Soil and Plant Nutrition

What does farmland productivity often suffer from?

Chemical contamination, mineral deficiencies, acidity, salinity, and poor drainage

How does healthy soil improve plant growth?

Enhancing plant nutrition

What do plants obtain from the soil?

Carbon dioxide, air, water, and minerals

Where do plants obtain their water (+ minerals)?

The upper layers of soil

How are soil particles classified by size?

From largest to smallest

What are the names of the classification of soil particles?

Sand, silt, and clay

Soil horizons

Soil stratified into layers

What is each layer of soil horizon classified as?

A, B, and C, horizon

Topsoil

Consists of mineral particles, living organisms, and humus

Humus

The decaying organic material

What happens to large spaces in the soil after a heavy rainfall?

Water drains from the larger spaces in the soil

What happens to smaller spaces of soil after a heavy rainfall?

Smaller spaces retain water

Why do smaller spaces in soil retain water?

Due to it’s attraction to clay and other particles

Loams

The most fertile topsoils

What do loams contain?

Equal amounts of sand, silt, and clay

What does a soil composition refer to?

It’s inorganic (mineral) and organic chemical components

Cations (K+, Ca2+, Mg2+)

Adhere to negatively charged soil particles

What does the adhering of cations prevent?

From leaching out of the soil through percolating groundwater

What occurs during cation exchange?

Cations are displaced from soil particles by other cations

What happens to the displaced cations?

They enter the soil solution and are taken up by plant roots

What do negatively charged ions do during cation exchange?

They do not bind with soil particles and are lost from soil by leaching

What type of soil does humus build?

A crumbly soil that retains water but is still porous

Why does the crumbly soil increase the soil’s capacity?

To exchange cations and serve as a reservoir of mineral nutrients

Detrivores

Organisms that help decompose organic material and mix the soil

What is the goal of sustainable agriculture?

Farming methods that are conservation-minded, environmentally safe, and profitable

Irrigation

A huge drain on water resources when used for farming in arid regions

Aquifers

The primary source of irrigation water known as underground water reserves

Subsidence

The settling or sinking of land that are a result of depleting aquifers

Salinization

The concentration of salts in soil as water evaporates

Fertilization

Replaced mineral nutrients that have been lost from soil

What are commercial fertilizers enriched in?

Nitrogen, phosphorus, and potassium

How does soil pH affect cation exchange?

Cations are more available in slightly acidic soil

What does erosion of soil cause?

Loss of nutrients

What can erosion be reduced by?

Planting trees as windbreaks, terracing hillside crops, cultivating in a contour pattern, practicing no-till agriculture

How does soil compaction affect the soil?

Slows gas exchange, reduces root growth, and pore space between soil particles

What causes an area to be unfit for agriculture?

Contamination of soil or groundwater with toxic pollutants

Phytoremediation

A biological nondestructive technology that reclaims contaminated areas

Where do plants derive most of their organic mass from?

The CO2 of air

What are plants also dependent on besides CO2?

Soil nutrients such as water and minerals

Essential element

A chemical element required for a plant to complete its life cycle

Macronutrients

Essential elements that a plant requires in relatively large amounts

What are the macronutrients?

Carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, potassium, calcium, and magnesium

Micronutrients

Essential elements that a plant needs in very small amounts

What are the micronutrients?

Chlorine, iron, manganese, boron, zinc, copper, nickel, and molybdenum

Hydroponic culture

Used by researchers to determine high chemical elements are essential

What do the symptoms of mineral deficiency depend on?

The nutrient’s function and mobility within the plant

How does deficiency affect a mobile nutrient?

By affecting older organs more than younger ones

How does deficiency affect a less mobile nutrient?

By usually affecting younger organs than older ones

What are the most common deficiencies?

Nitrogen, potassium, and phosphorus

What can genetic engineering improve?

Plant nutrition and fertilizer usage

What are examples of genetic engineering?

Resistance to aluminum toxicity, flood tolerance, smart pants

How does aluminum affect acidic soils?

