Soil pH and nitrogen changes following cattle and sheep urine deposition

The relationship between animal urine deposition and variability in soil chemical composition and crop growth is not well established in the semi-arid region of West Africa. This study was conducted to examine the changes over time in soil pH and mineral nitrogen (N) concentrations at the micro sites of cattle and sheep urine patches in comparison to those occurring in fertilizer urea placement zones. The urine and fertilizer solution containing each 400 mg N (800 kg N ha-1) were spread onto individual plots covering a surface area of 4-cm radius. The treatments included a control, which consisted of distillate water. Soil 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 mineral gradients develop in the vicinity of the fertilizer and urine placement 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 soil pH below the fertilizer placement sites declined to the control level by day 90. Concentrations of ammonium (NH4) + nitrate (NO3) also increased markedly in the immediate soil layers of the urine and urea placement zones, and then decreased over time probably due to N losses by volatilization and leaching. Concentrations of mineral N at the periphery of the placement site were similar for all treatments throughout the study period, indicating very little lateral N diffusion. These results provided evidence that animal urine causes significant variabilities in soil chemical composition, even in short distance from the deposition zones. The high soil solution pH in the vicinity of the urine patches alleviate the potential of aluminum (Al) toxicity while increasing the phosphorus (P) availability to crop plants.