“An olive orchard cultivated in a conventional manner is a bloody wound in nature,” declares Johannes Eisenbach as he drives – fast – south along the gleaming new Greek motorways towards Kalamata. The olives are harvested, the branches are burned, and all these nutritional elements leave the olive grove and never return.

Eisenbach is an ebullient German with a Bluetooth receiver in his ear, constantly switching between Greek, German and English as he takes calls from big German supermarkets including Lidl. He runs the Organic Marketing & Export Network, a group of 800 Greek and Cypriot organic farmers who sell to northern Europe. He’s also the accidental inventor of a new kind of compost that could kick-start vegan farming.

It is dawning on many vegans that although they eschew eating animal products, the fruit, vegetables and cereals they consume are grown with animal manure. Factory-farmed animal waste may contain antibiotic residues but even organic farmers have long argued it is not possible to maintain soil fertility without animal manure. Could Eisenbach’s invention change that?

Twenty-three years ago, seeking to better use wasted olive branches on his employer’s Greek farm, Eisenbach began a small trial, mixing olive leaves, olive cake – the dry residue after olives have been mechanically pressed – and grape pomace, the leftovers from local vineyards. He produced 80 tonnes of compost, which worked well.

Dr Johannes Eisenbach photographed at OIKOBIO farm in Makrochóri Verías, Greece. Photograph: Georgios Makkas/the Guardian

A few years later, a crisis in his employer’s business forced him to devote his energies to establishing the organic network. Too busy to sell his compost, Eisenbach grew vegetables on it. He assumed the crops would eventually exhaust the compost. Oddly, however, as the compost aged, his vegetable yields got bigger and bigger.

He dispatched old compost for laboratory tests. The lab scientist phoned him, baffled: he’d never seen such strange material. Nitrogen levels were unusually high for a compost; it also held moisture uncharacteristically well and released pure water – no nitrates washed out as they do with conventional, water-soluble fertilisers.

Eisenbach shows me his small plant on the edge of Kalamata where he makes what he calls biocyclic humus soil. There’s one small shed, two employees, and 12 long hummocks of black soil tended by a mini-tractor – a purpose-built Swiss composter. He first mixes grape pomace, olive leaves and olive cake. The temperature must be above 56C to kill harmful micro-organisms. For a month, the mini-tractor churns the compost like a whisk and adds water daily. For another three months, the compost is turned weekly to enter the first stage of “ripeness”.

“Even with a difficult raw material you can produce a fantastic ripe, balanced compost within five months,” says Eisenbach. “Everybody would say this is a ripe compost. But it is not a ripe compost.” As he accidentally discovered, extra benefits occur when this compost is left to mature for up to four years. In one row of maturing compost, Eisenbach is growing vegetables directly into the humus soil. He picks a lettuce – it is the size of a large pumpkin.

Demand for ‘vegan’ fruit and veg

Farmers are rightly suspicious of “miracle” products but the humus soil is bearing fruit on farms beyond Eisenbach’s compost plant. His work has helped created a new global certification, the biocyclic vegan standard, for crops grown only with plant-based fertilisers.

“There are a lot of biocyclic vegan products on the market already but people don’t know that they were actually grown vegan,” says Axel Anders, the Berlin-based coordinator for Biocyclic Vegan Agriculture. “It’s like organic farming 40 years ago. We experience the same resistance. People say using plant-based composts doesn’t work; even organic farmers have the same attitude.”

Farms and fruit orchards in Greece and Cyprus have been among the first to adopt its new certification, growing produce for export to German, Austria and the Netherlands, where there is increasing demand for “vegan” fruit and veg.

On the sunny plains of Northern Greece, groves of peaches and nectarines mingle with rectangles planted with potatoes and courgettes. Orange orbs of hokkaido squash ripen as birds sing in thick hedges. A luxuriant field of broccoli dances with scores of large white butterflies.

The abundance of bird and insect life is unusual and Óthon Grigoriádis and his daughter, Stephanie, do not resemble typical farmers. Grigoriádis is a studious engineer and wears a smart shirt; Stephanie wears luminous trainers and sportswear. Their farm, Oiko Bio, is organic and now has the biocyclic vegan standard too.

