Brassica cover cropping: I. Effects on weed and crop establishment

Abstract

The Brassicaceae contain glucosinolates, which hydrolyze to form compounds toxic to plants, fungi, nematodes, and certain insects. Lower weed density and biomass in crops grown following incorporation of brassica cover crops suggest that they may contribute to weed management in agricultural systems. Field experiments were conducted to determine whether incorporated brassica cover crops, including canola, rapeseed, and yellow mustard, reduce subsequent weed and crop establishment; a companion paper describes separate but related field experiments that examined the influence of brassica cover crops on plant growth. Emergence rate and total emergence of sixteen weed and crop bioassay species were measured following brassica cover crops, fallow, or incorporated residues of other short-season cover crops including oat, crimson clover, and buckwheat. The bioassay species, representing a range of seed sizes, were chosen to determine whether larger seed size confers protection from residue-mediated effects on emergence. Averaged over bioassay species, brassica cover crops reduced emergence by 23 to 34% compared with fallow; emergence following brassicas was delayed by approximately 2 d. The effects of the incorporated brassica residues were similar to those of the other short-season cover crops, which reduced emergence of the bioassay species by 19 to 39% and delayed emergence by 2 d. Seed size was a poor predictor of a species' establishment. These results suggest that brassica residues are capable of delaying seedling emergence and reducing establishment, although the magnitude of their effects were comparable to other widely available cover crops.

Crop response to current and previous season applications of phosphorus as affected by crop sequence and tillage

“…However, flax seed yield was higher after wheat than canola both sites in all years. The effect may be due to a number of factors, including some degree of allelopathy from canola residue (Haramoto and Gallandt 2005), early-season competition from volunteer canola plants or restriction in mycorrhizal colonization after canola. In a study evaluating sequencing of 10 different crops in North Dakota, Tanaka et al (2005) noted that flax seeded on canola was intermediate in yield in the first year of the study when moisture was 186% of normal, but produced the second lowest yield, after flax seeded on flax, in the second year when precipitation was 104% of normal.…”

Allelopathic Weed Suppression Through the Use of Cover Crops

“…Glucosinolates occur in many plant species, but are widely known to be produced by species within the Brassicaceae family ( Figure 2) (Haramoto and Gallandt 2005;Malik et al 2008;Mithen 2001). Members of this family include: wild radish (Raphanus raphanistrum L.), white mustard (Sinapis alba L.), turnip (Brassica campestris L.), and rapeseed (Brassica napus L.).…”

“…Members of this family include: wild radish (Raphanus raphanistrum L.), white mustard (Sinapis alba L.), turnip (Brassica campestris L.), and rapeseed (Brassica napus L.). Glucosinolates, secondary metabolites containing sulfur and nitrogen, are enzymatically hydrolyzed by myrosinase in the presence of water to form isothiocynates, the active allelochemicals (Haramoto and Gallandt 2005;Norsworthy and Meehan 2005;Petersen et al 2001;Price et al 2005). Previous research examining extracts from glucosinolate-producing plant species have shown inhibition of other species through reduced germination, reduced seedling emergence and reduced size, as well as delayed seed germination (Al-Khatib et al 1997;Brown and Morra 1996;Malik et al 2008;Norsworthy et al 2007;Wolf et al 1984).…”

“…A l t h o u g h s p e c i f i c m o d e s o f a c t i o n h a v e n o t been thoroughly investigated for each compound, it is evident that some plant species are able to tolerate these allelochemicals more readily than other species (Norsworthy and Meehan 2005). Some suggest that seed size variability plays a role in determining inhibitory effects of these allelochemicals; however, this may not be the only determinant for tolerance to these compounds (Haramoto and Gallandt 2005;Westoby et al 1996). Future research with these allelopathic compounds will likely seek to answer this question, along with identifying the mode of action for plant inhibition, in order to utilize these compounds more effectively in agricultural production.…”

Evaluation of Crop Seed Powders as Amendments for Purple Nutsedge (Cyperus rotundus) Control Compared to the Traditional Herbicide, Roundup

“…Although complete season-long weed suppression using only glucosinolateproducing plant residues seems unattainable, future studies should continue to test the effects of utilizing higher concentrations of seed powder treatment, especially under field conditions (Haramoto and Gallandt, 2005;. Increased treatment concentrations should improve the longevity of allelopathic compounds in the face of heavy precipitation.…”