Weeds - Phase 1 - Research Highlights

Summer weeds

What the report is about

This project provided valuable information about water use at different densities of summer weeds and enabled the development and validation of a summer weeds module for APSIM, the Agricultural Production Systems Simulator. The module will be incorporated in Yield Prophet^® so that farmers will have easy access to the information.

Please click here for the full report.

Who is the report targeted at?

This research will help farmers make decisions about the profitability of controlling summer weeds. Further, it will assist with determining the impact of summer weeds during a time of climate change, when it is expected there will be a reduction in winter-spring rainfall and an increase in summer rainfall.

The summer weeds module models soil water loss as a result of weed growth and clearly demonstrates the adverse effect of summer weeds on potential wheat yield. Using southern Mallee meteorological data and running the model over 60 years (1950 to 2009), it was estimated that uncontrolled summer weeds resulted in a loss of 1.0 tonnes a hectare in wheat yield (wheat yields where summer weeds were controlled, 3.8 tonnes a hectare; summer weeds not controlled, 2.8 tonnes a hectare). The expected consequences of a changed climate in north-western Victoria are reduced winter and spring rain and increased summer rain, so controlling summer weeds will only become more important.

Where are the relevant industries located in Australia

Southern Australian cropping regions.

Background

Summer weeds have an adverse effect on farm viability in southern Australian cropping regions. They use water and nutrients that could otherwise be used by ensuing crops. In the future the importance of summer weeds will increase, since climate change scenarios foresee a greater proportion of annual rainfall occurring during summer. At present our understanding of the economics of summer weeds and their management is inadequate. We need to create the tools necessary for quantifying the costs and benefits of summer weed control, both for the current climate and under changed climatic conditions. This will allow the development of a framework for targeted research and extension aimed at mitigating summer weeds' impact on production and farm viability.

The water use of heliotrope and camel melons was monitored during the 2009-10 summer in Victoria's southern Mallee. In November and early December 2009 close to 100 millimetres of rain fell in the region, and weed growth was prolific following the rain. The debate about whether it was worth controlling these weeds was robust. This project assessed summer weeds' impact on the amount of stored soil water and, through modelling, looked at the benefits or otherwise of controlling those weeds.

It was found that summer weeds such as heliotrope, at high density, used 50 millimetres of stored soil water that would otherwise have been available to the following crop.

This project provided valuable information about water use at different densities of summer weeds and enabled the development and validation of a summer weeds module for APSIM, the Agricultural Production Systems sIMulator. The module will be incorporated in Yield Prophet^® so that farmers will have easy access to the information.

The summer weeds module models soil water loss as a result of weed growth and clearly demonstrates the adverse effect of summer weeds on potential wheat yield. Using southern Mallee meteorological data and running the model over 60 years (1950 to 2009), it was estimated that uncontrolled summer weeds resulted in a loss of 1.0 tonnes a hectare in wheat yield (wheat yields where summer weeds were controlled, 3.8 tonnes a hectare; summer weeds not controlled, 2.8 tonnes a hectare). The expected consequences of a changed climate in north-western Victoria are reduced winter and spring rain and increased summer rain, so controlling summer weeds will only become more important.

Aims/objectives

• collecting detailed data on the growth and water and nutrient use of two of the main summer weeds in Victoria's southern Mallee-heliotrope (Heliotropium europaeum) and camel melon (Citrellus lanatus)
• development of parameters and validation of modules for these summer weeds in the farming systems model APSIM, the Agricultural Production Systems sIMulator
• using the summer weeds module in conjunction with both historical meteorological data and down-scaled climate change scenarios to conduct analyses of the impacts of summer weeds on subsequent crops over multiple sites and seasons and under different climate change scenarios.

Methods used

In summary, the methods used for the project were as follows:

• site-located on a sandy clay loam (calcarasol) at JilJil, 32kilometres north of Birchip in Victoria's southern Mallee
• soil water-initial and final gravimetric soil water measured in November 2009 and March 2010; weekly neutron probe readings taken over the summer of 2009-10; and calibration of the neutron probe for the specific soil type, including bulk density and soil DUL (drained upper limit) and CLL (crop lower limit) measurement
• weed growth-summer weeds ( heliotrope and camel melon) monitored; plots with different densities of each of these weeds established, with four densities for each weed (heliotrope at 0, 10, 20 and 55 plants per square metre and melon at 0, 1, 2 and 4 plants per square metre); dry matter production and other plant growth characteristics of these weeds assessed until plant senescence
• model requirements-soil classification for model initialisation; records of daily summer rainfall during trial; summer weed plant water use (from soil water extraction)
• model outcomes-operational for summer soil water use; model outcome of water use in different years; model impact of summer weeds' water use on subsequent cereal crop production; model impact of shifts in rainfall patterns, from dominant winter rain to increased summer rain.

Results/key findings

The summer weeds module models soil water loss as a result of weed growth and clearly demonstrates the adverse effect of summer weeds on potential wheat yield. Over 60 years (1950 to 2009) the model estimated uncontrolled summer weeds resulted in a loss of 1 tonne a hectares in wheat yield (wheat yields where summer weeds were controlled, 3.8 tonnes a hectare; summer weeds not controlled, 2.8 tonnes a hectare). The return on investment (the cost of herbicide plus application compared with the return in extra grain yield) was between one in five and one in nine depending on the price of wheat. This clearly demonstrates the importance of early and effective summer weed control.

The model will be further tested in the Grains Research and Development Corporation water use efficiency project and in the weed field trials carried out by the Birchip Cropping Group during the summer of 2010-11.

Implications for relevant stakeholders

This project clearly demonstrates the importance of farmers controlling summer weeds. In the summer of 2009-10 summer weeds such as heliotrope used 50 millimetres of soil water that would otherwise have been available to the ensuing crop. In dry-land crop production regions such as the Victorian Mallee this is equivalent to potential additional wheat production of 1 tonne a hectare.

The summer weeds module developed for APSIM makes a significant contribution to our ability to model soil water change over summer resulting from uncontrolled summer weeds and what impact this has on modelled yields over time. In addition, taking into account a changing climate, the summer weeds module demonstrates the increased importance of controlling weeds during summer.