Evaluation of Phosphorus Availability on Growth and Leaf Nutrient Concentrations in Wheat, Oats, and Rye.

Adequate phosphorus (P) availability is critical for the growth and sufficient nutrient content of forages for grazing animals.  On low fertility soils, it has been found that tall fescue, a cool-season perennial grass, responded to P fertilization with increased yields and improved leaf nutrient concentrations of P, magnesium, calcium, and potassium in winter months.  Adequate leaf concentrations of these nutrients are important to avoid nutritional disorders in grazing cattle, such as grass tetany.  Our objective is to examine the effect of P availability on growth and leaf nutrients in annual cereal grains commonly grown for winter forage.  Soft red winter wheat (Triticum aestivum), oats (Avena sativa), and cereal rye (Secale cereale) were grown hydroponically in greenhouse conditions in complete nutrient solutions with varying P concentrations of 0, 200, 400, and 800 µM P.  Seedlings were suspended in 400 ml containers with aeration with three containers of each treatment solution in three replicate blocks.  After 30 days of growth, plants were separated into roots and shoots, dried, weighed, and stored for nutrient analysis.   Shoot growth of both wheat and oat responded to P treatments.  Wheat increased 3-fold, and oats 1.5-fold from 0 to 200 µM P.  Wheat shoots also increased an additional 17% from 200 to 400 µM P.  Root growth responded to P treatments only in wheat, with a 73% increase from 0 to 200 µM P and 42% increase from 200 to 800 µM P.  The third species, rye, is currently being grown and further evaluations of leaf and root nutrient contents are being performed, as well as measurements of photosynthetic capacity and leaf conductance.