Researchers:
- R.P. Voroney, B.J. Farquharson, K.J.
Janovicek, E.G. Beauchamp and T.J. Vyn, University of Guelph, Guelph,
Ont. and M.C. Fortin, Agriculture Canada, Ottawa, Ont.
Executive Summary
Evaluation Summary
(Tech. Transfer Report Summaries)
View / Download Final Report [1026 KB pdf]
Completed: July, 1992
Key Words:
crop residues, conservation tillage,
canola, corn, red clover, rye, soybeans, winter wheat, crop rotation,
soil moisture, soil temperature, residue cover, phenolic acids, volatile
fatty acids, phytotoxin, calcium nitrate, zero-till, yield
Field Studies
The presence of crop residues on the soil
surface in conservation tillage systems affected soil water content and
temperature, and plant growth. When the spring season was dry, residues
retarded evaporation resulting in soil temperatures cooler in comparison
to a conventional tillage system. However, the extra water retained in
the soil also promoted plant growth. During a wet season, plants
appeared pale and growth was stunted due to cooler soil temperatures and
wetter soils. Nevertheless, soil temperature and moisture measurements
could not totally explain the reduction observed in corn plant
development in the presence of specific plant residues, particularly
residues of red clover and canola.
Phenolic acids (PCs) and volatile fatty
acids (VFAs) generally were not found in concentrations considered to be
phytotoxic in field soil samples. Field sampling in the spring showed
the presence of PCs which tended to decrease in concentration from May
to June. However, within 48 hours after a 40 mm rainfall event in late
June, PCs were detected in plots with residue cover. The presence of
VFAs was detected only once during the three years of study in the
field. This was after a shower in early June from a plot receiving rye
residues (4 t/ha).
The addition of calcium nitrate to soil
amended with crop residues significantly reduced accumulation of VFAs in
a laboratory study. However, under field conditions the addition of
calcium nitrate with the seed did not overcome the yield reduction
effects of rye residues.
Laboratory Studies
The production of VFAs is dependent on the
nature of the crop residue, soil water content and temperature. Green,
readily decomposable residues such as legumes had the greatest potential
for the accumulation of VFAs when soil temperatures were high (15-25° C)
and soil water potential was above field capacity. The potential for VFA
production decreased as the plant materials matured to harvest stage and
underwent weathering.
There was little difference in the
accumulation of VFAs under soil moisture conditions ranging from field
capacity to saturation. Phytotoxic concentrations could be produced in
the laboratory within 48 hours of incubation, a period which could be
expected in the field.
The accumulation of VFAs was much greater
at high temperatures (25° C) than at low temperatures (4° C). During
incubations there was a lag period of about 2 days followed by a rapid
increase in VFA accumulation to a maximum at about 14 days. This was
followed by a rapid decrease in soil VFA concentration indicating that
these compounds were readily utilized by soil microorganisms. A second
but much smaller peak was observed on day 28, especially for rye and
soybean residues. Under low temperatures (4° C), VFA accumulations were
small but steady over the entire incubation period. Total phenolic
concentrations were never as high as those found for VFAs. This may be
because VFAs are a by-product of anaerobic decomposition whereas PCs are
released as the residue undergoes decomposition.
Bioassays using corn and winter wheat
were performed to assess phytotoxic affects. Selected VFAs and PCs
inhibited germination and early growth of corn, although not all hybrids
were affected equally. Phytotoxicity increased with decreasing solution
pH. Combinations of the phenolic acids appeared to affect corn radicle
growth in a non-additive manner.
The winter wheat bioassay showed that
VFAs were more inhibitory to plant growth than PCs. Acetic acid was
inhibitory to both radicle and coleoptile growth, irrespective of crop
variety or VFA concentration tested. Propionic and butyric acid also
inhibited plant growth but to a lesser extent than acetic acid. Vanillic
acid was inhibitory to germination and early seedling growth whereas
p-hydroxybenzoic acid and p-coumaric acid stimulated early seedling
growth.
In conclusion, the field research
indicates that phytotoxins are produced from decomposing crop residues
which can significantly reduce plant growth. However, the nature of
these phytotoxic compounds is not clear. VFAs and PCs accumulated in the
soil to phytotoxic concentrations during the decomposition of particular
crop residues in laboratory studies. However, these compounds were not
detected in field studies. Future research should consider the dynamics
of both the production and utilization of phytotoxin compounds during
decomposition of crop residues. In addition, there is a need to examine
other potential phytotoxins, such as the volatile C6 through
C9 organic compounds.
(From Technology Transfer Report Summaries -
A. Hayes, L. Cruickshank, Co-Chairs)
The aim of this study was:
- to evaluate surface placement of
coarsely-chopped overwintered corn and fresh rye plant residues for
phytotoxin production using corn as the test crop,
- to evaluate the effects of various
crop residues and residue placement options on zero-till corn
performance,
- to evaluate calcium nitrate amendments
to seed row using corn as the test crop
- to determine the soil environmental
factors controlling the production and accumulation of phytotoxins,
- to compare the production of volatile
fatty acids and phenolic compounds from weathered versus fresh manure
residues under saturated conditions and 15° C,
- to determine the effects of volatile
fatty acids and phenolic acids on early corn radicle growth,
- to determine the effects of volatile
fatty acids and phenolic acids on winter wheat bioassays.
The study concluded that the presence of
crop residues on the soil surface in conservation tillage systems
affected soil water content and temperature, and plant growth, however
measurements of the soil moisture and temperature could not totally
explain the reduction in corn plant development particularly under
residues from red clover and canola.
The phenolic acids (PCs) and volatile
fatty acids (VFAs) were not found in concentrations considered
phytotoxic in field soil samples, however they were detected in some
plots after certain June rain events.
Calcium nitrate reduced accumulation of
VFAs when added to soil in the laboratory study, however when added with
the seed under field conditions the yield reduction effect of rye
residue was not overcome.
In the laboratory VFA production was
found to be greatest under green readily decomposable residue such as
legumes, under high soil temperatures (15-25° C), and soil water
potential above field capacity. The potential for VFA production
decreases as the plant materials matured to harvest stage and underwent
weathering. Phytotoxic concentrations could be produced within 48 hours
of incubation, and increased to a maximum at about 14 days.
- From the corn bioassay it was
determined that some VFAs and PCs had a phytotoxic affect, although
not all hybrids were affected equally.
- From the winter wheat bioassay it was
determined that the VFAs were more phytotoxic than the PCs.
Comments:
This study set out to answer some of the
questions farmers have been asking about phytotoxicity of crop residues.
While the acids were found at toxic levels in the laboratory, they were
not detected in the field.
Future Research: ( )
indicates reviewers suggestion for priority, A - high, C - low.
(B) This study considered certain VFAs and
PCs, whereas other compounds such as the volatile C6 through
C9 organic compounds could be examined. Future research
should consider the dynamics of both the production and utilization of
phytotoxin compounds during decomposition of crop residues.
Created: 05-28-1996
Last Revised:
Thursday, May 19, 2011 04:09:49 PM
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