corn growers are accustomed to looking at corn fields where
all plants are the same height. The uniformity of height
was missing in many Minnesota fields during the early portion
of the 2003 growing season. In fact, the uneven corn growth
stimulated several telephone calls.
many problems there is probably no single easy answer to
this one. There are several factors that could cause uneven
growth. For many fields, the problem could be attributed
to more than one.
In some situations, the uneven growth can be attributed to a deficiency of
one or more essential nutrients. In 2003, deficiencies of potassium, sulfur,
and zinc have been noted in parts of some fields. Research trials and experience
with precision farming have taught us that there can be a wide range in relative
levels of plant nutrients in soils. For example, an analysis of a composite
soil sample may show that the potassium value is in the medium or high range.
Yet, there may be areas having a low soil test for K in the field. These areas
having the low test, without the adequate application of K, may be the cause
for stunted corn and subsequent uneven growth. The same explanation can apply
to zinc. The soil test values for zinc may vary more than soil test values
deficiencies, do not explain all stunted corn situations.
Observations from the fields where stunted corn has been
a problem include: 1) high fertility, 2) a nice loose seedbed
at planting, 3) one pass with a field cultivator for secondary
tillage, 4) no problems in recently manured fields, and 5)
taller corn in wheel tracks associated with the secondary
should corn be taller in parts of the field usually associated
with some compaction (wheel tracks, for example)? A reasonable,
but not proven, explanation combines our knowledge of root
growth and nutrient uptake.
are known to move to plant roots by the three processes of:
1) mass flow, 2) diffusion, and 3) root interception. Nitrogen
as nitrate – N (NO3-N) moves to roots by mass flow
as water is absorbed from the soil by plant roots. Phosphorus
as (H2PO4- or HPO4=) and K+ reach the root by diffusion and
root interception. In the diffusion process, the nutrient
moves from an area of higher concentration (the soil particle)
to an area of lower concentration (the root). Root interception
is the process whereby the root comes in contact with the
nutrient as it grows. Therefore, N can move over longer distance
compared to P and K. The relative distances of movement of
these three nutrients in soils is shown in Figure 1.
Figure 1. Relative movement of N, P, and K in soils.
loose at planting this past spring. As a result, the pore
space (the open area between soil particles) had a high percentage
of air and less water. In general, there were not heavy rains
during the early part of the growing season. There was less
air space under wheel tracks or where some other form of
compaction existed. As roots grew into the pore spaces in
these more compacted areas, there was more space occupied
by water. Thus it was easier for young roots and young corn
plants to get needed nutrients. As a result, plants in slightly
compacted areas showed better earlier growth. A general relationship
among soil particles, pore space, plants, and nutrients is
shown in Figure 2.
evidence for this explanation? Yes. Some crop advisors have
collected corn plants from the compacted and non-compacted
areas and found higher concentrations of N, P, and K from
the taller plants growing in the slightly compacted areas.
Crop advisors have also reported uniform height of corn in
field that, for some reason, received 2 or more secondary
tillage operations before planting.
Does all of this mean that compaction is good? NO! There are ample research
projects which have pointed to the conclusion that compaction has a negative
effect on yield. These situations observed in 2003 are the consequence of a
unique set of conditions that occurred at planting and for a short period of
time after planting.