Irrigation Requirements and Efficiencies

 

Irrigation plays a crucial role in agricultural productivity by ensuring crops receive adequate water for optimal growth and yield. Effective irrigation management requires knowledge of the different methods, timing, influencing factors, and efficiency measures to maximize water use while minimizing losses.

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General Methods of Irrigation

There are four primary methods of irrigation, each with unique requirements, applications, and suitability to land slope.

Surface irrigation, which includes flooding and furrows, is the most traditional method. In this system, water is conveyed by gravity and allowed to flow over the soil surface, either by flooding the entire field or directing it along furrows between crop rows. Field ditches, bunds, and channels are constructed to guide the water. This method is best suited for flat or gently sloping lands with fine-textured soils that allow uniform distribution of water. It is widely practiced in rice fields across Southeast Asia due to its low infrastructure costs and simplicity (Bouman et al., 2007).

Subsurface irrigation, on the other hand, delivers water underground directly to the root zone using perforated pipes, subsurface drains, or buried channels. By minimizing evaporation and surface runoff, this method ensures a more efficient supply of water. It is particularly effective on flat lands with uniform soil profiles and high water tables. Subsurface irrigation is often used for high-value crops such as vegetables and orchards, and it is a common practice in greenhouse vegetable production in the Netherlands, where precise soil moisture management is essential (van der Ploeg et al., 2002).

Drip or trickle irrigation is a modern and highly efficient system that delivers water directly to the root zone in small, controlled amounts through emitters attached to pipes. This minimizes losses from evaporation and deep percolation. The system typically includes mainlines, sub-mains, lateral pipes, emitters, and filters to ensure clean and consistent flow. Drip irrigation is particularly suitable for uneven or sloping lands, arid and semi-arid regions, and high-value crops like grapes, citrus, and vegetables. Israel has pioneered and revolutionized the use of drip irrigation, enabling farmers to cultivate crops in arid regions with limited water resources while achieving high water use efficiency (Postel, 2001).

Sprinkler irrigation is another widely adopted method, where water is sprayed into the air under pressure and falls onto crops like rainfall. This system requires pumps, pipelines, sprinkler heads, and risers to operate efficiently. It can be applied on lands with moderate slopes and permeable soils, making it versatile for a wide variety of crops, including grains, vegetables, and lawns. Sprinkler irrigation is especially popular in the U.S. Midwest, where it is used to irrigate large fields of corn and soybean, ensuring even water coverage across vast areas (USDA, 2019).

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Considerations Influencing Irrigation Timing and Quantity

The decision on when and how much to irrigate depends on several factors:

• Crop water needs – Different crops require different amounts of water depending on their growth stage.

• Water availability – Limited water resources necessitate efficient allocation.

• Soil water-holding capacity – The ability of the root zone to store water influences irrigation frequency and depth (Michael, 2008).

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Influence of Restricting Soil Layers

Restrictive soil layers, such as compacted horizons or hardpans, significantly affect root growth and irrigation practices:

• Roots concentrate above the restricting layer.

• A 10% reduction in soil voids generally prevents root penetration (Hillel, 2004).

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Stages of Growth Affecting Irrigation Practices

Different crop growth stages have varying water requirements:

• Vegetative stage – Water consumption increases steadily.

• Flowering stage – Peak water demand occurs.

• Fruiting stage – Water use declines gradually.

  • Wet fruiting – Occurs after flowering with high water demand.

  • Dry fruiting – Water demand decreases as transpiration ceases, leading to dormancy (Doorenbos & Kassam, 1979).

Notably, the depth of the root zone expands during vegetative and flowering periods.

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Estimating Irrigation Diversion Requirements

Standard Procedure

1. Steps

   • Determine crop evapotranspiration (ET).

   • Consider monthly rainfall.

   • Account for conveyance, seepage, and ditch losses.

   • Include dimensions of laterals and ditches.

   • Identify the total irrigated area.

