The concept of inoculating damaged or compacted soils to kickstart their biological processes is not a new one. Re-inserting specific soil microbes, or inoculating them with bacterial communities, has proven to have varied success. That success often depends on the level of soil degradation and denseness and often sees microbe populations surge but later decline, depending upon their ability to establish.
“Basically if you can get air into the soil, you will have biological growth, and inoculants can sometimes die off quite quickly if the conditions do not line up early on in establishment,” AgResearch senior scientist Seth Laurenson says.
“The AgResearch work was based on the theory that if you can provide some sort of refugia for soil microbes you are introducing so they can build up their numbers, then expand beyond that refugia, you could enjoy some success.”
The AgResearch team took a cross-discipline approach to addressing the challenge, combining the skills of an engineer, biologists and a soil scientist to create a 3D printed habitat for the valuable microbes.
The pointed, divot-shaped structure houses interior accommodation that amounts to a five-star suite for microbes. It offers them a carefully designed “staired” interior that can hold water well, with maximum surface area, and enable good air circulation, all contained within the tiny rhiome structure, shaped to also be easily pushed into the soil medium.
Called a rhiome (home for rhizobia), the trial habitat also contains a yeast extract and sugar food to ensure bacteria have a good energy source to fuel their rapid multiplication.
“In developing it as a proof of concept we ended up using polylactic acid as a key compound to try and make it more biodegradable, which it is to a point, but future work would look at something that is wholly biodegradable in the soil over time,” Laurenson said.
The team used a compacted heavy soil akin to what you might find in a dairy milking platform that has been stocked over a dry winter period. The researchers inserted the inoculated rhiomes populated with the common pastoral micro-organism rhizobium.
They found the use of the rhiome significantly increased the survivability of the microbes in the compacted soil, to a level similar to what rhizomes in non-compacted soil experienced, and was particularly effective when the rhiome was manufactured from a yeast and sugar material.
“We were quite taken with just how effective it has proven to be, and where the application could be in the future,” he said. This could include the likes of regenerative agricultural application, where farmers may be seeking a “no till” approach, but still need some means of keeping soils’ microbial action high, despite not aerating it with tillage.
Laurenson said the rhiome’s design has proven to be a good cross-discipline exercise and one that has created a prototype product that positions the project well for its next stage of field trial