Micronutrients Iron (Fe) Boron (B) Zinc (Zn) Copper (Cu) Manganese (Mn) Molybdenum (Mo) Principal...

MicronutrientsIron (Fe)Boron (B)Zinc (Zn)Copper (Cu)Manganese (Mn)Molybdenum (Mo)

Principal nutrientsNitrogen (N)Phosphorus (P)Potassium (K)

Secondary nutrientsCalcium (Ca)Magnesium (Mg)Sulfur (S)

Soil Chemistry and Plant Nutrients

Image: Jon Davis, author of this presentation (CC BY-SA 2.0)

Plants use soil nutrients to construct

• DNA and RNA: nitrogen, phosphorus)• Proteins: nitrogen (N), sulfur (S) • Many other metabolites (lots of elements) – i.e. chlorophyll, anti-herbivorous chemicals

Note: Plants use K (potassium) to regulate numerous metabolic processes and membrane permeability

Micronutrients in organic moleculesMagnesium in Chlorophyll

Chlorophyll is the green pigment, within chloroplasts, within cells, within a leaf

Image: http://www.flickr.com/photos/76944491@N00/2590848826/ by Melvin Pao. License: CC BY-NC-SA 2.0Image: https://commons.wikimedia.org/wiki/File:Chlorophyll_a.svg by David Richfield. License: Public Domain

Cations and Anions in Soil

• What are cations?– Positively charged ions (NH4

+, K+, Ca2+, Fe2+)

• What are anions?– Negatively charged ions (NO3

-, PO42-, SO4

2-)

Cation Exchance Capacity (CEC)

• Both organic and mineral components of soil are negatively charged

• Cations that are important for plants can bind to them.

• These bound cations are not leached from soil by water.

Cation Exchange Capacity

Image created by Jon Davis, the author of this presentation. License: (CC BY-SA-3.0)

Positively charged ions bind to soil

CEC depends on soil texture

Sands, light-colored: 3-5Sands, dark-colored: 10-20 Loams: 10-15Silt Loams: 15-25Clay and clay loams: 20-50Organic soil: 50-100

Units: milliequivalent of hydrogen per 100 g of dry soil(meq+/100 g)

Q: How can you maintain and improveCEC in sandy soils?

Maintain the organic layer Reduce tillage and erosion Use cover crops Maintain a diverse soil biota

Image: http://www.flickr.com/photos/soilscience/5105328004/ by Soil Science @ NC State. License: CC BY 2.0

Fuquay series soil profile from NC (sandy)

Reduced tillage or no-till

builds soil organic matter and increases cation exchange capacity.

Image: http://www.flickr.com/photos/nrcs_south_dakota/7489934494/ by USDA NRCS South Dakota License: CC BY-SA 2.0

Soil pH• What is soil pH?• A measure of H+ ions in soil water

H+

H+

H+

H+

H+ H+

H+

Image: https://commons.wikimedia.org/wiki/File:PH_Scale.svg by Edward Stevens (CC BY-3.0)

Soil pH around the world

Acidic Neutral Alkaline

Image: http://commons.wikimedia.org/wiki/File:World_Soil_pH.svg by Ninjatacoshell (CC BY-SA-3.0)

Why are acidic soils in wetter places?

• Rainwater is slightly acidic (pH 5.7)– Rain is also known as carbonic acid, due to a reaction with

CO2 in the atmosphere. This creates caverns around the world.

• Nitrification of ammonium in fertilizer releases H+

– Nitrification will be discussed later in this presentation.

• Plant roots emit H+ when taking up other cations– Cations are postively charged ions, like

• Weathering: Highly weathered soils contain lots of Al and Fe (as in tropical soils)

Problems of acidic soils and how to address them

• Aluminum toxicity• Deficiencies of calcium and magnesium

• Most common method of amelioration of acidity: adding lime

• Lime: calcium containing inorganic products (e.g. limestone, gypsum)

The nitrogen cycle

Image: http://commons.wikimedia.org/wiki/File:Nitrogen_Cycle.svgby Johann Dreo License: CC BY SA 3.0

Where does N from added fertilizers enter?

Image: http://commons.wikimedia.org/wiki/File:Nitrogen_Cycle.svgby Johann Dreo License: CC BY SA 3.0

And in what form do plants take it up?

Image: http://commons.wikimedia.org/wiki/File:Nitrogen_Cycle.svgby Johann Dreo License: CC BY SA 3.0

NPK

• The principal nutrients N: Nitrogen P: Phosphorus K: Potassium• Provided together in fertilizers• e.g., 15-15-15: the proportions of the element N and the

proportions of the oxides of P and Q

Image: http://www.flickr.com/photos/iita-media-library/8144240712/ by IITA image Library (CC BY-NC 2.0)

Laboratory activities

• For each soil sample, in each plot or treatment collected earlier, we will determine…– pH– CEC– N– P– K