Sugarcane (Saccharum sp. hybrids) crops typically grow for 16–24 months in the subtropics, with nitrogen (N) fertiliser generally applied as a single dose between 150 and 250 kg N ha−1 early in the season. High N fertiliser application coupled with intense rainfall in the subtropics can lead to nitrate leaching and denitrification events that result in low N fertiliser use efficiency and damage to the environment. We investigated whether the use of a slow-release N fertiliser, polymer coated urea (PCU), may be more agronomically effective than urea as an N fertiliser source, by better matching soil N supply to sugarcane N demand. Multi-rate N fertiliser trials comparing biomass production and N accumulation responses of ratoon sugarcane crops to urea and PCU products were conducted across four commercial sugarcane farms in the Australian subtropics, with N fertiliser applied in a band 100–150 mm below the soil surface 2–12 weeks after the previous cane crop was harvested. At two sites, buried mesh bags containing 90 d and 270 d PCU products were destructively sampled over 12–15 months to assess the N release rate under field conditions. Sugarcane biomass yields were responsive to applied N at two of the four sites (P < 0.05) and crop N accumulation was responsive to N fertiliser application at all four sites (P < 0.1). While the mesh bag study clearly indicated a delayed release of N from the PCU products over time, there was no significant effect of N fertiliser source (urea vs PCU) on crop biomass or N accumulation at any site. The lack of any improvement in agronomic N efficiency with the PCU products is attributed to the presence of active roots in ratoon crops combined with the absence of large rainfall events in the months following N fertiliser application in the seasons of study. Modelling, coupled with an understanding of the N release dynamics of PCU products across a different soils and climatic conditions, is required to develop recommendations for PCU products for sugarcane growers in the region, although further trials across a wider range of seasons may be warranted to verify any modelling predictions.

Background and aims Alkaline dispersive subsoils are characterised by multiple physicochemical constraints that limit plant water and nutrient acquisition. Subsoil amelioration through organic amendments (OAs) requires significant financial investment. Whereas large yield responses can result following amelioration, sometimes small or even negative yield responses can occur, resulting in a significant net financial loss for the farmer. For farmers to feel confident in investing in subsoil amelioration better prediction of the likely yield improvement is required and to achieve this an understanding of the underlying mechanisms such as nutritional and non-nutritional drivers, and the longevity of benefits are required. Our study aimed to ascertain the drivers of yield improvements from subsoil amelioration with OAs. Methods In a controlled environment, wheat ( Triticum aestivum L. cv. Scepter) plants were grown until maturity in a Solonetz amended with (i) poultry litter (PL; 20 t ha −1 ), and (ii) NPKS nutrients and (iii) model organic carbon (MOC) with equivalent amounts of nutrients and total carbon contained in the PL, and (iv) NPKS + MOC. Control (no amendments) and gypsum (5 t ha −1 ) were included as district practices. Before planting, amendments were applied as a vertical band at 20 – 40 cm depth and pre-incubated. Plant biomass, grain yield, root biomass, and physicochemical properties of the soil associated with the amendment band were quantified at harvest. Results Compared to the control, wheat grain yield was increased by 30% for PL, 43% for NPKS + MOC, and 61% for NPKS, but no differences in yield were detected for MOC or gypsum. The lower yield increase by PL than NPKS with or without MOC was likely due to the readily available form of plant nutrients in the inorganic fertilisers vs slower mineralisation of nutrients from the OAs. Improvement in soil physicochemical properties following amelioration of alkaline dispersive subsoil resulted in better root proliferation and subsoil water use. Grain yield showed a positive correlation with root biomass in the subsoil layers. Conclusions In the short-term (one crop cycle), organic amendments improved soil’s non-nutritional physical and chemical properties but had no additional nutritional effect on wheat grain yield compared to inorganic fertiliser application. Longer-term studies are needed to determine the legacy effect of the nutritional contribution in conjunction with the improvement of soil structure from the OAs in alkaline dispersive subsoils.

