lecture 2. edaphic factors

Edaphic Factors

Edaphic factor

• Gk ‘edaphos’= ground, soil

• Abiotic factor

• Relating to the physical or chemical components of the soil found in a particular area

– Temperature

– pH

– Mineral composition

Soil

• The biologically active, porous medium that has developed in the uppermost layer of the Earth's crust.

• Natural reservoir of water and nutrients

• Medium for the filtration and breakdown of injurious wastes

• Foundation of all terrestrial ecosystems.

– Habitat of billions of plants, animals, and microorganisms that take part in the cycling of nutrients

Soil

• Evolved through the weathering of solid materials. The bulk of soil consists of mineral particles composed of silicate ions combined with various metal ions.

Soil Profile

• Texturally distinct layers or horizons

• Different for every area

Soil Classification Map

Tropical climate

Soil Temperature

Color • Dark soil absorbs more energy than light colored

soil.

Slope • Greater absorption can be observed as the angle of

incidence of the sun's rays approaches perpendicular to the soil surface.

Vegetative cover of the soil • Bare soil warms and cools faster than soil with

vegetation.

Importance of Temperature

• Heat is the catalyst for many biological processes.

• Soil temperature is primarily important in growing plants.

Soil pH

• Soil pH greatly influences nutrient availability and solubility in plants.

– Acidic soils are often low in nutrient concentrations.

• Soil pH also determines the presence of different microorganisms

• An indicator of corrosiveness of the soil.

Factors affecting soil pH

• pH of the soil can be affected by different factors such as:

– mineral content of the soil

– climate

– weathering

– properties of rainfall

– induced fertilizers

Soil Moisture

• Water that is held in the spaces between soil particles

• Related to water-holding capacity of the soil and heat-capacity of soil

Organic Matter

• Serves as the “revolving nutrient bank account”

• Serves as a reserve for many essential nutrients, especially nitrogen

• Serves as an agent to improve soil fertility and hold important plant nutrients e.g. by adding organic matter to sandy soil, the ability of the soil to retain water increases

Organic Matter

• Organic matter is related to soil color

– The darker the soil, the more organic matter

Soil Nutrients

• Nutrients are required for plants to grow and develop.

• Low nutrient levels result in stunted growth, low flowering and fruit production

• Can be supplied by the addition of fertilizers (inorganic or organic)

• Two categories:

– Macronutrients • Primary nutrients - NPK

• Secondary nutrients – Ca, Mg, S

– Micronutrients (B, Cu, Fe, Cl, Mg, Mo, Zn)

Calcium

• Secondary macronutrient

• Construction of cell walls and proper functioning of growing tissue

• Calcium deficiency: extremely acidic soil

• Necrosis around the base of the leaves

Nitrogen

• Primary Macronutrient

• Green leaf growth chlorophyll

• Nitrogen deficiency

– Stunted growth

– Pale green and yellow leaves

Phosphorus

• Primary macronutrient, mobile

• Cell development, promotion of good root growth, flowering, fruiting, and ripening

• ATP component, biomolecules NA, phospholipids

• Limited in most soils because it is release vey slowly from insoluble phosphates

• Phosphorus deficiency – Intense green color, Poor root development

– Purplish leaves abnormal increase in sugar content & anthocyanin

Soil Texture

• Used to designate the proportionate distribution of the different sizes of mineral particles in a soil

Soil Pyramid 40% sand + 40% silt + 20 clay = loam

10% sand + 45% silt + 45% clay = ?

55% sand + 15% silt + 30% clay = ?

