Scoping study of soil properties and paddock zones in the Harden-Murrumburrah Shire

Ben Macdonald, CSIRO Agriculture and Food

Mark Glover, CSIRO Land and Water

Julia Jasonsmith, Murrang Earth Sciences

AGRICULTURE AND FOOD

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2

Executive summary

This report represents phase two of research investigating soil properties and paddock zones at

“Fairview” (the site), a property in the Harden-Murrumburrah area. Soil samples were collected

from three sites selected based on landscape position (“crest”, “midslope”, and “lower-slope”) and

located on a gentle slope under wheat. A brown Dermosol occurred at the top of slope at the site.

This transitioned to a brown Sodosol in a mid-slope landscape position, and a slightly vertic greyish

brown Sodosol on the lower slope landscape position. This transition is typical of the Binalong Soil

Landscapes which covers 178 000 ha (3.5%) of the Goulburn soil map sheet, with Binalong the

dominant soil landscape between Binalong, Yass, and Boorowa. These two main soil types,

Dermosol and Sodosol, cover 1.6, and 13% of Australia respectively. There is a slight colour

separation with reddish brown soils at the crest and greyer brown soils in lower slopes at the site.

This colour difference, in the top of the B horizon, coupled with the presence or absence of a

bleached A2 horizon, can be used as a quick diagnostic tool in the field to assess and identify

boundaries between soil types.

The largest wheat yield of 7t ha-1 was measured on the brown Dermosol at the top of slope and 4t

ha-1 on the Sodosol at the lower slope landscape position. This yield response is likely to be a

function of improved drainage in the crest and upper-slope landscape positions and the increasing

chemical (sodicity, salinity) and physical (structural, affecting root penetration and drainage) soil

constraints observed in the lower slope positions. Seasonal responses to soil-water interplay need

to be considered to optimise future management decisions with regards to these variations.

In terms of the topsoils (A horizons), all soil types had an acidic (pH <5.5) A2 horizon at a depth of

10 to 30 cm. This is symptomatic of the soil acidification common in the wheat belt of Australia,

resulting from the combination of natural soil forming processes and by agronomic management

practices. The presence of water extractable aluminium was most severe in the A2 horizon,

reflecting increased soil weathering as a result of acidity. Such combinations of acidity and

aluminium in the subsoil can have large effects on the yield of wheat.

All subsoil (B horizons) root zones in the Dermosol, brown sodosol, and grey sodosol, were very

dense, so drainage, root penetration is restricted and affects crop yield. These subsoils were also

sodic and alkaline as a result of parent material chemistry and soil forming processes. Organic

matter retention, minimised and controlled traffic, improved bioturbation, and the incorporation of

deep rooted perennials, gypsum and annuals into the crop sequence are recommended options.

Deep ripping of these soils is not recommended due to the generally steep slopes and the dispersive

soils.The range of soil nutrients, including calcium and sulfur, were considered likely to be deficient

in the soils at Fairview.

The results of this research show soil physio-chemical properties affect wheat yield and how more

efficient use of fertilisers can improve yields within the soils in question. This knowledge is critical if

soils are to be managed appropriately in different climate scenarios and under differing fertiliser

regimes. An understanding of the physiochemical nature of the soil, its function, its relationship to

landscape position and soil water characteristics, are important learning opportunities from this

work.

3

1 Introduction

This report represents phase two of research investigating soil properties and paddock zones at

“Fairview” (the site), a property in the Harden-Murrumburrah area. Phase one of this research

assessed how efficiently nitrogen added to the soil as variably applied fertiliser was taken up by

wheat crops, and examined how well soil attributes such as electrical conductivity and soil pH can

be measured using precision agriculture technology (Macdonald et al., 2016). The phase one

research raised questions regarding how physiochemical properties influenced soil nitrogen and

water use efficiency, and these were driving yield in wheat. Preliminary results indicated that soil

data collected using precision agriculture were useful indicators of soil quality but further work was

needed to understand how useful and the limits of this accuracy.

