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Volume 4, issue 3 | Copyright
SOIL, 4, 213-224, 2018
https://doi.org/10.5194/soil-4-213-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Original research article 13 Sep 2018

Original research article | 13 Sep 2018

Continental soil drivers of ammonium and nitrate in Australia

Juhwan Lee1, Gina M. Garland2, and Raphael A. Viscarra Rossel1 Juhwan Lee et al.
  • 1CSIRO Land and Water, G.P.O. Box 1700, Canberra ACT 2601, Australia
  • 2Agroscope, Zurich 8046, Switzerland

Abstract. Soil N is an essential element for plant growth, but its mineral forms are subject to loss from the environment by leaching and gaseous emissions. Despite its importance for the soil-plant system, factors controlling soil mineral N contents over large spatial scales are not well understood. We used NH4+ and NO3 contents (0–30cm depth) from 469 sites across Australia and determined soil controls on their regional variation. Soil mineral N varied regionally but depended on the different land uses. In the agricultural region of Australia, NH4+ tended to be similar (median 4.0 vs. 3.5mgNkg−1) and NO3 was significantly enriched (3.0 vs. 1.0mgNkg−1), compared to the non-agricultural region. The importance of soil controls on mineral N in the agricultural region, identified by the model trees algorithm Cubist, showed that NH4+ was affected by total N, cation exchange capacity (CEC) and pH. In the non-agricultural region, NH4+ was affected not only by CEC and pH, but also by organic C and total P. In each of the regions, NO3 was primarily affected by CEC, with more complex biophysical controls. In both regions, correlations between mineral N and soil C:N:P stoichiometry suggest that more NH4+ was found in P-depleted soil relative to total C and total N. However, our results showed that only in the non-agricultural region was NO3 sensitive to the state of C and its interaction with N and P. The models helped to explain 36%–68% of regional variation in mineral N. Although soil controls on high N contents were highly uncertain, we found that region-specific interactions of soil properties control mineral N contents. It is therefore essential to understand how they alter soil mechanisms and N cycling at large scales.

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Soil nitrogen (N) is an essential element for plant growth, but its plant-available forms are subject to loss from the environment by leaching and gaseous emissions. Still, factors controlling soil mineral N concentrations at large spatial scales are not well understood. We determined and discussed primary soil controls over the concentrations of NH4+ and NO3 at the continental scale of Australia while considering specific dominant land use patterns on a regional basis.
Soil nitrogen (N) is an essential element for plant growth, but its plant-available forms are...
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