How soils supply plant nutrients An Introduction to Soil Chemistry

1. How soils supply plant nutrientsAn Introduction to Soil Chemistry Prepared by: Richard Stehouwer Department of Agronomy

2. Title the one-pager appropriately to reflect the content. • Write two quotations form the reading. Use proper grammatical format. • Use three visual images to create focus to your page. • Place five essential vocabulary words around the images. Write the main idea of the reading. • Write two questions and answer them. • Put a symbolic border around the edges of the page.

3. Our questions • What is in soil? • Where do soil nutrients come from? • How do plants get their nutrients? • Is there a difference in the adsorption process for different nutrients? • What about salinity?

4. What makes up the soil?

5. About ½ of the soil volume is solid particles About ½ of the soil volume is pore space Soil ComponentsThe 4 parts of soil

6. Lets go back to 9th grade… • Important cell processes: • Protein synthesis • Photosynthesis • Cell respiration • What are the materials needed for these? • Phosphate (ATP) • Carbon • Oxygen • Nitrogen • Carbon dioxide

7. Macronutrients: (needed in large amounts) Nitrogen (N) Phosphorus (P) Potassium (K) Calcium (Ca) Magnesium (Mg) Sulfur (S) Micronutrients: (needed in small amounts) Chlorine (Cl) Cobalt (Co) Copper (Cu) Iron (Fe) Manganese (Mn) Molybdenum (Mo) Nickel (Ni) Zinc (Zn) A. Supplying Plant Nutrients Nutrients that plants obtain from the soil

8. 2. Where do plant nutrients come from? A. Decaying plant litter B. Breakdown of soil minerals C. Addition by humans • Commercial fertilizer • Manure • Lime • Other

9. A. Recycling plant nutrients N P K

10. Water Acid B. Breakdown of soil minerals Zn Ca K Ni Cu Mg

11. C. Nutrient additions by humans • Commercial fertilizers • Nutrients are in a form that is available to plants • Dissolve quickly and nutrients go into soil water • Lime • Dissolves slowly as it neutralizes soil acidity • Releases calcium and magnesium • Organic nutrient sources • Manure, compost, sewage sludge • Decay and nutrient release is similar to crop litter

12. How do plants get their nutrients?

13. N A. The soil solution • Soil water is a complex solution that contains • Many types of nutrients • Other trace elements • Complex organic molecules • Nutrients in the soil solution can be readily taken up by plant roots • If nutrients remained in solution they could all be quickly lost from the soil. P K Zn Ni Ca Mg Cu

14. Another word for this loss of nutrients is LEACHING.

15. - + B. Adsorption • Adsorption refers to the ability of an object to attract and hold particles on its surface. • Solid particles in soil have the ability to adsorb • Water (WHC) • Nutrients and other chemicals • The most important adsorbers in soil are • Clays • Organic matter

16. Is there a difference in the adsorption process?

17. A. Cation Exchange Capacity • Cation exchange capacity (CEC) is the total amount of cations that a soil can retain • The higher the soil CEC the greater ability it has to store plant nutrients • Soil CEC increases as 1. The amount of clay increases 2. The amount of organic matter increases 3. The soil pH increases

18. 1. Claya. Surface Area ¼ cup ¼ cup of clay has more surface area than a football field • The large surface area of clay allows it to • Adsorb a lot of water • Retain nutrients • Stick to other soil particles

19. b. Clay has a negative charge. Clay particles are stacked in layers like sheets of paper. Each clay sheet is slightly separated from those on either side. Each sheet has negative charges on it. Negative charges have to be balanced by positive charges called cations. 1/20,000 in

20. Cation Retention onSoil Clays Calcium, +2 Magnesium, +2 Potassium, +1 Ammonium, +1 Sodium, +1 Copper, +2 Aluminum, +3 Hydrogen, +1

21. 2/3. Organic Matter and pH Hydrogen Nutrients Increasing pH increases cation exchange capacity of organic matter Neutral pH, 7 (“sweet” soil) Low pH, 4 - 5 (acidic soil)

22. B. Negatively Charged Nutrients(Anions) • Some very important plant nutrients are anions. • Soils are able to retain some of these nutrient anions. • Retention of nutrient anions varies from one anion to another 1- 2- 2- 1- Nitrate Phosphate Sulfate Chloride

23. Phosphate retention in soil 3. Adsorption on oxide surfaces Phosphate anions - Each held by two chemical bonds to the iron oxide surface Iron oxide surface

24. Nitrate (NO3-) retention in soils • Unlike phosphate, nitrate is very weakly held by soils • Nitrate does not react to form new solids • Nitrate is not held by oxide surfaces NO3- If nitrate is not taken up by plants it is very likely to be lost from the soil

25. Plant Root H. Moving nutrients from soil to plants Nutrients in soil solution Nutrients on soil clay and organic matter

26. Plant Root Excessive Nutrient Loading Nutrients in soil solution X Nutrients on soil clay and organic matter Nutrient loss in drainage water

27. What about salinity? • Sometimes there is a build up of salt in the soil. (This is caused by our irrigation practices… DON’T worry we will look at it more next week) • When this happens osmosis occurs and draws the water out of the roots. This causes the plant to die. • Only specially adapted plants can survive such environments.

28. The black box is open • Soil consists of mineral and organic matter, air and water • Soils are able to adsorb nutrients and other chemicals • The most important adsorbers are clay and organic matter • Adsorbed nutrients are available to plants • Adsorbed nutrients are not prone to loss in drainage water • Soil adsorption capacity can be exceeded leading to greater nutrient loss