1. The topic is Soil Structure, Adsorption and Soil Stability. Three important considerations when evaluating soil amendments designed to improve

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Byron Eaton
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1 1. The topic is Soil Structure, Adsorption and Soil Stability. Three important considerations when evaluating soil amendments designed to improve sodic conditons or just plain poor soil conditons. 2. Some of the information in this module might surprise you. But we hope it will be valuable information when considering reclaiming poor soil structure caused by sodic conditons in the soil profile. 3. Click to next slide 1

2 1. Let s review what got us here. 2. Read slide. 3. Click to next slide. 2

3 1. Platelets are held by polyvalent cations -- calcium ions are good examples of polyvalent cations holding clay platlets together. 2. Here you see the 2+ calcium cations drawing and holding two platlets together through electrostatic attraction. Click to next slide. 3

4 1. The process in which molecules or particles bind to a surface is called adsorption. 2. Here you see the calcium cations being adsorbed to the two clay platlets 3. Click to next slide. 4

5 1. Two important areas of sorption form on the outside of the clay particle an inner sphere and and outer sphere. 2. Notice that most of the ions depicted in this illustration are surrounded by water molecules. 3. When water forms around an ion, it is deemed the ion s hydration shell. Sometimes hydration shells are made up of more than one layer of water molecules. 4. Click to next slide. 5

1. Here we see a soil surface, an area close to the surface called the Inner Sphere, an area further from the surface called the Outer Sphere, and finally another area, still further away call the

6 1. Here we see a soil surface, an area close to the surface called the Inner Sphere, an area further from the surface called the Outer Sphere, and finally another area, still further away call the Diffusion Ion Swarm. 2. In the inner sphere, we see two red ions that have attached (complexed) directly to the soil surface. No water molecules are between the ions and the surface. 3. Slightly further away, we wee 2 ions surrounded by water molecules (a hydration shell) which prevent direct contact but they are still held by electrostatic forces. 4. And we see other ions with hydration shells that are sitting in waiting to get their chance to move into either the inner sphere or outer sphere positions (usually in the soil solution). 5. Let s investigate this further. 6. Click to next slide. 6

7 1. Let s discuss these Outer Sphere Complex ions that are surround by a hydration shell but are held near the surface of the soil particle. 2. Read the characteristics of the outer sphere complex. 3. If we think about it, these characteristics can all be applied to nutrient cations because most nutrient cations are indeed, outer sphere complex ions. 4. Click to next slide. 7

8 1. Now we re going to look at a different breed of cat the inner-sphere complex ions. 2. Read through characteristics. 3. We ll look at some inner-sphere complex ions later. 4. Click to next slide. 8

9 1. Since calcium and sodium have water molecules between the ion and the soil surface, they are classified as Outer Sphere ions. 2. There is no direct connection to the soil surface. 3. Please take note that Sodium has a larger inner hydration shell than calcium. 4. Click to next slide. 9

10 1. So what we have become accustomed to seeing are clay platelets being held by calcium ions. Click to next slide. 10

11 1. Is now replaced by this. 2. Notice that the soil particles are not held as close as what may have been depicted in the past. 3. Click to next slide. 11

12 1. So both sodium and calcium are defined as Outer Sphere ions with relatively weak, reversible binding capabilities. 2. Click to next slide. 12

13 1. Furhermore, Calcium is subject to exchange reactions that puts soil structure in jeopardy. 2. Click to next slide. 13

14 1. Let s review the impact of sodic conditions in clay soils. 2. As sodium ions increase in the soil solution and outnumber calcium ions, calcium ions will exchange with sodium to balance the exchange environment. 3. This is called the law of mass action. 4. Click to next slide. 14

15 1. When one look at the relative flocculating power of sodium to calcium, it s not hard to guess what comes next. 2. Click to next slide. 15

16 1. Read text. 2. Click to next slide. 16

17 1. Read text. 2. Click to next slide. 17

18 1. Eventually the result is a fully dispersed, deflocculated soil particle. 18

19 1. Here we see two soil particles surrounded by dispersed soil particle constituents. 2. Click to next slide. 19

20 1. The result of deflocculation is the establishment of tight arrangement of dispersed soil particles with sodium that can reduce soil porosity and destabililize soil. 2. This same deflocculation / destabilizing effect can occur under acidic conditions where monovalent hydrogen ions displace or replace calcium on the soil particle surface. 3. Click to next slide 20

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23 1. We can add a lot of calcium to displace the sodium on the surfaces of dispersed soil platelets. 2. Click to next slide. 23

24 1. And let the electrostatic attraction from the calcium ions flocculate the platelets. 2. Click to next slide. 24

25 1. To this. 2. Still a bit wider than the previously depicted flocculated soil particles. 3. Click to next slide. 25

26 1. Some call it the oreo solution. 2. Click to next slide. 26

27 1. But then again, this tactic is easily reversible. 2. Click to next slide. 27

28 1. Is replaced by this. 2. Notice that the soil particles are not held as close as what may have been depicted in the past. 3. Click to next slide. 28

29 1. Review module 2B 29

Flocculation and Dispersion

Flocculation and Dispersion Flocculation is the process, where the individual particles of clay are coagulated to form floccular aggregates. The degree and permanence of flocculation depend upon the nature