Do you know the acidity or alkalinity of common fertilizers?

I. 
Inorganic chemical fertilizers 
(1) Acidic Fertilizer 
Ammonium sulfate: Physiologically acidic (referring to the release of H+ after plants absorb ammonium ions), long-term use can lead to soil acidification and requires the addition of lime for adjustment. 
2. Ammonium chloride: Physiologically acidic, with a high chlorine content. Use with caution on chlorine-sensitive crops such as potatoes and tobacco. 
3. Superphosphate: Chemically acidic, with a pH value of 3 to 4 and containing free acid, it is suitable for medium to alkaline soils. 
(II) Alkaline Fertilizers 
Diammonium phosphate: Chemically alkaline, it is weakly alkaline with a pH value of approximately 8.0. When applied to acidic soil, it can reduce the fixation of phosphorus by iron and aluminum, keeping phosphorus in a highly available state. Therefore, it is recommended to use diammonium phosphate on acidic soil. 
2. Calcium magnesium phosphate fertilizer: Chemically alkaline, with a pH value of 8 to 8.5. It is used to supplement phosphorus in acidic soil and contains calcium and magnesium trace elements. 
3. Sodium nitrate: Physiologically alkaline (referring to the release of OH- after plants absorb nitrate ions), excessive use can cause soil compaction. 
Ammonium bicarbonate also belongs to alkaline fertilizers. 
(3) Neutral or near-neutral fertilizers 
Urea: Neutral, but it generates ammonium ions after decomposition, causing short-term acidification. 
2. Potassium sulfate: Weakly acidic or nearly neutral, suitable for chlorine-sensitive crops. 
3. Potassium chloride: Neutral, long-term use can lead to soil acidification. 
4. Ammonium nitrate: Physiologically neutral (referring to the balanced absorption of ammonium and nitrate ions).

II. 
Organic fertilizer 
1. Composted farmyard manure (dung and compost): It is mostly weakly alkaline, with a pH value of 7.5 to 8.5. It is rich in organic matter and can adjust the soil pH value and improve soil structure. 
2. Cake fertilizer (soybean meal, rapeseed cake): It is acidic before fermentation and nearly neutral after complete decomposition. Uncompletely decomposed application is likely to burn roots. 
III. 
Mineral source fertilizers and soil conditioning mineral fertilizers 
Quicklime: Strongly alkaline, it can neutralize acidic soil, supplement calcium, and is used for improving acidic soil with a pH value less than 5.5. 
2. Sulfur: Acidic, it can lower the pH value of alkaline soil and is used for the improvement of saline-alkali soil with a pH value greater than 7.5. 
3. Wood ash: Alkaline, it can replenish potassium, increase soil pH value, and has antibacterial effects. It is used for improving acidic soil and for potassium-loving crops. 
IV. 
Application Principles 
Soil testing first. 
Ammonium sulfate should be used with caution in acidic soil (pH < 6.0), and it is better to apply calcium magnesium phosphate fertilizer and lime. In alkaline soil (pH > 7.5), sodium nitrate should be avoided and sulfur or acidic fertilizer can be used instead. 
2. Physiological acid-base balance 
When applying physiologically acidic fertilizers (such as ammonium chloride) over a long period, lime should be used alternately. Apply 1,000 to 2,000 kilograms per hectare every two years. 
3. Crop Demand Matching 
Ammonium sulfate and superphosphate are suitable for acid-loving crops such as tea trees and blueberries. 
Sodium nitrate is suitable for alkali-tolerant crops such as spinach and beet. 
4. Organic-inorganic combination 
The mixed application of farmyard manure and superphosphate can reduce phosphorus fixation and increase its utilization rate.