Sugarcane (Saccharum spp.) farming systems globally have largely transitioned away from burning the crop prior to harvest. Harvesting the sugarcane crop 'green' results in large volumes of biomass residues being left on the soil. Despite this, there is little evidence for increased soil organic carbon stocks. We investigated the role of surface application or incorporation (0-200 mm soil layer) of harvest residues (15 t dry weight residues ha(-1)) and its biochar (5.4 t ha(-1) based on the quantity of resource recovered after pyrolysis) on the priming of native soil organic carbon (SOC), the mineralisation of the organic amendments and the source of crop nitrogen (N) uptake (soil, organic amendment or urea). All treatments received urea at 180 kg N ha(-1). To achieve the separation of C and N sources, dual C-13 and N-15-enriched sugarcane residues and corresponding biochar (350 degrees C) were used in an 84-d controlled environment study. A three-pool isotope mixing model, utilising two levels of C-13 enrichment in residue (16.6 parts per thousand and 23.8 parts per thousand) and biochar (16.8 parts per thousand and 24.1 parts per thousand), was also applied to partition the C from three sources: 1) root respiration, 2) organic amendment mineralisation, and 3) SOC priming. The SOC mineralisation was increased following both surface-applied and incorporated residues, over the nil organic amendment (control) by 72.3 and 78.3 CO2-C m(-2) respectively over 84 days. In contrast, biochar lowered the mineralisation of SOC by 62.9 g CO2-C m(-2) compared to the control. The cumulative mineralisation of sugarcane residue biochar (18.9 g CO2-C m(-2)) was lower (P = 0.03) than surface applied residue (50.1 g CO2-C m(-2)) and incorporated residue (71.9 g CO2-C m(-2)) over the study period. While there were no differences in total crop N uptake between the organic-amended soils and the control, the source of N was significantly different. The sugarcane plants utilised 31.0% and 29.4% of the supplied urea N in the nil organic-amended control and biochar treatment, respectively. This was significantly reduced to 24.8% and 20.6% in the surface residue and incorporated residue treatments, respectively. In comparison, the plant uptake of N derived from the organic amendments was 27.8%, 15.4% and 6.4% from incorporated residues, surface-applied residues and biochar, respectively (P < 0.001). Results suggest that the increased mineralisation of SOC, partly driven by the high C:N ratio (73:1) and the unbalanced nutrient stoichiometry may lead to low SOC accumulation from surface residue application and that sugarcane residue biochar results in SOC stabilisation and an increase in the use efficiency of fertiliser N in sugarcane systems.

The use of biochar in avocado orchard soils has not yet been investigated in rigorous scientific experiments. We determine the effect of wood biochar on avocado growth, fruit production and economic benefit. Biochar was applied at 0%, 5%, 10% and 20% volume by volume basis. Biochar significantly improved the growth of avocado seedlings and increased fruit yield in the first three years after planting. There was an overall increase in soil carbon, fruit yield, tree diameter and height in all biochar treatments relative to the control over the seasons. Trees planted with biochar had 18-26% greater growth rates (in terms of height and stem diameter) than the control. Tree diameter was significantly greater with biochar (145.4 +/- 3.3 mm) relative to the control treatment (125.0 +/- 2.7 mm). Tree height was also significantly greater with biochar (3.7 +/- 0.1 m) relative to the control treatment (3.4 +/- 0.1 m). The fruit count from the biochar row was significantly greater (97%) in 2018. Heavy bearing trees typically have a lower yield in the subsequent year but despite this, the 2019 fruit counts were higher in aggregate for the biochar amended trees (20%) relative to the control. A cost-benefit analysis indicated that if yield surplus of fruit trees continued for three years, and assuming avocado prices remain at similar levels, then the discounted net benefit over a hectare would amount to US$8581, or US$105 per metric tonne of biochar applied.

