The water found in the pores of the soil is called the soil solution and carries dissolved nutrients as well as microbial life. Water is necessary to transfer soluble nutrients to all parts of the plant and must be present in sufficient quantities for the elongation of plant cells that contribute to growth. In waterlogged soils, water molecules displace the soil air that contains oxygen. This causes lower respiration rates in the roots and can actually decrease the ability of the plant to take up water from the soil, which causes the plant to wilt.
Rainwater is slightly acidic because of the carbon dioxide naturally present in the atmosphere and may become even more acidic as a result of pollution. Rain is also a transport vehicle for microbes that are swept into the atmosphere. If there is insufficient rainfall for healthy plants, a supplemental source is required. Commercial growers may have access to surface water, such as ponds and rivers with irrigation ditches used to divert water to the crops. They may also use a sprinkler system. Alternatively, wells are often used to supply irrigation water and are preferred because the water is less likely to transmit disease.
Water quality should be tested prior to planting. If the water supply is from surface water or a well, this can be done by sending a water sample to a laboratory. You want to check for pH, mineral content, and soluble salts, as well as toxic chemicals that could injure your plants. If you are using municipal tap water to water plants, you should ask the county or municipality for a water quality report, which they should provide to you at no charge. High levels of chlorine or fluoride in tap water may injure your plants. If your water is not good, you can invest in equipment to purify it.
The method used to irrigate water may depend upon climate, the size of the garden, and proximity to the water source. One method is to irrigate from overhead and the other is to provide water directly to the root zone. Fertilizer is sometimes applied dissolved in the irrigation water; this is referred to as fertigation. There are advantages and drawbacks to both methods.
Overhead water washes off leaves and may help deter foliage pests, but water can be lost to evaporation and may not reach the roots, especially in hot, dry weather. Overhead rinses with organic amendments such as compost tea or kelp extracts have been reported to increase plant vigor. Pivot irrigation is an overhead sprinkler system that projects water out from a central source in a circular motion moving like the hands on a clock, which results in a circular patch of irrigated land that looks like big green circles when viewed from overhead (Figure 4.3).
When plants are exposed to a frost, an early morning rinse with water to wash frost off the leaves will prevent damage as long as the leaves have not yet been exposed to sunlight. Plants can be protected from frost by covering them with cloth or plastic or by moving potted plants to a sheltered area. Your local weather report will give you notice if a frost is expected overnight.
Water applied directly to the root zone by drip irrigation concentrates the water by the roots where the plant can access it. Drip irrigation delivers water through a soaker hose, which is perforated. This method is more easily applied in the small garden
than in large commercial fields, which may have problems with clogging. The hose is laid on the ground close to the stems of your plants and can be covered with mulch to reduce evaporation.
Water that is applied too late in the day, close to dusk, or after nightfall may create problems because of conditions that favor the growth of fungi. Many types of fungi thrive in cool, moist conditions and reproduce with spores. The spores are
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