- Agronomic: wheat
- Crop Production: no-till
- Education and Training: on-farm/ranch research
- Pest Management: chemical control, integrated pest management, weed ecology
- Soil Management: soil quality/health
Global wheat production is threatened by the escalating selection of herbicide resistant weed populations. The continuing evolution of herbicide resistance in major crop weeds is a driving force to develop new weed control strategies in field crops and also to preserve the utility of herbicides. However, weeds are not only a threat in conventional agriculture but also a threat to organic agriculture and often cause these systems to fail. More sustainable practices that reduce the dependence of herbicides or soil tillage are needed to control weeds in crop production systems.
In Australia, weed scientists have had promising results with practices that target collection or destruction of weed seeds at grain harvest (Walsh et al., 2013). These practices include the use of chaff carts, bale direct systems, the Harrington seed destructor (HSD), and narrow windrow burning among others. This project will concentrate on the potential benefits of the use of chaff carts and bale direct systems to reduce weed infestations in wheat-production systems in the Pacific Northwest (PNW). The HSD has produced good results, but the cost of a single unit is beyond this project’s budget and its efficacy to control weeds is comparable to that of a chaff collection system. Narrow windrow burning is a practice with a high risk of causing fire and detrimental effects on air quality. The use of chaff carts and bale direct systems are two harvest practices that have not yet been adequately evaluated in the PNW. Their efficacy to control weeds is unknown because the proportion of weed seed per species collected by the combine and ejected with the chaff or straw has not been investigated. The objectives of this study are: 1) Evaluate chaff collection and chaff plus straw collection at harvest to reduce weed species density and dispersion, 2) Evaluate seed production, seed height, and seed retention of important weed species at harvest, 3) Determine the effects of chaff or chaff and straw removal on soil organic matter and moisture content, and 4) Disseminate knowledge gained from the research via extension activities oriented to farmers, ag-professionals, students and stakeholders.
Field experiments with two treatments and three replications were established on naturally occurring weed-infested areas at each participating farm (three farms in Oregon and one farm in Washington). The two treatments were harvesting with the combine alone (control treatment) and harvesting with either a chaff cart or a bale direct system behind the combine. We did not expect participating farmers to work with both practices on the same farm because the adoption of one or the other practice depends in many cases on their residue management system.
In addition to the on-farm experiments, we conducted supplemental experiments on university research farms. The research farm experiments applied both practices, i.e. chaff cart and bale direct system, with four replications. In all experiments (commercial and research farms), weed infestations were characterized and evaluated before crop harvest, and the following spring for three years to determine the efficacy of each harvest practice. Seed production, seed height, and seed retention were measured to determine the quantity of seed per species that were collected by the combine. In the research farm experiments, the soil organic matter and moisture were measured monthly to look for differences between treatments.
The final goal of this project was to determine the ability of chaff collection and chaff plus straw collection practices during harvest to reduce weed infestations over time and determine some recommendations to maximize the effectiveness of these practices.
1) Evaluation of chaff collection and chaff plus straw collection practices at harvest to reduce weed species infestation
An experiment was established in naturally infested areas on participating farms in spring 2016. The experiment was a randomized complete block design with two treatments on approximately one acre of land. The two treatments were 1) harvesting with the combine alone (control treatment) and 2) harvesting using a chaff cart or a bale direct system behind the combine. A similar experiment was established on two research farms in spring 2016. The research farm experiments, in addition to natural weed infestations, had an artificial infestation of one important weed species not already in the seedbank to evaluate weed dispersion in addition to density. The research farm experiments allowed us to evaluate both practices at the same location. The infestation in each plot was monitored annually. This objective allowed us to assess the ability of chaff carts or bale direct systems to reduce weed infestations in density and area over time. This objective started in spring 2016 and finished by summer 2019.
2) Evaluation of seed production, seed height, and seed retention of important weed species at harvest
In the same fields established for objective 1, we evaluated seed production, seed height, and seed retention rate of the dominant weed species at each experimental site. This objective allowed us to determine the optimal cutting height to maximize control depending on the weed species and determine the potential percentage of control per species if none of the weed seed harvested is returned to the seedbank. This objective started in summer 2016 and was completed in the fall of 2019.
3) Effects of chaff or chaff and straw removal on soil organic matter and moisture content
The organic matter and soil moisture content was monitored in one of the research farm experiments from June 2016 to February 2020. This objective allowed us to determine differences between residue removal treatments in soil organic matter and soil moisture content.
4) Conduct several extension activities oriented to farmers, ag-professionals, students and stakeholders
Educational materials were developed to instruct producers on the use of chaff carts and bale direct systems to improve weed control and enhance agricultural sustainability. Scientists participated in seminars and conferences to reach larger audiences. This objective began in the fall of 2016 and will finish by March 2020 and beyond.