On-Farm Research of
Biologicals, 1986 - 1994
Practical Farmers of Iowa
February 7, 1995
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a pdf file of this report.
The term “biologicals” covers a range of products, from trace elements, to
live cultures of microbes. If there is a common thread, it may be that these materials are
intended to utilize natural processes and interrelationships in the
agroecosystem. That is
a goal of many farmers who are working to make their farms more sustainable. The question
is: “Will biologicals help you get there?”
That is what this on-farm research is about. These were well-designed experiments
carried out by farmers to see if biological products would pay off. Maybe someone was
trying to sell them a particular item, or maybe they were following up on a biological
because the promotional material sounded plausible to them. In some way, they probably all
hoped these products would work. But they started with a test on a few acres. Often they
asked the salesperson or company consultant how best to use the biological in the trial.
The results that appear here imply neither endorsement nor
condemnation of any particular product. In most of the trials reported here, biologicals
did not increase yields. However, producers are encouraged to carry out their own trials
to find what works in their operations. PFI members have carried out close to 400
experiments on farms, and we have some good methods worked out if you are interested in
doing your own testing. In reports of trials that involve proprietary products, we include
brand names solely for purposes of information. The following explains how to interpret
the table and describes the way these field trials were done.
Reading the Numbers, Knowing the Terms
Valid and reliable farmer-generated information is a cornerstone of Practical Farmers
of Iowa. Consequently, PFI has worked to develop practical methods that safeguard the
accuracy and credibility of that information. PFI members use methods that allow
statistical analysis of their on-farm trials. Chief among these are: 1)
“replication,” and 2) “randomization.” (See figure below, a typical
PFI trial layout.) They have repeated, or “replicated,” the farming practices
compared in a trial at least six times across the field. So trial results do not depend on
a single comparison only, but on six or more. The order of the practices, or
“treatments,” in each pair is chosen with a flip of the coin. This
“randomization” is necessary to avoid unintentional bias. PFI on-farm trials
have been recognized for their statistical reliability, which increases confidence in
arriving at an unbiased conclusion. So, while PFI members don’t have all the answers,
they do have a tool for working toward those answers.
When you see the outcome of a PFI trial, you also see a statistical indication of how
seriously to take those results. The following information should help you to understand
the reports of the trials. The symbol “*” shows that there was a
“statistically significant” difference between treatments; that is, one that
probably did not occur just by chance. We require ourselves to be 95% sure before we
declare a significant difference. If, instead of a “*,” there is an
“N.S.,” you know the difference was “not significant,”
that is, the yields are not different.
Average statewide yearly prices for inputs were assumed in calculating the economics of
these trials. For uniformity, average fixed and variable costs and time requirements were
also used. These can vary greatly from farm to farm, of course. Labor was charged at $6.00
per hour until 1993, when $7.00 was charged. We costed labor at $8.00 per hour in 1994.
Dollar amounts shown in parentheses ( ) are negative
numbers. A treatment “benefit” that is a negative number indicates a relative loss.
Researching Biologicals, Researching Systems
The farmers who carried out these trials have no way of knowing if the products were
increasing the soil life or doing other things not visible to the naked eye. They were
usually only measuring crop yield and, indirectly, profitability. Some people say you
can’t test biologicals in strip plots because the “good bugs” swim across
strips to wherever they are needed. The strips in these experiments were generally eight
to sixteen rows wide. The reader will have to judge whether these were valid trials.
Another criticism is that biologicals must be tested as part of a whole farming system.
In some of these trials, farmers did maintain the experiment for several years, looking
for cumulative effects. The systems question goes both ways. Systems with diverse crop
rotations, manure, cover crops, and residue management are systems with plenty of native
soil biological activity. The amount of additional microbes that can be added as a product
is very small compared to what is already there. And added microbes face fierce
competition from the native “bugs.” That could be why biologicals had little
measurable effect on the farms reported here. On the other hand, if the farming system
itself does not create the conditions that encourage soil biological activity, any added
microbes will face a harsh environment in that soil, too. The best success with soil
inoculants has been with symbiotic microbes - those that find a safe home in
another organism. The common example is the Rhizobia bacteria added to the seed
of soybeans, alfalfa, and other legumes.
Again, producers are encouraged to do their own testing to find out
what works in their farming system. PFI has written a brief guide to setting up a
replicated on-farm trial. For a copy of the guide, or to discuss trial results, contact:
Richard Thompson, 2035 190th St., Boone, IA 50036, 515-432-1560; or
Rick Exner, 2104 Agronomy Hall, ISU, Ames, IA 50011, 515-294-5486.
