Condensed Guide to Magnesium Sulfate Fertilization
Magnesium sulfate is a high-quality agricultural fertilizer that supplies essential magnesium (boosting photosynthesis and fruit quality) and sulfur (aiding protein synthesis). Its high solubility and fast absorption make it vital for crop growth, but improper use often leads to poor results or damage. This condensed guide covers key application methods, crop-specific plans, and precautions.
I. Core Fertilization Methods & Dosages
Magnesium sulfate application focuses on two key stages: base fertilization (before sowing/transplanting) and topdressing (during growth), with adjustments based on soil fertility and crop needs.
1. Base Fertilization
Ideal for preparing soil before planting, especially for magnesium-deficient soils (less than 60mg/kg magnesium) or magnesium-hungry crops. Mix with decomposed organic or compound fertilizers, then plough 15-20cm deep into the soil (or use hole application for small plots/pots). General dosages: 5-8kg per mu for field crops, 8-12kg per mu for cash crops, and 5-10g per 20cm-diameter pot for potted plants.
2. Topdressing
Used during rapid growth (e.g., fruiting/expansion stages) when base fertilizer is insufficient. Two main approaches:
· Foliar Spraying: For emergency magnesium (e.g., mild leaf yellowing). Dilute to 0.2%-0.8% (higher for fruit trees, lower for vegetables/field crops), spray on leaf surfaces (focusing on lower leaves) in cool hours. Apply 50-120kg per mu, 2-3 times at 7-15 day intervals.
· Drenching/Drip Irrigation: For long-term supply in large-scale farms. Dissolve in water and deliver to roots. Use 3-6kg per mu per application (adjust for crop age), 2-3 times during growth at 15-20 day intervals; 3-5g per pot monthly for potted plants.
II. Crop-Specific Fertilization Plans
1. Vegetables
· Tomatoes: 10-12kg per mu as base fertilizer. Topdress with 0.2% foliar spray at seedling stage, 4-5kg per mu drench at fruiting stage, and 0.5% foliar spray at expansion stage.
· Cucumbers: 8-10kg per mu base fertilizer. Drench 3-4kg per mu at early fruiting, and spray 0.3% solution every 15 days at peak fruiting.
· Peppers: 8-10kg per mu base fertilizer. 0.2% foliar spray before flowering, and 3-5kg per mu drench twice (20 days apart) during fruiting.
2. Fruit Trees
· Grapes: 10-15kg per mu base fertilizer (post-harvest). Drench 5-6kg per mu at germination, 0.6% foliar spray twice (10 days apart) at expansion, and 4-5kg per mu drench at color transition.
· Citrus: 8-12kg per mu base fertilizer (post-pruning). 0.3% foliar spray at spring shoot stage, 5-6kg per mu drench at expansion, and 0.5% foliar spray post-harvest.
· Apples: 10-12kg per mu base fertilizer (post-harvest). 0.4% foliar spray post-flowering, and 5-6kg per mu drench at expansion.
3. Field Crops
· Corn: 5-6kg per mu base fertilizer. 0.3% foliar spray at jointing, and 0.2% spray at filling.
· Rice: 4-5kg per mu base fertilizer. 0.2% foliar spray at tillering, and 0.3% spray at booting.
III. Key Precautions
· Avoid Alkaline Mixes: Magnesium sulfate is weakly acidic; do not mix with alkaline fertilizers/pesticides (e.g., plant ash, Bordeaux mixture). Use 7-10 days apart if needed.
· Soil pH Adjustments: Increase dosage by 10-20% in acidic soils (pH <5.5) (add quicklime to reduce loss); use foliar spraying or mix with acidic fertilizers in alkaline soils (pH >7.5).
· Prevent Over-Application: Excess magnesium inhibits calcium/potassium absorption. Stop use if leaves curl/scorch, and water to dilute.
· Choose Agricultural-Grade: Use ≥95% purity agricultural-grade magnesium sulfate (GB/T 26568-2011 standard); avoid industrial/medical grades.
Conclusion
Successful magnesium sulfate fertilization relies on matching method (base/topdressing, foliar/drenching) and dosage to crop type, growth stage, and soil conditions. This ensures no magnesium deficiency-related yield loss or over-application damage, supporting healthy crop growth and better yields.