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Potato fertilization on irrigated soils

Optimum potato growth depends on many management factors, including a sufficient supply of nutrients.  Potatoes have a shallow root system and a relatively high demand for many nutrients (Table 1). A comprehensive nutrient management program is essential for maintaining a healthy potato crop, optimizing tuber yield and quality, and minimizing undesirable impacts on the environment.

Irrigated potatoes are usually grown on coarse-textured soils low in organic matter. Typically, these soils are sandy loams or loamy sands, low in native fertility, and quite acid. The crop's high nutrient demand coupled with low native fertility means that potatoes often have high fertilizer requirements. Over the years, however, continued fertilizer applications can build up the soil test levels of certain nutrients. Base your nutrient management program on soil test recommendations, plant tissue testing, variety, time of harvest, yield goal and the previous crop in the rotation.

Nutrient removal by the potato crop

The amount of nutrients removed by a potato crop is closely related to yield (Table 1). Twice the yield will usually result in twice the removal of nutrients. The vines take up a portion of the nutrients needed for production. The rest goes to the tubers and is removed from the field with harvest. The purpose of Table 1 is to provide relative uptake of essential elements for potato production. Do not use the table as a basis for fertilizer recommendations.

Table 1. Uptake of soil nutrients by potato vines and tubers as a function of tuber yield.

Nutrient Nutrient uptake from vines Nutrient uptake tuber yield:
200 cwt/A
Nutrient uptake tuber yield:
300 cwt/A
Nutrient uptake tuber yield:
400 cwt/A
Nutrient uptake tuber yield:
500 cwt/A
Nutrient uptake tuber yield:
600 cwt/A
Nitrogen (N) 90 lb/A 86 lb/A 128 lb/A 171 lb/A 214 lb/A 252 lb/A
Phosphorus (P) 11 lb/A 12 lb/A 17 lb/A 23 lb/A 28 lb/A 35 lb/A
Potassium (K) 75 lb/A 96 lb/A 144 lb/A 192 lb/A 240 lb/A 288 lb/A
Calcium (Ca) 43 lb/A 3.0 lb/A 4.4 lb/A 5.9 lb/A 7.4 lb/A 8.9 lb/A
Magnesium (Mg) 25 lb/A 5.9 lb/A 8.9 lb/A 11.8 lb/A 14.7 lb/A 17.6 lb/A
Sulfur (S) -- 8.8 lb/A 13.2 lb/A 17.6 lb/A 22.0 lb/A 26.4 lb/A
Zinc (Zn) 0.11 lb/A 0.70 lb/A 0.11 lb/A 0.14 lb/A 0.18 lb/A 0.22 lb/A
Manganese (Mn) 0.17 lb/A 0.03 lb/A 0.04 lb/A 0.06 lb/A 0.07 lb/A 0.08 lb/A
Iron (Fe) 2.21 lb/A 0.53 lb/A 0.79 lb/A 1.06 lb/A 1.32 lb/A 1.58 lb/A
Copper (Cu) 0.0 lb/A 0.04 lb/A 0.06 lb/A 0.08 lb/A 0.10 lb/A 0.12 lb/A
Boron (B) 0.14 lb/A 0.03 lb/A 0.04 lb/A 0.05 lb/A 0.06 lb/A 0.07 lb/A

Soil testing

Fundamental to any effective nutrient management program is a reliable soil analysis and soil test interpretation. Take samples in the top six to eight inches, representative of the area you will fertilize. The soil test will help to determine whether the crop needs lime or nutrients and the rate of application. A typical soil analysis for potatoes should include pH, organic matter, phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn), and boron (B). Soil nitrate tests are not reliable for nitrogen (N) recommendations on irrigated sandy soils, because nitrate can move rapidly and fluctuate widely. We recommend nitrate testing for the finer textured soils and drier conditions of western Minnesota. 

You can test sulfur (S) can on sandy soils if you suspect a problem, although the soil test for S on sandy soils is usually low. Copper (Cu) and manganese (Mn) soil tests are reliable only for organic soils in Minnesota. Iron (Fe) deficiencies are more related to soil pH than to soil test levels. Tissue analysis (see next section) is an alternative method of monitoring the adequacy of Cu, Fe, and Mn. These nutrients are not likely to be limiting on the acid, sandy soils commonly used for potato production, but may be deficient in alkaline soils.

