The weather so far this spring seems to indicate it could be one of those springs when crops are planted between rain showers. And if it's anything like almost nay other season ever, there will be the 'wrong' days to plant. Since there is no way to predict them in advance, odds are good you may wind up with at least a field or two planted in that window. The result is usually stands that aren't up to par.
Then comes the two-fold question. Is the stand good enough to leave? If the answer is no, obviously you plant over. If it's yes, there's a second question, especially if you were planning to apply nitrogen after planting. Should I drop back on my rate since I don't have the stand that I expected to have?
Agronomists from the Indiana Certified Crop Advisors Group caution against being too quick to pull the trigger, especially on dropping back nitrogen rates. What you consider a sub-par stand may not amount to that much loss of yield potential.
For example, suppose you wanted 30,000 plants per acre and wind up with 26,000 plants per acre instead. The plants remaining are relatively healthy and fairly evenly distributed up and down each row. Marty Park, a CCA and account manager for Pioneer in northwest Indiana, says that you still have 87% of your desired population. If the hybrid has a lot of flex bred in, it could make up a lot of this gap in actual desired population by harvest time, he notes.
Furthermore, with most plants healthy and evenly distributed, and assuming planting took place at a reasonable time, there's only a 1 to 2% predicted decrease in potential yield for that 4,000 plant drop off your intended goal, Park notes. He bases that on data in the 2009 Purdue University Corn & Soybean Field Guide. It's a pocket guide published every year by the Purdue Diagnostic Training Center, affiliated with the Purdue Agronomy Department.
How much play you built into the rate in the first place may come into focus, he adds. If you were going on the high side for your yield goal with N rates, you might now have some room to fine-tune the rate a bit. However, if you has already shaved rates down more closely, then you might want to resist playing with rates.
Bryan Overstreet, also a CCA and Extension ad educator in Jasper County, advises caution before cutting back your order of anhydrous, or dialing back the applicator rates. "I think I would use the normal rate of ammonia," he says. His thinking is based largely on the same logic- that a 4,000 plant cut could only amount to a 1 to 2% yield loss.
Tests at Purdue's Throckmorton farm last year by Jeff Phillips of Tippecanoe County Extension seem to confirm that finding. The ideal population in a population test was 30,000 plants per acre. But in a second test where nitrogen sidedressing rates and populations were evaluated, highest yields actually came from 26,000 plants per acre.
The scenario would change if populations are much lower, or if stands are uneven. Consult Purdue's Field Guide for more info. Look for a full discussion of this issue in Crops Corner in the June issue of Indiana Prairie Farmer.