• Cation exchange: Process by which plant’s roots donate hydrogen ions to the soil in
exchange for cations. (positively charged ions) such as those of calcium, magnesium, &
potassium which plants use as nutrients. The soil particles then replenish these cations
by exchange with soil water. [this is how plants get nutrients].
- Cation exchange capacity: expresses a soil’s ability to hold cations (preventing from
leaching & making them available to plants). As, soils pH becomes lower the cation
exchange capacity diminishes, nutrients leach away. Soil may instead supply plants
with harmful aluminum ions. (Acidic ppt. can harm soils & plant communities).
Healthy soil is vital for agriculture. Productive soil are the renewable resources. If it gets
leached or when the nutrients get washed away faster than the rate at which it can be
renewed then it becomes non renewable energy resource, because it gets depleted.
• Agriculture: practice of raising crops & livestock for human use & consumption.
• Cropland: land humans use to raise for plants & fibre.
• Rangeland: land used for grazing livestock.
As population & consumption increase, soils are being degraded. With rise in population,
we need to either change our diet plans or increase agricultural productivity. We need to
do it sustainably.
• Extensification: Increase in resource productivity by bringing more land in production.
- Now days, grassland have turned into desert. Poor agricultural practices have resulted
countless fertile soil to be blown & washed away. - More then 80 million each year, we lose 5 million - 7 million hectares of productive
• Soil degradation: damage or loss of soil.
- Global grain production reduced by 13% on cropland & 4 % on rangeland. It is
important to maintain the integrity of the soil.
Agriculture began to appear around 10 000 years ago. First it was hunter- gather then,
scatter seeds --> a plant was grown, then it became fruit selected by people. ( Selective
process). Same process of selective breeding with animals- creating a livestock from wild
- Agriculture & sedentary lifestyle reinforced each other.
- The need to keep the harvest crop sedentary, it made sense to plant more crops (
POSITIVE FEEDBACK cycle).
- Agriculture is a form of intensification.
• Intensification: A way to increase the productivity of a given unit of land, usually
applying new techniques to enhance the productivity.
- Intensification can increase the carrying capacity of the land area.
- Technology advancement = increase in population.
- The ability to grow excess farm enabled people to leave off the farm & eat the food
others produce. This led to development of professional specialties, commerce
technology, densely populated urban centers, social stratification & politically powered
- Earliest widely accepted archeological evidence for plant domestication is from “FERTILE CRESCENT”, region Middle East about 10 500 years ago.
- Earliest domestication of animals, is also from that same region, 500 years later.
- Crop remains have been dated by using radiocarbon dating.
• Traditional agriculture: Biological powered ( human & animal muscle power)
• Subsistence agriculture: Farming that families do to produce enough food for
themselves & do not use large scale irrigation, fertilizers or teams of laboring animals.
• Industrialized agriculture: demands vast fields be planted with single crop.
• Monoculture: Uniform planting of single crop. (opposite to polyculture farming - mix )
• green revolution: Intensification of industrialization of agriculture, 20th century. It has
led to dramatically increased crop yields per unit area of farmland. Practices include:
devoting large areas into monocultures crops for high yields & rapid growth (heavy use
of fertilizers, pesticides & irrigation water).
- It introduced new technology, crop varieties & farming practices.
Soil degradation: Problems & Solutions:
- The most desirable soil for agriculture is a loamy mixture, with pH close to neutral that
is workable & capable of holding nutrients.
- Common problem affecting the soil productivity: Erosion, desertification, salinization,
water logging, nutrient depletion, structural breakdown & pollution.
- Rainforest system have high primary productivity. Most of the nutrients are tied up in
the plants. e.g. Amazon readily leaches minerals & nutrients out of the topsoil. Those not captured by plants are taken down to the water table. Out of the reach from the
plants. High temp. decomposition of leaves litter & uptake of nutrients of plants.
Amount of humus remain is small, topsoil remains thin.
- When forest is cleared for farming, cultivation quickly depletes the soil’s fertility.
• Swidden agriculture: Farmer cultivates a plot for 1 to a few years & then moves on to
clear another plot, leaving the first to grow back to the forest. ( Works with low
- Saskatchewan grassland, rainfall is low, nutrients remain high. Plants take nutrients &
return to the topsoil, when they die, the cycle maintains the soil fertility.
Erosion can degrade ecosystem & agriculture:
• Deposition: The arrival of eroded material at its new location.
- Erosion & deposition are natural processes.
- e.g. FLowing water can deposit eroded sediments in river, valley & deltas producing
rich & productive soil. This is why floodplains are excellent for farming & flood-
control measure decreases the productivity of agriculture in the long run.
- Erosion takes place much faster than the soils are formed.
- Topsoil, which are valuable are first eroded.
- People have increased vulnerability of fertile lands to erosion through 3 main practices:
1. Over cultivating fields through poor planing, excessive ploughing, disking, harrowing.
2. Overgrazing rangelands with more livestock than the land can support.
3. Clearing the forest areas on steep slopes or with large clear cuts. Soil is eroded by several mechanisms:
a. Splash erosion: occurs as the raindrops strikes the ground with enough force to
dislodge small amount of soil.
b.Sheet erosion: results when thin layers of water traverse broad expanses of sloping
c. Rill erosion: leaves the small pathways along the surface where water has carried
d.Gully erosion: cuts deep into soil, leaving large gullies that can expand as erosion
- Universal Soil loss Equation (USLE) was developed as a tool for estimating the erosion
losses by water from cultivated fields, different soil & management influence soil
- Deflation: all loose fine- grained material is picked up from the surface.
- Wind erosion: Aeolian erosion.
- Abrasion: wind- transported particles become “projectiles”, striking with other rocks &
causing them to breakup.
A= R X K X LS X C X P
E= f (I C K L V) Soil erosion is a global problem:
- Bruce Wilkinson, geologist, concluded that humans are more than 10 times as
influential at moving soil than all other natural processes on the surface of planet
- 85 % of crops in Canada, was in the risk of water- related- erosion.
- 22% improvement in 15 years.
Desertification reduces productivity of arid lands:
• Desertification: Type of land degradation that occurs in arid & semi- arid areas results
from climatic variations & human activities.
• Land degradation: reduction or loss of the biological or economic productivity of the
- In Kenya, 80% desertification of land due to rapid population growth.
- In a positive feedback cycle, the soil degradation forces ranchers to crowd onto
more marginal land & farmers reduce fallow periods, both of which exacerbate
- UN: desertification will worsen the climate change, & could displace 50 million
people in 10 years.
The Dust Bo