Abstract
Immobilisation of fertiliser nitrogen (N) by soil microorganisms can reduce N availability to crops, decreasing growth and yield. To date, few studies have focussed on the effect of different plant species on immobilisation of fertiliser N. Canola (Brassica napus) is known to influence the soil microbiome and increase mineral N in soil for future crops compared with cereals. We tested the hypothesis that canola can reduce immobilisation of fertiliser N by influencing the composition of the rhizosphere microbiome. To investigate this, we conducted a glasshouse soil column experiment comparing N fertiliser uptake between canola and wheat (Triticum aestivium) and partitioning of fertiliser N between plants and microorganisms. Plants were grown in soil to which high C:N ratio wheat residues and 15N-labelled urea fertiliser were applied. There was no difference between wheat and canola in fertiliser N uptake despite differences in fungal community composition and the carbon metabolising enzyme alpha-glucosidase in the rhizosphere. Canola obtained more soil-derived N than wheat. There was no significant difference in the rhizosphere bacterial communities present between wheat and canola and unplanted controls. Our results highlight the capacity of canola to increase mineralisation of soil N compared with wheat although the study could not describe the microbial community which facilitated this increase.
Highlights
Nitrogen (N) deficiency is considered the main impediment to achieving water-limited potential yield in Australian wheat (Triticum aestivum) production systems [1]
There was no interaction effect of total microbial biomass N (MBN) to plant species or N treatment (Figure 1), the microbial uptake of fertiliser N in mg increased with application rate for both plant treatments (p ≤ 0.001)
There was no interaction effect of total MBN to plant species or N treatment6 of 14 (Figure 1), the microbial uptake of fertiliser N in mg increased with application rate for both plant treatments (p ≤ 0.001)
Summary
Nitrogen (N) deficiency is considered the main impediment to achieving water-limited potential yield in Australian wheat (Triticum aestivum) production systems [1]. In addition to inadequate application rates, Australian wheat crops are estimated to use only 40% of N fertiliser in the season it is applied [3]. A recent simulation study projected that microbial immobilisation was the main source of N fertiliser inefficiency in southern Australian cropping systems with retained stubble [4]. Rates of immobilisation are high in grain production systems where residues are retained because the presence of high C:N ratio cereal crop residues encourages microbes to use available N to support residue decomposition [6]
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