Irrigation Journal Winter 2013 Sample

The Journal FOR Irrigation PROFESSIONALS

Contractors Corner:

Irrigation Australia

Regional Conference, 28 – 30 May

clearing the mist

Irrigation

The Official Journal of Irrigation Australia limiTed

WINTER 2013 • Volume 29 No 02

In This issue: Irrigation in the MIA Know your irrigation water quality Soils and chemistry Professional Development and Training Committee update

w w w.i r r i gat io n.o r g.au

ISSN 0818–9447 PP 100002571

industry directory

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Irrigation-Management Solutions for Agriculture, Turf and the Environment

industries

Contents Features SOILS Feature Soils and Chemistry Know your irrigation water quality Managing soil water repellency in turfgrass on sands Years of soil improvement boosts capsicum yields The Living Soil

IRRIGATION AUSTRALIA’S REGIONAL CONFERENCE

10 12 14 16 18

2013

28-30 May 2013 GRIFFITH, NSW

CONFERENCE Feature Introduction Speakers' summary Preliminary conference program Sponsors list MIA Feature The Murrumbidgee Irrigation Area: a rich history Water company committed to customer service and efficiency The lowdown on irrigation retailing

22 22 24 27

6

28 30 32

Feature ARTICLES Recycled water trial tests diluting recycled water with rainwater Potentiating energy efficiency savings (Part 2) Tasmania - irrigation hotspot Certification - got yours yet?

33 34 46 56

IRRIGATION DIRECTORY 2013

51

Regular Items From the Editor

2

CEO's Message

3

Irrigation Technology: Urban

4

Irrigation Technology: Rural

6

Around Industry

The production of this publication has been funded

by HAL using voluntary contributions from Irrigation Australia Ltd and matched funds from the Australian Government.

16

20

7

Research

20

Bookshelf

36

Professional Development

38

Business Feature

40

State Roundup

41

Contractors Corner

42

ICID Insights

44

Smart Approved Watermark

45

New Products & Services

48

ON THE FRONT COVER Nick and Susan Salvestro grow citrus on their property near Griffith in the Murrumbidgee Irrigation Area in NSW. Irrigation was developed in the MIA a hundred years ago and since then has been central to the MIA community and economy. All roads lead to Griffith from 28 to 30 May, when IAL will be holding Irrigation Australia Regional Conference (see pages 22 – 27).

51

30 51 10 winter 2013

1

IAL office PO Box 863, Mascot NSW 1460 P (02) 8335 4000 F (02) 8335 4099 www.irrigation.org.au CEO: Duane Findley

PUBLISHER www.commstrat.com.au Level 8, 574 St Kilda Road Melbourne VIC 3004 PO Box 6137, St Kilda Rd Central 8008 T (03) 8534 5000 F (03) 9530 8911

EDITORIAL Editor: ANNE CURREY

DESIGN & PRODUCTION Art Director: Annette Epifanidis

ADVERTISING National Sales Manager: Brian Rault E brian.rault@halledit.com.au T (03) 8534 5014

Advertising Advertising in this journal is managed by CommStrat on behalf of Irrigation Australia

Editorial Welcome to the autumn edition of the journal, where we feature soils and water for better irrigation outcomes and irrigation in the Murrumbidgee Irrigation Area (MIA).

Readers will note that the theme of soils and water for better irrigation outcomes is woven into a number of our regular columns as well as there being a number of feature articles. In our irrigation technology: rural article, Sam North from NSW DPI describes an unusual problem that an irrigator identified in his lucerne crop which was irrigated using a centre pivot. The upshot of Sam’s investigation reinforced an important message about matching application rate to infiltration rate, otherwise problems such as waterlogging are likely to arise.

In the irrigation technology: urban article, Shane Holborn from BioScience Australia uses the example of trials done in the turf sod production industry to underline the importance of vegetation cover in maintaining soil stability and controlling erosion during periods of rainfall and when irrigating.

As well as these features, we have articles on the importance of knowing on what basis soil tests are done, e.g. method of EC used, as this has an important bearing on how you interpret the results; describing how a capsicum grower in Queensland improved his soils and the resulting irrigation water and power savings; and the importance of biology in promoting healthy soils.

