- T.J. Gillespie, C.J. Swanton, C.S. Wagner Riddle, University of Guelph,
Evaluation Summary (Tech. Transfer Report Summaries)
View/Download Report [615 KB pdf]
Associated SWEEP/LSP Research
Completed: August, 1991
cover crop, soybeans, winter rye, soil water, soil temperature, timing,
spring growth, fall, model, SOYGRO
Many of the advantages of the conservation tillage systems currently
in use derive from the presence of crop residue on the soil surface. Crop
residues reduce soil erosion losses, therefore increase soil water infiltration,
and decrease soil water loss by evaporation (Griffith et al., 1986).
Additionally, crops can be grown specifically for the purpose of covering
the soil during periods between main crops, to then be killed and left as
a mulch on the soil surface before planting of the main crop. The management
practices used in the spring will then influence the value and effectiveness
of cover crops (Triplett, 1986).
The timing of killing of the cover crop is a critical decision dependent
on climate. Adequate amounts of mulch have to be present after killing,
to assure that the soil water conserving properties of the mulch are maximized.
On the other hand, delay in the timing of killing can have adverse effects
on subsequent crop growth if soil water is limiting, such as during a dry
spring or on soils with low water holding capacity. During a wet spring,
the possibility of removal of excessive moisture by the growing cover crop
suggests that a late killing could allow the timely planting of the main
In addition to the soil water conserving properties of a mulch, effects
such as a decrease in soil temperature variations can be an advantage for
the growth of the subsequent crop, and should be considered in the management
practices of the cover crop.
Winter rye is among the cover crops extensively used due to its winter
hardiness, low fertility tolerance, early spring growth and persistence
of the mulch produced (Moschler et al., 1967). In this study, soybeans were
chosen as a standardized main crop and winter rye was used as the preceding
cover crop on a sandy, a loam and a clay soil.
The use of a model linking climate to the effect of a rye mulch on soybean
growth would be very useful in determining optimum management of the cover
crop for various weather scenarios.
Therefore, the main research objectives of this project were:
to study the timing of rye killing in a rye/soybean system, where the
rye is planted in the fall, chemically killed and mowed in the spring,
and soybeans are no-tilled through the rye mulch;
to investigate the effect of a rye mulch on soybean growth and yield;
to measure the effect of rye mulch on soil water and soil temperature.
to model the effect of a rye mulch on soybean growth under various
The rye mulch/soybean system studied proved satisfactory for soybean
production on a sandy and a loam soil. On a clay soil, difficulties associated
with excess fall moisture and winter kill interfered with cover crop establishment,
while planter problems and slug damage in the spring decreased soybean yield
on mulched plots. More research would be necessary if the system is to be
adapted to clay soils, but our experience was not encouraging.
On the sandy and the loam soil site, rye mulch amount was significantly
larger for the late killing date as opposed to an early killing date. Differences
between soil drying rates under early killed rye mulch and late killed rye
mulch were observed in 1990 at Delhi, but generally soil water content between
the two mulch treatments was not different. Soil water conservation under
mulch, although significant for short periods early in the season during
one year, did not affect early soybean growth due to timely rainfalls.
For rye mulch amounts larger than 2000 kg/ha, no significant increases
in percentage ground cover were gained by delaying rye cover crop killing.
Also, mulch decomposition proceeded at a faster rate for large mulch amounts.
Although the rye mulch had a significant effect on the soil surface drying
rate early in the soybean growing season, shading of the soil surface by
the soybean canopy plus a substantial decrease in the amount of mulch present
on the soil surface, resulted in little difference between mulch and no
mulch conditions later in the season.
Analysis of hourly soil temperatures measured under mulch and no mulch
treatments revealed that extreme temperatures are more frequent under the
bare soil condition. Over the whole growing season these differences were
limited to a small percentage of hours, but the lower variability of temperature
under the mulch may have benefited microbial activity and root growth slightly.
The change in the moisture and temperature regimes of the soils studied,
induced by the presence of a rye mulch on the soil surface, did not result
in significant soybean yield increases or decreases. Delays or decreases
in soybean emergence observed for some treatment-years were compensated
by the plants as the seasons progressed. If other beneficial aspects of
the no-tillage system are considered, such as reduced soil erosion (Phillips
et al., 1980) and weed suppression (Weston, 1990), rye mulch is recommended
to be used in no-till soybeans.
A rye mulch/soybean computer simulation model was constructed, using
the CERES-Wheat and SOYGRO as building blocks. The water balance subroutine
(WATBAL) used in SOYGRO was modified to include the effect of rye mulch
on soil evaporation and rainfall interception. Good agreement between simulated
and observed soil water content, rye biomass, and soybean pod yield was
obtained even with data that was not used to calibrate the models. Based
on the simulation results obtained, killing the rye cover crop approximately
one week before soybean planting resulted in the best soybean yields under
a variety of simulated rainfall conditions, on both medium and sandy textured
(From Technology Transfer Report Summaries - A. Hayes, L. Cruickshank,
The study examined no-till soybeans and winter rye cover crop on clay,
loam and sandy soils. The objective was to study early versus late killing
of fall planted rye; the effect of rye mulch on soybean growth and yield;
soil water content and temperature. The use of modelling to predict the
effect of rye mulch on soybean growth under various spring weather conditions
was also examined.
The rye mulch/soybean system proved satisfactory for sandy and loam soils.
Excess fall moisture and winter kill, on the clay soil site, interfered
with crop establishment. Planter problems, and slug damage decreased soybean
yield on mulched plots. The results on the clay site were not encouraging.
Rye mulch amounts larger than 2000 kg/ha did not significantly increase
the percentage of ground cover, and little is gained by delaying kill to
obtain larger amounts. Soil drying rates generally showed no difference
between early and late killing dates. Extreme temperatures were measured
more frequently under bare soil conditions. However, over the entire growing
season, the temperature difference was limited to a small percentage of
hours. The change in soil water content and temperature due to the rye mulch
did not significantly increase or decrease soybean yield.
When other benefits of no-till are considered, for example reduced erosion
and weed suppression, the study recommended that rye mulch be used in no-till
The model, when given the variables obtained from the field study, performed
well as a predictor of soybean growth and soil moisture for bare and covered
The title of the study may be misleading. The study furthers research
on growth models, however, there seems to be little in the way of practical
advice for farmers. The field study was used to compare the accuracy of
the model predictions and not to determine the benefits or effectiveness
of using residue management for soybeans. No effort was made to determine
the feasibility of producing high amounts of mulch prior to spring planting
or planting into excessive levels of residue.
The use of a rye-soybean rotation, or part of a rotation, is not representative
of rotations in the Norfolk area. It is also questionable as to whether
this type of rotation is representative of Ontario.
Future Research: ( ) indicates reviewers suggestion for
priority, A - high, C - low.
(C) Should soil moisture conditions (excess or deficiency) in various
tillage regions become an important issue, then future research should be
directed at those soil and crop rotation combinations of concern. These
combinations should, however, be representative of Ontario conditions and
Thursday, May 19, 2011 02:42:50 PM