Dairy pastures can be a major source of soil nitrous oxide (N2O) emissions due to the combination of intensive nitrogen (N) fertiliser use and high soil water content, from either rainfall and/or irrigation. Biochar application is a promising approach to lower soil greenhouse gas emissions, particularly under high soil moisture conditions where denitrification is the primary N-transformation pathway. In a replicated field trial, we evaluated the effects of two contrasting biochars derived from poultry litter and from hardwood on soil N2O emissions, soil ammonium (NH4+) and nitrate (NO3−) status, pasture productivity and herbage nutrient content. A liming treatment to mimic the liming equivalence of the poultry litter biochar was used to separate any effects observed from changes in soil pH. To further separate the effects of biochars on soil N status, N2O emissions and pasture N uptake, high and low N fertiliser doses (annual application of 672 kg N ha−1, 336 kg N ha−1) were superimposed across all of the treatments. The N fertiliser dose had no significant impact on pasture yield. Application of poultry litter biochar resulted in significant increases in pasture productivity under both high and low N inputs. This was achieved by alleviating soil P, and possibly K nutritional constraints that are typical in Australian Ferralsols. Under the high N fertiliser dose, emissions of N2O from the treatments and control were not significantly different (p > 0.05) and ranged between 1.14 and 1.78 kg N2O-N ha−1 across the 11-month study. The low N dose resulted in significantly lower emissions of N2O of between 0.80 and 0.84 kg N2O-N ha−1, but biochar had no significant effect on net emissions across the season. The lack of impact of biochar on N2O emissions was attributed to the relatively dry conditions over the trial period resulting in nitrification being the most likely N-transformation pathway. During brief episodes of high soil moisture, peak emissions from the biochar plots were lower than from the control or lime treatment, but these differences did not impact on the emission budget over the 11-month sampling campaign.

Numerous controlled-environment studies have found significant reductions in soil nitrous oxide (N2O) emissions following amendment of soil with woody biochar, but there is limited evidence to support these findings under field conditions. We evaluated N2O emissions from soils amended with 1) 5 t ha(-1) surface applied poultry litter; 2) 5 t ha(-1) incorporated poultry litter; 3) 5 t ha(-1) poultry litter + 11 t ha(-1) woody biochar; 4) 5 t ha(-1) poultry litter + 10 t ha(-1) woody mulch; 5) 4 t ha(-1) poultry litter biochar + 11 t ha(-1) woody biochar, in a coppiced Melaleuca plantation over two years. Melaleuca biomass, total soil carbon (C) and nitrogen (N) and soil C fractions did not differ among treatments 12 months after amendment. Woody mulch applied with poultry litter resulted in significantly lower N2O emissions compared to the incorporated and surface-applied poultry litter in the second season, but the addition of woody biochar had no significant impact on cumulative N2O emissions. However, N2O emissions per unit of N applied were significantly (P < 0.05) lower in the woody mulch and woody biochar treatments compared to poultry litter alone in the second season. In both seasons, cumulative N2O emission and N2O emissions per unit of N applied were significantly lower in the poultry litter biochar + woody biochar treatment, supporting the notion that pyrolysis of poultry litter is a management practice that could substantially reduce N2O emissions from the agricultural sector. (C) 2016 Elsevier B.V. All rights reserved.

Acid soils constrain legume growth and biochars have been shown to address these constraints and enhance biological N2 fixation in glasshouse studies. A dissection of causal mechanisms from multiple crop field studies is lacking. In a sub-tropical field study, faba bean (Vicia faba L.) was cultivated in rotation with corn (Zea mays) following amendment of two contrasting biochars, compost and lime in a rhodic ferralsol. Key soil parameters and plant nutrient uptake were investigated alongside stable 15 N isotope methodologies to elucidate the causal mechanisms for enhanced biological N2 fixation and crop productivity. Biological N2 fixation was associated with plant Mo uptake, which was driven by reductions in soil acidity following lime and papermill (PM) biochar amendment. In contrast, crop yield was associated with plant P and B uptake, and amelioration of soil pH constraints. These were most effectively ameliorated by PM biochar as it addressed both pH constraints and low soil nutrient status. While liming resulted in the highest biological N2 fixation, biochars provided greater benefits to faba bean yield by addressing P nutrition and ameliorating Al toxicity.

