Fertilizers
Fertilizer Application Methods
Mineral-based fertilizers can be applied before a crop is planted, during planting, after the crop is growing, or in some combination of the three. Fertilizer placement is an integral part of efficient soil nutrient management. Correct placement often improves efficiency by which plants take up nutrients and minimizes the loss of nutrients. There are four general methods of applying fertilizers: (1) broadcasting, (2) banding, (3) fertigation, and (4) foliar application. Each method has some advantages and disadvantages and may be suitable for different situations. Often some combination of the four methods is used.
Broadcasting
When the fertilizer is spread across the soil surface before planting corn, small grains, or perennial forages, it's called a "broadcast" application. The broadcast method is the most economical and most appropriate way when a large amount of fertilizer is being applied with the aim of raising the fertility level of the soil. Often the broadcast fertilizer is mixed into the soil layer by means of tillage, but in some situations, it is left on the soil surface and allowed to be carried into the root zone by percolating rain or irrigation water.
Banding
Banding is the application of fertilizer where the fertilizer is applied in concentrated strips, either on the surface or sub-surface. There are at least three reasons why fertilizer is often more effectively used by plants if it is placed in a localized concentration rather than broadcasted. First, localized placement reduces the amount of contact between soil particles and the fertilizer nutrient, thus minimizing the opportunity for adverse fixation reactions as in the case of phosphorus and potassium. The result can be a faster start for the plants and a greater ability to compete with weeds. Second, nitrogen applied in a narrow band below the crop residues so immobilization is not a factor.
Fertigation
Fertigation is the application of fertilizers or nutrients via the irrigation network, wherein the nutritious inputs are dissolved into water and then absorbed directly by plants when they uptake water. Fertigation can be used in conjunction with several different irrigation methods including sprinkler, drip (Figure 12.6), and soaker irrigation systems, although drip is the most compatible and beneficial irrigation type. In addition to greater flexibility in application timing and optimal placement, fertigation increases the rate of nutrient uptake and predictability of the crop’s response to fertilization compared to broadcast and band applications.
Foliar Application
Foliar spraying can provide specific nutrients to the crop on a timely basis during critical stages of growth, flowering, and fruit development. Foliar application is an excellent means to supply plant requirements of micronutrients like manganese, zinc, manganese, copper, boron, iron, and molybdenum. This is for two reasons: (1) it takes a very small amount to correct the deficiency, and (2) many micronutrients are readily fixed by most soils, so they soon become unavailable to the plant with soil fertilization. Foliar application of micronutrients is more effective than soil application in the short-term with the exception of iron.
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