The Rural Voice, 1986-02, Page 16INTERACTION FOR MAXIMUM YIELDS,
PART II
by Mervyn Erb
How do we get corn yields mov-
ing again and on the road to the
400 bu/ac potential projected by
Dr. Thys Tollenaar of the Univer-
sity of Guelph, who has calculated
the potential for corn yields in
southwestern Ontario if con-
trollable factors are managed pro-
perly? Can we any longer expect
the kinds of breakthroughs that
sent yields skyrocketing in the '50s
and '60s? Many think not. Few
major breakthroughs are on the
horizon.
Yet, there are the high yield
achievers who provide us with
breakthrough examples.
Remember Roy Lynn of Michigan
who produced 352 bushels per acre
in 1977? How did he do it? The in-
teresting thing is that one can't
point to any one miracle product
or practice that was responsible. It
was his ability to put together a
system or a total package of prac-
tices in the right combination and
amounts.
The same holds true for Herman
Warsaw of Saybrook, Illinois, who
broke all his own past records in
1985 by producing 372 bu/acre,
and the corn variety he used was
one he has been using for 10 years.
And we certainly can't forget
Ken Stevenson of Ridgetown Col-
lege who also broke his past
records this summer and grew 293
bushels of corn and a phenomenal
96 bushels of soybeans. As well,
Dr. Gus MacKenzie of MacDonald
College, near Montreal, had a
maximum yield corn experiment in
1985 that yielded 244 bu/ac. Yes,
you read it right — Montreal,
Quebec! Again, it was the total
package of practices in the right
combination and amounts.
Most progress towards high
yields will be achieved only in in-
tensive, highly charged biological
Co
14 THE RURAL VOICE
Mervyn Erb, a
regular con-
tributor to the
Rural Voice, is
crop specialist
at the Hensel)
District Co-op
systems where we substantially
modify and supplement nature. It
isn't natural for soils to contain the
amount of P or K or N or other
elements that it takes for 350
bushels or even 200 bushels of corn
or 10 tons of hay.
And speaking of hay. In 1985
Dr. Bob Shead of Guelph Univer-
sity, recorded the highest attalta
yield ever in Canada, of 9.4 tons
per acre (at 12 per cent moisture) at
Chatham, Ontario. Dr. Sheard
suggested that record yields were
due to a combination of factors —
insect control, five -cut system,
phosphorous and potassium nutri-
tion, and variety selection."
Significant progress is more like-
ly to come from getting a good fit
of the components of high yields
than it is from any dramatic
breakthrough with a single practice
or product. Central to the whole
effort will be a better understand-
ing of interactions so the positives
can oe maximizea ana the
negatives turned into positive
forces. Balanced fertility is the
result of the process of putting
high yield components together in
ways that cause positive interac-
tions to happen.
The problem is to identify these
interactions so appropriate action
can be taken. This is today's
greatest challenge to researchers.
The day of single -factor emphasis
must give way to the systems ap-
proach — not just balanced nutri-
tion but the total package that in-
cludes hybrid or variety, insect and
disease control, plant population,
tillage practices, etc. The systems
approach is more costly and com-
plex, but single -factor responses
ignore important interactions, par-
ticularly at high yield levels.
Even when research is designed
to study interactions, positive ex-
pression is often missed. To il-
lustrate how easy it is in research to
stop short of yield increases suffi-
cient to produce a positive interac-
tion, let's take a look at results of
alfalfa studies in New Jersey
(Table 1).
Obviously the top yield was not
great enough to conclude that
positive interaction occurred. In
fact, the response was less than ful-
ly additive. Phosphorous and
potassium each gave a response,
but when the two were applied
together, the response was less
than the sum of the independent
actions. This should quickly alert
the researcher to the fact that the
full yield potential had not been
reached, even though the increase
between the check and the best
treatment was substantial. What
were the interfering factors?
Maybe varietal regrowth ability,
possibly another nutrient besides P
and K.
Some Illinois corn research in-
dicates dramatic effects of NPK on
yield and profit (Table 2). This
data strongly suggests positive in-
teractions, including a three-way
NPK one.
Undoubtedly, it would be safe to
conclude that attempting to grow
corn without N is a costly mistake,
as would be expected. No com-
bination of the two nutrients max-
imized profits. It took all three
together. Without the ability to
evaluate interactions, there is no
way to determine if yields reached
even the fully additive level.
It should be recognized that
simply achieving positive interac-
tion does not assure maximum
yields, but it is a significant step
beyond additive effects. Only
when the ultimate point of elimina-
tion of all possible negative in-
teracting factors is reached, will
full potential be realized.
Yield can be thought of as the
product of genetic, cultural, and
environmental interactions.
Let's look further at some of the
known interactions between
nutrients. For many crops, it is dif-
ficult to find good examples
because such research at high -yield
levels is scarce. Therefore, some of
the yields in the next few tables are
not extraordinary, and the infor-
mation is from U.S. land grant
universities, which is what I hap-
pened to have on hand.
Nitrogen/Phosphorous
An N/P interaction effect on
corn grain yields is clearly il-
lustrated in Table 3. Nitrogen ac-
ting alone increased yield by only 9
bushels. Phosphorous by itself did
a little better with a 17 bushel in-
crease. When the two interacted,
yield was boosted sharply by 82
bushels. Therefore, the sum of the
separate actions was only 26