Phosphorus is an essential plant nutrient and very important for numerous plant processes and crop production. It is a vital component of DNA and RNA, the building blocks of proteins and protein synthesis. Phosphorus also plays a major role in the stimulation of new root growth.
Studies have shown that an almond crop will remove about 18-20 pounds of P2O5 with every 1,000 pounds of kernels removed. For a 4,000-pound crop, that’s upwards of 80 pounds of P2O5 that the crop requires. Understanding how phosphorus fertilizers react in the soil and with other inputs is essential to ensure your crop will receive the required amount.
“Tie up” within the soil is the primary concern with phosphorus fertilizers. In acidic soil conditions, P will tend to get tied up by iron, aluminum and manganese. In basic soil conditions, calcium will be the major component of phosphorus tie up. Phosphorus is most available to the plant in a soil pH range of 6.3-6.8. It is a common practice for growers to make gypsum (CaSO4) applications in the fall to help flocculate soils for better water penetration and to help mitigate salt buildup in the soil. It is also common for growers to apply dry fertilizers, such as SOP (0-0-50) and MAP (11-52-0), in the fall. If an application of gypsum and MAP are both made to an orchard in the fall, the chances of the phosphorus from the MAP being tied up by the calcium component of the gypsum are very high. Common liquid fertilizers, such as ammonium polyphosphate (10-34-0) and orthophosphate (9-18-9), applied in the early spring also have a likely chance of being tied up if a gypsum application was made in the fall.
The Right Source
Choosing a phosphorus fertilizer that is protected from tie up will ensure that you get the most out of your fertilizer investment and that your crop will receive the required amount of phosphorus needed. If you have questions or concerns about a crop nutrition plan, remember there are experts in this field available for consultation. Using all available resources will help guide sound recommendations, and a sustainable future for our industry.