Improving wheat production with deep banded Oil Mallee Charcoal in Western Australia
Paul Blackwell1, Syd Shea2, Paul Storer3, Zakaria Solaiman4, Mike Kerkmans5, and Ian Stanley6
Agchar Initiative Conference Terrigal New South Wales. April 29 - May 2, 2007
SUMMARY
• There can be benefits to wheat income from deep banded oil mallee charcoal in the low rainfall areas of WA; the trials on acid sandy clay loam and acid sand in 2005 showed up to $96/ha additional gross income at wheat prices of $150/ha; especially when applied with mineral fertilisers and inoculated soil microbes. Much of the yield improvement can be explained by better grain survival, associated with reduced drought stress.
• There were encouraging effects of charcoal on arbuscular mycorrhiza (AM) colonisation. Banded oil mallee charcoal improved AM colonisation of wheat roots by 3 fold, when used with mineral fertilisers and AM is inoculated with the seed in the acid sandy clay loam with a low population of indigenous AM. Early phosphorus uptake was not improved by AM colonisation; P supply from the soil and applied fertiliser was already adequate.
• AM colonisation in spring was related to effects of charcoal application on grain survival in inoculated mineral fertiliser treatments. This infers AM hyphae may have improved water supply to reduce drought stress and loss of grains in these treatments.
• The true economic value of oil mallee charcoal will be clearer when the cost of charcoal production and application is better known and long term effects of charcoal, especially with inoculated AMs and mineral fertilisers is better understood. The potential to achieve a commercial return from the sequestration of charcoal as an offset for carbon
dioxide emissions in broadscale agriculture will also help calculate true economic value.
• More research is worthwhile on the long term effects of incorporated charcoal in a range of soil conditions and seasons, from various sources and how low the banded charcoal rate needs to be to encourage better yields from mineral fertiliser with inoculated AM.
INTRODUCTION
Oil Mallees are the first native woody perennial species to be promoted as a commercial crop in the lower rainfall areas of the southwest land division of Western Australia, primarily stimulated by the need to ameliorate salinity caused by the clearing of native vegetation for agriculture (Bartle and Shea, 2002). Mallees are hardy plants that are well suited as a perennial crop through their ability to re-sprout from the large lignotuber after the above
ground mass has been lost through fire or harvesting. In 2000 a group of Oil Mallee growers from Kalannie (300 km NE of Perth, Western Australia) began producing eucalyptus oil for the Australian market (see the Oil Mallee Association www.oilmallee.com.au ). Integrated processing of mallee biomass to produce electricity, activated carbon and eucalyptus oil in a central processing facility has been the main emphasis of industry development since the late 1990’s. Western Power, Enecon and the Oil Mallee Company have successfully developed a ‘test of concept’ Integrated Wood Processing (IWP) plant at Narrogin. Bell and Bennett (2002) estimated that the NPV of the net benefit to landowners of planting mallees in a local catchment area to supply a 5MW IWP would be about $6.2 million over 20 years. Charcoal is a valuable by-product of such IWPs and a possible by-product of farm based distillation of eucalyptus oil.
It has become well recognised in Japan and some other parts of Asia that charcoal from forestry products and rice hull can stimulate indigenous soil microbial activity (Ogawa, 1994; Nishio, 1996). Charcoal has especially encouraged arbuscular mycorrhiza (AM) which can help supply phosphorus symbiotically to many agricultural crops (Ogawa et al., 1983) and rhizobia, which can fix nitrogen from the atmosphere to supply leguminous plants (Nishio and Okano, 1991). Field experiments in Indonesia (Yamato et al. 2006) showed charcoal made from tree bark applied at 10 L/ha could increase the yield of maize by about 50%, to 15 t/ha, when added to 500 kg/ha of NPK (15:15:15) fertiliser on an acid highly weathered infertile tropical soil; associated with increased AM fungal colonisation. Lehmann and Rondon (2006)
also identify numerous benefits of bio char to plant nutrition and microbial activity in the humid tropics. Benefits of charcoal to soil microbial activity have also been recognised in temperate forest environments (Zakrisson et al. 1996; Pietikainen et al. 2000).
Charcoal seems to assist microbial activity by having a porosity that provides a favourable microhabitat, weak alkalinity and by being a substrate unfavourable for saprophytes (Saito and Marumoto, 2002). AM fungi easily extend their extraradical hyphae into charcoal buried in the soil and sporulate in the particles (Ogawa, 1987). Postma et al. (1990) show evidence that rhizobia in pores <50 _m are protected from predation by protozoan predators; this
could be an important microhabitat property provided by charcoal in soils with low clay content.
Encouragement and establishment of AM fungi in Western Australian soils has encountered many challenges. “The objective of identifying procedure for managing mycorrhizal fungi is more appropriately restated as managing conditions to suit the growth and activity of beneficial populations of mycorrhizal fungi” (Abbot and Gazey, 1994). Introduced AM fungi can suffer competition with indigenous AM fungi and be ineffective for crop phosphorus supply due to high levels of background soluble P (Gazey et al. 2004). Australian native grass species can also be much more efficient at accessing insoluble forms of phosphate than introduced wheat varieties; whose rhizosphere colonies can be very different (Marschner et al. 2006). This may be an adaptation to the low clay content environment of many Australian topsoils; low clay content reduces the amount of small pore space to help some microorganisms prosper. Charcoal in suitable amount and form may provide the missing microhabitat in WA topsoils to help introduced AM fungi and other microbes survive and colonise introduced agricultural crops.
One commercial fertiliser company (Western Mineral Fertilisers; Tenterden WA) has developed products which minimise the abundance of readily soluble phosphorus to encourage symbiotic and other processes of inoculated soil microbes. Zeolite was initially included and intended to provide enhanced ion exchange capacity, and also a micro habitat
within the zeolite pores; however the pore volume may not be sufficient. It was a reasonable hypothesis that charcoal addition may improve the microhabitat further than the use of zeolite.
The opportunity to test hypotheses about charcoal effects on soil and use of soil microbes to improve crop nutrient supply came about in 2005. There was an intensive research effort to examine the efficacy of very wide rows of wheat on shallow soils in the low rainfall areas east of Geraldton (Blackwell et al. 2006; Blackwell 2007). With some support and encouragement from the Oil Mallee Company and Western Mineral fertilisers we developed the following experiments using no-till methods for crop establishment and very wide rows to minimise drought stress. Attempts to follow the long-term effects at Pindar failed due to a very dry winter season in 2006.
See complete paper attached and at:http://www.oilmallee.com.au/pdf/Improving_wheat_prod.pdf
See oral presentation at:
http://www.iaiconference.org/images/Blackwell_-_Improving_Wheat_Production_with_Mallee_Charcoal.pdf
1Department of Agriculture and Food, Geraldton WA, 2 Oil Mallee Company of Australia, 3Western Mineral
Fertilisers, 4University of Western Australia, School of Earth and Geographical Sciences, 5Oil Mallee
Association of WA, 6 "Bungadale", Kalannie , WA
