Soil (The physical environment)

Soil fertility

The ability of soil to sustain plant growth

Features of fertile soil

Water content, soluble materials, air content, dead organic matter, pH, soil biota, soil texture

Water content (fertile soil)

Fertile soil needs good drainage so it’s not waterlogged, but has enough water for survival of soil biota

Soluble materials (fertile soil)

Fertile soil contains macro nutrients such as nitrogen, phosphorus, potassium all present in ionic form.

They also contain micro nutrients eg. Boron, cobalt, copper, iron, manganese and magnesium

Behavioir of water between soil particles

1- Hygroscopic water held by adhesive forces on the minera particle cant be absorbed by plants

2- mineral particle

3- gravitational water, can be absorbed by plants, drains easily

4- capillary water, water held by soil particles so does not drain from the soil but can be absorbed by plants

Air content (fertile soil)

Living organisms and other processes that increase fertility are aerobic = more aerated soils are likely to be more fertile

Dead organic matter (fertile soil)

Fertile soils have high content of dead organic matter which releases plant nutrients as it decomposes Whig also increases water retention and provides food for soil biota

pH (fertile soil)

Usually on range of pH5.5-pH-7.0 which is the range of tolerance for most plants and soil biota

What is soil biota

Living organisms involved in soil processes that affect soil fertility

Soil biota (fertile soil examples)

Detritivores such as millipedes, wood lice, slugs break up dead organic matter releasing nutrients into the soil

Nitrogen fixing bacteria oxidise ammonium ions to nitrate pins then nitrate ions

Soil structure (fertile soil)

Soil particles form aggregates called peds bound together by polysaccharide gums produced by decomposition. The ped type affects soil properties and fertility

Crumb peds - small, round, produce good drainage and easy root penetration improving soil fertility

Platy peds- large, flat, reduce drainage and root penetration, produce less fertile soils

Soil depth (fertile soil)

Deeper soils are less likely to become waterlogged or to dry out rapidly

How human activities affect soil fertility

Aeration by ploughing and drainage, soil nutrient levels, irrigation, soil compaction

Aeration by ploughing and drainage (human activities-soil fertility)

Ploughing and drainage make soils more aerobic increasing nitrogen fixation nitrification and decomposition of organic matter

Soil nutrient levels (human activities-soil fertility)

Farmers increase levels by adding inorganic fertilisers, organic matter or supporting natural processes eg. Bacterial nitrogen fixation

Farming decreases levels due to soil erosion, biomass removal, inhibiting natural processes eg increased leaching of dissolved nutrients

Irrigation (human activities-soil fertility)

Increases fertility where water is a limiting factor on growth, sufficient water allows plants to keep stomata open and continue gaseous exchange

Soil compaction (human activities-soil fertility)

Excessive use of machinery/livestock causes soil compaction reducing aeration making water logging more likely

Soil texture

Is the proportions of sand silt and clay in the soil

Soil profile

Unique to an area due to climate, properties of original rocks/minerals, time, relief

Sand soil characteristics

Has large air spaces, best drainage rate, but may lead to nutrient loss

Clay soil characteristics

Smallest particles, small air spaces, prone to waterlogging, lower temperature due to high water retention impacting biota enzymes

drainage pipe systems

Installed systems in soil to prevent flooding and maintain oxygen levels for aerobic processes

Zero-tillage farming

Method of farming that avoids disrupting soil structure to maintain fertility and stable humus levels eg ploughing

Why does crop harvesting reduce fertility

Crops remove nutrients during growth and store them in their biomass

Green manure

Crops grown alongside main crops ploughed back into the soil to increase organic matter instead of being harvested

Leguminous crops

Crops containing nitrogen fixing bacteria in their root nodules deciding the need for fertiliser use

Stomata

Pores on a plants lead for gas exchange, importsnt for photosynthesis and respiration, allows water to leave the plant tissue