Tissue analysis

You can use plant tissue analysis or tissue testing to: 1) diagnose a nutrient deficiency or toxicity, 2) help predict the need for additional nutrients (primarily nitrogen), and 3) monitor the effectiveness of a fertilizer program. Optimum nutrient ranges provide the basis behind tissue analysis (Table 2). If the level of a nutrient falls outside its sufficiency range, then take corrective measures.

Tissue test the petiole (leaf stem and midrib) of the fourth leaf from the shoot tip. Younger or older tissue will have different nutrient concentrations and can lead to erroneous interpretations. For sampling, collect approximately 40 leaves from randomly selected plants. Strip and discard the leaflets. Petioles are then sent to a laboratory for analysis. We base most diagnostic criteria for tissue analysis on a sample taken during the tuber bulking stage. Samples taken too early in the season or soon after a fertilizer application may not accurately reflect the nutritional status of the crop because the roots have not taken up applied fertilizer. In general, tissue analysis should begin about one week after final hilling and at least four days after a fertigation. Nitrogen is an exception to the rule because sufficiency ranges have also been developed for the vegetative and tuber maturation growth stages.

You can use whole leaves for analysis, but you'll need different diagnostic criteria for interpretations. Petioles are generally preferred as the tissue to use for predictive purposes, because they more accurately reflect the immediate nutritional status of the plants and whether they are currently taking up sufficient nutrients. Nutrients are ultimately transported from the petiole to the leaflets and the whole leaf provides a more integrated nutrient status since nutrients tend to accumulate in the leaflets. Therefore, leaves are better indicators of the cumulative nutritional status of plants and whether nutrient uptake has been adequate up to the present. Table 2 presents a comparison of nutrient sufficiency ranges for petioles vs. whole leaves. Note that K sufficiency levels are much higher for petioles compared to whole leaves. Also note that we use total N for whole leaves but nitrate-N for petioles. Most N in petioles is in the nitrate form and measurement of nitrate-N is a more straightforward procedure than total N. However, there is much less nitrate-N in leaflets and total N provides a more accurate measurement of N status for whole leaves.

Table 2. Suggested nutrient concentration sufficiency ranges in potato tissue collected from the 4th leaf from the top of the shoot during tuber bulking stage (3 growth stages for petiole nitrate-N)

Element Petiole sampled Whole leaf (leaflets + petiole) sampled
Total N -- 3.5-4.5 %
Vegetative Nitrate-N 1.7 - 2.2 % --
Tuber bulking Nitrate-N 1.1 - 1.5 % --
Maturation Nitrate-N 0.6 - 0.9 % --
Phosphorus 0.22 - 0.40 % 0.25 - 0.50 %
Potassium 8.0 - 10.0 % 4.0 - 6.0 %
Calcium 0.6 - 1.0 % 0.5 - 0.9 %
Magnesium 0.30 - 0.55 % 0.25 - 0.50 %
Sulfur 0.20 - 0.35 % 0.19 - 0.35 %
Zinc 20 - 40 ppm 20 - 40 ppm
Boron 20 - 40 ppm 20 - 40 ppm
Manganese 30 - 300 ppm 20 - 450 ppm
Iron 50 - 200 ppm 30 - 150 ppm
Copper 4 - 20 ppm 5 - 20 ppm

Rather than sending samples into the lab for nitrate analysis, diagnostic criteria have been developed for nitrate analysis of the petiole sap. This provides a quick procedure to determine the N status of the plant without having to wait for results from a laboratory. Sap nitrate analysis is primarily used for irrigated potatoes because the water status of the plant is more uniform. It provides inconsistent readings in non-irrigated soils because sap nitrate concentrations can fluctuate with the water status of the plant. Table 3 provides petiole sap nitrate-N sufficiency ranges for Russet Burbank potatoes at different growth stages. Other potato varieties may differ slightly in their sufficiency ranges, but Table 3 is still a suitable starting point for determining the need for additional N.

