Crop Competition for Weed Control

Crop Competition for Weed Control in Southern NSW

Project Partners: GRDC, FarmLink, Landmark
Project Code: FLR00008
Project Duration: 2017 - 2018
Project Location: Temora, Southern New South Wales

Project Aim

FarmLink’s Crop Competition for Weed Control in Southern NSW project will provide local validation of research work conducted to demonstrate potential yield increases and improvements in weed control achieved through narrow row spacing, increased seeding rates and/or broadcast seeding. The project will establish a replicated trial at Temora comparing seeding treatments in Canola, Wheat and Barley to capture data on the impact of these approaches to seeding on crop yield and profitability.


The project delivers local validation of row spacing and seeding rate work that has been conducted in other areas around Australia. It is generally recognised that wide row spacing sacrifices yield & increases weed burden due to reduced crop competition (Scott etal, 2013). Scott etal (2013) concluded that achieving maximum yield in wheat requires growers to use the narrowest crop row spacing that is practical. Peter Newman (GRDC update paper) reporting on row spacing and seeding rate trials conducted in WA in 2013, concluded that wheat seeding rate and row spacing is all about maximising crop yield and minimising weed seed set and that “it is more efficient and cost effective to increase crop competition through narrow row spacing in combination with optimal plant density than simply increasing seeding rate for current row spacing”. One possible solution to improve crop competitiveness while maintaining stubble clearance and not requiring new equipment is broadcast sowing. This technique was found to produce satisfactory wheat yields in a low rainfall area of South Australia (Holloway et al. 2000) and to increase yield and reduce weed fecundity, particularly when combined with appropriate seeding rates (Mathews 2002).
This project combines outcomes of previous research work to validate locally the impact of row spacing, seeding rate and seeding method on yield and crop weed competition.

Identified Issues

SNSW farmers adopted wide row spacing as part of their minimum till, stubble retained systems. It is generally recognised that row spacing is a compromise between crop yield, ease of stubble handling, mechanical efficiency and weed control (GRDC, 2011). Scott et al. (Graham Centre Monograph No 3, 2013) quoted a long-term study by Riethmuller (2005) which showed that over time, even with chemical controls and crop sequencing, sustained wide row spacing resulted in increased rye grass populations. Higher seeding rates and more competitive cultivars are also promoted as effective tools for decreasing reliance on herbicides (Condon et al. 2017). Both practices have been shown to reduce weed biomass and weed seed set (Lemerle et al. 2013, Zerner et al. 2016). Despite these findings, crop management for improved weed competition has not been widely adopted by growers in SNSW. This project aims to increase adoption of crop/weed competition strategies through local validation of increased seeding rates and broadcast seeding as management practices to reduce weed effects in canola, wheat and barley.

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