Phase two of the research, this phase, aims to understand the soil properties driving wheat yield in

the Harden-Murrumburrah area. This understanding will reduce the environmental impact of

unused/unnecessarily added fertilisers to farms in the area and help to identify the importance soil

testing undertaken by farmers in the future. This research focuses on soil nutrients including organic

carbon, phosphorous, sulfur, calcium, magnesium, sodium, potassium, zinc, copper, and boron, as

the drivers of yield variation. Soil quality parameters such as electrical conductivity, acidity,

exchangeable sodium percentage, cation exchange capacity, and bulk density are also investigated.

The following objectives will be addressed to meet the aims of this report:

1. Identify the concentration and mass of nutrients in the soil

2. Identify the concentration and mass of nutrients being exported from the Site in wheat grain

3. Identify nutrients that may be limiting wheat growth

4. Identify soil quality parameters (e.g. pH, EC, bulk density) that may be limiting wheat growth

The work undertaken to address these objectives will now be presented.

4

2 Methods

This research involved the collection of soil and wheat samples. A description of soil sample

collection methods is followed by those used for wheat.

2.1. Soils

The Fairview property is 13 km south-south east of Boorowa and 15 km north-north west of Binalong

in New South Wales (Figure 2-1). The soil samples were collected from three sites selected based

on landscape position (“crest”, “midslope”, and “lower-slope”) and located on a gentle slope under

wheat. Soil sampling was done on 19th December, and 21st and 22nd December 2015 using a

mechanical push-tube corer to collect samples at set depth intervals (0-5, 5-15, 15-25, 25-40, 40-60,

60-80, 80-105, 105-135, 135-165, and 165-190 cm). Samples for chemical analyses were collected

from a single core divided in the field into the set depth increments. The samples were bagged,

dried at 60oC in the laboratory and then finely ground using a puck mill. The samples were further

divided for analysis using the following USEPA and Australian methods (Rayment, et al., 2011,

USEPA, 2007), and described in the following sections.

Three additional cores were removed for bulk density and volumetric water measurements using

methods outlined below.

Figure 2-1 Location of “Fairview” within a) Australia; b) South-Eastern Australia; and c) the Harden-Murrumburrah area; and d) the location of sites along the catena within the paddock in which research was conducted

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2.1.1 Bulk density

Bulk density samples were collected from each site at each location by placing a steel ring of a known

volume onto the soil which was to be sampled. This ring was then hammered into the soil until it

was filled. The ring and the soil contained within it were removed from the soil. The soil at the top

and bottom of the sample ring was carefully trimmed off using a palette knife. The soil was then

extracted from the ring, weighed, and placed into a pre-weighed and pre-labelled paper bag. The

sample was dried in the lab at 105 OC and reweighed for water content. Bulk density was calculated

according to the method in McKenzie, et al. (2002).

2.1.2 Total cation concentrations

Samples were digested in a microwave oven using a 3:1 mixture of nitric acid and hydrochloric acid

(US EPA Method 3051A). The resulting solution was then analysed for cations using an inductively

coupled plasma optical emission spectrometer (ICP-OES).

2.1.3 Exchangeable cation concentration and cation exchange capacity

The concentration of exchangeable cations and cation exchange capacity (CEC) was determined

using Method 15D2, whereby samples were pre-treated for soluble salts. Exchangeable cations

were then extracted using NH4Cl solution at either pH 7.0 or pH 8.5, depending on whether soils

were of neutral or basic pH respectively. The concentration of calcium magnesium, sodium, and

potassium were then measured using Flame Atomic Absorption Spectrometry. Cation exchange

capacity ammonium and chloride were analysed using Flow Injection Analyser.

2.1.4 Extractable phosphorous concentrations

Extractable phosphorus was determined by segmented flow colorimetry (Lachat QuikChem 8500

series 2) following Colwell extraction using 0.5M NaHCO3 at pH 8.5 (Method 9B2).

