1. Soils

2. What determines the type of soil?
Parent Material – the type of rocks naturally found in an area
Quartz sand based rocks create nutrient depleted soil that is not good for farming
Soil with calcium carbonate parent material will have plenty of calcium, a high pH and be good for farming
Climate
need non-freezing temps to encourage decomposition plus climate determines vegetation which provides the organic matter for soil
Topography – geographical features of the area
Steep slopes will constantly erode leading to poor soil
River deltas have seasonal flooding that deposit nutrients and silt which lead to good soil
Organisms
Organisms help churn soil mixing nutrients evenly plus they aid in decomposition and nutrient cycling
Time
It takes a long time for soil to form, so in general older soils are better and more established, but it depends on the vegetation.
Desert soil might be old, the lack of vegetation means it does not improve much with age

3. Soil formation Rock is broken down over time by weathering
Organisms live and die, adding nutrients and eventually organic matter
Rate: 1cm can take years
Over time, distinct layers called horizons form
A renewable resource, but a slow one

5. Soil profile Made up of soil horizons
Different textures and compositions
Can be observed by digging a soil pit
Mature soils have 3 or more horizons

6. O-Horizon May or may not include the leaf litter layer
Organic detritus (bits of leaves, twigs, etc) on top of a layer of partially decomposed organic matter (called humus)
Soil is brown or black underneath litter

7. A-Horizon
Topsoil
Consists of partially decomposed organic matter, inorganic minerals, and living organisms.
dark brown or black usually = nutrient rich = good for farming
gray, yellow or red = low organic matter = poor for farming
Zone of biological activity A

8. E horizon – not always present or noted
Zone of leaching
A zone present in acidic soils,
either between the O and A horizon or below the A horizon
always above the B horizon
Nutrients and minerals move quickly through this layer are deposited in the B horizon

9. B-Horizon Yellow = alum oxides Sub Soil
Red = iron oxides
White = calcium carbonate
Sub Soil
Mostly inorganic – rich in Fe, Al, and humic compounds
Nutrients leached down from A horizon
Almost no organic matter
Roots may extend into this layer

10. C-Horizon
Weathered parent material. Broken rock fragments

11. Soil Profiles by Biome

12. Soil Matrix
Soil is a mixture of organic and inorganic materials such as air, water, plant and animal materials
50% = inorganic and organic particles
50% = open areas called pores

13. What is in soil? Organic Inorganic Pores Decomposing material Minerals
Leaf litter
Dead plants and animals
Provide nutrients!
Living organisms
Bacteria
Soil-invertebrates
DECOMPOSERS
All require oxygen
Inorganic
Minerals
Macronutrients
primary – N, P,K
Secondary – Ca, Mg, S
Micronutrients
B,Cu, Fe, Cl, Mn, Mo, Zn
Rock
Pores
Store O2 and nitrogen gas
May fill with water and roots

14. Soil Texture Textures Sand - biggest particles (0.05 – 2.00mm)
Silt – ( mm)
Clay – smallest components (less than .002mm)
Determined by the % of each type of particle
Gritty = sand
Smooth = silt
Sticky = clay

15. Soil Texture Importance
Impacts
Too sandy = rapid infiltration and nutrient loss
Too much clay = no infiltration, too hard, roots suffocate, drown, or can’t penetrate
Too silty = compact easily, crusty surface
Loam
a mixture of sand - silt - clay
BEST for farming!
Promotes drainage while also
retaining nutrients

16. Porosity Permeability The percentage of open pore space in soil
Silty soil holds water well
Coarse soil holds air
Permeability
The rate at which water flows through soil
Determined by porosity and structure

17. Soil pH The pH scale goes from zero to fourteen. pH correction
The soil pH is a measurement of the acidity or alkalinity within the soil.
Soil pH is the negative logarithm of the hydrogen ion concentration.
The pH scale goes from zero to fourteen.
< 7 = acidic
7 = neutral
> 7 = basic
A pH of is best for most crops
pH correction
Too acidic
Add lime to neutralize
Must be used with organic fertilizer
Too Basic
Add sulfur which is converted to sulfuric acid
Very SLOW

18. Acidic soils Acidic soils Soil in California tends to be basic
Hinder nutrient availability
Increase availability of toxic heavy metals
Major problem for urban gardens in the northeast US
Increase pesticide runoff
Decrease bacteria populations less nitrogen fixation
Soil in California tends to be basic
Soil in the northeastern US is more acidic

19. Soil Profiles from Time Magazine

20. A toxic white crust runs through irrigated fields in Grand Valley, Colorado: Moisture evaporating from the soil has drawn underground salt to the surface. To keep the salt from damaging the roots of their crops, farmers must add even more water.

21. Thick, six-foot-long roots of sunflowers, side-by-side with the roots of assorted prairie grasses, delve deep into a plot of earth near Salina, Kansas. This soil has never been broken by a plow. These perennials have root systems that expand and strengthen year after year—unlike annual crops that demand much of the soil but provide little in return. Such growth not only helps prevent erosion but also serves as a water-storage system that enables the plants to survive during droughts.

22. Virgin Prairie—Kansas, United States.
Rancher Jim Duggan holds a stalk of big bluestem, one of the native grasses growing on 40 acres of his farmland that have never been plowed. "This land is the best there is," he says. "It's class-one river-bottom soil." Compared with tilled fields, the parcel has deeper, richer topsoil and soaks up more rain.

23. Reclaimed Fields—Keita District, Niger.
Mariama Abdoulaye feeds her family with millet she grows on once barren land. After severe droughts in the 1970s and ’80s, the UN Food and Agricultural Organization enlisted Abdoulaye and 10,000 other women to plant millions of trees. Tree roots block wind-driven erosion and help rain penetrate the earth.

24. Rice Terrace—Yunnan Province, China.
Perched on an earthen retaining wall, Zhu Minying holds cords used to bundle harvested rice. Soil here reflects human activities that began with reshaping hillsides into grand staircases of grain. Rice stubble left to decay in the field, manure, and fish raised in the paddy water, all add nutrients to Zhu's soil.

25. Dry Land—Khanasser Valley, Syria.
Farmers like Ismail Hassoun Hariri struggle to grow even hardy barley in this parched land. Soil and rock eroded from surrounding hills lie thick in the valley, but annual rainfall averages only nine inches. In some very dry years the barley crop fails to mature and can only be used to feed sheep and goats.

26. After losing a foot of soil from parts of their Iowa corn farm, the Reed family changed the way they prepare fields for planting, to limit erosion. Cletus Reed, 80, hopes his grandson, Sam, will work these acres someday. "The land takes care of us as we care for it," he says.

27. Tiny earthworks stipple bare slopes in China's Zizhou County, each intended to cradle a single sapling. Government mandated reforestation programs are intended to halt erosion, but many earlier efforts here in the Loess Plateau failed when newly planted trees died.

28. Organically farmed soils (at left) have a more cohesive structure, which results in less silty runoff than found with conventionally farmed soils (at right). These samples come from the Farming Systems Trial at the Rodale Institute near Kutztown, Pennsylvania. For 28 years, a plot of land there has been managed organically: Researchers rotate crops regularly, grow cover crops in winter, and apply no chemical fertilizers or pesticides. Laboratory analysis shows that organically managed soils produce lots of glomalin, a gluey protein that helps earth hold its ground.