Our feature on the MIA is included to introduce readers and conference participants to this important irrigation community. Included is an article describing

the fascinating 100-year history of irrigation in the area. We also talked with Joe Catanzariti who manages and part-owns Watertek, an irrigation retail and installation store based in Griffith, about the mainstays of his business and his perspective on the future. And Raveen Jaduram Managing Director at Murrumbidgee Irrigation provides some background on the company and its plans for the future.

For those of you going to the conference or still thinking about it, we include a taster consisting of summaries of four papers being presented at the conference, as well as the preliminary program. The range of papers – policy, technology, research, rural and urban –is very impressive. There is certainly something for everyone in the industry today.

For those of you interested in historical matters, Contractors Corner features a reprint of an article from Irrigation & Green Industry Magazine outlining the development of sprinkler heads over the years by companies such as Rain Bird, Hunter, Toro and Nelson.

It is a textbook description of how the need for water conservation drove innovation upon innovation and led to the variety of sprinklers available in the industry.

I hope you enjoy this edition of your journal. As always, if you have ideas for stories or topics you would like to see us feature, I would love to hear from you.

Anne Currey Editor in Chief

Limited. Irrigation Australia Limited takes no responsibility for the technical accuracy of article content. All contact with businesses and organisations about advertising is made

by CommStrat sales staff, who must identify themselves and the fact that they work for CommStrat on behalf of the IAL. No special

GOT AN OPINION ON AN IRRIGATION ISSUE? we would love to hear what you have to say.

material is concerned. Decisions about editorial

A number of readers have asked for a Letters to the Editor page and here at Irrigation Australia we’d love to hear what you think about an issue in the irrigation industry - any issue.

content and the front cover are the prerogative

Send your letters to Anne at email anne@naturallyresourceful.com.au

consideration will be given to any advertisers as far as editorial content or front cover

of the editor and the National Board of the IAL. Advertising enquiries should be directed to the National Sales Manager.

2

Welcome

chairman’s REPORT The appointment of a chief executive officer is one of the most important decisions that a board makes. The strategic review of IAL commenced by the Board in December 2012 reinforced that the contribution of the CEO will be critical to our future growth.

When CEO Ian Atkinson announced that he was leaving IAL in February to take up the position as CEO of the Nature Foundation SA in Adelaide, the Board started an extensive search for a new CEO. The search attracted a very strong field of candidates for the position and the Board has appointed Duane Findley as IAL’s new CEO. Duane comes to IAL after holding senior positions in Australian Business Limited, PricewaterhouseCoopers, and the Housing Industry Association. He has a Bachelor of Commerce degree and an MBA. Duane has a strong track record of enhancing member and customer services, developing existing businesses and creating new commercial opportunities.

Duane started with IAL in April and he will be at the Irrigation Australia Conference in Griffith so if you are there, take the opportunity to introduce yourself and welcome him to the association.

On the subject of Griffith, after the late move of the 2013 regional conference from Perth to Griffith as a result of the high costs of running the event in WA, the Griffith conference chair Iva Quarisa and her dedicated team have done a great job getting things organised in time.

The conference promises a great program around the theme Better knowledge sharing for better irrigation outcomes. I am particularly pleased to see the strong focus on the IAL special interest groups and committees in the program as they will be the driving force behind our future growth and influence.

The new IAL website has been up and running now for several months and it is attracting a lot of interest. There has been a big jump in the number of visitors to the site and the feedback has been good.

• codes of practice, standards development and certification of irrigation professionals • funding sources.

Actions to advance these priority areas are being developed and refined taking into consideration IAL’s capabilities and resources and collaborative Future strategic challenges and opportunities. The principles being used to guide opportunities this work are that it must: Water is arguably our most precious commodity • increase the professionalism of the industry we need it for survival. With the world population • add value to members. now over seven billion people, the demands During the period without a CEO, I covered part for water in food production, energy, industry, of the role and I learned so much more about IAL. environment and domestic use are ever increasing. It is doing some really good things but not getting These conflicting pressures mean competition this message out and there are so many other things between all water using sectors and highlights the that it can do better. With the new CEO now in need to continue to build the professionalism of the place and the Board focusing less on operationsindustry we are in. related matters and investing more time and effort IAL has entered a new era. The global economic into important strategic issues, I believe IAL is downturn, the reduction in external project funding positioned to go onto bigger and better things. and trends in member associations across Australia The next Board meeting is in Griffith just before are all affecting IAL. The economic conditions the start of the conference, after which there will be have hit many businesses and they are reducing an IAL general meeting. I encourage you to attend the amount spent on training, development and the general meeting to the meet the new CEO marketing. People are asking what IAL can do for Duane Findley, to hear the Board’s thinking on the them and their businesses. future directions of IAL and have the opportunity In December 2012, the Board started a review of to ask questions of the Board and CEO. Check the IAL’s strategies and all aspects of what IAL does and conference program for details. how it does it. The departure of the CEO and the I look forward to meeting you at Griffith. new CEO recruitment has extended the timelines for this review. With Duane Findley’s appointment Ian Moorhouse the Board is finalising the strategic review and IAL Chairman will provide members with the opportunity to comment on the draft outcomes.