Óthon Grigoriádis, founder of Oiko Bio farm in Makrochóri Verías, with a hokkaido squash. Photograph: Georgios Makkas/The Guardian

What’s really remarkable about this “vegan” farm is the size of its vegetables. Organic yields are typically 20-30% lower than farms that use synthetic fertilisers and chemical pesticides. But Oiko Bio has had a spectacular harvest this year. One hokkaido plant has produced nine squashes; plants often produce only two. Stephanie shows me photos of their earlier courgette harvest. She taps her phone for more data. This 0.2-hectare (0.5-acre) field produced 1,500kg of courgette: 7.5 tonnes per hectare. The previous year, on the same field, with similar weather, it was five tonnes.

Like most farmers, Stephanie and her father are naturally cautious. “I’m not sure about anything if I don’t see the results,” says Stephanie. Does the biocyclic humus soil really work? “Yes, I’m sure, and I see a difference in the broccoli here.”

Is there a demand for vegan vegetables? “In other European countries, maybe,” she smiles. “In Greece, we are still thinking about vegans. I’m not sure about vegans. In Greece people still eat a lot of meat.”

It’s a point reiterated by Dimitrios Bilalis, professor of agronomy at the Agricultural University of Athens. “Ten years ago if you said you were vegan in Greece, it was a joke,” he says. Now a third of his students are vegan. “Unfortunately,” he grins.

Organic hokkaido squash at Oiko Bio farm. Photograph: Georgios Makkas/The Guardian

Bilalis and his colleagues have been studying the qualities of Eisenbach’s humus soil. These include Eisenbach’s daughter, Lydia, who was so interested in her father’s compost she sought to scientifically test its capabilities. Bilalis, Lydia Eisenbach and colleagues measured yields of tomato and sweet potato growing in humus soil, an inorganic fertiliser and a control. Tomatoes’ average marketable yield was 7.95 tonnes per hectare in humus soil compared with 4 tonnes in the plots with the inorganic fertiliser and even less in the control; the sweet potato yield was 24.3 tonnes per hectare in humus soil compared with just 3.2 tonnes in the inorganic fertiliser plot. One of these studies has already been published in a peer-reviewed scientific paper, and the group expects another to be published shortly.

What are the constituent parts of biocyclic humus soil and why is it so effective? “There is not a concrete answer in science,” says Lydia Eisenbach, who since graduating from the Agricultural University of Athens now works alongside her father. “We don’t know all the chemical substances within this complex of organic matter that is called humus. It’s carbon but it’s not only this.”

According to Bilalis, the humus soil contains natural hormones that help root development; crops grown on it have particularly good root architecture, which penetrates the soil more deeply. He believes that the humus soil probably produces similar yields to animal manure fertilisers but he is alive to its additional benefits. Produced on a larger scale, he says, it would better use olive grove and viticulture waste. Its lack of solubility means nitrates won’t wash into and pollute rivers.

Organic broccoli at Oiko Bio. Photograph: Georgios Makkas/The Guardian

There is no patent on this humus soil, so why is it not ubiquitous? “Agro-terrorism,” grimaces Bilalis. He argues that big chemical corporations hinder simpler solutions that are better for people, crops and wildlife. “It’s very difficult to penetrate the market because the barriers come from big companies. Unfortunately the food we serve in big cities is industrial food – the fruit has to be the same size, the same colour, like cars.”

But there is also a catch. Doesn’t the four years it takes to turn good compost into humus soil make it too expensive for large-scale use? Eisenbach anticipates demand for (expensive) mature humus soil from small-scale urban growers who can cultivate vegetables in rooftop soil bags. But he hopes that conventional organic farmers in his network will buy it as affordable “ripe compost” and ripen it on their land. While letting it mature into humus soil, they can grow vegetables in it, so land is not wasted.

Can he convince farmers to store it for four years? “We have to persuade them,” smiles Eisenbach. He considers biocyclic humus soil a kind of open source software, and hopes farmers will test it. He’s convinced it can be produced beyond Greece – using other plant materials – as well. “At the moment we are producing agricultural products looking at nature as our enemy,” he says. “We try to fight to get fertiliser into the soil. We just have to understand that nature is in favour of us. We will not be perfect because there is nothing more perfect than nature, but we have to imitate nature as closely as possible.”