Pollination and groundwater

Post by Sam Zipper

As July quickly passes us by, we get closer and closer to corn pollination season. Driving down to Monroe over the weekend, I noticed some fields beginning to tassel, which filled me with both excitement (over the excellent science opportunities in the near future) and dread (due to my allergies to corn pollen). However, having a stuffed up nose and itchy eyes is a small price to pay for the important data that our team is able to collect during and after pollination.

Corn tassels, prior to the release of pollen. Each tassel has over 2 million grains of pollen!

Corn tassels, prior to the release of pollen. Each tassel has over 2 million grains of pollen!

The corn flowering & pollination process is relatively brief in the life of a plant, lasting less than two weeks, but absolutely the most critical period for farmers to achieve high yield. Pollen is released by the plant’s tassels, which drifts down and lands on the corn silks of nearby plants. Each silk is connected to a potential kernel formation site, and if a pollen grain lands on a silk, that site will be fertilized and a kernel will develop.

Corn silks on top of a growing ear. These silks have already been fertilized. Each cob has ~750-1000 silks, or potential kernels.

Corn silks on top of a growing ear. These silks have already been fertilized. Each cob has ~750-1000 silks, or potential kernels.

So, why do we care so much about pollination, and how does this relate to our groundwater research?

First, about 50% of the mass of a fully grown, healthy corn plant is grain, and it is much more energy-rich than the vegetative parts of the plants. This means that farmers are counting on successful pollination to produce lots of grain.

Second, the pollination period is a time when stress on the plant can have especially large impacts on year-end yield. Stress can throw off the timing of the tassel/silking process, so that the silks may not be ready to receive pollen when the tassels are releasing it. This will lead to lower pollination success rates. Because each successfully pollinated silk produces a kernel, the kernel count on a mature corn cob can act as an archive, or record, of how much stress a plant was experiencing during the pollination time of year (fun fact: WSC researchers, mostly our dedicated undergraduates, have counted over 40,000 corn kernels from the 2012 and 2013 growing seasons!).

Comparison of pollination success rate at 3 sites with varying groundwater levels.

Comparison of pollination success rate at 3 sites with varying groundwater levels.

The above graph shows kernel counts from different parts of our field site near Deforest from the 2012 growing season. On average, plants in our ‘shallow’ groundwater regions had 4x more kernels than the deepest regions, indicating that the plants were under less stress in parts of the field with shallower groundwater. This was likely due to 2012’s severe drought prior to and during the pollination period. Plants with access to groundwater were able to tap into these reserves, which made them more resilient to drought.

Groundwater doesn’t tell the whole story, though. Different types of soil are able to retain precipitation longer in the root zone, which impacts the influence of drought and groundwater. This summer, we are continuing our groundwater monitoring while collecting and analyzing soil samples from throughout our field site to understand how groundwater and soil texture interact to influence year-end yield.

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