Potato Nitrogen Management
Alan Blaylock, Ph.D.
Dr. Alan Blaylock brings extensive North American and international experience in nutrient management to the agronomy team. University studies and service as a university extension soils specialist prepared him for a long career in the fertilizer industry. Having managed both domestic and global research and education programs, Dr. Blaylock has a wealth of experience in applying science-based nutrient management principles and products to solving practical questions. Dr. Blaylock earned Bachelor of Science and Master of Science degrees in agronomy and horticulture from Brigham Young University and a Ph.D. in soil science from Iowa State University. He has been in agriculture his entire life — from his childhood on an irrigated farm in eastern Oregon to teaching soil science at Iowa State University to his current role as an agronomist at Nutrien. These diverse experiences helped Dr. Blaylock develop the skills to excel in translating complex scientific principles into practical solutions. Although early in his university studies he explored computer science as a profession, deep family roots in agriculture brought him back to the people and values of his heritage. His career satisfaction comes from helping others improve the performance of nutrients and cropping systems.
Nitrogen is the nutrient element that usually has the greatest impact on potato yield, quality, and profitability and is one of the most important inputs in potato production. Proper nitrogen management is critical to yield, quality, and profitability. Improper nitrogen application can also lead to water- and air-quality impairment.
A unique combination of intersecting soil and management considerations complicates potato nitrogen management. Potatoes are also a high-value crop that is very sensitive to timing and amount of nitrogen available to the crop. Nitrogen is needed to establish the proper vegetative, or vine, growth needed for high yields, but excess nitrogen can produce excessive vine growth, increase susceptibility to disease, delay tuber bulking, thereby reducing yields, and negatively affect several important quality variables. Maintaining the proper amount of nitrogen in the root zone is made more complicated by the sandy soils coupled with irrigation and/or high rainfall in which potatoes are usually grown. The nitrogen-management objectives are, therefore, two-fold: 1) minimize nitrogen loss from the root zone and 2) carefully regulate the amount of nitrogen in the root zone through the growing season.
Nitrogen loss from cropping systems occurs through three main processes: leaching, denitrification, and volatilization. Leaching is the downward movement of nitrogen with water. Leaching loss is greatest in coarse-textured soils and is, therefore, the loss mechanism of greatest concern in potato production. Leaching may occur anytime during the season when nitrate is present in the soil and is accompanied by rainfall or irrigation in excess of soil water-holding capacity.
Denitrification occurs when the soil becomes saturated or nearly saturated. Denitrification results from anaerobic soil bacteria converting nitrate-nitrogen into gaseous nitrogen forms, including nitrous oxide (N2O), a potent greenhouse gas, that subsequently escapes from the soil. Denitrification occurs mostly in fine-textured soils, so is not an important loss mechanism in most potato production, except for short periods during irrigation or heavy rainfall events.
Volatilization is the loss of ammonia gas from the soil and commonly occurs when urea-containing fertilizers are surface applied and not incorporated. Urea is converted to ammonia by a soil enzyme called urease. If the urea conversion occurs on or near the soil surface, some ammonia can escape to the atmosphere. Volatilization is at a maximum within a few days after urea application if the urea is not incorporated with tillage, rainfall, or irrigation. Volatilization losses are usually minimal in potato production because most nitrogen is incorporated or applied with irrigation water and is seldom left on the surface long enough to volatilize. Potato nitrogen need corresponds to growth stage. Growth stages, vine and tuber growth, and nitrogen uptake are shown in Fig. 1 below for Russet Burbank after Zebarth and Rosen. Varieties vary in the duration of growth stages, timing, growth rate, and nitrogen uptake but follow the same general pattern. Growth stages are as follows: I. Planting to emergence; II. Vegetative growth; III. Tuber initiation; IV. Tuber bulking; and V. Tuber maturation. During seedling development and early vegetative growth little nitrogen is needed. Excess nitrogen during this time can lead to excess vine growth, delayed tuber initiation and shortened tuber bulking time, greater vine disease, and eventually greater internal defects in tubers. Peak nitrogen demand occurs during tuber bulking where uptake ranges from two to four pounds of nitrogen per acre per day, or more in high-yielding environments.1 During late tuber bulking and tuber maturation, nitrogen uptake slows as the plant matures, allowing the skin to thicken, or “set” on the tubers. Excess nitrogen during maturation can decrease tuber-specific gravity, delay skin set, and increase potential for leaching loss.
Potato growers optimize nitrogen management by dividing their decisions into four basic components and asking questions such as those posed below. Each of these decisions should consider specific variety nutrition needs, the growing environment and potential for nitrogen loss, equipment, irrigation and fertigation capabilities, available nitrogen sources, and other factors.
- Plan for regulating nitrogen supply to the crop.
a. How much potential for nitrogen loss exists?
b. Do I have fertigation capability for in-season nitrogen applications?
c. Is mechanical in-season nitrogen application feasible?
d. Is controlled-release nitrogen, such as ESN, an option? It has been proven effective at regulating nitrogen supply in potato production.
