MINNEAPOLIS — Some of you have noticed and commented that the spring wheat crop is shorter when compared to the last few years and subsequently questioned its yield potential. A few weeks ago, Dr. Joel Ransom wrote a nice article in the Crop & Pest Report explaining why the spring wheat crop was shorter and whether its yield potential had already been reduced.
The physiology of grain fill has been well researched and we have a good understanding how temperature and droughts tress affect grain fill and grain quality. Table 1 summarizes the results of one of the published studies that illustrates how daytime and nighttime temperatures affect the length of the grain fill period and ultimately yield. The bottom-line is that higher nighttime temperatures are more detrimental than the maximum daytime temperatures.
Just in the last two days has the grain fill suffered some heat-stress, as maximum temperatures had not yet reached above 85F in the two weeks prior while minimum temperatures were mostly in the fifties in the same period (Table 2).
Therefore, I am optimistic about this year’s yield potential, despite the shorter than normal crop as the first weeks of grain fill have been favorable, allowing for a larger proportion of the grain being produced de novo rather than being recycled from the shorter canopy.
The only caveat in this optimism is that the crop didn’t suffer any other stresses these past two weeks. Drought stress poses the greatest threat but the cooler temperatures also reduced the crop’s daily water consumption considerably.
Table 1 – Effect of daytime and nighttime temperatures on the length of the grain fill period and the average kernel weight (after Altenbach et al, 2003)
|Length Grain Fill
|Thousand Kernel Weight (grams)|
Table 2 – The daily maximum and minimum temperatures at 3 NDAWN locations in NW Minnesota and the number of days the temperatures were outside the optimum range for grain fill for spring wheat.
|# Days Tmax>85||2||–||2||–||2||–|
|# Days Tmin>60||–||1||–||2||–||2|
— Jochum Wiersma, University of Minnesota Extension
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