Karnataka, Maharashtra, Madhya Pradesh, Chhattisgarh, Odisha, Jharkhand, and Uttar Pradesh. Droughts must be prevented in all of these states through effective water resource management. In essence, irrigation scheduling is deciding how much and when to apply water to a field or crop. The primary objective of irrigation scheduling is to maintain an optimal level of soil moisture by applying an adequate depth of water while maximizing irrigation efficiency without compromising crop yield. Several methods are available for determining the appropriate timing of irrigation, including the, climatic approaches, soil water depletion method (deficit irrigation), plantbased indices, climatic approaches, and the critical growth stage method. Evapotranspiration (ET) estimation and irrigation scheduling are two applications of the residual method of energy balance. Its foundation is the idea that sensible heat flux (H), latent heat flux (λET), or ground heat flux (G) all use the energy that is available at the surface. India has the lowest productivity among the major mustard-growing countries. While China, the highest producer, achieved a productivity of 4.10 tonnes per hectare, India's average yield was only 1.4 tonnes per hectare during 2019-20. The highest productivity among Indian states was recorded in Haryana (2,058 kg/ha), followed by Gujarat (1,745 kg/ha), Rajasthan (1,720 kg/ha), Punjab (1,523 kg/ha), Uttar Pradesh (1,483 kg/ha), and Madhya Pradesh (1,422 kg/ha), with an overall national average of 1,499 kg/ha. In Uttar Pradesh, the average demand for mustard is 40 lakh metric tons. However, in the previous year, mustard was cultivated on 7.01 lakh hectares in the state, yielding a total production of only 10.08 lakh metric tons. This reveals a significant gap between demand and production in Uttar Pradesh. To bridge this gap, increasing mustard productivity through effective irrigation management is crucial. With this objective, research was conducted to develop empirical models for irrigation levels and the benefit-cost ratio of mustard cultivation under energy balance residual. 2.1 Calculation of soil moisture content: on the basis of oven-dry method (a soil sample is retrieved from the field, weighed, and then placed in an oven set at 105 °C for 24 hours) moisture of soil is calculated:-
Study Area
Total available water (TAW):
By deducting the quantity of soil water at the permanent wilting point from the amount at field capacity, the total amount of water for plant growth that is accessible between those two points is known as the capillary water. Permanent wilting point, (%), Zr = Effective root zone depth, (m). Using soil moisture constants, firstly total available water is determined for the experimental soil. For the purpose depth of effective root zone is taken 1m for mustard crop.
Readily available water (RAW):
The portion of the total accessible water (TAW) that easily obtainable by plants from the soil is known as readily available water. Crop rooting depth, soil type, and irrigation systems all play a major role in radial available water.
RAW = p TAW (2)
IW-depth of irrigation to be applied in one irrigation (mm).
The depth of irrigation:
The available water holding capacity of root zone TAW = 1000(θfc-θwp) x Zr TAW = 1000(0.28-0.16) x 1 TAW =120 mm, Water depletion from soil (p) for mustard crop = 0.5 from FAO-56 .Net depth of irrigation water in the root zone = water holding capacity of the root zone x Water depletion from soil (p). Net depth of irrigation = 120 x 0.5 = 60 mm.
Treatment details of residual method of energy balance
With three replications and five treatments, the field experiment is set up using a randomized block design. A 60 mm net irrigation depth is used. In terms of energy received per unit area, water depths can also be described.
Results and Discussion
Irrigation production efficiency for various irrigation schedule based on the residual method of energy balance showed in table The relationship between yield and depth of water (mm) influenced by residual method of energy balance.
Empirical model between irrigation levels and economic returns
Conclusion
In case of residual method of energy balance 240 mm depth of water seems to be desirable for highest yield of mustard crop (Varuna T-59) in sandy loam soil trans Yamuna area of Prayagraj under humid subtropical arid zone. The highest benefit-cost ratio (BCR) of 3.43 was observed with this treatment. Moreover, the residual energy balance method showed a strong correlation between the benefit-cost ratio and irrigation depth, with a coefficient of determination (R² = 0.6808).
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