Through the review process to date, the Board has reaffirmed IAL’s mission statement as: Leading the development of a professional industry for healthy, sustainable urban and rural communities and their environments.

As well, the Board has identified the need to focus on the five key strategic areas of: • knowledge management • stakeholder engagement • training and professional development

If you have not yet checked it out, I encourage you to do so. The development of the website has been a big undertaking and a strong platform is now in place for the future, with further developments planned.

winter 2013

3

TECHNOLOGY: URBAN Soil loss from excessive runoff An example from the turf grass industry

The loss of soil from cultivated land is a disturbingly common phenomenon. After another Australian summer characterised by heavy rainfall persisting over extended periods of time around many areas of the country, the issue of soil erosion and loss of productive soil has again come to the fore.

Even if soil is exposed for only brief periods the risk can be high as Australia’s notorious summer storms can dump dozens of millimetres of rain in mere hours. This is particularly so on agricultural land where large areas can be left exposed before planting after harvest.

When combined with regular irrigation scheduling, even the most vigilant irrigator can be caught unaware and unintentionally exacerbate soil movement and loss. The danger of this was illustrated in a recent example from a turf farm in Queensland, which showed how startling the comparative scale of soil loss from exposed areas compared to areas with full or even partial vegetative cover. While this example is from a turf production farm, the lessons are no less relevant to other crops and areas of turf such as recreation areas and golf courses.

In turf sod production, both harvested and unharvested areas often coexist in the same paddock, with both needing regular irrigation to maintain growth.

Trial compares soil loss A field trial was conducted on a turf production farm in 2011 comparing soil loss from an area of bare earth, an area of full turf and an area sprigged with turf grass plugs. This happened to coincide with very heavy rain and flooding experienced in South-East Queensland during that summer. In fact, the trial began a week before the rains that brought on the Brisbane and Toowoomba floods, so although the results were derived from an extreme event, it emphasised the risks of exposing bare soil to the erosive powers of water.

The trial area was situated on a hillside with slope varying from 6 to 8%. The three plots ran lengthways (30 x 10 m) down the slope, next to one another.

The bare earth plot (i.e. 0% vegetative cover), the sprigged area (starting at ~10% ground cover and 4

growing into around 85% over the period of the trial) and the fully turfed area (~100% coverage) were established within a few days of each other.

A sediment collection trough was situated at the end of each plot and the soil collected in each was removed regularly providing a cumulative total of soil loss per plot, which was then extrapolated to provide soil loss per hectare figures. The entire trial area was serviced by a centre pivot irrigation system.

ha from the fully vegetated site (see Table 1). The soil loss from the sprigged plots fell predictably between those two figures at 35.8 t/ha and reduced proportionately as the sprigs established and grew in across the site, i.e. soil loss from the sprigged plots decreased as percentage vegetative cover increased.

Soil loss from the sprigged plots decreased as the sprigs established and grew in across the site.

Table 1. Cumulative soil loss by treatment during the trial period (January – February 2011).

Plot treatment

T/ha soil loss

Bare earth

60.5

Sprigged (turf)

35.8

Full cover (turf)

0.55

By the end of the trial, the bare earth plot displayed common signs of erosive forces at play that would be expected from sheet and rill erosion.

The erosion damage to the slope worsened over time, acting to exacerbate soil loss by channelling flow and focussing the erosive power of the water through deepening rills and channels.

The turf plots in the trial consisted of (top to bottom): bare earth, sprigged area and fully turfed areas.

