Horticulture Principles and Practices

It is neither practical nor safe to apply major elements to leaves directly. Foliar spraying
is often used to correct deficiency problems of trace elements. Since trace elements
are required in minute amounts, it is safe to administer them by foliar application.
Fertigation Fertigation, also called chemigation, entails applying fertilizer to crops
through the irrigation water. This method is usually used in the greenhouse. The drip
irrigation method is particularly suitable for fertigation. In effect, it is a kind of topdressing
application. Critical issues of concern in fertigation include the solubility of the fertilizer
and the quality of irrigation water. Water-soluble fertilizers should be used in
fertigation. Hard water with excessive amounts of dissolved calcium can be problematic if
the irrigation system is incapacitated through blockage of holes by calcium deposits. The
advantage of this method is that in soils that drain very freely (e.g., sandy) and for fertilizer
elements that are prone to leaching (e.g., nitrogen), irrigation can be controlled to
deliver the right amounts of moisture and fertilizer at rates that the plant can utilize efficiently.
Small-scale fertigation systems are available for home use. They usually consist of
a handheld unit containing a dry formulation of the fertilizer. The unit is connected to a
watering hose that runs water through the container before sprinkling on the area to be
irrigated. These units are used for watering vegetable gardens, flower beds, lawns, and
other plants in the landscape.
4.4.6 TIMING OF APPLICATION
Fertilizers are applied supplementarily to the nutrition plants obtain from the soil. Plants
go through growth phases, each phase with special nutritional needs to support the growth
and development activities taking place. Fertilizers are subject to a variety of environmental
factors that cause them to be depleted in the soil. For example, under aerobic conditions,
nitrogen is lost through denitrification (a process whereby bacteria convert nitrates into unusable
nitrogen gas). Nitrogen fertilizers are readily leached or, in some cases, volatilized.
Phosphorus and potassium are prone to fixation. Appropriate rate and type of fertilizer must
therefore be chosen, and the application must be timely. Fertilizers are most beneficial to
plants when applied as close as possible to the time of maximum need.
Fertilizers release their nutrients at various rates and over varying periods of time.
Organic fertilizers release their nutrients as the material decomposes; consequently,
they are not useful when immediate supplemental nutrition is required. Dry application
of fertilizers requires moisture availability to enable use of the nutrients. Rain or
irrigation is needed after application of dry fertilizer. On the contrary, irrigation or rain
is undesirable after foliar application because it will wash the nutrients into the soil.
4.4.7 FERTILIZER RECOMMENDATIONS
After a soil test, fertilizer recommendations are made based on a number of factors,
including the following:
1. The regional information on weather and soils.
2. The cropping history of the land.
3. The crop yield target or goal desired by the grower.
4. The crop to be fertilized (in terms of how it responds to fertilization).
For small-scale growers such as home gardeners who have no set yield and profit targets,
the general goal of gardening is to produce a good, healthy, and attractive crop. Homeowners
and gardeners often overfertilize their gardens and lawns. For some, it is a seasonal
ritual or tradition to fertilize the lawn and garden crops. Many people do not conduct soil
tests on their plots and hence may not derive optimum benefits from their efforts. Since no
specific yield goal is set in home gardening projects, a moderate application of fertilizer is
all that may be needed. A general application may be 10 to 20 pounds per 1,000 square feet
(4.5 to 9 kilograms per 92.9 square meters); a complete fertilizer (10:10:10) is often sufficient
for gardens and lawns.
4.4 Fertilizers 125