Jennifer Carson Profile Jennifer grew up spending time on her uncle and aunt’s market garden in Spearwood but never considered a career in Agriculture. The possibility was first brought to her attention in first year uni when she saw “Soil Science” on the list of majors right above “Wool Science” and wondered who in earth majored in such obscure subjects. Four years later she graduated from the University of Western Australia with a Bachelor of Science majoring in Soil Biology. During university, Jennifer became interested in the challenge of increasing the sustainability of agriculture and in the possibility that organic farming might offer some solutions to this challenge. After university, she worked at Rick and Annie Dunn’s organic market garden in Perth for 18 months before working as a laboratory assistant at UWA and then travelling overseas. On returning to Perth, Jennifer commenced a PhD at UWA with the Soil Biology Group which she has recently completed. Institute of Agriculture
Institute of Agriculture Influence of rock fertilisers on soil microorganisms in an organic pasture Jennifer Carson Prof Lynette Abbott & Dr Deirdre Gleeson Institute of Agriculture
Outline • Introduction : • Soil microorganisms and rock fertilisers in organic farming • Evidence that rock fertilisers may influence soil bacteria • Experiments – Rock fertilisers influence bacteria because of their: • Composition • Particle size • Implications : • Organic farming – Rock fertilisers can alter structure of bacterial communities • Soil biology – Influence of soil minerals on bacterial communities underestimated Institute of Agriculture
Introduction Microorganisms & rock fertilisers in organic farming • Microbial processes improve soil fertility, but uncertain response to management • Particularly important in organic farming • Field trials in Australia • Identify practices that improve soil conditions for microbial processes – Potential of rock fertilisers • Rock fertilisers • Rock phosphate, basalt, mica, lime • Often poorly effective due to slow dissolution • Exception – sandy soils with pH<5 Institute of Agriculture
Introduction Evidence rock fertilisers affect microorganisms • Increase biomass & activity when increase plant biomass & soil pH • In other habitats, composition of minerals affects microbes • Rock fertilisers can alter particle & pore size distribution, but not linked to effect on microorganisms Hypothesise rock fertilisers affect microbial communities due to: • Effect on plant growth & pH • Composition • Particle size Institute of Agriculture
Composition Composition of rock fertilisers • Soil is spatial heterogeneous: • Microbes affected by properties of microhabitats • Microhabitats differ in mineral composition & size D • Mineral composition affects bacteria in other habitats • Different minerals colonised by distinct microbial communities • Preferential colonisation of minerals containing nutrients � “hotspots” of activity • Role of soil minerals overlooked • Microbial community on stones different from soil � “stonesphere” Institute of Agriculture c
Composition Hypothesis: • The microhabitats of different rock fertilisers in soil select distinct bacterial communities. Experimental design: • 3 rock fertiliser treatments: mica, basalt and rock phosphate. • 2 fraction treatments: rock fertilisers (>1 mm) & soil (<1 mm) • 3 pasture treatments: T. subterraneum (clover), L. rigidum (ryegrass) and unplanted. Institute of Agriculture
Composition Composition of soil & rock fertiliser differed 10cm % Composition of soil & rock fertilisers (XRF). P 2 O 5 CaO K 2 O MgO SiO 2 Soil 0 0.1 0 0 99.7 Mica 0.5 1.6 3.9 3.2 73.2 Basalt 0.3 9.5 0.5 5.1 53.7 Rock P 34.7 50.0 0.1 0.3 8.5 Picture mica grains here With organic Organic matter mica basalt rock phosphate Institute of matter removed Agriculture
Composition Microcosm experiment 1. 1-2 mm grains 2. Incubate in soil 10 w. rock fertilisers added to soil. 3. Sieve 1 mm. 4. Total DNA extracted from fractions & region >1 mm: Rock amplified by PCR. fertiliser fraction � Community structure (composition & relative <1 mm: abundance) Soil fraction Institute of Agriculture
Composition Statistics • PCO (ordination): • Samples plotted in 2-D space. • Distance between samples shows difference. • PERMANOVA • Permutational multivariate analysis of variance. • Treatment effects and pairwise comparisons. • DISTLM (multivariate multiple regression): • Model variation in bacterial communities using soil properties • Modelled values for samples can plotted in 2-D space (RDA) Institute of Agriculture
