QUIZ # 10- ABE-1-MODULE 6 Flashcards
are those activities which maintain or enhance the productive capacity of the soil, water and vegetation in areas prone to degradation through
* prevention or reduction of soil erosion,
compaction, salinity;
* conservation or drainage of water and
* maintenance or improvement of soil fertility
Soil and water conservation (SWC)
are agronomic, vegetative, structural and management measures that control soil degradation and enhance productivity in the field
SWC technologies
are ways and means of support
that help to introduce, implement, adapt and apply SWC technologies in the field.
SWC approaches
are those farming operations and management strategies conducted
with the goal to control soil erosion by preventing or limiting soil particle detachment and transport in water or air (Baumhardt et al., 2014)
Soil conservation practices
- the detachment of soil materials (gravel, sand, silt, and clay) and subsequent transport by an agent to an area of deposition
SOIL EROSION
comes from erodere, a Latin verb meaning “to gnaw”
___________ gnaws away at the earth like a dog at a bone
“Erosion”
most important agent of erosion in humid tropical areas
water
important agent in many parts of the world (in areas with arid climates)
wind
important agent during landslides, mudflows and bankfalls
gravity (mass wasting)
Over a short period, the process of erosion is almost ___________.
invisible
Erosion arises from two types of problem:
◼ Geological problem
◼ Social and economic problem
◼ weathering of surface layers of rock by water and biosphere
◼ Normal geologic erosion - 0.1 t/ha/yr
◼ Geological problem
◼ Urbanization and population growth
◼ Accelerated erosion - 10 to 700 t/ha/yr
◼ Social and economic problem
Erosion events are very _____________.
irregular
Factors affecting Soil Erosion
- Climate ( rainfall, wind )
- Soil erodibility
◼ Soil texture
◼ Soil structure - Vegetation or plant cover
- Relief (Slope)
- Man’s activities
Soil erosion by water depends on:
(1) the slope
(2) the soil structure
(3) the volume or rate of flow of surface
runoff water
steep, sloping fields are more exposed to erosion;
slope:
_____ soils are more sensitive to erosion
light
_________ or ___________ flows induce more erosion
larger or rapid
usually heaviest during the early part
of irrigation, especially when irrigating on slopes.
Erosion
The dry surface soil, sometimes loosened by cultivation, is easily removed by flowing water. After the first irrigation, the soil is moist
and settles down, so erosion is _____________.
reduced
__________ areas are more sensitive to erosion, especially in their early stages.
Newly irrigated
Forms of Erosion by Water
◼ Raindrop splash erosion
◼ Sheet erosion
◼ Rill Erosion
◼ Gully erosion
◼ Stream channel erosion
◼ The first step in the erosion
process begins as raindrops
impact the soil surface.
◼ Raindrops typically fall with a
velocity of 20-30 feet per second.
The energy of these impacts are
sufficient to displace soil particles
as high as two feet vertically.
◼ The impact of a rainfall on a bare
soil can compact the upper layer of
soil, creating a hard crust that
inhibits plant establishment.
Raindrop splash erosion
is the even removal of a very thin layer or “sheet” of topsoil from sloping land.
occurs as runoff travels over disturbed ground, picking up and transporting
particles dislodged by splash erosion.
The process of _______________ is uniform, gradual and difficult to
detect until it develops into rill
erosion.
Sheet erosion
The potential for _____________ is
dependent on the soil type,
velocity, and quantity of flow over
the surface. Long slopes, steep
slopes, and slopes that carry
higher volumes of runoff are
more susceptible to _______________
sheet erosion
◼ only a thin layer of topsoil; or
the subsoil is partly exposed;
sometimes even parent rock
is exposed
◼ quite large amounts of coarse
sand, gravel and pebbles in
the arable layer, the finer
material has been removed
◼ exposure of the roots
◼ deposit of eroded material at
the foot of the slope
Sheet erosion
occurs as runoff begins to form small
concentrated channels. As __________begins, erosion rates increase dramatically due to the resulting
concentrated higher velocity flows.
rill erosion
◼ Construction sites that show signs of ________________ need to be re-evaluated and additional erosion control techniques employed. Rilling can be repaired by tilling and should be repaired as soon as possible in order to prevent gullies
from forming.
rill erosion
is the removal of soil by a concentrated water
flow, large enough to form channels or gullies;
results from water moving in rills, which concentrate to form larger
channels (when rill erosion can
no longer be
must typically be repaired utilizing earthmoving equipment. _______________ can be prevented by quickly repairing rill erosion and
addressing the cause
Gully erosion
The signs of _____________ on an irrigated field are:
◼ irregular changes in the shape and length of the furrows
◼ accumulation of eroded material at the bottom of the furrows
◼ exposure of plant roots
gully erosion
-consists of both stream bed
and stream bank erosion.
◼ Stream bed erosion occurs as flows cut into the bottom of the channel, making it deeper and reaches a stable
slope. - The resulting slope is dependent on the channel materials, and flow properties.
Stream channel erosion
◼ Stream bank erosion can also occur as soft materials are eroded from the stream bank or at bends in the channel. This type of stream bank erosion results in meandering waterways.
◼ One significant cause of both steam bed and stream bank
erosion is due to the increased frequency and duration of
runoff events that are a result of urban development.
