Nitrogen mineralization in a silandic andosol fertilized with dairy slurry and urea

Abstract

Knowledge about the size and cycle of inorganic N pool on grasslands is necessary to develop adequate fertilization strategies and to determine the potential pathways of N losses. The objectives of this study were to: 1) quantify the N mineralization rates in permanent grassland on an Andosol of southern Chile; and 2) determine the effect of high N application rates as urea and dairy slurry on this process. Mineralization was measured over a three years period on grassland fertilized with 400 kg N ha -1 yr -1 by acetylene inhibition method, incubating soil cores under field conditions. Subsequently, a laboratory assay was carried out to determine potential residual N mineralization rate by anaerobic incubation method. Higher N mineralization was measured on the urea treated plots (314 – 420 kg NH 4+ -N ha -1 yr -1) followed by slurry (320 – 344 kg NH 4+ -N ha -1 yr -1) (p<0.05). Most of the N was mineralized during spring and summer seasons (p<0.05). Laboratory results indicate that slurry treated soil had greater net potential N mineralization rates than urea (p<0.05). Results suggest that in Andosols of southern Chile, N mineralization can be a major N input into the soil N budget, with implications for grassland fertilizer managements and pathways of N loss.