Addition of biochar produced through thermal decomposition of biomass has been seen as a strategy to improve soils and to sequester carbon (C), but wide scale implementation of the technology requires to devise innovative profitable solutions. To develop biochar utilisation with an integrated system approach, an innovative program was implemented in 2012 on a 53-ha farm in Western Australia to determine the costs and benefits of integrating biochar with animal husbandry and improvement of pastures. Biochar was mixed with molasses and fed directly to cows. The dung-biochar mixture was incorporated into the soil profile by dung beetles. We studied the changes in soil properties over 3 years. Biochar extracted from fresh dung and from the soil to a depth of 40 cm was characterised. A preliminary financial analysis of the costs and benefits of this integrated approach was also undertaken. The preliminary investigation results suggested that this strategy was effective in improving soil properties and increasing returns to the farmer. It was also concluded that the biochar adsorbed nutrients from the cow's gut and from the dung. Dung beetles could transport this nutrient-rich biochar into the soil profile. There was little evidence that the recalcitrant component of the biochar was reduced through reactions inside the gut or on/in the soil. Further research is required to quantify the long-term impact of integrating biochar and dung beetles into the rearing of cows.

An incubation study with four contrasting soils (Vertosol, Ferrosol, Calcarosol and Tenosol) and three biochars (oil mallee [OM-], wheat chaff [W-]) and poultry litter [PL-] all produced at 550 degrees C) applied at 1% w/w to each of the soils was conducted (n = 4). The soils were packed in cylindrical chambers and were subjected to five cycles of four weeks of wetting and four weeks of drying. The soils received 10 atom % N-15-KNO3- in the 1st and 5th wetting cycles. Two of the four soils (Ferrosol and Tenosol) were applied with labile carbon (C) between the 2nd and 5th wetting cycle, while the other two soils (Vertosol and Calcarosol) were amended with labile C in the 5th wetting cycle only. Peak nitrous oxide (N2O) emissions in the Tenosol, Ferrosol and Calcarosol occurred within the 1st wetting cycle, whereas the Vertosol without labile C did not emit N2O. However, the co-application of labile C with N-15-NO3- to the Vertosol in the 5th wetting supported N2O emissions. The greatest reduction in N2O emissions following biochar amendment occurred due to the use of OM-biochar in the Tenosol; which decreased the emissions from 1.95 kg N2O-N ha(-1) to 0.58 kg N2O-N ha(-1) across the first 4 wetting/drying cycles. The majority of N2O emissions occurred during the first wetting cycle (85% water filled porosity). In contrast, application of PL-biochar did not result in a statistically significant reduction in emission of N2O. Assessing the source of emissions, the initial N2O from the Ferrosol and the Calcarosol was principally from native N-sources, while in the Tenosol between 31:57% of N2O originated from the added NO3-. While biochars reduced the overall emissions of N2O in the Tenosol, they also reduced the proportion of the N2O originating from the supplied NO3- during the first wetting cycle, possibly by limiting NO3- availability to denitrifers. Towards the end of the incubation period bacterial nitrifier gene abundance (amoA) in the unamended Tenosol was lower (p < 0.05) compared to the earlier wetting cycles, a trend which was not evident in the biochar amended Tenosol treatments. The nitric oxide reductase (norB) component of the denitrifier community was not significantly affected by biochar amendment but increased (p < 0.05) with labile C addition in all of the Tenosol treatments (biochar) in the later stages of the incubation. The Tenosol had the lowest abundance of nitrous oxide reductase (nosZ) suggesting that its capacity to further reduce N2O to dinitrogen (N-2) was lower than the other soils tested. We hypothesise that biochar amendment lowered emissions of N2O in the Tenosol by providing conditions suitable for nosZ such as increased soil pH and microbial respiration. This was evidenced by higher nosZ gene abundance in the Tenosol amended with biochar, relative to the nil-biochar control. Crown Copyright (C) 2014 Published by Elsevier B.V. All rights reserved.

