News > 2020.8.05 CFS Growing Insights

2020.8.05 CFS Growing Insights

Aug 05, 2020

Conditions Update
Crop progress across MN from the week ending August 2nd, 2020 has corn conditions at 28% excellent (27% last week), 57% good (57%), 12% fair (13%), and 3% poor/very poor (3%). Soybean conditions are at 22% excellent (22% last week), 62% good (62%), 13% fair (13%), and 3% poor/very poor (3%).

Southern MN continues to outpace the 30-year average GDU accumulation, with 2020 total’s so far about 130-180 GDU’s ahead of normal. We are still sitting more than 1” below normal for rainfall, but in still fairly good considering parts of MN seeing abnormally dry to moderate drought conditions.
Night Temperatures during Grain Fill
How do temperatures (especially at night) impact corn as it hits the reproductive phase? Phenological development in corn is caused by the accumulation of heat units. The higher the temperature, the faster the corn plant runs. During the day, photosynthesis produces sugars and starches that are stored in the plant. At night, dark respiration occurs (respiration = burning/using). The sugars/starches made in the day are then used for cell growth, or for cell maintenance and cooling. Photosynthesis makes the fuel in the day that the plant needs at night to carry out dark respiration. When night time temperatures are below 70 Fo, there’s a greater amount of net photosynthesis. Increasing nighttime temperatures (above 70 Fo) means more energy is required for corn to stay alive and remain cooled, and not used for growth. The increase in plant respiration rates uses up energy which could have went to support kernel development. Cooler temperatures mean more energy can be partitioned for grain fill. Take a look at the graph below, especially up to the 86-degree vertical line, where more photosynthesis is occurring than the plant needs for respiration! At 86 and above, the lines cross, which is the high temperature we use as a maximum, for calculating daily GDU’s.

High night temperatures (and day temperatures) shorten the reproductive grain fill window and reduce yield. Faster development means a lower amount of photosynthesis carried out by the plant post-tassel, and less sugars to fill kernels.
We’ve had very reasonable temperatures at VT/R1 this year, so the potential for a longer grain fill period will be focused on health of the solar panels (leaves) and their ability to photosynthesize the next few weeks!
Corn Growth Stages
With most of the countryside’s corn a few week’s past tasseling, there are a few things to keep in mind:
  1. Estimate pollination and fertilization with the “ear shake.” Gently remove the husk to expose the silks and the ear, and shake the ear. This helps determine successful pollination by showing the silks of fertilized ovules that drop away, while the silks from unfertilized ovules stay attached. There’s a silk tube attached to every kernel, and the pollen has to grow down the tube to fertilize the kernel. You can look for “blank” kernels throughout the ear that aren’t currently blistered to estimate if there was any unsuccessful pollination. It is not out of the ordinary to see a few kernels missing, but higher levels may occur from damage from insects, or periods of high temperatures, low relative humidity’s, and inadequate soil moisture levels that delay silk emergence or interrupt pollination.
  2. The largest yield reduction usually occurs at silking. Nutrient or water stress will result in poor pollination and eventual seed set.
  3. When silk’s emerge, it tells us we are 50-55 days away from maturity. Many acres of corn are somewhere in the bloser stage or early milk stage. Use the table below to walk you through the rest of the reproductive stages.
Soybean Growth Stages
Research from Purdue helps estimate soybean reproductive stages and when beginning maturity may set in. R1 is about 70 days from R7 (beginning maturity), R2 is about 65 days, R3 is about 55 days, R4 is about 45 days, R5 is about 35 days, and R6 is about 20 days before beginning maturity. Considering these are averages, and parts of MN had earlier planting dates that increase the duration of soybean development time, maturity could occur at a faster rate depending on the weather throughout August. Below is a guide to understanding the reproductive stages of soybeans.

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