| Term/Question | Definition/Answer |
| Importance of soil chemistry? | chemical properties of soil determine soil fertility and nutrient availability;
impacts soil pH;
Determines availability of toxic chemicals;
can influence physical properties and moisture, OM |
| What four things are essential to plant nutrients? | Carbon, hydrogen, and oxygen;
Primary macronutrients - nitrogen, phosphorus, potassium;
Secondary macronutrients - calcium, magnesium, sulfur;
Micronutrients |
| Carbon, Hydrogen, Oxygen | obtained by photosynthesis, NOT soil nutrients |
| Primary macronutrients - Nitrogen, Phosphorus, Potassium | NPK is nature's source of nitrogen;
Nitrogen and Phosphorus are most common fertilizers applied |
| Secondary macronutrients - Calcium, Magnesium, Sulfur | Sulfur is common fertilizer need in sandy soils;
Calcium and magnesium are found in many soil parent materials |
| Micronutrients | Boron, Chloride, Copper, Iron, Manganese, Molybdenum, Zinc, Nickel |
| What element is essential for Nitrogen-Fixation by Legumes? | Cobalt - only N-fixation |
| What are three other important soil Elements? | Sodium - high levels cause soil crusting;
Aluminum - becomes toxic to plants in acidic soils;
Silicon - Abundant in soils, no benefit or harm |
| What are two sources of soil nutrients? | most come from SOIL MINERALS, but nitrogen comes from ORGANIC MATTER |
| What are the four pools of soils elements? | Soil minerals;
Organic matter;
absorbed on soil colloids;
soil solution |
| Soil Colloids | clay and humus particles;
carry slight negative charge;
quantity of colloids in soil determined by soil texture/OM;
interact closely with chemicals that have positive charge |
| What are positively charged ions called? | cations |
| Cations | Potassium - K+;
Sodium - Na+;
Ammonium - NH4+;
Hydrogen - H+;
Calcium - Ca++;
Magnesium - Mg++ |
| Typical proportions of Cations in Soils | Calcium - 75-85%;
Magnesium - 12-18%;
Potassium - 1-5%;
Sodium - 1%;
Others - 1% |
| Soil Test = Cation Exchange Capacity | Total number of exchangeable cations a soil can hold;
relative to negative charge, Clay and OM have greatest influence, measures as milliequivalents per 100g of soil |
| Negatively charged ions = | anions |
| Anions | Chloride - CL-;
Nitrate - NO3-;
Sulfate - SO4-2;
Borate - BO4-3;
Phosphate - H2PO4, H2PO4-2 |
| Anion Retention in soils | Phosphate held strongly due to quick formation of insoluble compounds;
Nitrate and Chloride not held in soils and move freely with soil water;
Sulfate held loosly in some low pH soils |
| What is Soil pH? | soil reaction (pH) is an indication of the acidity/basicity of the soil;
at pH 7, Hydrogen ion concentration equals the hydroxyl ion concentration |
| Hydroxyl ion vs. hydrogen ion | Hydrogen causes acidity;
Hydroxyl causes basic condition (alkaline) |
| pH | negative logarithm of the hydrogen ion activity (concentration);
pH = -log[H+];
as pH decreases by one unit, acidity increases 10-fold |
| What is the importance of soil pH? | influences availability of plant nutrients;
may influence toxicity of aluminum;
influence activity of soil microorganisms;
influence soil applied herbicide activity |
| Plant Nutrients Availability | direct effect on Fe, Mn, Ca, Zn, Mo;
Neutral pH favors mineralization from organic matter |
| Aluminum Toxicity Influence | acidity releases aluminum from soil minerals |
| Soil Applied Herbicide Application | determines if able/available to kill weeds;
determines the degradation rate |
| What are some of the main ways soils become acidic? | parent material is acidic (sandstone);
application of nitrogen fetilizers;
heavy precipitation;
native vegetation = forested land;
crops grown;
burning fossil fuels |
| Form of nitrogen fertilizer application? | ammonium/ammonium phosphate |
| heavy precipitation = | leaching of bases |
| because crops grown, | basic compounds removed by harvest |
| What are some of the sources of soil acidity? | Active acidity - measured directly by pH meter to test Hydrogen in soil solution;
Reserve acidity - hydrogen held on soil exchange sites/organic matter that is available to replace the hydrogen in soil solution: Al3+ + H+ |
| What element can be added to raise the soil pH? | lime or calcium carbonate: CaCO3 |
| What are some steps to managing soil pH and Lime? | soil test to determine lime required;
plan ahead bc lime takes time;
lime particles size determines how fast neutralization occurs;
limes works best when applied early |
| Soil tests for lime? | soil pH and CEC |
| How can you manage to lower the soil pH? | apply elemental sulfur to naturally high pH soils;
high pH caused by poor drainage |
| Poor drainage: | install subsurface till drainage |
| Elemental sulfur: | soil bacteria converts to sulfuric acid;
not economical for field crops |
| Salinity | high concentration of total salts |
| What are some causes of salinity? | Poor Drainage;
Shallow Water Table;
Seepage Zones;
Parent Materials |
| Where is salinity in soils a problem in Nebraska? | Lancaster and Saunders counties |
| What is salt? | and inorganic material/mutually charged molecule that can dissolve in water |
| How is salinity measured? | estimated by measuring the Electrical Conductivity (EC);
mmhos/cm |
| What are two different ways to manage saline soils? | leach soils with enough non-saline water that salts are moved below root zone (adequate drainage required);
grow salt tolerant crops |
| What are the minimum requirements for saline soil reclamation? | assess problem;
make sure there's mechanisms for drainage;
have clean water supply |
| Sodicity = | high concentration of sodium (Na) |
| What changes may sodic soils (sodium) make to soil physical properties? | soil aggregates are destroyed;
causes poor drainage/crusting |
| What are two things you need to know when managing sodic soils? | the basic rule;
may need to grow salt-tolerant crop until process in complete |
| The Basic Rule | good drainage - outlet to send sodium when it is displace;
source of calcium/exchange process - gypsum (CaCO4 x 2H2O);
source of water to flush sodium from system |
| In what ways is salinity stress similar to draught? | salts have pulling force on water;
soil salinity = root salinity water less likely to enter roots;
soil salinity is to high - water is pulled back into soil and plant wilts and dies;
(most plants respond to salinity in same way as water deficiency) |
| What can an accumulation of Na+ do? | damage cell mechanisms |
| What can an accumulation of Cl- do? | inhibit photosynthesis |
