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State of Soil Science WA

Soil Science Australia WA Branch

Conference

4-6 December 2019

The University of Western

Australia, Perth, Western Australia

#WASoils2019

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State of Soil Science WA

Soil Science Australia WA Branch Conference 4-6 December 2019

The University of Western Australia, Perth, Western Australia

Compiled by Dr Lucy Commander

© 2020 Australian Society of Soil Science Inc.

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Contents

Welcome to State of Soil Science WA Conference ... 3

Sponsors ... 4

Organising Committee, Soil Science Australia WA Branch... 5

Conference Venue Information ... 6

Opening Address ... 7

Professor Tony O’Donnell ... 7

Keynote Speakers ... 8

Professor Daniel Murphy ... 8

Dr Juhwan Lee ... 9

Annual Boodja Lecture in Soil Science ... 10

Mr Andrew Watson ... 10

Conference Programme ... 11

Posters... 17

Abstracts of Oral Presentations ... 19

Abstracts of Poster Presentations ... 46

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Welcome to State of Soil Science WA Conference

Henry Smolinski

SSA WA Branch President

On behalf of the Conference Organising Committee, welcome to the 2019 WA Soils Conference, hosted by Soil Science Australia. Our theme this year is “The State of Soil Science in

WA” and I am pleased to see that all disciplines of the field of the science of soils is represented at this year’s conference.

Our soils are one of the most valuable natural resource assets to support and sustain our existence. Soil is the engine room for our food production, the filter for our water systems, and the foundation for our infrastructure. The study of soil is fundamental in understanding our earth’s dynamic and diverse processes.

We are delighted to have Prof. Daniel Murphy, Head of School, UWA School of Agriculture and Environment and Dr Juhwan Lee, Research Fellow in Soil and Landscape Science, Curtin University provide our keynote presentations. Prof. Daniel Murphy’s research interests focus on soil microorganisms and how ecosystem respond to the challenges of climate change and the need to feed the world’s growing populations. Dr Juhwan Lee’s research focus is land use and soil management options with specific interests in spatial and temporal analysis of plant production, soil carbon and nitrogen balances and greenhouse gas emissions. The insights of our keynote presenters are highly relevant to current State and National interest in carbon sequestration, regenerative agriculture and rangelands reform.

This year’s annual premier lecture in soil science for WA (The Boodja Lecture) is presented by Mr Andrew Watson who has a long-standing career as Western Australia’s Soil and Land Conservation Commissioner. Andrew will discuss aspects of the last phases of one million acres per year of land clearing and development in the south west land division, together with how soil and land resource information is used to underpin changing land use and development, especially in WA’s north, where opportunity exists to avoid many of the problems encountered in the south west (and perhaps what has been forgotten and why many Kimberley projects have failed).

We hope that you will take this opportunity to learn more about innovations in soil science and network with peers /colleagues, old and new, to improve the management of soil in our wonderful state.

Soil Science Australia’s commitment is to encourage a wider appreciation of soil across our community. In the coming year the WA branch will be delivering a range of soil refresher training courses and field tours for students. We look forward to your participation and contribution, and encourage you spread the word about these events. The SSA (WA branch) AGM officially closes the conference. All are welcome!

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Sponsors

Thank you to the generous sponsorship from the following organisations:

• The Department of Primary Industries and Regional Development

• The University of Western Australia

• Soils West

• Soil CRC

And in-kind support from:

• Richgrow

• Pauline Gazey from Science with Style

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Organising Committee,

Soil Science Australia WA Branch

Tim Overheu

Conference Chair and Vice President Henry Smolinski

President Chris Gazey Past President Isaac Kelder Secretary Louise Barton Treasurer Bede Mickan

Industry representative Richard Bell

Committee member Deborah Prichard Committee member Miaomiao Cheng Student representative Lucy Commander Conference Manager

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Conference Venue Information

Wifi: UnifiConf | Username: soil2019 | Password: tark66

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Opening Address

Professor Tony O’Donnell

Executive Dean Science,

Faculty of Science, The University of Western Australia (UWA)

Tony O’Donnell leads the Faculty of Science at UWA and is a member of the University’s Executive leadership team at the University of Western Australia. He was born and educated in the UK, graduated from the University of Glasgow in 1976 and completed his PhD at the University of Bristol in 1980. He holds visiting positions at Kasetsart and Naresuan Universities in Thailand and with the Institute of Subtropical Agriculture, Changsha, PRC. Before moving to Western Australia in August 2008, he worked at the University of Newcastle in the Northeast of England where he held senior

research and administrative positions. Whilst at Newcastle he established and was the first Director of the multidisciplinary Institute for Research in Environment and Sustainability (IRES). In 2012 he was awarded a Visiting Professorship for Distinguished International Researchers by the Chinese Academy of Sciences and in 2015 received an Honorary Doctorate from Naresuan University in Thailand for his contributions over many years to Higher Education in Thailand.

Central to Professor O'Donnell's research is the need to understand the functional consequences of the interactions between the soil microbiome and management of the abiotic soil environment. Soils are complex, multi-organism systems that are becoming amenable to analysis through the expansion of post-genomic technologies into environmental genomics. In the last ten years, the importance of the microbiome in maintaining a sustainable biosphere has been widely recognized. This has resulted in a surge of activity in environmental microbiology, and the development of novel technologies to better interrogate the role of microorganisms in soil. Professor O’Donnell has used these techniques to investigate gene: environment interactions in a range of systems, including agricultural soils and contaminated land.

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Keynote Speakers

Professor Daniel Murphy

Head of School,

School of Agriculture and Environment Faculty of Science, The University of Western Australia

Professor Daniel Murphy is the Head of the UWA School of Agriculture and Environment. His research focuses on how the diversity and functions of soil organisms are impacted by land management practices and climate, paying particular attention to nutrient cycling and greenhouse gas emissions.

Growing up in rural Australia, Professor Murphy connected to agriculture and the land from a young age. His early research years were spent at Rothamsted Research in the United Kingdom, where he worked on the oldest agricultural trial in the world. The trial, established in 1843, includes management treatments to build soil organic carbon and alter nutrient levels, and has been replicated across agricultural regions in China where Professor Murphy holds High-End Foreign Experts status.

Professor Murphy currently manages a research program addressing issues relating to the development of sustainable management practices for agriculture, horticulture and mine sites under rehabilitation.

The major focus of this research is the biological fertility of soil. UWA staff and students employ a range of molecular, isotopic, biochemical and enzymatic tools to study microbial ecology and nutrient cycling and issues relating to microbial function and diversity. The research is primarily funded through the Australian Grains Research and Development Corporation, the Department of Agriculture Fisheries and Forestry, the Australian Research Council and industry partners.

