Evolution of Nitrogen and Phosphorus in Tunisian Agricultural Soil Under Controlled Conditions

The over-supply of nitrogen and phosphorus as a mineral fertilizer can lead to decreased soil organic matter (OM). The objective of this study is to evaluate the temporal evolution of the quantities of nitrogen and phosphorus mineralized in an agricultural soil to demonstrate the impact of the physicochemical properties related to ammonium (NH₄⁺) and phosphorus (PO₄³⁺) applied on their availability in low-limestone soil of vertical character. A short-term incubation experiment of six weeks was carried out under controlled conditions of the laboratory, on a Tunisian agricultural soil (Xerofluvents Vertic) (Siliana-North Tunisia). The soil was subjected to two inorganic inputs, ammonium (NH₄⁺) and phosphorus (PO₄³⁺). These two products are provided at a rate of 0.5 and 1 N in the soil and incubated at a temperature of 25 and 30 ± 1 °C. These treatments are compared to samples from the same soil without input.

The main results, during the incubation experiment, following the addition of (NH₄) and (PO₄), on the soil studied, show an increase in the availability of ammonium and phosphorus, at the beginning of the experiment, and there was also an increase in salinity (electrical conductivity, EC) and instead a decrease in pH. This “in situ” study proves that it is essential to choose fertilizers and the appropriate contents according to the soil components to obtain appropriately reasoned mineral fertilization respecting the environment and precisely the physicochemical properties of soils and groundwater.