It’s a broken record but the Drought Monitor shows thing essentially unchanged from the previous week. The six to ten day outlook (February 19 to 23) has normal to below normal precipitation and below normal temperatures. Looking out eight to 14 days again indicates below normal precipitation and normal to above temperatures. The 30 day outlook is for equal chances for above or below normal temperatures and precipitation with the 90 day outlook basically the same. Today, let’s focus on an aspect of weather that we may not think about much regarding crops – day length.
Everyone learns in school that plants take carbon dioxide and water in the presence of sunlight and are able to convert it into sugar and give off oxygen. But many are unaware that light plays other important roles in a many plants life cycle in terms of day length.
• A crop like winter wheat, a plant that must overwinter, needs to develop winter hardiness or the ability to survive through the winter. It and other plants like it go through a series of growth and physiological changes to accomplish this. But how does the plant “know’ winter is coming? Decreasing temperatures play a role, however, the plant must make these changes before real cold develops. The other big key is decreasing day length. As day length decreases the plant “senses” this and starts to key physiological and growth changes. Prostrate, or flat, versus erect growth is one change. Another is the change in cell contents that serve as a kind of antifreeze to protect the growing point.
• The other major role day length plays regards flowering. A summer annual plant needs to complete its life cycle, i.e. produce viable seed, before freezing temperatures arrive. Winter annual plants such as winter wheat need to try and make sure they don’t try to flower and produce seed before winter and freezing temperatures are over. Perennials, whether cool or warm season, deal with a similar dilemma. So how does day length play a role for these temperate climate plants?
• The responses detailed below are caused by two plant hormones, phytochrome red and phytochrome far red and their relative ratios to each other.
• For winter annuals, they sense increasing day length. Here, days are shortest around Dec. 21 and then days become longer. As the amount of day length increases, it eventually, depending on the variety, will key physiological changes leading to flowering. These are long day/short night plants.
• For summer annuals like soybeans, they need to beat winter so their flowering is keyed to increasing night length. Depending on the variety, once the length of uninterrupted night reaches a certain point, the plant will initiate flowering. And if the darkness is interrupted if only for a brief period of time, the plant will never flower. These are short day/long night plants.
• The two previous points regard plants growing in temperate regions where there is winter and day length changes significantly. But what about plants near the equator that really don’t deal with seasons. These are day neutral plants. Examples are corn and corn.
Dr. Victor L. Martin is the agriculture instructor/coordinator for Barton Community College. He can be reached at 620-792-9207, ext. 207.