The total soil loss per hectare varied substantially, by a factor of 100 times, between the bare earth area and the fully vegetated turf area. The exposed earth plot was calculated to have lost a staggering 60.5 t/ha compared to a relatively meagre 0.55 t/

Erosion damage to the bare earth plot worsened over time exacerbating soil loss.

The extremely heavy rain over the trial period also provided an interesting observation as a result of a wash-out of one of the plots. A breakthrough

area was discovered on the bund next to the fully vegetated area. Sediment from the exposed earth area upslope of the trial had penetrated the turfed area and was entirely captured within the first 6.5 m of the site. This illustrated the ability of turf grass to halt the movement of entrained material by slowing the flow of water, allowing infiltration and settling of the material and trapping the sediment.

This photo shows the ability of turf grass to act as a barrier to erosive forces by slowing water flow and allowing infiltration of sediments etc.

The nature of turf production can increase the risks of soil loss when soil exposed after harvest is irrigated by centre pivots or booms that continue over bare earth areas and fully turfed areas indiscriminately. Fortunately, many turf producers do not harvest the entire cut face but use a method which leaves strips between cut runs to allow the turf to regrow from the remaining strip. This provides a mechanism to reduce material initially eroded, slow water flow across the site, trap some of the material that might be entrained in the flow as well as promote a rapid return of cover from regrowth.

Leaving strips between cut runs allows turf to regrow from the remaining strip, minimising soil loss.

Strategies to minimise soil loss For turf producers the trial derived a number of strategies to protect against soil loss: • reduce exposed areas as much as possible and ensure vulnerable slopes are at least sprigged before high risk times (times when heavy rainfall could be expected) • schedule harvest times from steeper slopes away from heavy rainfall periods wherever possible • incorporate contour banks and leave turf buffer strips on the contour to reduce soil movement and enhance sediment trapping potential These strategies can be generalised to provide the basis for irrigators of other agricultural crops (or any land manager) to minimise their losses.

The underlying principle behind these results and the prevention of soil loss is groundcover.

For large areas, living plants provide this function most efficiently by reducing the impact of rain drops; reducing the speed of overland flow, allowing infiltration (unlike non-permeable ground covers) of the water and fixing the soil in place by binding it within the roots of the plant.

Landholders need to plan to prevent erosion.

There are general principles that should be incorporated into the property management plan to help in ensure that neither irrigation nor heavy or unexpected rainfall will exacerbate erosion issues.

These include strategies such as: • Ensuring the irrigation falls where it is needed and not on paths, tracks and roads and not when the risk factors are high.

• Managing the flow of water across your property with appropriate drainage and flow ways to control the water and its power.

• Identifying steep areas or areas that are prone to waterlogging and managing irrigation events to ensure minimal erosion or sedimentation occurs.

• Minimising soil disturbance (through cultivation or construction works) and only disturbing the minimum area possible. If work or cultivation needs to occur, ensure it happens at a time of optimal soil moisture content (i.e. not too dry or wet) and be especially vigilant on steep or sloping areas.

• Stabilising roads and tracks, especially if they are exposed areas formed by wear from use.

Of course all of these issues can be managed and minimised by controlling where and reducing how much water is moving around the property.

Most turf producers and irrigators know the benefits of a professionally designed, installed and maintained irrigation system, especially systems that can adjust scheduling to account for current weather conditions. This trial, however, highlights the risks of being caught by an unexpected, sudden weather event and the scale of the losses of productive soil when these events hit unexpectedly – and unfortunately, that is when they often hit hardest.

About the author Shane Holborn has been involved with horticulture industries for over 10 years as Team Leader of the Queensland Government’s Lifestyle Horticulture Research and Extension Team. He now operates his own private research company BioScience Australia and is currently the project leader for the national Erosion Demonstration and Research Facility.

Acknowledgments This trial was led by Turf Queensland and conducted by Queensland Government Lifestyle Horticulture Research Team members Cynthia Carson, Brock Dembowski and Shane Holborn.

The trial was conducted at the property of John Keleher, then President of Turf Queensland and principal of Australian Lawn Concepts.

Shane Holborn, BioScience Australia, Brisbane

TECHNOLOGY: RURAL

Left: The lucerne crop after the application rate was reduced to match infiltration rate. The result was even crop growth across the irrigated area.

