Estimate of the global warming potential of the Tasmanian pyrethrum industry in comparison to other crops, potato and onion

A desktop study was undertaken to assess the environmental sustainability and contribution of the pyrethrum industry in Tasmania to on-farm greenhouse gas (GHG) emissions in comparison to potato and onion. Pyrethrum used significantly less diesel in transport than potato or onion. This was mainly due to the lower weight of dried flower harvested from pyrethrum (4.8 and 3.2 t/ha in year 1 and older fields, respectively) in comparison to the weight of crop from potato and onion fields (60 t/ha). First harvest pyrethrum required a similar amount of diesel to potato and onion for tractor and harvester operations. However, older pyrethrum crops required only 41% of the diesel used in potato and onion crops due mainly to the perennial nature of pyrethrum and the absence of cultivation in subsequent years. Pyrethrum required greater inputs (kg a.i./ha) of herbicides and lower inputs of fungicides than potato and onion. All three crops required little input of insecticides. Pyrethrum had substantially lower inputs of N and P than potato or onion. First-harvest pyrethrum required only 38% and 59% of the N required by potato and onion respectively. Moreover, pyrethrum required lower K than potato, but higher K than onion. The electricity consumption associated with pyrethrum and onion were similar, and amounted to 39% that of potato, due to the higher irrigation requirement of potato (5.1 ML/ha) in comparison to pyrethrum and onion (2.0 ML/ha) in Tasmania. The annual global warming potential (GWP) per hectare of first-harvest pyrethrum, older pyrethrum, potato and onion in Tasmania was estimated at 4128.8, 2184.7, 5284.0 and 4875.3 kg CO2-e/ha. The annual GWP of first year pyrethrum was therefore 78% that of potato and 85% that of onion, while the annual GWP per hectare of older pyrethrum fields was 41% that of potato and 45% that of onion. The GWP of the Tasmanian pyrethrum industry was estimated at 9,319.0 t CO2-e, based on current production of 1,200 ha of first year and 1,990 ha of older pyrethrum crops. By comparison, the 6,618 ha of potato and 1500 ha of onion grown in Tasmania would have an annual on-farm GWP of 34,968.5 t CO2-e and 7,313.0 t CO2-e respectively. This study indicated that the on-farm production of pyrethrum is a relatively low contributor to GHG gas production on a per hectare basis, in comparison to other annual crops often grown in rotation. Other indicators of environmental sustainability are also discussed.