Biochar amendment of infertile Western Cape sandy soil: Implications for food security

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1 Biochar amendment of infertile Western Cape sandy soil: Implications for food security Dr Ailsa G Hardie 1 Prof Alf Botha 2 1 Dept. of Soil Science 2 Dept. Microbiology Stellenbosch University

Sandy soils are very common in Western Cape, South Africa Sands are difficult to manage: Low water holding capacities Prone to erosion (weak structure) Poor nutrient holding capacities Pollution of

2 Sandy soils are very common in Western Cape, South Africa Sands are difficult to manage: Low water holding capacities Prone to erosion (weak structure) Poor nutrient holding capacities Pollution of surface and groundwater by fertilizers There is current growing global interest in biochar (pyrolyzed biomass) as a soil amendment due to its potential to: Permanently sequester carbon in soils (slow to degrade compared to compost or manure) Improve the fertility of degraded soils Pyrolysis can potentially be used to generate electricity Sources of biomass currently used included alien invasive vegetation and sawmill waste Introduction

3 Objectives The objectives of our study were to: Investigate the effect of applying locally-produced, (readily available) biochar on the quality (chemical, physical and biological properties) of infertile, sandy soil from the Western Cape, RSA Investigate the effect of biochar on the leaching of nitrogen fertilizer from the sandy soil Investigate the degradability of the biochar under different soil water and nutrient conditions, which is essential if biochar is to be considered as a carbon sequestration agent

Experimental Design The biochar was produced from pinewood sawmill waste using slow pyrolysis (450 C). Acidic, sandy soil (Kroonstad form) was collected from the Brackenfell area, Cape Town.

5 Experimental Design The biochar was produced from pinewood sawmill waste using slow pyrolysis (450 C). Acidic, sandy soil (Kroonstad form) was collected from the Brackenfell area, Cape Town. Wheat (monocot) and bean (dicot) pot trials were carried out for 3 months, with four biochar application levels (0.05, 0.5, 2.5, and 10 % w/w) and a control (no biochar added) Leaching of N-fertilizer (NH 4 NO 3 ) was investigated using columns (25 cm depth) containing sand and biochar-amended sand (0.5, 2.5 and 10 % w/w) that were weekly leached for a period of 6 weeks Degradation of biochar under different water and nutrient conditions were examined

6 Biochar Characteristics % Volatile % Fixed C:N ph (H 2 O) Ash% % C % N matter carbon ratio CEC 7.0 (cmolc.kg -1 ) :1 34.3

7 Effect of biochar on soil fertility

8 Effect of biochar on soil C:N ratio and ph

9 Effect of biochar on wheat growth

10 Effect of biochar on bean growth

11 Effect of biochar on nitrogen uptake by wheat

12 Effect of biochar on trace element uptake by wheat

13 Effect of biochar on soil physical properties and water use efficiency of wheat

14 Effect of biochar on soil aggregation

15 Effect of biochar on wheat root structure and soil aggregation No biochar 2.5 % biochar

16 Effect of biochar on Ammonium Nitrate fertilizer leaching Ammonium (NH 4+ ) Nitrate (NO 3- )

17 Aerobic degradation of biochar only biochar + NPK fertilizer + glucose

18 Carbon % Oxygen % Degradation of biochar under field conditions (Stellenbosch) Carbon Oxygen Fresh biochar Fynbos Wetlands Pasture 9

19 Conclusions Biochar is able to enhance carbon sequestration, nutrient and water retention, and improve soil structure in low potential sandy soils These effects all contribute to long-term sustainability of farming on sandy soils However, quality of the biochar is critical: alkalinity and C:N ratio. Biochar degradation is promoted under nutrient rich and wet conditions; this should be also kept in mind. Our findings suggest that an application rate of 10 t/ha should not be exceeded when applying biochar on acidic, sandy soil.

21 Root associated biomass Wheat pot trials were carried out for 3 months, with pots containing alternate sand an biochar layers. The pots received a single application of macronutrient fertilizer to the following recommendation: N:101 ; P:50 ; K:75 ; Ca:30 ; Mg:23 ; S:30 kg/ha. Omnispoor trace element fertilizer was applied twice (2 and 8 weeks) as foliar spray. Root dry mass and soil microbial biomass were determined in the layers.

