Ontario - Canada Logos
SWEEP Banner

SWEEP Report #43

The Use of Cover Crops for Nutrient Conservation

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.

Executive Summary

Evaluation Summary (Tech. Transfer Report Summaries)

View / Download Final Report [2007 KB pdf]

Associated SWEEP/LSP Research



List By Number | List By Sub-Program

Completed: March, 1992

Key Words:

cover crops, red clover, oilseed radish, ryegrass, corn, winter wheat, barley, nitrogen, phosphorous, nitrate leaching, crop response.

Executive Summary

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 or wheat.

Oilseed radish had a considerably greater P concentration and biomass P content (kg ha) than either ryegrass or red clover.

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.


Evaluation Summary

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

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.

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 #36 - Red Clover Cover Crop Studies 1987-1990

  • 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

  • SWEEP Report #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.




List By Number | List By Sub-Program | LSP Report List


Created: 05-28-1996
Last Revised: Thursday, May 19, 2011 03:21:01 PM