Buying a spring – with summer weed control
‘Buying a spring’ – the water and nitrogen cost of poor fallow weed control
Colin McMaster (NSW DPI), Neroli Graham (NSW DPI), John Kirkegaard (CSIRO), James Hunt (CSIRO), Ian Menz (NSW DPI)
Abstract
Research in southern NSW demonstrated that 50% of yield potential can be attributed to summer rainfall and summer fallow management as a result of increased stored water (increased by 49 mm) and nitrogen (N) (increased by 49 kgN/ha).
This paper reports experiments conducted near Forbes in central NSW (2011 & 2012) to further evaluate the impact of summer weed control on subsequent crop yield, to investigate interactions with other macro-nutrients (P, K and S) and assess the profitability of replacing lost N (via summer weed uptake) with N fertiliser.
Controlling summer weeds increased canola grain yield by 1.0 t/ ha due to increased stored water (85 mm PAW) and mineral N (69 kgN/ha) at sowing. For every 1mm of stored water stored through summer weed control, soil mineral N increased by 0.6 kgN/ha. Summer weeds had no significant impact on topsoil P and K levels, or S to a depth of 90cm.
Every $/ha invested in fallow herbicides returned $8/ha. Despite poor topdressing conditions, profitability of applying N fertiliser improved from $1 return on every $1 invested when weeds were not controlled to $3 return on every $1 invested in the complete weed control treatment. The study demonstrates the value of strict summer weed control to improve productivity and resource-use efficiency in southern cropping systems.
© 2015 “Building Productive, Diverse and Sustainable Landscapes”
Proceedings of the 17th ASA Conference, 20 – 24 September 2015, Hobart, Australia.
Web site www.agronomy2015.com.au
