New Zealand Journal of Agricultural Research abstracts

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Short communication

Grassland soil microbial respiration responses to urea and litter applications

F. M. Kelliher¹

J. R. Sedcole²

I. Emery³

L. M. Condron²

¹Manaaki Whenua - Landcare Research
PO Box 40
Lincoln 7640, New Zealand
kelliherf@landcareresearch.co.nz

²Agriculture and Life Sciences
PO Box 84
Lincoln University
Canterbury 8150, New Zealand

³University of Washington
School of Medicine
Box 357710, Seattle
WA 98195-7710, USA

Abstract   Ground ryegrass (Lolium perenne L., 5300 kg C ha^–1, 12 g C kg^–1 (soil)) and urea were applied to a grassland soil with the same dose of nitrogen (N), 500 kg N ha^–1, 1.1 g N kg^–1 soil, and microbial respiration responses measured in the laboratory. Microbial respiration rate in control, ryegrass- and urea-amended soil averaged 2.1 ± 0.2, 25.0 ± 1.7 and 10.6 ± 0.7 µg CO₂ kg^–1 soil s^–1, 1.5 h after treatment applications. Microbial respiration rates in ryegrass- and urea-amended soil were significantly greater than the controls for 17 and 6 days, respectively (P = 0.05), after treatment application. Integrated over the 24-day-long study, microbial respiration in ryegrass- and urea-amended soil increased 9.9 and 0.2 g CO₂ kg^–1 soil over the controls, excluding CO₂ production by carbonate hydrolysis. After ryegrass application, a multi-component, time-response model fitted the data well including rapid and, 2 days later, delayed, up-regulation responses of the microbial community followed by a protracted asymptote.

Keywords   nitrogen; ryegrass; soil respiration; urea fertiliser application

A06050; Online publication date 3 July 2007; Received 9 September 2006; accepted 28 March 2007

New Zealand Journal of Agricultural Research, 2007, Vol. 50: 321–326
0028–8233/07/5003–0321 © The Royal Society of New Zealand 2007

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