Trialing two starter fertilizer programs in potatoes to address early-season NPK and micronutrients

Michigan State University Extension and Agro100 partnered to trial two potato starter fertilizer programs in a commercial potato field.


In 2017, Presque Isle County Michigan State University Extension trialed two liquid in-furrow starter fertilizer programs in potatoes in an effort to ascertain if these products would increase potato yield and quality over an untreated control. One program was 2.1 gallons per acre ProTuber. ProTuber is a liquid fertilizer product from Agro100 designed for in-furrow placement in potatoes (7-24-6 + 0.50 B, 0.01 Zn and an auxin, density = 11.22 pounds per gallon).

The second treatment was a custom pop-up fertilizer program used by the collaborating grower, which consisted of 14 gallons per acre 7-25-5, plus 1 gallon per acre of a micronutrient blend (1 qt. Zn, 1 qt. Mn, 1 pt. Cu, and 0.5 pt. B), plus 6 gallons per acre Bio-Gro Premium 6 humic acid, plus 2 gallons per acre Bio-Gro Plant X Bio-SBN.

Materials and methods

The trial was conducted in a commercial potato field near Metz, Michigan, on Emmet sandy loam and Hagensville fine sandy loam soils. A preliminary aggregate soil sample indicated low potassium, manganese and boron levels, requiring amendment with fertilizer inputs. Approximately 200 pounds per acre ammonium sulfate, 200 pounds per acre Kmag and 200 pounds per acre 0-0-60 potash was broadcast and incorporated pre-plant. Silverton potatoes were planted at a 9-inch spacing in 34-inch rows May 26, 2017.

Plots 17 feet wide, corresponding to the grower’s six row planter width, and 100 feet long were established in the field running, and also stacked, east-west. The two fertilizer treatments and a control treatment were replicated four times in a randomized complete block design. The grower’s standard program was applied to the entire field area outside of the ProTuber and Control plots strip, and plots were demarcated north of, and adjacent to, each block for the grower’s treatment.

Both fertilizer treatments were diluted with water to achieve a final application volume of 22 gallons per acre. An additional 12 gallons per acre 10-34-0 was applied in a two-by-two band to all plots at planting.

Potato tissue nutrient status was evaluated during the early tuber development stage July 7, 2017. Potato yield was measured Oct. 6, 2017, by harvesting a 23-feet strip from the middle left row in each plot, followed by hand grading and weighing of the harvested tubers.

Results and discussion

Yield data from the lowest yielding plot receiving the grower’s treatment was thrown out of our analysis after confirming placement over a former irrigation access road. This also addressed unequal variances in the data set. Upon analysis of the remaining dataset, a significant difference in total yield and U.S. No. 1 yield was observed between the ProTuber and control treatments, with the grower’s standard program being intermediate and not significantly different from the ProTuber or control treatments (Table 1).

This is somewhat surprising, given that aggregate tissue sampling did not reveal any notable differences in tissue NPK, or Zn concentrations between the treatments (Tables 2 and 3). All three treatments provided less than sufficient boron for the potato crop, and were low in potassium and boron at the time of tissue sampling. Yet, the order of treatments by tissue boron concentration did match the yield data. This may be the best evidence for a treatment effect, given that ProTuber provided about 0.12 pound acre boron, the growers about 0.07 pound per acre and the control treatment provided no boron.

Tissue analysis did also reveal higher average magnesium levels in the ProTuber treatment relative to the other treatments, which were Mg deficient. Yet, this cannot be directly attributed to the ProTuber product, because it does not contain Mg.

It is possible that any early season differences in nutrient status between treatments may not have persisted until our tissue sampling date. Also, the auxin in the ProTuber and grower’s treatments and humic acid and biological ingredients in the grower’s treatment may have affected root growth, which could help to explain observed differences between the treatments in nutrient status (B, Mg) and yield.

In summary, both the ProTuber and the grower’s standard program appear to have performed quite well, supporting U.S. No. 1 tuber yields 97 and 46 hundredweight (cwt) better than the control respectively. This data results from a single site-year and must be replicated to support any definite conclusions. Limitations of this work, for example, include the lack of information on yield per plant versus per area.

Also, the grower’s standard program was not fully incorporated into the RCB trial design to expedite planting of the trial. Finally, tissue analysis data was not replicated at the plot level, limiting our ability to fully analyze the tissue analysis results, and constraining our confidence in any hypothesis explaining observed yield differences.

Table 1. Average potato yield by treatment and means separation at the 0.05 level.


Total yield (cwt/a)

US No. 1 yield (cwt/a)

Less than 4 oz in %

Pickouts in %

Greater than 10 oz in %


523.93 a

481.45 (92%) a





465.43 ab

430.49 (93%) ab





410.93 b

384.83 (94%) b




Table 2. Average tissue macro and secondary nutrient concentrations by treatment on July 7, 2017.


N (%)

P (%)

K (%)

Mg (%)
















Table 3. Average tissue micronutrient concentrations by treatment on July 7, 2017.


ZN (ppm)

B (ppm)










The authors wish to thank Agro100 for supporting this research and Cliff Wilk for his time and effort in conducting the trial.

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