2.1.5 Acidity and electrical conductivity

Soil acidity (pH) and electrical conductivity (EC) were determined on 1:5 soil/water extracts of

subsamples, whereby 10 g air dried soil was shaken with 50 mL water for one hour and then left to

settle for 20 minutes (Method 3A1). Electrical conductivity followed by pH was determined on the

resulting supernatant using a Metrohm 815 Robotic Processor.

2.1.6 Water extracted salt concentrations

Water extracted salt concentrations were determined on 1:5 soil/water extracts prepared as

described in Section 2.1.5 (Method M). Salt concentrations were measured using ICP-OES, while

anions were measured using a Dionex ICS-250 ion chromatographer.

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2.1.7 Soil landscapes

The soil profiles were classified using the Australian Soil Classification (ASC) scheme (Isbell, 1996)

and classification of the soil landscapes was based on Hird (1991)1.

2.1.8 Mass calculations and data in-filling

The mass of soil (ms(layer)) in each layer of soil was calculated using Equation 1:

Equation 1.

𝑚𝑠(𝑙𝑎𝑦𝑒𝑟)(𝑡 ℎ𝑎)⁄ =(𝑑𝑙𝑎𝑦𝑒𝑟(𝑐𝑚) × 100 000 000 𝑐𝑚2/ℎ𝑎) × 𝐵𝐷(𝑔 𝑐𝑚3⁄ )

1 000 000 (𝑔 𝑡)⁄

where d(layer) is the depth of the soil layer in centimetres and BD is the bulk density of the soil in

grams per cm3.

The mass of analyte (mx(layer)) in each layer of soil was calculated using Equation 2:

Equation 2.

𝑚𝑥(𝑙𝑎𝑦𝑒𝑟) 𝑘𝑔 ℎ𝑎⁄ =𝑚𝑠(𝑙𝑎𝑦𝑒𝑟)(𝑡 ℎ𝑎)⁄ ×𝑐𝑥(𝑙𝑎𝑦𝑒𝑟)(𝑚𝑔 𝑘𝑔⁄ )

1000 (𝑘𝑔 𝑡⁄ )

where Cx(layer) is the mean concentration of the analyte within the soil layer.

Data with NA values were replaced with values 0.65 times the laboratory limit of reporting prior to their plotting (e.g. Güler et al., 2002; Buccianti et al. 2014; Olsen et al., 2012; Palarea-Albaladejo and Martín-Fernández, 2013; Halsel 2012 in: Palarea-Albaladejo et al., 2013).

2.2. Plants

Straw and grain were separated from the wheat samples collected. These were then weighed before

being sent to CSIRO’s Adelaide Laboratory for analyses of cations by acid digestion (US EPA Method

3051A).

1 Availability of soil chemical data has altered our ASC classification of the mid-slope soil type from a “Chromosol”, as described in the “Phase One” report, to a Sodosol describe here. This is due to the fact that upper 0.2m B horizon Exchangeable Sodium Percentage (ESP) was >6% in the mid-slope site

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3 Results and discussion

3.1. Soil Landscapes

The site is underlain by Douro Volcanics (Hird, 1991). Soils were formed in situ from alluvial-colluvial

material derived from this parent material, with Quaternary aeolian deposition also contributing to

soil development, especially at the top of slope. The soil sampling sequence (catena) sampled is set

on a gently undulating rise with a local relief of 9-30m and gradients of 3 to 10% (Speight, J.G., 2009).

A brown Dermosol occurred at the top of slope at the site (Figure 3-1). This transitions to a brown

Sodosol and then a slightly vertic greyish brown Sodosol on the lower slope. This transition is typical

of the Binalong Soil Landscapes which covers 178 000 ha (3.5%) of the Goulburn soil map sheet,

with Binalong the dominant soil landscape between Binalong, Yass, and Boorowa (3.5%, Hird, 1991).

