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Key message Potential benefits of biochar and compost soil amendments may not be realised in high-input perennial horticultural systems such as an apple orchard. Abstract Mechanistic understanding of how biochar affects tree physiology is deficient. We determined the effects of biochar amendment on crop yields, growth and tree physiology of a high-input perennial horticultural system. The biochar was acacia whole tree green waste that had undergone pyrolysis in a continuous flow kiln at temperatures up to 550°C for 30-40 min. Tree growth, crop yield efficiency and fruit quality were assessed to investigate the effects of biochar, compost and combined biochar and compost (B ? C) treatments on the productivity of a newly planted apple orchard over a four-year period. The site was characterised by an A1 horizon 38 cm deep with a CEC of 35.15 cmol kg -1 , pH CaCl 2 of 5.7 and an organic carbon of 2.42 %. All treatments received approximately 42.5, 5.98, 131.1 and 12 kg ha -1 year -1 of N, P, K and Ca via fertiliser and green fowl manure inputs, respectively. Leaf gas exchange, leaf nutrient concentration and water status were recorded during the second cropping season in the biochar and control treatments only. Crop yield and fruit quality parameters were unaffected by the soil amendment treatments. Trunk girth was significantly higher than the control in the B ? C and biochar treatments, in the first year and fourth year, respectively, while compost had no effect in any year. Neither photosynthetic capacity nor leaf nutrient concentration was influenced by treatment. Seasonal daily tree water use was similar between biochar and control treatments. The general lack of difference between treatments suggests that perennial horticultural systems characterised by high inputs of nutrients and water may not respond to biochar. This is the first report investigating the whole-plant physiology of apple trees with biochar amendment.

Nutrient leaching from agricultural soils is a worldwide problem that has been implicated in deleterious impacts on the environment. Application of biochar to soil has been proposed as a means to reduce nutrient leaching and improve fertilizer use efficiency. The potential for biochar to reduce nutrient leaching and increase fertilizer use efficiency was tested by applying 47 Mg ha hardwood biochar before replanting a commercial apple () orchard, in the Huon Valley, Tasmania. Passive wick flux meters were installed at the base of the A1 horizon at a depth of 25 cm to monitor leachate volume and the concentration of nutrients leached below the A1 soil horizon over a 38 mo period. Biochar application significantly increased the concentration of phosphorous in the leachate, while having no significant effect on nitrate or potassium concentration. The volume of leachate collected in the flux meters was significantly higher in the biochar treatment, which resulted in significantly higher amounts of potassium and phosphorous being leaching from the biochar treatment than the control. Biochar application had no significant effect on either the concentration or the flux of nitrate leached from the A1 horizon. Nonetheless, nutrient application was well in excess of tree requirements, such that between 53 to 78% of the applied nitrogen, 5 to 11% of the applied phosphate, and 69 to 112% of the applied potassium were leached below the A1 horizon.

The effects of environmental parameters, land-use history, and management practices on soil organic carbon (SOC) concentrations, nitrogen, and bulk density were determined in agricultural soils of four soil types in Tasmania. The sites sampled were Dermosols, Vertosols, Ferrosols, and a group of texture-contrast soils (Chromosol and Sodosol) each with a 10-year management history ranging from permanent perennial pasture to continuous cropping. Rainfall, Soil Order, and land use were all strong explanatory variables for differences in SOC, soil carbon stock, total nitrogen, and bulk density. Cropping sites had 29–35% less SOC in surface soils (0–0.1 m) than pasture sites as well as greater bulk densities. Clay-rich soils contained the greatest carbon stocks to 0.3 m depth under pasture, with Ferrosols containing a mean of 158 Mg C ha–1, Vertosols 112 Mg C ha–1, and Dermosols 107 Mg C ha–1. Texture-contrast soils with sandier textured topsoils under pasture had a mean of 69 Mg C ha–1. The range of values in soil carbon stocks indicates considerable uncertainty in baseline values for use in soil carbon accounting. Farmers can influence SOC more by their choice of land use than their day-to-day soil management. Although the influence of management is not as great as other inherent site variables, farmers can still select practices for their ability to retain more SOC.