During seedbed preparation, any nutrient deficiencies should be corrected with fertilizer. Regardless of whether you use an organic or chemical (granular) fertilizer, the application should be based on a soil test report. Contact your local county or state Cooperative Extension office for information on soil testing.

With the exception of nitrogen, all the recommended nutrients should be applied during bed preparation. Only a portion (30 to 40 percent) of the crop's total nitrogen requirement should be present in the soil at planting because too much nitrogen applied prior to planting can result in delayed fruiting. For most vegetable crops, this portion is equivalent to 40 to 50 pounds of actual nitrogen per acre, enough to get your garden off to a good start. If a nitrogen deficiency is reported, consult your soil test report for a pre-plant nitrogen fertilizer recommendation.

Typically, additional nitrogen is supplied by one or more fertilizer applications over the life of the crop. Fertilizer should be applied to the soil surface around plants (topdressed) at critical stages of crop growth. For a few vegetable crops, Table 3 lists topdressing times based on stage of growth.

Although topdressing addresses the problem of overfertilization, it does have limitations, the most obvious being its incompatibility with plastic mulch. The plastic film acts as a barrier to the fertilizer. Second, the practice of topdressing is not calibrated to the nitrogen requirement (growth curve) of plants. Figure 2 illustrates the relationship of a crop's nitrogen requirement to its stage of development or growth curve. Early in the life of a crop, plants are small and devoid of fruit; their requirement for nitrogen is limited. As plants grow, their demand for and ability to use nitrogen increase, peaking during reproduction (fruiting).

Matching fertilizer application to a crop's growth curve is a far better way to fertilize and is best accomplished by using your drip irrigation system to deliver small, frequent doses of soluble fertilizer to the plant's root system, a process referred to as fertigation. Under plastic, drip fertigation permits precise nutrient placement with less waste.