Decision support systems (DSSs) have been developed to assist producers and consultants with weed management decisions. WeedSOFT is a DSS currently used in several states in the north-central region of the United States. Accurate estimates of crop yield loss due to weed interference are required for cost-effective weed management recommendations. WeedSOFT uses competitive indices (CIs) to predict crop yield loss under multiple weed species, weed densities, and relative times of weed emergence. Performance of several WeedSOFT versions to predict soybean yield loss from weed competition was evaluated using CI values in WeedSOFT version 9.0 compared to new CI values calculated from weed dry matter, weed volume, and soybean yield loss in two soybean row spacings (19 and 76 cm) and two relative weed emergence times (at soybean emergence and first trifoliate leaf stage). Overall, new CI values improved predictions of soybean yield loss by as high as 63%. It was especially true with using new CI values based on yield loss compared to those based on weed dry matter or weed volume. However, there were inconsistencies in predictions for most weed species, suggesting that additional modifications are needed to further improve soybean yield loss predictions.
Nomenclature: Soybean, Glycine max (L.) Merr.
Additional index words: Crop modeling, competition, decision support systems, simulation, Abutilon theophrasti, Amaranthus retroflexus, Amaranthus rudis, Ambrosia trifida, Echinochloa crus-galli, Helianthus annuus, Setaria faberi, Setaria glauca, Xanthium strumarium, ABUTH, AMARE, AMATA, AMBTR, ECHCG, HELAN, SETFA, SETLU, XANST.
Abbreviations: AE, average error; ACI, adjusted competitive index; CI, competitive index; DM, WeedSOFT version based on weed dry matter; DSS, decision support systems; RCBD, randomized complete block design; TCL, total competitive load; TDM, total dry matter; V1, soybean first trifoliate leaf stage; VE, soybean emergence; VP, soybean planting; VOL, WeedSOFT version based on weed volume; WS, WeedSOFT version 9.0; YL, WeedSOFT version based on yield loss.