Malcolm McCaskill1, Richard Richards2, Debra Partington1, Penny Riffkin1
1 Agriculture Victoria, 915 Mt Napier Rd, Hamilton, Vic, 3300, firstname.lastname@example.org
2 CSIRO Agriculture and Food, Canberra, ACT, 2601
Diffuse radiation is more effective at penetrating into thick crop canopies than direct radiation, leading to a higher radiation use efficiency. To quantify the fraction of diffuse radiation in Australia’s high rainfall zone, a sensor that distinguishes between diffuse and global (diffuse + direct) radiation was used at Hamilton for the 2016 growing season. Monthly means from these measurements were highly correlated (R2 = 0.99) with values derived by a surrogate that uses daily radiation from the SILO database. Using the surrogate, diffuse radiation accounted for 62% of global radiation at Hamilton between June and October, which is the core of the growing period. Across other sites in the high rainfall zone, diffuse radiation during this period ranged from 49% at Canberra to 61% at Cressy (Tasmania) and Lake Bolac (Victoria). Given the high proportion of diffuse radiation during the growing season in the high rainfall zone, it is proposed that the ideal crop architecture is planophile (flat leaves) as a seedling, followed by erectophile (erect leaves) as the canopy develops.