Last revised February 15, 2010
AN-20, ammonium thiosulfate (and mixtures of these two materials), as well as monocarbamide dihydrogensulfate, can be used as N sources in a number of crops, while also providing ancillary weed control. The amount of nitrogen per gallon of material, the rate at which it is applied, and the phytotoxicity of the material determines the crops on which these can be used.
All of these fertilizer materials, when applied at the proper time and manner, have the added benefit of ancillary control of many small (less than 3 inches) broadleaf weeds such as groundsel, pineapple weed, shepherdspurse, mallow, pigweed, hairy nightshade, chickweed, and many others. Poor or no control is obtained on lambsquarters, purslane, henbit, black nightshade, knotweed, sowthistle, malva goosefoot and grasses.
When any of these N solutions is used as an N source and timed to provide ancillary weed control, N sidedressings should be reduced by at least half the N applied with the solutions.
Cautions
When using these nitrogen sources in foliar applications, follow cautions listed below. Severe crop injury may occur if cautions are not observed. General cautions that apply to nitrogen liquid fertilizer formulations are:
* Apply only after the first true leaf is as tall as the flag leaf and before the plants are 8 inches tall.
* Do not apply within 4 days of a period of cool, cloudy or rainy weather, or if free water is present on the leaves.
* Discontinue application if spray droplets do not roll off or "bead-up" on the crop leaves. This indicates a deficiency of adequate waxy cuticle, and may be a temporary condition due to rapid growth, cloudy or rainy weather, or more seriously, the lack of adaptability of the variety.
* Do not apply within 4 days after a foliar pesticide has been applied, or with any wetting agent.
* Use large nozzles to minimize misting and possible injury to the crop growing point.
AN-20 fertilizer formulation:
This is a manufactured 20-0-0 formulation (containing 20% N) that may be applied at 50 to 70 gal product/acre as a foliar spray. This formulation weighs 10.55 lb/gal and contains 2.11 lb N/gal of product and would provide approximately 100 to 140 lb N/acre (but some N is lost through volatilization). Do not irrigate for 48 hours after application, but then irrigate to move the fertilizer into the root zone.
Note: This formulation is different from a solution that could be prepared by dissolving ammonium nitrate in water. Such a solution would not have the same concentration or weed-killing effect.
To prevent crop injury, follow the cautions listed above.
Ammonium Thiosulfate:
This is a manufactured 12-0-0-26 formulation (containing 12% N and 26% sulfur) and weighs 9.33 lb/gal. It may be applied at 50 to 70 gal product/acre as a foliar spray. This solution contains 1.12 lb N and 2.4 lb S/gal of product and would provide approximately 55 to 75 lb N/acre (some N may be lost through volatilization). At the application volume mentioned, about 150 to 168 lb S/acre are also applied. Do not irrigate for 48 hours after application, but irrigate then to move the fertilizer into the root zone.
When this treatment is used, subsequent N sidedressings should be reduced by a portion of the amount of N applied in the treatment.
Note: Mixtures of AN-20 and ammonium thiosulfate (usually 1:1) can be made which will reduce the amount of nitrogen applied, provide some sulfur (compared to AN-20 alone, and reducing the S compared to ammonium thiosulfate alone), and be as effective as either material alone. Application rates are still held at 50 to 70 gal of the mixture/acre.
To prevent crop injury, follow the cautions listed above.
Monocarbamide Dihydrogensulfate (monourea sulfuric acid, 15-0-0-16, N-pHURIC fertilizer):
This product can be used on onions (bulb and green), shallots, leeks and garlic only, at 10 to 30 gal product/acre as a foliar spray. It weighs 12.65 lb/gal and contains 1.9 lb N and 2.0 lb S/gal of product. It is most generally used at about 15 to 20 gal/acre providing approximately 28 to 38 lb N/acre (but some N is lost through volatilization). Apply in sufficient water to get good foliar coverage (approximately 1:1 dilution). Do not irrigate for 48 hours after application, but irrigate then to move the fertilizer into the root zone.
CAUTION: This solution is corrosive, and can injure skin and damage spray equipment. Use proper safety precautions and suitable spray equipment (stainless steel).
To prevent crop injury, follow the cautions listed above, and FOLLOW ALL LABEL INSTRUCTIONS.