At 4:52 AM -0000 10/2/97, T Hodges wrote:
>We run over 300 bu/ac under good conditions in south central
>Washington. Thats in an area of maximum solar radiation, no
>rain, warm days, cool nights, and lots if irrigation.
In response to:
>In article <60obnc$jhd at net.bio.net>, Freddie Lamm <FLamm at oznet.ksu.edu> wrote:
>>What is the current thinking on the maximum potential yield for field
>>corn???. Also a citable reference would be useful???
A theoretical examination of the biophysical limit on maize productivity is:
Tollenaar, M. 1985. What is the current upper limit of corn productivity?
Proceedings of the Conference on Physiology, Biochemistry and Chemistry
Associated with Maximum Yield Corn. Foundation for Agronomic Research and
Potash and Phosphate Institute. St. Louis Missouri, 11-12 Nov. 1985.
With the help of his physiological simulator (the Ontario Corn Yield
Predictor), Tollenaar set up several scenarios featuring combinations of
the factors:
Total season duration
Grain fill duration
Quantum efficiency
Daily rate of grain during linear phase
and assumed that canopy dry matter production was the ultimate limitant to
yield (as opposed to the sink capacity).
In brief, he estimated a theoretical maximum of 502 bu/a (approx. 32 t/ha).
This involved no appeal to improved physiology, just optimization of
currently feasible levels of performance and environmental conditions (and
obviously, no losses due to stresses and pests). Specifically, he used a
quantum requirement of 8 (28% efficiency), PAR as 50% of total incident
radiation, 15% loss of incident energy due to reflection/transmission, 30%
respiratory losses (both maintenance and growth), and 50% partition
coefficient. The resulting theoretical photosynthetic potential was
therefore 0.28 x 0.5 x 0.85 x 0.7 = 8.3%.
Extending this, he played with those factors he believes are amenable to
improvement, in particular the quantum efficiency (which has been measured
under idealized greenhouse conditions at 16, grain fill duration, partition
coefficient, and leaf area index. When maximizing these factors to
realistic levels (based on observed values in controlled environments) he
computed a theoretical maximum of 1,312 bu/A (83.3 t/ha).
Tollenaar concluded that due to our current limitations in understanding
maize yield formation completely, the best we can do is estimate that
maximum realizable yields of the maize plant as we now know it will fall
somewhere between the range of 32 to 83 t/ha. Note that currently the yield
record for maize (which was obtained in the very year of 1985 when
Tollenaar delivered this paper) is at 370 bu/a (23.5 t/ha), or about 73% of
the lower value of the range defined by Tollenaar, and about 56% of the
midpoint of this range.
One last word. The record yield was measured on 20 acres (i.e., not a
small-scale experiment station plot) on the farm of Herman Warsaw, near
Saybrook, Illinois, and was obtained WITHOUT irrigation, under natural
rainfall conditions during a year when annual precipitation summed to 24
inches (610 mm). Warsaw attended the above conference and presented his
production methods. His approach can be summed as relying on deep tillage,
extremely high nutrient ammendments, and a genotype with stay-green
characteristics (FS854) planted at high density (37,000 seeds/A, or
92,500/ha). Needless to say, he was a superb agronomic manager. However,
the story is not complete without noting that exciting as was his approach
to maximizing yield it was also one that without doubt had high
environmental impact. Note his fertilizer applications:
18-46-0 at 200 lb/A, fall-applied
0-0-60 at 250 lb/A, fall-applied
28-0-0 at 1,070 lb/A, preplant with herbicide
21-0-0-22 S at 500 lb/A, preplant
46-0-0 at 165 lb/A at cultivation
13-13-13 at 200 lb/A as starter
Some analysts have pointed out that the particular field that he employed
was also unique. It was a natural depression with deep soil over a
relatively impermeable layer, and in a sense helped him to create a
'hydroponic' environment in the field.
Ricardo J. Salvador E-mail: mailto:salvador at iastate.edu
1126 Agronomy Hall Voice: 515.294.9595
Iowa State University Fax: 515.294.8146
Ames IA 50011-1010 WWW: http://www.public.iastate.edu/~rjsalvad
