Compost for Sustainable Soil Fertility & Disease Suppression

July 24, 2010

ABOUT A THIRD of farm energy used for food growing supplies fertility. In Florida alone, the energy used to manufacture the 2 million tons of food crop fertilizer each year equals the energy content of 100 million gallons of diesel fuel. Thus, recycling or composting waste materials into fertilizers and mulches can save energy while reducing pollution and enhancing human and crop health.

In the book Farmers of Forty Centuries; Or, Permanent Agriculture in China, Korea and Japan, early-1900s agricultural scientist Franklin Hiram King observed amazing levels of soil productivity where rural and urban human wastes were recycled back to the land and farmers planted legume (e.g. soybean; adzuki bean; clover) and other green manure cover crops and crop rotations.

“Japanese society once faced the prospect of collapse due to environmental degradation, and the fact that it did not is what makes it such an instructive example,” writes Azby Brown in his 2010 book, Just Enough: Lessons in Living Green from Traditional Japan. “Japan entered the Edo period in 1603 facing extreme difficulties in obtaining building timber, suffering erosion and watershed damage due to having clear-cut so many of its mountains for lumber, and virtually unable to expand agricultural production…All the more remarkable, then, that 200 years later the same land was supporting 30 million people-2.5 times the population…Deforestation had been halted and reversed, farmland improved and made more productive, conservation implemented…Overall living standards had increased, and the people were better fed, housed, and clothed, and they were healthier. By any objective standard, it was a remarkable feat, arguably unequalled anywhere else, before or since.”

Human waste, euphemistically called night soil, became a valuable soil fertility commodity in old Japan. Perhaps not quite worth its weight in gold, but a valuable commodity bought, sold, traded, and transported long distances from cities to farms. Rather than causing cholera and other diseases by entering the water supply as was common in European cities of the same era, sanitation and composting blessed Japan with multiple dividends. Considerable energy was “expended on toilet design to allow these waste products to be easily collected and processed,” writes Brown. This has culminated in modern dry composting toilets that “by allowing natural composting heat to occur inside a well-ventilated compartment…turn human waste into a dry, nearly odorless compound that looks and feels like peat moss.”

Farmers in old Japan spent their own money to “build toilets and urinals along well-traveled roads for public use, in the hopes of increasing their yields of fertilizer.” Contrast this with the modern difficulty of finding a decent, well-maintained public toilet along roadsides or in cities. China, says Brown, “is poised to become the global leader in composting toilets, partly because relatively few communities are served by the sewer infrastructure and the government is promoting these new designs as an attractive alternative that will help mitigate its freshwater problems as well.”

In the modern Western world, scientists in Germany and the USA have advanced the conversion of animal manures and green plant wastes into composts and tea sprays that boost plant growth and suppress pests. Though long a staple of biodynamics and organic gardening, in the 1980s University of Bonn researchers like Heinrich Weltzien, Andreas Trankner and Ketterer provided experimental proof that watery compost tea sprays high in beneficial microbes reduced powdery mildew on grapes and late blight disease on potatoes. Indeed, in some experiments compost tea sprays formulated from grape marc, earthworm compost, and animal manures equalled synthetic fungicides.

In the USA, in 1969 reports surfaced that some Ohio nursery growers had conquered root rot diseases in rhododendrons, cyclamens, and other ornamentals using pine bark composts and no longer needed methyl bromide soil fumigations. Ohio State University’s Harry Hoitink embarked on scientific studies of this phenomena. To reliably control the plant pathogens causing root rots and other soil diseases, hardwood bark composts were aged like fine wines for 6-12 months or fortified with special biocontrol microbes. In Australia, eucalyptus bark is similarly composted to combat Pythium and Phytophthora root rot pathogens in container or potted plant soils and avocado orchards.

Insect pests can also be controlled with composts. For example, Cornell entomologists like Michael Villani and Roxanne Broadway stopped white grub beetle larvae from attacking turf and lawns using crude proteins extracted from composted leaves and kitchen food wastes. Composted chicken manure and feathers worked best against caterpillars (moth larvae). Cornell University’s Eric Nelson and others have spent years formulating composts to combat root rots on golf greens and maladies like dollar spot and brown patch.

It may take a year or two of aging to brew the right combination of pest-suppressive beneficial microbes in composts. In Japan, composted golf course grass clippings are specially inoculated with a strain of the beneficial bacteria Bacillus subtilis to hasten suppression of the fungus Rhizoctonia solani on golf courses.

However, compost is not always a quick cure. For example, several years of compost applications are needed to control soybean cyst nematodes in agricultural fields or to restore Japanese forest soils. That is because plant ecosystems are complex adapative systems.