Explanation : "Standing state" is a term used in ecology to denote the amount of nutrients such as carbon, nitrogen, potassium, calcium, etc., present in the soil at any given time. It provides an estimate of the availability of these nutrients in the ecosystem. On the other hand, "Standing crop" is a term used to describe the total biomass (the mass of living biological organisms) of an organism in a particular area or volume at a specific time. "Humus" refers to the organic component of soil, formed by the decomposition of leaves and other plant material by soil microorganisms. "Detritus" is dead particulate organic material. It typically includes the bodies or fragments of dead organisms, as well as fecal material. Detritus is typically colonized by communities of microorganisms which act to decompose it.