- Establish a base, pre-plant (or early side-/top-dress) nitrogen program.
a. What are the specific needs for the variety being grown? Some varieties may need more nitrogen during early vegetative growth while others need much less.
b. Should the early nitrogen be applied before/at planting or at emergence for the specific variety and growing environment?
c. Do I have soil-nitrate tests? Are they meaningful for my production area?
d. How much is needed to feed the crop until in-season applications commence?
e. Will pre-plant nitrogen be broadcast or banded? What nitrogen sources and equipment are available?
f. Is this a good time to consider a controlled-release nitrogen fertilizer, such as ESN as a component of the base program? ESN, when properly used in potato production, has been demonstrated to be an effective means of both controlling nitrogen loss and regulating supply to the crop.
- Consider potential starter benefits.
a. What equipment do I have? Can I apply starters while planting?
b. Will starter phosphate, potassium, micronutrients, and biostimulants enhance the overall effectiveness of the nitrogen program by stimulating growth, eliminating limiting factors, and enhancing plant health?
c. Are there liquid tank-mix limitations or considerations that govern starter applications?
d. Will my equipment apply dry starter blends?
- Develop a plan for in-season nitrogen applications.
a. Are mechanical nitrogen applications in-season feasible and practical? If fertigation is not available or not practical with available equipment, mechanical top-dress applications may be needed.
b. Is fertigation available if potatoes are irrigated? Application with irrigation water is relatively low cost and, in most systems, has great flexibility in timing and amount of nitrogen delivered.
c. Will soluble calcium be needed during tuber bulking? Soluble calcium sources often contain nitrogen, which should be included in the nitrogen budget.
d. Will foliar nitrogen applications be useful in supplementing other nitrogen applications?
e. Will in-season diagnostics be available to monitor crop nitrogen status?
Fortunately for growers, there are tools available to help mitigate the potential for nitrogen loss and regulate nitrogen supply. In-season nitrogen supply is one of the most effective tools in potato nitrogen management, both in regulating supply to the crop and in controlling losses. Split nitrogen applications, spoon feeding through fertigation, and controlled-release nitrogen fertilizers such as ESN can help achieve the two main objectives of controlling nitrogen supply to the crop and reducing losses. All help control the soil nitrate concentration, a major factor in leaching loss. Early top-dressing at emergence is effective as it is usually accompanied by a hilling operation which incorporates the nitrogen. This is an excellent time to apply ESN for full-season varieties. Foliar applications have the advantage of rapid absorption for immediate correction of deficiencies but have the disadvantage of higher cost and low application rates. Use crop diagnostic tools, such as tissue testing and remote sensing, to monitor crop nitrogen status. Petiole nitrate analysis is the most common tissue diagnostic test used in potato production.
|Nitrogen Treatment||Yield||Tubers > 6oz||N Uptake||NO3 leaching||Direct N2O Emissions|
|Urea + DCD||538||66.7||169||59||0.62|
|Urea + DMPP||543||67.1||167||65||0.71|
|Urea + DMPP + NBPT||540||66.5||165||64||0.70|
Nitrification inhibitors, which slow conversion of ammonium to nitrate, while not effective for regulating nitrogen supply, may reduce losses from leaching and denitrification by reducing nitrate-nitrogen levels in soil. In a recent Minnesota study, nitrogen stabilizers did not significantly increase tuber yield, size, or nitrogen uptake, but did reduce nitrous oxide emissions.3 Also observed in this study is that urease inhibitors had no significant benefit. Because volatilization is likely a minor loss pathway in potato production, urease inhibitors are not likely to prove beneficial.
Finally, no discussion of nitrogen management in potatoes would be complete without including the importance of irrigation management. Irrigation must be uniform, should meet crop demand but not exceed soil water-holding capacity, and should employ scheduling tools that improve irrigation efficiency. Fertilizer applied through fertigation will only be as uniform as irrigation-water application. Improper, excessive, or non-uniform irrigation will foil the best nitrogen management practices, decrease nitrogen-use efficiency, reduce yield and crop quality, and lead to environmental impairment. If irrigation presents challenges, consult a local crop advisor or irrigation specialist for assistance.
Five key elements to successful nitrogen management in potatoes:
- Plan ahead for nitrogen application options.
- Know your environment and potential nitrogen loss pathways.
- Apply the correct amount of nitrogen at each growth stage.
- Use in-season applications, including fertigation where available, to control nitrogen supply and minimize losses.
- Observe and adjust in-season as needed according to growing conditions and crop need.
1Hopkins B.G., Stark J.C., Kelling K.A. (2020) Nutrient Management. In: Stark J., Thornton M., Nolte P. (eds) Potato Production Systems. Springer, Cham, New York. Online ISBN 978-3-030-39157-7. Print ISBN 978-3-030-39156-0. https://doi.org/10.1007/978-3-030-39157-7_8
2Zebarth, B. J., & Rosen, C. J. (2007). Research perspective on nitrogen BMP development for potato. American Journal of Potato Research, 84(1), 3-18. https://doi.org/10.1007/BF02986294
3Souza, E.F.C., C.J. Rosen, R.T. Venterea. 2019. Contrasting effects of inhibitors and biostimulants on agronomic performance and reactive nitrogen losses during irrigated potato production. Field Crops Res. 240:143-153. https://doi.org/10.1016/j.fcr.2019.05.001