Thus, the phosphates present in the plants through irrigation or through natural absorption of soil water, become part of the constituents of growing plants in the ecosystem. Plants, however, do not remain unused; they are consumed by herbivorous animals, as fodder and by man as herbs and vegetables. As a result, phosphorous, in the form of the phosphates originating in the weathering of rocks, enters into the bodily systems of herbivorous plants and animals, and unites in the process of transformation or metabolism to form other chemical compounds of phosphorous. The process does not end there, as both man and animal pass out waste matter in the form of urine and excreta (Joiner, 75). Man and animals pass these out into or onto soil, or into lavatories (from lavatories, these wastes ultimately arrive in the soil). Alongside these process is the decomposition of dead plant or of animal and human bodies, which releases already absorbed or digested phosphates ( Mariah, 95). Thus, converted phosphates enter the soil, and close the cycle there.
The above description is basically the process of the phosphorous cycle. ...
Sewage farm, for instance, is farm which is irrigated with "sewage irrigation" (i.e. irrigation by sewage liquid), while sewage grass is grass grown on land fertilised by sewage. Thus phosphate waste matter is used to nurture plants, which store them up for animal and man, and for the enriching of farm soils, from which plants take nourishment or off which they may be washed into rivers and streams.
Also relevant in the phosphorous cycle is the aquatic system, which includes plants and their environmental streams and rivers. Phosphates (from fertilisers or weathering of rocks, for example) not used by aquatic plants find their way into streams and rivers, and settle at the floor these waters. When these waters are stirred up (perhaps by man or fish), part of these settled sedimentary phosphates may re-enter the phosphorous cycle, through spilling over onto soils.
In summary, therefore, the phosphorous cycle involves the transformation of phosphates from some liquid form into some solid form - or vive-versa - through the internal chemical processes of the interaction of the ecosystem constituents. Beginning with assimilation of phosphates into soils through rock weathering, its ends with the assimilation of phosphates back into the soil through the decomposition and excretion of plant, man, and animal.
However, while phosphates are advantageous and essential to life and agriculture, they do at times have their adverse effects. A typical instance is its negative effect on fresh water. Typical fresh water is neutral, i.e. it has a PH value of 7; it is colourless, tasteless and odourless; perfectly fit for drinking, for cooking and for washing. But when excessive phosphates are allowed to enter into a reservoir or pool of fresh water