Soil particle size classification

USDA System ISSS System

Category Size (mm) Category Size (mm)

Clay <0.002 Clay <0.002

Silt 0.002-0.05 Silt 0.002-0.02

Very fine sand 0.05-0.10

Fine sand 0.10-0.25 Fine sand 0.02-0.2

Medium sand 0.25-0.5

Coarse sand 0.5-1.0 Coarse sand 0.2-2

Very coarse sand 1.0-2.0

USDA – US Dept. of Agriculture ISSS – International Soil Science Society Milne et al. 1991. Soil Description Handbook. DSR. Land Resources. Lower Hutt

Soil particle size classification

For large particles (Milne et al. 1991)

Category Size (mm)

Fine gravel 2-6

Medium gravel 6-20

Coarse gravel 20-60

Very coarse gravel 60-200

Boulders >200

USDA – US Dept of Agriculture ISSS – International Soil Science Society Milne et al. 1991. Soil Description Handbook. DSR. Land Resources. Lower Hutt

Soil Structure

• Refers to the grouping of soil particles into porous compounds; arrangement of aggregates into larger clumps

• Influenced by soil texture

• Types of aggregate arrangements: – Granular

– Blocky

– Prismatic

– Columnar

– Platy

– Singly grained

Types of Soil Structure

• Granular – resembles cookie crumbs; usually less than 0.5 cm in diameter; commonly found in surface horizons where roots have been growing

• Blocky – irregular blocks that are usually 1.5 – 5.0 cm in diameter

• Prismatic – vertical columns of soil; usually found in lower horizons

Granular Blocky Prismatic

Types of Soil Structure • Columnar – vertical columns of soil having salt ‘caps’ at the top; found

in soils of arid climates

• Platy – thin, flat plates that lie horizontally; usually found in compacted soil

• Single grained – soil is broken into individual particles that do not stick together; loose consistency; commonly found in sandy soils

Columnar Platy Singly grained

The size and shape of clumps affect the capacity of soil to hold water, air, and nutrients.

GRANULAR PLATY BLOCKY

Field Capacity

• Maximum amount of water that a particular soil can hold

• Water exists in soil capillaries; pores small enough to hold water against gravity

• Soil texture

– Field capacity will be reached faster in coarser textured soil (loamy soil) than fine-textured soil profiles (clay)

• Soil structure

– Amount of aggregation determines the amount of pores available to hold water

• Since forces holding water are surface-attractive forces, the more surface area a soil has, the greater is the amount of water adsorbed.

• Field capacity comparisons

– SAND: LOWER FIELD CAPACITY lower surface area, large pores favor rapid water infiltration and drainage

– CLAY: HIGHER FIELD CAPACITY, higher SA, small pores greater active surface for adhesion of water molecules.

Field Capacity

Cation-Exchange Capacity (CEC)

• Ability of the soil particles to adsorb and exchange cations that are loosely bound to its surface

• Measure of how many negatively-charged sites are avaialble in the soil

• Highly dependent on soil texture and OM content

– More clay, more OM higher CEC

– Clay

• weakly (-) charged: higher affinity to cations

• higher surface area exposed

– Organic matter

• has both (+) and (-) sites

Cation-Exchange Capacity

• Measure of fertility, nutrient retention capacity, and the capacity to protect groundwater from cation contamination

• Ideally, CEC for agricultural soils is between 10 and 30 meq*/100g (sandy loam- loam)

– Higher CEC – more clay

– Lower CEC – more sand

* Milliequivalents takes into account both the weight and the charge of the cation

Determine the following parameters:

• Temperature

• pH

• Soil moisture

• Amount of organic matter

• Presence of nutrients (calcium, nitrates, phosphorus)

• Soil texture

• Soil inhabitants

Act. 2: Edaphic factors and the soil inhabitants

Act. 2: Edaphic factors and the soil inhabitants

1. Examine important ecological properties of soil.

2. Compare soil characteristics in various habitats.

3. Determine what organisms live within the soil medium as well as their adaptation, abundance, and over-all ecology.

Soil Profile

Dig at least 1 ft. below the ground

Collect soil samples in each major soil horizons

Take note the differences in color, structure, and thickness within the major horizons

Soil Temperature

Equilibrate thermometer for two minutes

Bury thermometer 3-6 inches below the ground and take 5 readings.

