GardenDrumTopsoil loss the world’s biggest threat

Have you got BAD GARDEN HABITS? We talk a lot about climate change as our world’s great Sword of Damocles, but it’s actually TOPSOIL LOSS that’s the rapidly unfolding global disaster. In 40 years we’ve lost ONE THIRD of our arable land to erosion and pollution. Are you contributing to that?

Sydney Harbour Bridge in the 2009 duststorm Photo Mrcricket48

Sydney Harbour Bridge in the 2009 duststorm Photo Mrcricket48

Although the latest report from the Grantham Centre for Sustainable Futures at UK’s University of Sheffield is about industrial agriculture, we keep on perpetuating many of the same bad habits in our own home gardens, so we’re still part of the problem on a micro-scale (as well as our over-consumption and wastefulness of that farmed food).

Nearly one third of the world’s arable land has been lost either to erosion or pollution in the past 4 decades. Most of this has come from intensive agriculture that continues to use 20th century industrial farming techniques, such as ploughing and the heavy use of manufactured fertilisers.

SOIL EROSION
The industrial problem: ploughed fields have 10-100 times more erosion than the rate of topsoil formation, which is about 2.5cm per 500 years.
The home garden problem: double digging vegetable beds, digging in soil improvers, leaving soil uncovered, and not mulching are still common practice among home gardeners. Digging over your garden soil exposes more nutrients to the air and temporarily lifts soil fertility but also exposes it to wind and water erosion, especially when you have built-up beds. If you ever see muddy water running off your garden beds, that’s precious topsoil being washed away.

Solutions:
♦  no-till agriculture for both farms and home gardens
♦  spread compost over the soil but don’t dig it in – earthworms and other soil biota can do that much more efficiently for you, aerating the soil as they go
♦  use a cover crop when you want to give a garden bed a resting period (fallow)
♦  cover any bare soil with 50mm (2 inches) of chunky mulch to protect it from wind and water
♦  don’t over-water. Holding a hose on the garden until you see water running off doesn’t just waste water – it carries soil away too. Always use a water-breaker head on your hose to make soft, rain-like droplets, never a jet
♦  if you’re having any building or landscaping done, make sure you strip, save and cover the topsoil beforehand for later reuse

Water-breaker head Photo trinitakunst

Water-breaker head Photo trinitakunst

SOIL POLLUTION
The industrial problem: heavy use of manufactured fertilisers require high inputs of inorganic nitrogen via the industrial Haber-Bosch process, which uses up 5% of the world’s natural gas production and 2% of its annual energy supply.
The home garden problem: reliance on packet fertilisers created in the same industrial process as those used on farms, rather than using bulky and less convenient natural manures and composts. We also make many wrong assumptions about what nutrients our plants need, rather than looking at our gardens as a closed-loop system in which those essential nutrients are probably there, but locked away from plants due to other soil issues, such as lack of good soil biota or pH problems.

Plants cannot tell from what source their nutrients have come – nitrogen is nitrogen whether it’s from a industrial process or a manure – but gardeners who use manufactured fertilisers are much likely to overfeed their plants causing nutrient toxicities and acidification. And of course these fertilisers rely on burning fossil fuels like natural gas to create ammonium nitrate.

Compost bins Photo Antranias

Compost bins Photo Antranias

Solutions:
♦  instead of reaching for quick-impact packet fertilisers when your plants look pale and wan, sustain long-term soil health and soil biota with manures, composts and rock dusts.
♦  every time you put a clipping in the green-waste bin, you’re sending nutrients out of your garden that you’ll need to replace. Compost everything except weed seeds, or at least chop it up finely and sprinkle it back over the soil surface. In tropical and subtropical areas this is a very practical solution and just as fast as composting.

More at the Grantham Centre for Sustainable Futures

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3 thoughts on “Topsoil loss the world’s biggest threat

  1. Great to see lessons from industrial agriculture being applied to gardens.

    It’s so easy to think that as gardeners we are on the side of the angels, and that all the problems are caused elsewhere. Plus, as you say, it’s in our own interests to get this right, both for the planet and for our own gardens.

    The Grantham Centre at Sheffield does some really interesting research (and I don’t just say that because my husband does some work for them…).

  2. We are about to do a large reno and we are going to stockpile the topsoil. My husband wasnt happy about it but when i explained the reasons he was all for it. Lucky we have the room to store it though.

  3. If you have no topsoil for your veggie patch (like my yard – all development clay and rock with a token grass cover over the top) you can generate it on the cheap by fertilizing your lawn and then composting your grass clippings. A little tub of NPK costs about 5 bucks at coles, and gives you a hell of a lot of growth, which you can then ‘process’ into organic compost, or use as mulch!

    I have filled up my 1m x 3m garden bed with top quality compost like this for 5 bucks!

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