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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