When fertilizer is applied to a field its nutrient analysis should match what is claimed on the fertilizer product label (ex. 28% nitrogen). This means that the buyer gets what they want and pay for, and the supplier is paid for what they delivered. This is almost always the case, but there are situations where there is a discrepancy.
When a fertilizer is offered for sale at any point in the supply chain (manufacturer, distributor, wholesaler or retailer) the seller and buyer need to be confident of the fertilizer analysis. Samples are often collected and either immediately analyzed or retained in case a question arises.
We recommend each incoming load of fertilizer be sampled. If the material is different from previous shipments (ex. color) it should be communicated to the supplier and a sample immediately sent for analysis. Retain samples of normal-appearing materials in case a future question arises. The length of sample retention is unique to each situation, but likely should be at least until the current crop is harvested.
Collection of fertilizer samples can be challenging, especially with bulk deliveries. The state’s fertilizer inspector can provide procedures for sampling of various fertilizers: liquid, granular, bulk, bagged, etc. When your facility is being inspected it is a good practice to ask the inspector to provide you with a sample collected at the same time as the one they will have analyzed. Should their sample show the fertilizer does not match the label the retained sample can be analyzed to independently confirm the analysis.
Retained fertilizer samples should be stored in air-tight containers to prevent moisture entry and spills. Small 4-8 ounce plastic bottles work well for liquid fertilizers. Solid fertilizers can be stored in zip-lock bags – compress the bag to remove air and then place in another bag. Keep retained samples in a controlled temperature area.