SOIL-PH AND NITROGEN CHANGES FOLLOWING CATTLE AND SHEEP URINE DEPOSITION

The relationship between animal urine deposition and variability in so il chemical composition and crop growth is not well established in the semiarid region of West Africa. This study was conducted to examine t he changes over time in soil pH and mineral nitrogen (N) concentration s at the micro sites of cattle and sheep urine patches in comparison t o those occurring in fertilizer urea placement zones. The urine and fe rtilizer solution containing each 400 mg N (800 kg N ha(-1)) were spre ad onto individual plots covering a surface area of 4-cm radius. The t reatments included a control, which consisted of distillate water. Soi l samples from three replicate plots were taken in 4-cm increments to a depth of 16 cm and distance of 16 cm on a grid pattern at days 1, 7, 21, 49, 90, 120, and 150 after application. Significant pH and minera l N gradients develop in the vicinity of the fertilizer and urine plac ement zones declining towards the periphery and the deeper soil layers . The pH at the center of the urine zone remained above 7.5 throughout the 150 days of the study period. After the initial increase, the soi l pH below the fertilizer placement sites declined to the control leve l by day 90. Concentrations of ammonium (NH4) + nitrate (NO3) also inc reased markedly in the immediate soil layers of the urine and urea pla cement zones, and then decreased over time probably due to N losses by volatilization and leaching. Concentrations of mineral N at the perip hery of the placement site were similar for all treatments throughout the study period, indicating very little lateral N diffusion. These re sults provided evidence that animal urine causes significant variabili ties in soil chemical composition, even in short distance from the dep osition zones. The high soil solution pH in the vicinity of the urine patches alleviate the potential of aluminum (Al) toxicity while increa sing the phosphorus (P) availability to crop plants.