ABSTRACT

When the Land-spreadings are on agricultural soil, the elements that can be assimilated by plants can also be recycled by the vegetation depending on its requirements. To Limit transports to aquifers or accumulation in arable horizons, spreadings have to be adjusted according to possible exportations by vegetation, the quantity supplied being calculated from the first element for which the requirements are met by the supply. This theoretical step is actually used by agronomists for the principal fertilisers (N, P, K), taking into account their particular characteristics. Phosphates have limited mobility; the quantities supplied during a spread may be available over several years unless they are stably immobilised. Potassium can also be stored and is available over several agricultural cycles, but its assimilation varies depending on availability and may lead to considerable excess consumption; excessive amounts may cause imbalances in the mineral composition of the plants.