Dermosols and Sodosols cover 1.6 and 13% of Australia respectively (Isbell, et al., 1997). There is a

slight colour separation with reddish brown soils at the crest and greyish brown soils in lower slopes

at the site. This colour difference, in the top of the B horizon, coupled with the presence or absence

of a bleached A2 horizon, can be used as a quick diagnostic tool to assess and identify boundaries

between soil types within the field. (Figure 3-2).

Figure 3-1 Soil landscape schematic for the Fairview site. The location of sampling sites: C=crest; MS=mid-slope

and LS=lower-slope, is shown

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Figure 3-2 Three soil cores collected from the Fairview site. A pair of 1 m cores are shown for each landscape

position (labelled), with the lower section placed below the upper section

3.2. Crop Yield

Crop yield varied along the soil catena as a function of soil type (Figure 3-3). The highest wheat yield

was achieved on the brown Dermosol at the top of slope and 2.5 t ha-1 lower on the Sodosol at the

lower slope. This variation leads to a number of conclusions and questions:

1. Dermosols are high yielding relative to the other soils.

a. What soil management should be undertaken to maintain or increase plant

productivity and soil health?

2. There is a significant yield gap between crops grown on a Dermosol versus the Sodosol.

a. Are there soil management strategies to overcome this yield gap?

b. Should management strategies be tailored to the different soil types?

Figure 3-3 Crop yield on the different soil types with the catena at Fairview

Grain Yield (t ha-1

)

0 2 4 6 8

Crest:- Dermosol

Midslope:- Sodosol

Lower slope:- Sodosol

Yeild gap due tosoil constraints

How to maintain soil health to achieve the maximum yield and and the value of the soil?

Are there management tools to overcome soil contraints to increase yield and the value of the soil ?

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3.3. Soil chemistry

All soil types had an acidic (pH <5.5) A2 horizon at a depth of 10 to 30 cm (Figure 3-4). This is

symptomatic of the soil acidification common within the wheat belt of Australia, resulting from the

combination of natural soil forming processes and by agronomic management

practices (Scott, et al., 2007, Scott, et al., 2000). Acidity can be controlled by the application of lime.

The surface soil at all locations was neutral reflecting the periodic liming that occurs at the site. The

acidity present in the A2, however, indicates that thus far the lime applications are not effective

enough to ameliorate acidity in the subsoil. This is considered to be a result either of poor lime

transport to the subsoil or acidification at levels exceeding the neutralising capacity of the lime

added. It is not clear from the data which of these was driving the acidity measured during this

research. Both the Sodosols became alkaline (pH>8) below 100 cm in the subsoil, whereas the

Dermosol was neutral at depths of 40 to 150 cm.

Water extractable aluminium was greater in the A2 horizon, reflecting increased soil weathering as

a result of acidity (Figure 3-4). Such combinations of acidity and aluminium in the subsoil can have

large effects on the yield of wheat (Scott, et al., 1997). Lucerne yield increased from 1.7 to

10.5 t ha-1, for example, when the acidity at depths of 20 to 40 cm was ameliorated

(Scott, et al., 2000). The treatment of subsoil acidity and aluminium is very challenging but may be

worth a cost benefit analysis (Fenton, G., 2003).

During the 2015 season, 100 kg ha-1 of nitrogen was applied to the field as di-ammonium phosphate

(DAP) and 130 kg ha-1 as urea. The conversion of the nitrogen in these fertilisers to the nitrate used

by plants (i.e. nitrification) produces acidity. In a worst-case scenario, where all the nitrogen is

converted to nitrate, 330 kg of lime would be required per hectare to offset the acidity produced

under the current nitrogen fertilising regime. A general rule of thumb is to assume 50 kg of the

nitrogen from fertiliser is lost through degassing before it enters the soil, however, with 195 kg lime

ha-1 instead more likely required.

