Farm News, IA
09-21-07
Experts: Corn roots grow deep in northwest Iowa
By Renae Vander Schaaf, Farm News staff writer
Joel DeJong answers questions at a recent root clinic held near Ireton. Farmers
were able to see the layers of soil and corn and root growth.
Corn roots grow deep in northwest Iowa Loess soils,” said Iowa State University
crop specialist Joel DeJong.
To prove this point, a 7-foot hole was dug at the edge of a Ron Hulshof’s corn
field near Ireton. The slice of soil exposed show that corn roots this year were
able to grow 7 feet down into the soil. The average for Iowa’s corn roots is 5 feet.
While the soil in northwest Iowa may be ideal for growing corn, the lack of rainfall
poses more of a problem. This year corn was stressed by a cool, wet planting
period followed by very little, if any rain for two hot months.
“Corn needs 22 to 25 inches of rain,” said DeJong. “A good soil can hold 2.2
inches of water per foot. This soil had adequate moisture in the spring. So if the
roots grew their average of 5 feet, they had 11 inches of water in the bank.”
The peak demand for water in corn is during the pollination period and shortly
after. At that time it requires 1/3 to 1/2 inch per day. The corn root growing
system is maximized when corn is teaseling. Corn roots will grow after that but it
takes energy away from growing a crop.
“It’s important to get the root system developed,” said DeJong. “No-till keeps the
soil loose. Soil compaction hurts root development. Even though our Loess Soils
are forgiving, years such as this one prove that less tillage is better. Hard zones
can stunt and even prevent root growth.”
The rains last spring kept coming and the days on the calendar kept flying by.
Many farmers took a chance and planted in wet conditions. This would have
worked if the rains had continued. Instead they stopped completely. Sidewall
compaction was a problem in many fields in northwest Iowa.
DeJong suggested that when planting corn seed 1 to 2 inches deep, it’s
important to dig not scrape the soil away to check how deep the seed actually is.
The last brace roots establish at the 14-to-16 collar plant stage. There needs to
be water at the surface to develop brace roots. No-till farming practices help to
conserve water so that it will be there when the corn roots need it. A timely rain
can add 30 bushels to the final yield.
By examining corn roots, farmers can read the history of the growing season.
Patterns in the plant root, DeJong examined at the field day told of the wet
conditions, root worm larvae feeding and even the one pass of field cultivation
the field had had prior to planting.
Stalk rot is a problem this year in fields. Farmers should scout fields before
harvest to see where the stalk rot is a problem. The fields with the most problems
should be harvested first.
Soybeans were also discussed at this field day. Surprisingly soybeans moisture
needs are about the same as corn. Their peak moisture levels differ as rain in
August is critical to soybean production. The heavy dews are beneficial.
Soybean roots also grow deep in the Loess soils. Roots could be found at least 6
feet down in this particular field. Soybeans are capable of penetrating
throughsome compaction.
“A good depth for planting soybeans is 1 1/2 to 1 3/4 inch. Soybeans need good
soil contact but planting deeper will not help the seed,” advised DeJong.
“Research shows that soybeans planted early to yield better. Soybeans will use
nitrogen from spring applied manure.”
It’s important to dig up roots during the growing season to check for soybean cyst
nematode. The multiple checks should be made from mid-June to August. If one
nematode cyst is found a defense plan needs to be activated. The cyst numbers
will multiply at an astonishing rate. Rotation of crops does help; but the best
defense is to look at soybeans that are resistant to the nematode. These
varieties have improved since they first were introduced.
Most nutrient uptake for soybeans is at 6 inches. Soil samples are a pretty good
indicator of nutrient uptake. Its important to replace what it is being used.
“I’m finding fields low in potash,” said DeJong. “There appears more of a need for
this in no-till operations. Every four to six years potash should be applied to
fields.” Starter fertilizer can show a yield response if soils are deficient; but
benefits are often marginal in no-till situations.