How should farmers choose the right fertilizers?

First, examine the soil (add what's lacking) 

- Sandy soil: Poor in nutrient retention → Choose slow-release fertilizers and organic fertilizers, apply in small amounts frequently 
- Clay soil: Poor air permeability → Apply more organic fertilizer, mix in compound fertilizer, and use less quick-acting nitrogen. 
- Saline-alkali land: Avoid chlorine-containing fertilizers, prone to salinization → Use humic acid and sulfur-based fertilizers 
- Acidic soil (pH < 6.5): Apply calcium magnesium phosphate fertilizer and lime to adjust the acidity. 
Alkaline soil (pH > 7.5): Use physiologically acidic fertilizers such as superphosphate and ammonium sulfate. 

The most reliable approach: Go to the agricultural technology station for soil testing and formula creation to precisely determine the deficiencies of nitrogen, phosphorus, potassium, and organic matter.

II. Look at the crops again (match the correct ones) 

- Leafy vegetables/forage grass: Require high nitrogen (such as 30-5-5) → Promote lush leaves and high yield 
Grains (rice, wheat, corn): balanced type (15-15-15) or high nitrogen and high potassium 
- Fruits and vegetables: Balanced base fertilizer, high potassium during fruit expansion period (12-8-20/10-5-30) 
- Root vegetables (potatoes / radishes): High potassium + sulfur-based → Bulbous growth, good quality 
For chlorine-sensitive crops (grapes/strawberries/tobacco/citrus fruits), only potassium sulfate is recommended; potassium chloride is prohibited. 

III. Understanding the Packaging (3 Key Points) 

- Look at N-P₂O₅-K₂O - The first position: **Nitrogen (N)** → Promotes leaf growth 
- 2nd place: **Phosphorus (P)** → Promotes root growth and flowering 
- 3rd: **Potassium (K)** → Strong stems, enlarged fruits, increased sweetness 
Only these three total nutrients are counted. A content of ≥ 40% is more reliable. 
Check the three certificates: the fertilizer registration certificate, the production license, and the standard number (GB/NY) it follows. 
- Observe the appearance: uniform granules, dry without clumping, and no pungent odor. 

IV. Selection by Growth Period (Base Fertilizer + Top Dressing) 

- Base fertilizer (before sowing): Organic fertilizer + balanced compound fertilizer → Long-lasting soil improvement 
- Seedling stage: High nitrogen → Promote seedling growth and strengthen roots 
Flowering period: High phosphorus → More flower retention and fruit setting 
- Fruit expansion/ripening stage: High potassium → Promotes fruit expansion, enhances coloration, increases sweetness, and prevents fruit cracking 

V. Avoiding Pitfalls and Cost-Effectiveness 

Don't buy products that are "three-no": no factory name, no address, no registration certificate. → Refuse. 
Don't be lured by extremely low prices: Prices that are over 30% lower than the market rate are often falsely marked and of poor quality. 
To calculate cost-effectiveness: unit price ÷ total nutrients → the lower the value, the more cost-effective it is. 
- Formal channels: agricultural supplies stores, direct sales from manufacturers, keep receipts 

VI. One-sentence Quick Notes 

Sandy soil releases nutrients slowly, clay soil is rich in organic matter, saline-alkali soil is chlorine-intolerant, and acidic soil needs to be alkalized; leafy vegetables require high nitrogen, fruits and melons need high potassium, sulfur-based fertilizers are not suitable for chlorine-intolerant plants, and soil testing is the most accurate.