Expert advocates compost over chemicals

Swapping chemicals for compost will "put the biology back in the soil" and lead to healthier crops, according to microbiologist and organic farming technologist Dr Elaine Ingham.

Ingham is director and founder of the US-based Soil Foodweb - an organisation that has helped farmers and growers around the world convert to organic farming. She told delegates at the Improving Life in Your Soil - Using Compost & Compost Tea seminar held last week at Laverstoke Farm, Hampshire, that pests, diseases and weeds can be controlled without pesticides by restoring the soil's biology with compost.

She said: "On a number of levels in society we are seeing that the 'nuke it' approach (to life) doesn't really work. If you look at the natural world, mother nature is not using any of these toxic chemicals.

"Pests, diseases and weeds are a result of improper biology in the soil. If you get the biology right in an organic system you will not have lower yields - more often than not, your yields will be higher."

She said that, when left to their own devices without any disruption from agricultural practices such as tilling, soils contain a natural balance of bacteria, fungi, mycorrhizal fungi, protozoa - flagellates, amoebae and ciliates - nematodes, earthworms and microarthropods.

In the right numbers, these organisms make for healthy soil and, in turn, healthy plants with healthier, deeper roots.

The organisms, she explained, eat/attack any "bad" micro-organisms and produce nutrients because "when bacteria and fungi eat other bacteria and fungi nutrients are released".

Healthy soil also decomposes any toxins and acts as a natural water filter to prevent the leaching of chemicals.

Erosion and run-off, she said, occurs when soil disturbance has destroyed the plant biology.

Ingham added that pesticides disrupt the soil by killing off many species - even the "good" ones.

She said: "If you use a nematicide to kill 'bad' root-feeding nematodes you are killing the good, predatory nematodes as well - and putting yourself in chemical-dependency mode."

Ingham also questioned the plate-count method, which she said is used by chemical companies to test the effect their pesticides have on "non-target" species.

She said companies commonly take two soil samples - one with the pesticide in it and one without - and put them in water solution in Petri dishes. They then compare what grows in each dish but only disease-causing organisms (pathogens) survive and breed in the anaerobic environment of the dishes. This, she said, makes Petri dishes "severely limited" in assessing the impact that pesticides have on all of the species in the soil as "most things do not grow in a lab".

Ingham encouraged growers who are keen to find out the condition of their soil to examine it under a microscope. One option is to have it analysed by the Soil Foodweb laboratory set up at Laverstock Park - where scientists can advice them on the kind of compost they need.

Different species, she revealed, thrive in different soil conditions. Row crops, for example, prefer soil with a funghi-bacteria ration of 1:1 while shrubs, vines and bushes thrive in a ratio of 2:1 to 5:1.

Ingham said that compost or compost tea - a liquid solution made by soaking compost in water - made from local materials such as green waste can help restore the soil's biological balance.

She said: "Use local materials. We cannot take compost from Scotland and expect that the organisms are going to work in England."

In other words, if the soil is nematode-infested, growers should use compost that has predator nematodes in it to fight them off rather than a nematacide.

However, Ingham warned growers not to invest in compost that contains more than 25 per cent manure, as its dominance can leave little space for air or water and cause the compost to go "anaerobic" - a layer in the compost pile that contains less than 5.5 parts per million (ppm) of oxygen and where temperatures can reach 70 degsC and anaerobic organisms are "partying".

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