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2007-2008 Fall Cover Crop Performance at E.V. Smith Research Center

On April 10, 2008, the fall cover crops were evaluated for establishment, ground cover, and weed cover.  The cover crops were beginning to flower.  They will soon be mowed down to prepare the beds for planting the summer tomato and pepper crop.

The objectives of planting the cover crops were weed control and enhancement of soil fertility – to build organic matter and to add nitrogen.  They also attract beneficial insects, which aid in insect pest control on the cash crop.  We tried different mixtures of cover crops (shown in the table below).  The mixtures that we planted in the permanent planting zones were mixtures of grasses and legumes.  We also chose cover crops that were relatively easy to terminate before planting season.  In the aisles, we mainly wanted weed control.   For these areas we selected cover crops for their superior biomass production, and we also experimented with others for use as living mulches—ones that would keep growing during the summer.  For the aisles we looked at some perennial cover crops, such as white clover and crimson clover, which would re-seed themselves.

Table:  Fall cover crops planted in organic field at E. V. Smith Research Center.

In planting rows                                                                Between rows

Rye + hairy vetch                                                             Companion grass

Triticale + Austrian winter pea                                          Triticale

Barley + hairy vetch                                                          Barley + crimson clover

Barley + Austrian winter pea                                             White clover

Rye + Austrian winter pea                                                 Rye

We planted the same cover crop combinations in two different plots.  Plot 1 had been planted in tomatoes and peppers last summer; Plot 2 had been planted in summer cover crops, which did not do well due to the drought of 2007.  The performance of cover crops in both plots is shown in the tables below.  Overall, the results varied for the same cover crop in the different areas.  Some of this may be due to the fact that the plots were planted without tilling so some residual seed from former years may have sprouted with the favorable spring weather we have had this year.  This seemed to be the case in Plot 2 where we planted companion grass this year.  In 2006 this plot had been in crimson clover, and that is what is growing there this year.

The cover crop stand is an estimate of how well the cover crop became established.  Percentage of weeds is the amount of the ground they cover. Percentages may add up to over 100% because their canopies overlap.  The cover crop canopy rating refers to how well the canopy covers the space and shades out weeds.

Plot 1

AWP = Austrian winter pea

*Cover crop canopy scale:

  1 = 0-20%

  2 = 21-40%

  3 = 41-60%

  4 = 61-80%

  5 = 81-100%

Plot 2

Overall, rye grew the tallest and produced the most biomass of the grass cover crops.  Hairy vetch usually performs well for us, but this year it did not. 

Companion grass, a mixture of creeping red fescue and dwarf ryegrass, was planted in the aisles between the rows as a living mulch.  It did not grow well; it was out-competed by the taller weeds and cover crops from former years and adjacent plots. 

Triticale became established and grew fairly well, but it was not a very tall plant, so it did not produce much biomass.   It also did not cover the ground very well when planted alone, which allowed weeds to become established.  When planted with Austrian winter pea, however, abundant biomass was produced and weeds were suppressed.

Barley was knocked back by low winter temperatures, although some survived, especially in the crimson clover mixture.  Barley did not get very tall and would doubtfully suppress weeds very well as a monoculture.

White clover did very well in the plot where we had planted it for two consecutive years.  In the other plot where it was grown for the first year, it did not establish.

Austrian winter pea produced abundant biomass in some rows but not in others.  It may have been damaged by cold temperatures, but the inconsistent performance warrants further study. 

Overall, our results with winter cover crops can be summarized as follows:

Previous findings:

The rye and triticale monocultures produced the greatest amount of biomass; rye/Austrian winter pea and rye/hairy vetch/crimson clover mixtures were not far behind them.  The living mulches, white clover and companion grass seemed to die out during the drought, but came back in the fall.  The cover crops producing the greatest amount of nitrogen were rye/hairy vetch/crimson clover, hairy vetch, and canola/crimson clover. 

This year’s results:

The cover crop stands that we obtained were often not the ones that we planted this year, but were mixtures resulting from seeds planted in previous years.  Rye sprouting from seed planted in previous seasons often out-competed the presently planted crops; the same phenomenon occurred with crimson clover.  Overall, rye and crimson clover produced the most biomass.

Overall conclusions/recommendations:

For weed smothering abilities and for building soil organic matter, rye is a very good choice.  If you wish to plant a cash crop following the fall cover crop, a rye/hairy vetch/crimson clover combination would be a good choice as it produces a lot of biomass and nitrogen.  Rye/Austrian winter pea would also be a good choice.  If using rye alone, you might need to supplement the following cash crop with more nitrogen.  Rye, crimson clover, and hairy vetch must be terminated when in full bloom.  If they are cut too early, they may immediately re-sprout; if they are left to go to seed, they will re-sprout the following fall.   Austrian winter pea does not re-seed.  We have not had much success with living mulches thriving in the summer and suppressing summer weeds in the aisles due to droughts the past two summers.  We do not irrigate the aisles.  We have found that the simplest method to control weeds in the aisles is just to keep them mowed.

Barley and Crimson Clover	Rye and Austrian Winter Pea