BM Flohr1, JR Hunt2, JA Kirkegaard3, B Rheinheimer3, T Swan3, L Goward3, JR Evans4, M Bullock3
1CSIRO Agriculture and Food, Adelaide, South Australia, Australia, firstname.lastname@example.org
2Department of Animal, Plant and Soil Sciences, AgriBio Centre for AgriBiosciences, La Trobe University, Melbourne, Victoria, Australia
3 CSIRO Agriculture and Food, Canberra, Australian Capital Territory, Australia
4 The Australian National University, Research School of Biology, Canberra, ACT 2601, Australia
The yield advantage of early sown slow developing (long cycle) wheat cultivars over fast developing cultivars sown later (short cycle) is variable. This variable response is likely due to environmental factors, but the precise set of conditions that confers an advantage to long cycle treatments is not known. We compared short and long cycle wheat cultivar x time of sowing combinations over four seasons in Temora, NSW. Two seasons (2011, 2012) had over 400 mm of summer fallow (December-April) rain which filled the soil profile to depth, and two seasons had summer fallow rain that was less than the site average of 208 mm (2015, 2016). Rainfall 30 days prior to the start of flowering (approximating the critical period for yield determination) in each year was 8, 6, 14, 190 mm respectively. We observed that there was only a yield benefit in long cycle treatments in seasons where there was soil water stored at depth, and there was little rain during the critical period for yield determination in wheat, forcing greater reliance on stored soil water for crop growth (2011, 2012). In these seasons the higher yield of long cycle treatments could be attributed to greater soil water extraction from deep in the profile (<1.0 m), and consequently greater dry-matter production, grain number and grain yield. In the other seasons, lower evaporation and higher biomass accumulation in long cycle treatments traded off against inferior harvest index such that yields were equivalent to short cycle treatments.