THE AVAILABILITY TO ALFALFA OF PHOSPHORUS FROM TWELVE DIFFERENT CARRIERS

Availabilities of the phosphorus in twelve different phosphate sources to alfalfa were determined in a growth chamber. Two crops of alfalfa were grown on two soils of high base status, Machete stony sandy loam and Westwold loam. Fertilizer materials containing monocalcium phosphate or materials such as calcium metaphosphate which are converted to monocalcium phosphate brought about the greatest increases in yield. However, yield increases also resulted from treatments with the ammonium phosphates and orthophosphoric acid. Ammonium phosphate fertilizers were the most effective in increasing the percentage of phosphorus present in the alfalfa tissue. Ammonium phosphate and monocalcium phosphate materials were equally effective in increasing total phosphorus uptake by alfalfa. The amount of CO 2 soluble phosphorus extracted from the Westwold loam, following treatment with the various phosphate sources, was correlated with the yield of the first crop of alfalfa. The average per cent P in the alfalfa tissue was found to be correlated with the CO 2 soluble P. Both the NaHCO 3 and CO 2 extractable soil phosphorus levels of the Westwold loam, after it had been treated with the different phosphate materials, were found to be highly correlated with the phosphorus uptake by the second crop of alfalfa and with the total phosphorus uptake.