Micronutrients Iron (Fe) Boron (B) Zinc (Zn) Copper (Cu) Manganese (Mn) Molybdenum (Mo) Principal nutrients Nitrogen (N) Phosphorus (P) Potassium (K) Secondary nutrients Calcium (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 molecules Magnesium in Chlorophyll Chlorophyll is the green pigment, within chloroplasts, within cells, within a leaf Image: by Melvin Pao. License: CC BY-NC-SA Image: by David Richfield. License: Public Domainhttps://commons.wikimedia.org/wiki/File:Chlorophyll_a.svg

Cations and Anions in Soil What are cations? – Positively charged ions (NH 4 +, K +, Ca 2+, Fe 2+ ) What are anions? – Negatively charged ions (NO 3 -, PO 4 2-, SO 4 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:3-5 Sands, dark-colored: Loams: Silt Loams: Clay and clay loams: Organic soil: Units: milliequivalent of hydrogen per 100 g of dry soil(meq+/100 g)

Q: How can you maintain and improve CEC in sandy soils? Maintain the organic layer Reduce tillage and erosion Use cover crops Maintain a diverse soil biota Image: by Soil NC State. License: CC BY 2.0http:// Fuquay series soil profile from NC (sandy)

Reduced tillage or no-till builds soil organic matter and increases cation exchange capacity. Image: by USDA NRCS South Dakota License: CC BY-SA 2.0http://

Soil pH What is soil pH? A measure of H + ions in soil water H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Image: by Edward Stevens (CC BY-3.0)

Soil pH around the world AcidicNeutral Alkaline Image: 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 CO 2 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: Johann Dreo License: CC BY SA 3.0http://commons.wikimedia.org/wiki/File:Nitrogen_Cycle.svg

Where does N from added fertilizers enter? Image: Johann Dreo License: CC BY SA 3.0http://commons.wikimedia.org/wiki/File:Nitrogen_Cycle.svg

And in what form do plants take it up? Image: Johann Dreo License: CC BY SA 3.0http://commons.wikimedia.org/wiki/File:Nitrogen_Cycle.svg

NPK The principal nutrients N: Nitrogen P: Phosphorus K: Potassium Provided together in fertilizers e.g., : the proportions of the element N and the proportions of the oxides of P and Q Image: 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