HANDOUT 1 GEOGRAFI TANAH

1. HANDOUT 1 GEOGRAFI TANAH PROGRAM STUDI PENDIDIKAN GEOGRAFI FAKULTAS KEGURUAN DAN ILMU PENDIDIKAN UNIVERSITAS MUHAMMADIYAH SURAKARTA

2. What is soil? Soil is the unconsolidated cover on the surface of the earth. Soil is made up of mineral particles, organic particles, air, and water. Soil is capable of supporting plant growth.

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

4. 1/100 in Soil Texture • The mineral part of soil consists of sand, silt, and clay particles • The amounts of each size particle determines the textural property of the soil • Coarse textured, loose (more sand, less clay) • Fine textured, heavy (more clay, less sand) • Loamy (more even mix of sand, silt and clay Sand 0.1 – 0.002 in 2 – 0.05 mm Silt 0.002 – 0.0001 in 0.05 - 0.002 mm Clay Less than 0.0001 in Less than 0.002 mm

5. Soil Structure The arrangement of sand, silt, and clay particles to form larger aggregates. • Organic matter is the glue that holds the aggregates together • Large pores (spaces) between aggregates are filled with air in a moist soil. • Small pores are filled with water in a moist soil. Even smaller pores inside the aggregates (not shown) are also filled with water. 1/10 inch

6. 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) Supplying Plant Nutrients Nutrients that plants obtain from the soil

7. Where do plant nutrients come from? • Decaying plant litter • Breakdown of soil minerals • Addition by humans • Commercial fertilizer • Manure • Lime • Other

8. Recycling plant nutrients N P K

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

10. 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

11. N 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

12. - + 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 • Nutrients and other chemicals • The most important adsorbers in soil are • Clays • Organic matter

13. Surface area of clay 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

14. Soil Chemistry • Chemical bonding • pH • Nutrient Availability • Cation Exchange Capacity (CEC)

15. What is “chemistry?” • Elements: the simplest kind of matter. They cannot be broken down into anything simpler. • Elements can exist alone. Nitrogen (N), Phosphorus (P), Potassium (K), Oxygen (O), are elements and they can be made to exist alone, but in nature they seldom do. • Elements tend to combine with each other. These are called “compounds.” When they combine, it’s called a “chemical reaction.”

16. What is “chemistry?” • Chemistry is the study of the “how” and “why” elements combine, and break apart, through chemical reactions. • Soil Chemistry is simply studying how and why compounds are formed and broken apart in the soil, and how these chemical reactions affect plants.

17. (+) - The Electron = negative charge The Nucleus = positive charge Hydrogen Chemistry Made Simple: The Atom

18. (+) - The Nucleus = positive charge Chemistry Made Simple: The Atom Hydrogen

19. (+) (+) (+) A Water Molecule H2O Hydrogen Hydrogen Oxygen

20. Common soil cations and anions, their chemical symbols and ionic forms

21. - - - - - - - - - - - - - - - Clay Particle - - - - - - - - - - - The Chemistry of Clay: Clay particles carry negative charges

22. The Strange Properties of Water: • Water ionizes: it falls apart into ions. • H2O ® H+ + OH- • Called the self ionization of water. • Only a small amount.

23. What is pH?: • It’s simply a measure of the relative amount of H+ ions • In the soil, it is driven by the ionization of water: H2O ® H+ + OH- • We us pH to measure the acidity or the alkalinity (basicity) of a solution (a soil solution)

25. Neutral Acid Basic Very strong Very strong Slight Strong Moderate Slight Moderate Strong 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Most desirable Most agricultural soils Extreme pH range for most mineral soils apple: 5.0-6.5 spinach: 6.0-7.5 tomato: 5.5-7.5 cranberry:4.2-5.0 cucumber: 5.5-7.0 carrot: 5.5-7.0 white pine: 4.5-6.0 black walnut: 6.0-8.0 Possible pH Ranges Under Natural Soil Conditions

26. Soil Clays • Clays are usually crystalline in nature • Some may be amorphous (e.g., allophane) • Three general definitions; • particle < 2 µm in dia • name of a group of minerals • soil textural class

27. Soil Clays • Crystalline clays have layers of Si and Al oxides held together by ionic bonds (attraction of positive and negative charges; no electron sharing) • Three or four planes of O layers with intervening Si and Al make up a layer. • One clay particle is made up of many layers and is called a micelle.

29. PO4-3 Mg+2 Ca+2 H+ Ca+2 - - - K+ - H+ Mg+2 Clay and organic particles have a negative charge Soil reactions in neutral to high (alkaline) pH conditions - - - - - - - - - K+ - Clay Particle - - - - - - - - Al+3

30. PO4-3 H+ Al+3 - - H+ - - - - Al+3 - - - - - - K+ - Clay Particle - - - - - - - K+ - - Al+3 H+ Al+3 Clay and organic particles have a negative charge Soil reactions in low (acid) pH conditions

31. Pertukaran Kation • KPK atau Cation Exchange Capacity (CEC) merupakan kapasitas tanah untuk menjerap atau menukar kation. Biasanya dinyatakan dalam miliekuivalen/100 g tanah atau me %, tetapi sekarang diubah menjadi cmolc/kg tanah (centimoles of charge per kilogram of dry soil • Permukaan aktif terdapat pada permukaan suatu koloid. • Koloid tanah yang menjadi merupakan pusat terjadinya reaksi kimia adalah koloid liat dan koloid humus.

32. Colloid: solid substance whose particles are very small (few micrometers, 0.001 cm) . • Predominant colloids in soil are clays and humus. • Colloids have a net negative charge (different reason for clays vs humus) and impart the soil cationexchange capacity (CEC): the ability to adsorb and exchange cations. • Soil pH is determined by the nature of the exchangeable cations on colloids (H+ + Al3+ vs Ca2+, K+, Mg2+, Na+).

34. Kejenuhan basa berhubungan erat dengan KPK tanah: % Kejenuhan basa =  [Jumlah Kation Tertukar (dlm me %) / KPK] x 100 Contoh : Kation Tertukarme  %Ca10 Mg5 K10 Na5 Jumlah30  Jika KPK tanah = 50 me %, maka % kejenuhan basa = 30/50 x 100 = 60 % Ada korelasi positif antara pH tanah dan persen kejenuhan basa. Secara umum jika pH tinggi, kejenuhan basa akan tinggi. Kejenuhan basa yang rendah berarti kandungan H+ yang tinggi. Kejenuhan basa biasanya dapat digunakan sebagai indikasi kesuburan tanah. Tanah sangat subur à derajat kejenuhan basa ≥ 80%, Tanah kesuburan sedang à derajat kejenuhan basa 50 % - 80 % Tanah tidak subur à derajat kejenuhan basa ≤ 50 %