Regenerative Rebuild Part 2: Soil remediation

In the second part of Regenerative Rebuild (Part 1 here), we look at how orchardists and horticulturalists might work with regenerative principles to get back on their feet, using advice from regenerative consultants Phil Schofield and Phyllis Tichinin.

For the next months and years at least, growers and pastoral farmers have the formidable job of figuring out what do to with the hundreds of thousands of tonnes of silt and debris that have been deposited on their lands.

This issue has hit the headlines recently, as the sheer scale of the job rubs up against economic imperatives. So, what would a regenerative grower do, or how might they approach this problem differently?

Schofield says that by far the easiest, quickest and most cost-effective way is to bring the silt back to life through revegetation.

“In most cases there is evidence that this is starting to happen, with earthworm activity. You need to do a few things. You need to reassure yourselves it’s not contaminated, and that is probably established just by looking upstream. Where are you, what’s around you and what would likely be the source of this sediment.

“You also need to understand what size it is – whether it’s silt, sand or clay – and then it’s about establishing a diverse mix of plants to start the soil rebuilding process. As the sediment dries in autumn you can get a mix of grasses and legumes and herbs established to grow through the winter.

“If you want to get life back into that soil, the best way to do that is with plants. You can do that now in winter, and then donate those crops back to the soil. If you were in pasture before the storm, you could then go back to pasture after growing a cover crop,” he says.

Tichinin seconds this important principle, and says the more you use different families of plant seeds, the more rapidly diverse species of microbes will grow and quickly create healthy fertile soil. 

“This means sowing some unusual seeds: from families like the daisy, amaranth, peas, beans, polygonacea, forbs and grasses other than rye. It doesn’t mean growing two variety of rye and three varieties of clover, because that’s only two families of plants. Seeds from five families of plants is considered a minimum for good results.”

However, she cautions growers against using mostly brassicas because they do not feed the highly beneficial mycorrhizal fungi, which are the foundation of growing living carbon in the soil.

“Mustard would be one of the worst things you could plant as it would be starving the very thing you want functioning. Lupin, perennial grasses, flower seeds, oats, buckwheat and lucerne, are probably a good combination. Even if it’s a small amount of each family of seed, it’s important for establishing diversity in the soil and seed bank. Use inexpensive seeds and older varieties.

“Let the weeds come away as well, they are important shock troops, the initial responders that feed the microbes and start to pull that silt, sand and clay particles together with the glues and gums that fungi and other bacteria create.”

Farmers probably need less volume of seed than the seed companies are suggesting, but much more diversity, she stresses.

“I would also suggest that they forgo any fungicide or seed treatment, all of which are poisonous to soil microbes,” she says.

At the very least, Tichinin says, test first and see if it’s really a problem to begin with. Or, try remediation through biological processes in the first instance with diverse cover crops and ideally grazing livestock.

“Why waste your money on what might only be a perceived problem and not an actual problem?”

Contaminated silt

If a sediment is contaminated, it can be remediated biologically, Schofield says.

“I’m aware of other areas where large stockpiles of contaminated soil and sediment have been biologically remediated. It’s a common practice globally and increasingly used.”

Fungi has been used overseas in many different situations to process hydrocarbons and to a certain point, heavy metals (it’s not possible to break these down into completely harmless minerals), says Tichinin.

“However, through fungi and the creation of humus we can achieve bio-sequestration. In healthy soils, those toxins that aren’t able to break down any further can be biologically encapsulated, which prevents them from being loose or absorbable by plants and animals. So, there are ways of reasonably inexpensively remediating this through natural processes,” she says.

What about all the wood?

And what about all that wood debris? The Regional Council has said wood debris will probably be chipped and stored, until it can be burned safely. But Tichinin says another approach would be to use the debris to build hugelkulture beds on orchards and paddocks.

“We need more stop banks, so we could be creating them, in part with the debris. That approach could be used to reestablish planting rows in orchards. It may take two or three years but if you create a big long mound of a mixture of the silt and soil, trunks, branches, wood waste and the chips and inoculate it with mostly fungal microbes and plant over the top it it, within a couple of years you can develop rich, elevated orchard rows to plant into. Burning it is just wasting more carbon into the atmosphere.”

Along with hugelkulture, chipped wood debris could be used as mulch, reincorporating it into the soil to get some productive value out of it. Wood chips make an excellent mulch, she says.

And as always, the regenerative clarion call – use diversity. Use whatever wood you’ve got on your property. Schofield says that poplars and willow – white woods – are particularly good for making lively compost.

Public interest journalism funded by New Zealand on Air.