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

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. 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.

Soil Components The 4 parts of soil About ½ of the soil volume is solid particles About ½ of the soil volume is pore space

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 – in 2 – 0.05 mm Silt – in mm Clay Less than in Less than mm 1/100 in

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

Supplying Plant Nutrients 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) Nutrients that plants obtain from the soil

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

Recycling plant nutrients

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

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 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

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 NiCaMg Cu K N Zn

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 + -

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

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

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.”

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.

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

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

A Water Molecule H2OH2O (+) Hydrogen Oxygen

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

The Chemistry of Clay: Clay Particle Clay particles carry negative charges

Water ionizes: it falls apart into ions. H 2 O  H + + OH - Called the self ionization of water. Only a small amount. The Strange Properties of Water:

It’s simply a measure of the relative amount of H + ions In the soil, it is driven by the ionization of water: H 2 O  H + + OH - We us pH to measure the acidity or the alkalinity (basicity) of a solution (a soil solution) What is pH?:

Possible pH Ranges Under Natural Soil Conditions black walnut: Most desirable carrot: cucumber: spinach: tomato: white pine: Very strong StrongModerate Slight ModerateStrong Very strong Neutral Acid Basic Most agricultural soils Extreme pH range for most mineral soils cranberry: apple:

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

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.

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

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

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 soilCation Exchange Capacity Permukaan aktif terdapat pada permukaan suatu koloid. Koloid tanah yang menjadi merupakan pusat terjadinya reaksi kimia adalah koloid liat dan koloid humus.

Colloid: solid substance whose particles are very small (few micrometers, 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 cation exchange capacity (CEC): the ability to adsorb and exchange cations. Soil pH is determined by the nature of the exchangeable cations on colloids (H + + Al 3+ vs Ca 2+, K +, Mg 2+, Na + ).

Kejenuhan basa berhubungan erat dengan KPK tanah: % Kejenuhan basa = [Jumlah Kation Tertukar (dlm me %) / KPK] x 100 Contoh : Kation Tertukarme % Ca 10 Mg 5 K 10 Na 5 Jumlah 30 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 %