Phosphorus Use Efficiency in Permanent Pastures in Andisols

The phosphorus (P) availability in volcanic soils is a main limitation for permanent pasture growth. Phosphorus use efficiency (PUE) must be improved to increase forage production with minimum impact on the environment. The aim of the present study was to assess at field conditions the PUE, P uptake efficiency (PUPE), P utilization efficiency (PUTE), and the P nutrition index (PNI) on permanent pastures grown in different environments under different P rates and P sources. Three field experiments were conducted in Southern Chile. Treatments resulted from factorial combination of (i) two P sources (phosphate rock and triple superphosphate) and (ii) different P rates. High variations in PUPE (0.004–0.108 kg P uptake kg −1 P available), PUTE (189–756 kg DM kg −1 P uptake), PUE (1.3–42.7 kg DM kg −1 P available), and PNI (0.32–1.33) were observed across experiments, P rates, and harvest dates. PUE was significantly related to PUPE. PUTE was related to PNI through a negative power function. Therefore, higher or lower PUTEs will be the result of pastures grown under P deficiency and luxury consumption conditions, respectively. A reference PUTE ranging from 212 to 321 kg DM kg −1 P uptake is proposed for pastures grown under optimal P nutritional status. The present study is the first proposing the PNI as a valuable tool to assess not only the P nutrition status, but also the PUTE in response to management factors such as P fertilization and harvest dates.