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  MG Manual Reference
Ch. 2, pp. 35 - 38
[Fertilizers: fertilizers | analysis | types | organic | applying | application | improving | compost ]


Soil type dictates the frequency of fertilizer application. Sandy soils require more frequent applications of nitrogen and other nutrients than do clay-type soils. Other factors affecting frequency of application include the type of crop, the level of crop productivity required, frequency and amount of water applied, and type of fertilizer applied and its release rate.
The type of crop influences timing and frequency of application since some crops are heavier feeders of particular nutrients than others. Root crops require less nitrogen fertilization than do leafy crops. Corn is a heavy feeder of nitrogen, while most trees and shrubs are generally light nitrogen-feeders. Corn may require nitrogen fertilization every four weeks, while most trees and shrubs perform nicely with one, good, well-placed application every year or two. A general rule of thumb is that nitrogen is for leafy top growth; phosphorus is for root and fruit production; and potassium is for cold hardiness, disease resistance, and general durability.
Proper use of nutrients can control plant growth rate and character. Nitrogen is the most critical nutrient in this regard. If tomatoes or squash are fertilized heavily with a nitrogen fertilizer into the summer, the plants may be all vine and no fruit. If slow-release fertilizers or heavy amounts of manure are used on crops that form fruit or vegetables, leaf and vine growth will continue into late summer, and fruit and vegetable development will occur very late in the season.
Remember that a nitrogen application will have its greatest effect for three to four weeks after application. If tomatoes are fertilized heavily on April 1, there may be no flower production until May 1, which will, in turn, delay fruit ripening until late June. For this reason, it is important to plant crops with similar fertilizer needs close together to avoid improper rates of application.
Late fertilization (after July 1) of trees and shrubs can cause new flushes of growth to occur on woody plants that are normally adjusting themselves for the coming winter. This may delay dormancy of woody plants and cause severe winter dieback of the new growth.
The following suggestions about groups of garden plants are given as general guides. Gardeners should be aware that individual species within these groups vary considerably. After each group of plants, the need for the primary nutrients (nitrogen, phosphorus, and potassium) is indicated as high, medium, or low.
Annual flowers
Perennial flowers
Deciduous shrubs
Evergreen shrubs
Deciduous shade trees
Evergreen shade trees
Medium to Low
Medium to High
Medium to Low
Medium to Low
Medium to Low
Application MethodsThere are different methods of applying fertilizer depending on its formulation and the crop needs.
Broadcasting — A recommended rate of fertilizer is evenly spread over the growing area and left to filter into the soil or is incorporated into the soil with a rototiller, or spade, with irrigation water. Broadcasting can be used over large garden areas or when time or labor is limited.
Banding — Narrow bands of fertilizer are applied in furrows 2 to 3 inches from the garden seeds and 1 to 2 inches deeper than the seeds or plants. Careless placement of the fertilizer band too close to the seeds will burn the roots of the seedlings. The best technique is to stretch a string where the seed row is to be planted. With a corner of a hoe, dig a furrow 3 inches deep, 3 inches to one side, and parallel with the string. Spread one-half the suggested rate of the fertilizer in the furrow and cover it with soil. Repeat the banding operation on the other side of the string, then sow seeds underneath the string.
For widely spaced plants, such as tomatoes, fertilizers can be placed in bands 6 inches long for each plant or in a circle around the plant. Place the bands 4 inches from the plant base. If used in the hole itself, place the fertilizer at the bottom of the hole, work it into the soil, and place a layer of soil about 2 inches deep over the fertilized soil before putting the plant in the hole.
Banding is one way to satisfy the needs of many plants (especially tomatoes) for phosphorus as the first roots develop. When fertilizers are broadcast and worked into soil, much of the phosphorus is locked up by the soil and is not immediately available to the plant. By concentrating the phosphorus in a band, the plant is given what it needs even though much of the phosphorus stays locked up.
Starter solutions — Another way to satisfy the need for phosphorus when setting out transplants of tomatoes, eggplant, peppers, or cabbage is through the use of a liquid fertilizer high in phosphorus, as a starter solution. Follow directions on the label.
Side-Dressing — Dry fertilizer is applied as a side dressing after plants are up and growing. Scatter fertilizer on both sides of the row 6 to 8 inches from the plants. Rake it into the soil and water thoroughly.
Foliar Feeding — Foliar feeding is used when insufficient fertilizer was used before planting; a quick growth response is wanted; micronutrients (such as iron or zinc) are locked into the soil; or when the soil is too cold for the plants to use the fertilizer applied to the soil. Foliar-applied nutrients are absorbed and used by the plant quite rapidly. Absorption begins within minutes after application and, with most nutrients, it is completed within 1 to 2 days. Foliar micro-nutrient fertilization can be a supplement to soil nutrition at a critical time for the plant, but not a substitute. At transplanting time, an application of phosphorus spray will help in the establishment of the young plant in cold soils. For perennial plants, early spring growth is usually limited by cold soil, even when the air is warm. Under such conditions, soil microorganisms are not active enough to convert nutrients into forms available for roots to absorb. A nutrient spray to the foliage will provide the needed nutrients immediately, allowing the plants to begin growth. Foliar application is also an excellent method for applying micro-nutrients in high pH soils. Micro-netrients applied in this manner are not tied up in the soil, but are directly available to the plant.

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