Dr Denis Curtin1, Dr Ed Gregorich2, Dr Mike Beare1, Dr Henry Janzen3, Dr  Ben Ellert3, Dr Bobbi Helgason4

1Plant and Food Research, Lincoln, New Zealand, 2Agriculture and Agri-Food Canada, Ottawa, Canada, 3Agriculture and Agri-Food Canada, Lethbridge, Canada, 4University of Saskatchewan, Saskatoon, Canada

Crop residues are an important resource for arable farmers as they add organic matter to the soil and recycle plant nutrients. Decay of plant residues is linked to many ecosystem functions, affecting atmospheric CO2, nutrient release, microbial diversity, and soil organic matter quality. The rate of decay, in turn, is governed by soil type, management, and environmental variables, some of which may be changing in coming decades. Our objective in this study was to evaluate effects of soil type, climate, residue placement, and their interaction on the decomposition and retention of residue-derived C.  We applied 13C-labelled barley straw (13C = 10.2 atom%; C = 37.9%; N = 0.95%; C:N = 40) at a rate equivalent to 2 Mg C/ha at five locations representing different soil types and climates. Four of the sites were in Canada: Ottawa, Ontario; Swift Current, Saskatchewan; Lethbridge, Alberta; and Breton, Alberta. Mean annual temperature (MAT) at the Canadian sites ranged from 2.1oC (Breton) to 6.0oC (Ottawa) while mean annual precipitation (MAP) ranged from 356 mm (Swift Current) to 869 mm (Ottawa). A fifth site was in New Zealand (Lincoln), where MAT was 11.5oC and MAP was 640 mm. The labelled residues were either surface applied or mixed into the top 10 cm of soil. Samples were collected periodically (up to 8 years after application) for determination of the remaining 13C. Data on the recovery and kinetics of decomposition will be discussed.


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