Gordon Johnson, Extension Vegetable & Fruit Specialist; firstname.lastname@example.org
As the season progresses, growers and consultants will use tissue tests to determine the nutrient status of vegetable crops and take corrective actions if necessary. As a rule, if levels are in the adequate range or are high no corrective action is needed. If levels have dropped to near deficient levels or are in the deficient category then additional mineral nutrients will need to be added. Critical tissue test values for many vegetables can be found in the Mid-Atlantic Commercial Vegetable Recommendations. The following are some guidelines for correcting low or deficient levels from tissue tests in vegetables.
If tissue results are low or deficient for Nitrogen (N) apply additional nitrogen as a sidedressing or through fertigation:
Watermelon, muskmelons, mixed melons: 40 lbs/a N
Cucumbers, squash: 20 lbs/a N
Tomatoes, peppers: 40-60 lbs/a N
Eggplant: 30 lbs/a N
White potato: 40 lbs/a N before tubers start to size
Cole crops, greens: 30-40 lbs/a N
Sweet corn: 40-80 lbs/a N
Beans: 20 lbs/a N
Additional nitrogen may be needed for extended harvest in some crops such as watermelons. Use non-acidic forms of nitrogen for blossom end rot sensitive vegetables such as tomato or pepper (calcium or potassium nitrate is recommended).
Foliar applications of N can benefit most vegetables if the plant is low in N. Urea forms of N are the most effective; methylene ureas and triazones are effective with less injury potential; and ammonium sulfate is also effective. Recommended rates are 1-10 lbs per acre N in sufficient water to have less than 2% salt solution. Multiple applications will be necessary to correct deficiencies, or combine with a soil application.
If tissue test results are low or deficient for potassium (K) apply additional K as a sidedressing or through fertigation. Note that fruiting vegetables often have low K levels in tissue tests if fruit loads are heavy and first harvest often brings them back in balance.
Watermelon, muskmelons, mixed melons: 40 lbs/a K
Cucumbers, squash: 20 lbs/a K
Tomatoes, peppers: 40-80 lbs/a K
Eggplant: 40 lbs/a K
White potato: 40 lbs/a K
Cole crops, greens: 30-40 lbs/a K
Sweet corn: 40-80 lbs/a K
Beans: 40-80 lbs/a K
Foliar sprays of potassium nitrate or sulfate (4 lbs/a K foliar) may be useful on tomatoes and melons.
If tissue test results are low or deficient for Phosphorus (P), apply an additional 20-40 lbs/a P for all crops as a sidedressing or through fertigation. Note that areas with high levels of calcium or magnesium in irrigation water can have problem with P precipitates clogging drip irrigation emitters and water may need to be acidified to prevent this.
If tissue test results are low or deficient for magnesium (Mg) apply 15-25 lbs of Mg as a sidedressing or through fertigation. Another option is to apply 2-3 applications foliarly (2-4 lb Mg/A) for sensitive crops such as tomatoes or melons.
For vegetable crops low or deficient in calcium (Ca), foliar applications of 2-4 lb Ca/A. Calcium chloride at the rate of 5-10 lb per 100 gallons per acre or calcium nitrate at the rate of 10-15 lb per 100 gallons per acre is recommended for fruiting vegetables (tomatoes, peppers, eggplant). Calcium chelates are also available. For potatoes, sidedress gypsum (calcium sulfate) at a rate of 500 lbs/a.
For vegetables low or deficient in sulfur (S) apply 20-30 lbs/A S as a sidedressing or through fertigation.
Ammonium sulfate and ammonium thiosulfate are effective ways to add both N and S at the same time. Gypsum is an inexpensive material to use to provide S.
For micronutrient metals (Iron – Fe, Manganese – Mn, Zinc – Zn) foliar application is often the most effective way to correct low or deficient levels. Suggested rates are: Fe, Mn, 1-2 lbs/a, and Zn ¼ lb/a.
The other micronutrient that can be effective as a foliar application is boron. Boron in the Solubor form is often recommended at 0.1 to 0.25 lbs/a for mustard family crops such as cabbage as a foliar application. Boron is very toxic to plants if applied in excess so applying at correct rates is critical. Do not use boron on bean crops.