From 2012 to 2016, Professor Murphy held an Australian Research Council (ARC) Future Fellowship, enabling him to concentrate his research on ecosystems of international importance to Australia – both in terms of global economy (China) and international stewardship (the Arctic).

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Dr Juhwan Lee

Research Fellow, Curtin University

Dr Juhwan Lee, is a Research Fellow at Curtin University working in the Soil and Landscape Science group, in the faculty of Science and Engineering.

Juhwan’s research focuses on the effects of climate and land use change on soil carbon and nitrogen cycling. His general approach is to use empirical and biogeochemical modelling to predict the complex interactions between soil, plants, carbon storage and greenhouse gas emissions in

agroecological systems across different spatial and temporal scales.

He received a B.S. in 1999 and an M.S. in 2001 from Inha University, South Korea. He received his PhD research in ecosystems and landscape ecology from University of California-Davis. After that, he worked as a Postdoc and a Project Scientist at University of California-Davis until January 2013. He worked as an Oberassistent at ETH Zurich in Switzerland from 2013 to June 2017 and as a Research Scientist at CSIRO from July 2017 to January 2019. He joined Curtin University in February 2019 as a Senior Research Fellow.

An extensive list of Juhwan’s publications can be viewed at:

https://www.researchgate.net/profile/Juhwan_Lee3

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Annual Boodja Lecture in Soil Science

Mr Andrew Watson

Commissioner of Soil and Land Conservation WA

Boodja is a Noongar word for “land” and the lecture series acknowledges the important role of aboriginal understanding in the responsible management of our soil and land.

On World Soil Day 2019, the WA Branch of Soil Science Australia is honoured to receive our annual lecture from Andrew ‘Nick’ Watson. Andrew is the Commissioner for Soil and Land Conservation in Western Australia and has excelled over a career spanning 45 plus years dedicated to the protection of Western Australia’s land and soil resources.

Andrew will recount stories from his early career in

Northern Libya through to the challenges of Soil Conservation in Western Australia.

Even Andrew’s passion about Series II and III Land Rovers might slide into the presentation!

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Conference Programme

Wednesday 4 December 2019 Conference field trip

Full day field trip

Swan Coastal Plain & Perth Hills

Ted Griffin, Henry Smolinski, Angela Stuart-Street 0800 for 0820

departure

Depart DPIRD office front car park (Baron-Hay Court, South Perth)

1000–1245

Perth Coastal Plain

Soil pits, road cuttings, open fields

1245–1330

Lunch

1330–1500

Perth Hills

Road cuttings, rocks, gravel and more

1500–1600

Dirt Drinks!

(Core Cider House, 35 Merrivale Rd, Pickering Brook) 1715 Field trip return

(to Baron-Hay Court, South Perth)

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Thursday 5 December 2019 UWA Business School

0730–0830 60 mins

Registration

(Exhibition foyer) 0830–0845

15 mins

Welcome to Country

Dr Richard Walley OAM 0845–0855

10 mins

Official opening

Professor Tony O'Donnell Executive Dean, The University of WA 0855–0900

5 mins

Important house-keeping notices

Tim Overheu (MC) 0900–0925

25 mins

Keynote address

Professor Daniel Murphy

Head of School, UWA School of Agriculture and Environment

Soil R&D Outcomes WA & Beyond

Session Chair:

Assoc Prof Louise Barton

0930–0945 15 mins

Subsoil constraints and their management:

Overview from five years of R&D

David Hall, Yvette Oliver, Shahab Pathan, Karen Holmes, Dennis van Gool, Geoff Anderson, Jeremy Lemon, Caroline Peek, Liz Petersen, Glenn McDonald, Ed Barrett-Lennard, Dana Mulvaney, Glen Reithmuller, Ted Griffin and Phil Ward

0945–1000 15 mins

Crop response to amelioration of agricultural soils are mediated by constraint combinations and soil type

Stephen Davies, Wayne Parker, Giacomo Betti, David Hall, Tom Edwards, Chad Reynolds and Glenn McDonald

1000–1030 30 mins

Morning tea & World Soil Day Celebration

(UWA Business School Terrace – see floor plan) 1030–1045

15 mins

Dynamics of water use by wheat and canola crops in compacted, acidic sands treated with deep strategic tillage and lime

Gaus Azam, Chris Gazey and Richard Bowles 1045–1100

15 mins

Soil nitrogen storage and availability to crops are increased by

conservation agriculture practices in rice–based cropping systems in the eastern Gangetic Plains

MD. Khairul Alam, Richard Bell, ME Haque, M.A. Islam and M.A. Kader

1100–1115 15 mins

Evolution of ryegrass resistance to glyphosate changes soil microbial diversity 14 years of continuous application

Zakaria Solaiman, Abul Hashem, Bede Mickan, Lynette Abbott, Paul Storer, Vivek Bhat and Andrew Whiteley

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15 mins

Gravel is soil is gravel

David Weaver, Ronald Master and David Rogers 1130–1145

15 mins

Simulating Australian soil organic carbon sequestration Juhwan Lee and Raphael A. Viscarra Rossel

1145–1155 10 mins

Extending the message of soil quality in the mobile device era Chris Gazey and Frances Hoyle

1155–1205 10 mins

SoilsWest – GRDC Launch of the next eBook in the Soil Quality series Peter Bird (General Manager, GRDC) and Frances Hoyle

1205–1250 45 mins

Lunch

(UWA Business School Terrace – see floor plan)

Soil Innovation & Development

Session Chair:

Chris Gazey 1250–1300

10 mins

iLime an app for assessing the management of soil acidity in agricultural systems

James Fisher, Jenni Clausen, Fiona Evans and Chris Gazey 1300–1315

15 mins

The forensic analysis of Perth’s soils

Kari Pitts, Richard Clarke, Talia Newland and Simon Lewis 1315–1330

15 mins

Topsoil slotting has potential to improve root pathways through hostile subsoils

Wayne Parker, Chad Reynolds and Glenn McDonald 1330–1345

15 mins

Black soldier fly technology can convert manure into valuable fertiliser Sasha Jenkins, Zhouda Huang, Bede Mickan, Morten Andersen, Luke Wheat and Lynette Abbott

1345–1400 15 mins

Soil classification based on spectral and environmental variables

Andre Carnieletto Dotto, Raphael Viscarra Rossel, Jose DeMatte and Rodnei Rizzo 1400–1415

15 mins

Rapid soil analytical techniques for international agricultural research and development

Wendy Vance, Mike Wong, Anthony Ringrose-Voase, Te Kim Sok Heng, Khin Myo Thant, Htay Hlaing, Phyoe Phyoe Win and Cho Mar Htwe 1415–1430

15 mins

Legacy phosphorus – have we fallen asleep at the wheel?

