When Carmen Felipe-Morales and Ulises Moreno got married 30 some years ago, they sought a novel solution to balancing a marriage, their careers and saving the planet. They bought a micro farm with depleted, sandy soil in Pachacámac, Peru, the ancient capital of a powerful, pre-Inca empire.

Carmen and Ulises commuted to their jobs as professors at La Molina Agricultural University, and raised their children on their one-hectare farm (“Casa Blanca�). One problem remained: what to do about Casa Blanca’s infertile soil, nearly stripped of all organic matter.

Guinea pigs are native to the Andes, so as Ulises explains “We started raising guinea pigs, not so much for the animals themselves but for their dung.� Now Casa Blanca has over 1,000 guinea pigs, which generate a ton of dung a month. It is mixed with chopped crop residues, pre-composted and then mixed with water and put into a Chinese-style bio-gas generator (basically a big tank in the ground) where it makes methane gas for cooking and for generating electricity. The spent dung is eventually shoveled out and put onto the garden.

Modern civilization is mining rock phosphorous so fast that it will soon be depleted and the only other source of phosphorous for fertilizer will be recycling. Over 100 years ago, the former US secretary of agriculture, F. H. King (1911), marveled at the agriculture of China, sustained for over 4,000 years on fertilizer made from night soil, human waste collected every day in chamber pots and returned to the soil. The trick for the future will be to handle human waste in a way that is reasonably pleasant and quite sanitary.

The flush toilets at Casa Blanca are clean and comfortable, but the waste water does not go to the sewer or the river. Carmen showed us how the toilets empty into an artificial “wetland� the size of a backyard pond. The wetland is covered with sand and gravel, with feathery papyrus plants waving over the surface. Carmen says they cut the papyrus and feed it to the guinea pigs. The water that flows out of the wetland is clear, nearly free of E. coli and is perfect for irrigation water.

I visited Casa Blanca with an international group of soil scientists. Steve Vanek from Cornell University measured the carbon in three soil samples. Patrick Lavelle, of CIAT and Elena Velázquez of Universidad Nacional de Colombia, counted the living creatures in the soil (the more life in the soil, the healthier it is) and José Benites, recently of the FAO, analyzed the soil structure.

The scientists admired the health of the soil, but one sample was particularly fertile, one taken from a plot of maize, which is tricky because corn is a demanding crop and can exhaust the soil. “We added organic fertilizer to that plot,� Ulises explains.

We learned two things that day. 1) Soil fertility and soil structure can be restored with recycling.

2) The fitness of the soil can be measured by observing the fauna (the more earthworms the better) and by analyzing its structure: look for soft, dark brown or black soil, with patches of different colors and textures, not too sticky and not too sandy, with a few “aggregates� (clods) formed by earthworms, which release native soil bacteria that digest nutrients in the soil and make it available to plants.

An easy way to analyze soil is crucial, because farmers often ask me how they can get a soil analysis to know if it is fertile or not. The farmers think they want a chemical analysis, but it is good to know that there are other, user-friendly, biological and physical ways of analyzing soil.

Almost all of humankind’s food now comes from a thin crust of endangered soil, which is rapidly being eroded, impoverished and paved over. But we can save it, one humble turd at a time.

My visit to Casa Blanca was sponsored by the McKnight Foundation’s Collaborative Crop Research Program (CCRP), especially as part of the conference “Una Mirada desde el Suelo� (A Look from the Soil), organized by Drs. Steve Fonte and Steve Vanek.

Reference cited

King, F. H. 1911 Farmers of forty centuries: or, Permanent agriculture in China, Korea and Japan. Mrs. F.H. King.