Soil Labs
3/29/2020 Soil Phosphorus and Potassium (Chapter 14) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
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Soil Phosphorus and Potassium (Chapter 14) Notes
Soil Phosphorus and Potassium (Chapter 14) Notes
Did you know .... Did you know there is an area in the Gulf of Mexico where animals and plants cannot live due to high levels of nutrients? Chapter 14 moves us down the nutrient line to discuss phosphorus and potassium in soils including eutrophication which contributes to the Dead Zone in the Gulf.
Lecture content notes are accompanied by videos listed below the notes in each submodule (e.g. Soil Phosphorus and Potassium (Chapter 14) Videos A though D). Print or download lecture notes then view videos in succession alongside lecture content and add additional notes from each video. The start of each video is noted in parenthesis (e.g. Content for Video A) within each lecture note set and contains lecture content through the note for the next video (e.g. Content for Video B).
Figures and tables unless specifically referenced are from the course text, Nature and Property of Soils, 14th Edition, Brady and Weil.
Content Video A
Soil Phosphorus
http://www.nasa.gov/vision/earth/environment/dead_zone.html
Phosphorus
AGRI1050R50: Introduction to Soil Science (2020S) LH
3/29/2020 Soil Phosphorus and Potassium (Chapter 14) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403429/View 2/10
p Essential Element
Energy Molecule – ATP DNA/RNA Phospholipids
Plant Photosynthesis, Flowering/Fruiting, Root Growth, Meristem Deficiency: Stunted growth, weak stem, dark blue/green Mobile in plant – moves old to young tissues
Plant Uptake – Low, Low P in soil solution HP042- or H2PO4-
Phosphorus and Soil Fertility Conundrum:
Total P low (200 to 2000 kg/ha in upper 15 cm) P Compounds in soil not plant available and insoluble Added P (fertilize, manures) become unavailable too
Environmental Quality Underdeveloped Countries – Lack of P fertilizer, limits crop production P Enrichment and Loss – Eutrophication
Content Video B
Phosphorus Cycle
3/29/2020 Soil Phosphorus and Potassium (Chapter 14) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403429/View 3/10
Soil and Environmental Quality, 2nd Edition, Pierzynski, et al.
Phosphorus Cycle Weathering P minerals primary source – Inorganic
Parent materials and weathering degree dictate sources Apatites (Ca-Alkaline) vs Fe/Al Oxides (Hi Weathered –Acidic)
Soluble P in solution – Low - 0.001 to 1 ml/L Ion Dictated by soil pH – HP042- or H2PO4- Fixation P – Strong – Not exchangeable Movement to roots is SLOW
Mass Flow Water Mycorrhizae
Losses P No real gaseous loss Plant Uptake Leaching not huge issue – strong affinity colloids Erosion/Runoff - major environmental loss mechanism under right conditions
Phosphorus and pH
3/29/2020 Soil Phosphorus and Potassium (Chapter 14) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403429/View 4/10
Inorganic P Fixation
More on Fixation
Fixation Capacity in Soils
3/29/2020 Soil Phosphorus and Potassium (Chapter 14) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403429/View 5/10
P Availability Soil Orders
Organic Sources of P Organic P – SOM
1/10 to ¼ of N levels Mineralization C:P< 200:1
Important in Hi Weathered Soils even with Low SOM Inositol Phosphates
Enzymes Phytic Acid – P grain storage
Non-Ruminants – hogs and chickens - cannot process Add to animal feed – high P levels in manure
Organic P More soluble - less fixation than inorganic P Greater likelihood loss in leaching, runoff Over application of organic forms P – manure
Content Video C
Point Source vs Non-Point Source Pollution Point Source – Identifiable source of discharge
Emission, Solids, Liquids Wastewater treatment facilities, industry
Non-Point Source – Unidentifiable source of discharge Nutrients and Pathogens Agriculture, Septic Tanks, Urban Discharge
3/29/2020 Soil Phosphorus and Potassium (Chapter 14) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403429/View 6/10
Forms of P in Runoff Form of P Name Description TP Total Phosphorus Total P in Runoff Volume TSP Total Soluble P Orthophosphates and Organic P SP Soluble P Soluble forms of Inorganic P SOP Soluble Organic P Soluble forms of Organic P PP Particulate P Total P in Sediment
BAP Bioavailable P Total P Readily Available
Eutrophication