Simon Clarendon, David Weaver and Robert Summers 1430–1500

30 mins

Posters on display – 'meet n greet' poster authors

(Foyer area, UWA Business School) 1500–1530

30 mins

Afternoon tea & extended poster display

(UWA Business School Terrace)

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Soil Policy, Planning & Governance

Session Chair:

Tim Overheu 1530–1545

15 mins

Monitoring ground cover and associated erosion risks using satellite remote sensing in the agricultural region of Western Australia

Justin Laycock, Nick Middleton, Tim Overheu, Buddy Wheaton and Karen Holmes 1545–1600

15 mins

Validating and extending the national Better Fertiliser Decisions for Pasture critical values for phosphorus

David Rogers, David Weaver, Ronald Master and Robert Summers 1600–1615

15 mins

Translating soils information into better land planning decisions: an example from the Peel-Harvey Catchment Western Australia Heather Percy, Ander Del Marco, Tom Lerner and Brett Flugge 1615–1700

45 mins

Posters on display

Annual Boodja Lecture in Soil Science

Session Chair:

Henry Smolinski 1700 for

1730–1830

A career in land & soil conservation

Andrew Watson

Commissioner for Soil and Land Conservation, WA 1830–2000

Post Lecture and Conference Dinner

(BHP Billiton Courtyard, opposite WesFarmers Lecture Theatre, UWA Business School)

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Friday 6 December 2019 UWA Business School

0730–0830

Registration

(Exhibition foyer)

0830–9000

Posters on display

(and through the day) 0900–0925

25 mins

Keynote address

Research Fellow Dr Juhwan Lee

Soil and Landscape Science, Curtin University, Western Australia

Soil Science Learning Outcomes

Real-life challenges stimulating student thinking

Session Chair:

Dr Deb Pritchard 0930–0945

15 mins

Bacterial processes associated with soil C and N following application of compost and manure to dairy pasture at the beginning and end of the growing season

Lynette Abbott, Bede Mickan, Zakaria Solaiman, Anjani Weerasekara, Sanja Schwab, Ian Waite and Sasha Jenkins

0945–1000 15 mins

Soil exchangeable cations increase microbial carbon use efficiency and microbial growth in acidic soils

*Emilia Horn, Emily Cooledge, Anna Ray, Davey Jones, Steve Rushton, Elizabeth Stockdale, Frances Hoyle, Yoshi Sawada and Daniel Murphy

1000–1015 15 mins

Vacuum drying soil samples is a low-temperature alternative to conventional oven drying when determining soil water repellence

*Enoch Wong, Philip Ward, Matthias Leopold, Daniel Murphy and Louise Barton 1015–1030

15 mins

Influence of lime and crop rotation on soil nitrogen, dry matter production and microbial biomass; a field trial, Merredin, WA

*Manjula Premaratne, Daniel Murphy, Craig Scanlan and Frances Hoyle 1030–1110

40 mins

Morning tea & poster display

(UWA Business School Terrace) 1110–1125

15 mins

Variable aluminium toxicity and root distribution in acidic soil profiles Paul Damon, Gaus Azam, Craig Scanlan, Chris Gazey and Zed Rengel 1125–1140

15 mins

The all new Australian Soil Classification Noel Schoknecht

1140–1155 15 mins

Identification and classification of “new” semi-arid soils from the Pilbara WA with potential additions to the Australian Soil Classification

Henry Smolinski, Dennis van Gool

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Promoting Soils

Industry Engagement & Extension

Session Chair:

Isaac Kelder 1155–1210

15 mins

What lies deep beneath – acid sulfate soil impacts on groundwater resources used for irrigation

Brad Degens 1210–1225

15 mins

Best practice soil sampling to depth the key to enable growers to manage soil acidity

Stephen Carr, Kevin Mincherton and Don Hook 1225–1255

30 mins

The State of Soil Science in WA

– a facilitated Q&A session Tim Overheu and Deb Pritchard 1255–1340

45 mins

Lunch

(UWA Business School Terrace) 13401400

20 mins

Early Career Science Awards

Poster & Presentation

Associate Dean Frances Hoyle

The University of Western Australia, Director, SoilsWest 1400–1425

25 mins

Conference closing address

Associate Professor Louise Barton The University of Western Australia

1425

Conference close

1430–1500

Soil Science Australia WA Branch AGM

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Posters

Display

number See also abstract booklet. Authors will stand next to their posters on Thursday afternoon.

*1 Efficacy of a phosphate bio-mineral fertiliser varied with P concentration and P solubility

Salmabi Assainar, Lynette Abbott, Paul Storer, Kadambot Siddique and Zakaria Solaiman 2 Topsoil evaporation in water repellent soil affected by tillage and claying:

Preliminary case-study results Giacomo Betti and Gaus Azam 3

Chemical nature of phosphorus in cropping soils from Western Australia characterised by 31P nuclear magnetic resonance spectroscopy Gustavo Boitt, Craig Scanlan and Zed Rengel

4 Designing soil covers for ecological restoration of mine waste

Lucy Commander, Luis Merino-Martin, Peter Golos, Carole Elliott, Jason Stevens and Ben Miller

5 Profile texture classes: A new data-driven functional soil classification for southwestern Australia

Ted Griffin and Karen Holmes

6 Are ironstone gravel soils in southwest Western Australia all the same?

Karen Holmes, Ted Griffin, and Dennis van Gool

*7 A native symbiotic fungus increases shoot biomass and grain yield of canola (Brassica napus)

Khalil Kariman, Craig Scanlan and Zed Rengel

8 NRINFO 2019 release: WA natural resource information available through web portal

Justin Laycock, Angela Stuart-Street and Dennis van Gool

9 Engineering in situ soil and plant microbiomes to improve agricultural productivity Falko Mathes, Fiona McDonald and Peter Keating

10 A fast and inexpensive molecular biological assay to assess soil health Fiona McDonald, Falko Mathes and Peter Keating

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Investigation of the common mycorrhizal network concept: plant growth

responses in simulated intercropping of a legume and grass under water stress Bede Mickan, Miranda Hart, Zakaria Solaiman, Kadambot Siddique, Sasha Jenkins and Lynette Abbott

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Nutrient recovery via anaerobic digestion of supermarket food waste and re-use as fertiliser in potting media for the urban retail market; a proof of concept using digestate and biochar

