soil fertility ability of a soil to provide nutrients for plant growth involves storage and...

27
UNDERSTANDING SOIL CHEMISTRY

Upload: milo-patrick-powell

Post on 31-Dec-2015

218 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

UNDERSTANDING SOIL

CHEMISTRY

Page 2: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

IMPORTANCE OF SOIL FERTILITY Soil Fertility

Ability of a soil to provide nutrients for plant growth

Involves storage and availability of nutrientsVital to a productive soil

Fertile soil is not necessarily a productive soilWhy?

Poor Drainage, Insects, Drought, and other factors can limit production

Page 3: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

Existing plant-soil relationships affect soil productivityExternal factors control plant growth

Air Temperature Light Mechanical support Nutrients Water

Plants rely on soil to provide all these except light

IMPORTANCE OF SOIL FERTILITY

Page 4: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

Water and air fill pore spaces in soilFactors that affect water relationships also

affect soil air Nutrient availability is influenced by soil

and water balance and temperature Root growth is influenced by soil

temperature as well as soil, water, and air

IMPORTANCE OF SOIL FERTILITY

Page 5: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

UNDERSTANDING SOIL

CHEMISTRYSoil Productivity

Page 6: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

What is organic matter?Plant, animal, and microbial residues

Varying stages of decay

Adequate levels of O.M. benefit soil by: Improving physical condition and tilth Increases water infiltrationDecreases erosion lossSupplies plant nutrients

ROLE OF ORGANIC MATTER

Page 7: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

Organic matter contains about 5% NN is not immediately availableDecomposition must occur first

Fertilizer (inorganic) N is needed for non-legume plants

Organic matter also provides soil with a variety of other mineral elements that plants need to be healthySome include: phosphorus, magnesium,

calcium, sulfur, and others

ROLE OF ORGANIC MATTER

Page 8: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

ROLE OF SOIL DEPTH Soil Depth

Depth of soil material favorable for plant root penetration

Plants need soil to be:DeepWell-drainedCorrect textureCorrect structure

Deeper soils provide for more nutrient storage

Page 9: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

Roots can extend 3-6 feet or more when soil depth permitsRooting depth is affected by

Physical barriers Chemical barriers High water tables

Hardpans, Shale beds, Gravely Layers and accumulations of salts are very hard to correct

ROLE OF SOIL DEPTH

Page 10: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

ROLE OF SURFACE SLOPE Surface slope is part of what?

Topography Determines the amount of runoff and

erosion Also determines:

Irrigation methodDrainageConservation practices

The steeper the land the more management is neededMore labor and equipment costs

Page 11: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

At certain slopes, soil is no longer suitable for row crops.What are some row crops?

Potential productivity is largely determined by ease of erosion along with percent of slope

ROLE OF SURFACE SLOPE

Page 12: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

ROLE OF SOIL ORGANISMS Many different organisms live in the soil

Usually in the first foot of top soilDepend on organic matter for food

Factors that affect the amount soil organisms:MoistureTemperatureAerationNutrient supplySoil pHCrop that is being grown

Page 13: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

Some of the microscopic organisms cause many favorable soil reactionsdecay of plant and animal residuesspeed nutrient cycling.

Other reactions can be injuriousdevelopment of organisms that cause plant

and animal diseases

ROLE OF SOIL ORGANISMS

Page 14: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

ROLE OF NUTRIENT BALANCE Nutrient balance is a vital concept in soil

fertility and crop production Nitrogen is the first limiting nutrient in

non-legumes Without adequate amounts of the other

nutrients, N cannot do its best As Nitrogen fertilization raises yields,

the crop demands more of the other nutrients

Page 15: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

UNDERSTANDING SOIL

CHEMISTRYSoil pH

Page 16: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

SOIL PH The measure of acidity

or alkalinity of the soil pH is determined by the

concentration of hydrogen ions(H+) and hydroxyl ions(OH-) in the soil solution

Pure water has an equal number of H+ and OH-

Page 17: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

SOIL PH Another term for alkaline is basic

Acid = high in H+ Basic = high in OH-

A soil with a pH of 6.0 has 10 times as much active H+ than neutral

Page 18: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

SOIL PH Plants will not thrive in soil that is too

acid or too alkalineThe soil pH directly affects the availability of

mineral nutrients Example

Low pH: phosphates may be bound chemically in the soil so plants are unable to access them Also means that nitrate production in the soil is

reduced

Page 19: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

SOIL PH Several factors influence Soil pH

Organic matterParent materialRainfall

leachingForest vs. grasslandHarvesting cropsLegumesSoil depthFertilizer applicationFlooding

Page 20: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

SOIL PH How to measure soil pH

Indicator dyespH meter

Which do you think is more accurate?

The meter

If our soil’s pH was too acidic what would we add to amend it?Lime

Page 21: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

LIME REQUIREMENT Soil pH is not the determining factor on

how much lime to addWhat else do we need to consider?

Texture of soil Amount of organic matter

The amount of clay and organic matter in a soil will determine the ability of a soil to resist pH changeMore clay/organic matter = more pH

buffering The process is very complex

Example: Al and water

Page 22: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

LIME REQUIREMENT Lime requirement

Amount of Ag limestone needed to establish the desired pH range for the cropping system being used

Lime reduces soil acidity Look at Al and water example Uses Ca ion

Soil will become more and more acidic if a liming program is not followed

We do not apply lime to soils here in Northern Utah very often… Why?

Page 23: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

LIME REQUIREMENT In the case of high pH

Lowering pH is not usually economical These are generally high in salts

Find plants that tolerate high salt levels

Page 24: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

CATION EXCHANGE CAPACITY As soils form

Some particles are broken down into extremely small particles

Chemical weathering breaks them down until they cannot be seen with the naked eyeThe smallest are called colloids

Colloids are responsible for chemical reactivity in soil

Each colloid has a negative(-) charge

Page 25: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

CATION EXCHANGE CAPACITY The neg. charge will attract

positively(+) charged particlesWhat does that mean if they run into

another negative? Cations: Positive Charge Anions: Negative Charge

Colloids act like a magnet and holds cationsOther cations can take their placeThey are exchangeable

Page 26: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

CATION EXCHANGE CAPACITY Can a soil hold more cations than it has

colloids?no

We need to know our soil’s CEC

Higher CEC = more cations can be held Depends on clay and organic matter

Lots of clay = higher CECMore organic matter = higher CEC

Page 27: Soil Fertility  Ability of a soil to provide nutrients for plant growth  Involves storage and availability of nutrients  Vital to a productive soil

CATION EXCHANGE CAPACITY Leaching is reduced by higher CEC

Knowing our CEC will help determine how much fertilizer to apply and how often