- Nitrogen as ammonium nitrate applied at the rates of 0, 120, 240, and 360 lb/acre in three applications and 480 lb/acre in four applications.
- Nitrogen applied in 40 lb/acre increments with a frequency to maintain the crude protein of leaf tips between 24 and 26%.
- Phosphorus as triple super phosphate applied at the rates of 0, 40, 80, and 120 lb P2O5/acre incorporated into the soil prior to planting.
One month before planting, two soil cores will be taken from each plot. Each core will be divided into four depths, 0-6 inches, 6-12 inches, 12-24 inches, and 24-36 inches. Samples will be composited by depth within plots. Soil from the surface depth will be augmented with samples taken with a hand probe from 10 sites within each plot. Soil sampling will be repeated within a week after the last harvest of the season.
The five levels of nitrogen fertilizer and four levels of phosphorus fertilizer will be applied to 14' x 33' plots in four replications in a factorial arrangement of treatments. The nitrogen fertilizer to maintain crude protein level will be applied to one plot in each replication that will also receive 80 lb P2O5/acre. Fertilizer combinations will be repeated on the same plots during each successive year of the experiment.
The plot area will be located under a pivot irrigation system to provide supplemental water. Annual ryegrass (cv TAM-90) will be seeded at the rate of 30 lb/acre. Rainfall as well as supplemental water will be measured and recorded for each replication.
All plots will be harvested whenever the estimated yield of the most productive plots exceeds 1200 lb/acre and at the end of the growing season. Harvested material will be weighed and sampled for dry matter, protein, and fiber determinations.