Bede Mickan, Somayeh Zarezadeh, Sasha Jenkins, Aitian Ren, Zakaria Solaimon and Megan Ryan

*13 The methodology for farm-scale modelling for spatio-temporal prediction of soil carbon sequestration under climate change

Lynette Abbott, Jolene Otway, Louise Barton and Jennifer Dungait

14 Impact of lime and gypsum on wheat yield, soil and solution properties in the short and long term

Geoffrey Anderson, Shahab Pathan, David Hall, Rajesh Sharma and James Easton 15 Yield response to deep ripping of canola, wheat and barley on soils with multiple

constraints

Shahab Pathan, David Hall and Tony Murfit

*16

Humic acid coated phosphatic fertilisers enhance growth, yield and phosphorus uptake of maize crop in alkaline soil

Muhammad Shafi, Muhammad Sharif, Dost Muhammad, Ahmad Khan, Farmanullah Khan and Zakaria Solaiman

17 Grazing into the future: Building soil carbon using perennial pasture species Zakaria Solaiman, Lynette Abbott, Natasha Paul, Rob Rex and Caroline Rex

18 Talking the same soil language – a simple guide for describing WA soils Angela Stuart-Street, Nicolyn Short and Tim Overheu

19 Continental-scale soil organic carbon composition and vulnerability regulated by regional soil and environmental controls

Raphael Viscarra Rossel, Juhwan Lee, T. Behrens, Z. Luo, J. Baldock and A. Richards 20 Assessing the suitability of black soldier fly castings produced from piggery waste

as a fertiliser

Luke Wheat, Lynette Abbott, Ian Waite and Sasha Jenkins

*21 Topsoil water repellence increased early wheat growth and nutrition Simon Yeap, Richard Bell, Craig Scanlan and Richard Harper

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Microalgae and phototrophic purple bacteria for nutrient recovery from agri- industrial effluents; influences on plant growth, rhizosphere bacteria, and putative C & N cycling genes

Somayeh Zarezadeh, Bede Mickan, Sasha Jenkins, Tim Hulsens, Hossein Riahi and Navid Moheimani

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Abstracts of Oral Presentations

(presented in alphabetical order)

Bacterial Processes Associated with Soil C and N Following Application of Compost and Manure to Dairy Pasture at the Beginning and End of the Growing Season

LYNETTE ABBOTT1,2 BEDE MICKAN1,2,3, ZAKARIA SOLAIMAN1,2, ANJANI WEERASEKARA1, SANJA SCHWAB1, IAN WAITE1,2, SASHA JENKINS1,2

1UWA School of Agriculture and Environment (M087), The University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia

2The UWA Institute of Agriculture (M082), The University of Western Australia, Perth WA 6009, Australia

3 Richgro Garden Products, 203 Acourt Rd, Jandakot Western Australia 6164, Australia

This study investigated the impact of dairy manure and compost on bacterial

community composition and functional diversity in a dairy pasture in south-western Australia. Bacterial activities are involved in both the retention and loss of soil C and N, during the degradation of organic matter. Bacterial communities respond to addition of manure and compost, and play a key role in the incorporation of these C resources into the soil matrix. In this study, bacterial communities in dairy soil amended with manure or compost in a field experiment were characterized in soil collected at the beginning of the growing season in ‘winter’ and at the end in

‘summer’ using community profiling of 16S rRNA genes. Soil had been amended in the field with inorganic fertilizer in combination with 2t/ha dairy manure, or compost applied at 3t/ha or 6t/ha. The dominant bacterial phyla were Proteobacteria,

Actinobacteria, Acidobacteria, Bacteriodetes and Firmicutes and their relative

abundances were influenced by the organic amendment type and application rate as well as the time of sampling. The occurrence of C degrading functional genes and N functional genes were predicted using PICRUSt. Predicted gene counts associated with breakdown of hemicellulose, cellulose and chitin were highest in the winter samples with the application of manure. Predicted C genes and N gene abundance of amoA associated with nitrification was lowest for soils treated with 6 t/ha compost in winter samples. This study illustrates the complexity of soil bacterial community responses to manure and compost applied to dairy pasture. One feature of this dynamic was reduced potential for degradation of soil C and mineralization of N and therefore higher C and N retention in soils when 6t/ha compost was applied

compared to application of 3t/ha compost and non-composted manure. Management practices that enhance C sequestration and N retention in agricultural soils may enhance crop productivity whilst will limiting C and N losses via greenhouse gas emissions and leaching.

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Soil Nitrogen Storage and Availability to Crops are Increased by Conservation Agriculture Practices in Rice–based Cropping Systems in the Eastern Gangetic Plains

MD. KHAIRUL ALAM1,2* RICHARD W. BELL1*, M.E. HAQUE1, M.A. ISLAM3 AND M.A.

KADER1,4, 5

1Agriculture Discipline, College of Science, Health, Education and Engineering, Murdoch University, Western Australia

2Soil Science Division, Bangladesh Agricultural Research Institute, Gazipur, Bangladesh

3Pulse Research Centre, Bangladesh Agricultural Research Institute, Ishurdi, Bangladesh

4Department of Soil Science, Bangladesh Agricultural University, Mymensingh, Bangladesh

5School of Agriculture and Food Technology, University of South Pacific, Samoa

On-farm adoption of minimum soil disturbance and increased residue retention will alter nitrogen (N) dynamics in soils and N fertiliser management in the intensive rice–based triple cropping systems of the Eastern Gangetic Plains. However, the consequences of changes in N forms, N mineralisation and N availability for crops in these cropping systems have not been determined. Field experiments were conducted at two locations (Alipur and Digram) of north–west Bangladesh to examine N cycling under three

planting practices (conventional tillage (CT), strip planting (SP) and bed planting (BP)) with increased (HR) or low residue retention (LR– the current practice) on Calcareous Brown Flood Plain and Grey Terrace soils. Total N and available N were measured on soil samples as was N uptake by crops at different growth stages in the 13–14th (Alipur) and 12–13th (Digram) crops since treatments commenced. At each location (0–10 cm soil depth), SP, including non–puddled transplanting of rice seedlings (NP), together with HR increased total N by 9 and 32 % relative to BPHR, and CTHR and by 62 % relative to the current farm practice (CTLR). In general, the cumulative available N in soils during mustard and rice cropping under CT with HR was higher than other crop establishment and residue retention practices while under wheat and jute, total availability of N did not vary among crop establishment types with increased residue retention. Nitrogen availability in the initial phase of crop growth (0–60 DAS) was generally higher with CT than SP and BP. By contrast, for all crops, the estimated potentially mineralisable N was higher and its decay rate was lower under SPHR than other crop establishment and residue retention practices. Conservation Agriculture practices (SP, and NP of rice, together with HR) have altered the N cycling by reducing the level of mineral N available to plants in the early growing season when crop N requirement is low but increasing soil total N (0-10 cm) and plant N uptake by enhancing the synchrony between crop demand and available N supply.

