crop production 6-soils

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PRINCIPLES OF CROPPRODUCTION

Soils


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LEARNING OUTCOME/Introduction

Learning Outcome

1. Discuss soil components.

2. Discuss soil properties.3. Discuss nutritional needs of plants.

4. Discuss soil degradation.

IntroductionThe soil is a medium for the production

and growth of plants and crops.

It provides an environment for plant roots


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Introduction

and nutrients essential for plantdevelopment and growth.

The ability of a soil to supply important

chemical nutrients or essential elements isdescribed as soil fertility.

Soils provide anchorage for plants.

Soils contain numerous organisms thatinteract including plants, bacteria, fungi,insects, and invertebrates.


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Soil components

1.Soil Components

Soils are a mixture of minerals, organicmatter, liquids, and gases.

Productive agricultural soils typicallyconsists of about half solids and half porespace.

The solids are minerals derived from rockand organic matter.

Pore spaces are filled with air and water.

Living organisms such as microbes,


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Soil components

earthworms, and rodents are alsoimportant components of the soil.

Essential elements

Those that are necessary for a plant tocomplete its growth cycle, whosefunctions cannot be replaced by other

elements.That are components of a molecule or an

enzyme within the plant.

Minerals derived from rocks provide many


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Soil components

of the essential nutrients for plant growth.

Seventeen elements are those that arenecessary for plant growth.

Of these elements, plants obtain carbon,oxygen, and hydrogen from the air.

Plants acquire the others from the soil.

Based on their average concentrations inplant tissue, elements are classified aseither macronutrients or micronutrients.


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Soil components

Macronutrients: Carbon (C), Hydrogen (H),Oxygen (O), Nitrogen (N), Phosphorus (P),Potassium (K), Calcium (Ca), Magnesium(Mg), Sulfur (S).

Micronutrients: Iron (Fe), Manganese (Mn),Copper (Cu), Zinc (Zn), Boron (B),Molybdenum (Mo), Chlorine (Cl), Nickel (Ni).

Additional amounts of nitrogen, phosphorus,and potassium are often added to soilsthrough fertilizers.


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Soil components

Organic Matter

The portion of the soil that includes animaland plant residues in various stages of decay.

Complex carbon compounds make up organicmatter.

Soil microbes rapidly digest compounds such

as starch, cellulose, sugars, and amino acids.Some soil fractions such as lignin and waxes

are resistant to decay and ultimately formhumus.

Over time, most of the carbon in organic


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Soil components

a small amount of resistant residue or humusremaining.

Particles of decomposed organic matter are

very small, yet they have a relatively largesurface area that is chemically reactive.

Overall, organic matter has a negativecharge.

This large surface area attracts water andnutrients, and influences the organicmatters function.

Organic matter serves as a reservoir for


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Soil components

phosphorus, and boron.

These nutrients are either attached to thesurface of the organic matter or are a

component of the organic matter.Organic matter is a binding agent that joins

the mineral portions of the soil together.

Aggregation of soil particles is important insoil tilth and aeration.

Organic matter absorbs water like a spongeand retains it for plant growth.


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Soil components

Soil Organisms

A healthy soil is alive with microorganismsand macroorganisms living together in a food

web that involves energy and nutrientconversions.

Fungi, bacteria, earthworms, insects, andmore complex vertebrate organisms such as

rodents and snake live in the soil.

Earthworm shred crop residues and initiatedecomposition of the organic matter bybacteria and fungi that feed on organicmatter.


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Soil properties

2. Soil Properties

Based on the relative proportion of minerals,organic matter, and pore space, soils have

textural, structural, and chemical propertiesthat affect their potential uses.

Soil Texture

Describes a soils fineness or coarseness.The soil texture, whether fine, coarse, or

somewhere in between, is determined by thetype and amount of specific soil particles

sand, silt, and clay.


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Soil properties

The weathering of rocks forms sand and silt.

Chemically, sand and silt are mostly silica(SiO2).

Sand is the largest soil particle and iscomposed mainly of weathered quartz, aprimary component of sandstone.

Sandy soils have large pore spaces betweenparticles.

Sand and silt are relatively chemically inertand contribute few nutrients to plant.

Clay is the smallest soil particle.


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Soil properties

Clay particles are crystalline and layered,and they are comprised of silica, aluminum,oxygen, hydrogen, potassium, magnesium,and phosphorus.

Clay is chemically the most reactive particleand provides the most qualities related tocrop growth.

Clay particles attach easily to one anotherand when wet, clay soils become very sticky.

Most agricultural soils are a combination ofthe three soil particles.


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Soil properties

Soil texture has a great effect on soilsphysical, chemical, and biological properties.

Water-holding capacity is an important soil

property influenced by texture.Sandy soils have a large pore space between

particles and hold less water than clay soils.

Clay soils have the greatest water content atfield capacity.

Loam soils are intermediate in texture.


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Soil properties

Soil Structure and Aggregation

Soil structure refers to the clustering of soilparticles into various shape.

Productive agricultural soils often have agranular structure in which clusters of soilparticles are bound together by organicmatter and clay.

Well-aggregated granular soils have goodaeration and tilth.

Tilth refers to soil having beneficial qualities

related to crop growth.


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Soil properties

Soils that are primarily clay or that havebeen damaged by excessive compaction donot have good soil structure, areimpermeable to water, and are hard to till.

Soil Chemistry

Soil has many chemical properties that affectplant growth, including cation exchange

capacity, pH, and salinity.

Cation exchange capacity

Small, crystalline clay particles and organic

matter in soil are chemically active with a


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negative surface charge.

