Soil and Water Conservation 3080

Modes of wind transport: saltation

- 0.1-0.5 mm particles, greatest magnitude of transport - Move by bouncing/saltating along soil - Can jump as high as 1 m (depending on size etc) - Coarse particles no higher than 1 cm - Velocity of parcels 1/3-1/2 wind velocity - During this process particles can break down and transfer into suspension

Modes of wind transport: Surface creep

- 0.5- 2 mm particles creep/roll along surface - May collide with no creeping parcels (pebbles, rocks etc) - During this process particles can break down and transfer into saltation - Accounts for 1/3 of transport

Erosivity of Rainfall: Terminal Velocity

- Accelerates its velocity unil the air resistance = the gravitational force and then falls at a constant velocity - (can) strike soils at 35 km/h - Displace soil horizontally 2 m - Displace soil vertically 1 m - Increases with increase in raindrop size - if 5mm in diameter terminal velocity is about 9 m/s

Erosivity of Rainfall: Intensity

- Amount of rain per unit of tim e( mm/h) - < 70 mm/h = temperate - (As high as) 150 mm/h for tropical - Intense stoms = short - Directly correlated with erosion - Models use kinetic energy based on it - Obtained from daily rain gauges

Erosivity of Rainfall: Drop Size

- Ranges between 0.25-8mm (avg 2-5 mm) - Intense storms can have sizes up to 8 mm - drop size increases with increase in rain intensity but has threshold of 100 mm/h - Drop stain paper and flour-pellet methods use to measure raindrop size distribution

Erosion control: Biological; soil conditioner

-Any material which measurably improves specific soil physical characteristics or physical processes for a given use or as a plant growth medium -Natural or synthetic substance that is added to the soil in small quantities which typically reacts rather rapidly with soil particles to improve one or several soil properties

Erosion control: Buffers

-Are strips or corridors of permanent vegetation used to reduce water and wind erosion -Designed to reduce water runoff and wind velocity, filter sediment, and remove sediment- born chemicals leaving upland ecosystems -Prevent slope failure, bind soil aggregates, improve the structure characteristics and increase soil organic matter content and water transmission characteristics

Erosion Processes: Splash Erosion

-Caused by the bombardment of soil surface by impacting raindrops -Involve raindrop impact, splash of soil particles, and formation of craters

Erosion Processes; run off erosion: Gully Erosion

-Creates either V or U shaped channels -Primarily formed by concentrated runoff converging in lower points of the field -Erosion in these channels are called concentrated flow erosion -As gullies grow more sediment is transported

Erosion Processes: Transport

-Detachment of soil releases fine soil particles which form surface seals -These seals plug the open-ended and water-conducting soil pores, reduce water infiltration, and cause runoff - Leaves behind coarser surface texture altering original texture of soil because of selective transport process (only small)

Erosion Processes; run off erosion: Interill/sheet Erosion; Due to and Function of

-Due to shallow flow -Runoff promptly develops diminute rills and the portion of runoff that flows between rills is called sheet or interrill erosion -70% of total soil erosion (most common type) -Function of particle detachment, rainfall intensity, and field slope

Erodibility of soil by water: Permeability

-Is correlated with with all aspects listed above ~ Texture: larger size of particles allows for greater permeability ie water flow through soil profile ~ The greater presence of aggregates indicates a greater structure strength and permeability ~ The increase of Organic matter increases structure and thus aggregates and porosity of a soil - BUT if any aspect past a certain threshold will negatively impact erosion and permeability

Erodibility of soil by water: texture

-More corse soils are less cohesive and detach quickly compared to fine soils (usually more well aggregated) -Once abraded into smaller particles they are detached and readily removed by runoff -Water infiltration is correlated with an increase in coarse soil particles allowing for greater permeability = more erodible (to a point)

Erodibility of soil by water: OM

-Physically, chemically, and biologically binds primary particles into aggregates -Supply cementing and binding agents and promote microbial processes responsible for the enrichment of soil particles into stable aggregates -Stability increases with an increase in organic matter content - But too much OM can cause water saturation, anaerobic conditions and erositvity

Erosion control: Biological; soil conditioner; PAM example

-Polymers with high molecular weights, are used to reduce soil erosion particularly in irrigated soils -Wide range of molecular weights and formulation types and can be cationic, anionic, and non-ionic -Applied on the soil surface and is not incorporated into the entire plow layer -Benefits include the reduction of runoff and soil loss and plant growth o Increases nutrient uptake, root and plant growth, and plant available water o Reduced runoff, sediment losses, losses of nutrients and the transport of microorganisms