The Sodosol soil types had very dense subsoils that will restrict root penetration, plant yield, water

drainage, and cause water logging (Figure 3-4). The poor crop growth noted at the site in the wet

winter of 2016 within the sodosol areas is evidence of this water logging. The Sodosol on the lower

slope was highly dense and is affected by periodic water logging. Agronomic practice on all soil types

should be aimed at reducing soil compaction. Deep ripping is not recommended, however, due to

the slope and the dispersive soils. Organic matter retention, gypsum applications, minimised and

controlled traffic, and the incorporation of deep rooted perennials and annuals into the crop

sequence are recommended options.

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Figure 3-4 (a) Soil pH; (b) water extracted aluminium; (c) bulk density, where points in the pink section are very

dense and those in the violet highly dense clays (Hazelton and Murphy, 2016); and (d) cation exchange

capacity, as a function of depth at sampling sites within “Fairview”

Another alternative to improve soil structure and mixing (i.e. decrease soil density) is to increase

bioturbation by fauna such as ants, termites, and worms. Bioturbation has been shown to increase

yield in a number of crops (Tian, et al., 2001), with wheat yields in Western Australian increased by

40% using this method (Evans, et al., 2011). Although it is not clear why this is the case, soil fauna

will improve porosity and nutrient availability. Soil fauna is adversely affected herbicide and

pesticide use, and removal of crop residues, with the costs and benefits increased bioturbation

would have needing to be holistically evaluated.

The soils had a low (between 0 and 20 cmol(+)/kg) cation exchange capacity (Figure 3-4). This is

caused by both the type of clay material in the soil and the low concentration of organic matter. The

low cation exchange capacity indicates soils with a reduced capacity to retain nutrients and hence

these soils have a relative small storage capacity for most nutrients applied as fertiliser.

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3.3.1 Sodium and sodicity

With the exception of the top 10 cm, soils along the Fairview catena were sodic, although not saline

(Figure 3-5). The acidic-sodic and alkaline sodic horizons in the Sodosols had weak structure and

physical properties that promote leaching in topsoils and lead to water logging. Alkalinity can induce

severe soil structural problems compared to neutral soils (Rengasamy, 2010), and is likely to be

contributing to the declining physical properties (i.e. increased bulk density and decreased porosity)

of the Sodosol, as well as lower wheat yields, compared to the Dermosol at the top of slope. Mean

exchangeable sodium concentrations ranged between 0.4 and 3.8 cmol(+) kg-1 at the site (Figure 3-5).

Sodicity increased with depth in all soil types, with this trend strongest in the Sodosols (Figure 3-6).

The Sodosols had four times more sodium than the Dermosol (mg/kg). This reflects the transport

and deposition of sodium by leaching from the upper slope and transfer to the subsoils in lower

slope positions. There is a large store of water extractable sodium in the B horizon of the Sodosols,

which is considered likely to be affecting yield (Figure 3-5). Sodium concentrations in grain and straw

increased as a function of sodium concentration in the soil.

Figure 3-5 Exchangeable and water extractable sodium content (kg ha-1) in each sampled layer. Crest=Dermosol;

Mid-slope=Sodosol and Lower-slope=Sodosol

Water extractable sodium (kg ha-1)

0 100 200 300 400 500 600 700

De

pth

(cm

)

0

50

100

150

200

Dermosol ChromosolSodosol

Exchangable sodium (kg ha-1)

0 5 10 15 20 25

De

pth

(cm

)

0

50

100

150

200

DermosolChromosolSodosol

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Figure 3-6 Exchangeable sodium percentage. Soils with values above 6 are considered sodic and are indicated by

points in the pink section. Crest=Dermosol; Mid-slope=Sodosol and Lower-slope=Sodosol

3.3.2 Calcium

Acid soils with low CEC in higher rainfall environments can have calcium deficiency, although it is

likely the plants at Fairview are accessing calcium from depths of 0 to 10 cm and below the acidic

A2 horizon (Bruce, 1999). The A1 horizon has greater calcium than the A2 horizon due to the historic

lime applications at the site (Figure 3-7). The availability of exchangeable calcium in the acidic A2

horizon was marginal, with ( 0.7 to 1.0 cmol+ kg-1 (Figure 3-8) ). Some water extractable calcium may

have leached down into the A2 horizon, but exchangeable calcium is less in this horizon compared

to the A1 and B horizons. This is most likely due to the presence of aluminium in the acidic A2

horizon.

