Abstract

BARRIOS, Marta; KILLORN, Randy  and  GARCIA, Judith. Nitrification of ammonium nitrogen from a controlled release fertilizer and conventional urea in two soils of Iowa, USA. Bioagro [online]. 2010, vol.22, n.3, pp.193-200. ISSN 1316-3361.

Retardation of ammonium nitrification rate is one of the most important factors to consider for reducing losses of fertilizer applied to soils. In this study, we compared the effects of ESN urea and conventional urea on nitrification rates in two soils (Harps and Nicollet), Iowa State, USA, varying in organic carbon content, pH and texture. Samples of soil were treated with solution containing 1,942 or 2,913 g·L^-1 urea (200 or 300 kg·ha^-1, respectively) and brought to 25, 50, 75 and 100 % of their water holding capacity. Then, soils were incubated for 0, 7, 15, 30, 45 or 60 days. At the end of the incubation, the contents were extracted with 2M KCl solution and the extract was analyzed for (NO₃^- + NO₂^-)-N and NH₄⁺-N. Nitrification rates were calculated, and regression analysis and determination of critical points were performed. The results showed a reduction of the maximum nitrification rate and an extended nitrification period in soils treated with ESN. The highest nitrate concentration was found in Harps, at medium moisture content, as compared to Nicollet and treatments with conventional urea.

Keywords : ESN; nitrates; nitrogen; nitrification rate.