The Root of the Matter

Plant roots are amazing. They anchor the plant into the soil and provide the main mechanism for nutrient and water uptake. They can be fibrous in structure, as in corn and sorghum, and they can be a taproot, as in soybean and alfalfa. While we normally focus on the above-ground plant (you have to admit, it’s much easier to evaluate vs. digging and washing), the underground portion – the roots – is really what matters most in realizing your crop’s full yield potential. You can fuss over genetics, fertility levels and subsoil moisture but if the root mass isn’t healthy enough to take advantage of it, then it’s all beside the point. Here are some interesting facts about corn and soybean roots ( courtesy Dr. Sotirios Archontoulis, Iowa State University):

  • You can see up to 2.75″ of root growth per corn leaf with growth between the row being similar to in the row.
  • The average corn leaf number when the roots meet in the row middle (30″ row spacing) is around 6. This is why we discourage row cultivation after this point – you’re physically pruning the roots.
  • No surprise but soil moisture and water table presence are huge factors in root growth.
  • Root growth requires oxygen and will stop growing when soil moisture levels reach around 97% (near saturation).
  • For corn, 65% of the total root mass is found within the top 12″.
  • Bulk density over 1.80 g/cm3 usually inhibits root growth. In context, we can have layers in the field, natural or man made, that are high enough in bulk density to prevent root growth.
  • Excess nitrogen does NOT encourage root growth. Most crops will cease root growth in the presence of excess nutrients. Call them lazy if you want but applying more nitrogen usually only encourages more above-ground growth.
  • Finally, root growth ceases around flowering. That’s it. No more.

Without question, roots matter. Of interesting note, when plants are healthy, the ratio of roots to shoots really doesn’t correlate to yield. That is, more roots doesn’t mean more grain. HOWEVER, anything we do that compromises root mass health can and usually does impact yield.

So as you begin to prepare or even finish preparing fields, evaluate whether the pass you’re about to make is necessary and whether it will negatively impact the soil in such a way as to possibly inhibit root growth. (Compaction is rarely a good thing and you’ll live with it the rest of the season.)

I encourage you to learn more about roots – in the beginning as the plants are becoming established; mid-season and during grain fill. Dig, wash, evaluate. While I cautioned in an earlier blog about “rinse and repeat,” root evaluation is an appropriate excuse for this strategy!

I want you to do well. God bless our farmers!

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