Soil Flashcards
What is soil fertility?
The ability of soil to sustain plant growth
What are the main features to check soil fertility?
Water content, soluble materials, air content, dead organic matter, pH, soil biota and soil texture
Why is water content important?
Ensures survival of biota and plant nutrient are absorbed dissolved in ionic form
What macronutrients are found in fertile soils?
Nitrates, phosphates and potassium ions
What micronutrients are also found in fertile soils?
Boron, cobalt, copper, iron, manganese and magnesium
What happens to toxic ions in fertile soils?
They adsorb onto the surface of mineral particles, usually clay, so they cannot dissolve in water where they may cause harm to organisms
What is hygroscopic water?
Water held on the surface of mineral particles by adhesion- this cannot be absorbed by plants
How does air content affect soil fertility?
Many processes and living organisms are aerobic so aerated soils are more likely to be fertile
How does dead organic matter content impact soil fertility?
High content will release plant nutrients as it decomposes increasing the fertility of the soil, it also increases water retention and provides food for soil biota
What is the typical pH of fertile soils?
5.5-7 (the range of tolerance for most plants and soil biota)
How do acidic soils affect fertility?
Increase leaching of plant nutrients and damage root cell membranes
How do alkaline conditions affect the fertility of the soil?
Phosphates may become insoluble
What are some essential soil biota?
Detritivores, decomposers, nitrogen fixing bacteria, nitrifying bacteria and mycorrhizal fungi
What are some examples of detritivores?
Beetle larvae, millipedes, woodlice and slugs
What do detritivores do?
Break up dead organic matter and release nutrients into the soil
How do worms aid soil fertility?
They are detritivores that also increase soil drainage and aeration by creating tunnels in the soil
What are some decomposer examples?
Bacteria and fungi
What do decomposers do?
Hydrolyse dead organic matter
What’s the difference between decomposers and detritivores?
Decomposers secrete digestive enzymes and rely on detritivores to physically break up the DOM and increase it’s surface area
How does nitrogen-fixing bacteria aid soil fertility?
Converts gaseous nitrogen into ammonium ions
How does nitrifying bacteria aid soil fertility?
Oxidise ammonium ions to nitrite ions then to nitrate ions
How does mycorrhizal fungi aid soil fertility?
Form symbiotic relationships with plant roots and aid phosphate uptake by the plants
What are the three soil particles types?
Clay, Silt and Sand
What’s the smallest and largest soil particle?
Clay is the smallest, then silt and sand is the largest
Whats the standard ratio of soil texture in loam soils?
40:40:20 (clay)
How is soil texture determined?
The proportions of the different size categories of mineral particles present in the soils
What are some feature of sandy soils?
Large pore spaces, no capillary water, cannot adsorb nutrient ions easily, low thermal capacity (less water) so warm rapidly, root penetration easier, lack of adhesion
What are some features of clay soils?
Poorly drained, allows capillary rise of water, more likely be water logged with low aeration, nutrient ions adsorb easily, high thermal capacity, poor root penetration and high adhesion
What are peds?
Aggregates of soil particles
How are soil particles bound together?
Polysaccharide gums (produced by decomposition), fungal hyphae, roots, action of soil biota and hygroscopic clay particles
What are the two different types of peds?
Platy and crumb
What are the features of crumb peds?
Small and round
How do crumb peds improve soil fertility?
Produce good drainage, aeration and easy root penetration
What are the features of platy peds?
Large and flat
How do platy peds reduce soil fertility?
Reduce drainage, aeration and root penetration
How does soil depth affect soil fertility?
Deeper soils are less likely to become waterlogged or to dry out rapidly, they can also aid good root anchorage
What human activities can affect soil fertility?
Ploughing, drainage, inorganic fertilisers, organic matter addition, irrigation, soil compaction
How can farmers aerate soils?
Ploughing and drainage
How does ploughing and drainage affect soil fertility?
Increases the rate of nitrogen fixation, nitrification and decomposition of dead organic matter
How can farmers deplete soil nutrient levels?
Soil erosion, biomass removal, inhibiting natural processes
How does irrigation help plants?
Increases water levels to keep stomata open and allow gas exchange and dissolves ions for the plant
How do farmers contribute to soil compaction?
Excessive use of heavy machinery or high livestock densities
How does soil compaction affect soil fertility?
Reduces aeration and makes waterlogging more likely
How does pH control affect soil fertility?
Ensures nutrients are soluble but not too easily leached
What is soil erosion?
The removal of soil particles by wind or water
When are soils likely to be loose with little cohesion?
When they are dry or with low clay content
How can soil deposition after erosion be a problem?
Cover crops or land in urban areas
What are the three types of water erosion?
Rain splash erosion, surface runoff erosion and slumping and landslides
What is rain splash erosion?