The negative surface charge of theseparticles enables them to attract positively

charged ions (cations), water, and otherchemical compounds such as pesticides.

The amount of exchangeable cations a soilcan sustain is called the cation exchange

capacity.

Soils that have a high cation exchangecapacity hold nutrients and are fertile.


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Soil Reaction

Soil reaction describes the concentration ofhydrogen ions in a soil.

Soil reaction is also described as pH.

The pH scale runs from 0 to 14.

A pH of 7 is neutral; a pH of 0 up to less than

7 is acidic; and a pH of greater than 7 up to14 is alkaline or basic.

Plants vary in the required pH range for bestgrowth and yield.


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Some crops such as potato grow best at pH 5or less.

pH influences the nutrients available to

plants.A soil pH of 5 may limit phosphorus

availability to plants even though soilphosphorus levels are adequate.

Low soil pH may cause toxic levels ofavailable aluminum and manganese in thesoil.

Aluminum toxicity inhibits root growth and


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Soil properties

restricts calcium uptake.

pH affects the growth of beneficial soilorganisms that form symbiotic relationships

with legumes and facilitate biologicalnitrogen fixation.

Salinity

Salinity occurs due to the accumulation ofsoluble salts (sodium, calcium, andmagnesium) that dissolve in water.

Salts form as a result of a chemical reaction

between an acid and a base.


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Soil properties

Most soil salts are sulfates and chlorides.

Saline soils typically occur in dry regionswhere salts rise to the soil surface during

water evaporation and then accumulatethere.

Soil is frequently saline in irrigated, dry landregions where the evaporation rate exceeds

the rate of leaching of salts down into thesoil by rainfall.

Salts cause plant dehydration.

Crops vary in their tolerance of soil salinity,


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Nutritional needs of plants

3. Nutritional Needs of Plants

Some soils are naturally fertile because theywere derived from minerals rich in elements.

Over time, most soils require fertilization formaximizing crop yields.

Fertilizers

Fertilizer is a material applied to the soil topromote plant growth.

There are two basic classes of fertilizers:organic and inorganic.


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Organic fertilizers

Derived from living matter and contain theelement carbon.

Animal manures, composts, and greenmanures are examples of commonly usedorganic fertilizers.

Organic matter from animal manures andplants must first decompose to release theirnutrients into the soil.


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Inorganic fertilizers

Synthetic or mined and processed fertilizersthat producers can apply to soil.

Macro- and micronutrient fertilizers areavailable.

Inorganic fertilizers are used to supply

additional amounts of phosphorus,potassium, nitrogen, and calcium.

Phosphorus fertilizers are obtained from themining of phosphate rock deposits.

The rock can be crushed and moved directly


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Common dry phosphorus fertilizers are triplesuper phosphate (20% P) and ammoniumphosphate (23% P and 20% N).

Potassium fertilizers are also obtained frommining and purifying of potassium deposits.

Muriate of potash (potassium chloride)contains 60% K and is a common dry

fertilizer.

Urea and ammonium nitrate are the mostpopular dry nitrogen fertilizers.

Calcium is typically applied via crushed


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Limestone is basic in pH and is applied toincrease the soil pH which influences soilfertility.

Applying fertilizer

Fertilizers are applied at different timesand in different manners depending on the

crop.Basal dressing- application of fertilizers

before the seeding of crops.

Top dressing- application of fertilizers


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after seeding.

Banding- fertilizer application at planting,the seeding equipment is capable of

depositing a band of dry fertilizer within 2inches of the seed.

Fertigation- crop fertilizers by injecting thefertilizers into the irrigation water.


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Soil degradation

4. Soil Degradation

The widespread use of land for agriculturehas accelerated the rates of soil erosion.

There is great concern that with high rates ofsoil degradation, we will have an insufficientsoil resource remaining to meet the worldsfood needs in the future.

Erosion is the accelerated loss of soil throughthe action of wind or water.

With wind and water erosion, soil particles

are detached and moved.


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With water erosion, falling raindrops disturbsoil particle and surface aggregates.

Flowing water then removes the soil

particles. In wind erosion, the wind initially loosens

coarse soil particles such as sand.

Tumbling sand particles then loosen smallersilt and clay particles that becomesuspended in the air.

Erosion is a challenge to crop production

because it removes the topmost, fertile layer


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Soil conservation

Though water and wind erosion cannot beeliminated, they can be greatly reduced.

The most important crop managementstrategy for minimizing both wind and watererosion is to maintain a permanentvegetative cover over the soil.

Vegetation cover prevents the initial loosingof soil particles and reduces wind and watervelocity.

When perennial crops cannot be maintained,


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reduces erosion.

Another strategy to reduce erosion is tomaintain a high soil organic matter content.

Soil with high organic matter content hasincreased soil aggregation, water infiltration,and soil particle stability.

High amounts of soil organic matter can beachieved through the growth of perennialcrops and he addition of residues.

Other strategies for soil conservation include

conservation tillage, crop rotation, contour


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Soil degradation

tillage, strip cropping, and grass waterwaysand windbreaks.

Conservation tillage enables at least 30% of

the crop residue to remain on the soilsurface and provides a rough, uneven soilsurface.

This practice is effective at reducing both

wind and water erosion.

Conservation tillage can be accomplished byusing several approaches including no-till,chisel, and disk plowing.


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Crop rotations that involve both annual andperennial crops provide for greater year-round cover and greatly reduce soil erosion.

Erosion losses are usually greatest for annualrotations such as corn-corn or corn-soybean.

Adding perennial crops to such crop rotationsdecreases wind and water erosion.

On sloping land, crops can grown in strips atsimilar elevations along the contour of alandscape.

crop production 6-soils

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