Potato Crop Productivity Estimator for the Columbia Basin

N. R. Knowles, Postharvest Physiology and Biochemistry Lab, Dept. of Horticulture and Landscape Architecture, Washington State University, Pullman, WA

Background to the Crop Productivity Calculator

This website was developed by the Potato Postharvest Research Group under the direction of N.R. (Rick) Knowles at Washington State University to illustrate the effects of seed source and stem numbers on tuber set and size distribution of Ranger, Russet Burbank and Umatilla Russet seed potatoes in the Columbia Basin of Washington.

Estimates of tuber set and size distribution from stem numbers via the algorithms in this website are based on 2- to 3-year average yields from different physiological ages of seed tubers planted in replicated plots at Othello, WA. Spacing was 34 inches between rows and 10 inches between seedpieces (1.75-2.25-oz/seedpiece) within a row. Seedpieces were planted 8 inches deep. Stem numbers were counted just prior to row closure (mid June) and averaged over at least 100 ft. of row. All crops were grown for an average of 160 days under a linear move irrigation system. The estimates of percentage tubers in each size category from stem numbers will vary with spacing.

For a particular cultivar and seed source, early-season comparisons of potential productivity can be made by entering the average stem numbers per plant for crops growing under the same management conditions in the Columbia Basin. Stem number/tuber set response models were developed for seed from northern (54oN latitude, e.g. Alberta) and southern (47oN latitude, e.g. Montana) growing areas. Therefore, one must choose the seed source that most closely matches the origin of the seed for which yield estimates are to be made. For comparisons among crops or seedlots, up to five average stem numbers can be entered simultaneously in the table below.

Seed butanol content was measured at the end of a 200-day storage period, just prior to planting (mid April). The expected stem number per seedpiece (i.e. per plant) can be estimated by entering the seed butanol concentration. The resulting stem number per plant estimate is then entered into the yield calculator to assess potential productivity of the seed prior to planting.



Enter seed butanol content (ng/g fresh weight): and .


Stems Per Plant
Yield Component
Less than 4oz (%)
4oz - 6oz (%)
6oz - 10oz (%)
10oz - 12oz (%)
12oz - 14oz (%)
Greater than 14oz (%)
Tubers per stem
Tubers per plant
Grams per tuber
oz per tuber
Tubers per acre (x1000)
Tons per acre

Limitations of Prediction of Relative Seed Productivity and Crop Performance

The limitations for estimating relative crop and/or seed performance from stem number counts after planting, or from 2-methyl-1-butanol content of seed prior to planting include:

  1. The correct models must be applied to the correct seed source (e.g. northern vs. southern seed) and cultivar (selected from the drop-down menu on the website).

  2. Tuber set and size distribution estimates from this website are only valid over the stem number and butanol ranges that we obtained experimentally for each cultivar and seed source. The ranges will likely increase as we update the site with additional years' data.

  3. Comparisons should only be made among two or more seed lots or established crops within a particular growing season (not between years).

  4. Seed lots and/or established crops can only be compared if they are planted in close proximity and are grown under the same environmental conditions and management regimes.

  5. Absolute yields cannot be determined with precision - only relative yield profiles (percentage tubers in each size class, approximate average tuber weights, and relative numbers of tubers/A) of seed lots or established crops (e.g. from stem counts in early to mid June) can be estimated. Seed lots or established crops should only be compared to end up with a relative ranking of expected productivity.

  6. While the underlying stem number/tuber set relationships presented in this website are valid for each cultivar regardless of production area, productivity estimates are only relevant for seed planted in the Columbia Basin. The differences in length of growing season and climatic variables inherent in other production areas will modulate tuber set and bulking to affect tuber size distribution and yield.