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Dynamics of Water Use by Wheat and Canola Crops in Compacted, Acidic Sands Treated with Deep

Strategic Tillage and Lime

GAUS AZAM1, CHRIS GAZEY1 AND RICHARD BOWLES1

1 Department of Primary Industries and Regional Development, 75 York Road, Northam WA 6401, Australia

Incorporation of agricultural lime by ‘strategic deep tillage’ is one of the quickest methods for managing subsurface soil acidity. Such soil amelioration practice decreases soil resistance by removing compaction and increases soil pH, which allows deep penetration of crop roots, and hence increases the acquisition of soil water from deeper in the soil. As a result of improved soil physical and chemical properties, crop yield also increases and so does the water use efficiency (WUE).

Under broadacre cropping conditions, WUE is generally estimated from crop yield and weather data; actual measurement of soil water uptake can lead to more accurate interpretation of results, especially where soil profiles are ameliorated to varying degrees. In this trial we measured the soil water status of soil profiles, which differed due to amelioration treatments. We used two recently developed soil

moisture sensors (Diviner 2000 and EnviroPro®), to improve our understanding of the variability in soil water uptake, yield and WUE by wheat and canola. The

experiment was established in 2018 in Kalannie, WA, involving three treatments: (i) control, (ii) removal of compaction by tillage to 0.45 m depth, and (iii) removal of both compaction and acidity by lime incorporation to 0.45 m depth. All soil water

measurements were calibrated against gravimetric soil water measurements using soil cores from relevant profiles. Mace wheat was grown in 2018 and Bonito canola was grown in 2019. Removal of compaction reduced soil resistance to an optimum level, which allowed wheat roots to grow to the depth of tillage, but the canola roots were restricted by low pH and aluminium toxicity. Removal of both compaction and acidity reduced soil resistance and increased soil pH to optimum levels almost immediately, which allowed both wheat and canola roots to grow to 0.65 m depth. In 2018, the wheat crop extracted more water from the subsoil from the treated plots than from the untreated plots, however, there was no difference between the treated plots. In 2019, a significant difference was noticed in soil water extraction by the canola crop – water uptake was significantly higher in plots where both the

compaction and acidity constraints had been removed compared to the control plots or where compaction only was removed. In both seasons, none of the crops

extracted any soil water from below 0.20 m in the control plots. New technologies were found to overestimate soil water content but, once calibrated, provided useful hourly soil water status in the different soil profiles.

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Best Practice Soil Sampling to Depth is the Key to Enable Growers to Manage Soil Acidity

STEPHEN CARR1, KEVIN MINCHERTON2, DON HOOK2

1Aglime of Australia

2Precision SoilTech 1/110 Robinson Ave, Belmont WA 6184, Australia

Soil acidity affects approximately 50 million hectares of agricultural land in Australia, predominantly in Western Australia (WA) and New South Wales (State of the

Environment 2011 committee). Subsurface acidity below 0.1 m, in particular, is a major land degradation issue throughout the WA wheatbelt. Soil acidification is an inevitable consequence of productive agriculture, largely through the addition of acidifying fertilizers, leaching of nitrates and removal of alkaline plant products.

Precision SoilTech (PST) conducts contract soil sampling for growers to receive both fertiliser and lime recommendations. Over the past 15 years in excess of 250,000 geo-located sites have been sampled for growers across the WA wheatbelt.

Approximately 55% of these sites have been sampled to 30 cm in 10 cm increments.

This deeper sampling regime differs considerably from soil sampling primarily to inform fertiliser recommendations, which is usually restricted to the top 10 cm. To effectively manage soil acidity, knowledge of the extent, depth and severity of soil acidity is essential, as is a targeted and ongoing liming program. We show evidence that sampling to depth is critical to the long-term success of growers in better managing soil acidity and maximizing yield potential of WA wheatbelt soil. Growers achieving target pH down the soil profile is something on which DPIRD has placed considerable extension effort. Why? Because there is good evidence that this approach both protects soils and optimises the economic return from farming. The proportion of soil sampling sites that PST has sampled that meet or exceed DPIRD targets down the soil profile (>5.5 in the soil surface, and >4.8 in the subsurface) has increased from nil 15 years ago, to nearly 50% currently – a rapid and outstanding achievement. Why has this occurred? We suggest it is because the better growers are adopting best practice soil sampling to depth and apply lime at the rate and locations required. Growers who sample to depth are better at managing soil acidity, because they typically apply 50% more agricultural lime than growers who only sample surface soil. We also suggest that growers who are willing to pay for contract soil sampling are more likely act on the recommendations offered compared to their colleagues who sample only 0–10 cm for fertiliser inputs. The different sampling approaches that are in place mean that making direct comparisons between the sampling-to-depth and the topsoil-only practices is not possible. However, by looking at the proportion of surface soils sampled that are above the DPIRD target of 5.5, growers sampled by PST appear to be managing soil acidity better than their

colleagues who typically only have sampled surface soil. The evidence, derived from hundreds of thousands of sampling sites is compelling, and at the same time

concerning.

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23

Legacy Phosphorus – Have We Fallen Asleep at the Wheel?

SIMON CLARENDON1, DAVID WEAVER2,ROBERT SUMMERS3

1Department of Primary Industries New South Wales, 4 Marsden Park Road, Calala NSW 2340, Australia

2Department of Primary Industries and Regional Development, 444 Albany Highway, Albany, WA 6330, Australia

3 Department of Primary Industries and Regional Development, 45 Mandurah Terrace, Mandurah, WA 6210 Australia

Reducing nutrient loss from agricultural landscapes using management practices in Australia has long been advocated to improve water quality. Water quality, i.e.

