A four year study by Stephen Joseph et al on the use of biochar in avocado farming showed significant improvements in tree growth, fruit yield, soil carbon and economic returns.
Method of Applying Biochar in Avocado Farming
Biochar was applied at 5%, 10% and 20% (volume basis calculated on a depth of 500 mm). The biochar was applied in two applications. The first half was applied at a depth of 500 mm and a 250 mm layer of subsoil placed on the biochar which was incorporated with a rotary hoe. This process was repeated with the second half of the biochar applied and the topsoil replaced on top, followed by rotary hoeing.
Two rows of 36 trees were planted, with each tree planted 4.5 m apart and each row 9 m apart. The first row was the control, and the second row contained the biochar.
Trees were planted in early December 2014, all with the same under tree fertiliser mix. . Trees were also mulched with a mixture of chicken litter, hardwood sawdust and wood chips. Both the biochar and control rows were on the same line for irrigation and had exactly the same water allowance.
Results
From the visual and measured observations, trees planted with biochar had 18–26% greater growth rates than the control with no difference between the various application rates of biochar. Fruit yield however, gave a different result. The 5% and 20% of treatments give significantly more fruit on average than the control and the 10% treatment. This indicates that there could be different interactions between the biochar, soil mineral and organic matter, added fertiliser in the 10% treatment than in the other two treatments which could partly account for the lower yield.
Economic Benefits
The study indicated that there was a net benefit of US$105 for every tonne of biochar applied and the average net profit per tree was US$35.
This farmer designed trial has demonstrated that biochar can significantly improve the growth of avocado seedlings and increase fruit yield. This is an important study and crucial to development of the biochar industry in Australia. It provides evidence that biochar has environmental and economic benefits to the farming and horticultural sectors. Read more about biochar boosts yields in Avocado farming.