Objective: investigate the effects of allelopathic cover crop mixes on weed counts, species diversity, and cash crop yield in rotation years following either roller-crimping or incorporation of the cover crops.
Allelopathic cover crops:
- Hairy vetch
- Annual ryegrass
• Determine the impact of this cropping system on soil drainage and water holding capacity
• Provide evidence to producers that spring sown cover crops aid to increase water availability in the soil
• Encourage adoption of agricultural sustainable practices and build resiliency to climate change side effects such as flooding and drought
Allelopathy is the direct or indirect impact on plant individuals, whether they belong or not to the same species. Established as substances composed of secondary metabolites, allelopathy can a) affect growth and yield of another plant and b) develop autotoxicity, where plant individuals’ secrete chemicals that prevent propagation and development of seedlings of same species growth.
Allelopathy can be used as a strategic tool to mitigate chemical weed management. Residues of allelopathic cover crops not only provide benefits to the soil but also help to reduce weed populations during their growth and likely for the cash crops seeded in the season thereafter.
There was more biomass in the Ultimate mix compared to the other cover crop mixes. It is important to note that, despite producing 32% more than the other NPARA blends (P=0.0076), its mean biomass value was statistically the same than biomass found in Pinpoint in NPARA blends 5 and 6 (P=0.0151). In contrast, NPARA blends 1 and 4 which were the blends that produced the lightest mean biomass. It can be argued that blends 5 and 6 as they have corn in their cover crop mix, which is a heavy and bulky plant and ryegrass, which is an early emergence high yielding cover crop. Blends 1 and 4, have cereal rye as part of their mix, but biomass produced from these stands is not as copious as that found in annual ryegrass.
Protein values were the highest in ultimate and pinpoint blends (P<0.0001). As such, Ultimate and Pinpoint had 54 and 42% more protein respectively compared to NPARA protein values combined. Protein content in NPARA blend 3 was the same as that found in Pinpoint blend in comparison to the other blends from NPARA, likely due to white clover being part of such blend.
Acid (P=0.0279) and neutral (P=0.0184) detergent fibre were also greater in the ultimate blend. Acid and neutral detergent fibre were 30 (P=0.0153) and 26% (P=0.0452) respectively compared to those found in NPARA blends. From the blends selected at NPARA, blends #2, 5 and 6 showed statistically similar ADF and NDF values to Ultimate and Pinpoint blends. Lowest ADF and NDF values on the other hand were attributed to blends 1 and 4, possibly due to presence of cereal rye in a greater proportion with respect to the other blends. Total digestible nutrients were greater in Ultimate and Pinpoint blends (P=0.0022). Values were 43 (P=0.0002) and 32% (P=0.0087) greater than those found in NPARA blends.
Soil organic matter (P=0.9045), Cation Exchange Capacity (P=0.0669), pH (P=0.7063), P (P=0.1634), K (P=0.1623), Mg (P=0.7874), S (P=0.2400), Zn (P=0.9525), Fe (P=0.2619), Cu (P=0.4967), B (P=0.3848), Al (P=0.9629) and Na (P=0.9629) as well as nitrate (P=0.2096) were the same for all treatments. Moreover, insects were monitored every two weeks and data suggests that number of insects did not differ across treatments (P=0.0950).
Overall, NPARA blends 1 and 4 more digestible for the animal to eat compared to the other NPARA blends. However, NPARA blend #3 might also be a good choice of energy as it provides as much protein as that found in the Pinpoint blend.
Soil infiltration measurements are preliminary and do not provide any effect made by the treatments themselves. It is expected that in following seasons, soil analysis and infiltration conducted can be used to compute and further analyse differences among treatments.
