Humus from decomposing leaves transforms poor soil

Not so many years ago, in October and November, we smelled smoke from burning leaves almost every day.

Gardeners who knew the potential benefits of these leaves were disappointed to see all this valuable plant material go up in smoke.

Fallen leaves are an important part of recycling nutrients that trees can use next year. In forests, more than half of the nutrients from old leaves are absorbed by the trees.

Gardeners can take advantage of all the nutrients stored in the leaves and transfer them to their gardens or compost bins.

By weight, about 2.5% of the leaves are minerals that can be directly used by plants. Most of the rest are carbon-based compounds.

Earthworms, arthropods and other small creatures feed on the leaves and break them into smaller pieces. Fungi and bacteria further degrade the material.

The product of the last stages of decomposition of plant residues is called humus. You can actually see the humus, which is what gives the soil its dark brown color. As a rule, the darker the soil, the more humus it contains.

Humus is essential for healthy soil. Improves loosening and soil structure. It is also home to valuable and beneficial microorganisms.

Probably the most overlooked property of humus is its high cation exchange capacity (CEC).

CEC is a measure of the soil’s ability to hold soil minerals needed by plants.

Positively charged molecules are cations; these include minerals such as calcium, magnesium, potassium, ammonium and others.

Soils with high clay content have high CEC values. The clay particles are almost microscopic and have a flat, sheet-like structure with a large surface area. Various elements present in clay give it a negative charge. The negative charge, distributed over a large surface area, attracts and holds positively charged mineral cations.

On the other hand, sandy soils have a very low CEC. Relatively large sand granules are usually composed primarily of quartz and are largely chemically inert. They also have a very small surface area, so minerals are not held in place.

Humus, due to its special configuration, has 5 to 50 times more CEC value than clay. Adding humus will greatly improve the soil’s ability to retain minerals. The relationship between humus and soil is more complex than the brief information I have described here.

Ideally, we would like at least 2-3% of garden soil to consist of organic material containing humus. This is difficult to achieve in sandy soil, since the relatively large space between the soil granules contains a lot of air, which causes humus to quickly decompose and disappear.

Consistent application of organic matter such as leaves or compost will increase the percentage of organic matter in the soil and will increase the CEC over time in any soil type. This is a good reason to add chopped leaves to your garden beds every year.