Erodibility of soil by water: structure

-Soils with poor soil structure are more detachable, unstable, and susceptible to compaction, thereby have a low water infiltration and high runoff rates (coarser soils)

Erosion control structures: WASCob; Broad Based

10:1 side slope, enables berm (berm and pipe stick our of land) to be entirely cropped and no land taken out of production

Tolerable Soil Loss (T value) =

11 Mg/ha*yr;

Erosion control structures: WASCob; Narrow Based

3:1 side lopes, permanently vegetated, lower cost as less soil used in construction Parameters used to determine berm location: beams parallel to one another spaced 91 m over 700 m with slope that exceeds 5% Fairly steep 20 ha watershed needed to protect against rill erosion by drainage way

Modes of wind transport: suspension

< 0.1mm particles suspended in air as too small to over come upward current - Remain in air (floating) until upward wind drops below threshold level of particle weight - Also deposit on soil when rains

Erosion control structures: WASCob advantages

Aid in sheet/rill and gully erosion when row cropped

Tillage systems: Conservation Tillage

Any system that reduced the number of tillage operations, maintains residue cover on the soil surface, and reduces the losses of soil and water relative to conventional tillage Set of innovation technologies including no till and various reduced or minimum tillage systems such as mulch tillage, strip tillage and ridge tillage

Tillage systems: Conventional tillage

Any tillage system that inverts the soil and alters the natural soil structure Refers to moldboard plowing which is the ultimate means of soil disturbance

Erosion control: Buffers; Grass barriers

Are narrow strips of dense tall and stiff stemmed perennial grass; stiff robust stems adapted to local soil types and climates and are commonly planted to native warm grass species Established perpendicular to the field slope to control erosion while decreasing slope with

Erosion control structures: Grassed Water Ways

Are natural or contrasted channels of dense and deep-rooted grass species Established along the bottom perimeter of upland agricultural fields to drain and retard surface runoff while preventing formation of gullies and runoff erosion along the waterways

Cropping systems: Rotation

Are systems in which different crops are grown sequentially on the same field in alternative season or years Switching crops in a recurring fashion under a planned sequence contrasts with continuous monoculture

Tilth

As the physical condition of a soil described by its complex and dynamic macro and micro scale (physical, hydrological, thermal, chemical and biological attributes affecting tillage, seedling emergence, root penetration and plant growth)

Benefits of tillage system

Conserves soil and water while improving tilth and increasing soil organic matter Depends on the soil specific, topographic and climate characteristics Impacts noted within the upper soil horizons where most crop residues are concentrated

Cropping systems: fallow system

Consist of leaving a cropland either uncropped, weed-free or with volunteer vegetation for at least one growing season in order to control weeds, accumulate and store water, regenerate available plant nutrients and respire soil productivity.

Erosion control structures: Grassed Water Ways: Plant

Cool season and sod like forming species are mostly used for constructing waterways in the US Mixture of native and warm season species such as switch grass and big bluestem are recommended

Cropping systems: Monoculture

Cropping system in which the same crop is grown in the same field on a continuous basis Single most common cropping system worldwide Large scale or industrialized farming Makes planting and harvesting easy but it makes the soil susceptible to erosion hazard, weed invasion and pest and disease infestation

Erosion control structures: Grassed Water Ways: Shape

Cross sectional area is often trapezoidal, parabolic or triangular, depending on the field topography Flat bottomed channels spread concentrated runoff, increase runoff residence time and enhance water infiltration more than V shaped waterways

Erosion control: Biological; soil amendments

Defined as any material that is either left on the soil surface or incorporated into the surface layer to decrease runoff and soil erosion while also improving soil properties. -Effective when used in conjunction with the introduction of conservation tillage systems as opposed to traditional practices where amendments are plowed under - Benefits including reduction of soil erosion and improvement in soil physical, chemical and biological properties

Erosion Processes; run off erosion: Gully Erosion; control structures: Chute Spillways

Designed to control over flows within gullies and grassed waterways Using concrete blocks, gabion mattresses, rock ripraps, geotextile revetments, and wood materials to transport concentrated runoff water down steep slopes and convey it all reduced velocities

Tillage systems: Moldboard plowing

Designed to control weeds, loosen compact soils, incorporate residues and fertilizers into the soil, and improve seed germination Changed the shaped of fields and increased the size of the cultivated area Increased food supply in developed counties

Erosion control structures: Terraces

Earthen embankments established across the dominant slope partitioning the field in uniform and parallel segments Break the field slopes and reduce the scouring capacity of the incoming runoff Main goal is to conserve soil and water

