Estimating available soil phosphorus increases after phosphorus additions in Mollisolls

GERARDO RUBIO; M. J. CABELLO; FLAVIO H. GUTIERREZ BOEM; E. MUNARO

SOIL SCIENCE SOCIETY OF AMERICA JOURNAL

SSSA

Año: 2008 vol. 72 p. 1721 - 1727

0361-5995

Accurate critical levels must be accompanied by predictive models on the amount of P required to increase P availability to a target value to obtain reliable P recommendations.  Based on information on soil properties, we estimated the increase in soil available P after the addition of a unit of P (b coefficient), in an area of homogeneous though geographically distant soils. All 71 selected soils were non-calcareous, belonging to the Mollisol order and located at the Pampean Region (Argentina). Samples (0-20 cm) were incubated for 45 days after the addition of 5 doses of P. Soils were characterized for parameters related to soil P availability: pH, particle size distribution, organic carbon, total P, initial soil available P, and two P retention indices, differing in the interaction period between the added P and the soil matrix (1 or 18 hs). Obtained b values ranged from 0.27 to 0.74. Soils located at the Northern area of the study region had higher b values (mean=0.58) than Southern ones (mean=0.42). The best multiple regression model for estimating coefficient b (R2 = 0.70) included the variables initial soil P, a binary variable that accounts for the localization of the soil, and the P retention index with the shorter interaction period. The strong effect of the geographical position of the soil on the estimation of b coefficient led us to hypothesize about a possible role of the mineralogical characteristics of the parent material on P dynamics. Our results indicate that single independent variable models may not be enough for predicting b coefficient in homogeneous soils.