Great Bend Tribune
Published June 23, 2019
The current “active” weather pattern doesn’t appear to be in the mood to go anywhere. On the plus side, for those with corn, beans, and grain sorghum in the ground, we are starting to see some heat. You may have heard producers and analysts saying we need heat, lots of it for corn and grain sorghum, and a late frost. Today let’s explore that statement and the importance of planting date for these three crops. We are leaving aside insurance considerations and any FSA programs here.
First, we’ll tackle corn and grain sorghum. Their development is essentially heat driven. It takes the accumulation of so much heat to germinate, emerge, for each leaf, to flower and reach maturity. Grain sorghum, milo, is a bit different in that it can switch into an “idle” when it gets close to flowering until conditions improve. For corn we commonly define it as so many days from emergence to physiological maturity (the seed could be planted and germinate). A better way to look at it is the accumulation of so many GDUs (growing degree units). The fuller season a corn, or milo, hybrid is, the greater its yield potential. However, dryland producers typically use hybrids earlier than possible to waste less water on vegetative growth, to avoid pollination during stress periods, or to be able to plant wheat in the fall.
To take advantage of the fullest season hybrid practical, producers should have corn in the ground in our area no later than the end of the first week of May for corn and early June for milo. As these dates pass, several risks are apparent: inadequate heat accumulation for full-season hybrids; pollination and grain fill during peak heat and moisture stress, and late of time for grain maturation and dry down. So as you plant later you must switch to an earlier maturing hybrid that decreases yield potential and even then allows for the risks just described. A point is reached where, unless you are going to chop or ensile it, the risks are too great and the yield potential too low. Some producers were willing to switch from corn to milo but rains in many areas hurt that option. Milo is still possible but the safest course is to select an early maturing variety and treat it as a double-crop situation.
Soybeans are a bit different from grain crops. They also have maturity classes from very early to very late. We typically plant mid to late Group III and Group IV soybeans in our area, even under a double-crop situation, producers will stay with a Group III. Soybeans also need heat but their development is dramatically different from grain crops. Corn and milo bloom once while soybeans are indeterminate and bloom over an extended time. Corn and milo complete vegetative growth and then flower. Soybeans continue to grow vegetatively while starting to bloom. And normally only about half of the blooms go onto to produce seed so they have some wiggle room with adverse conditions. And the biggest difference is soybeans planted in our area don’t accumulate “X” amount of heat and then bloom. Flowering is keyed to daylength for beans. They need a certain amount of uninterrupted night length to flower. They wait for nights to become longer and then start to flower. So planted now there is less vegetative growth to support seed production. Whereas planted ideally, early to mid-May, they have more time to establish vegetatively before flowering starts. Beans can be planted now and produce a crop but it should be treated as a double-crop situation, not full season.