"You can't separate the quality of our health, from the quality of our food, from the quality of our soil."

With these words, Kay Baxter - one of New Zealand's best-known organic gardening pioneers - sums up her current quest to regenerate our health and the Earth's health at the same time.

Kay and the team at Koanga Institute, based in remote northern Hawkes Bay, are on a mission to teach people how to get the nutrition that allows the human body to thrive. And so they have become evangelists of healthy soil.

The nutritional status of many farm soils is frightening. "We know that we've lost 80% of the minerals in American soils since 1920, and New Zealand is following the same path," Baxter says. The dilemma is simple: It takes 84 different minerals to grow a healthy plant. But for generations, many farmers have harvested all of those minerals out of the soil, and only put back three or four minerals as fertiliser.

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As a result, our soils have become the foundation for a societal health crisis. If minerals aren't in the soil, they won't get into food crops - and if the minerals aren't in food crops, they won't get into our bodies.

"Every disease is linked to nutrition," Baxter says. "It's old news that our doctors don't want to know about, that they aren't trained to know about."

It's a radical-sounding statement, but backed up by decades of research. The connection between diet and diseases has been affirmed by the World Health Organisation (WHO); the agency's report Diet, Nutrition and the Prevention of Chronic Diseases documents many of the links. The WHO also has cautioned that while people in poorer countries are most at risk of malnutrition, people in developed countries suffer from high rates of "type B malnutrition" - that is, we have enough food to fill our bellies, but it doesn't have the right nutrients in it.

The above facts, taken together, partly explain why even people in wealthy countries now experience chronic health complaints not seen in previous generations. We are literally starving in the midst of affluence.

Although it might be tempting to reach for a bottle of multivitamins to fill the void, pills are not the answer, Kay Baxter suggests. Many supplements contain minerals in forms not easily assimilated by the human body.

Baxter and the Koanga team are currently aiming for the roots of the problem - literally. Koanga is best known for its work saving heritage seeds, and this continues to be the core business; the Institute sells hundreds of seed varieties, many of them not available anywhere else. However, they are also now delving into soil-based nutritional education. The team believe that simply buying sacks of fertiliser with all the right minerals is not a long-term solution; instead they are trying to do it with as many local materials as possible. "We're really focused on re-learning how to make good compost," Baxter says.

At their Urban Garden Research Project, the Koanga team are building a model for the healthy, self-nourishing family of the future. The setting is rural, but the garden is designed for compressed urban settings, jammed with beds of vegetables and grains, fruit trees and vines trained into small spaces, chickens and rabbits, and feed sources for the animals. The goal, in Baxter's words, is "to see how much of a family's nutrition you can get out of 200 square metres." She's calculated exactly what a family needs to eat in a year to get all the required vitamins and minerals, and Koanga are aiming to coax all that nourishment from this small plot of land.

They don't know yet exactly how much food the space can grow, as the fruit trees and a fish production system haven't started producing; but it's looking possible to fully sustain a family of four. Already, from the eggs and veges alone, a calculated $800/month worth of organically grown, nutrient-dense food is coming out of the garden.

People from across New Zealand are joining the Urban Garden project for a ten-week internship ¬- enough time to learn many of the necessary skills and take them home to their own communities.

Impressive results are still possible on smaller, simpler sites. Baxter has calculated that a 40-square-metre home garden can produce over $2500 worth of veges in a year. She lays out her methods in a Beginner Garden Booklet, available on Koanga's website.

The project also draws nutritional inspiration from indigenous cultures. Baxter cites the work of Weston A Price, an early 20th century dentist who travelled the world studying traditional diets. All over the world, despite vast differences in environment, he found that indigenous peoples had developed remarkably similar approaches to nutrition.

For example, cultures worldwide have designated sacred foods rich in vitamin A. For Maori, this traditionally was fish heads or fish oil; in old Ireland, it was butter; in other lands it was animal livers. Vitamin A is essential for health; without it, we fail to absorb other vitamins and minerals. Indigenous peoples prizing such food sources did not officially "know" this fact - and yet somehow they did know it.

Perhaps the greatest vindication of Koanga's methods is the vitality in the people who live and eat there. "We have a lot of people coming through here - a lot of staff, a lot of students," Baxter says. "There's a profound shift in almost everybody." She lists some of the most common health improvements: "brain fog lifts, healthy teeth, achy joints recover... Our bodies are made to heal themselves. But they can't do it if you don't give them the nutrition they need."

Compost of the Gods

Kay Baxter and the Koanga crew have been getting creative with their compost-making. Some of Baxter's top tips for nutrient-dense compost (and thus, nutrient-dense food) include:

• Most soils are deficient in calcium, so get some into your compost. Baxter makes bone broth, saves spent bones in a barrel, then turns the bones into biochar which goes into the compost heap. (Burning the bones in a fire and adding the ashes to the compost also works.)

• Growing specific crops for the compost heap can get key minerals into the compost. For example, oats accumulate otherwise unavailable phosphorus from the soil; putting the plants into the compost heap means that phosphorus will be available to future generations of plants. Comfrey, lupins and alfalfa, selected for their nutritional profiles, also go into Koanga's compost.

• Seaweeds are an excellent source of many micronutrients; get them into your pile.

• For city-dwellers, the fallen leaves of deciduous trees such as oak and maple are great mineral sources.

• Combat iodine deficiency by putting iodine into the compost. Baxter gets half a cup of animal iodine from the vet shop, mixes it with ten litres of water, and pours it into the pile.

• The compost needs to be aerobic, but you don't have to turn it ("I don't like making work for myself," Baxter quips.) Just get your ratios of materials right. Baxter uses three parts "mature material," half a part of "immature material" (i.e. fresh green matter), and a quarter part of soil to hold onto nutrients released from the decomposing organic matter.

For more detail, Koanga's Art of Composting booklet will be available on their website soon.

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