By damaging roots and greatly reducing crop yields

What can the introduction to bacterial genes in plant genomes cause?

Plants secreting acids that bind and tie up aluminum

How do waterlogged soils affect the plants?

It deprives the roots of oxygen and causes buildup of ethanol and toxins

Submergence 1A-1

A gene responsible for submergence tolerance in flood-resistance rice

What do “smart” plants do to prevent plant damage?

They inform the grower of a nutrient deficiency before damage has occurred

What does a blue tinge in a plant cell indicate?

It indicates when plants need phosphate-containing fertilizer

What type of relationship do plants and soil microbes have?

A mutualistic relationship

What do dead plants provide the soil microorganisms with?

Energy

What do secretions from living roots support?

A wide variety of microbes in the near-root environment

Rhizosphere

The layer of soil bound to the plant’s roots

What causes high microbial activity in the rhizosphere?

Sugars, amino acids, and organic acids secreted by roots

Where do free-living rhizobacteria thrive in?

In the rhizosphere or through entering roots

What kind of roles do Rhizobacteria play?

Producing hormones that stimulate plant growth, antibiotics that protect roots from disease, and absorbing toxic metals (making nutrients available to roots)

What is the purpose of the nitrogen cycle?

To transform nitrogen and nitrogen-containing compounds

Where does most soil nitrogen come from?

Actions of soil bacteria

In what way do plants absorb nitrogen?

As either NO3- or NH4+

How is Nitrification carried out?

By a bacteria that converts NH3 into NO3-

Nitrogen fixation

The conversion of nitrogen from N2 to NH3

What do symbiotic relationships with nitrogen-fixing provide plant species?

A built-in source of fixed nitrogen

Where do key symbioses occur?

Between nitrogen-fixing bacteria and plants, including the legume family (peas, beans, and other similar plants)

Nodules

Swellings found along a legume’s roots

What are nodules composed of?

Plants cells “infected” by nitrogen-fixing Rhizobium bacteria

Bacteroids

A form assumed by the Rhizobium bacteria inside of the root nodule

Where are bacteroids contained?

Within vesicles formed by the root cell

What is the mutualism between the bacteria of a root nodules and a plant?

The bacteria of a root nodule obtaining sugar and supplying the same plant with fixed nitrogen

What is each legume species associated with?

A particular strain of Rhizobium

What does the development of a nitrogen-fixing root nodule depend on?

A chemical dialogue between Rhizobium bacteria and root cells of their plant hosts

What does crop rotation take advantage of?

The agricultural benefits of symbiotic nitrogen fixation

How is the concentration of fixed nitrogen restored in the soil?

A non-legume (maize) and a legume is planted every other year

Why is the legume crop plowed instead of harvested?

To decompose as “green manure” and reduce the need for manufactured fertilizer

Which types of non-legumes benefit from nitrogen-fixing bacteria?

Alder trees, certain tropical grasses, and rice

Mycorrhizae

Mutualistic associations of fungi and roots

What does the fungus benefit from the host plant?

A steady supply of sugar

What does the host plant benefit from the fungus?

The increase of surface area for water uptake and mineral absorption

What is the importance of mycorrhizal relationships?

Their commonness and aid in plants first colonizing land

What occurs during ectomycorrhizae?

The mycelium of the fungus forms a dense sheath over the surface of the root

What do these hyphae form?

A network in the apoplast, which no longer penetrates the root cells

What occurs in endomycorrhizae?

Microscopic fungal hyphae extends into the root

What do these mycorrhizae form?

Branched arbuscules within root cells after penetrating the cell wall

How do farmers and foresters promote the formation of mycorrhizae?

Inoculating seeds with fungal seeds

How do invasive exotic plants affect plants and their mycorrhizal fungi?

By disrupting their interactions

Epiphyte plants (non-mutualistic)

Grow on other plants and obtain water and minerals from rain

Parasitic plants (non-mutualistic)

Absorb sugars and minerals from their living host plants

Carnivorous plants

Photosynthetic but obtain nitrogen by killing and digesting mostly insects