Temperatures Effect on Maturity

How much did the recent cooler than normal weather pattern impact the 2017 crop?

Data from my local weather station shows us we had only one day above 90 degrees during the month of August. Even though we entered the month of August, ahead YTD for Growing Degree Days (GDD’s), that lack of heat in August and into September, has significantly delayed the maturity of the crop.

 

thermometer

The secondary factor in the delay of maturity, may have been overlooked. Low night time temperatures had an impact. Growing conditions like we’ve seen this summer are infrequent enough that there is still much debate about the full impact of night time temperatures in the 40’s and 50’s during grain fill. The last season we had a similar growing pattern was 2009. In 2009, we saw a similar growing season, a warmer than normal March-April, followed by cooler, damp conditions for much of the summer, and then a lot of cool nights toward the end of the growing season.

 

Canadian researchers, a few years back, documented that the rate of photosynthesis declines sharply, as much as 30%, following nighttime temperatures in the 40’s and low 50’s. Multiple nights in a row may also compound that effect. The photosynthesis process is critical to building yield as it converts sugars into starch and grain fill. The cold night temperatures seem to make the plant sluggish, and it takes bright, sunny, warm days to snap the plant back into full productivity. As you look back over the past 30 days, we have had cool temperatures, followed by a significant amount of cloudy days. So, to wrap it all in a nutshell, the lack of GDD’s in August and September, compounded with cloudy skies and cool nighttime temperatures, has compounded the delay in maturity and harvest.

 

Once corn reaches physiological maturity, black layer, you can track GDD’s to estimate the time of harvest. Generally we figure it takes 150 GDD’s to drop the grain moisture from 30% down to 25%, and it takes another 40-45 GDD’s to extract each point of moisture below 25%. So far, here in the month of September, we are accumulating around 13-15 GDD’s each day.

 

One of the benefits of slower GDD accumulation like we had this year, is the lack of heat stress on the crop, and the extended grain fill period that comes with a delay in maturity. Often the combination of these two factors contribute to longer, larger kernels that build more yield. We have been blessed with a very good crop this year.

Soybeans are not affected as much by heat unit accumulation, since they are a light sensitive crop. As you look at the soybean crop, we grew a lot of foliage early in the growing season, but have lacked the bright sunny skies needed to maximize productivity. Flowering, pod set, and pod fill can all be impacted by the amount of sunlight the crop receives during critical stages of growth. As the soybean crop nears maturity, bright sunny days will help the plant produce larger fruit, building more yield.