The vital role of humus

After a wet winter, Steve Holloway, Soil Fertility Specialist with Soil Fertility Services, considers what can be done to breathe new life into sad soils.

When soils sit wet over extended periods consequences can arise, including the development of anaerobic conditions in the soil.

 This is because water-logged soils lack sufficient oxygen supplies to allow the beneficial aerobic micro-organisms to support healthy plant growth. This can lead to a decline in soil fertility and nutrient availability. Additionally, prolonged wetness contributes to a decrease in soil temperature.

Colder soils can impede seed germination and slow down root development, affecting the overall growth and vigour of these crops. This reduced metabolic activity can also limit nutrient uptake and photosynthesis, further compromising yield potential.

Imagine how much more productive your soil would be if it could hold onto water in drier times; what if the soil “sponge” was large enough to soak up excessive rainfall, limiting the standing surface water – and what if that sponge could also hold onto more nutrition for the growing crop that could be used in times of need?

It’s worth considering the different holding capacities of soil constituents for water and for nutrients. If you flattened out the same volume of sand and clay, sand would cover a dining table while clay would cover about an acre. Humus, however, has over four times the surface area of clay and can also hold up to 90% of its weight in water. These qualities underlie its importance, which is why we should be improving its levels in the soil.

Humus is the result of things rotting down; it cannot decompose any further. It acts as food for soil dwellers and performs much like a soil glue, creating stable aggregates, and ultimately, will be the “biological buffer” in times of hardship. So how do we begin to build this safety net?

It might be easier to consider what destroys it: Excess tillage and fertiliser can effectively burn off organic matter by speeding up its breakdown process, thus creating a less stable form of carbon. In times of need the plants and their biological neighbours will use this valuable, but depleting resource. Some soil systems are already completely depleted and, without this safety net, have a narcotic dependence on synthetic inputs.

For humus to form it requires a mix of aerobic and anaerobic soil conditions, where fungi and bacteria break down the organic matter (OM) into its simplest elements. Some of the OM resists complete breakdown and undergoes a transformation into a more stable, complex, organic, material known as humus. This process is called humification. Humus is highly resistant to further decomposition, making it a vital and longer-lasting component of soil.

Just applying compost and FYM to the field won’t guarantee a healthy content of humus. OM, including muck and compost, has to fully break down to form humus. So it’s the rate of decomposition, rather than volume of OM, that brings humus. You need soil dwellers like fungi and microbes to turn OM into humus, so having soil that can breathe is critical to the critters.

The regen farmer may say they are “maximising soil biodiversity and utilising cover crops, minimising soil disturbance,” when simply put, it is about improving your soil and get it cycling air, water, and nutrition better.

For years, Soil Fertility Services have been recommending Humic SC to growers where soils haven’t quite been performing as well as they should. It helps the soil breathe better by actively opening those tighter spaces. Humic SC contains anionic surfactants that act as “soil conditioners” by modifying the surface properties of water and soil, making it easier for water to penetrate compacted or tight soils. This promotes even moisture distribution, better root growth and an overall improvement in soil structure which leads to better biological activity.