The quality of a potato harvest might have more to do with how seeds were stored than how they were treated in the field the previous year.
Alison Nelson, agronomist and researcher at Carberry’s Canada-Manitoba Crop Diversification Centre, says warming up seed before planting may have more impact on a processing crop than most in-season management of the seed crop the year before.
The AAFC researcher is studying how planting date, harvest date, moisture and storage of a seed crop might impact a daughter crop grown from those seeds. To test this, Nelson designed a multi-year trial first manipulating seed crop management, then returning with those seeds to measure changes in the processing crop the next year.
Nelson spaced out seed crop planting and harvest dates by two to three weeks to test early or late timing. Alternately, she thought, a processing crop might be impacted if its seed crop had been irrigated or dryland managed.
Finally, she wanted to test what would happen if that seed was kept in a constant environment leading up to seeding, compared to if temperature ramped up in the weeks before seeding.
The team requested temperature be brought up half a degree each day for the ramped-up samples, starting a month before their target seed date and eventually bringing temperature to 10 C and keeping it there. The remaining seed was kept constant until 10 days before Nelson was scheduled to pick it up. Those seeds were warmed at that point to avoid shock when they were planted, she said, but spent no storage time in the warmed environment.
To Nelson’s surprise, storage temperature stood out as one of the few, and certainly the most dramatic factor, impacting processing crop.
Ramped-up seed emerged earlier in both years of the trial, she said, although the constant temperature plants caught up within 30 days. More significantly, ramping up storage temperature translated into more tubers and more stems per plant. The warmed seed returned 182 tubers an acre with an average 4.3 stems per plant, compared to 159 tubers an acre and 3.9 stems per plant with constant temperature.
Related to that, temperature was also correlated to changes in size profile. With more stems, tubers from the ramped-up seed were smaller. Most of the tubers (40.7 per cent) were between three to six ounces when seed was warmed, compared to 31.7 per cent when temperature was constant. The tables were turned for potatoes between six and 10 ounces; 40.2 per cent of tubers from constant-temperature seed fell in that larger range, compared to 35.4 per cent of warmed-seed potatoes.
“I guess I was surprised that there weren’t more significant impacts of the management practices in season on the results. The storage temperature just sort of overwhelmed everything else,” Nelson said.
Leonard Rossnagel of the Seed Potato Growers Association of Manitoba said the study might offer insight for producers aiming for optimal yield and size.
“Younger seed tends to produce fewer stems, larger tubers,” he said. “So if you have a short season, you may want a few fewer stems per acre so that your tubers will get to an adequate size, whereas when you have a long season, well then hey, you can go with more tubers and you’ll have the time to size those up.”
In reality, he said, late planting will have already aged the seed, resulting in more stems on top of the short season size impact.
“If you’ve got a nice long season, then it certainly makes sense to warm those tubers up so that you can take advantage of the extra numbers and size them. I think you can better manage a long season by warming them up,” he said.
What’s common practice?
Nelson admitted that the ramp-up was likely more extreme than what most producers do.
Processed potato growers might tap into several options when it comes to their seed, Rossnagel said. In some cases, process growers take over seed management during the winter. Larger seed growers, however, may do custom cutting and will store the seed and prepare it before delivering to the producer.
It is common practice to warm seed, he added, although the process is usually a fine line between warming seed and having it start to grow in the bin.
“You want the seed to be ready to grow, but you don’t want it to be growing before you plant it because if the sprouts are very long, then those get knocked off during the handling and planting operation, so that’s a bit of a waste of the seed’s resources,” he said.
Other seed crop management had little impact the following year.
Planting date was the only other factor to impact either stems per plant or tuber size in the process crop, although it had no impact on gross yield or number of tubers per acre. In fact, no factor, including storage management, impacted gross process crop yield.
Seed crops planted before May gave more stems (4.2 per plant, compared to four stems per plant when planted two to three weeks later), and fewer extremely large tubers. Seven per cent of processing potatoes were over 12 ounces when sourced from early-planted seed, compared to nine per cent when the seed crop was planted late. Smaller sizes showed no significant difference.
Moisture, meanwhile, turned the only other significant results of the trial. Irrigated seed crops had more defects the following year (six per cent compared to four per cent from dryland plots), but otherwise made no significant difference to yield, tuber size or stems per plant.
Nelson did not stop with the four management impacts alone. The study combined different mixes of planting dates, harvest dates, storage and moisture programs to measure any interactions between those factors.
Again, to her surprise, results showed few significant interactions between management practices.
“There were a few instances where, we would say, our less than ideal levels combined across a couple of those factors (and) did impact our quality or our emergence patterns, but nothing that really struck out as a strong result like our main factors did,” she said.
“I would think that as you start to layer less than ideal practices, one on top of another, that we would start to see an impact on the processing crop,” she added. “Maybe we just didn’t pull those differences far enough to the extremes to really emphasize that.”
Future results may be interesting to watch, however, she added, since 2017 was much drier than all other years so far.
“I’m thinking that the moisture regime of the seed crop is going to look different this year than it did over the last two years where we had rainfall that was really sufficient to carry the seed crop. This year we did see, coming out of year one, those dryland seed pieces are more stressed than the previous two years.”