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Irrigation Management

Are you delivering water to your plants in the right amounts at the right time? Or do your plants get regularly scheduled "showers," lapping up what they can while the excess runs off?

Too much water causes erosion and leaching, polluting water supplies with your valuable soil, fertilizers and pesticides. Too little water slows plant growth, cutting yields and quality. Just as with expensive pesticide and fertilizer inputs, incorrect irrigation management removes profits from your bottom line.

Click the links below for more information on Irrigation Management.

Irrigation System

1. Irrigation Systems
2. Scheduling Irrigation
3. Water and Pest Management
4. How to Use "Estimating Moisture" Chart
5. Estimating Moisture Chart


1.

Irrigation Systems


Open irrigation systems allow water, nutrients and soil particles to leave the irrigated area. Open systems include hose watering; fixed or movable overhead booms; sprinklers; or flood, furrow or seepage irrigation. Open systems are generally less expensive to install initially, but deliver only 50 to 85 percent of the total amount of water applied to the plant roots where it is needed.

Improve open systems by proper maintenance, adding drop nozzles to deliver water closer to the soil, converting to more efficient micro-sprinklers, laser-leveling soil to deliver uniform coverage, and/or recycling water in flooded or furrow-irrigated fields.

Closed systems cost more to install but achieve long-term savings with water use efficiencies approaching 95 to 100 percent. Surface or subsurface drip systems deliver water and fertilizer to the root zone of the crop with little or no evaporation or runoff. Proper water treatment, filtering and flushing systems are essential to prevent root penetration and sediment from clogging lines.


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2.

Scheduling Irrigation


In the past, irrigation was applied according to the calendar. Amounts and timing were determined by guesswork and habit. Now we have scheduling tools, enabling a more thoughtful approach.

A "water budget" uses a checkbook-like process. Best suited to climates where rainfall and underground water table are not significant contributors to plants, a water budget starts with the amount of water available in the soil, adds any rainfall, and subtracts amounts used up by plants. The result, or ending balance, is the amount of water to replace with irrigation.

Evapotranspiration (ET) is a commonly used estimate of water use by plants. ET formulas calculate inches of water lost per day from transpiration (breathing) by plants and evaporation from the soil. ET values are often available for your region from university or National Weather Service sources.

Soil monitoring is another way to schedule irrigation scientifically. Using the correct tools and techniques, you can decide if and when to irrigate to maintain optimal soil moisture levels at all times. Soil moisture meter, irrometers, watermark meter/sensor and pH and moisture meter are some of the tools available to help you monitor.


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3.

Water and Pest Management


Did you know that improper watering can cause disease problems? In many fruit and vegetable crops as well as turf and ornamentals, some diseases develop only after an extended period of leaf wetness and warm temperatures. If your irrigation system wets plant foliage and fruit, it's often a good strategy to irrigate in the hours just before dawn. At that time, air temperatures are lowest and plant surfaces, often already wet with dew, will dry quickly.

Other possibilities include disrupting a pest's normal behavior with strategically timed irrigation. For example, many insects lay eggs at a very specific time of day. By turning sprinklers on at that time, egg laying can be prevented. The best time for most pesticide sprays for insects, diseases or weeds is after plant parts have had time to dry from irrigation.


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4.

How to Use "Estimating Moisture" Chart


You can get a quick "ballpark" estimate of your irrigation needs by comparing the feel and appearance of your soil to the descriptions on the chart on this page.

Step 1: Take a separate sample of soil from each one-foot depth interval within the plant root zone (i.e., one sample each at 0-1', 1-2', 2-3' and 3-4' for deep-rooted crops). For shallow-rooted crops, a sample or two within the top 0-1' of soil may suffice. Check with your Cooperative Extension agent or private consultant to confirm proper depths for your plants.

Step 2: Record your results. Click here for a printable PDF.

Step 3: Compare each sample to the descriptions and graphics on the Estimating Moisture Chart below for your soil type.

Step 4: Repeat this procedure at least three times in each field, selecting a different portion of the field for each sample. Average your results over the three samples. Your average percent soil moisture available for the field can help you estimate the amount of irrigation needed to restore your soil to field capacity. For most crops, decisions about when to begin irrigation should be based on the amount of moisture available in the upper one to two feet of soil (i.e., the root zone). Irrigate when the available soil moisture in this zone falls below 50%.


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5.

Estimating Moisture Chart

Dominant Texture

Fine Sand and Loamy Fine Sand

Fine Sandy Loam

Sandy Clay Loam and Loam

Clay, Clay Loam or Silty Clay Loam

Inches of water per foot soil will hold at field capacity

0.60" - 1.25"

1.2" - 1.5"

1.4" - 1.9"

1.5" - 2.3"

Available soil moisture as a percent

Soil moisture deficit in inches per foot when the feel and appearance of the soil is as described

0 to 25%

Dry, loose, single grained, flows through fingers.

1.25" - 0.60"

Dry, loose, flows through fingers.

1.5" - 1.0"

Powdery, dry, sometimes slightly crusted but easily broken down into powdery condition.

1.9" - 1.4"

Hard, baked, cracked sometimes, has loose crumbs on surface.

2.3" - 1.5"

25% to 50%

Appears to be dry, will not form a ball with pressure.

0.60" - 0.45"

Appears to be dry, will not form a ball.

1.0" - 0.65"

Somewhat crumbly but holds together under pressure

1.4" - 1.0"

Somewhat pliable, will ball under pressure.

1.5" - 1.0"

50% to 75%

Tends to stick together slightly, but crumbles easily, will not form ball.

0.45" - 0.20"

Tends to ball under pressure but seldom holds together.

0.65" - 0.30"

Forms a ball, somewhat plastic, will sometimes stick slightly with pressure.

1.0" - 0.50"

Forms a ball, ribbons out between thumb and forefinger.

1.10" - 0.55"

75% to 100%

Tends to stick together slightly, sometimes forms a very weak ball under pressure.

0.20" - 0.0"

Forms weak ball, breaks easily, will not stick

0.30" - 0.0"

Forms a ball, is very pliable, slicks readily if relatively high in clay.

0.50" - 0.0"

Easily ribbons out between fingers, has slick feeling.

0.55" - 0.0"

At field capacity (100%)

Upon squeezing, no free water appears on soil, but wet outline of ball is left on hand.

0.0"

Acknowledgment: Adapted from Estimating Soil Moisture By Feel and Appearance, by M. Risinger, A.W. Wyatt and K. Carver, published by the High Plains Underground Water Conservation District No. 1, Texas.

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