The soil is one of our most precious resources. Up to 50% of earths biodiversity depends on the soil and about 95% of global food crops are grown in topsoil. Soils store vast amounts of carbon. Paul Butler tells us how we can protect our soils.
Aall over the world soil is being degraded. Approximately 10 – 20% of drylands and 24% of the world’s productive lands are degraded. 24 billion tonnes of fertile topsoil are lost every year to erosion. The UN FAO predicts that there are about 60 years of harvests left, before soils fail completely.
According to Teagasc research, the picture in Ireland is much the same with most soils being degraded to some extent and the majority of soils below the target levels for pH, P and K. On many farms, sub-optimal soil fertility will lead to a drop in output and income if allowed to continue.
This degradation is caused by a variety of factors most of which have to do with human management of the soil. Erosion due to increased rainfall associated wit climate change, organic matter decline, loss of biodiversity, compaction, sealing and contamination are some of the factors. Degradation is both chemical and physical.
Over 60% of Irelands land use is agricultural and almost 12% is forestry. There is therefore great scope for remedial action and even soil improvement.
Soil Biology Featured
Examples of mitigating actions are
Returning organic matter to the soil
Keeping the soil covered with vegetation at all times
Reducing to a minimum the use of chemical fertilizers
Avoiding physical damage to the soil by machinery
Using a greater diversity of crop plants
Specifically in relation to forestry there are various options under the new Afforestation grant scheme that are very beneficial to soil integrity. They incorporate many of the mitigating measures outlined above.
For example the Agroforestry option and the Continuous Cover Forestry option, both offer a greater variety of species per hectare, an almost continuous vegetation coveron the ground, a potential reduction in the need for chemical inputs, and a greater natural recycling of nutrients.
Apart from management practices such as these, there are various soil additives that have been shown to provide long term stability to soil. As mentioned earlier one of these is the return of organic matter to the soil in the form of manure or compost. This has been shown to have long term benefits to soil structure and function.
Biochar
Another useful additive is Biochar. Biochar is the term used for the residue left after burning biomass quickly, at high temperatures, and in a low oxygen environment. The process is known as pyrolosis. Ash production is kept to a minimum and the idea is to make a form of charcoal which is then macerated to a finer grade. This product is very stable and has several characteristics that make it useful as a soil additive, as well as many other uses.
Most of the carbon in the original biomass heap is stored in the Biochar, and, as Biocharis very stable, this carbon is stored long term.
Biochar has an interesting structure that resembles ocean coral. This structure provides an enormous area of tiny micro-pores that act as air pockets and as habitat for a multitude of soil bacteria and fungi. All of this is hugely beneficial to the soil.
Biochar also has a particular Cation Exchange Capacity (CEC) that allows it to facilitate the storage and release of nutrients in a very efficient way. This means that Biochar can act to prevent leaching and at the same time store and release nutrients.
Biochar can moderate the pH of soil.
It can absorb contaminants. Research by Teagasc has shown that Biochar is one of several materials that can reduce emissions from slurry for example.
Biochar can also alleviate soil compaction over time by opening up soil structure.
One of the other great benefits of Biochar is that almost any biomass can be used as a fuel source.
Particularly interesting from the forestry point of view, is the possiblity of using small diameter material from forests as Biochar fuel. This material is very suitable for Biochar production.
And using Biochar as an additive at planting time may have significant long term benefits for tree crops as well as soil stability. Biochar production also lends itself to both industrial and domestic scale production.
The Biochar can also be enhanced as a nutrient source by soaking it in a suitable organic fertilizer source or mixing it with compost. Once added to the soil, the Biochar releases these nutrients slowly over a long period.
Overall, it seems that Biochar may be an additional useful tool for soil protection and enhancement and may become a further profitable product from our forest estate.
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