Stubble and its impact on temperature in chickpea crops

Take home messages

• Chickpea sown into flattened residue had lower (av. 1.00C) minimum temperatures compared to standing residue
• Chickpea sown into flattened residue had higher (av. 3.40C) maximum temperatures compared to standing residue
• Stubble thresholds are unknown at this stage

Introduction

Stubble affects soil physical properties such as temperature and moisture. The effect on temperature is due to landscape features such as whether a paddock was on top of a hill, on a hill slope or at the lower end of a slope because cold air (due to its higher density) tends to flow downhill and settle in the lower parts of the landscape, leading to colder pockets where temperatures decline the most.

Stubble cover also affects air and soil temperature. During the day the stubble reflects radiation due to its 'albedo'. A bare, darker soil absorbs more solar radiation than a stubble-covered soil and warms up more readily. The stubble also acts as insulation - it contains a lot of air which is a poor conductor of heat.

Finally, the stubble affects the moisture content of the soil. It takes more heat to warm up moist, stubble covered soil than dry, bare soil. This causes soil temperature of a bare soil to be higher than stubble covered soil during the day (especially in the afternoon). At night, however, the bare soil loses more heat than stubble covered soil due to the lack of insulation (the air-filled mulch being a poorer heat conductor). This is especially noticeable when skies are clear. The air above the bare soil is therefore warmer during the night than the stubble covered surface.

This can affect canopy temperature profiles in crops.

What we did?

PBA HatTrick was sown at 30 plants/m² into paired 0.50 m rows with a skip row configuration leaving a gap of 1.0 m between skip rows.

Tiny tag™ temperature sensors were placed in mini Stevenson screens within chickpea experimental plots to measure temporal changes in temperature at ground level. Temperature sensors were placed between 1.0 m wide rows in;

1. plots sown into standing stubble with bare soil between chickpea rows
2. plots sown into flattened stubble with surface stubble between chickpea rows

The sensors recorded temperature every 15 minutes and were left in the plots right thru to harvest in mid-December.

What we found

Chickpeas were sown into 5.84 t/ha of wheat stubble, either standing or flattened.

Standing stubble plots with bare soil between rows:

• had minimum temperatures 1°C warmer at the base of the canopy than surface-stubble plots during vegetative period
• had maximum temperatures -3.4°C cooler at the base of the canopy than surface-stubble plots during flowering and grain fill period
• recorded 5 days with maximum temperatures > 350C compared to 27 days of maximum temperatures > 350C where stubble was flattened.

Plant components for the stubble treatments are shown in table 1. Plants sown into bare soil between standing wheat rows had higher grain yields which were achieved thru more pods being set and more seeds being produced per square metre.

Table 1. Effect of stubble treatment on selected plant components.

Conclusions

• Flattened surface residue led to lower minimum temperatures in crop than standing residue
• Flattened residue had higher maximum temperatures during flowering and grain fill than standing residue;
• Flattening and spreading residue can increase crown rot infection in the following wheat crop
• Keep wheat stubble standing in defined rows and sow chickpeas between wheat rows

Acknowledgements

The research undertaken as part of project DAN00171 is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC. The authors would like to thank them for their continued support. Thanks to Mat Grinter and Michael Nowland for their technical assistance in the trial program.

Contact details

Dr Andrew Verrell
NSW Department of Primary Industries
Ph: 0429 422 150
Email: andrew.verrell@dpi.nsw.gov.au