MATCH APPLICATION TO infiltration Farmer Phil Snowdon at Finley in the Riverina had a problem with a lucerne crop under one of his centre pivots. Earlier this year he came to Sam North and Adrian Smith, who are based at Deniliquin with NSW DPI, and explained that his crop was patchy; in most of the circle he was getting good production, but there were large patches where production was quite low and they appeared to be getting worse.

The pivot was on a red-brown earth, with 15 to 20 cm of sandy-loam top-soil overlaying a light clay subsoil. This is one of the lighter soil types in the Riverina and is generally well drained, making it ideal for lucerne and sprinkler irrigation. Problems with waterlogging or infiltration are not normally associated with it.

Lucerne had been grown on this circle for seven years before the drought but low water allocations stopped production in 2006. The circle was then out of production for five years before it was sown to wheat in 2011. Heavy rain in early March 2012 flooded the entire circle. The current lucerne stand was sown in early spring 2012, but dry conditions and “windbasting” killed many seedlings and re-sowing was necessary.

Despite this hard start, an inspection of the crop in late February showed it was well established. However, it was also apparent that large patches in the outer third of the circle were drought stressed and production was being affected. A walk through the crop showed that it was more even on the inside of the circle compared to the outside and, while there were no signs of drought stress, there were patches where excess water was ponding.

“The strange thing was that the lucerne in the adjacent circle, which was on the same soil and being irrigated by the same machine, was not patchy and was producing well,” says Sam. “Phil was applying about 70 to 80 mm to each circle over an eight-day period but, to reduce work load and minimise shifting, he was only shifting the machine every four days. So he was putting on 70 to 80 mm in 15 mm lots in four days to two circles.”

Unlike the problem circle, the adjacent circle had been in continuous lucerne production and was irrigated during the drought.

“It sounded like a non-wetting problem with the soil,” explained Sam. 6

Narrowing the cause Non-wetting in soils is caused by an organic coating around sand grains and it has been associated with lucerne.

It was thought that organic matter built up in the top-soil under the lucerne before the drought may not have decomposed (because of the circle was not irrigated) and this, combined with intense drying and wetting (i.e. the flood) cycles, may have caused the soil to become partially non-wetting.

“We did a range of simple field tests to check our theory and see whether we could narrow down what the problem was,” explained Sam. “We asked Phil to sprinkle some water with a wetting agent in it onto both the ‘good’ and ‘poor’ patches using a watering can and when we visited we had a look for differences in slaking/dispersion and in infiltration.”

These tests showed there was no apparent difference in the soils under the good and poor patches: the wetting agent had no effect, the soil did not slake or disperse, and infiltration rates were similar but very slow. As well, the roots on plants dug from good and poor patches were similar, so compacted layers or soil restrictions to root development did not appear to be the issue, though the soil in the poor patches was very dry and the plants wilted. However, soil tests in the two adjacent circles showed the “problem” circle had higher levels of organic carbon.

Phil was wondering whether he might have to apply some sort of ameliorant like gypsum, but Sam and Adrian thought the answer was in the irrigation schedule.

“My conclusion was that organic matter had built up in the previous lucerne crop and the long, hot, dry period without irrigation during the drought, followed by the flood, had resulted in the sandy-loam topsoil becoming partially nonwetting,” said Sam. “It was obvious when we went for a walk that parts of the circle were getting too much water and other parts too little, yet Phil was applying the correct amount of water to meet crop demand in our part of the world in summer.”

It appeared that the sprinkler application rate (15 mm/pass) was higher than the soil infiltration rate and the result was that water ponded on the soil surface.

Although the paddock is very flat, there are still differences in elevation, so the ponded water ran off higher areas, leaving them dry, and into lower areas, causing waterlogging. The problem was worse on the outside of the circle because instantaneous application rates are greater towards the outside of the circle.

Match application rate to infiltration rate The solution was a simple one, in that Sam and Adrian recommended to Phil that he cut the application rate back from 15 mm/pass to 10 mm/pass by running the pivot more quickly, while still applying the 70 to 80 mm needed in each day four-day period. With less water being applied with each pass, it was able to infiltrate the soil and avoid the problems of sheeting and ponding.