Application of poultry litter (PL) to soil can lead to substantial nitrous oxide (N2O) emissions due to the co-application of labile carbon (C) and nitrogen (N). Slow pyrolysis of PL to produce biochar may mitigate N2O emissions from this source, whilst still providing agronomic benefits. In a corn crop on ferrosol with similarly matched available N inputs of ca. 116 kg N/ha, PL-biochar plus urea emitted significantly less N2O (1.5 kg N2O–N/ha) compared to raw PL at 4.9 kg N2O–N/ha. Urea amendment without the PL-biochar emitted 1.2 kg N2O–N/ha, and the PL-biochar alone emitted only 0.35 kg N2O–N/ha. Both PL and PL-biochar resulted in similar corn yields and total N uptake which was significantly greater than for urea alone. Using stable isotope methodology, the majority (~ 80%) of N2O emissions were shown to be from non-urea sources. Amendment with raw PL significantly increased C mineralisation and the quantity of permanganate oxidisable organic C. The low molar H/C (0.49) and O/C (0.16) ratios of the PL-biochar suggest its higher stability in soil than raw PL. The PL-biochar also had higher P and K fertiliser value than raw PL. This study suggests that PL-biochar is a valuable soil amendment with the potential to significantly reduce emissions of soil greenhouse gases compared to the raw product. Contrary to other studies, PL-biochar incorporated to 100 mm did not reduce N2O emissions from surface applied urea, which suggests that further field evaluation of biochar impacts, and methods of application of both biochar and fertiliser, are needed.

The sugarcane industry in many parts of the world produces food and energy (stationary and fuel). The industry is well positioned to offer greenhouse gas abatement and climate change mitigation. The thermal conversion, via a slow pyrolysis process, of cane residues such as green harvest trash and bagasse can produce thermal or electrical energy as well as biochar. Studies have shown that a commercial slow pyrolysis unit could generate over 1 MWhr of electricity from every two tonnes of trash (dry basis), with a biochar recover of between 31.3–33.6 %. Due to its highly stable nature, biochar has recently been suggested as a sequestration pathway to remove CO2 from the atmosphere. One tonne of bagasse derived biochar would sequester in the order of 2.3 tonnes of CO2 equivalents. In addition to C sequestration, biochar has other significant benefits (when used as a soil amendment) such as offering improved soil quality, higher CEC and nutrient availability, and improved soil physical characteristics. This work demonstrates that biochar application can reduce emissions of greenhouse gases from cane soils, such as nitrous oxide. Biochars derived from cane trash and bagasse were applied in incubation studies to soils from the Burdekin region in Australia. We found declines in emissions of the greenhouse gas nitrous oxide (N2O), from urea-fertilised soil when bagasse biochar was applied at a rate of 10 t/ha. The agronomic performance of biochar is being assessed in a 15 plot trial conducted on a sugar cane property in the Tweed Valley, NSW. Biochars (from non-sugarcane sources) were tested using relevant controls. Each plot consists of 3 rows of cane and was 30 m in length to enable commercial-scale harvesting. Although no significant effects in yield have been recorded this trial is expected to continue for several more seasons allowing additional data on yield effects to be evaluated. Our work has demonstrated that implementing slow pyrolysis and biochar utilisation in the sugarcane industry has potential to provide (1) renewable energy (2) income from waste (3) climate mitigation through stabilisation of carbon and (4) climate mitigation through reduced emission of N2O from soil. Further research is required to demonstrate agronomic benefits of sugarcane biochars and to develop an understanding of how they may address soil constraints in these systems.

