# Humus Humus is the part of soil that makes it look black. Humus consists of millions of compounds, including important ones such as humic acid, fulvic acid and carbonic acid. But no one really knows how it works. Humus is usually found in the top 10-30 centimeters of the earth. It's what makes the difference between topsoil and dirt. Humic acid is amphiphilic, which means it is attracted to water and fats, so it helps to store them in the soil. It was first identified in 1761, and isolated in 1786. Liebig identified nitrogen, phosphorus and potassium as the limiting factors for plant growth in 1840. But even now, scientists don't quite understand how humus works. They know it is a polymerised carbohydrate (sugars that are broken down and transformed with nitrogen), but how it's made is as mysterious as alchemy. For the longest time, the easiest way to find humus in soil was to burn it. The more heat was given off, the more humus there was, since humus is made of organic matter, which is the only part that burns. --- # Origins of composting Composting is a method of mimicking nature in order to create humus. It was first described methodically by a British botanist, Albert Howard, in the 1920s. He was based at Indore, a research station in Madhya Pradesh, a central province of India. His techniques were distilled in a booklet entitled *The Waste Products of Agriculture* in 1931. Known as the Indore method, it is still the basis of most compost methods today. His work was built on the prior work of F.H. King, a scientist at the U.S. Department of Agriculture, who wrote a book called *Farmers of Forty Centuries* in 1911. King travelled extensively in China, Japan, and Korea, and found that their farmers were able to harvest crops for centuries while keeping the land fertile. He estimated that the Japanese were supporting three people per acre, whereas in Holland they could only support one person per acre. --- # How composting works Composting works by balancing the ratio of carbon and nitrogen. Too much nitrogen can make the compost turn anaerobic (airless, with no oxygen), becoming slimy and smelly. The smell comes from excess nitrogen turning into gas. Too much carbon makes the compost loose and slows down the process, because microbes need nitrogen to do their work. Initially, a ratio of 30:1 carbon to nitrogen works best. Over time, this can drop as low as 10:1. Things high in carbon are brown. Those high in nitrogen are green. Meat and manure are high in nitrogen. --- Source: [[Soil]] See also: [[Our evolving understanding of humus]]