Exploiting Waste Heat from Combine Harvesters to Damage Harvested Weed Seeds and Reduce Weed Infestation

Abstract

Weeds are mainly controlled with herbicides in intensive crop production, but this has resulted in increasing problems with herbicide-resistant weeds and public concerns about the unwanted side-effects of herbicide use. Therefore, there is a need for new alternative methods to reduce weed problems. One way to reduce weed infestation could be to collect or kill weed seeds produced in the growing season. Crop and weeds are harvested simultaneously with the combine harvester, but most of the weed seeds are returned with the chaff to the field creating new problems in future growing seasons. During the harvesting process, the harvester produces heat. Under normal harvest conditions, the exhaust gas temperature measured directly behind the turbocharger of the engine of a combine harvester may reach between 400 • C and 480 • C depending of the size of the engine. These high temperatures indicate that there is a potential for developing a system which perhaps could be utilized to kill or damage the weeds seeds. We investigate how much heat is needed to damage weed seeds significantly and focuses on the germination patterns over time in response to these treatments. We investigated if heat treatment of weed seeds could kill the seeds or reduce seed vigour or kill the seeds before they are returned to the field. The aim is to avoid harvested viable weed seeds being added to the soil seed bank. During the threshing and cleaning process in the combine harvester, most weed seeds and chaff are separated from the crop grains. After this separation, we imagine that the weed seeds could be exposed to a high temperature before they are returned to the field. Seeds of nine common weed species were treated with temperatures of 50 • C, 100 • C, 150 • C, 200 • C, and 250 • C for 0, 2, 5, 10, and 20 s, respectively. Afterwards, the seeds were germinated for fourteen days. Seeds were differently affected by the heat treatments. We found that 50 • C and 100 • C was insufficient to harm the seeds of all species significantly at all durations. Heating with a temperature of 50 • C and 100 • C showed a slight tendency to break the dormancy of Alopecurus myosuroides Huds. and Papaver rhoeas L., but the results were not statistically significant. Seeds treated with 150 • C gave varying results depending on the duration and the weed species. The germination of A. myosuroides was significantly repressed when seeds were exposed to 250 • C for 5 s. Most species were significantly damaged when they were exposed to 250 • C for more than 10 s. Our results showed that there is a potential to explore how the waste heat energy produced by combine harvesters can be exploited to either kill or reduce the vigour of weed seeds before they are returned to the field with the chaff.

Seed production and retention at maturity of blackgrass (Alopecurus myosuroides) and silky windgrass (Apera spica-venti) at wheat harvest

“…At the moment, a new system using the heat source from the exhaust gas of the combine harvester to kill weed seeds is under consideration (Jakobsen et al 2019). The intention is to bring the chaff fraction and contained weed seeds into contact with hot exhaust gases to kill the weed seeds before returning this material to the field (Andreasen et al 2018;Glasner et al 2018;Jakobsen et al 2019). The critical question is how much of the total weed seed production in a growing season is retained on the weed plants at crop harvest.…”

Harvest Weed Seed Control: Seed Production and Retention of Fallopia convolvulus, Sinapis arvensis, Spergula arvensis and Stellaria media at Spring Oat Maturity

“…We have now shown that a large proportion of seeds produced during the growing season of common weed species potentially can be collected and removed or destroyed [43][44][45] by a combine harvester at crop harvest. The next step will be to test how large a fraction of this potential a combine harvest actually collects, as it depends on several factors such as harvest height and the number of seeds dropping to the soil surface under the harvesting process.…”

Killing Weed Seeds with Exhaust Gas from a Combine Harvester

“…The experiments were repeated later (series 2), but then the temperature could not be lowered to less than 85 • C because the ambient temperature had increased by 13 • C. We prevented temperature variation by keeping the throttle at the position that resulted in the desired temperatures, and we monitored the exhaust gas temperature with a thermometer continuously during the experiments (Table 2). Considering both the time it takes seeds to pass through the combine harvester and the risk of fire at high exhaust gas temperatures, we chose three temperatures for the heat treatment of the seeds based on earlier studies [23]. Seeds in the round pincer filter (Figure 1) were exposed to three temperatures (75 • C or 85 • C, 110 • C, and 140 • C) and three durations (2, 4, and 6 s).…”