In this study biochar mixtures comprising a Jarrah-based biochar, chicken litter (CL), clay and other minerals were thermally treated, via torrefaction, at moderate temperatures (180 and 220°C). The objectives of this treatment were to reduce N losses from CL during processing and to determine the effect of both the type of added clay and the torrefaction temperature on the structural and chemical properties of the final product, termed as an enhanced biochar (EB). Detailed characterisation indicated that the EBs contained high concentrations of plant available nutrients. Both the nutrient content and plant availability were affected by torrefaction temperature. The higher temperature (220°C) promoted the greater decomposition of organic matter in the CL and dissociated labile carbon from the Jarrah-based biochar, which produced a higher concentration of dissolved organic carbon (DOC). This DOC may assist to solubilise mineral P, and may also react with both clay and minerals to block active sites for P adsorption. This subsequently resulted in higher concentrations of plant available P. Nitrogen loss was minimised, with up to 73% of the initial total N contained in the feedstock remaining in the final EB. However, N availability was affected by both torrefaction temperature and the nature of the clay minerals added.

The effect of a low mineral ash biochar on biomass production and nitrogen (N) uptake into plants was tested with wheat and radish in a Yellow Earth used for commercial vegetable production. The biochar had an acid neutralising capacity <0.5% CaCO3, a total C content of 75%, and a molar H/C ratio of 0.45, indicating stability due to its aromaticity. A pot trial was established under climate-controlled conditions. Five rates of N fertiliser (0, 17, 44, 88, 177 kg N/ha) were applied as urea in combination with 5 biochar rates (0, 1.1, 2.2, 4.4, 11% w/w). Analysis of biomass production revealed a significant biochar × N fertiliser interaction. In particular, increasing biochar concentrations improved biomass production in both crop species at lower N application rates. The highest biochar application rate resulted in significantly greater accumulation of NO3 –-N in the soil and lower NH4 +-N averaged across the 5 N application rates. The biochar also decreased available P, and significantly increased microbial activity measured using the fluorescein diacetate method. Increasing N fertiliser application resulted in greater accumulation of NO3 –-N with no changes to NH4 +-N averaged across the 5 biochar application rates. Nitrogen fertiliser application did not influence microbial activity or biomass C. The trial suggests that in some cropping systems, biochar application will enable reduced N fertiliser input while maintaining productivity.

The amendment of two agricultural soils with two biochars derived from the slow pyrolysis of papermill waste was assessed in a glasshouse study. Characterisation of both biochars revealed high surface area (115 m2 g−1) and zones of calcium mineral agglomeration. The biochars differed slightly in their liming values (33% and 29%), and carbon content (50% and 52%). Molar H/C ratios of 0.3 in the biochars suggested aromatic stability. At application rates of 10 t ha−1 in a ferrosol both biochars significantly increased pH, CEC, exchangeable Ca and total C, while in a calcarosol both biochars increased C while biochar 2 also increased exchangeable K. Biochars reduced Al availability (ca. 2 cmol (+) kg−1 to <0.1 cmol (+) kg−1) in the ferrosol. The analysis of biomass production revealed a range of responses, due to both biochar characteristics and soil type. Both biochars significantly increased N uptake in wheat grown in fertiliser amended ferrosol. Concomitant increase in biomass production (250% times that of control) therefore suggested improved fertiliser use efficiency. Likewise, biochar amendment significantly increased biomass in soybean and radish in the ferrosol with fertiliser. The calcarosol amended with fertiliser and biochar however gave varied crop responses: Increased soybean biomass, but reduced wheat and radish biomass. No significant effects of biochar were shown in the absence of fertiliser for wheat and soybean, while radish biomass increased significantly. Earthworms showed preference for biochar-amended ferrosol over control soils with no significant difference recorded for the calcarosol. The results from this work demonstrate that the agronomic benefits of papermill biochars have to be verified for different soil types and crops.

