09 Feb 2010

Effects of climate change on N dynamics

A report presented by Dr Norton at the Fertilizer and Lime Research Centre meeting February 2010 on how high carbon dioxide affects soil and plant N processes.


Robert M Norton1,2, S K Lam2,3, D Chen3, G. Fitzgerald4, R Armstrong4
1 International Plant Nutrition Institute, 54 Florence St, Horsham, Victoria, Australia.
Email: rnorton@ipni.net
2 Department of Agriculture and Food Systems, The University of Melbourne, Private Box 260, Horsham, Victoria 3401, Australia.
3 Department of Resource Management and Geography, The University of Melbourne, Victoria, 3010, Australia.
4 Victorian Department of Primary Industries, Private Bag 260, Horsham, Victoria, 3401, Australia.


The Australian Grains Free Air Carbon Dioxide Enrichment (AGFACE) facility was established to compare wheat growth, yield and development under ambient (~380 (mol/mol) and elevated (~550 (mol/mol) carbon dioxide (a[CO2] and e[CO2]). Experiments on fertilizer N recovery and straw decomposition have been undertaken to estimate how e[CO2] and a changing climate could affect N supply and demand for annual crop production systems.

When grown under e[CO2], wheat crops showed higher crop biomass at the end of tillering, anthesis and maturity. Although plant and grain N contents declined, crop N uptake was 24% higher with e[CO2]. Stubble C:N ratio was not affected by e[CO2].

Wheat was grown with 15N enriched urea in PVC microplots in the AGFACE facility. Harvest biomass increased by 23% and N uptake increased by 17% under e[CO2]. Like the main experiment, stubble C:N ratio was not affected by e[CO2] and it had no significant effect on the proportion of N derived from fertilizer (%Ndff) for grain, stem and root. There were no significant effects of e[CO2] on 15N recoveries in soil and total fertilizer N losses.

The effects of e[CO2] and irrigation on straw decomposition and soil respiration was also undertaken within the AGFACE experiment. Pure cotton cloth, wheat straw and pea straw were decomposed using litter-bag method for 140 days. The mass remaining was the highest for cotton cloth (90%), then wheat (73%) and pea (50%). Total C content of wheat and pea straw and total N content of pea straw were reduced only under e[CO2] and irrigated conditions. Soil CO2 emissions were increased by e[CO2] only under irrigation.

In these experiments, the C:N ratio and degradation of organic residues in the wheat crop was not affected by carbon dioxide levels, although larger quantities of residue would enter soil nutrient cycles. These data indicate that e[CO2] increases plant N demand but does not increase the efficiency with which fertilizers are used nor the likely supply of N from residues. Further research is planned to investigate mineralization and N fixation under e[CO2] and these data will be used to develop N strategies for future cropping systems.
Norton FLRC 2010 PPT.pdf (size: 0.75 MB)

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