Water conservation, as it relates to garden irrigation, begins with appropriate garden planning. Ideally, one should only plant those crops and amounts he/she will actually use. And for a productive garden, one should always fertilize properly and control weeds, insects, and diseases. Plus, if you follow early crops with late crops you will be efficiently utilizing your garden 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.
Wilting reduces transpiration. It doesn't harm most crops if it occurs for only an hour or two in the afternoon. However, it is detrimental if it persists. There are materials that can be sprayed on foliage to reduce transpiration. These usually are white to reflect sunlight. They contain an emulsified wax that coats the foliage and acts as a vapor barrier. Neither these materials nor withholding water are recommended for reducing transpiration losses.
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. <br>Plant growth combines water with organic compounds to produce plant tissues that are composed mainly of water. This accounts for only a minor portion of the water used, but it is the most important portion.
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. In addition, percolation often is heavy at the upper end of the garden. Some communities forbid watering with an open hose – at least some time of the year.
In the right agricultural situation, furrow irrigation is quite efficient. It can supply water to a crop with minimum evaporation and energy consumption even when it is windy, because the water is not sprayed into the air and the foliage and most of the soil surface remains dry.
Furrow irrigation is much less efficient when used to germinate seed and when used on gravelly or sandy soil. To germinate seed, it is necessary to keep the water in the furrows until it has soaked over to the seed, which may take as long as a day, while on gravelly soil, too much water is lost through percolation.
Soaker usually consists of a canvas 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.
Trickle 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, 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. Black plastic, for example, has been shown to conserve water, control weeds and generally increase garden productivity.
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 1 foot or more.
After seeds are planted, they may be sprinkled with a hand-held hose until seedlings emerge. This should occur one or more times a week depending on the depth of planting and climatic factors. Once seedlings emerge, they can do without water for two or more weeks while their roots get established. At this point, more frequent waterings saturate the soil and prevent deep rooting.
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.
At the crumble-stage, the average soil will hold 1 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.
Water consumption for a garden will gradually increase up to 1 1/2 inches of water per week during hot weather, and then taper off as the weather cools.
Gravity Feed Water to a Garden
Using rain barrels to gravity feed water to a garden
Attach a hose to the spigot at the bottom of the barrel. Water is supplied as needed by adjusting the spigot.
A soaker hose that snakes through a garden will disperse stored water throughout the garden over a prolonged period of time. A 55-gallon rain barrel with a soaker hose takes about 12 hours to drain. Or, a spigot in the middle of the barrel can be used to fill a watering can.
Success depends on the barrel being sufficiently elevated above garden level.
Occasionally an air lock can form in the soaker hose, this problem is easily remedied by providing a bleed valve at the terminal end of soaker hose.
To help conserve dispersed water, cover soaker hose with mulch.