Michigan State University Extension
Soils & Soil Management - Fertilizer - 06109712
07/10/97
Potato Fertilizer Recommendations Extension Bulletin E-2220, April 1990
Maurice L. Vitosh Extension Soil Specialist Department of Crop and Soil Sciences
Zinc Recommendations
Zinc fertilizer applications to potatoes should be based on soil pH and a Zn soil test. Zinc deficiency does not occur in mineral or organic soils when the soil pH is below 6.7. One ppm of 0.1 N HCL extractable Zn is normally sufficient for potatoes grown on acid, sandy soils (soil pH). (See Table 6 for Zn recommendations based on the soil pH and Zn soil tests.) As the soil pH increases above 6.7, Zn availability rapidly decreases. Thus, higher soil test levels are needed at higher soil pH's to prevent a deficiency. Likewise, more Zn fertilizer is recommended at higher pH levels for a given Zn soil test. ==================================================== Table 6. Zinc fertilizer recommendations for potatoes grown on mineral and organic soils. *
Soil test Soil pH
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7.0 7.2 7.4 7.6
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ppm lb Zn/acre
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2 2 3 4 5
4 1 2 3 4
6 0 1 2 3
8 0 0 1 2
10 0 0 0 1
12 0 0 0 1
14 0 0 0 0
* Recommendations in this table are for band application of an inorganic zinc carrier. When using zinc chelates, divide these rates by 5. ==================================================== When Zn is needed, the best placement is in a starter fertilizer banded at planting time. Alternatively, a broadcast application of 25 lb of elemental Zn per acre may be used to correct the soil Zn levels for a longer period of time. Soil test levels of Zn can also be built up with repeated low rates of Zn fertilizer over time.
Foliar applications of Zn may be used if, for some reason, soil applications of Zn were not made and the possibility of a deficiency exists. Because plants require very small amounts of Zn, foliar application is possible; however, soil applications usually provide longer & availability. For foliar applications, use 0.25 lb of Zn as zinc sulfate in 30 gallons of water when plants are smalls and 0.5 lb of Zn for larger plants.
Zinc Fertilizer Sources
In the fertilizer industry, both inorganic and organic Zn sources are used. Inorganic zinc sulfate is the most commonly recommended Zn fertilizer. Granular zinc oxide is not recommended unless it has been finely ground. Both inorganic sources are blended with solid starter fertilizer. Zinc chelates are normally used with liquid starter fertilizers. True chelates, such as Zn-EDTA and Zn-NTA, are recommended at one-fifth the recommended rate of inorganic sources because of their greater availability in soil. Some chelates, such as natural chelates found in wood extracts, are not as good as the true chelates. Fertilizer Placement
Nutrient Management to Protect Water Quality Extension Bulletin WQ-25, January 1996
Maurice L. Vitosh and Lee W. Jacobs Extension Soil Specialists Department of Crop and Soil Sciences Michigan State University
Band-applied starter fertilizer to the side and below the seed is considered the most efficient placement for P. K and most micronutrients. When soil test levels are low, broadcast applications are less efficient and will normally result in lower yields than band applications. When soil test levels are high, broadcast applications are not likely to improve yields but will build or maintain soil test levels. Broadcast applications of P should be incorporated to improve nutrient recovery by plants, minimize economic losses and prevent excessive runoff. Surface applications of fertilizer on snow-covered or frozen sloping land should be avoided because of the high risk of loss to surface waters in the spring.