Biochar, compost and biochar-compost: effects on crop performance, soil quality and greenhouse gas emissions in tropical agricultural soils

Jenberu, Getachew Agegnehu (2017) Biochar, compost and biochar-compost: effects on crop performance, soil quality and greenhouse gas emissions in tropical agricultural soils. PhD thesis, James Cook University.

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Abstract

Background and aims: Chapter 1 highlights the introduction and summarizes the literature search in the area of the study. Soil fertility depletion, declining agricultural productivity because of reduction of soil organic matter (SOM), nutrient imbalance, and climate change due to increased greenhouse gases (GHG) emissions, are major constraints in most tropical agricultural soils. The aims of my PhD study were to: 1) investigate and compare the effects of different soil fertility treatments in relation to biochar, compost, and their mixture on soil physicochemical properties and soil fertility; 2) determine the response of crops to biochar, compost, and their mixture on different soil types; 3) evaluate the effect of different soil fertility treatments in relation to organic amendments and nitrogen (N) fertilizer on nutrient uptake, N recovery, and use-efficiency of barley; 4) determine nutrient retention and leaching under alternative organic amendments; and 5) investigate the impact of biochar, compost, and their mixture with respect to GHG emissions and carbon sequestration.

Methods: The present research comprised three separate experiments, which were conducted under two agro-ecosystems and soil types in north Queensland, Australia, using maize and peanut, as well as in the central highlands of Ethiopia using barley as test crops. Both greenhouse and field experiments were carried out to test the hypothesis that application of biochar improves soil fertility, fertilizer use efficiency, plant growth, and productivity, particularly when combined with compost. Treatments comprised: untreated control; mineral fertilizer; willow biochar (WB), acacia biochar (AB); compost (Com); WB + Com, AB + Com, and co-composted biochar-compost (COMBI). Mineral fertilizer was applied uniformly to all treatments. The treatments were laid out using a randomized design, each with three replicates. In the Ethiopian experiment, factorial combinations of five organic amendments (control, B, Com, B + Com and COMBI) and five levels of N fertilizer were investigated in a split-plot design with three replicates, with organic amendments as main plots and N levels as sub-plots.

Results: Chapter 2 presents results from a greenhouse pot trial which indicated that application of compost with fertilizer significantly increased plant growth, soil nutrient status, and plant nutrient concentration, with shoot biomass decreasing in the order F + Com (4.0) > F + WB + Com (3.6) > F + WB (3.3) > F + AB + Com (3.1) > F + AB (3.1) > F (2.9) > control (1.0), with the ratio of the value to that of the control given in brackets. The shoot and root biomass exhibited significant positive correlations with soil water content, plant nutrient concentration, and soil nutrient concentration after harvesting. The results of a principal component analysis (PCA) showed that the first component (PRIN1) provided a reasonable summary of the data, accounting for about 84% of the total variance. As the plants grew, compost and biochar additions significantly reduced leaching of nutrients.

Chapters 3 and 4 present field trial results showing that application of biochar, compost, and their mixture increased maize yield by 10 - 29% and peanut yield by 17 - 24%, compared to fertilizer alone, in trials conducted in the Atherton Tablelands, Australia. Biochar, compost, and their mixture significantly improved the availability of plant nutrients, which appeared critical in improving crop performance. Soil organic carbon (SOC), soil water content (SWC), nitrate and ammonium concentrations were significantly higher in biochar treated plots than fertilizer alone, implying that potential exposure of nitrate and ammonium to the soil microbial community was significantly lower in biochar and COMBI treated plots compared to the fertilizer only and compost treatments. Emissions of CO₂ were highest in the fertilizer treatment and lowest in the COMBI treatment. Emissions of N₂O were the highest in the fertilizer treatment and all biochar amended plots reduced N₂O emission compared to the control.

