“Knowledge is like paint. It does no good until it is applied.” – Unknown.
We spend a lot of time talking about Grid and Zone sampling and do an excellent job of managing the variability in your fields through agronomically sound prescriptions based on soil test levels and crop removal. However, we can take that knowledge to the next level by understanding what situations make phosphorus unavailable to the plant based on the chemical and physical soil properties of the soil. This is a bigger problem than we would like to admit and one that can present issues in any field.
Conditions like Soil pH, Soil P levels, the ratio between P1 and P2 levels, and base saturations of your CEC all affect Phosphorus availability. What happens to Phosphorus after an application is relatively simple to explain; it is quickly tied up and made unavailable to plants. This occurrence happens because phosphate is negatively-charged and is attracted to all things positively-charged (like free Calcium, Aluminum and Iron ions) to make Calcium, Aluminum and Iron phosphates which are unavailable for plant uptake until mineralized at a later date (not sure when; just later). This tie-up in phosphate is so great that roughly 75% of the Phosphorus we apply is made unavailable to the plant. That means today if you were to go out and apply 100 lbs/A or $22.50/A of 11-52-0 only about 25lbs or $5.60/A of that applied fertilizer would be available for crop uptake.
To be able to keep up with crop removal and slow the decline of phosphorus levels in the soil; we have two choices: either apply more MAP or think about utilizing some other tools in our toolbox. I believe this is where working with your Central Valley Ag ACS Specialist and FSA has a pretty distinct advantage. Between the two of them, there is a deep situational awareness of what is happening in your fields and what we can do about it.
That “other tool” in the tool box is AVAIL from Verdesian Life Sciences; AVAIL is a polymer that coats applied Phosphorus fertilizer particles and protects it from becoming unavailable to the plant. Much like phosphate AVAIL is negatively-charged but has a much greater affinity for positively-charged cations like those mentioned above. This greater affinity or valence allows much more of the phosphate to maintain its availability to the plant in year one. We have seen AVAIL-treated MAP in both fields, and lab studies provide an 85% increase in plant-available Phosphorus in the first year after application. This has resulted in a 7-bushel increase over the past five years of research in corn. So not only are you recapturing about $19.10/A worth of Phosphorus you are getting approximately a $22.00 increase in revenue from increased yield. Using a product like AVAIL is one way we can manage our fertilizer applications with a greater amount of confidence in their success.
This is just another reason why Grid or Zone sampling is important to the management of your operation. Then, one must obtain all the information about what is going on in the soil to fully understand the interactions that affect nutrient availability. Then we can reach for the best tools to use and how to use them most effectively to help you manage your bottom-line. In the above case, we can apply AVAIL-treated phosphorus fertilizer exactly where it is needed the most and protect it from tie-up, thus increasing phosphate availability to the crop.