Soils & Plant Nutrition

Rodney PondPhD Student

School of Environmental and Forest Sciences

Overview

• What are the essential plant nutrients & why?• What are the sources essential nutrients?• How do nutrients become available to plants? • How do plants take up nutrients? • What are the factors that limit nutrient

availability for plants? • How do you cultivate soil for optimal

nutrients?

Essential Plant Nutrients16 essential nutrients needed for plant growth

CHOPKNS CaFe Mg B Mn CuZn MoCl(C. Hopkins Café – Managed by my cousin Michael)

Macronutrients - needed in large quantities

Primary nutrients- carbon, hydrogen, oxygen, nitrogen, phosphorus, and potassium

Secondary nutrients-calcium, magnesium, and sulfur

Micronutrients - needed in small quantities

boron, copper, iron, chloride, manganese, molybdenum, and zinc

Roles of nutrients in plant growth

Primary macronutrients

Carbon – energy capture, energy storage & physical structureHydrogen – same as above + osmotic potentialOxygen – same as carbon plus terminal electron acceptorPhosphorus – cell membranes, DNA/RNA, proteins, energy

storage & trasnsferPotassium (K) – enzyme activation, cellular transport, protein,

sugar and hormone formationNitrogen – Building block for amino acids and proteins,

DNA/RNA

Roles of nutrients in plant growth

Secondary macronutrients

Calcium – Cell walls, regulation of nutrient uptake

Magnesium - ChlorophyllSulfur – Amino acids, proteins, enzymes,

defensive chemicals

Roles of nutrients in plant growth

Micronutrients

Boron – Translocation of calcium, sugars & plant hormones, regulation of plant structures

Manganese – Chlorophyll synthesisCopper – Enzyme co-factor in photosynthesisZinc – Enzyme co-factorIron – Chlorophyll synthesis & functionMolybdenum – Enzyme co-factor in amino acid synthesis,

nitrogen metabolismChloride – Osmotic balance

Roles of nutrients in plant growth

Also important to some plants

Silicon – Strengthens cell wallsNickel – Nitrogen metabolismSodium – replaces K in some plantsCobalt – Key to nitrogen fixation

Nutrient Sources

Non-mineral nutrients- carbon, hydrogen, and oxygen

Supplied by water and air

Mineral nutrients – All the rest

*Supplied by organic matter and weathering of rock

What about nitrogen?

Both mineral and non-mineral sourcesnitrogen fixation

Nutrient Acquisition

PhotosynthesisCO2 + H2O = C6H12O6 + O2

Stomata

Nitrogen fixationN2 + 8H+ + 8e- = 2NH3 + H2

Root nodules

Nutrient Acquisition

Everything else?

*Active transport through roots from the soil solution

Plants can ONLY uptake mineralized nutrients

Nutrient Availability

Chemical & physicalweathering of rock AKA soil formation

• slow & in minute quantities

Decomposition of organic matter AKAmineralization

• main source of nutrients

Nutrient Availability

Nutrient cycling

Movement of nutrients through organic to mineral forms through ecosystems

Nutrients can be gained, stored, and lost

Nutrient Availability

Gained – fixed into living matter

Stored – in living and decomposing matter

Lost – by transport, volatilization, and leaching

Disturbed ecosystems in general have lost their ability to gain and/or store nutrients

Nutrient Availability

Limitations to nutrient availability

Primary production – formation of organic matter

Decomposition rate – how fast mineralization happens

Soil moisture

Soil temperature

Soil chemistry – pH & cation exchange capacity

Nutrient Availability

Soil moisture & temperature primarily effect nutrient availability through decomposition

rateWarmer & moister = faster decomposition

BUT fast does not mean better

Balancing storage & loss

Nutrient AvailabilityStorage in soil

Humus – a complex of multitudes of organic molecules that are the products of decomposition

Clay – the smallest class of soil particles & the only chemically reactive one

Colloids!

Negatively charged therefore hold on to cations in the soil solution therefore anions easily lost via leaching

Cation exchange capacity – very important soil characteristic!

Nutrient Availability

Cations – H, K, Ca, Fe, Mg, Mn, Cu, and Zn

Anions – OH-,P, S, N, B, Mo, and Cl

Soil pH regulates availability of cations & anion in solution

Managing Soil for Nutrients

All comes down to feeding & care of the soil biota

What do soil organisms need?

AirWaterFood

Habitat

Managing Soil for Nutrients

AirSoil biota are largely aerobic heterotrophs – they

need O2

Plant roots need O2 as well

N2 for nitrogen fixation

*Therefore soil needs to be well aerated

Managing Soil for Nutrients

Water

Soil biota largely live in the soil solution i.e. they’re more or less aquatic organisms

As OM decomposes and nutrients are mineralized water transports and stores nutrients

*Therefore soil needs to retain moisture

Managing Soil for Nutrients

Food

The soil ecosystem runs on organic matter – dead organisms and the shed parts of live organisms

The rate at which OM is decomposed is restricted by nitrogen availability – C:N

Therefore there needs to be a consistent source of food

Managing Soil for Nutrients

Habitat

Organisms need space to live – less space means fewer organisms means lower decomposition

rate

Therefore soil must have an open structure – pores

Managing Soil for Nutrients

A “healthy” soil has a porous structure that allows for the movement of water, air, and

organisms.

Any action that preserves and promotes a porous soil structure improves nutrient

availability

Managing Soil for Nutrients

Amendments

Organic – compost & other formsInorganic – chemical fertilizers, mined minerals

Surface protection AKA mulch

Organic – woodchips, straw, covercrops, etc.Inorganic – plastic sheets, weed blocker, etc.

Managing Soil for Nutrients

Plant symbionts

Mycorrhizae, nitrogen fixing bacteria

More is not necessarily better when using soil additives!

Assess and test your soil to know what it needs BEFORE adding anything

It’s got what plants crave