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Small Grains Are Short At Heading – Will It Impact Yield? (06/15/17)

I received a call this week from a grower wondering why his wheat was so short as it approached heading. He explained that his crop had not suffered unduly from drought stress; it had tillered well, and had a nice green color.

Small Grains Are Short At Heading – Will It Impact Yield?

I received a call this week from a grower wonderingransom.1 why his wheat was so short as it approached heading. He explained that his crop had not suffered unduly from drought stress; it had tillered well, and had a nice green color. In my research plots and in growers’ fields near Fargo that have already headed, that plants do seem abnormally short this year (see Figure 1). In any given field, the determinants of the height of a small grain crop are genetics and the environment. The genetic expression of plant height is determined by air temperature and water stress. Drought stress reduces photosynthesis which in turn reduces the rate of plant growth. In response to this stress, however, the plants hasten development. With regards to temperature, small grains (wheat, oats, and barley) are cool season crops that develop their highest yield potential in relatively cool environments. Like water stress, warmer than optimum temperatures hasten plant development (the time between growth stages is shortened). When plant development accelerates because of temperature and/or drought stress, they tend to be smaller as do their spikes, leaves and tillers and end up being shorter in stature than is normal. Plant height is sensitive to these stresses when they occur prior to heading.

When I observed the shorter plants near Fargo, I assumed it was due to primarily to water stress as we are way behind on rainfall. However, subsurface moisture is still adequate in many fields as late fall rains recharged the profile. When I looked at growing degree accumulations and compared them to the previous two years (both of which were excellent for wheat yield), I was surprised to see that growing degree accumulations this year were very similar, so it appears that on average this spring has not been warmer than the previous two years. However, averages do not tell the entire story. This spring we have had colder than average temperatures for a couple of weeks, followed by warmer than average temperatures for a couple of weeks. I propose that one of those two-week periods that was well above normal for temperature corresponded to some key developmental stages that may have affected plant height.

Regardless, the important question is whether these shorter plants will have reduced yield. Generally a plant smaller will have a smaller spike and less yield potential. Never the less, small grain plants with reduced spike size have the ability to add yield by increasing kernel numbers and increasing kernel size. One of my students, Nicholas Schimek, has become an expert in crop modeling, I asked him to run some simulations so that we could get a better handle on what the yield potential of our current crop might be. Accordingly, I had him run the DSSAT model using this year’s weather data through June 12th followed by simulations for the remainder of the growing season using weather from each of the past 26 years. Although these are just computer based simulations, I think that they do provide some insight into the impact of our weather to date and the range of outcomes we might anticipate as the season continues (see Table 1). Since these data are from simulations, they must be viewed with some caution. Having said that, I think we can make the following useful observations:

1-      This year’s unfavorable early season weather has taken more than 10 bu/acre off the top in some areas.

2-      Depending on the weather the remainder of the growing season, there is still considerable upside for yield in most regions of the state, if the weather for the rest of the season is favorable. In some locations, the expected “highest” yield could be respectable.

3-      Just as there is a potential upside, there is a potential downside. Dry and warmer than normal weather has the potential for dragging yields down further. The recent rain that fell in some parts of the state was sorely needed, and additional moisture will be needed to carry the crop through flowering and grain fill. High temperature during grain fill as well as drought stress can be particularly damaging to yield.

4-      It will be interesting to see how these simulated results compare to what is actually achieved at harvest in order to determine the value in simulation modeling.

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Joel Ransom

Extension Agronomist for Cereal Crops

 

Nicholas Schimek

Graduate Student, Plant Sciences


 

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