When soil particles are dislodged by the splash of a raindrop and dispersed in all directions
What are the dangers of rain splash erosion?
Over time, it can cause downhill movement of large amount of soils
What is surface runoff erosion?
Caused by the surface runoff when the soil infiltration capacity has been reached
When does surface runoff erosion occur?
In times of heavy or prolonged rainfall or if the soil is relatively impermeable
How do slumps and landslides occur?
When soil on slopes becomes wet the increased mass and lubrication of the water makes the movement of large amounts of soil more likely
When do slumping and landslides occur?
Deep soil on steep slopes becomes less stable following deforestation
How does vegetation reduce soil erosion rates?
Natural windbreak, cover from rain, organic matter binds soil together, roots hold soil together, increase infiltration capacity
How does vegetation act as a natural windbreak reduce soil erosion?
Reduces wind velocity and therefore the kinetic energy to carry away soil particles
What is humus?
The decaying organic matter within soil
What human activities increase the rate of soil erosion?
Vegetation removal, ploughing vulnerable soils, overgrazing, reduced soil biota, soil compaction and cultivating steep slopes
How does overgrazing contribute to soil erosion?
Removal of vegetation by livestock, increases the exposure of the soil and the risk of erosion, the disturbance and root damage by hooves increase the risk of erosion
How can soil biota be reduced?
Ploughing, removing organic matter and agrochemical
How do soil biota reduce soil erosion?
Break down organic matter to release nutrients for plant cover, humus produced creates adhesion and worms aerate the soil
How does soil compaction occur?
Heavy machinery use, high livestock density and reduction in detritivores
How does the cultivation of steeper slopes increase soil erosion rates?
The surface runoff flows more rapidly so it has more kinetic energy to pick up and carry soil particles
What is accelerated soil erosion?
The natural equilibrium between formation and erosion is broken and the erosion rate is exceeding
What are the effects of accelerated soil erosion?
Reduced productivity, sedimentation in rivers and reservoirs , increased atmospheric particulates and desertification
How does soil erosion reduce productivity?
When erosion occurs it is often the most fertile topsoil that is lost, remaining soil is less fertile and the erosion may leave shallower soils which make root penetration more difficult
How does soil erosion lead to sedimentation in rivers and reservoirs?
Soil particles carried into water are deposited if the water slows down and has less kinetic energy
How does soil sedimentation negatively impact the river?
Reduces flow capacity so the river is more likely to overflow and cause flooding following heavy rain
What health problems can an increase is atmospheric particulates cause?
Worsen problems such as asthma
How does soil erosion contribute to desertification?
Important part of the combination of processes that cause the expansion of deserts, it makes it more difficult for vegetation to grow so more erosion occurs and less rainfall
What are some methods of reducing soil erosion?
Long-term crops, zero-tillage cultivation, contour ploughing, tied ridging, terracing, row of stones, windbreaks, multi-cropping, increase soil organic matter and livestock management
How does plantation of long-term crops reduce soil erosion?
Reduces soil disturbance
What are some long-term crops?
Permanent grassland or bush and tree crops such as fruit, tea, coffee and cotton
What is a method of zero-tillage cultivation?
Direct drilling of seeds rather than ploughing or sowing
What is contour ploughing?
Ploughing at 90° rather than vertical on slopes
How does contour ploughing reduce soil erosion?
Reduces velocity of surface runoff and therefore kinetic energy so the soil particles are less likely to be carried away
What is tied ridging?
Used on land that is almost flat, the field is divided with a criss-cross of intersecting ridges
How does tied ridging reduce soil erosion?
The ridges retain water when it rains, increasing infiltration and decreasing runoff
What is terracing?
Creation of narrow fields with the soil held in place by retaining walls built along the contours on sloping land
How does terracing reduce soil erosion?
Water flowing over the walls flows quickly, but it slows down as it flows across the fields, much of the water infiltrates the soil
How do rows of stones reduce the soil erosion?
Can slow runoff and reduce the erosion rate, any disturbed soil is deposited behind the stone rows
What are some examples of windbreaks?
Hedgerows or rows of trees
When are windbreaks needed?
When the crops are removed for harvest and the soil is exposed
How effective are hedgerows at reducing soil erosion?
Reduce wind velocity for a distance up to 30 times its height
How does multi-cropping reduce soil erosion?
Reduce exposure to wind erosion if they are harvested an re-sown at different times
When does multi-cropping work easiest?
When the farming uses human labour rather than machinery as machinery uses ‘strip cropping’ which is most effective at 90°
How does mulch reduce soil erosion?
Protects the soil from wind ad the impact of rain drops
What is the USLE?
Universal Soil Loss Equation
What factors determine the rate of soil erosion?
Rainfall erosivity factor, Soil erodibility factor, Slope length, Slope gradient, Cropping management and Erosion control
