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