El agua y las raíces pueden El agua y las raíces pueden pasar entre los macro porospasar entre los macro poros

Suelo de partículas dispersados Suelo de partículas dispersados destapan los macro porosdestapan los macro poros

Superficie de costra

Cationes FloculadosCationes Floculados

• Podemos dividir los cationes a dos categorías– Floculadores

malos• Sodio• Potasio

– Floculadores buenos• Calcio• Magnesio

IonPoder Relativo de

Floculación

Sodio Na+ 1.0

Potasio K+ 1.7

Magnesio Mg2+ 27.0

Calcio Ca2+ 43.0

Proporcion de Adsorción de SodioProporcion de Adsorción de Sodio

La proporción de los floculadores ‘malos’ a ‘buenos’ provee una indicación del estatus relativo de estos cationes:

Na+++

+ + ++

+

Ca2+ and Mg2+++

++++++++++

++

Matemáticamente, está expresado como el “radio de adsorción de sodio’ o RAS:

donde las concentraciones están expresados en mmoles/L

SAR = [Na+]

[Ca2+] + [Mg2+]

Ca2+ and Mg2+Na+

RAS

CE

La estabilidad de aglomerado (dispersión y floculación) depende en el equilibrio (RAS) entre (Ca2+ y Mg2+) y Na+ así como la cantidad de sales solubles (CE = Conductividad Eléctrica) en el suelo.

Suelo Floculado

Suelo Dispersado

++++++

++++

++

+ + +++++

+

+

CE más baja CE más alta

Na+

RAS

CE

Las partículas de suelo floculan si las concentraciones de (Ca2+ + Mg2+) están mas elevados relativamente a la concentración de Na+ (RAS está disminuído).

Suelo Floculado

Suelo Dispersado

+

++

Ca2+ and Mg2+

++

++++

++++

++++

++++

++

Na+

RAS

CE

Suelo Floculado

Suelo Dispersado

+

++

Ca2+ and Mg2+

++++++

Las partículas de suelo se dispersan si las concentraciones de (Ca2+ + Mg2+) están disminuidas relativamente a la concentración of Na+ (RAS está aumentado).

++

+

+

Partículas de suelo floculan si la cantidad de sales solubles en el suelo se aumenta (CE aumentada), aunque existe mucho sodio.

Suelo Floculado

Suelo Dispersado

Na+

RAS

CE

Ca2+ and Mg2+

CE más baja CE más alta

++

++

+

+

+

++

++++

++++

++++

++++

++

Partículas de suelo se pueden dispersar si la cantidad de sales solubles en el suelo se disminuyen (i.e. si CE esta disminuido).

Ca2+ and Mg2+

Na+

RAS

CE

CE mas baja

Suelo Floculado

Suelo Dispersado

CE mas alta

++++

++

+

++

Terrazas en NepalTerrazas en Nepal

FIN

Soil ErosionSoil Erosion

Erosion ProcessesErosion Processes

• Detachment– Destruction of aggregation: raindrops, flowing

water, ice, tillage, wind, animals, vehicles

• Transport– Movement of detached particles: ice, gravity,

wind, water

• Deposition– Eroded particles find a new home

Erosion by WaterErosion by Water

• Raindrop Splash Erosion– Causes initial detachment.

Can be minimized by good soil cover.

• Surface Flow– Causes transport. Can be minimized by

good soil cover and anything that reduces slope or slope length.

Sheet erosion

RillsRills

Gullies - ArizonaGullies - Arizona

Texturing Soils by Hand

START: Place approximately 3 tablespoons of soil in palm. Add drops of water and knead the soil to break down aggregates. Soil is at the proper consistency when it is plastic and moldable. If soil is too dry, add more water; if it is too wet, add more soil.

Does soil remain in a ball when squeezed?

Place ball of soil between thumb and forefinger, gently pushing the soil with the thumb and pushing upward to form a ribbon. Allow the ribbon to emerge and extend over the forefinger, breaking from its own weight.

Does soil form a ribbon?

Is the ribbon1 inch

long before breaking?

Is the ribbon1-2 inches

long before breaking?

Is the ribbon >2 inches

before breaking?

Excessively wet a pinch of soil in palm and rub with forefinger.

Does soil feel very gritty?

Does soil feel very gritty?

Does soil feel very gritty?

Does soil feel very smooth?

Does soil feel very smooth?

Does soil feel very smooth?

Neither grittiness or smoothness predominates

Neither grittiness or smoothness

predominates

Neither grittiness or smoothness

predominates

NOSAND

NO

LOAMY SAND

NO NO

NO

NO

SANDYLOAM

SILTLOAM

LOAM

NO

NO

NO

NO

SANDYCLAYLOAM

SILTYCLAYLOAM

CLAYLOAM

SANDYCLAY

SILTYCLAY

CLAY

USDA Texture USDA Texture TriangleTriangle

12 12 TexturalTextural Classes Classes

10

20

30

40

50

60

70

80

90

100

10

20

30

40

50

60

70

80

90

100

100 90 80 70 60 50 40 30 20 10

SandLoamySand

SandyLoam

Loam

SandyClay Loam

Clay Loam

Silt Loam

Silt

Silty ClayLoam

SiltyClay

Clay

SandyClay

SAND (%)

SILT

(%)

CLA

Y (

%)

18 17

1416 15

94

13

12 11

106

57

8

321

Universal Soil Loss EquationUniversal Soil Loss Equation(for water erosion)(for water erosion)

A = R . K . LS . C . P

A = erosion loss in tons/acre/yrR = rainfall factor (amount/intensity)K = soil erodibility factor (texture/ SOM)LS = slope-length factor (angle/length of slope)C = cover and management factor (crop/tillage)P = practice factor (erosion control measures)

Average Annual Rainfall Factor (R)

Soil Erodibility Factor (K)Soil Erodibility Factor (K)

• Depends on– rate of water infiltration– structural stability

• High K factors (high erodibility) caused by:– Soils high in silt and fine sand– Platy or massive soil structure

• A value is assigned to each soil series

Soil Erodibility Factor (K)Soil Erodibility Factor (K)Texture Organic matter content

<0.5% 2% 4%

Sand 0.05 0.03 0.02

Loamy sand 0.12 0.10 0.08

Sandy loam 0.27 0.24 0.19

Loam 0.38 0.34 0.29

Silt loam 0.48 0.42 0.33

Silt 0.60 0.52 0.43

Clay loam 0.28 0.25 0.21

Clay 0.13 – 0.29

Length-Slope (LS)Length-Slope (LS)

Cover (C)Cover (C)

Controlling Water ErosionControlling Water Erosion

• Control detachment– protect the soil surface from rain, mechanical

disturbance– encourage soil aggregation

• Control transport– Slow down water movement

Reduced TillageReduced Tillage

Grassed WaterwaysGrassed Waterways

Strip Strip CroppingCropping

Terracing in NepalTerracing in Nepal

Terracing - LebanonTerracing - Lebanon

These rock-walled bench terraces have been in use for thousands of years.

Erosion is much easier to prevent Erosion is much easier to prevent than to stop !than to stop !