Soil, Organic Matter and the Archers

There has been some public grumbling about story lines in ‘The Archers’ recently– which is a shame because Ambridge is really onto something important right now: soil quality.

To bring you up to speed: Ambridge got flooded this spring and when Adam inspected his wheat fields he was shocked by the amount of soil erosion, the flood had just washed away the top soil.

So on a Sunday in April he took a spade and, with civil partner Ian in tow, went to look at neighbour David Archer’s field which had been flooded too. The wheat looked much greener and healthier, remarked Ian, the chef. And that was before Adam dug a little hole and made him feel ‘how soft and crumbly’ this ‘dark and rich soil’ was, ‘with a good bit of organic matter in there’. And of course they spotted plenty of earthworms. But then the story moved on which is a little sad because the cast of characters in the soil and what they are up to is definitely worth a closer look.

It takes only a heavy downpour to wash POOR soil away, and during a drought the soil of a whole field can take off in a dust cloud on a windy day. By contrast, GOOD soil can absorb a 4-6 inch rainfall in an hour*, retaining much of it during dry periods.

So what is soil? It consists of minerals and mineral particles like sand, silt or clay and of organic matter or humus. That’s the term for organic matter - plant parts like leaves and manure - that have been broken down into small bits. And then there are gazillions of soil organism that make the whole system work.

Good soil contains between 2% and 10% of organic matter and it has a soft, crumbly feel. This structure, the tilth, lets it absorb rainwater, retain it and resist erosion. And that’s not all: humus stores plant nutrients like nitrogen or phosphorus and it provides food for the microorganisms.

When it comes to soil inhabitants, earthworms and a few other bugs and beetles usually are all we think about. And they are very important: some make up to 2m long vertical channels and transport particles of fresh organic matter down to deeper soil layers, much appreciated by microorganisms living there. Other worms burrow horizontal channels. No matter which direction they dig, they help aerate the soil by turning it over. And worm poo is rich in nutrients, plants love it. But the vast majority of soil inhabitants are the ones we don’t see because they are way to small. With names like protozoa or nematodes they sound like species from another galaxy. Under an electronic microscope they look rather beautiful and their numbers easily run into trillions per acre. Fungi and bacteria go into quadrillions (that’s a figure with 15 zeros, I looked it up). Together they do an amazing job: apart from producing humus and nutrients like nitrogen they help plants to absorb them, some supply what Harold Willis calls ‘plant vitamins’ that help them grow, others protect plants from pests and diseases. In return plants provide sugar through their roots to some of their helpers and of course eventually lots of organic matter. Not that it’s all a love-fest down under, nematodes feed on fungi, protozoa eat bacteria – but that’s part of a healthy soil system.

This situation changes dramatically once above the ground a farmer, grower or gardener spots a pest or some blight and decides to treat it with whatever the chemical industry has on offer for this plant’s particular problem. Most pesticides, herbicides and fungicides have a lethal 'side'-effect on many of the microorganisms in the soil and that affects the balance of the soil system: the use of agrochemicals including chemical fertiliser reduces humus production and therefore has a negative impact on soil fertility.

Organic farming does not allow the use of agrochemicals, there are other ways to treat against pests, for example, through pheromone traps or by encouraging beneficial insects.

But most importantly: organic agriculture does not just focus on crop and yield, it looks at whether the crop is growing in a functioning ecosystem. And a major part of that system is healthy soil with a high content of organic matter. There are lots of things farmers and gardeners can do to nurture the soil, from composting to crop rotation. The latter is what David Archer said was the secret behind the excellent soil quality on his field and the wheat looking so lush and green despite of the flooding. These guys in Ambridge really are onto something here....

* For these and other facts on soil check out Harold Willis, Foundations of Natural Farming. Acres USA, 2008