Fixed on nitrogen

September 13, 2017

South Australian senior research scientist Ross Ballard talked about strategies to improve N2-fixation by sub-clover and lucerne.

Sub-optimal nitrogen fixation is easily overlooked, according to South Australian senior research scientist Ross Ballard.

Mr Ballard said to improve contributions of nitrogen from fixation, good legume density was important.

‘‘Good legume density, resulting from choosing cultivators that are adapted to the soil type and rainfall and employing pasture management practices that favour legume growth, should be first considered to improve contributions of nitrogen fixation,’’ he said.

Mr Ballard said clovers and lucerne had been reliant on inoculant strains for a long time but after years of cultivation this was changing.

‘‘Australia lacked productive forage legumes in its indigenous flora, and so clovers and medics (including lucerne) and their rhizobia have been introduced since European settlement,’’ he said.

‘‘Hence the success of sub-clover and lucerne has been reliant on the provision and use of suitable inoculant strains.

‘‘After many decades of clover, medic and lucerne cultivation, the situation is now very different.

‘‘The rhizobia that nodulate sub-clover and lucerne are now probably only absent in reasonably undisturbed or natural landscapes or occur at numbers below what is needed for prompt nodulation in very acidic soils,’’ Mr Ballard said.

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