Why Do Arkansas Soils Require Adjusted Irrigation Practices

Arkansas agriculture spans a wide range of climates, crops, and soil types. From the Mississippi Alluvial Plain in the east to the Ozark Highlands in the north and west, soil physical and chemical characteristics vary enough that the same irrigation approach will perform well in one place and fail in another. This article explains the key soil properties that force growers and water managers in Arkansas to adjust irrigation timing, method, and volume, and provides concrete, practical guidance for making those adjustments in common cropping systems.

Overview of Arkansas soils and why they matter for irrigation

Soil controls how water moves, how much water is available to plants, how quickly salts accumulate or leach, and whether applied water will pond or run off. In Arkansas, major soil-related drivers of irrigation decisions include texture and structure (sand, silt, clay content and aggregation), profile depth and restrictive layers, drainage class and water table depth, organic matter content, bulk density and compaction, and spatial variability across fields.
Arkansas features three broad soil-landscape zones that illustrate the differences:

• The Mississippi Alluvial Plain (Delta): deep silty clay loams, clayey soils, high shrink-swell clays in places, variable drainage (poorly drained depressional areas to well-drained ridges). These soils tend to hold water but have slow infiltration and drainage.
• The West Gulf Coastal Plain and loess-covered terraces: silty loams and sandy loams with moderate water-holding capacity and better infiltration than heavy clays.
• The Ozark and Ouachita Highlands: shallow soils over bedrock, coarser textures in places, lower water-holding capacity, and rapid drainage.

Each of these soil conditions changes how and when irrigation should be applied to maximize crop yield, minimize water loss, and reduce environmental risk.

Key soil properties that dictate irrigation adjustments

Texture and infiltration rate

Soil texture is the primary determinant of infiltration rate and plant available water. Coarse-textured soils (sands) have high infiltration and low water-holding capacity; fine-textured soils (clays) have low infiltration and relatively high water-holding capacity per unit depth but may restrict root growth.
Practical effects and responses:

• Sandy fields dry out quickly and require more frequent, smaller irrigation events to avoid stressing the crop and to reduce deep percolation losses.
• Clayey fields infiltrate slowly; applying water too quickly causes runoff and uneven wetting. Use lower application rates, multiple cycles (pulse irrigation), or surface practices that improve infiltration.

Approximate available water holding capacities (AWHC) to consider:

• Sand: 0.5 to 0.8 inches of water per foot of soil.
• Loam: 1.5 inches per foot.
• Clay loam/clay: 1.6 to 2.0 inches per foot.

These numbers help determine how much water to apply to refill the active root zone.

Soil depth, restrictive layers, and perched water tables

Shallow soils over rock or with hard pans restrict root depth and reduce the volume of soil that can supply water. Conversely, soils with impermeable layers near the surface can create perched water tables that maintain wetness near roots even when the rest of the profile is dry.
Management responses:

• Measure effective root zone depth for your crop and adjust refill targets accordingly.
• In fields with restrictive layers that cause poor drainage, consider tile drainage or surface drainage improvements before heavy irrigation.
• Avoid over-irrigating shallow soils; apply smaller, more frequent amounts based on the reduced available water.

Compaction and bulk density

Compaction reduces infiltration and root growth, causing more runoff and less usable water. Fields that have experienced heavy traffic or poor tillage practices will often require adjusted irrigation scheduling and remediation.
Corrective measures:

• Use deep tillage or subsoiling where appropriate to break compaction.
• Adopt controlled-traffic farming and reduced axle loads to prevent re-compaction.
• Apply irrigation at rates that match reduced infiltration until structure is restored.

Salinity and sodicity risks

Although Arkansas is not generally a highly saline region, localized salinity and sodicity issues can occur, particularly where irrigation water quality is poor, drainage is inadequate, or sodic parent materials occur. High sodium levels disrupt soil structure and reduce infiltration.
Practical guidance:

• Test soil EC and SAR and test irrigation water quality periodically.
• For sodic soils, apply gypsum as an amendment and ensure sufficient leaching to remove displaced sodium.
• In saline situations, increase leaching fraction through periodic higher-volume irrigations when drainage is available.

Crop-specific considerations in Arkansas

Rice, soybeans, corn, cotton, and specialty crops each interact with soils differently and require tailored irrigation strategies.

