5.3. SOIL DEGRADATION AND CONSERVATION
Knowledge and Understanding
fertile soils require significant time to develop through the process of succession
human activities may reduce soil fertility and increase soil erosion
soil ecosystems change through succession - fertile soils contain a community of organisms that work to maintain functioning nutrient cycles and that are resistant to soil erosion
Soil degradation
two processes causing it
process that take away soil (erosion) - mainly occurs when there is no vegetation on the soil - wind and water can take the soil away
processes that make the soil less suitable for use - various chemicals end up in the soil and turn the soil useless in the long run
Human activities that lead to soil degradation
overgrazing
deforestation
unsustainable agriculture
total removal of crops after harvest - leaves soil open to erosion
growing crops in rows with uncovered soil between - erosion will occur especially if crops are grown on a slope and the rows are in the direction of the slope
excessive use of pesticides - long term will make soil too toxic for further use
monoculture - same crop year after year means same nutrients are depleted from soil and soil loses its fertility
Soil erosion
if natural vegetation covers soil processes that could damage soil structure are largely eliminated - leaves deflect heavy rain, roots hold soil together and humus absorbs large quantities of water - if removed soil is prone to erosion
3 major processes of soil erosion
sheet wash - large areas of surface soil are washed away during heavy storm periods and in mountainous areas moving as landslides
gullying - channels developed on hillsides following rainfall - overtime these channels become much deeper
wind erosion - on drier soils high winds continually remove the surface layer
Improving soil
Addition of soil conditioners
e.g. lime and organic materials - add crushed limestone or chalk to increase pH and counter acidification
Soil acidity
acid precipitation
break down of organic matter releases carbon dioxide through respiration - then dissolves into the soil water creating carbonic acid
nitrification of ammonium ions to nitrates increases acidity
removal of basic ions through leaching adds to soil acidity
Wind reduction
by planting trees or bushes between fields (shelter belts) or by alternating low and high crops in adjacent fields (strip cultivation) - or build fences
Soil conserving cultivation technique ss
cover crops - fast growing crops to cover the soil between rows of main crops or between harvest can keep soil particles in place
Terracing - method to reduce the steepness of slopes by replacing slopes with horizontal terraces separated by walls
Plowing- breaks up soil structure and temporarily increases drainage
Contour farming - plowing and cultivating along contour lines by plowing parallel to slope run off is reduced
Improved irrigation techniques - covering irrigation canals prevent evaporation before it even reaches the field (there have been cases where up to 50% of water never even reaches the field + trickle flow irrigation (drip irrigation) via small pipes can lead to uptake of water by roots before it evaporates - esp effective in desert like conditions
Crop rotation or fallow periods