Improve soils with diverse microbes mix

Wendy Taheri addresses the SANTFA conference.
Wendy Taheri addresses the SANTFA conference.

WITH MOST arable country in the world already farmed, better nutrient use efficiency is needed in agriculture to ensure we can feed the nine billion population expected, according to United States microbiologist Wendy Taheri.

Dr Taheri was a popular speaker at the SA No-Till Farming Association conference last week, outlining the importance of microbial diversity in soil management, particularly arbuscular mycorrhizal fungi.

“Microbial diversity makes our ecosystems nutrient use efficient, and our soils need to feature as many AMF species as we can get,” she said.

Dr Taheri said AMF improved soil fertility, soil structure, salinity resistance and plant nutrition efficacy, protected against nematodes and diseases, resulted in earlier flowering, increased biomass, and so on.

“But one species of AMF can’t do this all by themselves,” she said. 

“They need to be part of a multi-AMF species community, alongside other fungi organisms, organic matter, bacteria, nematodes, arthropods and animals for diversity. 

“The more organisms in your soil ecosystem, the more resilient your soil is.”

Dr Taheri said farmers could undertake different management practices to increase soil diversity, such as reducing phosphorous inputs (a deterrent if too high), selecting plant varieties that respond to AMF, and reducing soil disturbance.

“Tilling breaks down the soil structure, creating dust bowls and the consequences are immense, environmentally and socially,” she said. 

“This is mostly avoidable with no-till and cover crops.”

Dr Taheri said covering the soil made a tremendous difference in preserving it.

“Many farmers are already working on a degraded resource, or soils that weren’t meant to grow today’s crop varieties,” she said.

“They are having to rebuild new ecosystems in their soils, and that starts with plant decisions made on the surface.

“Each plant species has its own different microbes underneath, and they cycle nutrients to make them available to plants.

“The more plant diversity, the bigger the microbial diversity below the soils.”

But recent farming practices have reduced plant diversity above ground.

“Agriculture has simplified the environment to one-crop systems,” she said.

This is where cover cropping could become more important, Dr Taheri said.

“Cover crops introduce plant diversity, which then increases microbial diversity,” she said.

“Cover crops also increase soil organic matter, which improves the water-holding capacity of the soil – a 1 per cent increase in soil organic matter can equate to gains of up to 100,000 litres of water retained in your soil.

“And with minimal rainfall in some parts of Australia – you want to capture every bit you can. You don’t want it running off the surface or evaporating quickly because of a lack of cover.

“Plant roots also create channels for the water to enter the soil and because of increased carbon levels, the roots will hold that water longer.

“The end result is a stronger, more resilient ecosystem.”