Summer weeds reduce moisture and nitrogen—Forbes 2011 and 2012

Abstract

Key findings In 2011, 58% of canola (Hyola® 575CL) grain yield was attributed to increased stored soil moisture and nitrogen retained from a weed-free fallow. • Controlling summer weeds increased: »» canola grain yield by 0.83 t/ha where full weed control was implemented »» plant available water (PAW) at sowing by 86 mm and 50 mm in 2011 and 2012, respectively »» mineral nitrogen by 69 and 45 kg N/ha in 2011 and 2012, respectively. • For every 1 mm of moisture lost through summer weed growth, mineral nitrogen levels were reduced by approximately 0.56 kg N/ha. • Summer weeds used soil moisture to a depth of at least 1.2 m. • Every dollar invested in controlling summer weeds returned up to $7.20/ha. • Where full fallow weed control was implemented, the return on investment (ROI) was up to 720%.