The study looked at how different types and amounts of nitrogen fertilizer affect the acidity and base saturation of purple soil. They found that the pH of the soil decreased as nitrogen fertilizer leached through it, with the type of nitrogen affecting the acidity levels. Exchangeable acidity increased with nitrogen application, mainly depending on exchangeable aluminum. Base saturation decreased with nitrogen application, with urea, nitramine, and thiamine showing different effects. Overall, the pH decreased and exchangeable acidity increased in purple soil, while base cations helped increase pH.