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 in organic agriculture where weeds often cause these systems to fail. More sustainable practices that reduce the dependence on 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 are the use of chaff carts, direct bale systems, the Harrington seed destructor (HSD), and narrow windrow burning. This project will concentrate on the potential benefits of the first two practices the use of chaff carts and direct bale 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 direct bale systems are two economically and environmentally sustainable 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. Combine harvesters are important seed dispersal vectors within an arable farming system (Cousens & Mortimer 1995; Barroso et al., 2006). 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 will be established on naturally occurring weed-infested areas at each participating farm (four farms in Oregon and four farms in Washington). The two treatments will be harvesting with the combine alone (control treatment) and harvesting with either a chaff cart or direct bale system behind the combine. We do not expect participating farmers to work with both practices on the same farm because the adoption of one or the other practice will depend in many cases on their residue management system. In addition to the on-farm experiments, we will be conducting supplemental experiments on university research farms. The research farm experiments will have both practices, i.e. chaff cart and direct bale system, with four replications. These experiments will allow us to focus on other important weed species (such as jointed goatgrass and cereal rye) that are not present in the seedbank at each site before the beginning of the experiments so that we can study weed dispersion with greater precision than on the participating farms. In research farm experiments, natural infestations will be studied as well. In all experiments (commercial and research farms), weed infestations will be characterized and evaluated before crop harvest and the following spring during the three years of the project. The characterization will consist of evaluating weed density per species in areas of approximate 10 ft2 across each 20 ft x 200 ft plot. Seed production, seed height, and seed retention will be measured to determine the quantity of seed per species that are collected by the combine. The weed reduction will be determined by the decrease in weed density and area infested. In the research farm experiments, the soil organic matter and moisture will be measured monthly to look for differences between treatments. The final goal of this project will be to determine the ability of chaff collection and chaff plus straw collection practices during harvest to reduce weed infestations over time and improve the sustainability of our agro-ecosystems. Our hypothesis is that the use of chaff carts or direct bale systems will help to reduce both weed density and area infested.
Project objectives from proposal:
1. Evaluation of chaff collection and chaff plus straw collection practices at harvest to reduce weed species density and dispersion
An experiment will be established in naturally infested areas on participating farms in spring 2016. The experiment will be a randomized complete block design with two treatments on approximately one acre of land. The two treatments are 1) harvesting with the combine alone (control treatment) and 2) harvesting using a chaff cart or direct bale system behind the combine. A similar experiment will be established on two research farms in spring 2016. The research farm experiments, in addition to natural weed infestations, will have an artificial infestation of one important weed species not already in the weed seedbank to evaluate weed dispersion in addition to density. The research farm experiments will allow us to evaluate both practices at the same location. We will monitor the infestation in each plot twice per year. This objective will allow us to assess the ability of chaff carts or direct bale systems to reduce weed infestations in density and area over time. This objective will start in spring 2016 and will finish in spring 2019.
2. Evaluation of seed production, seed height, and seed retention of important weed species at harvest
In the same field experiments established for objective 1, we will evaluate the following on 10 mature plants per species: seed production, seed height, and seed retention rate of the dominant weed species at each experimental site. This objective will allow us to determine the optimal cutting height to maximize control depending on the weed species, and also determine the potential percentage of control per species if none of the weed seed harvested is returned to the seedbank. This objective will start in summer 2016 and will be completed in the fall of 2018.
3. Effects of chaff or chaff and straw removal on soil organic matter and moisture content
The organic matter and soil moisture content will be monitored in both of the research experiments from June 2016 up to March 2019. This objective will allow us to look for 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 will be developed to instruct producers in the use of chaff carts and direct bale systems to improve weed control and enhance agricultural sustainability. Scientists will participate in seminars and conferences to reach larger audiences. The scientists with teaching appointments involved in the project will include the new knowledge from this project in appropriate courses. We will also contact community college teachers of the region to investigate the possibilities of speaking about this project in some of their classes. This objective will begin in the fall of 2016 and will finish by the end of the project.