Potential mineralization and nitrification in volcanic grassland soils in Chile

Abstract

A proportion of the nitrogen (N) applied to grasslands as organic or inorganic fertilizers can be lost to water courses as nitrate and to the atmosphere as nitrous and nitric oxides. Volcanic soils from Chile are not generally prone to leaching, possibly due to net immobilization of nitrate and/or ammonium, and/or due to inhibition of nitrification by either chemical or physical processes. In laboratory studies we found large mineralization potentials in soils from three different Chilean soils after 17 weeks of incubation, totalling 215 and 254 mg kg-1 dry soil for two Andisols and 127 mg kg-1 dry soil in an Ultisol. Nitrification occurred after a short period, and was lowest in the Ultisol. In addition, microbial analysis showed nitrifiers to be present in all three soils. Adsorption of ammonium was two-fold stronger than for nitrate, ranging from 29 to 180 kg N ha-1. The highest potential for N adsorption in the 0-60 cm soil profile was with the Ultisol (398 kg N ha-1), but was similar in both Andisols (193 and 172 kg N ha-1, respectively). The combination of ammonium retention together with delayed nitrification could account for the low leaching rates in these soils. © 2013 Copyright Rothamsted Research Ltd.