The anthropogenic causes of acidification became apparent only in the second half of the twentieth century. Since then, the problem of soil acidification, and especially the problem of toxic substances appearing as a result of strong soil acidification, has been the most serious factor of low productivity of arable soils and low efficiency of mineral fertilization in Poland (Lipiński 2005, Tkaczyk and Bednarek 2011). Human activities related to air pollution, the functioning of industry to a greater extent, the use of mineral fertilization, mainly nitrogen, ammonium, amide and potassium, acid rains and the intensification of agriculture are the main factors causing soil acidification. The reason for acidification to a large extent is the elevation of CaO together with the yield from 50 to 300 kg ha-1. The soil becomes acidified also after fertilization with manure and slurry as a result of the ongoing process of ammonium nitrogen nitrification.
Table 1 shows the effect of mineral and natural fertilizers on soil pH. The use of mineral fertilization significantly affects the pH of the soil. The effect of mineral fertilizers on the pH of the soil depends on their properties. Nitrogen fertilizers and slurry strongly acidify the soil, when calculating the acidification strength with a calcium equivalent, it can be assumed that in order to balance one kilogram of nitrogen you need:
2 kg CaO for urea, ammonium nitrate
4 kg CaO for ammonium sulphate