ABS 360 ARIZONA STATE UNIVERSITY Topic 7 – Soils and Fertilizers 2020.pdf

Kye AuClaire

ABS 360

Topic 7 – Soils and Fertilizers

Soils and Fertilizers Terms

oTopsoil: The layer of soil that has the highest concentration of organic matter and

microorganisms and is where most of the Earth’s biological activity occurs.

oSoil Texture: Measurement of the proportion of mineral particles of different sizes

that are found in the same sample of soil (sand, silt, clay).

oSoil Structure: The way that individual particles – sand, silt, clay – are arranged

into larger distinct aggregates. It is the major factor determining how fast air and

water enter and move through the soil.

oSoil Pores: Air spaces in between soil particles that allows the passage or

absorption of fluids.

oSoil pH: A measure of the acidity or alkalinity of soil. It is measured on a negative

logarithmic scale of 1-14, with 7 as the middle or neutral value.

oAcid and alkaline soil: Soil pH less than 6.5 is acidic. Soil pH greater than 7.5 is

alkaline. Soil pH between 6.5 and 7.5 is neutral.

oNutrient Deficiency: Inadequate supply in soil of one or more of the essential

elements for plant growth and development; 16 elements needed for plant growth.

oOrganic matter: Carbon-based plant or animal remains in soil that have decayed

beyond recognition.

oComposting: The aerobic, active, and directed decomposition of organic matter.

Soils Video

oDust Bowl Era: 1930’s drought and soil eradication.

“A Nation that destroys its soil destroys itself” Prez FDR

oSoil is the foundation of everything for life – gardening

oSoil: Weathered surface portion of the earth’s crust

Large parent rock material broken down into small particles of less than 2

mm in diameter

oSOIL IS NOT DIRT

oSoil is a precious resource.

oFive Component Parts of a Healthy Soil:

Weathered mineral particles

Macro- and micro-organisms

Decomposing organic matter

Water

Air

oSoil has various layers

oThe profile of a soil is organized into layers called “horizons”

The arrangement of horizons is known as the “soil profile”

oThree main soil horizons

“A” Horizon (Surface)

“B” Horizon (Subsoil)

“C’ Horizon (Substratum)

oOrganic horizon is above A, R (bedrock) horizon is below C

oDesert soil horizons are:

Highly variable

Shallow

Limited to non-existent surface layer of organic matter

oSoil Texture

Classifying soils by the size of the dominant soil particles

Sand, Silt, or Clay

Sand: 2.00-0.05 mm

Silt: 0.05-0.002 mm

Clay: Less than 0.002 mm

Determine your garden soil texture by doing the “Feel Test” – 5:40

Gritty is a sand texture

Silky smooth is silt texture

Sticky is a clay texture

Loam soils have a mixture of sand, silt, and clay particles

Loam soils are best for plant growth and development

oThe sandier soil will need to be irrigated more

oRhizosphere

Support and anchor the plant

Reservoir for water, oxygen, and essential plant mineral nutrients

Substrate for interactions with other organisms

Root rot caused by bacteria and fungal pathogens

oRhizosphere Interactions

Most associations that roots have with other organisms are symbiotic and

can even be beneficial to the plant

Mycorrhizae Fungi: an intimate and often beneficial soil association

between fungi and roots

Fungi provide phosphorus to the plant in exchange for carbon

TIP: Organic amendments will improve soul aeration and drainage

Soil pH: Describes a soil’s chemical condition

Math: - log (H+)

1-7 is acidic, 7-14 alkaline, 7 is basic

Soils around the world that support plant growth range in pH from

4-9

Southwest desert soils are generally alkaline with pH values of 7.5-

8.5

Alkaline soils affect plant growth by limiting the availability to

roots of several key mineral nutrients

Fertilizers Video:

oPlants are autotrophic

oPlants make their own food

o13 naturally occurring mineral nutrients from soil are required by plants to survive

2 groups

Macro-nutrients

oNitrogen, phosphorus, potassium, calcium, magnesium,

sulfur

o2-4 % of N

Micro-nutrients

oIron, Zinc, Manganese, Boron, Copper, Molybdenum,

Nickel

oSoils lack several nutrients in the Southwest

oNitrogen and Iron are often in short supply in desert garden soils

oPlant deficiencies in Nitrogen and Iron are displayed by the plants VERY

DIFFERENTLY

oNitrogen Deficiency Symptoms

Slowing of growth or a lack of plant vigor

General yellowing or reddening of older leaves on the lower parts of the

plant

oIron Deficiency Symptoms

Iron is central to the formation of the green plant pigment chlorophyll

Yellowing of new and younger leaves on upper parts of the plant

Yellowing has a netted appearance

oZinc and Manganese nutrient deficiency symptoms look the same as Iron

oIron, Zinc, and Manganese deficiencies are common in garden plants in desert

alkaline soils

oAlkaline soils bind Iron, Zinc, or Manganese making them unavailable to plant

roots for uptake

oHow to manage the desert soil of your home garden?

Depends on the type of home garden that you have

Ornamental and desert native gardens do not need regular amendments or

fertilizers

Vegetable and fruit garden need regular amendments or fertilizers

TIP: Organic matter amendments release humic acids into the soil slowing

lowering the soil pH

Fertilizer Definition by AZ State Law – 9:36

Fertilizers are classified by origin and chemistry

Origin – Natural or Manufactured

Chemistry – Inorganic or Organic

oOrganic – by product of living organisms

Has the element carbon

oFertilizer Purchase Tips

Fertilizer products must have a label

Read the label, follow the instructions

oAnalysis of Grade

19-10-5

19 – Total Nitrogen

10 – Available Phosphorus

5 - Soluble Potash or Potassium

% content by dry weight of product

The higher the numbers are the more concentrated the element in the

fertilizer product

Micro-nutrients will be listed separately on the label

oSynthetic and inorganic fertilizers are more concentrated

oNatural and organic fertilizers are less concentrated

oAll fertilizers when dissolved in the soil are salts and can interact with other

chemical elements in the soil

oOrganic fertilizers dissolve very slowly in water

oControlled Release Fertilizers – 14:45

oThe Doctor’s Choice

Natural, organic, or controlled release fertilizers are best because of their

slow release rate of mineral nutrients

Natural and organic fertilizers support healthy populations of beneficial

soil bacteria and fungi

oThe BIG Question

Cam the normally alkaline pH of a desert garden soil be lowered to a

slightly acidic to neutral pH to increase availability of Fe, Zn, and Mn for

root uptake?

oFertilizers and Amendments to Lower Soil pH

Acid forming fertilizers

Elemental Sulfur

Ammonia Fertilizers

Organic soil amendments such as peat moss

Be Sustainable

Avoid unnecessary soil disturbances

Layer garden soil surfaces with compostable organic mulches

Select garden plants that grow well in alkaline soul

Use organic and natural fertilizers as needed

oMyth Buster

Gypsum does not work

Gypsum is calcium sulfate – can not lower pH

Gypsum amended into compacted soil improves soul aeration and

drainage

oFertilizer Use, Handling and Storage

Read the product label, follow the instructions

Wear non-absorbing, water resistant gloves

Wear a facial mask

Always store fertilizers in a dry and secure location

Store different fertilizer products in separate containers, DON’T MIX

ABS 360 ARIZONA STATE UNIVERSITY Topic 7 – Soils and Fertilizers 2020.pdf

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