22 Root associated biomass Wheat pot trials were carried out for 3 months, with pots containing alternate sand an biochar layers. The pots received a single application of macronutrient fertilizer to the following recommendation: N:101 ; P:50 ; K:75 ; Ca:30 ; Mg:23 ; S:30 kg/ha. Omnispoor trace element fertilizer was applied twice (2 and 8 weeks) as foliar spray. Root dry mass and soil microbial biomass were determined in the layers.

23 Nitrogen Fixation Bean pot trials were conducted for ca. 1 month, with four biochar application levels (0.05, 0.5, 2.5, and 10 % w/w) and a control (no biochar added) Seedlings inoculated with Rhizobium leguminosarum and Kompel-chemicult hydroponic nutrient powder was applied weekly as fertilizer. Dried plant biomass was determined and plant elemental analyses, including isotope analysis (δ15n) were conducted.

24 Different Biochar % Volatile % Fixed C:N ph (H 2 O) Ash% % C % N matter carbon ratio CEC 7.0 (cmolc.kg -1 ) :

25 Total dry weight (g) Mycorrhizal colonization of Wheat Wheat pot trials were carried out for 2 months, with four biochar application levels (1.0, 2.5, 5, and 10 % w/w) and a control (no biochar added) At planting each pot received a single application of Long Ashton nutrient solution contain macro- and trace elements. Dried plant biomass, mycorrhizal colonization, as well as plant elemental analyses was determined Percentage biochar (w/w)

26 Mycorrhizal colonization (%) P concentration in plant (mmol/g) & P uptake rate (mmol P/ g root/ day) Mycorrhizal colonization and P uptake Percentage biochar (w/w) Mycorrhizal colonization P concentration P uptake rate

27 P uptake rate (mmol P/g root /day) P uptake rate Percentage biochar (w/w) P uptake rate

28 Conclusions Biochar increased soil microbial biomass Affected nitrogen fixation of root associated bacteria Increased mycorrhizal colonization (low nutrient conditions). Despite mycorrhizal colonization, P uptake rate tend to decrease at higher Biochar concentrations competition?

29 Potentially Biochar Enhances Soil aggregate stability Increases Nutrient and water retention Increases Activity of beneficial soil microbes May ensure long-term sustainability of farming on sandy soils However Biochar Production and Application must be well managed Commercial biochar in SA is currently expensive Feasibility increases when combined with electricity generation and alien vegetation harvesting

30 Future Research Prospects Long-term field trials Effect of cultivation and irrigation practices on movement of biochar in agricultural soils Effect of biochar on plant pathogens

31 Acknowledements Honours student: Ian Belford MSc students: Makhosana Sika, Sarel Oliver, Angelique Zeelie, Leandra Moller Collaborators: Drs AB Rozanov (Soil Science), JE Hoffman (Soil Science), AJ Valentine (Botany) Funding: Food Security Initiative (HOPE Project, Stellenbosch University), NRF, S&P Carbon (Pty) Ltd. for donating biochar

N uptake rate (mmol N/ g root/ day) Growth efficiency (g/ mmol N/ day) Effect of biochar on nitrogen uptake and use efficiency of wheat 0.18 0.16 0.14 0.

32 N uptake rate (mmol N/ g root/ day) Growth efficiency (g/ mmol N/ day) Effect of biochar on nitrogen uptake and use efficiency of wheat Percentage biochar (w/w) N uptake rate N growth efficiency

33 K uptake rate (mmol K/ g root/ day) & K growth efficiency (g/mmol K/day) K concentration in plant (mmol/g) Effect of biochar on K uptake rate and use efficiency of wheat Percentage Biochar (w/w) K growth efficiency K uptake rate K concentration

Biochar and the nitrogen cycle: Unravelling the interaction. Daniel Dempster

Biochar and the nitrogen cycle: Unravelling the interaction Daniel Dempster Acknowledgements My Supervisors Assoc/Prof. Deirdre Gleeson Prof. Daniel Murphy W/Prof. Lyn Abbott Grains Research and Development