phosphorus (P) concentrations are commonly used to measure the effectiveness of management practices at the paddock level. However, the effectiveness of paddock scale management practices is often not reflected at a catchment scale, in part due to levels of implementation, but also due to the equilibrium effects of legacy P. The average equilibrium P concentration (EPC0; the concentration where no P was retained or released) of stream sediment in agricultural catchments of the south coast of Western Australia was compared to median P values of historic water quality data from the mid 1990’s and late 2000’s. The 8 sample sites were located in the southern region of the Wilson Inlet catchment and the mid to northern regions of the Oyster Harbour catchment. Stream sediment (both <2mm and >2mm size fractions) are currently net retainers of P, contributing to legacy P stocks. The catchment scale effectiveness of paddock-based management practices will therefore be influenced by the EPC0 dynamics of stream sediment, which under some circumstances will be net retainers of P, and in others net contributors of P. This concept of legacy P and EPC0 is directly applicable to soils, and assists to understand the dynamics of paddock-based P loss. To illustrate the legacy P and EPC0 concepts, differences in the dynamics of P loss from disparately sized (30 ha and 4000 ha) sandy catchments to which P binding soil amendments were applied will be provided. Communicating the notion of legacy P to broader stakeholders, including the public and politicians is required so that expectations around management practice effectiveness, along with the time required to achieve water quality targets is clearly understood. In some countries, depletion of legacy P stocks in soils and sediments are estimated in hundreds of years. We could expect a decadal time horizon for the Swan Coastal Plain given the sandy nature of its soils. Reductions in nutrient loss at a catchment scale can be made by implementing management practices at a paddock scale, but expectations over the timing of improvements need to be realistic given the

influences of legacy P and EPC0.

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24

Crop Response to Amelioration of Agricultural Soils are Mediated by Constraint Combinations and Soil Type

STEPHEN DAVIES1, WAYNE PARKER1, GIACOMO BETTI1, DAVID HALL2, TOM EDWARDS2, CHAD REYNOLDS1, GLENN MCDONALD3

1Department of Primary Industries and Regional Development, 20 Gregory Street, Geraldton, WA 6530, Australia

2Department of Primary Industries and Regional Development, Meljinup Road (PMB50), Esperance, WA 6450, Australia

3Department of Primary Industries and Regional Development, 444 Albany Highway, Albany, WA 6330, Australia

Over the past decade alternative strategic deep tillage approaches have been developed to complement more established soil amelioration methods. Strategic tillage takes the form of a one-off or occasional intervention, implemented to overcome a number of soil and biotic constraints. Deep ripping can effectively remove subsoil hardpans and potentially delve up some subsoil to the surface depending on tine design. Deep soil mixing, using rotary spaders or large disc ploughs, can mix and incorporate topsoil and amendments deeper into the soil profile and reduce topsoil repellence. Soil inversion, using mouldboard, square or one-way disc ploughs, can bury surface-applied amendments, as well as repellent topsoil and weed seeds. While these techniques principally address soil constraints, some also improve weed control and reduce frost damage. A review of published and unpublished crop response data collated from replicated research trials and on- farm large scale strip trials over the past 12-years was undertaken to assess the impact of tillage and soil type on crop yield response. Subsoil compaction is a key constraint on deep sandy-textured soils and deep ripping gives first-season average wheat yield increases of 0.7 t/ha (36%), provided it is deep enough to effectively remove the hardpan. Shallower ripping is less effective with first year average wheat yield increases of 0.25 t/ha (12%). Rotary spading has similar cereal grain responses to inversion ploughing in the first two seasons post treatment. Size of the average yield gain reflected yield potential of soils and environments. Average gains in cereal yields from soil inversion were 0.5 t/ha (61%) on pale deep sand, 0.7 t/ha (42%) on a higher yielding deep sand over clay or gravel duplex soil and 0.9 t/ha (29%) on forest gravels in the higher rainfall zone. In cases where the inversion did not significantly increase yield, seasons were very dry or crop establishment was poor due to

herbicide and/or wind damage or surface crusting. Higher yield potential, more fertile soils, maintained the cereal yield benefits for a longer time after amelioration than the pale deep sands. For the pale sands, the average increase in yield benefit for soil inversion or deep mixing after three or more years was 0.2 to 0.3 t/ha and for about half the sites the response was not significant. For the other soil types average yield benefits in excess of 0.5 t/ha were maintained for three or more years after

amelioration.

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25

What Lies Deep Beneath – Acid Sulfate Soil Impacts on Groundwater Resources Used for Irrigation

BRAD DEGENS1

1Water Science and Data Division, Department of Water and Environmental Regulation, Prime House, 8 Davidson Terrace, Joondalup, 6027, Australia

Over 17 years have passed since the hazards posed by Acid Sulfate Soils (ASS) were recognised in WA with a catastrophic oxidation event during dewatering of a

development in Perth’s northern suburbs. Since then, regional mapping has identified ASS risks lies beneath over 6000 km2 (about half) of the Swan Coastal plain. The risks posed by these soils are mostly to water quality and aquatic ecosystems rather than the directly to soils for agricultural production purposes. However, this may not be the case where water is used for irrigation. In many situations, the effects of oxidising ASS go unnoticed but this is likely to change under a drying climate and increasing pressure on water resources. Two contrasting examples of how ASS in southern WA are impacting groundwater resources and the potential implications for irrigation uses of this water have been examined in detail. The first example, to the north of Perth where ASS are coupled with the Gnangara regional groundwater system - groundwater in this location is acidifying beneath 380 km2 of the mound. This has been caused by drying and oxidation of ASS following the decline in groundwater levels over more than two decades. In a contrasting situation, ASS in the Myalup irrigation area south of Perth has contributed to increasing groundwater salinity caused by neutralisation of the acidity in shallow

sediments. The divergent impacts of increasing acidification or increasing Calcium Sulfate (Ca-SO4) dominated salinity, carry different implications for irrigation uses. These will be discussed in the context of climate and water use trends.

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26

Soil Classification Based on Spectral and Environmental Variables

ANDRE CARNIELETTO DOTTO1, RAPHAEL A. VISCARRA ROSSEL1, JOSE A. M.

DEMATTÊ2,RODNEI RIZZO2

1School of Molecular and Life Sciences, Curtin University, Kent Street, Bentley, WA, Australia 6102, Australia

2 Department of Soil Science, College of Agriculture Luiz de Queiroz, University of São Paulo, Ave. Padua Dias, Piracicaba, SP, 13418-900, Brazil

In the last decades, the volume of soil data collection has increased significantly.

