soil exam3

What is a soil catena?

The sequence of different soils down a slope, the soils usually derived from the same or similar parent materials but they vary with relief, drainage, and land use. Every disturbance affects all the ecosystems around it.

what are the effects of routine soil disturbance?

Short-term- Increase in porosity that allows water infiltration, facilitates seed germination, and establishment of seedling

Long-term

• increase in bulk density and decrease in porosity

• decrease organic matter content and reduce microbial diversity

• Reduce ability to store water and nutrients

what are the effects of forest conversion on forest soil properties and erosion risk?

• increase in bulk density and penetration resistance(compaction)

• smaller aggregates(mean weight diameter)

• decrease in infiltration

• increased erosion risk because tree canopy is removed

How does forest conversion lead to water table rise and formation of saline soils?

Trees have deep roots that take up a lot of water and when they are replaced with shallow-rooted crops the water table rises. Salt content rises when the water table rises because the water and salt rise to the surface, the water dissolves and the salt stays.

What effects do grassland conversion have on soil properties?

• decrease in organic matter content

• Overgrazing can cause higher sand content

• Animals hooves lead to compaction

• smaller aggregates and lower infiltration rate

Why are wetland areas “attractive” for conversion to agricultural and commercial/residential uses?

• they make good ag fields because of high organic matter content

• wetlands in coastal areas are highly valued for residential development

What happens when the wetland is drained and converted to other uses?

• increases the rate of organic matter decomposition, more co2 emissions,

• soil subsidence

• Changes in properties, destroys soil peds and decrease in water holding capacity

• higher rate of nutrient mineralization. and release of complexed pollutants

What are the unique properties of urban soils?

• disturbed in a portion of profile or whole thing

• mixing, filling, and contamination creates a soil material that is unlike its natural counterpart

• could be contaminated with pollutants

Basics about soil loss process

Erosion- wearing away of the land by water or wind

• natural and accelerated erosion

• detachment, transport, deposition

• overgrazing, deforestation, mismanagement of cultivated lands

What are the leading causes of water-induced accelerated erosion?

1. overgrazing 35%

2. deforestation 30%

3. mismanagement of cultivated lands 28%

How do soil properties change because of erosion?

increase- crusting, compaction, sand content, salinity, acidity, water pollution, greenhouse gas(c02), eutrophication, organic matter decomposition

decrease- topsoil depth, structure, porosity, water infiltration, plant available water capacity, nutrient exchange, biomass production, organic matter

The wind erosion process. What are the different modes of wind-induced sediment transport?

wind moves 40% of soil tranported by erosion in us, problem in 75mil acres of land in us.

-saltation- short bounces along ground, 50-90%

-creep- rolling or sliding of larger particles, 5-25%

-suspension- fine sand is carried up into the air, 15%

What is agroforestry?

a land management system that combines trees and/or shrubs with agricultural crops and even liverstock production on the same piece of land. grows trees and crops, improves bulk density and water infiltration and yield, trees slow water erosion, give organic matter, buffer wind erosion, and can be additional income

Erosion control and rehabilitation of saline soils

cultural control- water(conservation tillage, cover cropping, mulching, proper timing of cultivation, addition of soil conditioners, contour cultivation, strip cropping or planting buffer strips/vegetation barriers) wind(maintain surface cover, conservation tillage, wind breaks, keep surface moist and rough)

engineering control- riprap, terracing, bioengineering, sediment traps, retention ponds

salinity- leaching soils by applying water or lower water table by drainage or by planting deeply rooted vegetation

conventional tillage

soil tillage such as plowing to produce a porous seedbed, and also the removal of the of the plant residue from the previous crop

conservation tillage

a system of soil cultivation that involves limited disturbance and leaves at least 30% of the soil surface covered with residues

types of conservation tillage

• no till

• strip till

• ridge till

short term and long term effects of soil tillage

• short term- increase in porosity that allows for water infiltration, facilitates seed germination, and establishment of seedling

• long-term- increase in bulk density and decrease porosity, decrease in oraganic matter and reduces microbial diversity, reduce ability to store water and nutrients

mono-cropping

planting the same crop year after year, decreasing soil fertilty, quality of physical properties, and microbial diversity

crop rotation

growing a series of different crops in the same area, improves soil fertility, organic matter content, and microbial diversity

forest

a non-agricultural land with at least 10% tree cover. 30% of total terrestrial surface

functions of forest soils

1. foundation of forest ecosystems and productions of forest products

2. carbon sequestration

3. water storage

slash and burn agriculture/ fire fallow

trees are cut down and burned for cultivation, farmers move on once the soil becomes infertile after a few years

grasslands

area where vegetation is dominated by grasses, thin soil, sloping areas, shallow water table, bad weather. they have great amounts of organic matter

overgrazing

having too many animals grazing in an area of keeping animals in one spot for too long. increases sand content, decreases organic matter, aggregate stability, and infilitration rate

wetlands

occur in transition zones between well-drained uplands and true aquatic habitats. has hydric soils, certain vegetation, and hydrology

hydric soil

soils formed under consitions of saturation, flooding or ponding long enough during the growing seasonto develop anaerobic conditions in the upper part. have unique features that are a result of organic matter accumulation and or redox reactions involving iron and manganese

soil subsidence

a drop in elevation of the soil surface resulting from the combined effect of organic matter decomposition due to aerobic conditions and decrease in volume of organic soils due to loss of water

urban soil

soil material previously utilized for more natural uses that has a man-made surface layer >50cm think produced by mixing, filling or by comtamination of land in urban and suburban areas

general characteristics of urban soils

1. great vertical and spatial variablity

2. modified soil structure leading to compaction

3. presence of a surface crust on bare soil

4. restricted aeration and water drainage

5. presence of anthropic materials and other contaminants

natural v. accelerated erosion

natural happens under natural environmental conditions and accelerated is more rapid usually as a result of human activities

to control erosion what part of the erosion process needs to be prevented

detachment

on site effects of soil erosion

• soil structural degradation and compaction

• nutrient depletion

• loss of soil organic matter

• poor seedling emergence and reduced crop yields

off site effects of soil erosion

sedimentation and sedment pollution

alteration of landscape

runoff

that portion of precipitation or irrigation in an area that does not infiltrate, but instead moves out of the area by surface flow

splash erosion

the detachment and airborne movement of small soil particles caused by the impact of raindrops on soils

sheet erosion

the removal of a relatively uniform thin layer of soil from the land surface by rainfall or irrigation and surface runoff; soil particles are easily transported in a thin layer by water flowing on surface. #1 cause of erosion is ag lands!

rill erosion

process on sloping areas in which numerous and randomly occuring small channels of only a few inches in depth are formed, occirs mainly on recently opened or cultivated areas

gully erosion

process where water accumulates and often recurs in narrow channels and over short periods removes the soil from this narrow area to considerable depths. too deep to easily repair with regular tillage equipment

stream erosion

erosion that occurs along the banks of streams

what is the threshold velocity for wind erosion to occur

15mph

factors affecting wind erosion

1. wind velocity and turbulance (15mph)

2. surface roughness

3. soil properties (moisture content, aggregate stability, and size of erodible fractions)

how many years does it take 1in of soil to form and how long does it take to wash away

500, 1 rain event

how to deal with land use changes

prevention, minimize impact, rehabilitate

how far do wind breaks protect the soil

30x the height of the tree