Erosion control structures: Division terraces

Established to redirect runoff to stable vegetated waterways Removed natural vegetation and adds sediment to water Wetland adjacent to the main channel of a river Created by pumping sediment and nutrient water or flooding from the main channel Perpendicular to main gully

Tillage systems: Tillage erosion

Gradual soil displacement downhill caused by plowing Important component of total soil erosion on sloping croplands Effect of tillage erosion on soil productivity is site specific Major problem on sloping terrains where agriculture is practiced on soils of 20-80% slope gradients Modified the soil profile, alters soil properties and reduced soil productivity

Erosion control: Buffers; Filter Strips

Grass or other permanent vegetation Planted between agricultural fields and streams FOR reducing sediment, nutrient and other pollutants in water runoff to improve downstream water quality

Erosivity of Rainfall: Amount

More rain = more erosion - Function of duration and intensity - Rain gauges measure this and dependent on specific gauge - Height of gauge and wind drift effect measurement - Available data only point estimates of area

Erosion control structures: Grassed Water Ways: Management

Must be as continuous and wide as possible to maximize their effectives

Erosion control: Buffers; Field Boarders

Narrow bands or perennial vegetation Established around of or at the edge of farm lands, around road ditches and grassed waterways Decrease wind and water erosion, Improve air quality, increase C biomass input, reduce incidence of invasion of insects to farms and improve farm aesthetics Differ from other buffer strips in the way they are establish uphill and downhill sides of the field

Erosion Processes: Rill Erosion; run off erosion; Due to and Function of

Occurs in small channels or rills -Due to concentrated flow; runoff water that concentrates in small channels erodes soil at faster rates than interrill erosion -Second most common pathway of soil erosion -Function of soil erodibility, runoff transport capacity and hydraulic shear of water flows

Erosion control structures: WASCob disadvantages

Only possible on more fine soils (not sand) Not possible on shallow sub-soils with properties limiting plant growth

Erosion Processes; run off erosion: Gully Erosion; control structures:Large diameter drop pipe

Permanent structure absorbs concentrated runoff and reduces gully erosion by directing runoff through a well-designed drop spillway

Erosion Processes; run off erosion: Gully Erosion; control structures: Gabions

Permanent structure consisting of rocks and stones wrapped in metallic fences and stacked atop one another and are part of the traditional techniques used for retaining walls, protecting culvert headwalls, stabilizing damns, dikes and channels Reduce gully erosion by reducing runoff velocity, by promoting sedimentation and by reducing flow channelization Advantageous of using this over concrete structures is their relative flexibility and natural adjustment to moderate changes in soil or foundation settlement

Cropping systems: Contour farming

Practice of tilling, planting and performing all cultural operations following the contour liens of the field slope This practice contrast with up and down slope farming which is the least desirable practice on highly erodible sloping lands

Reclamation (in regards to gullies mainly)

Procedures include deep ripping, contouring, revegetation with proper fertilization and liming, repacking and consolidation of soil surface, diversion of concentrated runoff and reduction of runoff ponding Attempt to bring back to similar conditions to the underoded portions of the fields which involves refilling the channels, re shaping surface with soil from neighbouring fields

Consequences of tillage systems

Reduce soil structure over time due to alterations of so profile continuously Can actually increase erosion

Tillage systems: Tillage

Refer to the mechanical operations performed for seedbed preparation and optimum plant growth Involves a sequence of mechanical operations including tilling the soil, chopping and incorporating crop residues, planting crops, controlling weeds before and during plant growth, applying fertilizers and pesticides and harvesting crops Tillage alters the soil tilth and the nature of the whole soil system Can modify soil tilth and cause significant amounts of erosion

Cropping systems: Strip cropping

Refers to the practice of growing crops in alternate strips of row crops of forage/grass Effective practice to reducing soil erosion because it breaks sloping landscapes in wide sediments with diverse vegetative cover which intercepts runoff and promotes water infiltration thereby reducing runoff and soil erosion

Cropping systems

Refers to the type and sequence of crops grown and practices used for growing them Maximize crop yields

Erosion Processes; run off erosion: Gully Erosion; Ephemeral

Shallow channels that can readily corrected by routine tillage operations Following removal tend to reform in the same points of the field if not controlled

Erosion control structures: WASCob

Stands for Water and Sediment control basin Consists of an earthen dam/berm spanning a natural drainage way Intercepts and temporarily ponds concentrated runoff Sized plastic pipe and stand pipe used to drain ponded area in 24 hrs Sometimes preferred over grass water ways

Erosion Processes; run off erosion: Gully Erosion; control structures: Dams

Temporary structure of tree branches, logs, stones and earthen dams which are constructed across gullies in series at short intervals along the channel

Management (in regards to gullies)

