A Pipe Dream

Around the world, growing populations are in greater need of food. Thus, farmers have to control and expand their yields through the use of organic or inorganic fertilizers.

From place to place, soil quality and crop requirements vastly differ. Over the last few decades, the industry has made serious progress by spending time focusing on these core foundations. Farmers are consequently now in a position where they can be sure they are using the proper quantity and quality of fertilizer at the proper time to get the best efficiency.

As a result, by knowing a crop’s specific requirement and having access to an in-depth soil analysis (which also indicates the remaining nutrients from the previous period), a farmer can calculate the quantity and quality of fertilizer to be sprayed on the field and the number and timing of application.

A fertilizer can be characterised by the total nutrient content and the ratio between these nutrients. For example:

• Urea contains 46% of nutrients with a ratio of 1-0-0 (nitrogen [N], phosphorus [P – expressed as phosphorus pentoxide (P₂O₅)], and potassium [K – expressed as potassium oxide (K₂O)] elements).
• Pure ammonium nitrate contains 35% of nutrients with a ratio of 1-0-0.
• 15-15-15 contains 45% of nutrients with a ratio of 1-1-1.
• 10-5-5 contains 20% of nutrients with a ratio of 2-1-1.

A plant’s needs vary according to their type and the period of growth they are in.

A general basic fertilizer with a ratio 1-1-1 can always be applied, but may not have the desired effect the farmer may be looking for. To promote root growth, a fertilizer with higher P content, such as with a ratio 1-2-1, is a much better option. Meanwhile, to promote flowers and fruits, more K is required, such as in the fertilizers with a ratio of 1-1-2, 1-2-2 or 2-1-2. To promote leaf growth and, generally speaking, vegetation, a nitrogen-rich fertilizer is preferred, such as in fertilizers with a ratio of 2-1-1, 3-1-1 or straight nitrogen fertilizers, e.g. urea and ammonium nitrate.

Consequently, dependant on the desired growth patterns, a wide variety of fertilizers are produced, ranging from single nutrient to multi-nutrient fertilizers.

• Single nutrient fertilizers that only produce N include ammonium nitrate, calcium ammonium nitrate (CAN) and urea.
• At the same time, triple superphosphate (TSP) and single superphosphate (SSP) only provide P.
• Meanwhile, fertilizers such as mono-ammonium phosphate (MAP), di-ammonium phosphate (DAP) and urea superphosphate (USP) provide both N and P.
• Finally, NPK fertilizers are those that provide crops with all three nutrients: N, P and K.

There are two main categories of NPKs, depending on how their constituents are combined. They can be produced, for example, by physically mixing together separate granules of ammonium nitrate, MAP and muriate of potash (MOP) in a process known as bulk blending. On the other hand, compound fertilizers can also be produced using a granulation process to combine all three nutrients homogeneously within a single granule.

Compound NPKs are generally preferred over NPK blends as they do not segregate during storage and transportation, helping to ensure that nutrients are spread evenly during field application.

Furthermore, compound NPKs can be manufactured using a range of different raw materials.

The N source is usually a mix of ammonia, ammonium nitrate or urea. However, ammonium sulfate can also be used, either sourced as an external product or produced in-situ from sulfuric acid and ammonia.

The P can be sourced from phosphate rock or phosphoric acid (even if the phosphoric acid originated from phosphate rock). However, the disadvantage of using phosphate rock is the calcium content of the rock, which remains as a diluent in the fertilizer. As a result, it is not possible to produce some fertilizer grades, such as MAP and DAP, or the calcium must be treated separately, generating a side production of CAN. Although phosphoric acid costs slightly more than source phosphate rock, it is still a good alternative if the fertilizer plant is located far from a phosphate mine, as the shipping and storage requirement are typically less demanding.

The K source can be potassium chloride, or in very special cases depending on market value, potassium sulfate.

To read the rest of this article, download World Fertilizer's May/June issue for free: https://bit.ly/2ZSj4XN

Read the article online at: https://www.worldfertilizer.com/special-reports/03062020/a-pipe-dream/