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Figure 3-7 (a) Mean calcium concentration in the grain and straw; (b) exchangeable soil calcium

concentrations; (c) calcium removal in the grain; and (d) calcium removal in straw for the Fairview

soil catena. Crest=Dermosol; Mid-slope=Sodosol and Lower-slope=Sodosol

Figure 3-8 Exchangeable and water extractable calcium content (kg ha-1) in each sampled layer. Crest=Dermosol;

Mid-slope=Sodosol and Lower-slope=Sodosol

Water extractable calcium (kg ha-1)

0 20 40 60 80 100 120 140 160 180 200

De

pth

(cm

)

0

50

100

150

200

Dermosol ChromosolSodosol

Exchangable calcium (kg ha-1)

0 10 20 30 40 50

De

pth

(cm

)

0

50

100

150

200

DermosolChromosolSodosol

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3.3.3 Magnesium

Exchangeable soil magnesium concentrations in the surface soil (0 to 5 cm) and in the acidic A2

(5 to 30 cm) at all sites was deficient (Figure 3-9). The concentration of magnesium in the grain and

the straw were similar for all sites. The highest magnesium removal from the site was at the top of

the slope where on average 6.1 kg of magnesium was removed from soils per hectare in grain, and

on average 3.6 kg of magnesium removed from the soil and stored in the straw. The lowest

magnesium removal occurred at the bottom of slope, where on average 5.6 kg/ha was removed in

grain and 3.2 kg/ha in straw.

Figure 3-9 (a) Mean magnesium concentration in grain and straw; (b) exchangeable soil magnesium

concentration; (c) magnesium removal in grain; and (d) magnesium removal in straw for the Fairview

soil catena. Crest = Dermosol; Mid-slope = Sodosol and Lower-slope =Sodosol

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3.3.4 Potassium

The potassium content of the soil was high in the Dermosol but only moderate in the acid A2

horizons of the Sodosols according to the threshold defined by Gourley (1999). The highest

concentrations of exchangeable potassium occurred in surface soils at the top of slope, with lower

concentrations in the mid and lower slopes (Figure 3-10). The mean concentration of potassium in

the straw was lowest on the Sodosol in the lowest landscape positions. The highest potassium

removal was at the top of the slope where on average 19.1 kg of potassium was removed from soils

per hectare in grain and on average 198 kg of potassium removed in straw. The lowest potassium

removal occurred at the lower-slope, where on average 14.4 kg/ha was removed in grain and

97kg/ha in straw.

Figure 3-10 (a) Mean potassium concentrations in grain and straw; (b) exchangeable soil potassium

concentrations; (c) potassium removal in grain; and (d) potassium removal in straw for the Fairview

soil catena. Crest=Dermosol; Mid-slope=Sodosol and Lower-slope=Sodosol

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3.3.5 Phosphorus

Surface soils (0 to 20cm) had sufficient phosphorous (>45 mg/kg) for grain crops (Figure 3-11), but

the subsoil had phosphorous concentrations that may limit growth (<45 mg/kg, Moody, et al., 1999).

While this source of phosphorous is adequate it has been shown that wheat crops do exploit subsoil

phosphorous in wetter years (McBeath, et al., 2012). At Fairview, the limited subsoil phosphorous

may be a constraint, however sodicity and waterlogging may also restrict plant access nutrients from

deeper layers.