Through stabilization of the gully head, bed and sides reducing their expansion This is appropriate for gullies to large and expensive to refill i.e. reclaim Used when reclamation costs> land value

Erosion Processes; run off erosion: Gully Erosion; Permanent

Too large to be smoothed by regular tillage or crossed by machinery traffic and require expensive measures of reclamation and control

Erosion control structures: Terraces; Broad based

Used in long and uniform fields with slopes <5% All sections of the terraces are farmed Aka channel terraces because the channels are all cultivated and are common in regions with flat and abundant land and where heavy equipment is available Channels gently graded to outlets for runoff disposal Sheet and rill erosion between terraces are higher

Erosion control structures: Terraces; Narrow based

Used in shallow and sloping lands unlike broad base terraces and have a steep narrow ridge Ridges are not farmed but are maintained and managed with permanent vegetation cover Cause lesser soil disturbance than other types of terraces Common in regions with limited land and with steep slopes

Tillage systems: No Till farming

Where crop is planted directly into the soil with no primary or secondary tillage Extreme form of conservation tillage in which soil remains undisturbed at all times expect during planting Leaves all the surface residues (stalks, cobs leaves etc.)

Erosion control: Buffers; Riparian

Wide strips of permanent mixture of woody and herbaceous vegetation, grasses, trees shrubs or a combination of these vegetation's When Wide (>10m) enough benefit the wildlife habitat 5- 30 m wide can reduce nutrient runoff Planted along agricultural fields Designed to mitigate sediment and nutrient flow to streams Used in both agricultural and urban soils along streams to control sediment transport

Erosion control structures: Terraces; Bench

Widely used throughout the world in places with hilly terrains Established on slopes>10% have steep back slopes Width of bench and height of steps are variable depending on the field slope A width 7- 7.5 m is used in moderately sloping lands Series of strips constructed across the slope at equidistant vertical intervals and separated by steep banks of stones and grassed revetments

Erosion control structures: Grassed Water Ways: size

Width ranges between 10 and 50 m

Difference between soil amendments and conditioners is

amendments are used in much larger quantities usually - Conditioners really just a subset of amendments, smaller range of products than that of amendments

General strategies for gully management, prevention and restoring

conservation tillage, grass buffers, contouring, strip cropping and terracing Maintaining a permanent vegetation cover Any measures that reduces rill erosion, runoff concentration and flow channelization prevents gullying Any restorative strategy must identify first the cause of the gully and then develop counteractive measures Timing is also an important factor to be considered when establishing control measures All vegetative and mechanical control measures must be established during dry season Reduction of runoff peak rates with the establishment of structures that intercept runoff, absorb its erosive energy and release it at low velocities Diversion of concentrates runoff above the lower points of the fields before it develops new or expands the existing gullies Stabilization of gully bed and sides if the previous two strategies are insufficient to control erosion In regions with severe gullying a combination of various measures must be used

Erosion control: Biological; soil amendments; examples

crop residues, food waste= organic - Lime, dolomite, gypsum = natural materials/by-products

Erosion Processes: Deposition

determines the distribution of the eroded material along the landscape - Usually in low landscape, downstream water

Erosion Processes: Detachment

discrete raindrops impacting the soil surface and detaching soil particles When dry form crusts of low permeability

Erosion control structures: WASCob designed to

handle MAX expected 10 year rainstorm: because equipment can only withstand so much impact from elements thus MAX of 10 years in place Waterways are designed around the expected peak volume of water to be contributed by the watershed for a 10-year return period storm, in other words a 1 in 10 year storm, an uncommon occurrence

Volume and velocity of runoff (3)

increases with runoff amount, velocity and turbulence

Geologic Erosion

is a normal process of weathering that generally occurs at low rates in all soils as part of the natural soil forming processes

Accelerated Erosion

is when the rate of erosion exceeds a certain threshold level and becomes rapid

Cropping systems: Organic Farming

no synthetic fertilizers or pesticides are used to produce food and fiber in contrast to chemically-based conventional farming systems Reduces soil erosion over conventional farming when the system maintains a more continuous soil surface cover with cover corps, green manure, and residue mulch Lower soil erosion rates are attributed to better soil granulation, higher macrosporosity and higher water infiltration rates

Volume and velocity of runoff is determined by

slope, watershed size and shape

Soil erodibility by wind (similar to water)

soil properties such as texture, structure, and water content in interaction with surface roughness and living and dead vegetative cover define the rate at which the soil is detached and eroded

Tolerable Soil Loss (T value) is

the estimated average tolerance (T) level of soil erosion used in soil and water conservation planning. It is the amount of soil erosion that does not significantly decrease soil productivity.