1. Organic cover crop weed suppression: diversity vs. functional traits
Mitch Hunter1, Meagan Schipanski1,2, Dave Mortensen1,2,3
1Department of Plant Science, 2Department of Ecosystem Science and Management, 3Ecology Intercollege Graduate Degree Program
The Pennsylvania State University
HYPOTHESIS
Cover crop species diversity and functional diversity enhance weed suppression in an organic grain rotation
Methods
ORGANIC FIELD EXPERIMENT
3 entries, 4 blocks, ~12 ha
Cover Crop Species Diversity
Does Not Drive Weed Suppression
Functional Traits Dominate:
Fall Vigor is Key
Early fall ground cover explains 49.8% of the variation in spring weed biomass (R2 = 0.498, p < )
Block 1
Block 2
Block 3
Block 4
Google Maps
Species diversity explains only 12.0% of the variation in spring weed biomass
(R2 = 0.120, p = )
Mac Burgess
CORN-SOY-WHEAT ROTATION
Sampled after-wheat cover crops
Fall Canola
Corn
Silage
Cover
Crops
Soybean
Winter
Wheat
Spring Weed Biomass
(Kg/ha)
Spring Weed Biomass
(Kg/ha)
Mac Burgess
Fall Clover
COVER CROP COCKTAILS
1-7 species per treatment
Planted 8/25-26, 2012
# Species 1 1 1 1 1 1 3 3 4 6 7
Early Fall Percent Cover
(39-44 days after planting)
Canola
Clover
Oat
Radish
Pea
Rye
3SppN
4Spp
6Spp
Xmix
Mac Burgess
3SppW
Path Model: Spring Growth Matters
Fall suppression is a stronger effect, but spring cover crop growth dynamics do impact spring weediness
Winter-Killed Cover Crops Can Control Spring Weeds
Oat and radish effectively suppress fall germination of winter annuals, reducing spring weed pressure
Mac Burgess
KEY MEASURES
% light Interception: LICOR quantum sensors above and below canopy
% cover: visual estimates in field and from photographs
Weed biomass: destructive sample of sub-plots
Path coefficients denote direct
effects of one variable on
another
Fall and spring latent variables are indicated by each season’s first % interception and
% cover readings
Fall Weed Suppression
Fall Radish
-0.498
0.363
Spring Weed Biomass
(Kg/ha)
Mac Burgess
STATISTICAL METHODS
Standard least squares regression in JMP 10
Weed biomass sqrt transformed
Block as random effect
PLS Path Modeling in R package “plspm”
Spring Radish
R2 = 0.387
GoF = 0.490
Spring Weed Suppression
Spring Weediness
Winter-Hardy
Cover Crops
Winter-Killed
Cover Crops
-0.236
Mitch Hunter
ACKNOWLEDGEMENTS
We thank Sadie Smith and Katy Barlow for their help. Funding was provided by the National Institute of Food and Agriculture (NIFA) Organic Research and Extension Initiative (OREI). This material is based upon work supported by the National Science Foundation under Grant No. DGE Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.
TREATMENTS
Monocultures: canola (Brassica napus), red clover (Trifolium pratense), oat (Avena sativa), Austrian winter pea (Pisum sativum), forage radish (Raphanus sativus), cereal rye (Secale cereale)
3 Species Nitrogen: red clover, Austrian winter pea, cereal rye
3 Species Weeds: red clover, oat, cereal rye
4 Species: canola, red clover, Austrian winter pea, cereal rye
Xmix (7 species): King’s Agri-Seeds Broadcaster Mix, oat, sunflower (Helianthus annus)
6 Species: all monoculture species