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  MG Manual Reference
Ch. 16, pp. 7 - 9
[Management Practices For Fertilization: lawns | gardens | ornamentals ]


As in the case of lawns, home vegetable and ornamental gardens can benefit from the use of fertilizers. Several management practices should be considered before using any fertilizers on the home garden to maximize the benefits to the plants while minimizing the possibility of groundwater contamination:
Soil Testing - Soil testing can be helpful if your garden is not performing as it should. Soil testing is costly for a home owner since home test kits are of little value for Arizona soil. To obtain an accurate soil test a soil sample must be sent to a certified soils laboratory. County Extension offices have a list of labs for your use. In general, soils in Arizona will be lacking in nitrogen and phosphate. Regular applications of these two elements should prevent the majority of problems due to nutrient deficiencies. To avoid over application of nitrogen it is best to apply small amounts of more frequently.
Tilling the Soil _ This can be beneficial if done at the proper time. Tilling aerates the soil and can help control weeds. Organic matter may also be incorporated when tilling. If done when the soil is too wet or too dry however, tilling can destroy soil structure, which may take years to rebuild. Tilling wet soil can also lead to the formation of a hardpan, inhibiting root growth. Both of these may contribute to soil erosion and loss of nutrients into groundwater supplies. A no-till approach or a system of raised beds can reduce nutrient and soil loss even more. Tilling in nutrients nitrogen and phosphate will help in the availability of these elements.
Organic Amendments - Compost, manures, and mulches can be very beneficial to the soil by improving its structure, adding nutrients, and increasing its water and nutrient holding capacity, and can lessen the chance of groundwater contamination. Albeit, on short lived or unstable soils organic matter won't accumulate.
Cover Crops - Cover crops, such as annual rye or wheat, planted in the garden in the fall, and tilled under in the spring, can also add organic matter and lessen the chance of groundwater contamination. A leguminous cover crop such as alfalfa or clover can also add nitrogen to the soil when tilled in. Cover crops, compost, and manures also add trace elements, which are essential for good growth, though only needed in small amounts.
Fertilizers - Fertilizers for the garden may be either organic or synthetic. Both organic and synthetic fertilizers can be fast or slow acting. Organic fertilizers can benefit long term soil conditions by increasing organic matter content. Garden fertilizers are generally described, by law, with three numbers such as 10-10-10, or 5-10-5. This is the same as with lawn fertilizers, although the first number (nitrogen) is normally lower in garden fertilizers.
Nitrogen is responsible in the plant for producing leaf growth and greener leaves. A deficiency causes yellow leaves and stunted growth. The second number, phosphorous, is important in seed and root development and fruit growth. Potassium, the third major element, promotes early growth, improves stem strength, and contributes to cold hardiness.
In the vegetable garden, fertilizer may be incorporated into the soil either by broadcasting it over the entire garden, or by applying it in narrow bands on either side of the plants in the row. Banding it is more efficient, because it uses less fertilizer and makes it available to the plant closer to the root zone.
Amount, Frequency, and Timing of Fertilizer Application - Vegetables vary in their nutrient requirements. Heavy feeders, such as broccoli, sweet corn, and tomatoes may need more frequent applications of larger amounts of fertilizers than medium feeders, such as beans, carrots, and cucumbers. A first application is generally made when the seed is planted, or the transplant set out.
Depending on the crop, a second application can be made when the plant flowers, or starts to set fruit. Some crops, such as corn, benefit from a third application when the silks form. By sidedressing, the fertilizer becomes available to the plant when it needs it most. It is important to remember that fertilizer not utilized by the plant has the potential to leach through the soil and contaminate the groundwater, or be washed into the water supply by erosion.

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