b'Andys Advice:Potato Stem NumberCan Improve ProfitsBy Andy Robinson, Extension Potato Agronomist, NDSU/UMNnumber is the physiological age of handled.Agedtuberswillhavethe tuber. Potato seed is aged in two more stems, more tubers and small-ways,chronologicallyandphysio- er average size as a result of compe-logically.Thechronologicalageis tition (Figure 1). thenumberofdaysthathavepassedsincethetuberswerehar- Now, lets focus more on some prin-vested. The physiological age refers ciplesinstemnumber.Researchtotheinternalageoftheseedas clearly shows that as stem numberaffectedbybiochemicalchanges increases,sodoestubernumber.thattakeplacewithinthetuber. HighstemnumberresultsinaPotatotubersageatagreaterrate smaller tuber profile and can reducewhengrowninstressfulenviron- overall yield and, even more impor-mentssuchastemperaturestress, tant, marketable yield (Table 1). TheAs you prepare to plant your potato moisturestress,fertilitystress,or oppositeisalsotrue.Withfewercrop this year it would good to take disease pressure, when stored under stems there are fewer tubers, whichsometimetoreviewtheeffectof fluctuatingtemperaturesorwarm resultinalargertuberprofilestem number on potato production. temperatures, or are bruised or mis- (Figure1).ThinkaboutthisforaThis is important because knowingyour stem number will likely affectyourproductionandprofitability.Becausepotatoesareinherentlyquite variable, seed will vary acrosslotsandwithinthesamelot.Growers most typically use the aver-age stem number to determine theexpectationofeachlot.Certainly,thedesiredsizeandnumberoftuberswilldependonthevarietybeing grown and the growing sea-son.Figure 1. Difference in tuber number and size when comparing a 2 vs. 6 stemThemainfactoraffectingstem Russet Burbank plant in the same field.12 POTATO GROWER APRIL 2021'