To prevent humic acid from crusting on topsoil and inhibiting seed germination:

You're facing a common issue with humic acid application crusting on the soil surface especially when using high-concentration formulations like yours (71% humic, 14% fulvic acid). Here’s how you can prevent crust formation and improve humic acid incorporation:

1. Mix Humic Acid Thoroughly with Soil

• Instead of only applying on the top 5 cm, try evenly mixing the product throughout the top 5–10 cm of soil before sowing.
• This avoids concentrated accumulation on the surface and promotes better distribution.

2. Use Smaller Doses in Split Applications

• Reduce the per-application rate (e.g., apply 9.5g instead of 18.98g) and apply in two or three intervals over time.
• This reduces the risk of crusting and allows more gradual SOC improvement.

3. Dilute and Apply as a Solution

• Dissolve the humic acid product in water before application to ensure finer dispersion.
• Use lukewarm or slightly acidic water (pH 5.5–6.5) to help the humic acid dissolve better.
• Then apply this solution evenly and follow it with light mixing or irrigation.

4. Cover Soil with Light Mulch After Application

• Use a thin layer of organic mulch like coco peat, straw or compost after application.
• This prevents surface evaporation, reduces crust formation and maintains better moisture for seed germination.

5. Pre-mix with Potting Soil Before Filling Pots

• Blend the humic product with the entire volume of soil before placing it in pots.
• This avoids surface concentration and provides even organic carbon enhancement throughout the root zone.

6. Try Foliar or Liquid Drench Application for Young Plants

• If germination is the main concern, apply humic/fulvic acid after seedlings have emerged using a foliar spray or soil drench which avoids disturbing seed germination entirely.

Both the preceding responses include 'dissolving the humic acid in water' which may or may not succeed.

Mai I suggest thorough mixing with the soil before spreading on the surface (say) 1 cm. Even then yu may need a wetting agent