Short corn and variable growth in 2013
But later planting dates usually result in taller corn than earlier planting dates since plants develop during periods with long days. Plant height increases because of elongated internodes during such days. So, what happened this year?
Soil temperature effect on corn height
We know that small differences in soil temperature and moisture affect both above- and below-ground corn growth. Root depth follows the downward progression of temperature increases. Generally, roots do not grow in soils much colder than 50⁰F.
Most reports dealing with corn height and development and correlations with soil temperatures are found in residue management research. More residue cover increases soil moisture content and decreases soil temperatures. Associated with the reduced soil temperatures is a decrease in plant height and decreased dry matter at specific calendar dates during vegetative development. However, corn grown with the same residue amounts had similar heights and dry matter when compared at the same vegetative development stages. Since seedling emergence is correlated with temperature, cold soils result in slow emergence.
Illinois researchers compared corn growth and development by altering soil temperatures (±9 ⁰F from ambient soil temperatures) with an underground heating system utilized through V5 - 5 collared leaves. In addition to delaying development in terms of calendar days, grain yield declined with the coldest soil temperatures. With these coldest soils, lower canopy leaves (leaves 1 to 13) had greater leaf area than upper canopy leaves (leaves 15-21). The opposite was true with the warm soil treatment. Upper canopy leaves contribute more to yield than lower canopy leaves.
All leaf development initiates while the growing point is still underground - before V6; soil temperatures up to V6 thus affect early crop development. Noticeable stalk elongation begins at around V5. Root development and leaf initiation have priority before that time. Cell expansion occurs near the internode bases. This process of cell expansion is influenced not only by the amount of light and day length – the latter discussed above in relation to late planting – but also by temperature. Early-season cold temperatures increase internode rigidity and limit cell expansion and internode elongation.
click image to zoomFigure 2. Soil temperatures in 2013 compared to those of 2012 and the 10-year average at Gilbert Iowa, Central Iowa. Data compiled from MESONET. Iowa soil temperature was 5 to 8⁰F colder than usual in the late April to May 5 period. Between May 6th and June 10th soils were again several degrees colder than usual. 2013 soil temperatures
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