A mixture of humus and particles weathered from rock. A cubic yard of soil will cover 300 square feet of ground to a depth of 1 inch. The major nutrients are nitrogen, phosphorus, and potassium. Bacteria and fungi produce humus. Half the volume of good soil is pore spaces. Microbial decomposers account for 60-80% of total soil metabolism; bacteria drive nitrification, sulfur oxication, and nitrogen fixation. Actinomycete microbes help form humus; they are the most numerous organisms after bacteria. Soil texture means the relative proportions of sand, silt, and clay. We live on 1/12 of the Earth’s surface but have discarded ¾ of its productive soil. Replacement of an inch of topsoil takes 500 years.