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return to Farmers
Independent Weekly
May
15, 2003
By Mario Tenuta, Department of Soil Science |
Swine
manure can keep soil-borne plant diseases in check
The
increasing concern of Manitoba farmers about soil-borne plant
diseases, such as early dying of potato or fusarium headblight
of wheat, and the pressing need to effectively and safely
utilize liquid swine manure spell opportunity for soil microbiologists
like me!
Research
conducted at Agriculture and Agri-food Canada in London, Ontario,
by Dr. George Lazarovits, Dr. Ken Conn and me focused on developing
organic amendments as alternatives to soil fumigants and pesticides
to control plant diseases. We identified several amendments
that had a remarkable ability to reduce plant diseases. Field
studies showed that amendments, such as chicken manure and
meat mixed with bone-meal, controlled a range of potato pathogens
such as the fungus Verticillium and the root-lesion nematode
Pratylenchus that causes early dying of potato, the bacterium
Streptomyces, scabies causing common scab of potato, and weeds.
These
amendments were all high in nitrogen content. In my doctoral
research, I showed that high nitrogen levels produced compounds
lethal to the pathogens. These compounds are quite common
- ammonia and nitrous acid. The fact that effectiveness of
these amendments varied from field to field was a stumbling
block to their practical use. Further work showed that effectiveness
was related to soil pH, organic matter and texture.
The fascinating
thing about research is that from time to time, you get results
that surprise you because they run counter to expectations.
Potato growers in particular are sometimes leery of applying
manure to fields because they're concerned about aggravating
plant diseases. When we added liquid swine manure to two potato
fields near Alliston Ontario, we discovered early dying of
potato and common scab were drastically reduced in the acidic
(manure) field compared to the one of neutral pH. We were
completely lost for an explanation. How could it be that manure
(liquid swine manure) can control plant diseases? Could it
be ammonia and nitrous acid? We figured out that these compounds
could not have been responsible given the amount of manure
applied so we turned to some of those compounds that give
liquid swine manure its smell!
Remember
that to a soil microbiologist, the smell of hog manure signifies
a banquet of compounds and nutrients to encourage the growth
of soil organisms. In particular, we looked for the presence
of volatile fatty acids (VFA), products produced by fermentation
of undigested feed in non-aerated liquid swine manure. These
compounds are familiar to you as acetic acid (vinegar) and
butyric acid (the smell of rotting butter).
In the
lab and in small plots, we were able to show that VFAs in
liquid swine manure added to soils of pH < 6 were converted
to a form lethal to plant pathogens. The great thing about
VFAs is that they are generally fed upon by soil microorganisms
within days of being added to soil so there are no residual
effects to crops. Research is continuing to develop best management
practices utilizing swine manure to control plant diseases.
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