Organic Matter

Profitable Soil ScienceChapter 3

What is Organic Matter?

• all plant and animal residues in the soil

What two things have greatly lowered the Organic Matter content of soil?

• soil erosion & continuous cropping

How can organic matter be increased?

• crop residues• barnyard manure• green manure

What is Green Manure?

• a crop grown for its organic matter

• green manure crops are generally plowed under while they

are still green

What other things make up soil organic matter?

• decomposed carcasses and excrements of worms, insects, larger animals and microorganisms

What is Mineralization?

• organic matter is broken down into simple mineral compounds

When organic matter breaks down, what is released for the crop's use?

• nutrients

How does Organic Matter Improve Soil?1) increase water holding capacity2) nutrients attach to O.M.3) O.M. improves tilth (aggregate)• The amount of humus in soil is directly

proportional to the amount of nitrogen in soil

• Soils high in O.M. are easily worked and may be described as having good tilth.

Benefits of Organic Matter

• Organic Matter promotes granulation of soil by binding soil particles into granules.

• O.M. makes clay soils less sticky and improve tilth.

• Deeper root growth and water entry and storage are improved as well as aeration of the soil.

Organic Matter & Sandy Soils

• Sandy soils have good aeration but dry out quickly. Sandy soils increase water holding capacity and have less erosion as O.M. is added?

What is the Organic Matter Content of Montana Soils?

• 2% to 4%

What is the largest source of O.M. in the soil?

• plant roots

Which is the most preferred green manure, legumes or non-legumes?

• legumes- added nitrogen

What is nitrogen tie-up?• microorganisms in the soil use the

nitrogen in the soil to break down organic matter, thus it is temporarily "tied up" (used as food)

• this is very important when considering recropping and not allowing the soil to have a year in fallow to allow for mineralization in order to reduce the nitrogen tie-up.

How many square feet are in an acre?

• 43,560

What is an acre-six inches?

• six inches of soil over an acre

An acre-six inches weighs how many pounds?

• 2 million

Soil ConservationA typical farmer is doing a "good job" of soil conservation if he loses less than 1/16" of topsoil each year. How many pounds of soil does he/she lose each year if he/she loses 1/16"? How many tons?(extra credit)

How long does it take to create soil?

It takes 100 to 400 years to create 1" of topsoil.