Table 3. Petiole sap nitrate-N sufficiency levels for Russet Burbank potatoes

Time of season Stage of growth Sap NO3-N
Early Vegetative/tuberization (June 15-June 30) 1200 - 1600 ppm
Mid Tuber growth/bulking (July 1-July 15) 800 - 1100 ppm
Late Tuber bulking/maturation (July 15-August 15) 400 - 700 ppm

Soil pH

One of the more important chemical properties affecting nutrient use is soil pH. Many soils used for potato production have become more acid over time due to use of ammonium fertilizers and leaching of cations from the root zone. Acid conditions are generally better for reducing common scab (Strepotmyces scabies), which is most widespread when soil pH is above 5.5. Use of liming amendments is often avoided to minimize scab. Controlling scab in this manner, however, can result in a soil pH that will cause nutrient imbalances. Once soil pH drops below 4.9, nutrient deficiencies and toxicities become more common. In particular, Mn and aluminum (Al) toxicity and P, K, Ca, and Mg deficiencies may occur in these low pH soils. The problem may not be prevalent through the entire field, but may occur in smaller areas where the soil consists of higher sand or lower organic matter content. In some cases, grid sampling a field for pH may be useful to identify areas that need correction. If you need to take corrective measures, lime the soil to a pH of 5.5 during a year in the rotation when potatoes are not grown. We also recommending using scab-resistant varieties to maintain desirable pH range. Irrigation water can be quite alkaline in Minnesota and may also help to slow down soil acidification processes.

Nutrient management suggestions

Potatoes have a relatively shallow root system with most roots located in the top 1.5 to 2 feet of soil. We recommend using banded fertilizer two to three inches below and two to three inches to the side of the tuber at planting to supply all or a portion of immobile nutrients, such as phosphorus and potassium. For most efficient fertilizer use, select a practical yield goal. Reasonable yield goals are usually set at 15 - 20 percent higher than a grower's average for the past 5 years. For potatoes, yield goal is associated with market class, growth habit (determinate or indeterminate) and the time of the season the vines are killed.


Calcium, magnesium, and sulfur

Potato production on acid sandy soils low in organic matter may require addition of one or more of the secondary nutrients (Ca, Mg, and S) for optimum tuber yield and quality. However, keep in mind that groundwater and irrigation can contain substantial amounds of Ca, Mg and S and may be able to supply all or part of the requirements of these nutrients, depending on irrigation amounts used. Groundwater concentrations of Ca, Mg and S in Sherburne County in a recent study were 55.8,21.3 and 5.3 ppm, respectively.



Most soils contain sufficient amounts of zinc (Zn), boron (B), copper (Cu), manganese (Mn), iron (Fe), chlorine (Cl), molybdenum (Mo), and nickel (Ni) to meet plant needs. However, in some areas, micronutrient shortages occur and may limit yields. Calibrated soil tests for mineral soils are only available for Zn (Table 10) and B (Table 11). Soil tests for Cu and Mn are only reliable for organic soils. You can use tissue analysis to monitor micronutrient status (Table 2). Sandy soils are often low in B and Zn and muck or peat soils are often low in Cu and Mn.

A 5-year Minnesota study on irrigated sandy soil found increases in potato yields with B and Zn applications, but not with Mn or Cu applications. In acid soils, Fe, Mn, and Cu should be available in adequate amounts to meet crop needs. Pesticide sprays often contain enough Cu and Zn to meet plant demands for these nutrients. In extremely acid soils (pH less than 4.8), Mn toxicity may be a problem. Tissue Mn levels greater than 1,000 parts per million are often associated with stem streak necrosis. Potato responses to Mo and Cl have not been reported in Minnesota. Little research has been done on Ni, but required amounts are very low and soil deficiency is probably very uncommon.

If soil or tissue tests show the need for a micronutrient, you can use foliar applications during the growing season. However, with B, we recommend soil application because B applied to the foliage is not readily transported to the tuber. Excessive B applications can be toxic. You can band soil-applied micronutrients with the starter fertilizer.

Table 10. Boron recommendations for irrigated potato production.

Boron soil test Relative level Boron to apply
0.0-0.4 ppm low 1 lb/A broadcast
0.5 lb/A banded
0.5-0.9 ppm medium 0 lb/A
1.0+ ppm high 0 lb/A

Table 11. Zinc recommendations for irrigated potato production

Zinc soil test Relative level Zinc to apply:
Zinc to apply:
0.0-0.5 ppm low 10 lb/A 2 lb/A
0.6-1.0 ppm medium 5 lb/A 1 lb/A
1.1+ ppm high 0 lb/A 0 lb/A

Carl J. Rosen, Department Head, Soil, Water and Climate

Reviewed in 2021

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