“I haven’t seen a problem like this (non-wetting soil) in this area before, but it is a timely reminder that an important aspect of irrigation is to match the system’s application rate to the soil’s infiltration rate or all sorts of problems can result,” said Sam.

around industry Philmac appoints new managing director Australian manufacturer of specialist pipe fittings and valves, Philmac, has recently appointed Mark Nykiel as its new managing director. While his background is in the building and manufacturing industry, Mark has always been aware of the position Philmac has held in the irrigation and rural markets.

“Philmac has always been a strong brand in the supply of high quality specialist pipe fittings and valves into the irrigation market. Working in similar sectors over recent years, I was aware of Philmac’s market position and I feel privileged to be joining a company with such great people and high quality products,” he said.

Mark stated that it was an exciting time to join the team at Philmac, which has strong growth potential sustained by strong support from the Australian market.

“Despite the challenging conditions facing the manufacturing sector and the adverse weather conditions we have been facing, I’m confident that Philmac can continue to deliver value to our Australian customers and end users,” he said.

Since taking up the position in early April, Mark has been busy meeting with staff and customers.

“I would like to acknowledge how important customer feedback is to our business improvement, product innovation and R&D program – making sure we can continue to invest in the innovative solutions Australian farmers and irrigators require.”

For information about Philmac products, phone the Australian Contact Centre, 1800 755 899 or go to website www.philmac.com.au

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around industry Antelco takes a new look at promotion Irrigation has always been a competitive business where finding an advantage in the market place and keeping it has required substantial promotional resources.

In the last year or so, Antelco has been taking a look at how it does promotion and has come up with some innovative ways of advertising its products and standing out from the crowd.

Earlier this year it launched a campaign promoting its eZvalve4. Unlike most campaigns, it didn’t revolve around traditional mediums such as photographs and media releases (although these were certainly part of the campaign), rather it decided to do something very different and create an artwork. The company commissioned an artist to create a colorful garden scene featuring the eZvalve4, and the result looks

like it would be just as suited to hang in a lounge room as on an irrigation shop wall.

The company is also experimenting with expanding the boundaries of its technical offerings on YouTube. Like most irrigation companies, Antelco has included short videos on installing and using products. Following on from its poster artwork, Antelco has taken this a step further and has produced the “Garden Gurus” show promo, and informative “how to install” video instructions. These videos can be viewed on www.antelco.com.

According to Antelco, the aims are to portray quality of product, show how correct performance results from through correct installation, and promote Australian made.

Adelaide desalination plant all go In March the Adelaide desalination plant was all go and fully operational after a successful

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commissioning phase, which has resulted in the supply of more than 14 GL of drinking water to SA residents and businesses. The plant has a 100 GL/year production capacity, up to half of Adelaide’s current drinking water needs.

AdelaideAqua Pty Ltd - a joint venture between TRILITY and ACCIONA Agua – now operates and maintains the Adelaide Desalination Plant under a 20-year contract with the SA Government owned water utility, SA Water. The joint venture took on management responsibilities for the plant 12 December 2012 as part of a handover from the consortium which has designed, built and commissioned the $1.824 billion infrastructure project.

According to SA Water, the fact that Adelaide has experienced lower than expected water inflows into its reservoirs over the past six months underscores the need for a desalination plant which will ensure the State’s population has a robust water supply.

Toro donates new controller to town bowlo The irrigation industry does have its share of community-minded companies committed to the philosophy of giving, especially to groups and organisations which are struggling for resources.

An example is Toro Australia which has just donated a new Irritrol 24-Station Total Control irrigation controller to Narrandera Bowling Club in southern NSW. The club has an old irrigation system of Toro 650 and 785 golf sprinklers on three bowling greens in place (24 heads in total). As they have very little money, greenkeeper Mick Dooley is upgrading the current system slowly (one sprinkler every six months) with Toro 855 Series sprinkler conversion assemblies.

Michael Lenehan, NSW Regional Manager for Toro Irrigation, helped Mick install the first conversion assembly in December 2012.

He said that while he was at the club, he noticed three very old Toro IC8 Dial controllers on the wall dating back about 30 years. One controller was not working anymore and Mick had to manually turn on the sprinkler heads each day as the club had no money to buy a new controller.

In a very practical gesture, Toro decided to donate the new controller which has made everyone’s lives, especially Mick’s, a lot easier.

Mick Dooley, greenkeeper at Nerrandera Bowling Club, was very pleased to have his 30 year-old-controller replaced by Toro Australia.

