|Abstract||Biochar is the charred by-product of biomass pyrolysis, the heating of plant-derived material in the absence of oxygen in order to capture combustible gases. It is generally accepted that biochar is a highly stable form of carbon and as such has the potential to form an effective C sink, therefore sequestering atmospheric CO2.
The objective of this report was to report on the findings of a SRDC/SRA funded Grower Group project that was undertaken in the Herbert cane growing region between 2012 and 2014 to assess the impact of biochar and compost in a sugarcane farming system. The trial was conducted on a low cation exchange capacity soil in the Lannercost farming area west of Ingham.
A large number of studies (on numerous crops) have been conducted where biochar application has shown significant agronomic benefits, with a minor number of studies showing no significant effects on crop productivity and some studies reporting adverse effects (Sohi et. al., 2009). These results clearly suggests that crop productivity is variable due to a multiple number of reasons which are not fully understood. The mitigation potential of biochar with regard to other greenhouse gases, such as N2O and CH4, through its application to soil is less well established and requires further research (Sohi et. al., 2009). In this particular trial there were no significant difference in levels of greenhouse gases measured for the various treatments accessed.
In the trial conducted for this project, there was no significant cane productivity (being measured as cane and sugar yield) or economic advantage from applying biochar. The only way biochar may become viable is if a carbon market is established. The economic value of sequestered carbon is still being researched and debated in scientific and political arenas, so while this is occurring it will be challenging for biochar to be economically viable based upon the results from this trial. If biochar is to be considered as a part of a carbon sequestration program, a whole of carbon life cycle analysis will be required to better understand the carbon pathways and potential loss mechanisms.
In this trial the use of biochar in a sugarcane farming system is uneconomical based upon the results obtained. The only way that biochar may be economically viable in a sugarcane farming systems is through a government or community carbon credit program whereby a grower may be paid for the amount of carbon sequestered.
Composts can be a useful source of nutrients, however the nutrient content of parent materials will need to be considered. This trial has shown that sugarcane can be produced using compost as a nutrient source. If composts are to provide the nutrients for cane growth, an assessment of total nutrients present and their availability and speed of release will be required. Because the nutrients are in organic forms in compost, the availability of nutrients may be variable.
Composts should only be applied when they are “stabilised” and are not being acted upon by microbial activity. In this trial it is suspected that the composting process was still active when the product was applied and the compost was not yet “stabilised”. Germination and establishment of the plant cane were negatively impacted upon, with the crop showing nitrogen deficiencies in early stages of growth due to the compost not releasing sufficient nitrogen for crop growth. Composts could be a useful source of nutrients to grow a crop, however the economics associated with purchase and application will need to be considered.