OUR FOOD, OUR SOIL: sustainable agriculture in the 21 st century Sina Adl Department of Biology Dalhousie University
fertilizers composted manure grazing manure and urine Producer subsystem CO 2 Decomposer subsystem
Long term impact of agriculture Exponential decrease in soil organic matter Loss of soil structure Wind/water erosion Nutrient depletion Poor water retention Loss of decomposition efficiency Yield decrease, disease susceptibility, weather sensitivity Long term footprint on soil
Paustian et al. 1997. Compilation
The land use history (1278-1990) of a mixed hardwood forest in western Belgium and its relationship with chemical soil characteristics Verheyen et al. (1999)
Conventional mitigation of impact Fertiliser Disrupted soil community Replaces natural N fixation Pollution Pesticides & herbicides Bioaccumulation Non-target effects Dispersal to ecosystems Pollution, toxicity Irrigation Soil erosion Salinity built-up Loss of ground water Compensation, subsidies
Impact of agriculture on soil Compaction Aeration, drainage Temperature Moisture retention Reduced biological decomposition, nutrient cycling
Is there a crisis in agriculture? Naturally poor vs Ag degraded soils Inhabiting fertile soils Water resources (oil, dams, ground water, waste)
Summary of criticisms Loss of organic matter Causes erosion and yield decline Pollution Water intensive Unsustainable yields Diversity loss Loss of biological function
Composts reverse soil degradation Organic matter input Return biological activity Improve mineral availability Reduce compaction Improve water retention Reduce pollutant leaching Improve chemical degradation Improve yields
Soil community structure
Fungi Responsible for most of organic matter decomposition
Mycorrhizae
Ameobozoa scale bar 10 microns
scale bar 50 microns Testate amoebae
Soil flagellates feed on bacteria 10 6 to 10 10 per gram
Nematodes feed on bacteria, fungi, protozoa and other nematodes predatory nematode
Soil mites feed on fungi, decomposing organic matter, or prey
Pseudoscorpions
Insect larvae
Earthworms (Oligochaeta) Enchytraeids
COMMON COMPOSTING PROBLEMS Unwanted material (metals, plastic, etc.) Toxic material (medical, pesticides, solvents, household chemicals, etc.) Stink prior to collection Pest reproduction Poor fermentation management Stinky fermentation Stalled fermentation Poor composting Poor quality product Variable product quality
SOLUTIONS Collection frequency, container design Source separation Facility design (smell and waste) Microbiological monitoring of fermentation Management of input organic composition Product quality control Whole system set of legislated standards Companies will do things as cheaply as the legislation and contract permits
Recommendations Source separation/triage before composting Implement industry standards and quality control Waste-collection is separate from product manufacture & marketing Hire fermentation & decomposition specialists Measure metal bio-availability in soil rather than total content
Uses for good quality composts: Organic matter amendment to agriculture Can substitute chemical fertilizers Including use of compost teas Metal levels well below guidelines Some salts may be high Moisture and C/N ratio is adjustable Can be a high quality product Doesn t need to end in landfill Mine site remediation, ecological restoration
Uses of composted MSW
Recovery of ped structure
Soil recolonisation rate Georgia USA, conservation farming chicken litter cotton no tillage
SOIL %C C/N ratio 5 Douglas COTTON soil %C 40 4 3 20 2 1 0 SPRING FALL Spring Fall 0 0 4 8 25 90 FIELD (YRS conservation) 0-20
Compost amendment can reverse soil degradation 120 Morphotypes g -1 100 80 60 40 Flagellate Gymnamoebae Testacea Ciliata 20 0 0 0 R 4-5 8-9 25-26 in FIELD (Years in no-till)
Tillage 10-13 thousand yrs ago Tigris, Euphrates,Nile, Indis, Yangtze valleys 8,000 YBP SE Europe Jethro Tull, populariser US moldboard plow Thomas Jefferson 1784 John Deere, mass market Accelerated erosion Tractors, dust-bowl 1930s Faulkner 1942, Plowman s Folly Short term fertility Long-term decline 95 million ha no-till today
Organic agriculture? Agriculture without Pesticides Herbicides Fertilisers Transgenic crops Lower-yield varieties Susceptible to disease Tillage management Storage limitations Off-site contamination, recalls
Axis 2 Soil quality indicators, management practices, month: comparison of organic and potato in Maritimes 1.6 Soil Quality Indicators CCA Biplot 1.3 0.9 July 0.6 Nematode Organic 0.3 Microbial Biomass PH % Moisture Testate Amoebae Microarthropod September -0.6 Bulk Density -0.3 0.3 0.6 0.9 1.3 1.6 C:N ratio -0.3 Conventional May Vector scaling: 0.70-0.6 Axis 1 Nesbitt thesis, SRES, 2006
Mathematical model of increased area under organic management (Adl, Iron & Kolokolnikov) Organic agriculture addresses pollution and chemical issue only Issue of food security, and food safety cannot be set aside
Towards sustainability Soil organic matter management Society C waste recycling, MSW composting Urban to rural C transfer Rethinking urban waste management Reduced tillage Improved soil properties, water budget, reduced pesticides/herbicides Biological approach to soil nutrient management Crop rotations, locally adopted varieties Rebuilding soil N fixation Both provide stable complete soil food-web improving decomposition
Concluding remarks Balancing competing interests Farm machinery, fertilisers, seeds, biotechnology Short term politics, business greed Public education on food production issues Managing how to feed the world is too serious an issue Must be detached from fads and pseudo-science
Main points Decades for natural recovery of soil diversity and function, can be accelerated through management Cheap sources of organic matter for recovery of ped structure and micro-habitats Main drivers for remediation are societal and political Healthy environments Carbon trading and carbon credits
from Gary Larson