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    Subsurface Drip Irrigation for Watermelon Cultivation in Sandy Soils

    Growing watermelon can bring a profitable trade to talented people who own small plots of land in hot, dry places. However, the typical soil in the region has little water storage, making stable water a difficult task. Overhead sprinklers or trench flows often lose much of their air and flow when poured over loose, air-filled soil. This risks low or mixed returns if plants do not have stable moisture levels in poor growing spots.

    Subsurface Drip Irrigation (SDI) provides a new craft that can help water flask tenders overcome the burden by placing wet pipes underground. In this narrative, I aim to show how SDI works, and stories from years of trying this pattern in my field. I hope to share the learnings fairly for others who wish to adopt this water-saving art to collect bounty in sandy soil. With careful planning and husbandry, I think SDI may prove to be the right solution for watermelon growth in tough spots.

    What is Subsurface Drip Irrigation?

    In a conventional drip irrigation system, emitters or drip tape are laid out on the soil surface beneath the crop canopy. While this method reduces evaporation compared to sprinklers, it still leads to some water loss through surface runoff on sandy soils. SDI improves on this by burying narrow-bore drip tape 4-6 inches below the soil line.

    Porous tubing with emitters spaced 12-24 inches apart is unrolled below the crop bed during land preparation. Backfill covers the tape, which is then connected to a buried mainline and filter station. Water is slowly applied directly to the root zone through ultra-low flow emitters, with minimal surface wetting to limit losses. Pressure compensating emitters ensure a consistent flow rate regardless of field elevation changes or distance from the source.

    Advantages of Subsurface Drip Irrigation

    SDI offers several advantages over surface irrigation for watermelons on sandy soils:
    • Reduces evaporation to 5% or less compared to 30-50% for sprinklers
    • Eliminates runoff through underground application
    • Applies water uniformly where roots can access it
    • Permits cultivation and weed control during irrigation
    • Less prone to damage from wind, freezing, or farm equipment

    With careful installation and management, SDI can achieve 80-90% application efficiency even on loose, rapidly draining soils. This conserves scarce water supplies while sustaining high yields.

    Site Preparation and Installation

    Proper site preparation and drip tape installation methods are crucial for ensuring a long-lasting and effective SDI system. The following steps are generally recommended:
    • Laser land leveling to grade the field within 1⁄4 inch over the entire area.
    • Soil analysis to determine texture, structure and pH to guide amendments.
    • For sandy soils, incorporate 2-4 inches of organic matter to improve moisture holding.
    • Lay out tape in straight lines on contour using stakes and twine for guidance.
    • Check for kinks and punctures as tape is unrolled. Bury at prescribed depth (6-10 inches for sandy soil).
    • Backfill carefully without shifting the tape or crushing emitters.
    • Flush and pressure test before planting to check for leaks.
    • Monitor system and adjust pressures as needed based on soil conditions.

    Proper installation is crucial to ensure uniform water distribution and tape lifespan. Taking time for thorough site preparation pays off in long-term system performance and yield stability.

    Fertilizer Management

    Efficient fertilizer management is also important when growing watermelons with SDI on sandy soils. Some best practices include:
    • Soil test to determine baseline nutrient levels and amendment needs.
    • Apply phosphorus, potassium and other slow-release nutrients in a band at tape depth during installation.
    • Use soluble nitrogen fertilizers compatible with drip systems in multiple small doses according to crop stage.
    • Inject fertilizers into the mainline rather than applying through emitters to avoid clogging.
    • Monitor crop growth and petiole nutrient levels to guide additional fertilizer needs.
    • Consider fertigation with micro-sprinklers or surface drip to supplement the root zone during periods of peak demand.

    Proper fertilization is key to support maximum yields, especially for heavy feeding crops like watermelons. SDI facilitates controlled nutrient delivery directly to roots for high fertilizer use efficiency.

    Managing System Operation of Subsurface Drip Irrigation

    Once installed, careful attention to system operation and maintenance is required to sustain optimal SDI performance over multiple growing seasons:

    1. Filtration

    A sand media filter cleans the water before it enters the system. Backflushing filters regularly according to pressure readings keeps emitters unclogged. Screen and disc filters provide additional protection for sandy water sources.

    2. Flushing and Inspection

    Flushing lines with chlorinated water after each harvest removes sediment buildup, controlling emitter clogging risks. Periodically inspect tape condition by digging up short sections, replacing damaged areas promptly.

    3. Pressure Regulation

    Pressure compensating emitters require regulated line pressure, usually 8-15 psi. Pressure gauges and inline pressure regulators ensure uniform flow along tape length for balanced moisture distribution.

    4. Irrigation Scheduling

    Soil moisture sensors or visual inspection guides irrigation event timing and duration based on crop water needs. Too frequent light irrigations can promote disease, while allowing soils to temporarily dry reduces pathogen pressure.

    5. Weed Management

    With no soil disturbance from cultivation, controlling weeds near tape lines requires careful spot spraying or mulching. Unchecked weeds compete severely for water on sandy soils.

    Proper system operation supported by regular monitoring and adjustments helps maximize SDI efficiency and watermelon yields over the long term even under water-limited conditions. Combined with other best practices, it can be a profitable solution.

    Additional Considerations

    A few other factors also merit attention for successful SDI-grown watermelon production on sandy soils:

    1. Mulching

    Organic or plastic mulches reduce evaporation, moderate soil temperature, and control weeds. They improve the microclimate for better plant establishment and yield potential.

    2. Cover Cropping

    Off-season green manures help increase organic matter content and improve the water holding ability of sandy soils over multiple years. They also scavenge excess nutrients that might leach below the root zone.

    3. Pollinator Habitat

    Watermelons require insect-mediated pollination, so maintaining flowering plants and ground nesting sites near fields supports robust populations of native bees. This enhances fruit set and marketable yields.

    With careful attention to all aspects of the production system, SDI shows great promise for sustainably growing watermelons and other moisture-sensitive crops on drought-prone sandy soils. Ongoing monitoring and adaptation to local conditions helps maximize its benefits for smallholder farmers.


    In conclusion, subsurface drip irrigation has emerged as an effective solution for watermelon cultivation in sandy soils prone to low and variable yields from conventional surface irrigation methods. By placing emitters below the soil surface, SDI conserves scarce water supplies through ultra-low evaporation and eliminates runoff losses common on loose, porous soils. Combined with proper site preparation, drip tape installation, fertilizer management, and operation/maintenance practices tailored to local soil and crop conditions, SDI can achieve reliable yields even during periods of water stress.

    For smallholders striving to earn consistent livelihoods from marginal lands, this precision irrigation technique deserves serious consideration. With continued adaptation, it shows great potential to strengthen food security in water-scarce regions. Please feel free to contact me if you have any other questions!

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