Agriculture and Forestry: Potato Fertilization

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Potato Fertilization

Agdex #: 163/541
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History: Revised February 3, 2000
The production of high yield quality potatoes depends upon many factors; these include disease-free seed, a deep seedbed, proper soil pH, freedom from disease and insects, adequate heat and moisture PLUS adequate fertility. The nutrients recommended on the attached report should give optimum yields if all other essential requirements are provided.
The recommendations for potatoes are based on the soil test results but are adjusted for a number of factors in the crop rotation as well as for some varieties. If the crop to be grown is indicated as POTATOES, then the recommendation is for general round varieties; if the variety is specified (eg. POTATOES - BURBANK), then the nitrogen recommendations are adjusted for that variety.
It is important that adequate fertility be applied for the crop; however, excess fertilizer can do more harm than good. Table 1 on page 3 indicates some of the problems which may result from deficiencies and excesses of common nutrients.
Fertilizer Applications for Potatoes
The application method will affect the amount to be applied. Broadcasting Phosphorus, for example, is very inefficient for potatoes and is not recommended. Nitrate-Nitrogen when either broadcast or banded at planting, can be lost in a wet spring before the crop can use it.
The four most likely ways to apply fertilizer to potatoes are:
Broadcasting all fertilizer prior to planting. Banding all fertilizer with the planter. A split application with all of the potash and some of the nitrogen broadcast prior to planting PLUS the remainder of the nitrogen and all of the phosphorus banded with the planter. A split application with all of the phosphorus and some of the nitrogen banded with the planter PLUS the remainder of the nitrogen and all of the potash broadcast after plant emergence, prior to one of the early hilling operations.
Of the 4 methods listed above, the first is not recommended because of the excessive losses of phosphorus. The second method listed, banding all fertilizer with the planter, is widely used and is very effective. The major disadvantages of banding all the fertilizers are:
excess nitrogen can be lost in wet springs, all fertilizer must be handled during the busy planting season, no adjustment can be made in fertilizer rate within a field to allow for fertility differences within the field.
The last two listed methods, using split applications, give maximum efficiency of nutrients yet flexibility within the fertilizer program. They do require two trips over the field but this extra cost and effort may be justified. The last method listed is the best method because it places the nutrients in contact with the crop at the most crucial period.
An example of a split application program would be as follows:
N Requirement - 145 Kg/ha; P2O5 Requirement - 190 Kg/ha; K2O Requirement - 100 Kg/ha
Banded Application: 400 Kg/ha of 18-46-0 * Broadcast Application: 500 Kg/ha of 15-0-20
The material to be banded in this example is 18-46-0 (diammonium phosphate). It is an excellent product for use in a planter because of its uniform particle size and ease of flowing despite high humidity. If the planter will not spread a rate as low as 400 Kg/ha, the 18-46-0 can be blended with fertilizer filler until an appropriate spreading rate is obtained. The broadcast product is 15-0-20 and it will be a blend of ammonium nitrate, or urea, and muriate of potash. Although it may become "sticky" in humid weather, this should not be a problem with most broadcast fertilizer applicators.
* Broadcast preplant or postplant prior to hilling, the latter being the better alternative.
TABLE 1: Nutrient Deficiencies and Excesses
ELEMENTS	DEFICIENCIES	EXCESSES
Nitrogen	Reduced total yield Reduced tuber sizing Pale stunted foliage	Delayed maturity Excessive top growth Hollow heart & growth cracks Increased susceptibility to disease Reduced tuber specific gravity Difficulty in top killing
Phosphorus	Reduced early vigor Delayed maturity Reduced yield	Ties up other elements such as calcium and zinc
Potassium (Potash)	Reduced nitrogen uptake Reduced yield Increased storage black spot	Reduced tuber specific gravity Reduced calcium and/or magnesium uptake Poor soil structure
Calcium	Reduced root growth Deformed foliage growth tips Reduced yield Reduced tuber quality Poor soil structure	Reduced magnesium uptake
Magnesium	Reduced photosynthesis rate Reduced yield Reduced tuber formation	Reduced calcium uptake