Blend or compound?

N, P and K can be spread as blend or compound fertilizer.

Which form is the most effective?

Nitrogen uptake

Figure 5: Increase of nutrient uptake after application of compound NPK as compared to a bulk blend comprising ammonium nitrate DAP and MOP.

Nitrogen is best absorbed as nitrate. Nitrate is highly soluble in the soil and immediately available for plants. Ammonium nitrate is the most efficient nitrogen form for compound fertilizers. In the soil, ammonium is converted into nitrate before it is taken up by crops. Ammonium thus provides a sustained nitrogen supply

Phosphorus and potassium

Figure 6: Segregation of blended NPKs (right) compared to compound NPKs (left).

Phosphorus in compounds shall be 100% plant available and comprise a combination of water soluble and a non aging phosphate form. Water soluble phosphate instantly stimulates root growth while the other phosphate source ensures sustained supply. Most compounds are based on MOP as a potassium source but for chloride sensitive crops SOP based formulation should be preferred.

Other nutrients

Compound NPK can include sulfur, magnesium and micronutrients like boron, manganese and zinc to complete plant nutrition. Since they are present only in small quantities, even spreading is important. Compounds ensure better results than blends, since each granule contains the same quantity of nutrients. With blends, large deviations from the targeted rate can occur.

Figure 7: Compound fertilizers enable homogeneous spreading over a wider distance than blended fertilizers since spreading width of light particles like Urea is less than those of heavier particles like DAP and MOP.

Figure 8: Uneven spreading generates significant losses, even if no visible striping occurs.

Spreadability and quality

Blends are mostly mixed locally with ingredients from different origins in different ratios. Compound fertilizers are produced in fertilizer plants according to a fixed nutrient ratio. Unlike blends, compounds will not segregate during handling, transportation and spreading. Compounds offer significant advantages over blends in terms of uptake efficiency and spreadability: 

  • Compounds include all nutrients in each grain, there are thus more grains for each nutrient. Each grain that falls within reach of plant roots immediately provides all essential nutrients to the plant. This is particularly beneficial regarding immobile nutrients, such as phosphorus, and micronutrients. Compound products therefore provide higher uptake efficiency and better nutrient synergy than blended products (fig. 5).
  • Compounds allow better spreading quality than blends. With blends, larger and heavier particles such as MOP and DAP will spread further while smaller and lighter particles such as urea will spread the least distance. Where different sized particles have different nutrient content, this leads to segregation of nutrients upon spreading. This in turn will lead to uneven crop growth and yield. Uneven spreading is frequent. As soon as striping becomes visible, 5 to 10% yield loss is to be expected (fig. 8).