By Claire LaCanne and Dr. Jeff Coulter et.al
The excessive rain and recent moderate temperatures in many parts of the state this growing season have resulted in extremely variable plant development. In the August 21 session of Strategic Farming: Field Notes, Dr. Jeff Coulter, Extension corn agronomist, and Dr. Seth Neave, Extension soybean agronomist, joined moderator David Nicolai, Extension educator - crops, to reflect on the crop growing season and discuss implications for harvest.
Review of the current status of corn across the state
Corn progress and development
According to the crop progress report from the United States Department of Agriculture National Agricultural Statistics Service (USDA - NASS) as of August 18, corn silking reached 95 percent. Corn that has reached the dough stage was at 62 percent, 10 days behind last year and 3 days behind the 5-year average. Corn in the dent stage reached 6 percent and 1 percent of the crop was mature. Corn condition was 61 percent good to excellent.
Corn development and yield estimates are highly variable. It seems like it is going to be really difficult to accurately estimate yield this year until the combine gets rolling.
At the start of the growing season, most weather models were predicting above normal growing degree days, but there was continuous rain and growing degree day accumulation has been less. We have had stretches of quite cool weather and not had many hot days or weeks that can be good for growing corn. We are slightly behind on growing degree unit accumulations, and then coupled with that, the hazy skies do not equate to optimal conditions for corn production. Typically, when there is sufficient soil moisture like this, daily highs of at least 86 degrees Fahrenheit or even into the low 90s, coupled with normal or cool nighttime temperatures are optimal for grain filling in corn.
As far as crop growth and development, the general guideline is 60 days from silking to black layer. A lot of the corn was silking between July 24 and August 1, or slightly later for corn that was planted late. Therefore, most corn should reach physiological maturity around September 24 or later. Generally, that should be sufficient time before the first hard freeze, but only time will tell.
Corn yield potential
It is unlikely that there will be exceptionally high corn yields, but taller corn that looks fairly normal has good yield potential, and in many cases it may be around 200 bushels an acre. However, even within that taller corn, there are smaller plants with ears that are smaller than normal. There is definitely unevenness in corn height and ear size within fields.
Even in the larger corn, the stand is often less than ideal in general. We do not have the targeted 32, 000 - 33,000 plants per acre out there. In many cases, we are seeing lower populations, which include shorter plants that emerged late and have small ears. That is going to take its toll on yield as well.
Additionally, there are areas where the corn has received excess moisture, and in many cases, has also been nitrogen deficient. That corn is shorter, the stalks are smaller, and the ears are very poor. In those cases, the yields could be about 100 bushels an acre. Again, there is going to be marked variability.
Something that researchers have seen this year in south-central Minnesota is that corn with spring-applied urea is shorter and more nitrogen deficient when compared to corn that received spring-applied ammonia. It seems that there was greater nitrogen loss with the spring-applied urea. Depending on the nitrogen source and timing, there are differences in corn nitrogen recovery, which is likely contributing to some of the variability in corn yield potential.
To attempt to get corn yield estimates, there’s the kernel estimate method. For today's hybrids under good conditions, yields are typically based on 75,000 to 85,000 kernels per bushel. Under drought stress when there are very small kernels, it may take 90,000 kernels to produce a bushel. On the other hand, if there are very large kernels, then it may only take 70,000 kernels to produce a bushel.
Though an accurate kernel count is possible, the tricky part is trying to estimate how many kernels per bushel. We are likely looking at somewhere between 75,000 to 85,000 kernels per bushel this year. But it is challenging to estimate kernel size at this point, because there is a month or more of the grain-filling period left.
There is an extreme amount of variability within and among corn fields this year, so one may want to consider what stands and ear size look like across the field, and try to average yield estimates out over the good and poor areas of the field. Aerial imagery that measures a vegetative index could help estimate the area within the field that has good versus poor yield potential.
How to prepare for corn harvest: Things to consider
While considering harvest, we will need to be mindful of variable plant heights and corn moisture in the field. It only takes two kernels per square foot to cause one bushel of yield loss at harvest. It will be important to be mindful of what the harvest losses are and make any adjustments to the combine if needed.
