Urease and nitrification inhibitors added to urea and losses of NH3 through volatilization

• Grant number: 09/06504-5
• Support Opportunities: Scholarships in Brazil - Master
• Start date: August 01, 2009
• End date: April 30, 2011
• Field of knowledge: Agronomical Sciences - Agronomy - Soil Science
• Principal Investigator: Heitor Cantarella
• Grantee: Johnny Rodrigues Soares
• Host Institution: Instituto Agronômico (IAC). Agência Paulista de Tecnologia dos Agronegócios (APTA). Secretaria de Agricultura e Abastecimento (São Paulo - Estado). Campinas , SP, Brazil

Abstract

Urea, the most common N fertilizer in agriculture, is rapidly hydrolyzed in soils by the enzyme urease and is subject to high losses of N through NH3 volatilization. Several products have been tested as urease inhibitors in order to reduce NH3 losses when urea is surface-applied to soils, including inorganic salts of Cu and B, and urea analogs such as N-n-(butyl) phosphoric acid triamide (NBPT). The inhibitory effect of inorganic salts usually is relatively low but they are of interest because they are also plant micronutrients; the rates of Cu and B that allow reduction of NH3 losses are not well established. NBPT has been shown to effectively reduce NH3 losses in laboratory and field studies in several countries. Data available from the literature suggest that NBPT is less effective under low soil pH, common in Brazilian agriculture. Recently nitrification (DCD) and urease (NBPT) inhibitors have been combined; however, data available suggest that DCD may increase NH3 volatilization losses from urea. It is not clear whether DCD affects NBPT's mechanism of urease inhibition or increase NH3 losses because it maintains higher NH4+ concentration for a longer period of time after urea application. Therefore, the objectives of the present study are to: i) evaluate the effect of rates of Cu and B added to urea on NH3 volatilization losses; ii) assess the effect of soil pH on the effectiveness of NBPT to reduce NH3 losses; iii) evaluate the temperature and storage time of urea treated with NBPT; and iv) evaluate the combination of DCD and NBPT added to urea on NH3 volatilization losses.