Flexible Plants And Crop Yield
DENNIS B. EGLI
LEXINGTON, KENTUCKY
The flexibility (plasticity) of a plant (plays an important role in many crop management decisions. But what is ‘plasticity’? A dictionary definition – “to mold or shape”- doesn’t tell us much. A more useful definition describes a plastic crop species as having the capacity to adjust the number of seeds that an individual plant produces when the productivity of the environment changes. Seeds per plant on a non-plastic species doesn’t change much as productivity changes.
Plasticity was an important plant characteristic as plants evolved because it allowed a plant to take advantage of a highly productive environment or a low population by increasing its reproductive output (seeds per plant) to help insure survival of the next generation. Consequently, all grain crop species were originally plastic although the mechanisms creating plasticity varied.
Small grains (wheat, barley) increased seeds per plant by producing seed bearing tillers. Soybean and other grain legumes branch in response to increased productivity, increasing pods and seeds per plant. Soybean can also increase flowers and pods at an individual node.
Corn is a unique species. The undomesticated corn plant was very plastic, producing ear – bearing tillers and multiple ears on the main stem. Domestication and the efforts of plant breeders converted it into a largely non-plastic species that seldom produces tillers or multiple ears. It seems that early corn producers preferred hybrids that produced only a single ear. There are, however, some hybrids that will tiller or produce a second ear under the right conditions.
What does plasticity have to do with crop management? Plasticity plays a major role in the response of a crop species to changes in plant population. Increasing population reduces the area per plant and the productivity of the individual plant. A plastic species can adjust seeds and yield per plant as population changes, maintaining a constant seeds per unit area and yield over a wide range in population. A non-plastic species cannot change seed number or yield per plant as population changes, so it is necessary to adjust the population to maximize yield.
To further complicate the situation, the optimum corn population depends upon the yield level (higher yield environments require higher populations), ear (florets per ear) and kernel size (kernels pe pound)(larger ears and kernels require lower populations). For example, a hybrid producing 250 bushels per acre with a 300 mg kernel (1513 kernels per pound) would have to produce 21.1 million kernels per acre. If the hybrid produces an 800 kernel ear, the population will have to be 26,440 plants per acre. A hybrid with a smaller ear (576 potential kernels per ear) would have to have a population of 36,722 plants per acre to produce the same yield. Ear size is important. Unfortunately, information on these reproductive characteristics may not be readily available for most hybrids.
Recent research in dry climates demonstrated the value of plasticity in corn. The crop in these climates is usually grown at lower populations which limits yield in years with above average rainfall. A hybrid that tillered was able to produce enough kernels at the low population to capture the higher yield in years with higher rainfall. Plasticity (tillering) allowed the crop to adjust to the higher yield environment.
Plasticity also effects the response of a crop to non-uniform spacings of plants in the row or non-uniform emergence. Widely spaced plants or plants that emerge first (dominant plants) receive more sunshine and grow faster than closely spaced plants or late emergers (dominated plants). The dominant plants of a plastic species have the flexibility to increase the number of seeds per plant to compensate for the reduction of seeds on the dominated plants so there is often no effect on yield. The dominant plants of a non – plastic species usually cannot make the adjustment and seeds per unit area and yield may be reduced. Uniform stands are important for maximum yield in corn (non-plastic) but not in soybean (plastic species).
Plastic species adjust to variation in population or productivity level by naturally changing yield per plant while the producer must create ‘plasticity’ in a non-plastic species by adjusting the population. Management of a plastic crop is easier because plasticity smooths out variation in population or plant spacing. Management of a non-plastic species is more difficult because the producer must adjust population or insuring uniform stand to maximize yield. Keeping management simple increases the chances it will be done correctly resulting in high yields.
“In this world there are only two tragedies. One is not getting what one wants, and the other is getting it. The last is much the worst”. Oscar Wilde (writer, 1854-1900)
Adapted from Egli, Dennis B. 2021. Applied Crop Physiology: Understanding the Fundamentals of Grain Crop Management. p. 105-111. CABI. ∆
DENNIS B. EGLI
PROFESSOR EMERITUS, UNIVERSITY OF KENTUCKY
