Should fertilizer rates be reduced when freezes reduce crop levels?

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Fruit crops utilize varying amounts of nitrogen (N) and potassium (K) to grow and mature a full crop of fruit. If the fruit crop is lost or reduced by freeze damage, the nutrient needs are also reduced to some degree. Here are some thoughts on fertilizing following frost damage.

The amount of nutrients that accumulate in the fruit of apples, stone fruit, grapes and blueberries is one estimate of how much fertilizer can be reduced if the crop is frosted out (Table 1). The N content of the fruit ranges from 8 lb per acre (blueberries, cherries) to as high as 50 lb per acre (15 ton per acre peach crop). The K contents range from 8 to 80 lb per acre. A good rule of thumb for grapes is that 5 lb K are contained in each ton of fruit. In the event of a total crop failure, fertilizer rates can be reduced by at least these amounts. Since plants obtain only part of their nutrient needs from added fertilizer (the rest from soil reserves), fertilizer rates can be reduced even more in some cases.

Table 1. Nitrogen and potassium removed from fruit plantings in harvested fruit (lb per acre).


If the fruit of apples or grapes is lost to frost, N rates can be reduced by 50 percent (on lighter, sandier soils) to 100 percent (heavier, fertile soils) of typical applications. If the entire crop of cherries, peaches or blueberries were lost, N rates can safely be reduced by a third on sandier soils, to as much as a half on heavier soils. Reduce rates proportionately in the case of partial crop failures.

The effect of crop loss on K requirements is difficult to estimate. Fruit are strong sinks for K, so the K demand is clearly reduced when no crop is produced. Frost-damaged plantings on heavier soils likely will not benefit from K additions this year. Plantings on sandy soils with a low K reserve or where tissue analysis has indicated a need for K, may benefit from K, but will require lower rates, perhaps half of the typical application. Applications of K could be discontinued this year where K levels in the soil are moderate to high, and an annual maintenance application of K is typically applied.

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