http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel/problems_in_environment/pollutionrev4.shtml
3/29/2020 Soil Phosphorus and Potassium (Chapter 14) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403429/View 7/10
http://extension.usu.edu/waterquality/htm/agriculturewq
Managing P Apply P to meet plant needs – Do not over apply P Apply in combination with N fertilizers
N fertilizers create acidity locally, keeps soluble, plant available Apply in band as Starter Fertilizer
Minimizes surface area for fixation Make plant available early, minimize loss
Enhance cycling of organic P Cover crops – Build SOM, etc. Mycorrhizal Symbiosis
Control soil pH – Near-neutral for max solubility Minimize tillage – Decrease loss runoff/erosion Buffer/Filter Strips – Catch P/N in runoff water/sediments
Content Video D
Soil Potassium
http://www.extension.umn.edu/agriculture/nutrient-management/potassium/potassium-for-crop-production/
http://www.extension.umn.edu/agriculture/nutrient-management/potassium/potassium-for-crop-
3/29/2020 Soil Phosphorus and Potassium (Chapter 14) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403429/View 8/10
production/
Potassium Essential Element
Not incorporated into structures Enzyme Activator
Plant Osmotic water potential – aids with water loss Photosynthesis, Protein Synthesis, N Fixation *Environmental Stress – Drought tolerance, winter hardiness, better resistance to fungal disease and insect pest. 1 to 4% Healthy Plant Tissue (Similar to N) Deficiency: Yellow spots on leaf edge, look burned/ragged
Plant Uptake – Generally large total quantities in soil, low availability K+ ion in soil solution
Potassium Cycle
Liming and Soil K Maintaining Neutral pH with Lime
3/29/2020 Soil Phosphorus and Potassium (Chapter 14) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
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Maintaining Neutral pH with Lime K+ more readily replace Ca2+ and Mg2+ (neutral) than Al3+ (acidic) Keeps K+ in soil profile
Potassium (K) Cycle Additions
Weathering parent materials and exchange on soil colloids Not associated with SOM Much total K not available: low solubility and fixation Fertilizer needed in cropping systems
Losses Leaching – Greater in acidic conditions Crop Uptake - Big loss
Luxury Consumption No gaseous loss
Forms of K in Soils Pools dependent on parent material, clay content, CEC Primary Mineral Structure – Micas/Feldspars
90-98% total soil K SLOWLY available – relatively unavailable pool
Non-Exchangeable K – Fixed in Clays
3/29/2020 Soil Phosphorus and Potassium (Chapter 14) Notes - AGRI1050R50: Introduction to Soil Science (2020S)
https://gotoclass.tnecampus.org/d2l/le/content/8094442/viewContent/60403429/View 10/10
Reflect in ePortfolio Download Print
Non-Exchangeable K – Fixed in Clays 1-10% total K Slowly available
Readily Available 0.1 to 0.2% Soil Solution K 1 to 2% Readily Exchangeable K – Soil Colloids
K Fixation Amount determined clay and pH
1:1 (Kaolinite) – Very little fixation 2:1 Clays (Vermiculite especially) – High levels of fixation
pH Liming increases fixation Closer to the soil colloids – 2:1 clays fixation
Managing Soil K Crop uptake – major removal SOIL TEST – Know what need! Commercial Fertilizer Addition – Potash (KCl)
Maintain adequate soil solution K for particular plant needs Many soils just need ‘maintenance K’ Highly weathered, acidic soils, or sandy soils - generally need more commercial K
Maintain soil pH
Review P and K What is P utilized for in the plant? What are the plant available forms of P? What are the challenges for P and soil fertility – both in developed and developing countries? What is the P Index? Can you describe Figure 14.9 – P and pH? Can you describe the mechanisms of P fixation – soil pH, orders, soil colloids, etc.? Why are organic forms of P important? Why are they more likely to be lost to leaching than inorganic P? Point Source vs Non-Point Source pollution Why is erosion and runoff loss a greater issue than leaching of P unlike N? Define Eutrophication – why is it environmentally important? What are some management strategies to manage soil P? What is a buffer strip? What role does K play in plant production? What form of K is available for plant uptake? What are the major additions and losses of K from the soil system?
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