Effects of Cereal Rye Mulch Rate and Planting Density On No-till Soybean Yield in the Absence of Herbicides.

Recent advancements in cover crop management have led to the development of a new soybean management system that: 1) has several environmental advantages over current production systems, 2) can effectively suppress glyphosate-resistant weeds, and 3) enables no-till planting in organic production. This system is based on the use of a fall-planted cereal rye cover crop that is mechanically managed with a roller-crimper at reproductive maturity in the spring to create a layer of mulch. Soybean seeds are then no-till planted or drilled into the soil and emerge through the mulch, while annual weed species with relatively small seed sizes are suppressed. In 2008 and 2009, we conducted an experiment in Pennsylvania and Maryland to test the effects of manipulating cereal rye mulch rate and soybean planting density on weed suppression and soybean yield. Five levels of each factor were arranged in a split-block factorial design resulting in a matrix of 25 experimental units that were replicated four times (n = 100) in each of the four site-years. Weed biomass ranged from 0 to 9,670 kg ha^-1 and was lowest in the highest cereal rye mulch level treatment (2x). Soybean yield ranged from 0 to 4,480 kg ha^-1. When pooled across all site-years, the greatest mean soybean yield (2,870 kg ha^-1) was observed in the intermediate rye mulch rate (1x) and highest target planting rate (740,000 seeds ha^-1) treatment, which had an observed mean cereal rye mulch of 1,000 kg ha^-1 and a soybean population of 380,000 plants ha^-1. This suggests the high planting rate compensated for poor soybean emergence and that additional research is needed to improve seed placement and seedling establishment in this system. Despite this challenge, our research indicates potential for a synergistic interaction between cereal rye mulch and soybean planting density on weed suppression and demonstrates that competitive soybean yields can be achieved without herbicides or cultivation.