SOILS feature Soils and Chemistry Why you are measuring or testing a soil requires some knowledge about what you are measuring, which in turn requires knowledge about the type of soil chemistry and the variance or statistical relationships of the elements you are measuring. It also requires that you be clear about what you are testing, e.g. to determine suitability for particular crops.

In simple terms, soils have a solid phase (the inorganic and organic particulates), a liquid phase (water in and around the particulates) and a gas phase (which we are not discussing in this article).

The sample of soil you send to the laboratory is a mixture of solids, liquid and gas.

The solid, liquid and gas phases of the soils are dynamic in their properties over time and depth, although the assumption is that they exist in equilibrium. This dynamic relationship is one reason that it is important to be aware of the chemistry of both the solid and the liquid phases of soil so an appropriate soil monitoring plan can be established.

Testing soil in a solid phase Besides the soil’s physical (particle size, texture and pedal arrangement) measurements, a common reason for measuring the chemistry of a soil is to identify what elements are potentially available for plants to access for optimum growth and at what concentrations they are available.

It is important to measure the cations such as potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), hydrogen (H) (measured as part of CEC until about 1950), manganese (Mn), iron (Fe), copper (Cu), silicon (Si) and (Al) aluminium as well as the anions chlorides (CL), phosphates (PO), sulphate (Su) which are presented as a weight (mg/L, ppm, mmol/L) measurement in reports.

These results need to be related to “standard plant growth experiments” to indicate what nutrients (elements) could or should be added to the soil to achieve the required response from a crop or pasture.

Soil test results reporting measurements based on the weight of the soil (generally 100 g) use an extractant that assumes how a root absorbs elements in a soil in a perfect situation. Most testing methods extract elements at a standard pH of 7 or 8 (which can be different to the soil pH) and then relate them to back to a standard soil bulk density, which is generally assumed to be 1.4 g3.

10

While there are potentially a number of compounding errors within the method of sampling and the calculations, when used with data from standard plant or crop growth experiments they are broadly acceptable.

probes were developed, measurements of dam and supply water became easier (ECw).

When you are looking at soil test results, it is important to know what method of EC was used and how it related back to the required crop yield.

Examples of different ways of measuring EC ECse or ECe Electrical conductivity of the soil as a saturated extract ECw Electrical conductivity of water e.g. tap, dam or irrigation waters EC1:2wgt/wgt Electrical conductivity of the soil in 1 part soil 2 parts water by weight EC1:5wgt/wgt Electrical conductivity of the soil in 1 part soil 5 parts water by weight EC1:2vol/vol Electrical conductivity of the soil in 1 part soil 2 parts water by volume Checking a soil profile and the physical properties is the first step in knowing your soil. Just as important is knowing its chemical properties

Testing soil in liquid phase Some measurements taken from the liquid phase of the soil solution include pH, redox (relates to the amount of oxygen within the soil water or chemistry equilibrium) and electrical conductivity.

Measurements of the soil’s chemical properties most often taken from the liquid phase are pH (the negative log of the hydrogen ion in solution) and salt levels or electrical conductivity.

Electrical conductivity (EC) measures the concentration of salts in the soil solution by measuring the conductivity of the soil water solution. The basic unit of measuring salinity is the electrical conductivity (EC) unit measured as deciSiemens per metre (dS/m) or sometimes microSiemens per centimetre (uS/cm).

There are different ways to measure EC. Early work used the saturated extract (water oozing from the soil paste) of the soil water (notations ECse).

Later, EC was measured by adding water to the soil so a probe could easily measure the solute (i.e. 1 part water to 5 parts water e.g. EC1:5water). As EC

EC1:5vol/vol Electrical conductivity of the soil in 1 part soil 5 parts water by volume ECem38 Electrical conductivity of the soil using an EM38 ECr Electrical conductivity of the rainwater Note. These are examples and other EC measurements can be used.

The gross quantity of salts in the soil water can also reported as a “weight”, e.g. parts per million (ppm) or milligrams per litre (mg/L). The estimate of concentration in ppm is generally made by converting from EC by multiplying EC by a factor of 540, 640, 670, or 720, subject to the convention used by the testing organisation, e.g. an EC1:5 of 1 dS/m could equivalent to 540, 640, 670 or 720 ppm.

We believe that the popular literature has not readily explained the relationship or differences between these different EC measurements.