The highest rates of phosphorous removal were at the top of the slope where on average 16.6 kg/ha

of phosphorous was removed from soils in grain and on average 5 kg per hectare in straw. The

lowest phosphorous removal occurred at the bottom of slope, where on average 12.4 kg/ha was

removed in grain and 4.7 kg ha-1 in straw. The amount of P removed from the soil in the grain and

straw was replaced by the 100 kg ha-1 DAP application at the start of the season in the Dermosol

and the midslope Sodosol. An excess of P was supplied to the lower slope Sodosol.

Figure 3-11 (a) Mean phosphorus concentration in the grain and straw; (b) Colwell phosphorus concentration in

soils; (c) phosphorus removal in grain; and (d) phosphorous removal in straw, for the Fairview soil

catena. Crest=Dermosol; Midslope=Sodosol and Lower-slope=Sodosol

17

3.3.6 Trace Nutrients

Soil tests for trace elements are difficult to interpret because they are not a reliable predictor of

pasture or crop responses. However, they are a tool to assist in assessing whether further

investigation is required. Trace element analysis are fundamental for mass-balance calculations and

the quantification of nutrient fluxes. In this study, we have used both tissue uptake and soil testing

to investigate trace nutrients at the site. However, a combination of tissue testing and strip tests is

needed to resolve exactly which elements determine micronutrient constraints. Total soil content

of trace elements does not indicate the amounts available for plant growth, only the total pool size.

Sulfur

Scott, et al. (2007) found that most (73 – 80%) soils sampled in the south west slopes of New South

Wales and the Riverina were low to marginal in sulfur (<10 mg kg-1 KCl-40 method). Water

extractable sulfur, which will underestimate plant response, was between < 10 mg kg-1 for most of

the profile at the site (Figure 3-12). This suggests that this element may be limiting (Ried, et al.,

2004), although portions of the soil profile have levels of sulfur (>10 mg kg-1). The change of fertiliser

manufacturing techniques in the 1970s that resulted in the removal of sulfur impurities is likely to

have lead to soil sulfur deficiency in Australian farming systems, and has been observed identified

in canola (Scott, et al., 2007). There was no difference in the mean sulfur concentration of the grain

and the straw between each of the sampled locations which indicating sulfur uptake was not limited.

Figure 3-12 (a) Mean sulfur concentration in the grain and straw; (b) exchangeable soil sulfur concentration; (c)

sulfur removal in grain; and (d) sulfur removal in straw for the Fairview soil catena. Crest=Dermosol;

Midslope=Sodosol and Lower-slope=Sodosol

18

The largest sulfur removal was at the top of the slope where on average 7.8 kg ha-1 of sulfur was

removed from soils. The smallest amount of sulfur removal occurred at the bottom of slope, where

on average 5.7 kg ha-1 was removed in grain. The sulfur that remained in the straw was 6.2 to

3.6 kg ha-1 per hectare in straw. Overall in the soil profile there is 1.3 to 1.9 t ha-1 of sulfur per

hectare, most of which was concentrated in the B horizon. There was only 26 kg ha-1 of sulfur in the

A1 horzion within all soils and 27 kg sulfur ha-1 in the acidic A2 horizon. To replace the sulfur removed

by the grain (~7 kg S ha-1) 30 kg gypsum ha-1 would need to be applied to every wheat crop. However,

larger inputs of gypsum would be required in a typical 2-3 year cropping/pasture rotation to meet

requirements for sulfur.

3.3.7 Zinc

Overall there is a large total zinc store in the surface soil (18 kg/ha) relative to the amount removed

by the crop and the average concentration in the soil profile was approximately 1.5 t/ha

(Figure 3-13). The surface soils appear to be deficient in zinc (< 1 mg/kg, Ried, et al., 2004). Similar

to the other trace elements, a large proportion of zinc was held in the B horizon, which may be

inaccessible to plants. It is not clear whether zinc supply is affecting plant growth.

