Drought Stress and its affect on Corn Pollination and Early Grain Fill

Despite Mississippi generally receiving abundant yearly rainfall, we often experience substantial drought stress growing corn.  The timing of our rainfall and the ability of our soils to store moisture are critical to corn productivity.  Moisture deficit and high temperatures usually combine to produce drought stress, but moisture deficit is critical, because moisture availability enhances the corn plant’s ability to tolerate high temperatures and conduct physiological processes, such as pollination.   However, high night-time temperatures burn up energy through respiration and do significantly limit corn productivity.

Corn prioritizes energy to the base of the ear. Thus, when stress limits energy supply shortly following pollination, kernels near the tip are quick to abort. Notice how growth near the tip lags, compared to other kernels.

Corn kernel number is the yield component determined during early reproductive stages when corn is most sensitive to stress.  Pollination is a buzzword that gets a lot of attention when we have drought, but except in extreme instances, kernel abortion is more likely to the primary factor causing yield loss.  Pollination is the process by which ovules are fertilized, stimulating kernel development.  These young embryonic kernels are extremely dependent upon high plant photosynthetic rate to supply energy.  Any type of stress or even cloudy weather during the first 20 days after pollination can limit energy supply, causing the plant to abort corn kernels near the ear tip, regardless of whether they were pollinated.  Stress thereafter, reduces productivity by limiting seed weight.

High temperatures alone rarely limit pollination, unless severe water deficit is also present.  Corn sheds most of its pollen early in the morning, before high temperatures and hot wind may affect it.  In fact, we had a dryland planting date study where late planted corn successfully pollinated in mid July last year when high temps were nearly 100 and night-time temps averaged about 75 degrees.  Producers also successfully grow very high yielding irrigated corn in the southern Great Plains region, where temperatures commonly exceed 100 degrees during pollination.  Therefore, proper irrigation should minimize potential pollination problems.  Pollination problems are more likely in dryland fields with extremely moisture deficiency.  Severe stress stunts corn silk growth and slows silk emergence relative to pollen shed.  Since pollen shed occurs in a relatively short (5-8 day) period and silks emerge slightly later than pollen shed initiation, pollination failure occurs if silks fail to emerge in time to receive pollen.   In other words, fertilization (pollination) failure occurs because pollen shed and silk emergence are no longer synchronized.  This synchrony problem often results in more blank kernels near the ear base, because basal silks are the last to normally emerge. 

Restricted or shallow root systems make corn plants much more intolerant to hot, droughty weather.  This is important even with irrigation, because plants need as much holding power as possible to tolerate the rise and fall of soil moisture inherent with furrow irrigation systems.  This is likely why Mississippi has historically produced our best irrigated corn yields when dry conditions persist during the spring, particularly during May, when the bulk of nodal root production occurs.  Early irrigation initiation can counteract this desired root development.   We need only to look back to 2009 to realize the considerable damage soil saturation has on corn productivity during mid to late vegetative growth stages.

Too much water can also reduce corn productivity. Our predominant furrow irrigation systems saturate soil, potentially causing issues if used too frequently.

Increasing the frequency of furrow irrigation events later in the summer will not necessarily cure this issue either, because soil saturation restricts oxygen supply which is critical to numerous plant physiological processes, including photosynthesis, respiration and transpiration.  As mentioned previously, young kernel development is extremely dependent upon photosynthetic rate. Transpiration helps cool plants and facilitates nutrient uptake.  Thus, too frequent and sustained irrigation, especially over the course of the whole summer, may actually limit photosynthetic energy and induce temporary heat stress and nutrient deficiency on corn plants.  This may be why we often see incomplete kernel fill in many irrigated fields, especially in heavier soils with limited drainage capability.