Good Stubble or Bad Stubble Loads

Background

Stubble retained systems has began to become common practice throughout the central western area. This has lead to the focus of current research being directed towards maintaining the profitability and environmental sustainability of retained stubble systems. The major agronomic drivers for the adoption of stubble retained farming systems has been minimising the risk of soil erosion as well as maintaining the in season benefits of soil moisture retention.

Take Home Messages

• The CWFS and CSIRO site trials have suggested that stubble loads greater than 3 t/ha can begin to limit yields.
• “No till with no stubble is no good” On hard setting red brown soil types. The issue is that the annual incorporation of stubble just prior to sowing by either cultivation or burning removal will result in the loss of the long term benefits of retaining stubble.
• “If you don’t measure it you cant measure it” By taking field measurements of your stubble loads you have just taken the first step in managing the impacts of your stubble loads.
• The options to manage a stubble load over 3 t/ha should be considered carefully in order to tie in other agronomic benefits of removing the stubble load.

In a GRDC update paper by James Hunt demonstrated that the benefits of stubble retention are achieved at stubble loads between 2-3t/ha. This leads us to believe that cereal stubble above 2-3t/ha past sowing is unlikely to provide any yield benefits and in favorable seasons can reduce yield. The issue is how do you go about managing these high stubble loads without placing your farm at risk of erosion and soil moisture loss.

Figure sourced from Good Stubble Bad Stubble

The above graph shows the relationship between growing season rainfall and the yield difference between stubble retained direct drill treatments. The graph shows that as the growing season rainfall increases the benefits of a 2-3 tonne stubble load diminish and even begin to negatively impact on crop yields.

Managing stubble loads greater than 3t/ha

There are several options when it comes to reducing stubble loads between harvest and sowing. It is important to make the decision based on interactive factors such as the control of weed seeds etc.

1. 1. At harvest with the header.

1. 1. Left undisturbed during the fallow, the do nothing option.

1. 1. Cultivated into the soil during the fallow.

1. 1. Mechanically managed but retained on the surface during the fallow.

1. 1. Burnt

1. 1. Removed e.g. bailed.

1. Grazed during the fallow.

An important point to make is that stubble management shouldn’t be placed ahead of fallow management for example the control of summer fallow weeds.

In the CWFS district it appears that majority of the benefits of stubble retention are obtained  by retaining 3t/ha and any more can risk reducing yields, particularly in favorable seasons. Monitoring your stubble loads is the first step when it comes to making the decision whether to reduce the stubble load. So remember you cant manage what you don’t measure.