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P. A. Barbieri, H. E. Echeverría, H. R. Sainz Rozas and
L. I. Picone
Australian Journal of Experimental Agriculture, 2006, 46, 535–543 |
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Abstract.
Studies of nitrogen (N) transformations under pastures are
necessary to improve N agronomic efficiency (AE). A 2-year field experiment was
conducted at Balcarce (37°45′S, 58°18′W), Argentina, on a pasture of tall
wheatgrass (Elytrigia elongata) on a Typic Natracuol. The objective was to
determine the effect of urea applied at varying rates (0, 90 and 180 kg N/ha) in
autumn (late March) on soil mineral N, NH3 volatilisation losses (VL), herbage
dry matter (DM) and plant accumulated N (Nplant) 46 days after fertilisation. In
1999, the accumulated VL were 3, 14 and 63 kg N/ha for 0, 90 and 180 kg applied
N/ha, respectively, whereas in 2001, the accumulated VL were 1, 12 and 19 kg
N/ha, respectively. Plant accumulated N was 32, 75 and 108 kg/ha in 1999,
whereas in 2001, Nplant was 12, 34 and 58 kg/ha for 0, 90 and 180 kg N/ha,
respectively. In both years, N AE ranged from 10 to 15 kg DM/kg applied N and
the N recovered fraction (RF) ranged from 46 to 25% of applied N in 1999 and
2001, respectively. In 1999, unaccounted N (Nunac.) ranged from 41 to 23%,
whereas in 2001, Nunac. ranged from 67 to 69% of applied N. Results of this
study indicate that VL and denitrification affected the RF, and, for weather
conditions of this area, VL would be the main N loss mechanism. These results
indicate that management strategies to improve N use efficiency could be the
utilisation of split N rates and N sources without urea.
Additional keywords: fate of urea, nitrogen losses, nitrogen transformation,
tall wheatgrass.
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