Crops: The Lynch File - Solving the mystery of the 'corn row effect'

Tuesday, August 4, 2009

Why do we not see it in all fields where corn starter had previously been applied? And why in only parts of fields?

by PAT LYNCH

This past spring, many wheat fields showed many of the "Forty Shades of Green" for which Ireland is famous. Some of this was due to manganese deficiency, some to nitrogen deficiency and some due to lack of phosphorus. Some of it was the result of poor root growth caused by various things.

Manganese deficiency showed up more in 2009 than 2008. Manganese is an interesting mineral and very reactive. If there is air in the soil, the oxygen reacts with manganese to form manganese oxide. Once manganese forms manganese oxide, it is unavailable to plants.
 
If air is excluded, as in wheel tracks the manganese reverts to elemental manganese which the plant can take up. In 2008, wheat plants had developed a better root system than in 2009 by the time the plants needed manganese. This better root system was able to search out more soil for manganese.    

This past May, some wheat fields showed the so called "corn row effect," the uneven growth often caused by residual fertilizer from the corn row – that is, if starter fertilizer was applied to the corn two years earlier. But have you ever seen this corn row effect where there was no starter fertilizer applied with the corn? And how come not all fields where starter was applied exhibit this phenomenon? Some believe that this corn row effect is caused by the corn roots rotting down and providing better growing conditions.

This corn row effect has generated a lot of controversy. Why do we not see it in all wheat fields that had corn starter applied two years before? Why are we only seeing it in parts of fields? And if it is a response to phosphorus, how much yield are welosing? Did we lose yield the previous year with soys because of low phosphorus levels? Do all the growers who do not use a starter fertilizer on corn have a "hidden corn row effect" in their fields? Are they losing yields in wheat fields because of low phosphorus soil tests?

Some of these questions can be answered by soil testing. Information from the Ontario agriculture ministry indicates that use of phosphorus fertilizer in Ontario has declined in the past few years. This is being validated by Guelph-based Agri-Food Laboratories, who tell us they have noticed a drop in the average phosphorus soil test levels through their lab in recent years.

This corn row effect is magnified when growing conditions are less than ideal. In the fall of 2007, wheat was planted early; there was lots of top growth and also root growth. In the spring of 2008, we saw little "corn row effect."

The point here is that good growing conditions allow the wheat roots to forage for phosphorus and other nutrients in the soil. There is a feeling that nitrogen with phosphorus helps the plants take up phosphorus. I think the extra root growth from nitrogen allows for a bigger root system, which allows the wheat roots a larger area to get the phosphorus they need.

So what is the solution? I think we are losing yield on many wheat fields because of lack of fall growth. In 2007, we saw extra top growth on fields that were treated with nitrogen. This past spring, many growers skipped the usual practice of applying P and K for wheat when before they planted soys. I think this fall it would be a good idea to add some nitrogen to certain fields before planting wheat.

Fields that are most apt to benefit from this are those testing low in phosphorus – those where "corn row effect" has been seen – and later planted fields.

Pat Lynch, CCA (ON), is an agronomist for Cargill in Ontario.