PP3: Soil and Nutrient Relationships

Mineral soil

• clay is a direct product of weathering- amount of clay in the parent material has a big influence on soil water and nutrients

• clay is the smallest soil particle, holds water and nutrients, but erodes easily and ponds water

  • Generally, around here, the more clay you have the more water and nutrients is ​

• sand has higher permeability, but holds little water and few nutrients

• Loam (mixture of sand, silt, and clay) is best scenario for plant growth

What is soil

soil is parent material that has been developed by precipitation/water and biota

what are the two components of soil?

mineral and organic components

how is mineral soil formed

weathering of rock/parent material

how is organic soil formed

from organic matter produced by biota and accumulated litter, including root mortality

what are the characteristics of sand in soil

sand has high permeability but holds relatively little water and few nutrients

why is loam considered good for plant growth?

loam is a mixture of sand, silt, and clay that provides a favorable balance of properties

what are the particle-size ranges

• sand: 0.05-2 mm

• silt: 0.002-0.5 mm

• clay: <0.002 mm

where does organic matter in soil come from

it comes from litter on and within mineral soil, much of which comes from root mortality

what is mull humus

organic matter that is well mixed into the A horizon

what is mor humus

organic matter that accumulates on the soil surface, with an E horizon developing below it

what is muck soil, and why does decomposition occur slowly in it?

muck is wet organic soil where low oxygen slows decomposition

how are peat and muck different

peat is lightly decomposed organic matter, while muck is more heavily decomposed organic matter

what are sapric, hemic, and fibric muck

• sapric: <17%

• hemic: 17-75%

• fibric: >75%

what nutrient commonly limits terrestrial ecosystems

nitrogen

what are the three major forest nutrients

N, P, and K

in what form are nutrients absorbed by plants

ionic form

which trees have high N demand

ash, hop-hornbeam, and basswood

which trees generally have low N demand

red maple, oaks, aspens, and conifers except white-cedar

what is a cation and why are cations important in soil?

a positively charged ion, many important plant nutrients occur as cations

which important plant cations should you know?

Ca²⁺, Mg²⁺, K⁺, NH₄⁺, Na⁺, H⁺ and Al³⁺

Which cations are not beneficial plant nutrients?

H⁺ is not a nutrient, and Al³⁺ is considered harmful to plants.

what are soil colloids and why are they important for nutrients

tiny, negatively charged particles with high surface area that can hold positively charged cations

why do cations stick to soil colloids

positively charged cations are attracted to negatively charged soil colloids

what important anions should you know

NO₃⁻, H₂PO₄⁻, SO₄²⁻, SO₃²⁻, and Cl⁻

why are anions generally more vulnerable to being lost from soil

anions are more easily leached than cations

how does weathering provide nutrients

weathering of parent material releases nutrients

why is sand a poor nutrient source

its mostly quartz, which provides relatively few nutrients

how does decomposition of organic matter provide nutrients

decomposition recycles nutrients from organic matter back into the soil

General equation for decomposition

what is mineralization

Organic N → NH₄⁺.

Under what soil conditions does mineralization occur

on moderately to severely acidic soils (below about pH 6), primarily by fungi rather than bacteria

what is nitrification

NH₄⁺ → NO₂⁻ → NO₃⁻.

under what conditions does nitrification occur?

in approximately neutral, aerobic soils

what is denitrification

NO₃⁻ is converted through intermediates to N gases

Where does denitrification occur

anaerobic conditions

how does rainfall add nutrients

removes dust from the atmosphere and deposits it on the land

what is dryfall

dust settles onto foliage and can be washed to the soil

what is throughfall

water/nutrients dripping from foliage to the soil

what is internal translocation

nutrients are removed from leaves before they fall

how can groundwater supply nutrients

nutrients dissolved from rock enter groundwater

how can air supply nutrients

some species can fix atmospheric N₂

what are the four major fates of nutrients

plant uptake, leaching, adsorption to colloids, or release to air

what is leaching

nutrients move out of the rooting zone with water

Which is more easily leached: NO₃⁻ or NH₄⁺?

NO₃⁻

what is podzolization

acid leaching that moves soluble constituents out of soil

what causes acidity in podzolization

Higher H⁺ concentration/lower pH.

what is the first step of podzolization

Water + CO₂ → carbonic acid (H₂CO₃)

what happens to carbonic acid

H⁺ dissociates, producing H⁺ and HCO₃⁻

The process of podzolization

1. water and CO2 (from respiration) combine to form carbonic acid

2. Hydrogen dissociates to form H+ and bicarbonate

3. H+ can then displace cations from soil colloids; bicarbonate combines with K to form an ion unusable to plants

Podzolization cont.

• podzolization causes iron and aluminum to leach down through the soil profile, leaving silica behind (thus a light E)

• iron and aluminum are deposited in the B horizon, often making it look reddish (Bs)

• humus can also be moved down (Bh)

• thus acidity is a good proxy for nutrient status: lower pH= higher concentration of H+ ions = more podzolization

Effects of acidity

• acidity means higher concentration of H+

• more acid= lower pH

• reduced activity of microorganisms

• decomposition and mineralization are reduced and organic material accumulates (mor humus)

• nutrients remain tied up in organic matter rather than used by plants

• Mor humus results in high seedling mortality

• inhibits absorption of nutrient ions; aluminum becomes soluble and very toxic and very low pH

NOT FINISHED