Gaseous nitrogen losses from urea applied to maize on a calcareous fluvo-aquic soil in the North China Plain
R. E. White, G. Cai, D. Chen, X. H. Fan, A. Pacholski, Z. L. Zhu and H. Ding
Australian Journal of Soil Research
40(5) 737 - 748
Published: 01 August 2002
Gaseous nitrogen losses, by NH3 volatilisation and denitrification, are mainly responsible for the low recovery of N fertiliser applied to irrigated maize on the North China Plain. Two field experiments were conducted to measure NH3 volatilisation and nitrification-denitrification losses from urea applied to maize (Zea mays L.) grown on a calcareous fluvo-aquic soil (Aquic Inceptisol) in Fengqiu County, Henan Province. The first was carried out in June 1998 (urea applied at 75 kg N/ha 3 weeks after sowing), and the second in July 1998 (urea applied at 200 kg N/ha 6 weeks after sowing). Each experiment included 3 treatments-control, surface-broadcast (SB), and deep point placement (DP) or broadcast followed by irrigation (BI). NH3 loss was measured by a micrometeorological method (NH3 sampler). Denitrification (N2 + N2O) was measured by the acetylene inhibition-intact soil core technique, and N2O emission was also measured in the absence of acetylene. The recovery of applied N was measured by a 15N balance technique.
When urea was surface broadcast (SB) 3weeks (75 kg N/ha) and 6weeks (200 kg N/ha) after sowing, 44 and 48% of the applied N was lost by NH3 volatilisation, respectively. The corresponding losses from the BI and DP treatments were only 18% and 11%, respectively. Denitrification was a significant process in this well-drained sandy soil, with average loss rates of 0.26-0.43 kg N/ha.day in the controls (from resident soil N), compared with 0.52-0.63 kg N/ha.day in the surface fertiliser treatments. Deep placement of urea reduced the denitrification rate to an average of 0.3 kg N/ha.day. The net denitrification loss from the fertiliser was <2% of the applied N, except for the SB urea treatment in the second experiment. The application of N fertiliser as urea increased N2O emissions from c. 0.3 to c. 2.3 kg N/ha over 57 days in the second experiment, with average N2O emission rates in the control and SB treatment of 0.006 and 0.042 kg N/ha.day, respectively. The significantly lower ratio of N2 /N2O in the urea treatments compared with the control suggested that nitrification of applied N may have contributed to N2O production. Alternatively, the ratio of N2 /N2O during denitrification may have changed with the greater supply of NO3 -.
Full text doi:10.1071/SR01011
© CSIRO 2002