A main goal for farmers is maximizing profits, and this is usually tied to getting the highest, most efficient yields possible.
But "yield" is a very abstract thing if you stop to think about it - what do we need to make "yield"?
These different "yield puzzle pieces" are yield components. That is, the different parts that influence and result in the final amount of grain.
Corn has 4 main yield components:
Plants per area
Ears per plant (sometimes combined with the first as ears/area)
Kernels per ear
Weight per kernel
1. Plants per area
The first yield component, plants per area, is determined very early in the season. This component is the easiest to directly manage (at planting), and the number of seeds to plant per area is an important decision. The goal is matching available field resources to plant requirements to avoid waste or overcrowding.
Too few plants, and you leave resources in the field that could have boosted yields higher.
Too many plants, and your plants are crowded without sufficient resources to reach their full potential.
A good analogy here is planning for a large dinner party - if you know 30 friends are coming over, you would need to plan on the appropriate number of pizzas, 2-liters of soda, etc. You would also need to decide which types of soda you should buy, as well as how many supreme vs meat-lovers pizzas you should order.
In agronomy, we do the opposite. Based on soil tests and knowledge of expected precipitation and irrigation capabilities, we can calculate that a given field has potential of about "20 pizzas" (soil N, adequate water, etc.). Based on this, we decide how many "friends" (plants) we can support. Again, matching plant population with available resources.
Our corn tiller project here at K-State adjusted this yield component by testing 3 different plant populations - 10,000; 17,000; and 24,000 plants per acre.
If these numbers don't mean much to you, these population densities would result in plants being 21 inches apart, 12 inches apart, and 9 inches apart in the crop rows if our rows were 30 inches apart, which is the typical spacing.
Planting is not the only event that can impact this yield component. Plants per area continues to be finalized through V5 (fifth collared leaf stage) or even later! Problems with emergence or damage due to hail, flooding, insects, disease, or animals can all reduce the final plant "stand".
2. Ears per plant
Ears begin developing in the plant as early as V5. The tassel is present before the stem starts elongating, and the ears are developing around the same time! Axillary buds are found at nodes 1 to 12 (although it can be higher - 14, for example) on the corn plant, and each has potential to develop into either tillers (nodes 1-5) or ears (upper nodes)!
"Nodes" are parts of a stem where new organs grow - such as where a leaf is attached. The analogy I use with my students is our "nodes" as humans - neck, shoulders, and hips.
The buds at lower nodes develop first, but the highest bud (typically around node 12) takes precedence and grows more rapidly. This is why the top ear is ALWAYS the primary ear. Any lower ears will be secondary and less developed than the top ear.
Corn plants typically only put on one ear per plant. Some prolific hybrids are able to put 2 or even 3 harvestable ears on each stalk! This ability to put on multiple ears is usually seen when fewer plants are put in per area. (Prolificacy should not be confused with flex, which is kernel number and NOT ear number - more on that in my post Let's talk about flex)
The number of ears is being finalized through approximately stage V12.
3. Kernels per ear
At stage V6, the kernels begin to develop. The number of kernels per ear is determined in two different ways:
First - the number of kernel rows around the ear, and
Second - the number of kernels in each row along the ear.
Which changes more? Typically, the same hybrid will put the same number of kernels around each ear. If the number of rows DOES change between fields or in different environments, it will not be by much.
The number of kernels per row (along the ear) is more plastic. The term "plastic" or "plasticity" refers to how much the plant can change its characteristics (leaf number, ear number, kernel number) or even its goals (selecting how many kernels to keep) to take advantage of "feast" scenarios and survive "famine" scenarios.
The number of rows per ear is set when the ears are first developed - as early as V5. This number will typically be even regardless of hybrid or environmental conditions (check out my post Odds or evens? Ear row edition for some fun facts on that!).
Potential kernel number is determined until just prior to R1 (flowering). Actual kernel number per row can be adjusted as late in the season as R3 through kernel abortion if the plant experiences stress.
4. Weight per kernel
Weight per kernel is inversely (oppositely) related to the other yield components. The plant has a set amount of resources to use, so it also has a set limit for the resources it can give to grain!
If the plant has more kernels, the weight of the kernels will be lower. If the plant has fewer total kernels, the available resources could be put into making the kernels bigger!
Test weight refers to the weight of a set volume of grain. The standard test weight for yellow corn is 56 pounds per bushel.
How much is a bushel? A bushel is the equivalent of 8 dry gallons.
Corn is sold in the US on a 56-pound bushel basis, and test weight is not directly part of the marketing process. This is 56-pound standard is considered a "dry bushel" - with grain moisture content at a 15.5% standard.
Test weight will change the number of kernels in a standard bushel, which typically ranges from 80,000 - 90,000 kernels. So although test weight is not directly involved in marketing, total bushels is determined by dividing grain weight by the 56-pound standard after moisture is adjusted. Heavier grain will ultimately result in "more" standard bushels, so heavier test weights are desired.
Example - Tiller Influence on Yield Components
Photos courtesy of Don Hineman (https://twitter.com/DonHineman)
left - Ears taken from three plants with tillers (left 6 ears) and three without (right 3 ears) tillers (notice the difference in ear sizes and kernel set)
middle - Prolific (multi-eared) corn plant with productive tiller
right - Ear size for main stalk with (left 3 ears) and without (right 3 ears) tillers (notice the similar sizes of kernels around between ears)
Plants per area - although tillers do not change the number of plants, this characteristic changes the number of SHOOTS per area, which is something usually not considered for corn with a single stalk. Tillering will increase the number of shoots!
Ears per plant - not ALL tillers put on ears, but we have seen that tillers are capable of putting ears on. Not all ears are productive though, such as the case of tassel ears or when pollination of tillers is delayed in relation to main plants, resulting in poor kernel set.
Kernels per ear - As mentioned previously, if more ears are present on the plant, the number of kernels on each ear will likely be reduced. In light of this, if tillers DO put ears on, the ear sizes across the plant could be reduced (see the main plant ears in Image 1 above). The dynamics of how main stalk ears and tiller ears interact and influence each other is something we are working on!
Weight per kernel - Again, this is inversely related to the other components mentioned to this point. Sometimes in the case of tillers, if pollination is poor, the kernels on the ears will be larger than those on main ears. Fewer kernels = bigger kernels.
So what's the takeaway?
Corn is able to adjust itself in ways to fit the environment it is growing in. These adjustments are the "yield components" that make up final yield. The yield components trade off and compensate for each other.
Tillers fit into this discussion because they change the yield puzzle pieces we're manipulating to create our final grain yield.
More coming soon on how tillers impact reproductive plasticity in corn!
Want to learn more about yield components?
Licht, M. (2017). Estimating Corn Yields Using Yield Components. Iowa State University. https://crops.extension.iastate.edu/cropnews/2017/08/estimating-corn-yields-using-yield-components#:~:text=There%20are%20five%20components%20of,sequence%20during%20the%20growing%20season.
Nielsen, R.L. (2021). Estimating Corn Grain Yield Prior to Harvest. Purdue University. http://www.kingcorn.org/news/timeless/YldEstMethod.html
KSRE MF3305 Corn Growth and Development https://bookstore.ksre.ksu.edu/pubs/MF3305.pdf
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