Humboldt Nutrients Master A is the first step in the Humboldt Nutrients A & B premium fertilizer program. This two-part amino acid-based fertilizer program has been specifically manufactured to meet the needs of the beautiful flowering plants in your grow area. The amino acids and organic acid complexes help make macro and micro nutrients available to your plants and set the Master A & B series apart from your standard base nutrient. You'll see results with this simple two-step fertilizer from Humboldt. This listing for 1 Quart of Master A only.