Narrow-windrow burning (NWB) is a form of harvest weed seed control in which crop residues and weed seeds collected by the combine are concentrated into windrows and subsequently burned. The objectives of this study were to determine how NWB will 1) affect seed survival of Italian ryegrass in wheat and Palmer amaranth in soybean and 2) determine if there is a relationship between NWB heat index (HI; the sum of temperatures above ambient) or effective burn time (EBT; the cumulative number of seconds temperatures exceed 200 C) and the post-NWB seed survival of both species. Average soybean and wheat windrow HI totaled 140,725 ± 14,370 and 66,196 ± 6224 C, and 259 ± 27 and 116 ± 12 seconds of EBT, respectively. Pre-versus post-NWB germinability testing revealed there was an estimated seed kill rate of 79.7 % in Italian ryegrass, and 86.3 % in Palmer amaranth. Non-linear two parameter exponential regressions between seed kill and HI or EBT indicated NWB at a HI of 146,000 C and 277 seconds of EBT potentially kills 99% of Palmer amaranth seed. 76% of soybean windrow burning events resulted in estimated Palmer amaranth seed kill rates greater than 85%. Predicted Italian ryegrass seed kill was greater than 97% in all but two wheat NWB events, therefore relationships were not calculated. These results validate the effectiveness of NWB’s ability to reduce seed survival, improving weed management and combating herbicide resistance.
Harvest weed seed control (HWSC) methods destroy, remove, or concentrate weed seeds collected during harvest. Depending on the method of HWSC, chaff and straw fractions may also be destroyed, removed, or concentrated. Observations at soybean (Glycine max (L.) Merr.) harvest in this study estimated the distribution of aboveground biomass between seed, straw, and chaff fractions and the nutrient composition of straw and chaff. Measurements were combined to predict nutrient consequences of HWSC, which have not been documented. The average harvest index of soybean was 0.57:1. Soybean biomass that enters the combine partitions into 7.25 ± 0.37% chaff, 36.05 ± 1.2% straw, and 56.7 ± 1.2% seed. Chaff and straw residues equal 13.4% and 68.5% of the seed weight, respectively. In a soybean crop yielding 3368 kg ha−1 (50 bu a−1), chaff yields 9.4, 0.8, 5.0, and 0.6 kg ha−1 and straw 31.6, 2.1, 1.1, and 2.0 kg ha−1 of N, P, K, and S, respectively. Using 5-year average fertilizer prices ending in 2021, the cost to replace chaff, straw, and the combination of both residues is USD 1.58, USD 5.88, and USD 7.46, respectively. These results give insight into the nutrient consequences and replacement costs of HWSC.
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