Stream channel erosion
Mechanics of Soil Erosion Process
- Soil detachment by rain fall
- Entrainment of Sediment
- Sediment Deposition
process by which raindrops splash
sediment from the soil surface into the water of overland flow or runoff water.
Soil detachment by rain fall
the process whereby overland flow
picks up sediments from the soil surface, whether in rills, between
rills and in sheet flow.
Entrainment of Sediment
the process which is the result of sediment settling out under the action of gravity.
The rate depends on sediment size, being very rapid for coarse (sand) and very slow for fine ( silts and clay) particles, thus the silts and clays are transported and deposited farther away from where they
- Sediment Deposition
occurs when eroded material that is being transported by water, settles out of the water column onto the surface, as the water flow slows
SEDIMENTATION
◼ Kinetic energy
◼ Slope of the land
◼ Cover
◼ Resistance of the soil to detachment
and transport based on chemical and
physical properties of soil
◼ Conservation factors
IMPORTANT FACTORS TO SOIL EROSION
◼ predicts the long term average annual rate of erosion on a field slope based on rainfall pattern, soil type, topography, crop system and management practices
A = R x K x LS x C x P
Threshold level of soil loss
- 8-12 tons/ha/yr
- 4 tons/ha/yr (thin topsoil)
Limitations:
can be used for splash erosion only
cannot be used in other country unless you modify R
Universal Soil Loss Equation (USLE)
was developed using the English system of units. Its equivalent form in the metric unit system is presented by Kent Mitchell and Bubenzer (1981) as
E = 0.224 R K L S C P
where:
E = sheet erosion loss in kg/m2
R = rainfall erosivity factor
K = soil erodibility factor
L = slope length factor
S = slope gradient factor
C = cropping management factor
P = erosion control practice/conservation factor
The UNIVERSAL SOIL LOSS EQUATION
has gained wide acceptance in the United States. It has recently been adapted by soil conservationists in many other countries.
The UNIVERSAL SOIL LOSS EQUATION
was developed from agricultural plots with certain ranges of variations in soil, climatological and slope conditions.
The UNIVERSAL SOIL LOSS EQUATION
Very simple to use, however, the validity of the _______ depends on how close the conditions to which it is
being applied at are to the range of conditions from which it was developed. It is best suited to small areas with low to moderately intense rainfall.
The UNIVERSAL SOIL LOSS EQUATION
◼ 72.6 ft long
◼ 6 ft wide
◼ 9% slope
◼ Bare
◼ plowed up and down the slope
◼ no conservation measure
STANDARD EROSION PLOTS
The control of soil erosion and
sedimentation needs to be based on the correct identification of source areas of sediment, a knowledge of the processes by which water and sediment are moved over the land surface, and an understanding of
how these processes are affected by the physical environment and socio-economic factors.
Erosion Control Principles
◼ use land according to its capability
◼ protect the soil surface with some form of cover
◼ control runoff before it develops into an erosive force
Three main principles
◼ The method used to prevent erosion from raindrop splash and sheet erosion is _____________.
stabilization
-temporary and permanent vegetation
-mulching
-compost blankets
-erosion control products that absorb the impact of raindrops
Examples of stabilizing techniques
Under erosion control practices
- Mulching
- Cover cropping
- Strip-cropping
- Crop Rotation
- Relay Cropping
- High Density Planting
- Multiple Cropping
- Alley Cropping (Sloping
Agricultural Land Technology ) - Agroforestry
Agronomic Measures
Under erosion control practices
1. Contouring
2. Minimum Tillage
3. Strip of Zone Tillage
(Precision Tillage)
4. Mulch Tillage
5. Subsoiling
6. Ridge-tying
Soil Management (Conservation Tillage)
Soil Management (Conservation Tillage)
1. Terracing bench
Zingg or conservation bench terraces
broad-based
2. Grassed Waterways
3. Structures (Farm ponds and check dams)
4. Toward Soil Conservation – oriented Farming Systems
Mechanical Methods
is an earth embankment or a ridge
and channel constructed across the slope at an acceptable grade.
terrace
- reduce sheet and rill erosion
- prevent gully formation
- moisture conservation
- moderate flood or overland flows
Functions of a terrace
TYPES OF A TERRACE
-BENCH
-ZINGG
-broad-based terrace
e.g. Banaue Rice Terraces
➢ used for maximum moisture conservation
➢ used where land is at a premium
➢ conventional
BENCH
e.g. Banaue Rice Terraces
➢ used for maximum moisture conservation
➢ used where land is at a premium
➢ conventional
BENCH
◼ easier to farm than conventional
◼ used for maximum soil and water
conservation
ZINGG
may either be graded or level.
◼ grade – fall in channel
◼ slope – fall in natural land surface
broad-based terrace
◼ Terrace location
◼ Factors that influence terrace location (e.g. land slope, soil condition)
Criteria for terrace location
◼ Minimum maintenance
◼ Ease of farming
◼ Erosion control
Planning the terrace system
- The allowable soil loss should be first estimated using relevant information on soil depth, fertility, land value, siltation damage downstream, etc.
- In the absence of soil loss information, the spacing may also
be estimated from appropriate erosion equations such as the universal soil loss equation. - No hard and fast rules can be laid down to follow in terrace layout because every field has its own individual problems.
- Good judgment and consideration of all factors are required to obtain the best possible layout terraces on each field.
Terrace Design
