Fertilizer quality can be easily overlooked, yet regulations state to ensure ‘quality fertilizer’ is always used. What is ‘quality’ and why is it important? The ‘why’ is very straightforward: quality fertilizer enables all nutrients to be applied as accurately as possible, in order to maximise productivity whilst minimising environmental impact. The ‘what’ is slightly more open to interpretation. If we consider the physical attributes of a fertilizer, they will differ depending on whether it is single or multi nutrient.
Single nutrient products – such as straight nitrogen – can vary in size, density and hardness. For example, nitrogen is available for purchase as a prill or granule. The former is hollow, less dense, and weaker, giving it less favourable ballistic characteristics compared to a larger, stronger, denser granular product. Strong granules are able to withstand greater force as they are hit by the spreader veins during application. This ensures less breakdown of the fertilizer, reducing dust and resulting in a more even spread pattern. This also enable spreading to much wider bout widths saving time, fuel and fewer tramlines (reduced compaction and increased crop area). For a visual analogy, compare the difference between throwing a table tennis ball vs a golf ball.
When it comes to multi nutrient products, we also have the differences between blends and compounds. Blends are fertilizers made up by mixing several raw materials to create a specific analysis of individual nutrients. The nutrients could be two – NS – or up to four – NPKS. A compound contains all nutrients in each individual prill or granule, at the specified ratio according to the requirement for the product. Application with a compound multi nutrient fertilizer is simple and accurate, requiring only the correct spreader setting specific to the product.
The same cannot be said for blended fertilizers. A blended fertilizer is typically made up from three products such as DAP, MOP and ammonium nitrate. Each of these products are physically different, requiring unique spreader settings when applied alone. They are then blended to create an heterogenous product that requires one spreader setting which is inevitably a compromise. The result of this is an uneven spread of nutrients across the field, which can result in an uneven response through increased lodging, reduced yields and poor quality.
Nitrogen is the key nutrient driving crop yield and quality, so it’s essential that application is not restricted. Tray testing was conducted on two blended products and the analysis showed that the average nitrogen application rate was 10% and 13% below the target rate. Such a deviation can potentially result in a 0.5 t/ha DM yield loss in grass or a crop of wheat. In monetary terms, this means an ROI of roughly 3:1 for quality, uniform compound fertilizer.
“Landing Sites” are an often overlooked issue when using blended materials. This is the number of nutrient granules or prills applied per unit area. In blended fertilizers, the single nutrient products used to make the finished product are typically highly concentrated. This naturally results in low application and inclusion rates but also applies a far lower number of granules or prills. When calculated, a compound fertilizer shows between 6 and 10 times more granules per unit area compared to a blend. This difference ultimately also affects phosphate fertilization. Phosphate is very immobile, with roots needing to find the nutrient. To ensure phosphate deficiency is avoided, an even spread is necessary, with as many landing sites as possible.
Some compounds – such as the YaraMila range – also utilise a beneficial type of phosphate. Phosphate products such as MAP, DAP and TSP are all highly water soluble as they are orthophosphates. This means that the phosphate is prone to rapid ‘fixation’ in the soil as other ions (e.g. Iron, Aluminium, Calcium) lock onto them making them unavailable for immediate crop uptake. YaraMila compound products, through their manufacturing process, contain two or three forms of phosphate. 70% being in the orthophosphate form whilst the balance is either DCP and/or polyphosphate, both of which are not fixed, becoming plant available over the days and weeks following application to give a season long supply to the growing crop.
In a 9-year study, a potato crop was supplied – in different plots – with exactly the same nutrients (NPK). One plot used straight, single nutrient products and the other used a YaraMila compound. The average response to the applied P and K single product was 15.9%. When P and K was applied as a YaraMila compound, this rose to 23.7%. These results remained consistent across every year of the investigation, equating to a 3.5 t/ha marketable yield increase. With potatoes valued at £190/t, this represents an extra £667 / ha increased revenue in this trial.
Fertilizer quality matters. For greater yields and optimal crop health, choose a multi nutrient compound fertilizer for high quality and an even spread.