ENV100Y5 Lecture Notes - Lecture 25: Hydrangea, Overgrazing, Hyperaccumulator

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20 Jul 2016
Mod 3
Lecture 25
Soil resources continued
Soil erosion: transport and deposition of sediment, natural process ( humans accelerate
it) problem occurs faster than new soil
Water erosion: splash, sheet, rill, gully
19 billion hectares of croplands are affected by humans
humans are the primary cause of erosion
soil degradation over the next 40 years in Africa could reduce crop yields by half
on-farm cost of agricultural land degradation in Canada is 670 million per year
erosion is caused by deforestation, agriculture, overgrazing and chemical contamination
in past 50 years global grain production < by 13%
grazing practices contribute to soil degradation: compacts soil which damages structure-
> decrease water infiltration degrease grass survival && removes grass exposes soil
water and wind erosion
holistic management: simulating behaviour of natural herds actually improves/preserves
the proposed problem with holistic management is that more roots= more carbon
stored= less in the atmosphere
irrigation boosts productivity but can cause long-term and soil degradation= ground
water depletion, waterlogging, salinization= build-up of salts in surface layers
salinization inhibits production on 20% of all irrigated crop land = >11 billion/year
problems with irrigation: expensive, alters root morphology, increases fungal
pathogens, can cause salinity and subsidence (downward shift of surface)
salinization is easier to prevent than to correct, very expensive and difficult
remediating soil toxicity: salinity, soil pH, heavy metal contamination
phytoremediation: using living organisms to clean up contaminants
phytoextraction: drawing chemicals up into plant biomass by action of plants that are
hyper accumulators (hydrangea and Al).
buy kale organically because it’s a hyperaccumulator: you’ll absorb the nutrients
desertification: loss more than 10% productivity of arable land, can be natural or
anthropogenic( accelerated), results from erosion
the dustbowl was a monumental event in north American history: farm land destroyed,
1930s, bankrupt farmers, mass migrations, poverty great depression
dust bowl caused by : rapid mechanization, rapid conversion of grassland, poor
agricultural practices (deep tilling) and weather
caused lung irritation, dust pneumonia, grasshoppers, GD brought intensive agricultural
Crop rotation: alternating crops grown in fields through seasons, cover crops protect soil
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