Biochars produced by slow pyrolysis of greenwaste (GW), poultry litter (PL), papermill waste (PS), and biosolids (BS) were shown to reduce N2O emissions from an acidic Ferrosol. Similar reductions were observed for the untreated GW feedstock. Soil was amended with biochar or feedstock giving application rates of 1 and 5%. Following an initial incubation, nitrogen (N) was added at 165 kg/ha as urea. Microcosms were again incubated before being brought to 100% water-filled porosity and held at this water content for a further 47 days. The flooding phase accounted for the majority (<80%) of total N2O emissions. The control soil released 3165 mg N2O-N/m2, or 15.1% of the available N as N2O. Amendment with 1 and 5% GW feedstock significantly reduced emissions to 1470 and 636 mg N2O-N/m2, respectively. This was equivalent to 8.6 and 3.8% of applied N. The GW biochar produced at 350°C was least effective in reducing emissions, resulting in 1625 and 1705 mg N2O-N/m2 for 1 and 5% amendments. Amendment with BS biochar at 5% had the greatest impact, reducing emissions to 518 mg N2O-N/m2, or 2.2% of the applied N over the incubation period. Metabolic activity as measured by CO2 production could not explain the differences in N2O emissions between controls and amendments, nor could NH4+ or NO3– concentrations in biochar-amended soils. A decrease in NH4+ and NO3– following GW feedstock application is likely to have been responsible for reducing N2O emissions from this amendment. Reduction in N2O emissions from the biochar-amended soils was attributed to increased adsorption of NO3–. Small reductions are possible due to improved aeration and porosity leading to lower levels of denitrification and N2O emissions. Alternatively, increased pH was observed, which can drive denitrification through to dinitrogen during soil flooding.

The compost worm Eisenia fetida was used to demonstrate the avoidance by worms of Cu contaminated soil. Soils were collected from two avocado orchards in north eastern New South Wales, Australia. In avoidance trials, worms preferred non-contaminated control soils, sourced from adjacent to the orchard or an OECD control soil, when Cu residues in the orchard soils reached 4–34 mg Cu kg−1. At levels of 553 mg Cu kg−1, 90% avoidance of orchard soil was observed. The worms showed preference for the soils in the order; uncontaminated field derived soil >OECD standard soil >Cu contaminated orchard soil. It was demonstrated that OECD standard soil was less favoured by worms than control soil derived from the test sites. While Cu was found to be the primary influence on worm avoidance in orchard soil, other factors, such as elevated soil Zn concentrations, could not be discounted. In a corresponding field study, it was shown that earthworms occurred at lower density in orchard soils with a history of Cu fungicide use. In one such orchard, soil Cu concentrations of up to 270 mg kg−1 were determined and no earthworms were found, while nearby control sites and less contaminated sites within the orchard had up to 40.7 g m−2 earthworm biomass. Considering the potential for Cu to accumulate in these soils and the subsequent impacts on soil biota, our results highlight the importance of limiting future application of Cu based fungicides.

The challenge exists for the Organics industry to manage disease whilst protecting soil health. The use of copper (Cu) fungicides has been effective in the control of many pathogens, however, it has come at a cost. Copper residues in an avocado orchard caused significant reductions in biomass carbon (Cmic), even though the soils had similar or elevated levels of total organic carbon (Corg). The Cmic:Corg ratio was significantly lower in all of the Cu contaminated soils. Microorganisms in the Cu contaminated soils were stressed as they had an increased metabolic quotient. The composting worm Eisenia fetida was shown to avoid soils with even relatively minor elevation of copper (44mg/kg). Very significant earthworm avoidance was found when copper residues increased above 100mg/kg. In a related study, severely depleted populations of both native and exotic earthworms were found in copper contaminated orchards. Copper residues from fungicide application at an avocado orchard have impacted upon key soil health indicators. To protect soil health, alternatives to copper for disease control will need to be developed, along with remediation technologies for reducing the impact of Cu contamination in soils.