Seed Size Distribution

A commercial Norkotah grower I was visiting with recently was trying to choose which of three seed lots he should buy for next year. His first thought was to stick with the seed grower he bought from last year, since that offer was the cheapest.

I asked him what he was trying to achieve. He said that to stay in business he needed to increase his yield and grow a much higher percentage of count cartons while getting the biggest return for every dollar he had to spend. He needed to keep seed costs low, but he wanted to make sure that the seed he purchased gave him the results he wanted.

He mentioned he could buy this seed lot from the same grower as last year for $8 per cwt. delivered, but he was concerned about last year’s results.

As I spoke with him, I found that last year he dug up a few rotten seed pieces. He also said he saw a lot of blind seed pieces that came through the six-cut bar. I asked him what the size profile was. He distinctly remembered a lot of huge tubers going through the six-piece cut. The grower also remarked that the seed supplier’s storage was old and he noticed a lot of sprouts being knocked off through the cutter.

He had been trying to achieve a 12-inch spacing. Due to seed piece decay and lousy distribution from uneven sized seed pieces he missed getting an even population. He ended up with a skimpy stand, and at harvest he had a few big tubers and too many undersize tubers.

The excessive aging of his seed in the poor seed storage and too much pre-sprouting pushed too many stems per plant, resulting in a lot of undersize tubers that went to the flake plant. Needless to say, his banker was not happy with the packout returns from last year.

To hit his real goal of a high yield of count cartons he needed a very even distribution of stems per foot of row or about four stems per plant with a 12-inch spacing. For this spring’s choices, we analyzed a lot similar to this seed lot as lot A at 212 tubers per cwt. with a 12-ounce top. I calculated that on lot A he could spend about $149 per acre for seed because he could cut the large tubers into six pieces.

He could buy a different seed lot (B) that has a 10-ounce top and size profile samples taken by the seed grower as he filled the seed bin at harvest. This lot averaged 271 tubers per cwt. This lot has very low virus readings and no black leg was noted in the second field inspection. The seed storage has good insulation and an evaporative cell. The price for this lot would be $10 per cwt. delivered. This lot I calculated would cost about $203 per acre but would have a good chance of producing a lot more count cartons and less undersize if the commercial grower can receive, cut and plant it without stressing this lot.

Another lot he could buy (Lot C) has an 8-ounce top and averaged 343 tubers per cwt. This lot has a lot of small seed that would be single drop or splitters with very few tubers going through the four- or six-piece cut bar. The disease readings are very low with no black leg. The seed storage has been remodeled and the seed grower installed a refrigeration unit as well as an evaporative cell so he could harvest earlier in the fall and keep the seed from sprouting too early in the spring.

This seed lot would allow the grower to cut the seed in a tight size distribution and allow his planter to perform without skips because the seed size will be very uniform. Shrink from chips lost during cutting will be lower. The population of stems per foot of row or stems per plant will be under better control so there should be less undersize tubers and more carton count. This lot would cost about $253 per acre. This 8-ounce top lot will cut with much less blind seed pieces.

Which lot would you buy? Which lot is really the most expensive? Which lot will net the most dollars per acre? If you can shift your harvested tuber count into more cartons through selecting a better seed profile, will it pay for the more expensive seed lot?

Some university researchers have begun to gather data that sprouts per seed piece along with the correct uniform seed spacing have a huge effect on the harvested size profile. Sprouts per seed piece are determined in great part by storage conditions and spacing is greatly influenced by seed-size profile.

If you are unhappy with your packout returns and see too many small checks from the flake plant, you should work with your seed grower to develop a seed-size profile target to produce a higher percentage of carton counts as well as proper seed aging.

75 Applewood Dr. Ste. A
P.O. Box 128
Sparta, MI 49345


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