Don’t Forget to Keep Your Alfalfa in Top Shape with Phosphorus!

High-yielding alfalfa in beds (Arizona)

Many factors are involved in producing a top-quality alfalfa crop.  Although many factors (like weather) cannot be controlled, many other critical components need to be carefully managed.  As the demand for high-quality hay increases, a closer look at the role of proper nutrition is needed.

There is no substitute for maintaining an adequate plant nutrient supply for production of high-yielding and high-quality alfalfa.  Alfalfa production removes large amounts of nutrients from the soil that must eventually be replaced to remain sustainable (about 15 pounds of P₂O₅ removed in each ton of hay).  Since phosphorus (P) has many essential roles in alfalfa, both yield and quality are reduced when this nutrient is limited.

Most P in the plant is rapidly converted into organic compounds involved in a variety of essential reactions. For example, P in alfalfa is essential for formation nucleic acids, phospholipids and ATP- associated with things like photosynthesis, protein formation and nitrogen fixation.

Root nodules -site of nitrogen fixation

In addition to direct plant growth benefits, P fertilization has also been shown to increase nitrogen fixation, nodule number and nodule size.  There are frequent reports that P or K nutrition have been found to improve disease tolerance or resistance.

Low P (L) and adequate P (R) alfalfa

Soils vary in their ability to supply P and nutrient deficiency symptoms in alfalfa are hard to detect before the deficiency becomes quite severe.  Therefore, soil testing is best way of predicting the potentially available nutrient supply.  It is generally best that P be applied prior to establishing the crop, since an adequate supply of P is critical for rapid stand development and a strong root system.  For established stands, surface applications are a good way to meet plant needs. 

Polyphosphate fluid fertilizer

Granular triple-super phosphate

Many sources of fertilizer P are successfully used for alfalfa production- including both solid and liquid forms.  A number of comparisons have demonstrated that most P fertilizer sources are equivalent, when properly used.  The selection of a specific P fertilizer is generally based on local availability, ease of application, and the cost per unit of nutrient.

Phosphorus fertilization is an essential component of alfalfa production.  High-yielding alfalfa removes large amounts of P which must be replaced when the soil P supply can not meet the plant demand.  Soil and tissue tests are useful for determining the appropriate amount of P to apply.  Failure to monitor and replace the nutrients removed in harvested hay will lead to losses of yield, plant stand, and profit.

Alfalfa is "ice cream in the making"