Search

Plants allocate their photosynthetic carbon (C) belowground through rhizodeposition, which can be incorporated into microbial biomass and organic matter, but can also be directly shared with arbuscular mycorrhizal fungi (AMF). In this study, we investigated how both rhizodeposition and AMF colonisation are affected by nitrogen (N) and phosphorus (P) availability in soil systems, and in mm, how these C allocation pathways influenced plant P uptake in four different wheat genotypes with variable root traits. Wheat genotypes (249, Suntop, Scout and IAW2013) were grown in pots and labelled continuously during their growth period with [sup.13]C[O.sub.2] to determine rhizodeposition. We applied two levels of N (25 and 100 kg [ha.sup.-1]) and P (10 and 40 kg [ha.sup.-1]) fertiliser. Plant root traits, plant P content, soil available P and N, microbial biomass C and P, and AMF colonisation were examined. We constructed a structural equation model to show how C allocation to rhizodeposition and AMF colonisation depended on P and N availability, and how these pathways affected plant P uptake and grain yield. Wheat genotypes with fine roots (Suntop, Scout and IAW2013) were associated with AMF colonisation for plant P uptake, and the genotype with the largest root biomass (249) provided more C to rhizodeposition. Both rhizodeposition and AMF colonisation increased plant P and grain yield under low P and high N availability respectively, while root biomass and root traits, such as specific root length and proportion of fine roots, determined which C allocation pathway was employed by the plant. Additional keywords: C allocation, [sup.13]C labelling, mycorrhizal colonisation, microbial biomass phosphorus, root traits, phosphorus uptake. Received 9 July 2019, accepted 18 November 2019, published online 4 December 2019, Introduction Many Australian soils are phosphorus (P)-deficient and P is one of the most critical and limiting nutrients in many soils of Australia (Viscarra Rossel and Bui 2016). Phosphorus is [...]

Land-use and management practices on limed acidic and carbonate-bearing soils can fundamentally alter carbon (C) dynamics, creating an important feedback to atmospheric carbon dioxide (C[O.sub.2]) concentrations. Transformation of carbonates in such soils and its implication for C sequestration with climate change are largely unknown and there is much speculation about inorganic C sequestration via bicarbonates. Soil carbonate equilibrium is complicated, and all reactants and reaction products need to be accounted for fully to assess whether specific processes lead to a net removal of atmospheric C[O.sub.2]. Data are scarce on the estimates of CaC[O.sub.3] stocks and the effect of land-use management practices on these stocks, and there is a lack of understanding on the fate of C[O.sub.2] released from carbonates. We estimated carbonate stocks from four major soil types in Australia (Calcarosols, Vertosols, Kandosols and Chromosols). In >200-mm rainfall zone, which is important for Australian agriculture, the CaC[O.sub.3]-C stocks ranged from 60.7 to 2542 Mt at 0-0.3 m depth (dissolution zone), and from 260 to 15 660 Mt at 0-1.0 m depth. The combined CaC[O.sub.3]-C stocks in Vertosols, Kandosols and Chromosols were about 30% of those in Calcarosols. Total average CaC[O.sub.3]-C stocks in the dissolution zone represented 11-23% of the stocks present at 0-1.0 m depth, across the four soil types. These estimates provide a realistic picture of the current variation of CaC[O.sub.3]-C stocks in Australia while offering a baseline to estimate potential C[O.sub.2] emission-sequestration through land-use changes for these soil types. In addition, we provide an overview of the uncertainties in accounting for C[O.sub.2] emission from soil carbonate dissolution and major inorganic C transformations in soils as affected by land-use change and management practices, including liming of acidic soils and its secondary effects on the mobility of dissolved organic C. We also consider impacts of liming on mineralisation of the native soil C, and when these transformations should be considered a net atmospheric C[O.sub.2] source or sink. Additional keywords: carbonate dissolution, land use change and acidification, limed acidic soils, management practices, soil carbonate stocks, soil types., Introduction Soils play an important role in the global carbon (C) cycle, and soil C is considered the largest terrestrial C pool, with nearly three times the amount of C [...]

The application of biochar technology for soil amendment is largely based on evidence about soil fertility and crop productivity gains made in the Amazonian Black Earth (term preta). However, the uncertainty of production gains at realistic application rates of biochars and lack of knowledge about other benefits and other concerns may have resulted in poor uptake of biochar technology in Australia so far. In this review, we identify important opportunities as well as challenges in the adoption of biochar technology for broadacre farming and other sectors in Australia. The paper highlights that for biochar technology to be cost-effective and successful, we need to look beyond carbon sequestration and explore other opportunities to value-add to biochar. Therefore, some emerging and novel applications of biochar are identified. We also suggest some priority research areas that need immediate attention in order to realise the full potential of biochar technology in agriculture and other sectors in Australia. Additional keywords: biochar characterisation, contaminants, herbicide efficacy, heavy metals, nitrous oxide, plant growth media, regulations., Introduction Biochar is a carbon (C)-rich, solid material produced by thermal decomposition of organic material or biomass in the absence, or under limited supply, of oxygen (Lehmann and Joseph 2009). [...]