ChileanJAR

in order to identify the soil properties affected by repeated fertilizations, P-Olsen, P fixation, Al- Morgan, pH, organic matter, N-total, C/N ratio, and K-extractable were determined in soil samples taken every 5 cm, down to 40 cm, and every 10 cm, from there down to 90 cm. The soil corresponded to one of the replications of a field trial carried on by G. Müller and A. Bustamante, at Carillanca Experiment Station, INIA-Temuco, with the objective of studying the response of alfalfa to different N, P and K fertilization treatments, repeated during 3 years. Phosphate fertilization modified the levels of P-Olsen and Al-Morgan in the sol) profile. The largest changes occurred with the highest doses applied (1,200 kg/ha P₂O₅, accumulated in 3 years), though these changes were also detected with 100 kg/ha/year. The lack of changes with 150 kg/ha K and 48 kg/ha N, accumulated in 3 years, can be explained by the limited doses applied. Phosphate fertilization reduced the amount of Al-organ in all the soil profile, down to 90 cm; but the enrichment with P-Olsen was limited to the upper 25 cm of the soil profile. It is not known if these changes occurred simultaneously or if one preceded the other. Highest alfalfa yields were obtained with the largest phosphate applications (400 kg/ha/year, during 3 years); soil acidity was not increased, but a drastic reduction of the Al-Morgan level was observed, in particular in the superficial horizon. Consequently, soil pH is not an adequate criterion to be associated with productivity; the level of Al-Morgan gives a better indication of soil productivity.