Fertilizer Applications (supplement)
If nutrient deficiencies occur in a growing potato crop, it is often possible to supplement the deficient nutrients, either by soil or foliar applications.
Supplemental nutrients, particularly micronutrients, should not be applied unless a deficiency is confirmed because unnecessary applications can result in adverse effects on the crop.
- If deficiencies occur with nitrogen, potassium, calcium, magnesium, or sulfur, it is best to apply nutrients to the soil as a broadcast or sidedress application. This is most practical early in the season before the rows have "closed in" when it is still possible to get through the field with a fertilizer spreader.
- Dry granular fertilizers should never be applied to crops when the foliage is wet or even damp, because the granules will sometimes stick to the leaves and cause leaf damage.
- If at all possible, granular fertilizers should be incorporated into the soil with a cultivation operation.
Certain general principles should be followed when applying foliar nutrients.
- Nutrients can be applied very effectively as foliar sprays
- Only small quantities can be applied in any single treatment, otherwise, "burning" of the foliage can take place.
- Foliar feeding is best used with secondary or micronutrients where plant requirements are relatively small.
- For major nutrients, such as nitrogen, it is often necessary to use several foliar applications in order to supply enough of that nutrient to significantly improve crop yield or quality.
Specific Nutrient Applications
- If nitrogen deficiency is obvious a source containing nitrate-nitrogen (eg: Ammonium Nitrate or Calcium Nitrate) may be used.
- If Urea is used, it should be incorporated into the soil on the day of application to prevent volatilization loss.
- Normal application rates should be 40-60 Kg/ha of actual nitrogen.
- Urea or nitrogen solutions are the only recommended nitrogen sources to use for foliar application.
- If Urea is used, only a foliar or fine grade urea should be applied.
- Normal application rates should be 2.5-5.0 Kg/ha of actual nitrogen.
- Two to four applications, each 7-14 days apart, will be required to overcome a nitrogen deficiency problem.
- Application of a dry granular phosphorus material to an established potato crop is not recommended due to its lack of mobility and lack of availability to the plant.
- Single source, water soluble phosphorus materials are not readily available.
- Application of a water soluble mixed fertilizer with high phosphorus content may be used.
- Normal application rates should be 1.5-2.0 Kg/ha of actual phosphate.
- Any common potassium (potash) source can be used to supplement potassium on potatoes.
- Normal application rates should be 40-60 Kg/ha of actual potassium.
- Applications of typical potash sources include: Muriate of potash, Sulfate of potash, Sulph-O-Mag
- Calcium Nitrate or Calcium Chloride are suitable water soluble sources of calcium for soil application.
- Limestone and gypsum are not recommended because of their limited solubility and availability to the crop.
- Application rates of 20-40 Kg/ha of actual calcium should overcome most deficiencies
- Supplemental soil calcium can be applied any time a deficiency is confirmed.
- Calcium Chloride and Calcium Nitrate can also be used as sources of foliar calcium.
- The source should be checked for purity to ensure that it contains no insoluble impurities which will plug sprayer nozzles.
- Normal application rates should be 0.5-1.0 Kg/ha of actual calcium. Two to four applications with intervals of 14 days should overcome confirmed deficiencies with the first application at full bloom.
- Sulph-O-Mag is the most suitable water soluble source of magnesium for soil application.
- Although dolomitic limestone is a good source of magnesium, it has limited solubility and may not become available to the crop fast enough to overcome deficiency problems.
- Application rates of 10-20 Kg/ha of actual magnesium should overcome most deficiencies.
- Supplemental soil magnesium can be applied any time a magnesium deficiency is confirmed.
- Magnesium Sulfate is a very effective source of magnesium.
- Normal application rates should be 0.4- 0.8 Kg/ha of actual magnesium.
- Two foliar applications , one at full bloom and one 2-3 weeks later, should overcome most deficiencies.
- Solubor is an excellent source of foliar boron.
- The application rate should be 0.2 Kg/ha of actual boron.
- Copper Sulfate is a suitable source of water soluble copper.
- The application rate should be 0.25 Kg/ha of actual copper.
- Zinc Sulfate is a suitable source of water soluble zinc for foliar application.
- The application rate should be 2 Kg/ha of actual zinc.
- If the fungicide used for regular blight sprays contains zinc, this by itself should overcome any zinc deficiencies.
- Deficiency may occur on calcareous soils, especially during cool, wet periods.
- When leaf symptoms are observed, the foliage is sprayed once or twice with a 0.5-2% solution of FeSO4