Tri-County News

Early corn, yellow soybean yields


The number of harvestable kernels per ear is an important contributor to the grain yield potential of a corn plant. Severe plant stress during ear formation may limit the potential ear size, and thus grain yield potential, before pollination has even occurred. Optimum growing conditions set the stage for maximum ear size potential and exceptional grain yields at harvest time. The size of what will become the harvestable ear begins by the time a corn plant has reached knee-high and finishes 10 to 14 days prior to silk emergence. By about the V5 or V6 stages of development (five to six visible leaf collars), the growing point of the corn plant finishes the task of initiating new leaf growing points and completes its developmental responsibilities by initiating the tassel of the plant. At about the same time that the tassel is initiated, the uppermost harvestable (and final) ear is also initiated. This uppermost ear is normally located at the 12th to 14th stalk node, corresponding to the 12th to 14th leaf of the plant. Ear size determination Row number and kernel number per row are two of several yield components in corn. Typically, from 750 to 1000 potential kernels develop on each ear shoot. The number of kernel rows multiplied by the number of kernels per row determines total kernel number per ear. Actual (harvestable) kernel number per ear averages between 400 and 600. For a 16-row ear, one kernel per row is equal to about five bushels per acre (for average populations). Kernel row number determination of the uppermost ear begins shortly after the ear shoot is initiated (V5 to V6) and is thought to be complete as early as V8. Kernel rows first initiate as “ridges” of cells that eventually differentiate into pairs of rows. Thus, row number on ears of corn is always even unless some sort of stress disrupts the developmental process. True row number is often difficult to visualize in tiny ears dissected from plants younger than about the 12-leaf stage. Row number is determined strongly by plant genetics and less so by environment. This means that row number for any given hybrid will be quite similar from year to year, regardless of growing conditions. Some exceptions to this include the effects of injury from the post-emergence application of certain sulfonylurea herbicides or nearly complete defoliation by hail damage prior to growth stage V8.  Potential kernel numbers The potential number of kernels per row is complete by at least V15 and maybe as early as V12. Kernel number (ear length) is strongly affected by environmental stresses. This means that potential ear length will vary dramatically from year to year as growing conditions vary. Severe stress can greatly reduce potential kernel number per row. Conversely, excellent growing conditions can encourage unusually high potential kernel number. Severe stress from about V5 to V12 (current growth stages) that severely limits photosynthesis can directly interfere with ear size determination and result in fewer kernel rows (less likely) or fewer kernels per row (more likely).  While such early stress can be important, recognize that severe stress that occurs shortly before to shortly after pollination has a far greater potential to reduce yield per day of stress. Dry soil conditions  and crop growth The critical growth stages of corn for water use will be at tassel until grain is fully formed. The highest water use by corn will be during July and August. For soybeans, critical growth stages for water availability are during bloom and fruit set. Shortage in moisture supply during these growth stages will cause yield reduction. The most critical time for corn to have enough water is from a week before pollination to about two weeks after pollination, so it is most important to prevent water deficits during this period. Corn also uses the most water per day during this time in the Corn Belt. On a hot, dry, windy day in mid-July, the corn crop can use up to one-third of an inch of water, or about 9,000 gallons per acre. Deeper soils that are high in silt (silt loams) can hold up to 3 inches of water available to the crop per foot of depth, while a sandy soil may hold less than one inch per foot of depth. The effect of early-season stress on the final corn yield is difficult to access. Although moisture stress reduces plant size, it has little effect on final yield if good crop production conditions prevail during the pollination and grain-filling periods. Source: Ear Size Determination in Corn; R.L. (Bob) Nielsen Agronomy Dept., Purdue Univ. Yellow soybeans Bruce Potter, University of Minnesota Integrated Pest Management Specialist, reports that yellow soybeans are common on alkali rims soils in western Minnesota. Before you blame all problems on poor iron chlorosis, that growers should investigate a couple of other potential causes: Check root systems for root rots induced by saturated soils and more importantly soybean cyst nematode (SCN). SCN resistant varieties have been widely adopted by producers in southern Minnesota. However, you can have a nematode problem on soybeans sold as SCN resistant for two reasons: 1) Low SCN resistance in the variety and 2) The selection for SCN races (Hg types) that can feed and reproduce on the source of resistance planted in the field. Scouting for SCN females on soybean roots is a convenient way to detect nematode infestation in a field. Root samples may be taken at any time from five weeks after planting through late season. In Minnesota, the best time to scout for females on the roots, however, is early to mid July through August when females of the first generation become white to yellow and are exposed to the outside of roots. When the plants are carefully dug with a shovel and the soil is gently removed from the roots, most females stay on the roots. These females are lemon-shaped and about 1/40 inch long and 1/60 inch wide and can be seen by the naked eye.

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