Salt removal from soil during rainy season of semi-arid climate following an assumed salt accumulation from previous cultivations fertilized with urine

Due to its high salt content, urine use as a fertilizer threatens agricultural land by causing soil sodification, especially in arid and semi-arid lands where limited water resources restrict full salt washout. This study investigated the management of salt accumulation in a soil in which urine was assumed to be previously directly applied as a fertilizer. Since feasibility studies of urine use as a fertilizer have been previously reported in the arid land of Burkina Faso in the Sahel region, we investigated the removal during rainy season using rainfall and evaporation data from Burkina Faso of the salts accumulated in the soil from previous cultivations assumed to be fertilized with urine. Column test experiments were carried out under greenhouse conditions. The experiment involved irrigation of planted and non-planted pots for 56 days with de-ionized water to reproduce the rainy season in Burkina Faso. Prior to the experiments, 400 mg/pot of NaHCO 3 was added to the top 10 cm of the soil columns, simulating the initial salt content in the soil due to the assumed previous irrigation using urine (pH = 7.63). Although, Na salts are the dominant salt in urine, sodium bi-carbonate has been used in this study as it has a buffering capacity to resist to sudden pH changes. The experimental study revealed that a significant portion of salt that accumulated in the column during cultivation is washed out of non-planted pots during the rainy season. In planted pots, the higher evaporation rate led to less washout and more salt accumulation in the soil. Of the original 400 mg/pot, 259 mg/pot was washed out of non-planted pots, while only 80 mg/pot was washed out of planted pots. Another 40 mg/pot was taken up by plants in the case of planted pots. A HYDRUS-1D model was then used to predict the fate of the salts in the soil (non-planted) under different conditions (e.g., variable calcium supply, variable initial Na concentration). Model calibration was performed using data from previous experiments. The application of Ca promoted lower sodic conditions in the soil. A Ca application of 14 g/m 2 is required to free all the remaining sodium salts via the cation exchange mechanism allowing their full washout from the soil.