Yield and Quality of Silage Corn as Altered by Johnsongrass Infestation

Abstract

Abstract Dairy and beef producers in the southern piedmont region of the USA with limited land often grow corn ( Zea mays L.), after corn, for silage even though stands gradually become infested with johnsongrass [ Sorghum halepense (L.) Per.]. The objective of this study was to quantify the influence of johnsongrass infestation on the yield and quality of corn grown for silage. Seven field trials were conducted over a 6‐yr period in the piedmont region of North Carolina on clayey, kaolinitic, thermic, Typic Hapludult soils. Corn was planted each year into johnsongrass‐infested sites. Herbicides were used to produce johnsongrass‐free plots and plots where johnsongrass was the only weed present. Additionally, to assess the influence of johnsongrass infestation level on the subsequent silage quality, physical mixtures of corn and johnsongrass forage were made which represented an infestation range from 0 to 100% by weight. In five of seven trials, corn forage yield was significantly increased with johnsongrass control. Where johnsongrass was not controlled, corn plant population was reduced by 13% and silage quality, estimated by in vitro dry matter disappearance (IVDMD), was reduced by 8 to 21%. Silage IVDMD decreased linearly 2.37 g kg −1 ( r 2 = 0.95, P < 0.001) for each percentage unit increase in johnsongrass infestation by weight.