What Is The Optimal Timing And Application Rate Of A Sulfur-based Fertilizer To Alleviate Sulfur Deficiency In Canola Crops Grown On Calcareous Soils With High PH Levels (above 8.0) And Low Sulfur Retention Capacity, Considering The Crop's Critical Growth Stages And Potential Interactions With Other Micronutrients Such As Boron And Manganese?

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To address sulfur deficiency in canola crops grown on calcareous soils with high pH and low sulfur retention, the following approach is recommended:

Optimal Sulfur Fertilization Strategy

  1. Fertilizer Source:

    • Use sulfate-based fertilizers such as ammonium sulfate, potassium sulfate, or gypsum (calcium sulfate dihydrate). These forms are immediately available to plants and suitable for high pH soils. Gypsum is particularly beneficial as it also provides calcium, enhancing soil structure and plant nutrition.

  2. Application Timing:

    • Split Application: Apply sulfur in two splits to ensure availability during critical growth stages.
      • First Application: At planting or shortly after emergence to support seedling establishment.
      • Second Application: During the stem elongation phase (around 6 inches tall) to coincide with rapid growth and development.

  3. Application Rate:

    • Apply 30-40 kg/ha of sulfur. Given the soil's low sulfur retention, the higher end of this range may be necessary. Calculate the product amount based on sulfur content:
      • Ammonium sulfate (24% S): ~125 kg/ha for 30 kg/ha S.
      • Gypsum (18% S): ~167 kg/ha for 30 kg/ha S.

  4. Application Method:

    • Broadcast before planting or use as a starter fertilizer. Topdressing during growth is effective, with foliar application as a supplementary option if needed.

  5. Micronutrient Considerations:

    • Ensure balanced levels of boron and manganese through soil testing to avoid antagonistic effects. Sulfate forms do not directly interfere with these micronutrients.

  6. Monitoring and Adjustment:

    • Conduct soil and tissue tests to confirm sulfur adequacy and adjust future applications as needed. Monitor for sulfur deficiency symptoms, such as yellowing leaves, and confirm with testing.

This strategy ensures a steady supply of sulfur, supporting canola's critical growth stages and optimizing yield potential in challenging soil conditions.