Managing Global Resources for a Secure Future

Mixing cover crop species in a mixture can be a way to expand the number of functions or services a cover crop can provide. Cover crop mixtures are becoming more popular among crop grain farmers who look for multiple services from their cover crops, such as weed suppression, nutrient supply and retention or increase organic matter. However, seeding a mixture does not always result in getting a mixture established in the field. The same five species cover crop mixture (triticale, Austrian winter pea, canola, crimson clover and red clover) was planted in 20 by 45 feet plots at 3 different planting dates (August 8^th, August 24^th and September 7^th 2016) in an organic field in central Pennsylvania. Planting dates were randomized following a randomized complete block design with 4 replicates. Biomass of each cover crop species and weed biomass were measured twice in the fall and once in spring by clipping all plants in two 0.25 cm quadrats. Both in the fall and in the spring, early planted cover crops were completely dominated by canola, whereas the cover crop planted in early September was a more even mixture, although canola still dominated. Weed biomass in the early planted cover crop was orders of magnitude higher than in the cover crops planted in late August and early September and was mainly composed of summer annual weeds. Cover crop biomass did not significantly explain weed biomass. Our results suggest that if cover crops mixtures are planted too early, dominant species such as canola can outcompete any other species in the mixture, thus jeopardizing the provisioning of functions by those species. However, early planting seemed to trigger the germination and growth of summer annual weed species compared to later planting dates, even within a highly competitive cover crop.