It is also a good idea to understand corn stalk quality and standability before harvesting. Areas of the field that have been under stress either due to excess water and/or nitrogen deficiency, and especially corn on corn, are scenarios where it is good to assess standability. Try the push test on the stalks or even cut them off and look at the pith at the base of the plant as we get closer to harvest. Stalks that are hollow on the inside or that break easily when they are pushed indicate that they are at higher risk for stalk lodging, meaning that those fields should be prioritized for earlier harvest.
Review of the current status of soybean across the state
Soybean progress and development
As for soybeans, soybeans blooming reached 96 percent as of August 18, 2024. Soybeans setting pods reached 78 percent, 9 days behind both last year and the average. Condition of the crop was 64 percent good to excellent.
This is a really unique year and we can trace delayed soybean reproductive phases back to the moderate to fairly cool temperatures we have had over the past month or so.
Soybean flowering is driven strongly by day length, but heat units become increasingly more important for those developmental stages through the summer. Development was right on track in Minnesota through July. Then starting in early August, heat units started to slip a little bit and now we are nine days behind, according to USDA-NASS. That difference is noticeable for many of us; the crop is clearly behind.
This is separate from the other issue that we have this year, which is short beans. This is caused by a combination of cool temperatures and the wet weather.
The importance of this delay in development is really critical, since it is shifting this reproductive phase. Researchers at the University of Minnesota are looking into the critical period in soybean, or in other words, the time period that is most important for yield establishment in soybean.
This work indicates that R4 - R5 and especially R5.5 is seeming to be the most critical period. Right now, we are at the peak of that critical period in soybean. It has been a fairly common notion that August makes beans, but we are currently in what is probably the most important week(s) in soybean development. Right now is when the crop is made. If we go back to R4, to the beginning of the critical period, soybean rows were at least closed by that time and the crop was capturing all the light out there. We did not have a lot of wasted light just hitting the ground. It would have been nice to have it earlier, but having it by R4 is the critical piece.
Disease pressure in soybean
Evaluating this year’s disease pressure may be able to help make selection and management decisions for next year. There are some diseases popping up, and we have an environment that could promote disease progression that may affect soybean yields. It is a good idea to see what is going on in a particular field and get out there to scout.
Before buying plant protection products over the winter, it is a good idea to understand what is going on out in the field and determine if a particular disease is an issue. This year could be a good year to identify what issues might be out there and where the problem areas might be, because some diseases could really make themselves evident this year.
Soybean yield potential
It is really this and next week’s weather that is going to make yield for us. Some good, warm weather would be helpful at this point. Cool temperatures are not going to help us very much and are going to hold the crop back just a little bit more. Even though photoperiod is important for setting the end period and maturity, we are mostly relying on heat units by the end, and cooler temperatures delay maturation a few days. It is likely that if we have good, moderate to warm temperatures all the way through the end of September, soybeans will be okay. But if we get hit by an early frost or a stretch of more cold weather, there could be significant problems.
At this point, soybean plants are short but have plenty of pods and plenty of seeds out there. People should not be concerned about limited numbers of pods or shorter plants unless they were in a really stressed area or in some tough areas within fields that were drowned out, delayed, or replanted. There's an opportunity to fill these pods, and there is still potential for exceptional yields. Short soybeans can produce very high yields. We could have large seed in some of these plants that are short with low pod set. If we have good weather, soil moisture is likely adequate enough to still result in good yields, despite how it might look based on the short plants out there.
As far as yield estimates, like corn, there is extreme variability within fields making it difficult to make reliable estimates. Any estimates are going to be poorer than they normally are because of the variability within fields, counties, and across the state.
The big takeaway is that soybean yield is being formed today, tomorrow, and next week. Whatever number is currently out there is a good indication of what the potential is, but everything else is a guess. At this point, there could be 40 bushels an acre or 60 bushels an acre. If soil moisture and temperatures are sufficient, there is potential to have some good yields this year.
Source : umn.edu