Agriculture consumes the largest amount of water, often less efficiently. To address the food crisis, there is no alternative but to increase the area under irrigation, which can only be achieved by using current water resources judiciously for irrigating agricultural crops.
This article discusses how to economically and efficiently use water to increase crop production while minimizing water wastage.
Water Use Efficiency in Crop Irrigation
Crops require irrigation at different stages, so the scheduling of irrigation must be planned systematically. In the early stages, crops usually require lesser amounts of water, and any excess water applied is either wasted or leads to excessive vegetative growth rather than deeper root penetration.
More water is required during tillering, flower formation, and fruiting stages. If the soil is alkaline, saline, or the water contains more soluble salts, the water requirement increases.
The need for water varies depending on different factors such as season, tillage practices, vegetative growth, cropping system, and land shapes.
Climatic conditions, genetic variation in plants, agronomic practices, reduction of evapotranspiration, water stress, fertilizer application, and plant protection measures, including pest control, are all crucial elements in irrigation management.
Water Use Efficiency (WUE) refers to the ratio of crop yield to the amount of water depleted through evapotranspiration (ET). Water utilization by crops is generally described in terms of kilograms (kg) of yield per hectare per millimeter of water in the field.
Water use efficiency can be increased either by increasing the crop yield through the integration of productive inputs or by decreasing evapotranspiration through the adaptation of plant varieties to the micro-environment and other genetic and climatic improvements.
Optimal irrigation and production efficiency should also be considered in the economic evaluation of water use by crops.
WUE = Crop Yield / ET
Where WUE = Water Use Efficiency and ET = Evapotranspiration
Genetic variation in plants influences water use efficiency. Plants with a higher rate of photosynthesis usually have a higher water use efficiency, such as maize, sorghum, and sugar cane.
On the other hand, pulses, oilseeds, and cereals like wheat, barley, and oats tend to have lower photosynthesis rates and water use efficiency.
It has also been observed that hybrids and modern varieties have a higher rate of water use efficiency, both for agronomic and climatological considerations.
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According to water use efficiency, a comparison among different crops helps in selecting the right crop for cultivation. The table below shows water requirements and water use efficiency for various crops:
S/NCrop VarietiesWater Requirement (mm)Yield (kg/ha)Water Use Efficiency (WUE) per mm of Water1Rice120045003.72Sorghum50045009.03Maize62050008.04Wheat400500012.5
Productivity of Cereals per Unit of Water
From the above table, wheat shows the highest productivity, followed by sorghum, while rice has the lowest water use efficiency.
Guidelines for Efficient Water Use in Irrigation
The following are guidelines to improve irrigation practices for different field crops:
- Before irrigating, check the soil moisture in the root zone at several locations and estimate the amount of water required to bring the soil to field capacity. The moisture should be close to field capacity throughout the rooting depth.
- Determine the depth of water applied during irrigation to ensure that it covers the rooting depth.
- Ensure that the water applied corresponds to the amount needed by the crop. This helps to prevent both over- and under-utilization of water.
- During irrigation, check whether the intake opportunity time is uniform throughout the field. When irrigation is done by the border method, does the water stand about as long at the lower and middle parts of the field as it does at the upper end? Sprinkler and drip systems typically have more uniform water distribution than surface methods.
- Observe the amount of irrigation water flowing out of the field as waste. Irrigation water should always be evenly distributed to avoid runoff and wastage.
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Economic Use of Water in Agriculture
Water provides essential goods such as drinking water, irrigation water, and services like hydroelectricity generation, recreation, and amenity uses, which are utilized by agriculture, industry, and households.
The provision of many of these goods and services is interrelated, determined by the quality and quantity of available water.
Water is considered a “bulky” resource, meaning that its economic value per weight or volume tends to be relatively low. Therefore, transporting water over long distances is economically viable only if large volumes are involved.
The costs of abstraction (removal), storage, and conveyance of water are generally high relative to the economic value assigned to the use of additional units of water.
This creates location-specific water values, where water is most valuable when located where it is needed.
Further, the quantity of water supply is determined by various factors such as water flow, evaporation from the surface, and percolation into the ground. In the case of surface water, supply is largely determined by the climate, meaning the quantity supplied is variable and often unreliable.
This variability can limit certain uses of water, such as the development of water-dependent industries, and affect water values for irrigation.
The quality of water, particularly the concentration of pollutants, can exclude certain uses (e.g., drinking water) but have little impact on others (e.g., hydroelectric power generation).
Economic use of water in agriculture can be achieved through modern irrigation techniques, increasing farmers’ income while reducing costs related to irrigation.
Irrigated agriculture consumes 80% of the world’s developed water resources. However, there is a very poor rate of utilization of surface irrigation methods, with an efficiency of around 40%. This has led to increasing demands for improved irrigation efficiency using modern technologies.
Techniques such as drip irrigation achieve efficiency rates of 70-80%, with some systems exceeding 90%. Nevertheless, economic water use is not only a question of applied techniques; it depends heavily on water management, the application of technology, and the surrounding technical, economic, and socio-cultural conditions.
If water resources continue to decline and the cost of water increases, more advanced techniques like surface drip irrigation (SDI) may become a serious alternative to conventional systems.
One recommended method for improving water use efficiency in irrigation farming is to curb the water supply.
This method, known as deficit irrigation, involves supplying less water than needed for maximum yield, accepting slightly lower yields to avoid high irrigation costs that would be required to saturate plant growth potentials.
In economic terms, cost reduction through deficit irrigation can be aimed at maximizing financial profit per hectare or per cubic meter of water used.
Water has always been a vital part of agriculture. The quality and quantity of water used must be closely monitored to ensure its efficient and economic use.
While agriculture is no longer the largest user of water, it remains the largest consumer and must manage and utilize water resources wisely for various agricultural purposes
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