Grain Physiological Maturity

As we pass through the critically important grain-fill period, each bit of rainfall and heat allows for more complete seed fill, better grain quality and higher yields. The crop spent the entire summer accumulating nutrients that are now being converted into stored energy for the next generation (grain starch). In this light, it is the plant’s job to “die gracefully”, as first indicated by the yellowing leaves on the plant. We hope for this to happen slowly and naturally, not being cut short by the onset of a disease, pest or environmental stressor. This process varies with genetics and the environment, but all follow the same steps along the way.

Soybean grain fill is characterized by beginning seed (R5) and full seed (R6). Corn grain fill is tracked through four growth stages: blister (R2), milk (R3), dough (R4) and dent (R5). First, or early dent, occurs prior to R5 or 30-35 days after silking, with full dent taking place 35-42 days after silking.

Newly dented corn contains less than half of what will be its total dry matter. As the milk line moves from the cap to the tip of the kernel, dry matter accumulates rapidly. At mid-R5, or 50% milk line, the kernel has accumulated ~90% of what will be its total dry matter. Combined with the moisture that still resides in the plant, one can imagine why this usually ends up being near the optimum time for silage harvest!

Physiological maturity occurs when the abscission layer, or black layer, is formed on the seed. This is R6 in corn and R7/R8 in soybean. Physiological maturity “cuts the cord” from the plant, so to speak. All nutrient and water flow from plant to seed has stopped. The black layer is a single dead layer of cells that is visible when dissecting a mature corn kernel with a fingernail. We also know it as the hilum on soybeans.

We aren’t really done yet! The grain will still be somewhere between 25% and 40% moisture at physiological maturity. Stay tuned in the coming weeks for a look at grain drydown and how it factors in to relative maturity of a variety.

Brian Weller Western Region 507.456.3034	Dan Ritter Central Region 219.863.0583	Branden Furseth Northern Region 608.513.4265	Mark Gibson Eastern Region 260.330.8968	Amanda Goffnett Eastern Region 989.400.3793

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