Potassium — sometimes called potash — for root development and resistance to drought and disease secondary nutrients — oxygen, carbon, hydrogen, calcium, magnesium and sulfur — are also necessary macronutrients but are often available in soil or air. micronutrients — including boron, chlorine, cobalt, copper, iron,... Fertibor boron, mined and purified boron, should be used in very small amounts (2-10 lb/acre) because it can become toxic to plants if over-applied. fertibor is a slow release, 15% boron for soil application. highly soluble; to calculate them amount of fertibor required, multiply the elemental boron required by 6.6 (based on a soil test) Calcium ammonium nitrate + boron properties of calcium ammonium nitrate + boron: the product can dissolve in water its high content nitrate nitrogen and water-soluble calcium can be absorbed by crops directly and absolutely, which can prevent the disease such as blossom-end rot fruit cracking and tip-burn. Application and benefits. granubor is a granulated form of refined boron, perfect for blending into fertilizer or direct application: with an average particle size of 2.8 mm, granubor is perfect for blending, providing a minimum of segregation in bagging, transport, and application.