Rolled Rye Mulch for Weed Suppression in Organic No-Tillage Soybeans

Abstract

Rising demand for organic soybeans and high price premiums for organic products have stimulated producer interest in organic soybean production. However, organic soybean producers and those making the transition to organic production cite weed management as their main limitation. Current weed management practices heavily rely on cultivation. Repeated cultivation is expensive and has negative consequences on soil health. Research is needed to improve organic reduced tillage production. Rye cover crop mulches were evaluated for weed suppression abilities and effects on soybean yield. Experiments were planted in 2008 and 2009 at three sites. Rye was planted in the fall of each year and killed at soybean planting with a roller/crimper or flail mower, creating a thick weed-suppressing mulch with potential allelopathic properties. The mulch was augmented with one of three additional weed control tactics: preemergence (PRE) corn gluten meal (CGM), postemergence (POST) clove oil, or postemergence high-residue cultivation. Roll-crimped and flail-mowed treatments had similar weed suppression abilities at most sites. There were no differences between CGM, clove oil, or cultivation at most sites. Sites with rye biomass above 9,000 kg ha−1of dry matter provided weed control that precluded soybean yield loss from competition. In Goldsboro 2008, where rye biomass was 10,854 kg ha−1of dry matter, the soybean yield in the rolled rye treatment was not significantly different from the weed-free treatment, yielding at 2,190 and 2,143 kg ha−1, respectively. Likewise, no difference in soybean yield was found in Plymouth 2008 with a rye biomass of 9,256 kg ha−1and yields of 2,694 kg ha−1and 2,809 kg ha−1in the rolled rye and weed-free treatments, respectively. At low rye biomass levels (4,450 to 6,606 kg ha−1), the rolled rye treatment soybean yield was 628 to 822 kg ha−1less than the weed-free treatment. High rye biomass levels are critical to the success of this production system. However, high rye biomass was, in some cases, also correlated with soybean lodging severe enough to cause concern with this system.

The Current State and Future Directions of Organic No-Till Farming with Cover Crops in Canada, with Case Study Support

“…Teasdale et al report that 97% mulch ground cover in the OrgNT system is required for a 75% reduction in weed biomass [31]. To achieve this level of mulch coverage, 8 to 9 tonnes of dry matter per hectare is required [13,32]. The relationship between biomass and weed control is not linear; at 7000 kg/ha of cover crop mulch, the ground area infested by weeds in OrgNT soybeans is 90%, while at 9000 kg/ha weed cover, it is reduced to less than 15% [13].…”

“…The methods supported by recent research rely heavily on cover crops to a greater extent than is already practiced in organic agriculture [10]. Since the majority of organic herbicides is ineffective at controlling weeds, mechanically terminated cover crops are placed on the soil surface as weed-suppressive mulch for the following cash crop, a crop considered by this paper to be any crop intended to be marketed [11][12][13]. There are a number of mechanical termination methods, but the roller-crimper is credited with making no-till more available to organic farmers in Canada and is most strongly supported by research [14].…”

Weed suppression and soybean yield in a no-till cover-crop mulched system as influenced by six rye cultivars

“…Bars extend to +1 standard errors of the estimate. *Suggested biomass threshold for optimal weed control potential (Smith et al, 2011). Soybean population counts also varied widely between rye termination dates in 2010 (Fig. 4) where rye termination date impacted soybean population (Table 4).…”

“…Bars extend to +1 standard errors of the estimate. * Suggested biomass threshold for optimal weed control potential (Smith et al, 2011). 1 Treatments consist of the two weed-free checks, no-till without rye cover crop plus herbicide weed control (NT + HB), rolledcrimped rye plus herbicide weed control (RC + HB), and SRCs: three early flowering types (Wrens Abruzzi, Wrens 96 and Maton II) and three late flowering types (Aroostook, Rymin and Wheeler).…”

“…To be an effective weed barrier, rye mulches must exceed approximately 8000-9000 kg ha −1 dry matter (DM) production depending on the region where the cover crops are grown (Teasdale and Mohler, 2000;Smith et al, 2011). Unfortunately, levels of rye biomass can vary widely from year to year and factors such as establishment and termination dates (Mirsky et al, 2009(Mirsky et al, , 2011 along with temperature and rainfall, can contribute to suboptimal rye biomass production (Travis et al, 1988;Mirschel et al, 2005).…”