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Mechanical weed control in pulse crops

Project code: PRR03-250

Project Lead

Eric Johnson - Agriculture and Agri-Food Canada


To evaluate and refine the use of a min-till rotary hoe to maximize its efficacy in weed control and minimize injury to organic pulse crops

Summary of Results

Dryland organic farming is growing in Western Canada. In 2005, 530,000 hectares of land were certified organic in Canada, and 85% of this production was located in the Prairies. The province of Saskatchewan accounts for most of that acreage, with 295,000 hectares in certified production in 2005. As synthetic inputs are not allowed in organic crop production systems, producers must rely on cultural and mechanical weed control methods, and this can increase the potential for wind or water erosion of the soil. The 2001 Organic Industry Needs Assessment study conducted by Saskatchewan Agriculture and Food found that weed control ranked second as a research priority for crop production.

Pulse crops are an important component of organic crop rotations. Studies at AAFC's Scott Research Farm in Saskatchewan have shown that field peas perform well under organic systems since they are able to fix some of their own nitrogen requirements. However, pulses compete poorly with weeds and some weed management is required to successfully produce pulse crops. The challenge in organic systems is to obtain sufficient weed control while minimizing the risk of soil erosion as a result of excessive disturbance of the topsoil. Any weed control method must ensure that sufficient residues are left on the soil surface to prevent erosion of the soil.

Recent surveys from the University of Saskatchewan indicate that in-crop mechanical weed control is not widely adopted by organic pulse growers. Post-emergence harrowing generally results in low selectivity, which is the ratio between weed control and crop injury. Despite this, a study at Scott found that post-emergence harrowing in field pea resulted in a 50% reduction in weed biomass and a 20% increase in field pea yield, when averaged over 3 years. It also found that selectivity could be improved with adjustments in harrow intensity. Therefore, there is potential to develop recommendations and visual guides for producers that will optimize selectivity in mechanical weed control.

This project was established to improve the efficacy of mechanical weeding while minimizing the loss of surface crop residues. The study evaluated both crop tolerance and weed control efficacy of two different mechanical weed control tools in pulse crops, and provided information which can be used to develop recommendations for organic growers. Two studies were conducted: the first, to evaluate tolerance and weed control of the min-till rotary hoe in lentil and field pea; and the second, to determine tolerance and weed control efficacy of the flex-tine harrow in field peas. The crop tolerance studies were kept weed free with herbicides, and weed control was assessed with the test crop present and with additional weeds planted to supplement the natural weed community.

Unfortunately, in 2 of the 3 years of the study the Scott Research Farm received severe hail, which resulted in the loss of many of the research plots associated with this project. Some data was salvaged and useful information obtained, but the weather problems prevented the researchers from developing the recommendations for growers within the timeframe of the project funding.

The data which were obtained from the experiments conducted with the min-till rotary hoe demonstrated that this implement will work in standing stubble and maintain surface residues.

In addition, lentil and field pea exhibited good tolerance to pre- and post-emergence rotary hoeing at five different crop stages (pre-emergence, ground-crack, 5-node, 8-node, and 11-node); however, there was less plant mortality when hoeing was conducted at later stages. Under weed-free conditions, both lentils and peas could tolerate two passes before yields declined.

The post-emergence harrowing trials conducted with a flex-tine harrow indicated that yield response in weedy conditions was highest when harrowing was done early. Regression analysis demonstrated that crop burial should not exceed 70% to optimize the harrowing benefit. Unfortunately, the ability to develop visual guides appears to be limited since harrowing has to be done so early, making it is difficult to distinguish non-buried plants in photographs. Therefore, other criteria will need to be developed to assist organic growers with this practice.

The incomplete data generated from this study was used to develop a follow-up study in 2007 to fine-tune weed control. This follow-up experiment was very successful and will be repeated. Thus, progress is being made in developing recommendations, and it is anticipated that a fact sheet on weed control for use by growers of organic pulse crops within the next two years.

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