Chapters 5 and 6 present field trial results from two sites in Ethiopia showing that the application of organic amendments and N fertilizer all significantly improved soil fertility and barley yield. In Ethiopia, the feedstock for biochar production was acacia (Acacia spp.), and compost was prepared from a mix of farmyard manure (FYM) and plant materials. Organic amendment by N fertilizer interaction significantly improved barley grain yield, with yield increments of 60% and 54% due to Com + B and 69 kg N ha⁻¹ and Com + 92 kg N ha⁻¹ at Holetta and Robgebeya, respectively, compared to the highest N rate only (92 kg ha⁻¹). Organic amendments significantly improved soil properties through increases in SWC, SOC, cation exchange capacity (CEC) and pH. Addition of B, Com and B + Com increased SOC and CEC by 23 - 27% and 20 - 24% at Holetta and 26-34% and 19-23% at Robgebeya, compared to their respective initial values. Soil pH increased from the initial value of 5.0 to 5.6 at Holetta and from 4.8 to 5.4 at Robgebeya at harvest, due to biochar soil amendment. The highest total N uptake was obtained from Com + B + 92 kg N ha⁻¹ at Holetta (138 kg ha⁻¹) and Com + 92 kg N ha⁻¹ at Robgebeya (101 kg ha⁻¹). Application of organic amendments and N fertilizer improved significantly the agronomic efficiency (yield increase per unit of N applied, AE), apparent recovery efficiency (increase in N uptake per unit of N applied, ARE), and physiological efficiency (yield increase per unit of N uptake, PE). Mean AE and ARE were highest at B + 23 kg N ha⁻¹ at Holetta and at B + 23 and B + 46 kg N ha⁻¹ at Robgebeya. The PE ranged from 19 - 33 grain kg⁻¹ N uptake at Holetta and 29 - 48 kg grain kg⁻¹ N uptake at Robgebeya. The effects of organic amendments and N fertilizer on AE, ARE and PE were greater at Robgebeya than at Holetta. The enhancement of N use efficiency through application of organic amendments emphasizes the importance of balanced crop nutrition, ensuring that barley crops are adequately supplied with N and other nutrients. Overall, the integration of both organic and inorganic amendments may optimize N uptake efficiency and reduce the amount of N fertilizer required for sustainable barley production in the long-term.

Conclusions: The results indicate that applications of biochar and compost either singly, or in combination, could be adopted as a sustainable agronomic strategy, since they have demonstrated a strong potential to improve SOC, soil nutrient status, SWC, crop yield and reduce GHG fluxes on tropical agricultural soils. Moreover, the integration of both organic and inorganic nutrient sources may optimize NUE and reduce the amount of fertilizer required for the sustainable production of barley in the long term. However, the amount by which conventional fertilizer could be reduced, and the resultant economic benefit because of addition of these amendments, need further study for longer-term economic and environmental sustainability.

Item ID: 51228
Item Type: Thesis (PhD)
Keywords: barley, biochar, carbon sequestration, CO2 and N2O fluxes, co-composted biochar, compost, composted biochar, ferralsol, greenhouse gas fluxes, mineral fertiliser, Nitisol, nitrogen fertilizer, nitrogen use efficiency, nitrogen, nutrient leaching, soil fertility, soil organic carbon, soil organic matter, soil physicochemical properties, soil quality
Additional Information:

Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2: Jenberu, Getachew, Bird, Michael I., Nelson, Paul N., and Bass, Adrian M. (2015) The ameliorating effects of biochar and compost on soil quality and plant growth on a Ferralsol. Soil Research, 53 (1). pp. 1-12.

Chapter 3: Agegnehu, Getachew, Bass, Adrian M., Nelson, Paul N., and Bird, Michael I. (2016) Benefits of biochar, compost and biochar-compost for soil quality, maize yield and greenhouse gas emissions in a tropical agricultural soil. Science of the Total Environment, 543 (Part A). pp. 295-306.

Chapter 4: Agegnehu, Getachew, Bass, Adrian M., Nelson, Paul N., Muirhead, Brian, Wright, Graeme, and Bird, Michael A. (2015) Biochar and biochar-compost as soil amendments: effects on peanut yield, soil properties and greenhouse gas emissions in tropical North Queensland, Australia. Agriculture, Ecosystems and Environment, 213. pp. 72-85.

Chapter 5: Agegnehu, Getachew, Nelson, Paul N., and Bird, Michael I. (2016) Crop yield, plant nutrient uptake and soil physicochemical properties under organic soil amendments and nitrogen fertilization on Nitisols. Soil and Tillage Research, 160. pp. 1-13.

Chapter 6: Jenberu, Getachew, Nelson, Paul N., and Bird, Michael I. (2016) The effects of biochar, compost and their mixture and nitrogen fertilizer on yield and nitrogen use efficiency of barley grown on a Nitisol in the highlands of Ethiopia. Science of the Total Environment, 569-570. pp. 869-879.

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Date Deposited: 17 Oct 2017 02:29
FoR Codes: 07 AGRICULTURAL AND VETERINARY SCIENCES > 0703 Crop and Pasture Production > 070304 Crop and Pasture Biomass and Bioproducts @ 30%
07 AGRICULTURAL AND VETERINARY SCIENCES > 0701 Agriculture, Land and Farm Management > 070101 Agricultural Land Management @ 30%
05 ENVIRONMENTAL SCIENCES > 0503 Soil Sciences > 050301 Carbon Sequestration Science @ 40%
SEO Codes: 82 PLANT PRODUCTION AND PLANT PRIMARY PRODUCTS > 8298 Environmentally Sustainable Plant Production > 829802 Management of Greenhouse Gas Emissions from Plant Production @ 20%
82 PLANT PRODUCTION AND PLANT PRIMARY PRODUCTS > 8204 Summer Grains and Oilseeds > 820401 Maize @ 20%
96 ENVIRONMENT > 9603 Climate and Climate Change > 960302 Climate Change Mitigation Strategies @ 60%
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