Miss Carla Milazzo1, Mr Christopher Ham1, Mr Geoff Moore2
1Department of Primary Industries and Regional Development, 2Department of Primary Industries and Regional Development
Biography:
Carla has been with the Department of Primary Industries and Regional Development for five years, in Albany and now Broome. In the Kimberley, she works on developing mosaic irrigation to support the northern cattle industry. Her trials investigate crop and pasture varieties, nitrogen-use efficiency and offsite impacts, pasture growth rates and grazing intervals. During her time in the Great Southern, she worked across a range of agronomic issues from soil amelioration to crop protection. Carla has a Bachelor of Agribusiness with first class Honours from Curtin University. Her thesis involved high-throughput genetic sequencing to study the fungal microbiome of barley.
Abstract:
The west Kimberley and Pilbara have seen significant private investment in the last decade in the cultivation of irrigated fodder and forage crops to intensify northern beef production. To support annual growth rates of up to 40t DM/ha for subtropical grasses, nitrogen (N) inputs are high. However, a void of locally-relevant information has allowed for excessive N recommendations.
The Department of Primary Industries and Regional Development has conducted replicated, randomised trials in Rhodes grass near Broome. The trials aimed to first, establish N (urea) response curves with five rates plus a zero-N control; second, measure nitrate leaching under different rates; third, create nitrogen-use efficiency (NUE) curves; and fourth, compare formulations and irrigation timing to maximise uptake. Trials were harvested every month to measure biomass yield and crude protein (as a proxy for nitrogen uptake). Data were collected from 23 harvests over two-years. Leachate was collected from lysimeters beneath a subset of plots.
The N rate at which yield plateaued was 2kg N/ha/day (i.e. 60kg N/ha applied after each cut). This produced crude protein levels of 11%, and protein increased steadily in response to N. However, it is estimated that NUE of urea in this system was about 60% at this rate, and decreased as N increased. Exceeding 3kg N/ha/day is not recommended due to observed soil pH changes and high nitrate leaching risk from wet season rainfall. These data have been used to inform fertiliser decisions and support proponents seeking necessary environmental approvals to sustainably develop irrigation on pastoral leases.