Effect of nitrogen and phosphorus addition on soil acidity and stoichiometry characteristics in a typical temperate grassland in Inner Mongolia

We conducted a two-year field experiment to investigate the effects of three fertilizers, each with different N∶P ratio, on soil pH and stoichiometry characteristics. Our results showed that, when compared to the control, N input (when in excess of 30 g·m-2) significantly decreased soil pH when both N and P were added. However, N input (when in excess of 10 g·m-2) also decreased soil pH when only nitrogen was added, and the value was much lower than that when treatments included addition of both N and P. Moreover, comparing to high N and low phosphate input, the low nitrogen and high phosphate input significantly decreased the concentrations of macroelements (K, Ca, and Mg), microelements (Fe, Mn, Cu, and Zn), as well as toxic elements (Al and Mn), and also decreased the soil N∶P. This is possibly due to P limited in this area, and high P low N inputs mitigate P limited on plant growth, simultaneously increased other nutrients uptake by plant, resulting in the decrease of nutrients in soil. Therefore, based on the available soil nutrients and the amount of nitrogen that is being added, appropriate addition of phosphate can mitigate the influence of nitrogen deposition on soil pH and stoichiometry characteristics.