Cover crop mixes were crafted to observe how different cover crop roots affect infiltration and fertility across the soil column. Consider treatments as four sets of three treatments. The first set consists of a brassica group (daikon radish, forage radish and forage turnip) which is sown at 1X, 2X and 3X of the recommended seeding rate. With the exception of the fallow treatment, all other sets have a brassica group at either of these seeding rates and field pea and sunflower. Thus, The second set was sown with oat, Japanese millet, sweet clover, chicory, in addition with the brassica group and afore mentioned crops. Third set had a brassica group with only field pea and sunflower and the last set of three was seeded with a brassica group, brown midrib corn, annual ryegrass and hairy vetch. Treatments were harvested for biomass yield and sent for feed analysis. Due to funding constraints, biomass was not collected for fallow plots and no subsequent feed analysis in the plots of this treatment were made. Biomass yield was statistically the same across all treatments (P=0.0582). Likewise, protein (P=0.4873) and acid detergent fibre (P=0.0982) were the same among treatments. Neutral detergent fibre (P=0.0029) on the other hand, was greater in mixes containing oat, Japanese millet, sweet clover, chicory, field pea and sunflower, despite brassica seeding rates. Moreover, mixes with only brown midrib corn, annual ryegrass and hairy vetch and single rates of the brassica group showed NDF as great as those found in previous mentioned mixes. Values of NDF were low in mixes were only the brassica group was present or when it was accompanied with field pea and sunflower. In fact, NDF in treatment sets with sown with brassica group, field pea and sunflower plus oat, Japanese millet, sweet clover and chicory was 113% more than that found in sets sown with only the brassica group. This same set were Japanese millet, oat, chicory and sweet clover were sown had 97% more NDF than sets were a brassica group plus field pea and sunflower were seeded and 69% more NDF than mixes including brown midrib corn, annual ryegrass and hairy vetch.
Allelopathy is the influence, usually detrimental, of one plant on another, where toxic substances are released when a plant dies or produced through decaying tissue. These secondary metabolites may establish direct or indirect impacts on populations of their own or different species. Allelopathy can a) affect the growth and yield of another crop (Batish et al. 2001) or b) develop autotoxicity, meaning chemicals expelled from plant residues of a species can hinder the growth of seedlings of the same species. Thus, if managed properly, allelopathy can be a great alternative in weed management.
Many of the cover crops seeded to protect the ground have allelopathic properties. Crops such as rye (Secale cereale L.), annual ryegrass (Lolium multiflorum L.), hairy vetch (Vicia villosa L.) and sunflower (Helianthus annuus L) have been shown to limit or reduce the growth of other plant species. Therefore, residues of these cover crops not only provide benefits to the soil but also help to reduce weed populations through allelopathy for the cash crops seeded in the season thereafter. In this experiment weeds were surveyed every two weeks after cover crop mix seeding to observe if allelopathic effects changed according to cover crop species or cover crop mixes. At the end of the season, plots were either roller-crimped or incorporated. The following growing season, canola, field pea and wheat will be sown perpendicular to the direction of these plots to observe if weed populations are still suppressed by the allelopathic effects of the cover crops and their mixes. Further, it will be assessed whether roller-crimping and incorporation impact weed suppression along with allelopathy.
Eight cover crop blends were subject to a nutritive analysis. There were significant differences in many of the nutritive indicators measured including dry matter (P=0.002), crude protein (P=0.001), TDN (P=0.02), and phosphorus content (P=0.03). ADF (P=0.18) and calcium (P=0.06) were statistically similar between treatments. NPARA Blend #6 produced 2.6 tonnes/acre of dry matter, the highest of any treatment. NPARA blends #4 and #1 had the highest level of crude protein at 33.4% and 31.5%, respectively. NPARA Blend #1, 75.1%, and Pinpoint Blend, 74.7%, exhibited the highest TDN. C.V. values were high for all except ADF and TDN.
In the previous year (2020), cover crops were also seeded, but C and N contents obtained through decomposition were not sufficient to show significant differences across cover crop blends. The impact of cover crop seeding on nitrogen and carbon content can take several years for differences to be observed. Furthermore, the use of cover crops for soil quality improvement is a process that requires steady and uninterrupted contributions.