|Abstract||This project supports the sugar industry’s intensifying efforts to reduce its nitrogen (N) footprint that is caused by inefficient use of N fertiliser by the crop. The industry aims to minimise N pollution of coastal waters and emission of potent greenhouse gas nitrous oxide from soil without negatively impacting the economic sustainability of sugar production. International research addressing this pervasive problem in grain and other crops indicates that effective approaches combine agronomic innovation of N supply and nitrogen-use efficient (NUE) crop varieties.
This UQ-SRA collaborative project, aimed to advance knowledge of N use efficiency of crop varieties through systematic testing of a considerable number of sugarcane clones with diverse genetic background (commercial varieties from Australia and overseas, identified water-use-efficient clones, crosses with ancestral canes). Additional value was derived from a collaboration with QLD DAFF (Andrew Robson) to advance remote sensing of crop N, and investigations of the effects of N fertiliser on soil biology (Graham Stirling-nematodes, UQ consortium-bacterial and fungal communities). Brazilian researchers (Sao Paulo State) have since established sister experiments based on this project.
Clones were cultivated with low or recommended N rates (20-40 or 160-200 kg N-fertiliser per year) in two field trials (Mackay, Burdekin). The contrasting N rates were based on concepts that (i) NUE traits are only obvious in low-N environments, and (ii) ideal crop varieties will be strongly responsive to N supply and efficiently acquire N from fertiliser and indigenous soil reserves.
NUE traits of 64 clones were characterised over three years (plant crop-1st ratoon crop-2ndratoon crop) by quantifying the effects of contrasting N supply on growth in early, mid and late season. Clone vigour and ratooning ability were evaluated, as was canopy development and photosynthetic performance, the ability to acquire and store nitrate, N allocation to stalks and leaves, and sugar and biomass yields.
Project deliverables focused on generating knowledge on the genetic variation in N response and NUE traits and ranking of clones across environments with different soils to study the magnitude and the robustness of NUE traits.
The overall deliverables and key findings include:
(i) Establishment of field experimental conditions with limited N availability suitable for screeningsugarcane populations for NUE and N-related crop attributes. The field trial set-up was demonstrably effective in evaluating a considerable number of clones over a 3-year crop cycle;
(ii) Knowledge of genetic variation for NUE in Australian sugarcane germplasm;
(iii) NUE screening for photosynthetic performance, N uptake and accumulation attributes and yield parameters (CCS, sugar and biomass yields) identified benefits/drawback of experimental approaches;
(iv) Generated data on trait variation across clones, crop stages and environments, demonstrating that environmental conditions markedly affected crop performance as evidenced by moderate (22%, Mackay) and strong (45%, Burdekin) reduction in yields with low N supply. Soil characteristics are a likely cause as clones at Mackay acquired on average 3- and 2-fold more N than at the Burdekin site over the plant-1st ratoon cycles at low and recommended N supplies;
(v) Plant vigour appears to be a major determinant of NUE in sugarcane;
(vii) Clones with contrasting NUE and N response have been identified for use in next-step NUE trait research; (viii) Remote sensing showed potential for screening sugarcane germplasm, but its application at early stages of crop growth requires further investigation.
Taken together, the project has achieved the stated objective and fulfilled a role in SRA’s focus area of (1) optimally-adapted varieties, Plant breeding and release. The project outcomes have been communicated to the industry nationally and internationally, have been evaluated in the context of global efforts in advancing NUE in crop and cropping systems, and are in preparation for peer review and publication in highly ranked international scientific journals. The project is strongly aligned with industry interests as evidenced by interest of growers, national and international collaborators. Logical next steps towards developing N use-efficient sugarcane in the Australian breeding program include advancing understanding the basis of clone sensitivity to N and tools for rapid selection of N-responsive clones.