Evaluating weed seed kill efficacy and horsepower draw of two impact mills for use in soybean production

Abstract Combine modifications for harvest weed seed control like the Redekop Seed Control Unit (SCU) and the integrated Harrington Seed Destructor (iHSD) have been successfully used to kill problematic weed seeds in small grain production in Australia. These seed impact mills could have a fit in U.S. soybean [ Glycine max (L.) Merr.] production. Testing the seed kill rate of problematic weed species in soybean is important for confirming the efficacy of the mills. Additionally, the mills may be affected by changes in crop yield and harvest residue moisture, which can have an impact on chaff flow rate and chaff moisture, respectively. This research aimed at determining the seed kill percent for problematic weeds and how varying chaff flow rates and chaff moisture content in soybean chaff affect the seed kill rate and horsepower draw of two different impact mills, the Redekop SCU and the iHSD. All testing was conducted using stationary test stands. Chaff flow rate and chaff moisture levels tested ranged from 0.5× to 2× standard combine throughput and 11.7% to 28.6% moisture, respectively. All tested species were killed at >98% by both mills. Increasing chaff flow rate resulted in a decrease in seed kill for all tested species with the iHSD and only common ragweed ( Ambrosia artemisiifolia L.) with the Redekop SCU. Increasing chaff moisture only resulted in a decrease in seed kill for Palmer amaranth ( Amaranthus palmeri S. Watson) with the iHSD. Data evaluating the horsepower needed to power the mills also indicated that chaff flow rate and chaff moisture resulted in a significant increase in horsepower draw. With generally high kill rates (>98%) and the ability to kill weed seeds at >98% in less than ideal harvest conditions (i.e., high-moisture chaff), seed impact mills could be used in soybean production to reduce weed seed inputs into the soil seedbank during harvest.