Assessing the Agronomic Consequences of Delayed Removal of Parthenium from Forage Sorghum (Sorghum bicolor)

Parthenium (Parthenium hysterophorus L.) is a serious invasive weed of sorghum and other crops in Pakistan. This two-year field study was conducted to investigate the impact of different weed-crop competition durations (4, 5, 6, 7, 8 weeks after emergance (WAE) and full season competition on parthenium growth, nutrient uptake, forage sorghum yield and quality traits. The highest parthenium dry biomass (35.18 and 44.23 g m(-2)) and nitrogen, phosphorus, and patassium uptake was recorded under its competition during the full crop growing season. Forage sorghum quality and yield were affected by increasing the duration of competition with parthenium weed. The plant height, fresh and dry forage yield, leaf area plant(-1), leaf to stem ratio, total ash contents and crude protein contents of forage sorgham were higher in weed free control, and started to decrease with weed competition duration of 5 WAE or more, and decrease was more at higher weed competition durations. The contents of acid detergent fiber (ADF) and neutral detergent fiber (NDF) of forage increased as competition period increased which showed forage quality deterioration. The period of 5 weeks competition seemed as critical period of competition beyond which parthenium caused more than 5% fresh forage yield losses. In conclusion, parthenium should be controlled within 1st five weeks after the emergence of crop to avoid quality and yield losses of forage sorghum. (C) 2020 Friends Science Publishers