Understanding our Garden’s Soil

What Does Soil Do?

• Provides nutrients for the plants– NPK

• Regulates water• Provides support for roots• Filters potential pollutants

SOIL COMPONENTS: Physical

• Mineral Particles–Sand–Silt–Clay–Organic Matter

• Air• Water

SOIL COMPONENTS: Living

• Microorganisms• Worms• Fungi• Bacteria

“It’s Alive!”In 1g of soil there are:• >100,000,00 bacterial

cells• >11,000 species of

bacteria• Fungi and larger

organisms

COMPOSITION OF SOIL BY VOLUME

Mineral Particles;

48%Water;

25%

Air; 25%

Organic Matter; 2%

SOIL FORMATION:ClORPT

•Climate

•Organisms

•Relief

•Parent Material

• Time

SOIL HORIZONS1. O-Horizon

1. Recognizable, recent2. Less recognizable3. Humus

2. A-Horizon– Mineral layer

3. E-Horizon– Elluviation layer

4. B-Horizon– Zone of Accumulation

5. C-Horizon– Clumps

6. Bed Rock

Physical Properties of Soil

• Color• Texture• Structure• Drainage• Depth

SOIL COLOR

• Light brown Low in organic matter• Dark brown High in organic matter• BlackVery high organic matter• Red Weathered/nutrient poor• Red-brown Good drainage• Yellow Moderate drainage• Grey Poor drainage• White, light greySandy

SOIL TEXTURE

• Sand, Silt, Clay– Excludes organic matter

Water holding capacityIrrigation frequencyNutrient holding capacityFertilization frequency

CLAY LOAM SANDhigh medium lowlow medium highhigh medium lowlow medium high

Structure, Drainage, and Depth

• Structure is the shape soil takes based on its physical and chemical properties– Destroyed by over-tilling and traffic

• Soil drainage is improved by adding organic matter

• The deeper the soil, the greater the storage capacity for water and nutrients

SOIL pH

• pH is a measure of the acidity or the basicity of the soil

0 2 4 6 8 10 12 14

ACID BASIC

NEUTRAL

PLANT GROWTH

Effects of pH on Nutrient Availability

Reprinted from the Arizona Master Gardener Manual, Chapter 2, page 20.

IRON CHLOROSIS

Iron deficiency appears on the youngest leaves of plants growing in alkaline soils.

SOIL AMENDMENTS• Complete fertilizers

– NPK• Incomplete fertilizers

– Missing at least one of the primary nutrients

• Organic fertilizers– Remains or by-products of

plants or animals– Release nutrients slowly

• Blood and bone meal• Fish emulsion• Manure

MANURES

% of N P KChicken manure 4.4 2.1

2.6Cow manure 1.9 0.7 2.0Pig manure 2.1 0.8 1.2Horse manure 1.4 0.4

1.0Sheep manure 3.5 0.6

1.0

NITROGEN• Necessary for formation

of chlorophyll, as well as building amino acids for proteins.

• Nitrogen deficiency symptoms– Yellowing leaves beginning

in oldest leaves– Leaf tips and margins

yellow and dies– Plants are stunted.

PHOSPHORUS• Phosphorus is necessary for

almost all aspects of plant growth and is essential for flower and fruit formation

• Phosphorus deficiency symptoms– Dark green foliage– Purplish foliage on stems– Reduced growth– Delayed maturity or reduced

flowering

POTASSIUM• Potassium is necessary for

the formation of sugars, starches, carbohydrates, protein synthesis and cell division in roots and other parts of the plant.

• Potassium deficiency symptoms– Leaf tips and margins burn– Affects oldest leaves first– Plants have weak stalks– Small fruit

Sources of NPKConventional Renewable

Nitrogen Synthesized from natural gas: Urea, anhydrous ammonia

Fixed from the air by rhizobacteria associated with legumes, Manure and compost; blood meal

Phosphorus Mined in Florida, CanadaRock phosphate

Manure, compost, bone meal; fish emulsion

Potassium Mined in Canada Green sand

Manure, compost

IMPROVING SOIL:Cover Cropping

• Mixing vegetable plants with other crops such as grasses and legumes.

• Add nutrients and organic matter to the soil

• Helps hold moisture• Improves soil texture• Prevents erosion

IMPROVING SOIL:Compost—Nature Recyles!

• Transformation of raw organic materials into biologically stable substances suitable for plants

• Improves soil structure, texture, and aeration.

• Increases water-holding capacity

• Increases nutrients

IMPROVING SOIL:Crop Rotation

• Planting crops in a prescribed rotation

• Builds soil nutrients• Crops help to fertilize

each other• “Tricks” pests• Adds diversity

IMPROVING SOIL:Reduced Tillage