、 Soil acidity (-) The cause of soil acidity 1. Climatic factor 2. Biological factor 3. Fertilizer application and irrigation 1. The source of hydrogen ions. (1 Water dissociation (2) Carbon dioxide (3) Organic acid (4 Inorganic acid(inorganic fertilizer) (5 Acid rain一、Soil acidity （一）The cause of soil acidity 1． Climatic factor 2．Biological factor 3．Fertilizer application and irrigation 1.The source of hydrogen ions （1）Water dissociation （2）Carbon dioxide （3）Organic acid （4）Inorganic acid (inorganic fertilizer) （5） Acid rain