SCSC 301 Exam 3 Questions With Complete Solutions

An important function of micro-organisms in soils is the fixation of correct answer: Nitrogen The well decomposed organic matter in the soil that is composed of ligno-proteins and contributes to the cation exchange capacity is: correct answer: Humus Bacteria are important to the decomposition of residues : correct answer: Under slightly acid to neutral conditions Assuming favorable climatic and soil environment conditions, the factor most often controlling the rate of residue decomposition in soils is: correct answer: Nitrogen content residue A product of the complete oxidation of organic residues is correct answer: H2O A principle chemical role of organic matter in soils is: correct answer: increase nutrient cycling A principle effect of organic matter on soil physical properties is to: correct answer: Decrease Bulk density The organic matter of soils tends to decrease with increasing frequency of: correct answer: Cultivation In order t have the longest period of time that the crop residue will remain on the soil surface, you should choose a cover crop that has an N:C ratio of correct answer: 80:1 The ratio of Al:H adsorbed on colloids tends to increase as the soil: correct answer: Becomes more acid At pH 5.5 of minerals soils the % base saturation is approximately: correct answer: 50 The addition of neutral salt solution (pH 7.0) to a soil having a pH of 5.5 will result in a soil-salt solution pH correct answer: less than 5.5 Hydrogen ion activity that is on the soil colloid determines the soil's correct answer: Reserve capacity Soil A is a Histosol; Soil B is a Vertisol; Soil C is an Oxisol. If all of these soils have the same % base saturation, the order of pH from lowest to highest will be. correct answer: A-B-C The principal sources of negative charge on soil colloids-a. carboxyl groups , b. particle edges, c. isomorphous substitution- arranged in order of decreasing acid strength are; correct answer: a-c-b Soils having a pH less than 3.0 are likely to have: correct answer: strong acids present The strong buffering actions in soils at pH 8.0 is due t the reactivity of; correct answer: calcium carbonate the colloid groups - a amorphous , b silicate clay , c hydrous oxides- arranged in order from most to least soluble are: correct answer: c-b-a On e of the eight most abundant elements in the earth's crust that will enhance the growth of some plants is correct answer: Sodium In describing the mechanism of cation exchange between colloids and soil solution, it can be said that adsorbed cations are: correct answer: easily exchanged The colloid groups - a. silicate clay, b organic, c. hydrous oxides- arranged in order from lowest to highest adsorptive capacity correct answer: c-a-b A soil conatins 1600 ppm of exchangeable Ca^2+ (MW=40g/mole). How many cmol Ca/kg of soil does this soil contain correct answer: 8