Figure 3-13 (a) Mean zinc concentration in the grain and straw; (b) exchangeable soil boron

concentration; (c) boron removal in grain; and (d) boron removal in straw for the Fairview soil catena.

Crest=Dermosol; Midslope=Sodosol and Lower-slope=Sodosol

19

3.3.8 Boron

The results indicate that the total boron store in the surface soil does not exceed 52 kg ha-1 and the

average soil profile does not exceed approximately 3 t ha-1 (Figure 3.14). This pool is large compared

to the amount of boron removed by the crop. The water extractable boron appears to be below

desirable limits (Ried, et al., 2004) and further investigations are required. Similar to the other

elements a large proportion is held in the B horizon, which may be inaccessible to plants. It is not

clear if boron supply is affecting plant growth. Further work is required to quantify the boron fluxes

in these landscapes.

3.3.9 Copper

Overall there was a large total copper store in the surface soil (13 kg ha-1) and average soil profile

has approximately 1.2 t ha-1 which is large relative to amount removed by the plant. The copper

concentration is below desirable limits (<2 mg/kg, Ried, et al., 2004) and further investigations are

required. Similar to the other trace elements a large proportion is held in the B horizon, which may

be inaccessible to plants (Figure 3-15). It is not clear whether copper supply is affecting plant growth.

Figure 3-14 (a) Mean boron concentration in the grain and straw; (b) water extractable soil boron concentrations;

(c) boron removal in the grain; and (d) boron removal in the straw for the Fairview soil catena.

Crest=Dermosol; Midslope=Sodosol and Lower-slope=Sodosol

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Figure 3-15 (a) Mean copper concentration in the grain and straw; (b) water extractable soil copper concentrations; (c) copper removal in the grain; and (d) copper removal in the straw for the Fairview soil catena. Crest=Dermosol; Midslope=Sodosol and Lower-slope=Sodosol

3.4. Conclusions

There is clear evidence that soil bulk density, acidity, sodicity, and waterlogging differences along

the catena are affecting yield. It noted that the Dermosol located on the upper slope and crest—the

soil type that consistently produces the highest yields—is compacted, acidic and with continuing

crop export of base cations, is becoming more sodic and degraded. At the Fairview farm, efforts

should be made to maintain or improve soil fertility of this high yielding soil type. This will not be

easy. The management of acid, sodic, and compacted soils on slopes is challenging and traditional

methods, such as ripping are not an option. It is recommended that nutrient, acid, sulfur and calcium

budgeting be undertaken to target the key issues of soil fertility and acidification. In terms of

micronutrients, and investigation into their potential limiting of crop yield should be considered. In

terms of overall soil management improvements need to be made in soil bioturbation and deep

rooted plants to improve soil structure and assist transfer of lime, gypsum, and organic matter into

the A2 and B horizons.

21

The observations of this and the previous phase of research (Phase 1) in this project have been

conducted at the catena hill slope scale. The weight of evidence based on soil physio-chemical

diversity down the hill slope, forms a strong basis for defining variable rate zones within similar

paddocks to match crop yield responses. The yield diversity was well known before this research

was undertaken, but the processes that drove that yield diversity were not clear. Now improved

investment decisions can be made with more confidence, both at this site and further afield where

similar soil properties are found, based on the soil properties measured e.g. increased inputs in the

hill crest landscape position may address yield gaps while improving longer term sustainability of

that soil resource. Alternatively lower input expenditure in the lower landscape soils where farming

is inherently challenging may improve the overall gross margin for the whole paddock. Seasonal

variation should also be considered within this evaluation as lower slope positions soils may deliver

greater yields in dryer years. Further, the 2015 season was a fair one but the crop response must be

viewed in relation to that season.

3.5. Acknowledgements

The authors wish to acknowledge the substantial contribution of time and effort to this project by

the Harden-Murrumburrah Landcare Group, especially Rob McColl. The authors acknowledge that

the Jaramas Foundation, who provided funding for this project. Billy Connelly provided mental relief.

22

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