For most of Wisconsin hybrids (~100 day), each plant typically develops 20-21 leaves, silks about 55-60 days after emergence, and matures about 120 days after emergence. All normal plants follow this same general pattern of development, but specific time intervals between stages and total leaf numbers developed may vary between different hybrids, seasons, planting dates and locations. The rate of plant development for any hybrid is directly related to temperature, so the length of time between the different stages will vary as the temperature varies. Environmental stress may lengthen or shorten the time between vegetative and reproductive stages. The length of time required for the yield components of ear density, kernel number, kernel weight varies between hybrids and environmental conditions.
During October, frost has no effect on yield. However, lodging from disease, insect damage or hail can result in physical loss of yield. Grain harvest usually begins at about 25% grain moisture and is completed by 20% grain moisture. Some grain drying is usually necessary to get moisture down to 13-15% for long-term storage.
Yield
Ears per unit area, kernel number per ear and kernel weight all contribute to yield. These yield components of corn are determined early in the life cycle of the corn plant. It is true that yield is the end product but the plant must go through a number of stages to produce yield. Understanding this process won't necessarily put "money in your pocket", but by knowing when yield components are determined helps to interpret management and environmental factors influencing yield.
Ear number, kernel number and kernel weight are determined at six critical stages: at planting and emergence (VE-V4) when the potential number of ears in an acre is at a maximum; when the ear sets the maximum number of kernel rows (V5-V6); when the ear sets the maximum number of kernels along length of the ear (V15-VT); when the maximum number of ovules are pollinated to form developing embryos (R1-R2); when the maximum number of kernels is determined (R4-R5); and when the maximum kernel size is established (R5-R6).
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| Figure 1.Yield Components of Corn. |
Moisture
While corn grain yield is determined over the full season, at some point during the growing season yield is no longer the main production objective. Rather grain moisture becomes the main production focus and directly influences grain quality during storage. Grain quality is often established by conditions at the very end of the growing season. During wet fall weather growers need to move quickly on deteriorating grain.
Table 1. Maximum storage time (months) of corn.*
| Temperature (°F) | Corn moisture content | |||||||
| 13% | 14% | 15% | 16% | 17% | 18% | 24% | ||
| 40 | 150 | 61 | 29.0 | 15.0 | 9.4 | 6.1 | 1.3 | |
| 50 | 84 | 34 | 16.0 | 8.9 | 5.3 | 3.4 | 0.5 | |
| 60 | 47 | 19 | 9.2 | 5.0 | 3.0 | 1.9 | 0.3 | |
| 70 | 26 | 11 | 5.2 | 2.8 | 1.7 | 1.1 | 0.2 | |
| 80 | 15 | 6 | 2.9 | 1.6 | 0.9 | 0.9 | 0.06 | |
| * Based on 0.5% maximum dry matter index - calculated on the basis of USDA research at Iowa State University. Corresponds to one grade number loss, 2-3% points of Total Damaged grain. | ||||||||
Post mortem
The corn ear can tell us much about a plant’s development during the growing season. Abnormal ear development has multiple causes – environmental stresses, pests, cultural practices. Combined with information on field history, knowledge of ear and kernel anomalies can be an effective diagnostic tool in troubleshooting corn production problems. Understanding how corn ears respond to stress can help determine the nature of the stress, when it occurred, and how it might be managed or avoided in the future. See “Troubleshooting Abnormal Corn Ears" at http://u.osu.edu/mastercorn/.
October is also the month to learn how your management style interacted with the environment. It is the time to evaluate your on-farm trials and observations. It is important to write down these observations about how your land responded to your management and decisions you made this past year.