Salinity and plant growth It is important to remember that the area around plant roots is a dynamic system which changes constantly with temperature, moisture content

(as a result of irrigation, rainfall etc), plant growth and soil pedology. For example, salinity caused by salt concentration in the soil will change as particular ions are absorbed by plants, and added water (rainfall and irrigation) will change the pH and the concentration of salts and pH. Salinity in soil water affects plant growth in two main ways, as follows: 1. A concentration of salts increases water potential (energy), effectively decreasing the amount of water available to the plant (not the volume of water in the soil).

2. An increase in the concentration of a particular element or a number of elements in the soil water which then affect the availability of nutrients for plants or directly affect plant growth; e.g. high sodium levels.

Water potential in the soil is a combination of the matric (soil particles) potential, osmotic (salts) potential, gravitational (this is due to gravity) potential and other potentials such as air pressure.

A number of fudge factors have been use to convert EC to other parameters, as shown in the formulas below.

(Water) Osmotic potential -0.36* (mmho/ cm) ≈ ψ° (Osmotic potential) bar Range 3-30 mmhos Total cations or anions from EC Total cations or anions (mEq/L) ≈ 10*EC (mmho/cm) Total dissolved salts (mg\L)from EC TDS (mg/L) ≈0.64* *EC(mmho/cm) Ionic strength (mole per litre) = ECse X 0.013

Formula for EC to Osmotic pressure, total cations and TDS. Bresler, E., McNeal, B. L., and Carter, D. L. (1982). Saline and sodic soils. Advances Series in Agricultural Science 10. (Springer-Verlag. Berlin Heidelberg New York).

Whatever the EC is measured at, it needs to be related to the ECse (saturated extract) in the soil.

Some early work in NSW was done to estimate multipliers for a range of different soil textures. The work produced the multiplier factors for different soil types, where ECse = EC 1:5 x multiplier factor.

With some knowledge, these fudge factors are useful monitoring measurement, e.g. if a soil or irrigation water (EC1;5 or ECw) is 1 dS/m, for sand it could be equivalent to ECse 17 dS/m, or a heavy clay 6 dS/m, based on the above table. Crop

Soil texture Multiplier factor Loamy sand, clayey sand, sand

17

Sandy loam, fine sandy loam, light sandy clay loam

11

Loam, loam fine sand, silt loam, sandy clay loam

10

Clay loam, silty clay loam, sandy clay, light clay, etc

9

Light medium clay 8 Medium clay

7

Heavy clay 6 Crop yield reduction is related to the ECse.

charts relating to yield loss can then be referred to for making decisions about plant types, fertilisers and management.

High and low salt levels (in the liquid phase) can affect soil structure. Slaking or sometimes dispersion of soil can be attributed to higher salt levels; an example of low salt levels is the irrigation of Vertisol soils in the Gatton and Lockyer valleys in Queensland. When it rains (ECw < 0.5 dS/m), the water ponds on the surface of these soil types. Bore irrigation water with a higher concentration of salts changes the total salt concentration of the water, aggregating soil particles and aiding movement of this excess surface water through the soil profile.

Soil chemistry can be as confusing as it is as complex but if you focus on why you are measuring something and what you are attempting to measure (the solid or liquid phase), it will be easier to interpret soil test results.

Soil pH – test it regularly More than twenty methods have been used worldwide to measure “soil” pH, which is a measurement of the hydrogen ion in the soil water (liquid phase). Each method will give a slight variation to the “measured pH figure”.

As the soil dries, the soil chemistry (or very simplistically – cation/anion exchange) can influence the pH reading. As you irrigate (town water pH 7 to 8 for Sydney) or it rains (average rainfall pH 4 .5 with a range from 4 to 8) this saturation of the soil water will change the pH reading of the soil water. This is one reason why the pH of soil water needs to be measured regularly, preferably at the same time each period (generally a year) and using the same method, to allow for comparison. pH comparison pH1:5 water range 5.0 – 5.4 = pH CaCl 4.6

David McKechnie, Sydney and Jeremy Cape, CapeAbility Pty Ltd

Measuring water repellency and soil pH and root depth on a golf green when changing holes (not a common method at all). The second photo shows barium sulphate (white powder), which reduces water repellency of the soil surface allowing the indicator solution to “wet the soil”. Lime also aids wetting of soils.

winter 2013

11