Influence of Past Soil Treatment on Yield, Composition, and Fertilizer Phosphorus Utilization by Alfalfa1

Abstract

Phosphorus fertilizer was used at five rates on established stands of alfalfa on irrigated Tripp very fine sandy loam in western Nebraska. One rate of phosphorus fertilizer was tagged with P32. Two 6-year rotations which included 3 years of alfalfa were used, one of which had received 12 tons of barnyard manure per acre per rotation cycle since 1912. Total phosphorus, Nitrogen, and cation concentrations; fertilizer phosphorus concentration for the tagged treatment; and yields of alfalfa were measured for 2 years. Residual effects of first-year fertilizer applications were measured through the use of second applications of tagged phosphorus fertilizer. All rates of phosphorus fertilizer increased the yield of alfalfa on the non-manured rotation while only the 160-pound P2O5 per acre rate caused a significant increase in yield on the manured rotation. The long-time use of manure increased the yield and phosphorus concentration of alfalfa. Phosphorus concentration in the alfalfa increased with increasing rates of phosphorus fertilization and decreased with plant maturity. The long-time use of manure and the prior use of phosphorus fertilizer decreased the relative uptake of applied fertilizer phosphorus. Application of phosphorus fertilizer had little effect on concentration of either nitrogen or cations in alfalfa.