Improving nodulation by understanding effects of fertiliser and soil type survival of rhizobia

On average, legume crops fix about 100 kg N per hectare, which equates to $4 billion annually in Australia.

Inoculation of legume crops with rhizobia is crucial for nodule formation and N fixation. Rhizobia are applied to the legume seed as live organisms and are sensitive to soil conditions such as pH, heavy metals and salinity. Any declines in rhizobia numbers can result in inoculation failure and a nitrogen-deficient crop.

Growers need to provide early nutrients to the crop through fertilisers, which they apply when sowing the inoculated seed. Preliminary laboratory results however have shown that some types of fertiliser are toxic to rhizobia. Fertiliser application at sowing can cause changes in pH, salt concentration and expose rhizobia to toxic trace elements, such as zinc. 

Different soil types can also play a role in the behaviour of fertilisers, and in some soils the impact of fertiliser on rhizobial survival and legume nodulation are more severe than in other soils. 

The effect of fertilisers that growers use at sowing, and the interacting effect of soil type on rhizobium survival and nodulation is important to improve N fixation in south Australian soils.