- M. H. Miller, E. G. Beauchamp, Department of Land Resource Science,
T. J. Vyn, G. A. Stewart, Dept. of Crop Science, J. D. Lauzon, Department
of Land Resource Science, R. Rudra, Engineering Department, University of
Guelph, Guelph, Ont.
Evaluation Summary (Tech. Transfer Report Summaries)
View / Download Final Report [2007 KB pdf]
Associated SWEEP/LSP Research
Completed: March, 1992
cover crops, red clover, oilseed
radish, ryegrass, corn, winter wheat, barley, nitrogen, phosphorous, nitrate
leaching, crop response.
Field experiments were conducted in
1990 and 1991 on a sandy loam soil at Ayr and a loam soil at Woodstock to
evaluate the effectiveness of cover crops for nutrient conservation. Three
cover crops, oilseed radish, annual ryegrass and red clover were established
in 1990 in or following harvest of barley and winter wheat to which 1/2,
1 and 2x the recommended rates of N had been applied. Attempts to establish
cover crops in corn were largely unsuccessful. Cover crops were sampled
periodically to determine biomass production and N and P uptake. Soil and
soil solution samples were taken periodically in the fall of 1990 and spring
of 1991 and analyzed for NH and NO3 nitrogen. Corn was grown
on all plots in 1991 without N addition to evaluate the release of N from
the cover crops.
The potential for contribution of N
and P to surface runoff by leaching from cover crops during the winter and
spring was evaluated in laboratory leaching studies using a rainfall simulator.
Cover crop dry biomass at Ayr ranged
from about 1000 kg/ha for ryegrass to over 4000 kg/ha for red clover. Differences
were much less at Woodstock with cover crop biomass ranging from slightly
below 2000 to slightly above 3000 kg/ha. Oilseed radish biomass following
wheat at Ayr increased with increasing rate of N applied to the wheat but
there were no other biomass responses to N rate on the main crop.
Red clover generally had the greatest
biomass N content (kg/ha) while ryegrass had the least due primarily to
the lower biomass production. Except for oilseed radish following wheat
at Ayr, biomass N content was independent of N rate applied to the barley
Oilseed radish had a considerably greater
P concentration and biomass P content (kg ha) than either ryegrass or red
Soil mineral N content (NH4
and NO3) in the upper 45 cm of soil was reduced by all cover
crops compared to the check (no cover crop) in September. Mineral N contents
decreased markedly at Woodstock by November even on the check plot. Mineral
N contents of soil at Ayr did not change appreciably between the September
and November samplings.
Concentrations of NO3-N
in soil solution at the 75-cm depth were very low at Woodstock at all sampling
times in the fall of 1990. This suggests that the decrease in soil mineral
N content between September and November was most likely due to denitrification
rather than leaching. At Ayr NO3-N concentrations at 75-cm depth
in September were below 10 mg/l under ryegrass and oilseed radish but were
between 30 and 50 mg/l under red clover and the check. These latter values
decreased to 2 mg/l by December indicating considerable leaching had occurred.
In April and May, NO3-N
contents of the soil profile were greater for oilseed radish than for other
cover crops or the check, indicating that N was being released from this
crop earlier than from ryegrass or red clover. In June, soil mineral N contents
were much greater for red clover than other crops on the check. Mineral
N contents on oilseed radish plots were only slightly greater than the check
plot while those on ryegrass plots were lower than the check.
The mineral N contents in the soil
were reflected in N contents of the 1991 corn crop in June and August which
were greatest following red clover and least following ryegrass. Final grain
yields reflected this greater N availability being greatest following red
clover and least following ryegrass. These results indicate that N in oilseed
radish is released earlier than desirable for use by the succeeding crop
whereas ryegrass immobilizes N, with less being available than where no
cover crop was grown. Release of N from red clover was closely related to
the demands of the corn crop.
The laboratory rainfall simulation
studies confirmed the ease of release of N from oilseed radish. A greater
proportion (10-11%) of N in oilseed radish was removed during the leaching
compared to 6-9% for ryegrass and 5-8% for red clover. In addition P concentrations
in leachate from oilseed radish were much greater (10-14 mg/l) than for
ryegrass (6-8 mg/l) or red clover (3-4 mg/l). Thus the potential for increased
dissolved P in runoff from oilseed radish is much greater than for ryegrass
or red clover.
