[Pollinator] Reduced crop density increases floral resources to pollinators without affecting crop yield in organic and conventional fields

[David Inouye]

Sidemo-Holm, W., et al. (2021). "Reduced crop density increases floral 
resources to pollinators without affecting crop yield in organic and 
conventional fields." Journal of Applied Ecology 58(7): 1421-1430.
     Effective weed control in agricultural crop fields increases 
yields, but simultaneously reduces floral resources for pollinators 
because many weed species provide pollen and nectar. Consequently, 
efforts to enhance crop yields on organic farms by using effective weed 
control methods risk compromising positive effects of organic farming on 
pollinating insects. Thus, it is important to find management strategies 
that alleviate the trade-off between crop yields and flowering weeds on 
organic farms. We investigated the relationship between cereal yields, 
flowering weeds and bumblebees on organic and conventional arable land. 
We also investigated the potential of adjusting crop sowing density to 
benefit flowering weed species richness and floral resources to 
bumblebees without affecting crop yield. Floral resources and species 
richness of flowering weeds were higher in organic compared to 
conventional fields and were negatively related to crop yield in organic 
but not conventional fields (where the variation of floral resources and 
flowering weed species richness was comparatively low). Bumblebee 
species richness was higher in organic compared to conventional fields, 
and abundance was twice as high in organic as in conventional fields, 
but not significantly so. Yields in organic fields were two thirds of 
those in conventional fields. When simultaneously testing the effect of 
farming type (organic vs. conventional), crop yield and floral 
resources, only floral resources were related significantly to bumblebee 
abundance and species richness. A lower sowing density of the crop 
increased floral resources without negatively affecting crop yield.
Synthesis and applications. We show that organic farming practices in 
cereals benefit bumblebees by allowing more flowering weeds, but at a 
cost in terms of lower yields. However, adjusting crop sowing density 
provides an opportunity to attain increased floral resources without 
negatively affecting crop yields. Thus, by increasing floral resources, 
adjusting crop sowing density may contribute to supporting high 
bumblebee densities, which in turn sustain pollination services to wild 
plants and insect-pollinated crops, such as oilseed rape and field 
beans, in agricultural landscapes. We suggest that sowing strategies 
have the potential to contribute to ecological intensification by 
supporting organisms that provide ecosystem services to agriculture.


-- 
Dr. David W. Inouye
Professor Emeritus
Department of Biology
University of Maryland

Principal Investigator
Rocky Mountain Biological Laboratory