Topic 8: Soil Fertility Flashcards
What is soil fertility?
Soil fertility is the ability of soil to sustain plant growth
What are the features of fertile soil? (9)
Water content
Soluble materials
Air content
Dead organic matter
PH
Soil biota
Soil texture
Soil structure
Soil depth
Why is the water content important in fertile soil?
A fertile soil allows good drainage- doesnt get waterlogged, but retains enough from the survival of soil biota
Nutrients needeed by plants are absorbed in the ionic form that are dissolved in water
What macronutrients do fertile soils contain?
Nitrogen
Phosphorous
Potassium
Present in ionic form: nitrates,phosphates,potassium ions
What micronutrients are found in fertile soils?
Boron
Cobalt
Copper
Iron
Manganese
Magnesium
Why are soluble materials important in fertile soils?
Toxic ions (e.g. aluminium and heavy metas) are absorbed onto the surface of mineral particles (usually clay) s they cannot dissolve in water where they could harm soil organisms
Why is the air content important in fertile soils?
Most living organisms in soil & many processes that increase fertility are aerobic
So well aerated soils are likely to be more fertile
Why is dead organic matter an important feature of fertile soils?
Fertile soils have a high dead organic matter content
It releases plant nutrients as it decomposes
It increases water retention and provides food for soil biota
Why is the PH relevant to a fertile soil?
Has to be in the range of tolerance for plants & soil biota
Acidic soils can increase leaching of plant nutrients & damage root cell membranes
In alkaline conditions, phosphates are insoluble
What is the PH of a fertile soil?
Between 5.5 and 7.0
What are the 5 important examples of soil biota?
Detrivores
Decomposers
Nitrogen-fixing bacteria
Nitrifying bacteria
Mycorrhizal fungi
Examples of detrivores and why they are important in fertile soils
They break up dead organic matter, release nutrients into the soil, increase soil drainage and aeration by tunnelling
E.g. worms. Beetle larvae, millipedes,wood lice,slugs
Examples of decomposers and their importance to fertile soils
E.g. bacteria and fungi
They break down dead organic matter
They secrete digestive enzymes
Rely on detrivores to physically break up dead organic matter and increase its surface area
What is the role of nitrogen fixing bacteria?
Convert gaseous nitrogen to ammonium ions
What is the role of nitrifying bacteria?
Oxidises ammonium ions to nitrite ions, then nitrate ions
What is the role of Mycorrhizal fungi and why are they important in soil biota?
They form symbiotic relationships with plant roots and aid phosphate uptake by plants
What controls the sol texture?
The proportions of different size categories of mineral particles present in the soil
What is the diameter range of clay?
Less than 0.002
What is the diameter range of silt?
0.002-0.02mm
What is the diameter range of sand?
0.02-2.0 mm
Compare the drainage rate of sandy and clay soils
Better drainage in sandy soils- poor in clay
Because of the large pore spaces in sandy soil, so rapid drainage, allowing more aeration but less water content
Compare the capillary action of sandy and clay soils
Tiny pore spaces between clay particles allow water underground to rise towards the surface
No capillary rise in sandy soils
Compare aeration in sandy soils and clay soils
Pore spaces are filled with air in well-drained sandy soil
Clay soils are more likely to be waterlogged with a low aeration rate
Compare nutrient retention in sandy and clay soils
Nutrients ions absorb easily onto clay particles but not onto sand particles
Compare the thermal capacity of clay and sandy soils
High termal capacity in clay soils because of high water content- warm up and cool slowly
Sandy soils have low thermal capacities, warm up rapidly after cold weather
Compare the root penetration of sandy and clay soils
Root penetration is easier in sandy soils because of the capillary water that holds together clay particles- it is harder for plant roots to penetrate that
Compare the ease of cultivation of sandy and clay soils
The lack of adhesion between particles in sandy soils makes it easier to cultivate than clay soils
Loam soils ae the most ideal for cultivating most crops. Why?
They have an even mix of sand,silt and clay (40;40;20)
Ideal properties: good drainage, water retention, high nutrients content
Explain the structure of soil
Soil particles form aggregates called peds
The particles are bound together by polysaccharide gums produced by decomposition, by fungal hyphae, by roots, by soil biota and by hydroscopic clay particles
The ped type affects the soil properties and fertility
What are the types of peds?
Crumb peds
Platy peds
Crumb peds
Small and round
They produce good drainage,aeration, easy root penetration and so improve soil fertility
Platy peds
Large and flat
Reduce drainage, aeration and root penetration
Produce less fertile soils
How does soil depth affect the fertility?
Deeper soils are less likely to become waterlogged and dry out rapidly
They can aid good root anchorage
How can human activities affect soil fertility by affecting aeration?
By ploughing and drainage
It makes the soil more aerobic, which increases rate of :
Nitrogen fixation
Nitrification
Decomposition of dead organic matter
How do human activities increase soil nutrient levels?
By adding inorganic fertilisers or organic matter
By supporting natural processes that increase nutrient levels e.g. bacterial nitrogen fixation
How can farmers deplete soil nutrient levels?
Soil erosion
Biomass removal
Inhibiting natural processes that increase nutrient levels
Increasing leaching of dissolved nutrients
How can irrigation, a human activity, affect soil fertility?
It increases fertility in areas where water is a limiting factor on growth
It can also dissolve nutrients so more can be absorbed by plants in ionic form
How can soil compaction by human activities affect soil fertility?
Excessive use of machinery or high livestock density can compact soil
Reduces aeration, increases chances of water logging
How can ph control by humans affect soil fertility?
It can ensure nutrients are soluble but not too easily leached
