Summer fallow weed management

Summer fallow management manual

A reference manual for grain growers and advisers in the southern and western grains regions of Australia

In a winter cropping system, the return on investment from managing weeds in summer fallow (i.e. the period between crops) is high. Economic benefits flow from both extra amounts of high value water and nitrogen, crop establishment benefits and reduced issues with weed vectored disease and insect pests.

Stopping weed growth in the fallow can lead to yield increases in the following crop via several pathways. These include:

  • Increased plant available water
  • A wider and more reliable sowing window
  • Higher levels of plant available N
  • Reduced levels of weed vectored diseases and nematodes
  • Reduced levels of rust inoculum via interruption of the green bridge
  • Reduced levels of diseases vectored by aphids that build in numbers on summer weeds, and
  • Reduced weed physical impacts on crop establishment.

How farming country is managed in the months or years before sowing can be more important in lifting water use efficiency (WUE) than in-crop management. Of particularly high impact are strategies that increase soil capture and storage of fallow rainfall to improve crop reliability and yield. 

Practices such as controlled traffic farming and long term no-till seek to change the very nature of soil structure to improve infiltration rates and improve plant access to stored water by removal of compaction zones. 

Shorter term management decisions can have an equal or even greater impact on how much plant available water (PAW) is stored at sowing. These include decisions such as crop sequence/rotation that dictate the length of the fallow and amount of stubble cover, how effectively fallow weeds are managed, stubble management and decisions to till/not to till at critical times. 

While many factors influence how much plant available water is stored in a fallow period, good weed management consistently has the greatest impact.

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GRDC Project Code ICN00012

Region South, West