The pessimist will tell you the glass is half empty, the optimist will tell you it is half full, the realist will argue it is both, and the scientist will ask you in what direction you measured.
So..is the glass half full or half empty - given the record-breaking early-season heat, lack of precipitation, and dwindling soil moisture reserves?
What we know for spring wheat, barley, and oats (and see today):
- The crop will be short(er) and less likely to lodge.
- The crop will likely lose some or all of its tillers depending on how severe the drought stress is or will become before any measurable precipitation is received.
- The crop will have fewer spikelets per spike/pannicle than most years if the crop reached the 5-leaf stage after the first of June.
What is still unknown:
- The number of kernels per spikelet.
- The average kernel weight of the kernels that are eventually harvested.
As of this moment, the spring wheat, barley, or oat crop in many fields is not past its wilting point, even if plants are aborting tillers and it looks like the crop is walking backward. Even those parts of the field that get that blue hue are not past their wilting point (albeit close) just yet.
Plants that do go past their wilting point will simply whither away. As a whole, the crop will try to get the heck out of Dodge before that point is reached. The main stem will remobilize everything out of the remaining leaves, put it towards a few kernels, and throw in the towel. Those are the years your grandchildren will remember as the time you harvested a quarter and did not even fill up the old tandem truck once.
Given the plasticity of the crop, it is difficult to say what yield potential remains as long as the combination of heat and drought stress does not push individual plants past their wilting point. A couple of rains sooner rather than later, daytime highs not much above 85F, and low dew points during grainfill will allow two of the four yield components to make up for lost ground just yet.
Meanwhile, we may see a weird phenomenon if the canopy collapses, sunlight reaches the ground again, and we do receive precipitation before harvest. The crown may initiate new tillers to create a second crop. These newly formed tillers will be small, will not replace the lost yield potential, and will make timing harvest difficult. Not all varieties are equally prone to produce these 'emergency' tillers and the ability of the crown to initiate them wanes as the main stem gets closer to physiological maturity.
Source : umn.edu