Mulching, reduced digging and raised beds
"Mulching" is the process of adding a layer of material to the soil surface (but here we are talking about layers of organic matter only, and not material such as black plastic sheets); "reduced digging" (also known as "no digging") is a soil management system that reduces the amount of digging to a bare minimum, relying instead on the addition of organic matter to produce a cultivable soil; and "raised beds" are what happen when mulching and reduced digging cause the soil surface to raise over time.
Why? The digging (and ploughing) of soil breaks up the soil structure and damages beneficial soil biota, such as earthworms and microbes, making the soil less fertile and less resilient to erosion. Reducing digging to a minimum lessens the damage caused, meaning a better-structured, healthier, more full-of-life, more fertile soil, which in turn leads to healthier more-productive more-resilient crop-plants. A thick layer of mulch also suppresses weeds. The triad of "mulching, reduced digging, and raised beds" is of central importance in the practice of organic small-scale vegetable production within a healthy environment. Healthy soil biota = healthy soil = healthy plants = healthy food/environment.
how? Instead of digging compost (see "How and Why - composting") into the soil, we apply it to the soil surface as a mulch, where it continues to decompose, thus releasing nutrients gradually downwards into the soil, helped by earthworms. Once taken down into the soil by worms, it is decomposed further by microbes, as happens in natural ecosystems. This microbial activity steadily releases nutrients into the soil, instead of giving the initial big hit of digging in compost, and avoids the possible nitrogen depletion that the latter can trigger. A continued and generous application of mulch (which can be of a coarser consistency than if we were digging it in as a compost) to the soil surface is essential for this system to work, so a steady stream of composted organic material is necessary.
When we converted to this reduced digging system, we opted for long beds of 150cm in width, just about narrow enough to be able to reach into the middle to weed and sow without standing on the bed. Standing on the beds is taboo as this compacts the soil, so all work is done from the paths, which are just wide enough to allow wheelbarrow access. At first, we double-dug the beds (so much for the no-dig system!) then added compost, to give a good soil at the outset. This and the continued and generous application of mulch to the beds have raised their level above the surrounding grassy paths. A cover-crop of oats is grown on the beds over winter, to suppress weeds, improve soil texture, and reduce the leaching of nutrients from the soil - they are pulled out in spring and composted, to be returned later as mulch. The addition of all this organic matter to the soil is an investment in the future, rather than the short-term cashing-in of the soil inherent in the year-on-year use of mineral fertiliser. In practice, we may hoe and/or rake the bed from time to time, just to break up the top soil layer for sowing seeds, to a depth of about 10cm. Reduced digging may indeed mean reduced labour, but there's still enough to keep us occupied with all that hot-composting, mulching, hoeing, raking be done!
Information sheet created by Hotel Posada del Valle. (