Almost every season we see fields of young purple corn in the springs, this purpling can often an early season Phosphorus (P) deficiency caused by cool weather. However, it is always a good reminder of P management.
Managing Phosphorus can be difficult due to its high affinity for fixation with soil particles. 80 to 90% of the applied P fertilizer will be “tied-up” in the soil and not available to the plant the season it is applied. The P that is tied-up is not lost; it is just in equilibrium between soil solution and soil particles. Understanding your soils, crop removal from the previous year and yield goals will help determine P fertilizer rates.
Phosphorus fertility is a long-term management issue, so many universities recommend a 4-8 year build up plan. MAP, DAP, TSP, APP are all common P fertilizers that provide adequate P to the soil and plant. Phosphorus utilization is not affected by liquid or dry fertilizers. Timing of P typically has little to no impact on crop use efficiency.
Fall applications every year or every other year are common in our region. Subsurface or banding P can increase yields compared to broadcasting in soils with thick residue or in soils with high P fixation. P is mostly immobile in the soil. Phosphorus additives, such as EcoPhos and EcoMAP, are available to increase P efficiency and plant availability.