Is smoke stunting pasture growth?

crop fire with smoke
Photo credit: EESC slide collection
Q:

I'm noting a reduction in the growth of our grass in the pasture. It has slowed down noticeably over the past month. This slowdown is more than normal due to increased temperatures of August. I was wondering if the smoke is having a filtering effect on the light that reaches the ground, particularly early to mid morning and then again towards evening. It appears the visible light is being reduced, for example I'm able to look at the sun and see it's shape clearly. Have you received any other similar observations?

- Crook County, Oregon
A:

The smoke is decreasing the amount of light which has also reduced the temperature each day by a couple of degrees compared to what it would have been without smoke. This run of hot weather and smoke since the end of June is almost unprecedented. In my 28 years here, I cannot think of a worse summer! Alfalfa and other legumes love this weather as long as you are irrigating properly, our cool season grass species on the other hand do not like this hot weather. The cumulative effect of the heat over two months has certainly upped the evapo-transpiration of the plants, so more irrigation water was needed to keep plants growing. If a person is grazing tight to the ground, this would also increase surface soil temperature and increase evaporation as well as hold the soil biological life in check as well (near surface).

Mylen Bohle
Extension Agronomist
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