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SWEEP Report #36

Red Clover Cover Crop Studies 1987-1990

J. Sadler Richards, Conservation Management Systems - A Division of Ecologistics Ltd., Lucan, Ont.

Executive Summary

Evaluation Summary (Tech. Transfer Report Summaries)

View / Download Final Report [122 KB pdf]

Associated SWEEP/LSP Research



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Completed: January, 1992

Key Words:

cover crop, red clover, erosion control, conservation cropping, residue cover, chemical kill, mechanical kill, corn, chisel plow, no-till

Executive Summary

In 1987-90 seven trials were conducted in Middlesex and Huron Counties in southwestern Ontario to study the effect of time and method of control of a red clover cover crop on the growth and yield of corn. Drought conditions during late spring and summer in 1988-89 affected the performance of the cover crop and main (corn) crop. Excessively moist conditions in the spring of 1990 affected plant emergence and final plant stand especially on the spring tillage treatment.

Results from three years of study indicate that in general those treatments which included the use of a mechanical method for controlling red clover resulted in grain corn yields approximately 11% higher than those achieved with the average no-till treatments, although the effect was not always statistically significant. However, this may be related to the previous crop stubble. Those sites which had red clover underseeded to winter wheat reported the greatest reduction in grain corn yield under no-till conditions compared to sites which had oats or oats and barley as the stubble crop. Under mechanical methods of red clover control the amount of soil surface residue cover left after planting was unacceptable from an erosion control standpoint. The chemical kill treatments provided somewhat lower corn grain yield with excellent residue cover remaining after planting. The mechanical kill treatment using the chisel plough produced yields which were similar to the October chemical kill treatments and may he used as an alternative to using the moldboard plough.

The amount of dry matter collected from each of the treatment plots was related to the date and method of control of the red clover. The chemical treatment applied in May recorded the greatest amount of dry matter after planting followed by the April timing whereas the least amount (if any) was collected on the moldboard plough treatments.

Results of the rainfall simulation indicated that the mechanical kill treatments (moldboard and chisel plough) recorded significantly higher runoff volumes, soil losses as well as total phosphorus losses compared to either of the chemical kill treatments (October and April). The difference in the results obtained for the chemical kill treatments for the above parameters were not significant indicating that the time of the red clover kill did not affect the erosion control of these treatments. In addition, no significant differences between the chisel and moldboard plough treatments were reported for these parameters.


Evaluation Summary

(From Technology Transfer Report Summaries - A. Hayes, L. Cruickshank, Co-Chairs)

This three year study evaluated the effects on residue levels and corn performance of various chemical and mechanical kill methods and times of kill, of a red clover cover crop.

Treatments consisted of chemical kill, mechanical kill with moldboard plow, and mechanical kill with chisel plow in either fall or spring. The chemical kill treatments were no-till planted. Measurements taken were soil residue cover, red clover above ground dry matter, corn plant emergence, corn plant height, 50% silking date, corn yield and associated factors.

At all sites, chemical kill plots had significantly more residue remaining (33-84%) after planting than the mechanical kill plots (3-26%). The level of residue on the moldboard plots was not high enough to provide sufficient erosion control. Spring chemical kill treatments resulted in more residue than fall kill. For each treatment, the amount of red clover dry matter was related to the date of kill (later kill, more dry matter). Chemical kill plots had significantly less soil loss than mechanical kill treatments.

Corn emergence was low at 14 days after planting (DAP) for chemical kill in May, while fall moldboard and fall chemical kill had higher emergence. Differences were less significant at 21 DAP, but in general fall kill treatments had more plants emerged. At most sites, moldboard treatments had taller plants at the 2-3 and 6-7 leaf stage and also reached 50% silking sooner.

Corn yields were considerably lower on chemical kill treatments than on mechanical kill treatments. Yields also tended to be higher and grain moistures lower for earlier killed treatments.

The study's authors believe that there may be some allelopathic effects of the previous year's cereal stubble or the red clover residue on the corn. Insects and slugs were also more of a problem in the no-till treatments. These factors may have contributed to the lower yields in the chemical kill treatments.

A red clover cover crop killed in the fall by chemical means or by chisel plowing is effective in reducing soil erosion and only reduces corn grain yields by a small amount, if at all.


The study was done on seven different sites, with up to four different planters, up to four different corn hybrids, four different previous crops and there was no check without red clover for the chemical kill treatments. These variables could have had a significant effect on the results of the study. The yield data shows an 11% reduction was experienced after winter wheat (chemical kill) but after oats, barley or red clover hay the chemical kill yields ranged from a 1% reduction to a 9% advantage. The straw was removed from the spring cereal crops and left on the winter wheat fields. There is a stronger case for the authors' conclusions applied to winter cereals than spring cereals. The hand harvest yields were done using the 10 average cob method which is not as accurate as shelling all the cobs. There may not be a need for a cover crop, if corn is no-tilled into wheat stubble, as the ground is well protected to begin with. Why complicate matters by planting red clover?

Associated SWEEP/LSP Research:

  • 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 #29 - The Effect of Organic Mulches on Soil Moisture and Crop Growth

  • SWEEP Report #32 - Optimal Herbicide Use in Conservation Tillage Systems

  • SWEEP Report #43 - The Use of Cover Crops for Nutrient Conservation

  • SWEEP Report #52 - Field Scale Tests of Cover Crops I and II

  • SWEEP Report #57A - Field Testing of Cover Crop Systems for Corn and Soybean Production

  • LSP7005 - Crop Rotations and Cover Crop Effects on Erosion Control, Tomato Yields and Soil Properties in Southwestern Ontario

  • LSP7009 - A Cover Cropping Strategy for First Early Potato Production

Future Research: ( ) indicates reviewers suggestion for priority, A - high, C - low.

(A) The authors recommend further research, including monitoring the amount of nitrate nitrogen being contributed to the corn crop from the red clover and initiating field scale studies on the fall kill treatments.




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Created: 05-28-1996
Last Revised: Thursday, May 19, 2011 02:59:05 PM