2. Required Data/Assumptions

   • ET per day (mm/d).

   • Percolation rate (mm/d).

   • Effective rainfall (mm).

   • Conveyance and seepage losses by soil type.

   • Drainage requirement (~25% of water requirement).

   • Gate leakage (~5% of farm delivery).

   • Canal leakage (~100% of seepage loss).

3. Computations

   • Water Requirement: WR = ET + P

   • Farm Irrigation Requirement: FIR = WR + farm waste – effective rainfall

   • Farm Turnout Requirement: FTR = FIR + farm ditch losses

   • Total Diversion Requirement: TDR = FTR + conveyance losses (CL)

Where:

• CL = seepage losses + gate leakage + canal leakage

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Irrigation Efficiencies

Efficiency metrics evaluate how effectively water is used in irrigation systems.

1. Water Conveyance Efficiency (Ec)
   $Ec = \frac{Wf}{Wr} \times 100$

   • Wf: Water delivered to the farm

   • Wr: Water diverted to the farm

2. Water Application Efficiency (Ea)
   $Ea = \frac{Ws}{Wf} \times 100$

   • Ws: Water stored in the root zone

   • Wf: Water delivered to the farm

   Losses include:

   • Rf: Surface runoff

   • Df: Deep percolation below the root zone

   Thus: $Ea = \frac{Wf – (Rf + Df)}{Wf} \times 100$

3. Water Use Efficiency (Eu)
   $Eu = \frac{Wu}{Wd} \times 100$

   • Wu: Water beneficially used

   • Wd: Water delivered

4. Water Storage Efficiency (Es)
   $Es = \frac{Ws}{Wn} \times 100$

   • Ws: Water stored in root zone

   • Wn: Water needed in root zone

5. Water Distribution Efficiency (Ed)
   $Ed = (1 – Y/D) \times 100$

   • Y: Average numerical deviation from average stored depth

   • D: Average stored water depth

6. Consumptive Use Efficiency (Ecu)
   $Ecu = \frac{Wcu}{Wd} \times 100$

• Wcu: Normal consumptive use of water

• Wd: Net water depleted from soil root zone

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Conclusion

Efficient irrigation is essential for maximizing crop yields while conserving water resources. By selecting appropriate irrigation methods, considering crop and soil characteristics, and calculating water requirements accurately, farmers can reduce losses and enhance sustainability in agricultural production. Case studies from around the world, such as drip irrigation in Israel, surface flooding in Asia, and sprinkler systems in the United States, highlight the diverse applications of irrigation methods and their importance in global food production.

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References

Bouman, B. A. M., Humphreys, E., Tuong, T. P., & Barker, R. (2007). Rice and water. Advances in Agronomy, 92, 187–237. https://doi.org/10.1016/S0065-2113(04)92004-4

Doorenbos, J., & Kassam, A. H. (1979). Yield response to water. FAO Irrigation and Drainage Paper No. 33. Food and Agriculture Organization of the United Nations. https://www.fao.org/3/i2800e/i2800e.pdf

Hansen, V. E., Israelsen, O. W., & Stringham, G. E. (1992). Irrigation principles and practices (4th ed.). Wiley.

Hillel, D. (2004). Introduction to environmental soil physics. Academic Press.

Michael, A. M. (2008). Irrigation: Theory and practice (2nd ed.). Vikas Publishing House.

Postel, S. (2001). Growing more food with less water. Scientific American, 284(2), 46–51. https://doi.org/10.1038/scientificamerican0201-46

USDA. (2019). Irrigation and water management survey 2018. United States Department of Agriculture. https://www.nass.usda.gov

van der Ploeg, R. R., Böhm, W., & Kirkham, M. B. (2002). On the origin of the theory of mineral nutrition of plants and the law of the minimum. Soil Science Society of America Journal, 63(5), 1055–1062. https://doi.org/10.2136/sssaj1999.6351055x