Rice

Rice is commonly grown in the Delta where soils are fine-textured and poorly drained. Flood irrigation for rice has unique challenges:

• In porous sandy patches or on levees, percolation losses can be high; manage water levels and consider lining or sealing channels.
• On heavy clays, maintain appropriate levee height and monitor seepage; controlled mid-season drainage improves root oxygenation in some systems.
• Adjust ponding depth and water turnover to match soil permeability. In high-percolation areas, more frequent water replenishment is needed.

Corn, soybeans, and cotton

These row crops demand timely soil water in the root zone during critical growth stages. Soil type dictates depletion thresholds:

• Sandy soils: irrigate when 30 to 40 percent of plant-available water (PAW) is depleted.
• Loam to clay soils: growers can allow 45 to 60 percent depletion before irrigating, depending on crop sensitivity and weather.

Using AWHC and root depth, compute the inches to replace and plan irrigation events to restore the profile to 80-90 percent of field capacity, adjusting for irrigation efficiency and distribution uniformity.

Practical irrigation scheduling method for Arkansas soils

1. Determine soil texture and effective root depth for the specific field and crop.
2. Calculate available water holding capacity (AWHC) for the root zone (AWHC per foot times root zone depth).
3. Establish the allowable depletion fraction (e.g., 40 percent for sandy soils for corn, 50 percent for deep loams for less sensitive stages).
4. Monitor current soil moisture with sensors (tensiometers, capacitance probes, or manual soil moisture measurement) or estimate using crop evapotranspiration (ETc = ETo x Kc) and rainfall.
5. Apply the calculated irrigation amount to refill the profile to the target refill point (usually 80-90% of field capacity), accounting for system efficiency and distribution uniformity.
6. After irrigation, monitor for runoff, ponding, or uneven distribution and adjust application rates or frequencies to match infiltration characteristics.

On-field tactics to match soil behavior

• Manage application rate to infiltration rate: avoid exceeding the soil’s infiltration capacity; for heavy clay soils a conservative application rate or multiple applications are often necessary.
• Use surge or pulsed furrow irrigation to increase infiltration in some soils while reducing runoff.
• Implement field leveling and precision grading to reduce variability and tailwater loss in furrow or flood systems.
• Install tile drainage or raised beds in poorly drained fields to improve aeration and rooting, especially for row crops.
• Consider subsurface drip irrigation in high-value specialty crops or where surface applications lead to excessive evaporation or runoff; choose tubing depth and spacing to account for soil texture and root architecture.
• Promote soil health practices such as cover cropping, residue retention, and reduced tillage to increase organic matter, improve aggregation, and boost water-holding capacity and infiltration over time.

Monitoring and tools recommended for Arkansas growers

• Soil moisture sensors (capacitance probes, tensiometers) installed at representative positions and depths to capture spatial variability.
• Portable infiltration tests, double-ring infiltrometers, or simple field tests (small bucket tests) to estimate infiltration rates before setting application rates.
• Periodic soil sampling for texture, bulk density, EC, and SAR to detect salinity and sodicity trends.
• Field mapping and management zones using yield maps and soil surveys to implement variable-rate irrigation where feasible.
• Crop water use calculators or local extension Kc/ETo tables to estimate ET and plan irrigations in the absence of continuous sensors.

Practical takeaways for growers and water managers

• Do not assume a single irrigation schedule fits all fields. Match schedule and method to soil texture, depth, and drainage.
• Test and know your soil: texture, AWHC, infiltration rate, and any restrictive layers determine application amounts and frequency.
• Use moisture sensors and simple scheduling rules based on allowable depletion rather than fixed calendar irrigations.
• Infiltration-limited soils require lower application rates or pulse applications; sandy soils require higher frequency and smaller depths.
• Address compaction and drainage issues proactively; these are often the largest drivers of poor irrigation outcomes.
• Monitor water and soil chemistry periodically to prevent build-up of salts or sodium, and apply amendments and leaching as necessary.
• Employ variable-rate and precision tools where field variability is high to save water and improve uniformity.

Conclusion

Arkansas soils are diverse, and that diversity necessitates adjusted irrigation practices to maximize efficiency, sustain yields, and protect water resources. By understanding the specific soil constraints in each field, measuring critical properties, and applying irrigation in ways that match infiltration and water-holding behavior, growers can reduce runoff and deep percolation losses, avoid crop stress, and maintain soil health. Practical, soil-aware irrigation management is both an economic and environmental imperative in Arkansas agriculture.