Suggested guidelines for nitrogen use are given in Table V . The preplant application rate of nitrogen is based on the estimated nitrogen level in the soil. If the organic matter level is high or manure has been applied, the only added nitrogen fertilizer needed is for those vegetables that benefit from high levels of nitrogen. Vegetables that need high levels of nitrogen include sweet corn, the cole crops, and leafy green vegetables. For these, one or two applications of nitrogen as a sidedressing after planting are recommended at specific growth stages as shown in Table V .
Onions also benefit from additional nitrogen.
By delaying the application until after emergence, the crop benefits and weed stimulation is reduced. Potatoes and tomatoes also respond to added nitrogen. Delaying the application improves tuber set of potatoes and reduces excessive vine growth of potatoes and tomatoes. It is important not to stimulate excessive vine growth for tuber or fruit type vegetables. Excessive vine growth of these crops usually results in poor crop yields due to a lower number of tubers or fruits.