Soil color is classified by
a. using a microscope
b. taking core samples
c. determining the proportion of minerals
d. using a color reference chart

Correct C). Determining the proportion of minerals

Soil color is known to be produced by the minerals in the soil and by the presence of the organic matter content in the soil.

Example: Yellow or red color of soil indicate that it has oxidized ferric iron oxides in it. The dark brown color of the soil shows the presence of high organic matter content.

The development of color in the soil is the result of biological and chemical weathering, especially the redox reaction.

step 1: nitrogen fixation- conversion of atmospheric no₂ into forms useful to plants by lightning, bacteria, and cyanobacteria.

step 2: nitrification-process of converting ammonia to nitrite or nitrate.

step 3: assimilation-plant roots absorb new form of nitrogen.

step 4: ammonification-conversion of organic nitrogen to ammonia by bacteria involved in decomposition.

step 5: denitrification-bacteria turns the decomposed matter back into n₂o, which is released into atmosphere; repeat cycle.