LAMBELLS LAGOON BIOCHAR

BIOCHAR CROPPING APPLICATION TRIAL


Earth Systems, with the support of TNRM (through funding from the Australian Government), conducted a field trial in the Northern Territory to investigate the effects of biochar on crop productivity and soil health in horticultural production. This was the first known trial of its kind to have been conducted in the NT and was carried out at an organic farm in Lambell’s Lagoon in the Litchfield Municipality, approximately 56 km south-east of Darwin.


The Darwin region is one of the three main horticultural regions in the Northern Territory. Crops grown in each region are specifically suited to the climate and conditions of those areas and horticulture is limited to small areas of suitable land and water, with the potential for growth constrained by the availability of natural resources. In the Darwin region, soils with horticultural potential are generally infertile with low carbon levels, soil moisture holding capacity and nutrient availability. Farmers are continuously required to maintain or increase soil carbon to ensure that the soil is enhanced biologically, chemically and physically to promote crop growth and productivity.


WORK PROGRAM


The project aimed to carry out preliminary biochar soil trials in the field to gain a better understanding of how the application of biochar in the soil could bring benefits to horticulture in the NT. With support from TNRM and working closely with David Boehme, a local farm owner and horticulturalist from the NT Farmers Association, Earth Systems conducted the biochar soil trials over a period of 4 months during the late dry season (July – November 2013). A site with sandy soils and covering approximately 2 hectares was selected, consisting of three separate trial plots in which zucchinis and watermelons were planted.


BIOCHAR PRODUCTION AND APPLICATION


The biochar used in the trial was produced and supplied by Earth Systems using the CharMaker MPP20 mobile pyrolysis plant  – a unit designed to convert waste wood into biochar. Key properties of the biochar included a high fixed carbon and organic carbon content, as well as a high pH and liming value.


Three application rates (approximately 5, 13 and 23 dry tonnes per hectare) mixed with organic fertiliser were trialled and a control was also established. As the biochar was moistened for transportation, application rates were measured in the field utilising the wet weight of the biochar and converted to dry weight basis. The biochar was applied to the soil using a spreader and incorporated to a depth of 10-15 cm with a power harrow. During the trials, the area was managed according to standard organic farming practices for irrigation, nutrient, weed and pest management.


SAMPLING AND MONITORING


At the end of the trial, soil samples were obtained from the plots and analysed for the following:

  • Soil properties such as total carbon, organic matter, cation exchange capacity, pH, and macronutrients;

  • Available water capacity in the soil;

  • Changes in soil microbiology.
     

Crop yield in the zucchini plot and soil moisture tension were also recorded.


PRELIMINARY FIELD RESULTS


An increase in total soil carbon and organic matter was observed in the trial plots as a result of biochar application. For example, total carbon levels observed in the highest biochar application rate (23 t/ha) were 1.93%, compared to 1.3% in the control.


An increase in soil pH was observed as a result of biochar application. This suggests that biochar with liming properties could be applied to soils that require liming as an alternative to conventional liming.
An increase in available water capacity was observed when biochar was applied to soil samples from the trial site and measured in the laboratory. Available water capacity almost doubled at the lower rates of bio-char and almost tripled at the higher rates.


A 25% increase in crop yield was observed in one of the biochar treatments in the zucchini plot. The farmer reported that the zucchinis produced from the trials were among the best that had been produced on the farm.


RESEARCH AND MANAGEMENT IMPLICATIONS


The results highlight a strong case for the potential of biochar as a soil enhancer for horticultural sites in the Top End, especially given the general soil limitations in the region. Given the short-term and preliminary nature of the trials, further research and larger field trials are required to fully quantify the long-term benefits of using this method. Additional trials will also provide a better understanding of the relationship between biochar, different soil and crop types, climatic zones and crop productivity.

CONCLUSIONS


Overall the results from the application of biochar in field trials were extremely positive, with an observed increase in carbon, pH and water capacity. This technology has the potential to enhance agricultural productivity in the Northern Territory and further trialling and use of biochar is recommended to identify optimum technical and economic application for different soil and crop types.

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