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Farm Advisor: Efficient Water Use In The Vegetable Garden

This article was provided to MyMotherLode.com by Calaveras County Farm Advisor Ken Churches.

San Andreas, CA — Water conservation begins with garden planning. Plant only the crops and amounts you will use. Fertilize properly and control weeds, insects and diseases. Trellis peas and cucumbers; stake tomatoes. Follow early crops with late crops for more efficient use of space. In short, anything you do to make the garden more productive results in more efficient water use per unit of production.

Use and Loss of Water

Water applied to the garden is used or lost in the following ways:

– Evaporation begins as soon as water is exposed to the atmosphere. Extremely high evaporation results when fine jets of water are sprayed into the air on a hot, dry, windy day. Fine jets produce mist-size droplets that have a vast surface area in relation to their volume. The wind, heat, sun and dry air combine to evaporate much of the water before it lands on the garden. Evaporation then continues from all moist surfaces of the garden until they dry. Water losses from evaporation can be reduced by using a coarse, low-pressure spray and by watering during cool, quiet evenings or early mornings.

– Transpiration begins when the plant produces its first green leaves. Water is lost from the leaves during the process of obtaining carbon dioxide from the air. This loss helps to keep the leaves cool. Transpiration losses are negligible when a seedling first emerges but increase with leaf area and warm weather.

– Percolation is the downward movement of water through the soil. When too much water is applied, water percolates below the root zone and is lost to the crop. In the process, water carries with it soluble fertilizer, especially nitrates, thus depriving garden crops and contributing to ground water pollution.

Methods of Irrigation

– Sprinkler irrigation is most common among home gardeners. Apply sprinkler water uniformly and at a rate slow enough to prevent runoff. A sprinkler should not produce a mist that is subject to drifting. Use a sprinkler that will water the garden at one setting so it won´t be necessary to walk into a wet garden to move the sprinkler.

– Furrow irrigating with a garden hose is generally not efficient unless the rows are short. While this type of irrigating does reduce evaporation losses, it has several disadvantages. It causes erosion and the hose needs to be moved each time a row has been irrigated.

– A soaker usually consists of a perforated rubber hose, 20 feet or more, which attaches to the garden hose at one end and is sealed at the other. It minimizes evaporation and applies uniform coverage. It must be moved often to prevent percolation losses.

– Drip irrigation involves the use of flexible capillary tubing to convey water to the individual plants. This system reduces evaporation and percolation to a minimum when properly installed and operated.

Mulches

Mulches, especially the film types that form a vapor barrier over the soil surface, help prevent evaporation of soil moisture. These mulches may be laid down and the crops planted through the mulch, or they may be laid between the rows after the garden is planted. Once the mulch is secured against the wind, the garden may be irrigated normally.

Amount and Frequency of Water

A plant can use only the moisture in contact with its seed or roots. After the seed germinates, roots are produced that continuously invade greater volumes of soil from which water may be extracted. Therefore, only the soil around the seed needs to be kept moist following planting. Toward the end of the season, the soil needs to be kept moist to a depth of one foot or more.

One way to determine when to irrigate is to take a soil core sample from the plant root zone and squeeze it into a ball. If the ball holds together in the palm of your hand, the soil has sufficient water. If it crumbles, apply water. A typical soil coring device is shown in Figure 1.

At the crumble-stage, the average soil will hold one inch of water per foot. If this water is applied with a sprinkler, determine its delivery by placing three or four cans under the sprinkler pattern to see how long it takes to accumulate an inch of water.

Please contact the Farm Advisor´s office or call (209) 754-6477 with your agricultural questions.

Ken Churches is the county Farm Advisor and director for the University of California Cooperative Extension.