Determine the soil temperature profile by plotting the soil temperature on the horizontal axis and the depth of the soil on the vertical axis

Soil pH

Mix soil and distilled water in equal amounts

(1:5 dilution; 10g with 50mL of water)

Allow soil particles to settle until a clear supernate forms

Take soil pH using a pH meter

Soil Moisture

Oven dry 10g of soil placed in a pre-weighed crucible

(105ºC for 24 hours)

Allow to cool in a dessicator. Weigh.

The dry weight sample is computed as the weight of the container with the oven-dried sample minus the weight of the

container alone: (Wd = Wo – Wc)

Calculations

Amount water = Fresh weight – Dry weight

% water in sample = Fresh weight – Dry weight

____________________________

Fresh weight

X 100

Soil Organic Matter

Take 1-5 g oven-dried sample and place onto a pre-weighed crucible (Wc). Weigh (Wo).

Heat in a furnace at 450ºC overnight. Cool. Weigh. (Wi)

weight of the ignited soil sample (Wi – Wc).

organic matter content (Wo – Wi), % of dry weight of the sample.

Calcium Test

Combine 10 drops of soil supernate + 10 drops of 5g ammonium oxalate solution in 100mL distilled water

Shake vigorously. Observe after 5 minutes.

POSITIVE: milky-white precipitate

NEGATIVE: no color change

Calcium Test

Add soil and 10% HCl in a crucible

POSITIVE: Effervescence. Amount is estimated using a table of determination of % CaCO3

Effervescence carbon dioxide in the atmosphere Higher calcium carbonate present, the louder effervescence

% CaCO3 Audible Effect Visible Effect < 0.1 None None 0.5 Faint None 1.0 Faint-moderate Barely visible

2.0 Distinct

Heard away from ear Visible from very close

5.0 Easily heard Bubbles up to 3 mm easily seen

10.0 Easily heard Strong effervescence

With bubbles of 7 mm

(After Clarke, 1957)

Determination of % CaCO3 in soil sample

Nitrate Test

Combine 10 drops of soil supernate + 10 drops of solution (0.33g diphenylamine

in 25mL H2SO4) in a test tube

Shake vigorously. Observe after 5 minutes.

POSITIVE: brown - blue color

Phosphorus Test

Combine 10 drops of soil supernate + 10 drops of solution (5g ammonium molybdate, 50mL distilled water and 50mL concentrated HNO3) in a test tube

Add a piece of tin. Shake. Observe after 5 minutes

POSITIVE: gray to deep blue coloration

Field Key To Soil Texture

SAND LOAMY SAND LOAM SANDY LOAM SILT LOAM CLAY LOAM SANDY CLAY LOAM

SILTY CLAY LOAM SILT CLAY SANDY CLAY SILTY CLAY

Preliminary • Feeling the soil grainy or sticky •Sandy or clayish, may color hand Moisten 10-15cm soil. Knead and try to mold into a ball. Follow key to make a rough classification.

Soil Inhabitants

Collect litter in the site and place in a plastic bag.

Add few drops of chloroform / ether. Wait for 5 minutes.

Empty the contents in a white paper and look for soil invertebrates. Preserve in a small jar of alcohol or formalin.

Soil Inhabitants

Place the collected soil sample in the Berlese-Tulgren apparatus.

Observe for any organisms that will fall in the receptacle. Identify. Leave for 2 days.

Continue observation and identification of soil invertebrates.

Berlese-Tulgren apparatus

• Made up of a light bulb, aluminum foil funnel, gauze, and a test tube with formalin.

• The organisms were forced to crawl downward because of the heat and light from the bulb.

– Light heats and dries soil

– Positive geotaxis in response to dryness

Berlese-Tulgren apparatus

• Limitation: Biased sample of soil fauna

– Based on specific avoidance behavior triggered by dryness

– Best captures mobile animals and those that do not dessicate easily

– Immobile larvae, endophagous nymphs and soft-bodied invertebrates such as nematodes not extracted by a Berlese funnel.

Area designation

Group Area

1 and 6 Lagoon

2 and 7 Old G. Silang Building

3 and 8 Water tank / Sining Lahi Headquarters

4 and 9 Gym / PE building

5 and 10 Oval