Abstract
Best fertilizer management practices such as adopting the right N sidedress timing can reduce N losses by volatilization, thus, raising N-fertilizer recovery and grain yield. To evaluate ammonia (N-NH3 ) losses, N-fertilizer recovery and grain yield as a function of urea sidedress timing in corn, a field study was conducted during the 2011-2012 and 2012-2013 growing seasons, adopting a complete randomized block design with four replications. Treatments consisted of urea sidedress timing (140 kg N ha-1) at V4, V6, V8, V10, and V12 growth stages, plus a control without sidedress N. The largest N losses by N-NH3 volatilization occurred when urea was applied at V10 or V12 growth stages, reaching losses of 35 and 41 % of the total applied N. Although climatic factors influences N-NH3 volatilization process, crop characteristics such as canopy development also seems to affect N-NH3 losses. Nitrogen application at V4 or V6 growth stages resulted in greater N-fertilizer recovery from urea sidedress, reaching values of 53 %. No increase in corn grain yield was observed with N application at different corn growth stages during the two growing seasons evaluated, most likely due to high N mineralization rates from the soil.
Highlights
Among N sources in Brazil, urea is the most commonly used, mainly because it has the lowest cost per unit of N compared to other solid N fertilizers currently available in the market
The higher N losses by ammonia volatilization were observed when urea was applied during the V12 or V10 growing stages, reaching values of 35 and 41% of the N applied, in 2011-2012 and 2012-2013, respectively (Figure 2)
Even when rainfall occurred few days after urea application for almost every treatment and for both growing seasons (Figure 1), except during V12 in 2011–2012, ammonia volatilization was higher as later the N application was performed (Figure 2)
Summary
Among N sources in Brazil, urea is the most commonly used, mainly because it has the lowest cost per unit of N compared to other solid N fertilizers currently available in the market. Urea undergoes hydrolysis by the action of an enzime called urease, converting R-NH2 to NH4+. 78% of total N applied (Lara Cabezas et al 2000). When urea is incorporated into soil, NH3 losses by volatilization decrease significantly Because of complex N dynamics in soil, N-fertilizer recovery efficiency generally does not exceed 50% (Lara Cabezas et al 2000, Scivittaro et al 2000, Gava et al 2006, Duete et al 2008), reaching very low values of 9% in some cases (Lü et al 2012). Nitrogen from fertilizer not recovered by the crop, in addition to being lost by volatilization, leaching and/or denitrification, can remain in the soil in organic or inorganic forms, without being absorbed by plants
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