Soil Microbial Responses to Biochars Varying in Particle Size,Surface and Pore Properties

Biochars are known for their heterogeneity, especially in pore and surface structure associated with pyrolysis processes and sources of feedstocks. The surface area of biochar is likely to be an important determinant of the extent of soil microbial attachment, whereas the porous structure of biochar is expected to provide protection for soil microorganisms. Potential interactions between biochars from different sources and with different particle sizes were investigated in relation to soil microbial properties in a short-term incubation study. Three particle size(sieved) fractions(0.5–1.0, 1.0–2.0 and 2.0–4.0 mm) from three woody biochars produced from jarrah wood,jarrah and wandoo wood and Australian wattle branches, respectively, were incubated in soil at 25?C for 56 d. Observation by scanning electron microscopy(SEM) and characterisation of pore and surface area showed that all three woody biochars provided potential habitats for soil microorganisms due to their high porosity and surface areas. The biochars were structurally heterogeneous,varying in porosity and surface structure both within and between the biochar sources. After the 56-d incubation, hyphal colonisation was observed on biochar surfaces and in larger biochar pores. Soil clumping occurred on biochar particles, cementing and covering exposed biochar pores. This may have altered surface area and pore availability for microbial colonisation. Transient changes in soil microbial biomass, without a consistent trend, were observed among biochars during the 56-d incubation.

Biochar-Soil Interactions in Four Agricultural Soils

Soils in south-western Australia are highly weathered and deficient in nutrients for agricultural production. Addition of biochar has been suggested as a mean of improving soil C storage, texture and nutrient retention of these soils. Clay amendment in sandy soils in this region is a management practice used to improve soil conditions, including water repellence. In this study a woody biochar(Simcoa biochar) was characterised using scanning electron microscopy before, and four weeks after, it was incorporated into each of four soils differing in clay content and organic matter. Scanning electron microscopy of Simcoa biochar after incubation in soil showed different degrees of attachment of soil particles to the biochar surfaces after 28 d. In addition, the effects of three biochars, Simcoa biochar, activated biochar and Wundowie biochar, on soil microbial biomass C and soil respiration were investigated in a short-term incubation experiment. It was hypothesised that all three biochars would have greater potential to increase soil microbial activity in the soil that had higher organic matter and clay. After 28-d incubation in soil, all three biochars had led to a higher microbial biomass C in the clayey soil, but prior to this time, less marked differences were observed in microbial biomass C among the four soils following biochar application.

Complementary effect of zoo compost with mineral nitrogen fertilisation increases wheat yield and nutrition in a low-nutrient soil

Excess nitrogen(N) fertiliser use in agriculture is associated with water pollution and greenhouse gas emissions.While practices and programs to reduce N fertiliser application continue to be developed,inefficient fertiliser use persists.Practices that reduce mineral N fertiliser application are needed in a sustainable agricultural ecosystem to control leaching and gaseous losses for environmental management.This study evaluated whether fully or partially replacing mineral N fertiliser with zoo compost(Perth Zoo) could be a good mitigation strategy to reduce mineral N fertiliser application without affecting wheat yield and nutrition.To achieve this,a glasshouse experiment was conducted to assess the complementary effect of zoo compost and mineral N fertiliser on wheat yield and nutrition in a sandy soil of southwestern Australia.Additionally,a chlorophyll meter was used to determine whether there was a correlation between chlorophyll content and soil mineral N content,grain N uptake,and grain protein content at the tillering(42 d after sowing(DAS)) and heading(63 DAS) growth stages.The standard practice for N application for this soil type in this area,100 kg ha^(-1),was used with a soil bulk density of 1.3 g cm^(-3) to calculate the amount of mineral N(urea,46% N) and Perth Zoo compost(ZC)(0.69% N) for each treatment.Treatments comprised a control(no nutrients added,T1),mineral N only(100 kg N ha^(-1),T2),ZC only(100 kg N ha^(-1),T7),and combinations of mineral N and ZC at different rates(mineral N at 100 kg N ha^(-1)+ ZC at 25 kg N ha^(-1)(T3),mineral N at 75 kg N ha^(-1)+ ZC at 25 kg N ha^(-1)(T4),mineral N at 75 kg N ha^(-1)+ ZC at 50 kg N ha^(-1)(T5),and mineral N at 50 kg N ha^(-1)+ ZC at 50 kg N ha^(-1)(T6)).The T6 treatment significantly increased grain yield(by 26%) relative to the T2 treatment.However,the T7 treatment did not affect grain yield when compared to the T2 treatment.All treatments with mineral N and ZC in combination significantly improved the 1 000-grain weight compared to the T2 treatment.Chlorophyll content was better correlated with soil mineral N content(r = 0.61),grain N uptake(r = 0.62),and grain protein content(r = 0.80) at heading(63 DAS) than at tillering(42 DAS).While ZC alone could not serve as an alternative to mineral N fertiliser,its complementary use could reduce the mineral N fertiliser requirement by up to 50% for wheat without compromising grain yield,which needs to be verified in the field.Chlorophyll content could be used to predict soil mineral N at the heading stage,and further studies are warranted to verify its accuracy in the field.Overall,the application of ZC as part of integrated nutrient management improved crop yield with reduced N fertiliser application.