Yield and yield components of soybean [Glycine max (L.) Merr.] are influenced by the timing of broadcast flaming

Weed management is a major constraint in organic crop production. Propane flaming could be an additional tool for weed control in organic soybean production. The objective of this study was to investigate the response of soybean to broadcast flaming as influenced by propane dose and crop growth stage. We initiated a 2-year field study at the Haskell Agricultural Laboratory of the University of Nebraska, Concord, NE using five propane doses applied at four growth stages of VC (unfolded cotyledons), VU (fully unrolled unifoliate leaves), V2 (second trifoliate stage) and V5 (fifth trifoliate stage). The propane doses tested were 0, 13, 24,44 and 85 kg ha(-1). Flaming treatments were applied utilizing a custom-built research flamer mounted on the back of a four-wheeler driven at a constant speed of 6.4 km h(-1). The response of soybean to propane flaming was described by using log-logistic models on the basis of visual ratings of crop injury, yield components (plants m(-2), branches plant(-1), pods plant(-1), seeds pod(-1) and 100-seed weight) and grain yield. In general, soybean at VC stage was the most tolerant whereas VU stage was the most susceptible to broadcast flaming resulting in the highest visual crop injury, and the largest loss of yield and its components. The maximum yield reductions with the highest propane dose were 19%, 96%, 54% and 30% for VC, VU, V2 and V5 stages, respectively. An arbitrarily assigned 5% yield reduction was evident with 55, 13, 21 and 47 kg ha(-1) propane for VC, VU, V2 and V5 growth stages, respectively, suggesting that soybean flamed at VC stage can tolerate higher dose of propane for the same yield reduction compared to other growth stages. It appears that flaming has a potential to be used effectively in organic soybean production when conducted properly at VC stage