Mycorrhiza. The effect of chemicals on soil biology. The Effect of Chemicals on Soil Biology. lockup, reduced drought

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1 The effect of chemicals on soil biology Alan Broughton Organic Agriculture Association 1 Soil biology: The new paradigm If some are suppressed, others will take their place Microbes recover Fertilisers increase carbon sequestration by increasing growth Not all chemicals harm all biology: Balance is changed Most valuable are most affected: Mycorrhiza, nitrogen fixers, methanotrophs, disease suppressors, earthworms Less than 20% of pesticides have ever been tested for soil biology effects Studies often short term, lab based, using active ingredients only, only measuring biomass Roundup is registered as an antibiotic A scientific literature ignored Are chemicals sacred? 2 Mycorrhiza Nutrient releasers, humus creators, disease combatants, rootzone extenders Suppressed by phosphates, nitrates, herbicides, fungicides The outcomes: Phosphorus lockup, reduced drought hardiness, no humus replacement, zinc & copper deficiency, weediness, increased root disease 3 1

2 Nitrogen fixers: Rhizobium, Azotobacter, Azospirillum Suppressed by nitrates, phosphates, herbicides Most common herbicides highly suppressive: Roundup, 2,4-D, atrazine, trifluralin Heavy metals (arsenic, cadmium, lead, mercury) Outcome: Increased need for nitrate fertiliser 4 Protozoa and algae Soluble nitrates particularly affect protozoa, the bacteria feeders Many herbicides, some insecticides & some fungicides kill algae 5 Methanotrophs: Methane feeders Suppressed totally by nitrates, phosphates, most pesticides Outcome: Ruminant methane is not processed and becomes a greenhouse gas Livestock are blamed for methane chemicals should be blamed 6 2

3 Disease suppressors Disease-controlling fungi (decomposers and mycorrhiza) reduced, disease causing fungi stimulated Beauveria affected by most herbicides Roundup increases Fusarium, Rhizoctonia, take-all, Pythium and Phytophthora 7 Earthworms Ammonium fertilisers (anhydrous ammonia, ammonium sulphate) Some herbicides (Roundup, 2,4-D, atrazine) Many insecticides (carbaryl, chlorpyrifos, malathion, diazinon) Some fungicides (benomyl, copper compounds) 8 Fertiliser and pesticide contaminants Phosphates contain cadmium Industrial waste is often added to fertilisers Roundup contains arsenic Cadmium and excess zinc highly suppressive of rhizobium Azotobacter very sensitive to heavy metals Heavy metals accumulate, do not degrade 9 3

4 Nitrates and carbon sequestration Nitrate induced bacteria bloom attacks humus Nitrates reduce root exudates Bacteria to fungi ratio changed, calcium lost 10. Pesticides don t work American farmers thirty years ago used 2265 tons of pesticides and lost 17% of their crops before harvest. Today, farmers use 12 times more pesticides yet the percentage of the crops lost before harvest has almost doubled (EPA, reported in New Ecologist, May/June 1978, p. 80) In Bangladesh a pesticide reduction program cut pesticide use by 76%, and increased yields by 11%. When the Indonesia government eliminated subsidies for pesticides in 1987 the use fell by 50%, and correspondingly there was a 15% increase in yield. Pesticides affect natural pest controllers Pests quickly develop resistance Pesticides weaken plants: Chaboussou Soluble fertilisers increase pest and disease attack 11 The nitrate treadmill Average world nitrate use increased from 8.6 kg/ha in 1991 to 62.5 kg/ha in Yield of maize declined from 226 kg per kilogram of nitrate used to 76 kg. Rice yield fell from 217 kg per kilo of nitrate used to 66 Soy yield fell from 131 kg per kilo nitrate used to 36 Wheat yield fell from 126 kg per kilo nitrate used to 45. As more nitrate is used, more damage is done and more nitrate is needed 12 4

5 More research is needed * Short-term pot experiments vs long-term field testing * Acute toxicity vs chronic toxicity * Effects on different soils, climates, ph, crop, organic matter levels, soil biology status * Combinations of chemicals There is no justification in claiming chemicals are benign for soil biology The most valuable components are most affected: mycorrhiza and nitrogen fixing bacteria For detail and references see: matunda7@hotmail.com 13 5