Because of that it is now possible to obtain a soil classification using spectral, climate and terrain attributes. The idea was to develop a soil series system, which intends to discriminate soil types according to soil, climate and terrain variables. This new system was called Soil-Environmental Classification. The spectra data from the visible to near infrared (350 – 2500 nm) was applied to obtain information about the soil, and climate and terrain variables to simulate the pedologist knowledge in soil- environment interactions. The most appropriate numbers of classes were achieved by the lowest value of AIC applying the clusters analysis, which was defined with 8 classes. A relationship between the Soil-Environmental Classification and WRB-FAO classes was found. Soil classes like Ferralsols and Nitisols share many soil and environmental characteristics and are difficult to distinguish, however other soil classes, such as Histosols, are relatively distinctive from the others and,

consequently, it was possible to categorize them in a particular Soil-Environmental Class. This innovative soil system facilitated the identification and grouping of soils with similar characteristics due to the use of not only soil but environmental variables for the distinction of the classes. The conceptual characteristics of the 8 Soil-

Environmental Classes were described. The development of Soil-Environmental Classification was conducted to incorporate applicable soil data for agricultural management, with less interference of personal, subjective, empirical knowledge (such as traditional taxonomic systems), and more reliance on automated

measurements by sensors. The development of this soil classification system can assist in the distinction of soil types and serve as a new source of soil information.

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27

Variable Aluminium Toxicity and Root Distribution in Acidic Soil Profiles

PAUL DAMON1, GAUS AZAM2, CRAIG SCANLAN2, CHRIS GAZEY2, ZED RENGEL1

1Soils West, The University of Western Australia, 35 Stirling Hwy, Crawley, WA

2Soils West, Department of Primary Industries and Regional Development, Govt of Western Australia, Northam, WA

Subsoil acidity currently affects two thirds of the arable soils in the WA wheatbelt. At acidic soil pH, aluminium (Al) is solubilised from the solid phase into soil solution, creating a direct and localised toxicity to plant roots. Aluminium toxicity to plant roots constrains crop productivity by reducing root proliferation through soil, and inhibiting the capacity of roots to tolerate other constraints, such as compaction. Ongoing acidification of the subsoil is a direct artefact of the productive farming systems that are required to feed our world’s growing appetite for grain and livestock products.

Soil acidification under cropping systems is primarily attributed to product removal (disturbances in the carbon cycle) and interruption of the nitrogen cycle. Currently, the incorporation of agricultural lime into acidic soil is the only widely applicable strategy for the amelioration of soil acidity in a broad-acre cropping scenario.

However, due to the slow movement of alkalinity in soil, the effects of lime application on soil acidity and Al toxicity are largely localised to the soil volume through which lime had been incorporated. Technical and economic constraints limit the capacity to incorporate lime through the acidic subsoil horizon, and current strategies result in a heterogeneous distribution of lime in the soil profile. As part of Soils West, a

collaboration between The University of WA (UWA) and the Department of Primary Industries and Regional Development (DPIRD), a series of glasshouse and field experiments have characterised the response of wheat root growth and distribution to heterogeneous distribution of lime in acidic, Al-toxic soil. The effects of lime

amendment on root proliferation are highly localised within lime-amended sections of soil, and do not extend beyond. Root length density can be many times greater in lime-amended, compared to adjacent acidic subsoil. Lime amendment of acidic subsoil increased cation uptake by plants in both field and glasshouse experiments, which is attributable to the increased root length within lime-amended soil sections.

Similarly, lime amendment of acidic topsoil increases the uptake of phosphorus by wheat plants, which is associated with increased root length within the lime-amended topsoil layer. Where lime slotting treatments were imposed on 80-cm-deep

constructed soil profiles in large plastic crates, wheat root proliferation in lime- amended slots, and subsequent plant growth response, was dependent on the distance of the crop rows from the lime amended slots. Wheat root proliferation within the lime-amended slots did not increase the capacity of plants to acquire water from the acidic subsoil horizon; however, it did allow roots to access water in deeper soil layers where slots of lime-amended soil traverse an acidic subsoil layer.

Understanding crop response to the variability of pH in the soil profile following lime incorporation will enable better evaluation of existing (and facilitate development of new) lime incorporation strategies.

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iLime - An App for Assessing the Management of Soil Acidity In Agricultural Systems

JAMES FISHER1, JENNI CLAUSEN2, FIONA EVANS3, CHRIS GAZEY2

1Désirée Futures, York Western Australia

2Department of Primary Industries and Regional Development, Northam Western Australia

3Premier’s Midcareer Fellow, Murdoch University and Curtin University

Awareness of soil acidity as a constraint to agricultural production in Western Australia has led to increased use of lime, but rates remain too low to manage existing acidic soil and ongoing acidification. To invest in lime, growers need confidence in likely economic and production responses. This paper describes the development of an acidification calculator, in app form, that was developed with input and feedback to ensure that it would meet the needs and requirements of users.

Information requirements regarding soil acidity and its management were sought from consultants and farmers. Acidification rates, the lime required to remediate soil acidity and to maintain target pH, the return on investment (ROI) for liming and comparisons of lime sources were consistently identified as important. In addition, information needed to be tailored to individual circumstances and available on mobile electronic devices. A draft acidification calculator was developed, based on a

validated model, ‘Optlime’ with an intuitive, user-friendly interface. Further development of the calculator was conducted over three drafts with input from

researchers, consultants and farmers. The ‘iLime’ app, was released in July 2019 and has been promoted widely since. The app is suitable for both iOS and Android and is available as a free download from either the AppStore or Google Play store. Once downloaded, it works completely off-line The app estimates the impact of

applications of lime on soil pH, yield and profitability (including net present value and ROI) over twenty years. Default lime, crop and soil parameters are provided, but these may be customised by the user. Eighty-six percent of respondents (n = 84) to a questionnaire about the app rated it as easy or moderately to use (31% easy, 55%

moderately easy). Respondents expected to use the app to compare lime sources (24%), evaluate economics (27%), investigate deeper placement (12%), priorities paddocks to lime (12%), determine when to re-lime (16%), assess rotational options (5%) or to raise grower awareness (1%) – multiple responses were allowed for this question. The app had been installed by 402 users to 30th September 2019. This app has filled a long-needed gap in the industry for an easy-to-use tool to evaluate the impact of lime applications on soil pH and economic responses. iLime will continue to be enhanced with added features and versions could be developed for other locations.