The ideal cover crop, in terms of nutrient
conservation, would be one which absorbs N rapidly in the fall, retains
the N (and P) during winter and spring, then releases the N during the summer
for use by the succeeding crop.
None of the three cover crops met all
three of these criteria. Although oilseed radish absorbed N rapidly in the
fall, it did not retain the N through the spring. In addition it increased
the potential for dissolved P in spring runoff. Ryegrass appeared to absorb
N and retain it through the winter and spring, but it did not release it
rapidly enough for the succeeding crop. Red clover was very effective in
retaining N through the winter and spring and in releasing it to the succeeding
crop. There was, however, considerable leaching of NO3-N from
the red clover plot at Ayr.
All conclusions from this study must
be interpreted with considerable caution because they are based on only
a one-year study.
(From Technology Transfer Report Summaries - A. Hayes, L. Cruickshank,
This study was conducted on a sandy
loam soil at Ayr and a loam soil at Woodstock to assess the effectiveness
of cover crops in preventing nutrient loss and providing nutrients to subsequent
crops. Red clover, oilseed radish and annual ryegrass were established in
or following crops of winter wheat and barley. The researchers were largely
unable to establish cover crops in corn. Each of the main crops received
1/2, 1 and 2x the recommended amount of nitrogen fertilizer.
Biomass production and nutrient content
of the cover crops were measured in September and November. There was no
response in cover crop biomass or nitrogen content to the nitrogen rate
on the main crop, except for oilseed radish following wheat at Ayr. Red
clover produced the greatest amount of biomass and had the highest N content,
while ryegrass had the least. Oilseed radish had considerably greater P
concentration and biomass P content than either ryegrass or red clover.
All of the cover crops reduced the
amount of mineral N (NO3 + NH4) in the top 45 cm of
soil compared to the check (no cover crop) in September. In plots where
significant leaching occurred, nitrate N concentrations in soil water at
75 cm depth were reduced below 10 mg/l under ryegrass and oilseed radish,
but were between 30-50 mg/l under red clover or no cover crop.
Soil nitrate contents in April and
May were higher under oilseed radish than under the other cover crops or
the control. This suggests that N is being mineralized from this crop earlier
than from ryegrass or red clover. By June, the red clover treatment had
the highest soil nitrate levels, while oilseed radish was only slightly
above the check and ryegrass was below the check.
Corn was grown on these plots with
no additional nitrogen fertilizer, to assess the nitrogen availability from
the cover crops. Corn nitrogen content, and final yield, were highest on
the red clover plots and least following ryegrass. This suggests that the
oilseed radish releases nitrogen earlier than it is able to be used by a
corn crop, while ryegrass immobilizes nitrogen so less is available than
when no cover crop is grown.
A laboratory study was also conducted
to compare the ease with which nutrients were leached from cover crop top
growth. A greater proportion of N and P were leached from oilseed radish
than from ryegrass or red clover, suggesting a greater potential for contamination
of surface waters with this cover crop.
The results of this study must be used
cautiously because they are based on only one year of data. None of the
cover crops studied is ideal from the standpoint of "nutrient relay" to
a subsequent crop of corn, because they either do not take up enough nitrate
in the fall, or they do not release enough (or enough at the right time)
for the subsequent crop. It would be interesting to see how the winter and
spring cereals would compare as a cover crop.
SWEEP Report #12
- Choice and Management of Cover Crop Species and Varieties for Use in Row
Crop Dominant Rotations
SWEEP Report #27
- Cereal Cover Crop Study
SWEEP Report #36
- Red Clover Cover Crop Studies 1987-1990
SWEEP Report #52
- Field Scale Tests of Cover Crops I and II
#57A - Field Testing of Cover Crop Systems for Corn and Soybean Production
#57B - Effect of Winter Rye Mulches and Fertilizer Amendments on Nutrient
and Weed Dynamics in No-Till Soybeans
Future Research: ( )
indicates reviewers suggestion for priority, A - high, C - low.
(A) As a minimum, this data must be
confirmed by a second years results. Much more information is required on
the uptake and release of nutrients from different cover crops, and the
influence of other factors on this process such as weather and soil type.
Thursday, May 19, 2011 03:21:01 PM