Three long-term trials end with a quasi-equilibrium between soil C, N, and pH: an implication for C sequestration
Mark Conyers A E , Philip Newton B , Jason Condon A , Graeme Poile A , Pauline Mele C D and Gavin Ash AA EH Graham Centre for Agricultural Innovation, Department of Primary Industries NSW and Charles Sturt University, Wagga Wagga Agricultural Institute, Pine Gully Road, Wagga Wagga, NSW 2650, Australia.
B Formerly Victorian Department of Primary Industries, Chiltern Valley Road, Rutherglen, Vic. 3685; now PO Box 572, Wodonga, Vic. 3689, Australia.
C Department of Primary Industries, Biosciences Research Division, Victorian AgriBiosciences Centre, 1 Park Drive, Bundoora, Vic. 3083, Australia.
D School of Life Sciences, LaTrobe University, Bundoora, Vic. 3083, Australia.
E Corresponding author. Email: mark.conyers@dpi.nsw.gov.au
Soil Research 50(7) 527-535 https://doi.org/10.1071/SR12185
Submitted: 28 July 2011 Accepted: 3 October 2012 Published: 13 November 2012
Abstract
The aim of this study was to assess the long-term changes in some key soil chemical properties at the completion of three long-term trials in south-eastern Australia and the relationship between those soil properties. From a soil organic matter perspective, the build-up of carbon (%C) requires an accumulation of nitrogen (%N), and the build-up of %C and %N fertility comes at the cost of soil acidity. Rotation, tillage, and stubble practices combine to alter the quantity, quality (C : N), and the depth distribution of organic matter in a soil, but the three soil chemical properties reported here seem to also be in quasi-equilibrium at the three long-term sites. The consequence is that if the build-up of soil organic matter leads to soil acidification, then the maintenance of agricultural production will require liming. The emission of CO2 when limestone reacts with soil acids, plus the C cost of limestone application, will negate a proportion of the gains from C sequestration as organic matter in soil. Such cautionary information was doubtless unforeseen when these three long-term trials were initiated.
Additional keywords: organic matter, soil acidification.
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