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Extending the Message of Soil Quality in the Mobile Device Era

CHRIS GAZEY1,3, FRANCES HOYLE2,3

1Department of Primary Industries and Regional Development, 3 Baron-Hay Court, South Perth WA 6151, Australia

2UWA School of Agriculture and Environment (M087), The University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia

3SoilsWest, The University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia

In this day and age, where everyone is time poor, making information easily and quickly available is paramount. However, with a topic as complex and as multi- dimensional as soil quality, a new approach to packaging information that is

evidence-based and relevant to the local environment is required. Apple multimedia digital books provide a platform capable of delivering layers of information on mobile devices. Furthermore, once installed, the books can be viewed independently of internet connection, making them accessible anywhere, anytime. SoilsWest with co- investment from the Grains Research and Development Corporation (GRDC) is producing the Soil Quality series of eBooks which, when complete, will comprise ten stand-alone books. Each book will cover a specific area related to soil quality. The first layer of information is the key messages, delivered in summary points, images and captions. The second layer presents the main narrative supported by interactive widgets. Widgets can be movies, presentations, animations, interactive illustrations, simple calculators and image galleries. Deeper learning is delivered through ‘learn- more’ popups which may be technical information, tutorials and videos providing ‘on- site’ experiences throughout the south-western agricultural region. These popups are activated by keen readers and students via strategically placed buttons, enabling an uncluttered interface to be maintained. A further feature of the books is the

comprehensive glossary, which is accessed by selecting the word of interest to summon additional information without leaving the current page. The series is focused on evidence-based aspects of soil quality relevant to dryland farming in Western Australia. Each book is authored by experts in their field with additional specialist pieces by guest authors. Case studies of on-farm trials, industry and farmer experiences support the technical information. The user interface and examples of the layers of information from the first four books: 1. Constraints to Plant Production, 2. Integrated Soil Management, 3. Soil Organic Matter and 4. Soil Acidity, will be demonstrated. Future topics include: Soil Biology, Soil Compaction, Soil Water Repellence, Sodic and Alkaline Soils, Nutrient Management and Gravel Soil. The ebooks can be found on Apple Books by searching for ‘Soil Quality’ and are available as free downloads.

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30

Subsoil Constraints and Their Management:

Overview from Five Years of R&D

DAVID HALL1, YVETTE OLIVER2, SHAHAB PATHAN1, KAREN HOLMES1, DENNIS van GOOL1, GEOFF ANDERSON1, JEREMY LEMON1, CAROLINE PEEK1, LIZ PETERSEN1, GLENN McDONALD1, ED BARRETT-LENNARD1, DANA MULVANEY1, GLEN RIETHMULLER1, TED GRIFFIN1, PHIL WARD2

1 Department of Primary Industries and Rural Development

2 CSIRO, Floreat

Subsoil constraints cost the grains industry more than $1.6b in lost production each year. Diagnosing and mapping subsoil constraints (SSC) was achieved at a shire scale using the DPIRD soils database and historic surveys. Diagnosing and mapping SSC at a paddock scale was difficult using remotely sensed geophysical data. Poor correlations were found between SSCs and combinations of EM and Gamma irrespective of whether the data was collected by intensive ground surveys or

extensive aerial surveys. Significant progress was made in correlating ground based geophysics with soil profile textural properties which are often related to specific constraints. Similarly, using additional soil texture data from the DPIRD soils

database, soil texture maps were developed giving farm scale resolution across the wheatbelt. Field and laboratory experiments were conducted to increase grain yields on deep water repellent sands, acidic sands, deep gravels, alkaline loams and sodic clays. Most of the trials investigated combinations of tillage and amendments that included gypsum, liming materials, acid sand, composted chicken litter (CCL) and elemental sulphur (ES). In terms of compaction yield responses to deep tillage decreased in order of the pale deep sands ≥ deep acidic sands > shallow duplex >

clays and loams. Crop yield responses to deep tillage and inversion tillage in deep sands were found to last for more than 5 seasons. Natural recompaction was

observed in deep sands. Crop production on acidic subsoils was improved through the incorporation of limesand, native (Morrel) liming materials and through gypsum application. Sodic soils were the most challenging to remediate. Yield responses to gypsum were confined to highly sodic (ESP > 15) clays and loams. Shallow

mounding and water harvesting technology for sodic soils has been shown to

increase crop yields while acidification using elemental S reduced pH and dispersion.

Adding nutrient rich CCL increased crop yields on sodic soils in medium rainfall regions. However, in low rainfall areas the additional nutrients resulted in early biomass production with no yield benefit. The CCL and ES amendments, while not currently profitable, enabled a greater understanding of how soils respond when changed chemically. The development of the ROSA economic model for ranking soil amelioration treatments across a wide range of soil types and climates is a key outcome for this and contributing projects. Soil water information has also benefited from this project through additional ApSoil profiles and improvements to the hosting and display of GRDCs network of soil water probes through http:/mylivefarm.

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Soil Exchangeable Cations Increase Microbial Carbon Use Efficiency and Microbial Growth in Acidic Soils

EMILIA HORN1, EMILY COOLEDGE2, ANNA RAY2, DAVEY JONES1,2, STEVE RUSHTON3, ELIZABETH STOCKDALE4, FRANCES HOYLE1, YOSHI SAWADA1 DANIEL MURPHY1

1SoilsWest, UWA School of Agriculture and Environment, Faculty of Science, The University of Western Australia, Perth WA 6009

2School of Natural Sciences, Environment Centre Wales, Bangor University, Gwynedd, LL57 2UW, UK

3School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK

4Farming Systems Research Group, NIAB, Cambridge, CB3 0LE, UK

Microbial growth and function is influenced by the properties of the surrounding soil where surface chemistry mediates interactions between individual organisms and their local microenvironment. We hypothesised that the addition of exchangeable base cations, necessary for microbial biochemical function, will increase microbial growth in acidic soils. Initially, we showed that the addition of base cations to acidic soils increased microbial carbon (C) use efficiency (CUE). The metabolic partitioning of C into either anabolic (growth and maintenance) or catabolic (respiratory) processes can vary widely between soils. Optimum concentrations of Ca2+ and Mg2+ for maximal microbial CUEin Western Australian soilswere determined using this data. We then investigated if the addition of base cations increased microbial growth (microbial biomass). Limed and non-limed field-plot samples from Merredin, WA were incubated in the laboratory +/- cations and +/- organic matter residue (as a supplementary C food source). Microbial biomass C increased in the non-limed soils with the application of base cations. No response to additional Ca2+ and Mg2+ was observed in the limed soils.

This response was expected as we predicted that there were sufficient inherent base cations in the limed soil for microbial function and growth. Lack of soil organic matter limited microbial biomass C in both the limed and non-limed samples. Finally, we developed a structural equation model (SEM) to explain the regulation of microbial biomass C in a wide range of managed topsoils across semi-arid Australia (n=1987 sites, 0-10 cm depth). Our findings show that the 10-fold variation in microbial biomass across the Western Australian agricultural region can be explained by organic matter (food source), base cations (required for cell biochemistry) and hydrophobicity (restricts access to organic matter and disconnects water films slowing biochemical reactions). We conclude that exchangeable base cations were a positive driver of microbial CUE and soil microbial biomass C. These findings highlight the underpinning importance of pH changes to soil chemistry that regulate microbes in soil; agricultural management practices are typically secondary to the underpinning soil surface chemistry.

References

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