Unplanted Composition Fraction treatments • Bacterial communities in rock fertiliser and soil fractions • Formed separate clusters • All pairwise comparisons were significant L. rigidum � Microhabitats of rock fertilisers selected bacterial communities with different structure to surrounding soil. Mica Basalt Institute of Rock phosphate Agriculture
Unplanted Composition Rock fertiliser fraction • Bacterial communities in microhabitats of different rock fertilisers • Formed separate clusters • All pairwise comparisons L. rigidum were significant � Microhabitats of mica, basalt & rock phosphate selected bacterial community with distinct structure. Mica Basalt Institute of Rock phosphate Agriculture
Unplanted Composition Soil fraction • Bacterial communities in soil with different rock fertilisers applied • Formed clusters • Fewer pairwise comparisons were significant L. rigidum � Applying different rock fertilisers to soil also influenced bacterial community in bulk soil. Mica Basalt Institute of Rock phosphate Agriculture
Composition Element composition • Composition of rock fertilisers & soil minerals explained variance in structure of bacterial communities: • Unplanted: 44% by P, Mg & Na • L. rigidum : 35% by P, K & Mg � Bacterial community structure partly determined by nutrient content of rock fertilisers and soil minerals. Institute of Agriculture
Composition Implications • Soil microorganisms in organic farming: • Rock fertilisers create new microhabitats in soil that select bacterial communities with distinct structure • Partly due to their elemental content • Effect of soil minerals on microorganisms: • Mineral types in microhabitats may affect bacterial community structure • Mineral heterogeneity may contribute Institute of to spatial variation in soil bacteria Agriculture
Particle size Particle size & spatial isolation • Rock fertilisers can alter particle & pore size distribution but not linked to change in bacterial communities • Theory predicting texture affects diversity of microbial communities • When not connected by water, diversity increases Theory predicts: • Evidence: • Texture • Water content Institute of Agriculture
Particle size Hypothesis: • Texture & water content affect structure and diversity of bacterial community. Experimental design: •2 texture treatments: • 100% sand & 10% silt+clay • Ground quartz (<10 μ m) so altered particle size not composition • 6 water potential treatments: • Between -15 cm and -55 cm • Potential so knew size saturated pores Institute of Agriculture
Particle size Column experiment Largest • Soil column connected to water reservoir Potential water-filled (cm) pores • Added 5 cm segments, packing to constant ( μ m) 60 51 bulk density 55 56 61 50 68 45 • Soil columns saturated & adjusted to water 77 40 potential of -10 cm at column base 35 88 30 102 25 122 • Incubated for 1 w at 25 ° C. 20 153 15 204 10 306 • Analysed structure & diversity bacterial communities Institute of Agriculture
Particle size 10% silt+clay Texture treatments 100% sand • Bacterial communities from 10% 15 different textures: silt+clay • Plotted in separate 25 regions of graph 35 • All pairwise comparisons 100% 40 15 significant 45 sand 55 20 • Bacterial diversity was not 25 affected by texture 40 55 � Texture affected bacterial communities due to changes in physical properties of soil � Supports theory Institute of Agriculture
Particle size 10% silt+clay Water content treatments 100% sand • Bacterial communities from 15 ‘wet’ and ‘dry’ soil: • Plotted in separate 25 regions of graph 35 • All pairwise comparisons 40 15 significant, except at 56% 45 55 WFPS 20 25 30 • Bacterial diversity was 40 55 higher in dry soil. Dry Wet � Water content influences diversity of complex bacterial community in field soil. Institute of Agriculture
Particle size Texture • Difference in physical properties of soil explained 38% variance in structure of bacterial communities Silt+clay content 13% Water content 15% Water in pores: 122-153 μ m 3.2% 88-102 μ m 3.8% 68-77 μ m 2.6% � Variation in bacterial communities statistically related to changes in physical properties of soil. Institute of Agriculture
Recommend
More recommend
