Linking soil functional biodiversity and processes to soil ecosystem services : biochar application on two New Zealand pasture soils : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Manawatu, New Zealand

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Sheep and beef farming and dairying are an important part of the New Zealand economy, occupying about 40% of land area used for the livestock. Maintenance of that land is an essential part of sustainable agriculture. For a long time, biochar has been used and considered as a multifunctional soil amendment adding to the natural capital stocks of the soils and contributing to a wide range of soil ecosystem services, provision of nutrients (soil fertility) through the increasing nutrient availability, neutralising acidity through liming, and mitigating climate change through carbon (C) storage. In this thesis I investigate the effects of biochar, made from willow at 350°С and added as an amendment, on soil ecology and biochemistry-based processes within an ecosystem services modelling framework. In the literature review (Chapter 2) I draw links between the importance of soil ecosystem services, including soil biodiversity and human needs. The potential role of biochar application in improving soil productivity and mitigating the negative impact of land management are also discussed. To evaluate the impact of biochar, added as an amendment, on the chemical and biological properties and processes in soil as it influences soil processes underpinning ecosystem services, and to explore any synergistic interactions between biochar, soil, functional groups of soil fauna and plants, two experiments were conducted: (i) a six-month mesocosm experiment in the glasshouse and (ii) a field-based mesocosm experiment that ran for 12 months. In both experiments two contrasting soils were used – an Andosol (Allophanic) and a Cambisol (Brown). Both soils cover extensive areas of New Zealand. In the mesocosm experiment in the glasshouse (Chapter 3) biochar had a significant positive effect on clover growth and biomass, and this effect was more pronounced in the presence of earthworms and in one soil type. On their own, biochar and earthworms increased clover growth more in the Cambisol, while the positive synergistic effect of biochar and earthworms on soil biochemical processes and clover growth was more evident in the Andosol The synergistic effect of biochar and earthworms was also observed in an increase in the abundance of Collembola and in soil fungal biomass. The field mesocosm experiment investigated how adding biochar as an amendment to a grazed pasture affects the soils biological and physico-chemical properties. The experiment was conducted at four locations with different livestock systems (dairy and sheep) and soils (Andosol and Cambisol) under contrasting management practices (two pastures, with or without dairy shed effluent addition on the Andosol, and two pastures with either low or high phosphorus (P) fertilizer input in the Cambisol) over 12 months. The three treatments were: (i) willow biochar produced at 350 °C (1% w/w); (ii) lime, added at the liming equivalence of the biochar application (positive control); (iii) no amendments (negative control). Results of the field experiment are reported in three chapters. Chapter 4 reports how adding biochar affected biological and physico-chemical properties and the plant root biomass at each of the four grazed pasture locations on Andosol and Cambisol. Biochar addition had a positive (P<0.005) effect on total nitrogen (N), organic C, Olsen P contents, bacterial (Cb) and fungal (Cf) C biomass, and Collembola abundance, compared with the control and lime treatments 12 months after addition. At all four locations, the increases in N, C and P in the biochar treatment were greater than the amount of N, C or P added in the biochar. On average, root biomass was 6.9 Mg ha-1 higher (P<0.005) in all four soils to which biochar was added, when compared with the other two than the other two treatments. Biochar addition also lowered (P<0.005) the bulk density of the soil, on average by 7% across the four sites, compared with the control. Earthworm abundance in lime-treated soils was higher (P<0.01) than in the negative control. In the presence of biochar, earthworm abundance was only higher (P<0.05) than the control in the Andosol without effluent. In biochar-amended soils, Collembola abundance was higher (P<0.005) than the controls in all soils, while there was no effect on Oribatida and Gamasina populations. Chapter 5 investigated the effect biochar addition had on the biochemical activity (soil enzymes) in the soils after 12-months. Dehydrogenase activity, which is strongly correlated with soil microbial biomass, was higher in the soils to which biochar had been added. Cellulase activity was also higher in the soil to which biochar had been added, reflecting the increased amounts of plant detritus entering the soil, from the greater root biomass following biochar application. When the geometric mean of all the enzyme activities was summed, biochar had a more pronounced effect than lime. An exception was peroxidase, which in contrast to dehydrogenase and cellulase, had higher activity in the soil treated with lime (positive control) and was positively correlated with earthworm abundance, which also was higher in the lime-treated soil. Biochar had less of an effect on both pH and earthworm abundance. There was a positive correlation between nitrate reductase and earthworm abundance, as earthworms increase nitrate concentration in soil. In Chapter 6 I attempted to assess the long-term impact of biochar on soil potential to provide ecosystem services and investigated the influence of the biochar application on the time dynamics of physicochemical and biological properties. Soil samples were collected at 6 and 12 months after the start of the field experiment. Except for mineral N (NO3--N and NH4+-N), the effect of sampling time was similar across sites. Biochar had a long-term positive effect on OC, TN and Olsen P in all sites. Reduced by biochar, soil acidity and BD remained at the same level after 6 and 12 months in all four sites. The effect of biochar on mineral N was not constant in time, and mostly depended on the soil order and management practices rather than on treatments. Soil biological and biochemical properties had patterns which can be interpreted as seasonal. Biochar increased bacterial and fungal biomass as well as abundance of arthropods and earthworms; these changes in soil biota were reflected in soil enzymatic activities. It was shown that biochar has a persistent effect on soil natural capital stocks and functions and showed itself as an effective amendment able to enhance the soil over time. In the Chapter 7 the results of the analysis of the effects of biochar and lime addition on soil physicochemical and biological properties (Chapter 4) and enzymatic activity (Chapter 5) were used to semi-quantify the effects and potential benefits of biochar and lime amendments application for the delivery of specific soil ecosystem services. In comparison with the control treatments, there was a significant positive impact of biochar on soil properties, including soil microflora, earthworms, OC, soil BD, pH and overall soil enzyme activity, associated with C sequestration. In comparison with control and lime, biochar increased components of soil natural capital stocks responsible for food and fibre production ecosystem service. There was also significant positive impact of biochar on soil properties associated with fertility maintenance. Biochar and lime had similar positive effect on water regulation and disease and pest control services. The thesis shows that application of willow wood biochar produced at low temperature has a significant positive effect on a number of the chemical and biological properties and processes in soils (up to 12 months) that extend to the rooting characteristics of the plant, and this might contribute to the productivity of pasture land, while increasing health and resilience to the impact of land management. Biochar, through its effect on soil properties contributes to dynamic interactions between soil, plant and functional groups of soil biota. As a result, biochar positively impacts on the dynamical links between components of soil natural capital and ecosystem services provided by the soil. In summary, biochar produced from willow wood at low temperature may be an effective tool in the pasture systems/soils investigated here as a part of sustainable farming practices, which can increase plant productivity, improve soil physical properties and fertility, reduce disease and pest risks, and at the same time might be used as an instrument to mitigate climate change.
Figures re-used with permission.
Biochar, Soil amendments, Pastures, Soil ecology, New Zealand