Tuesday, June 8, 2010


It seems the salesmen are active convincing growers to invest in foliar fertilizers for rice. They seem like a good deal, but are they? It greens the crop so it must be “doing some good”, right? Well, maybe for some micronutrients, but probably not for most nutrients.

For rice, zinc is the only fertilizer that the University of Arkansas recommends a foliar application. Even then, applying liquid zinc is not the preferred method. I have received questions about applications of boron, managanese, and other micronutrients to rice. We have no data to support these recommendations. Even in fields where soybeans do respond to boron, application of boron to rice has not been beneficial.

The major nutrients, such as nitrogen, potassium, phosphorus, and sulfur are needed by the plant in large quantities. The amounts taken up by the plant range from as little as 25 lbs/acre for sulfur to as much as 200 lbs/acre for nitrogen. Liquid fertilizer (almost all kinds) typically weighs about 10 lbs for each gallon. The amount of nitrogen in the fertilizer is about 3.2 lbs for each gallon (32%). To get 100 lbs of nitrogen, you need to apply over 30 gallons per acre. A pound is a pound is a pound. Regardless of the form, if the plant requires 90 lbs of potassium, the plant requires 90 lbs regardless of whether it is applied as a granule or in a liquid. When adequate amounts of liquid fertilizer are applied to rice, foliar burn is often a problem. Because of these problems, granular fertilizer is for the major nutrients are much more effective.

The only micronutrient that is recommended by foliar application for rice is zinc. The preferred method of applying zinc is to apply zinc sulfate (36% zinc) prior to planting. Zinc seed treatments are effective if the soil test levels are only moderately low. However, if the rice has emerged, foliar application of zinc is effective when applied prior to flooding. At least 1 lb/acre of zinc should be applied when using liquid zinc products. For most products, this will require a minimum application rate of 1 gallon of liquid zinc per acre. This is true for any product that is 10% zinc or less. While some products have been marketed at 1 quart or 1 pint per acre rates, these rates are not sufficient to prevent zinc deficiency on soils with low soil test zinc levels.

1 comment:

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