Overcoming constraints on sandy soils –
amelioration strategies to boost crop production
Melissa Fraser1, David Davenport1, Nigel Wilhelm2 and Brett Bartel1
1
Rural Solutions SA, PIRSA
2
South Australian Research Development Institute, PIRSA
Key Points





Crop productivity on infertile sandy soils can be greatly improved by
incorporating organic matter deep into the soil (>30 cm).
In some cases, crop yields are further boosted with the incorporation of clay
and/or fertiliser to depth.
Two years of recent research show that the best soil modification treatments
can increase crop yields by 70 to 200 %, even in challenging seasons.
Treatments that address multiple constraints in these soils provide greater benefit than those addressing
individual issues.
Crop yields are reduced when clay is poorly incorporated into the soil.
Background
Up to 40 % (4.1 million hectares) of the broadacre farming area of South Australia has soil constraints that could
be overcome through the application of new advances in technology, machinery and soil management. These
include non-wetting sands with low fertility and low water holding capacity and heavier soils with poorly structured
subsoils.
‘New Horizons’ is a South Australian Government funded program developed to capture an additional $800 million
in agricultural production per annum in South Australia from these badly constrained soils. In 2014, three trial sites
were established on sandy soils on the Eyre Peninsula, Murray Mallee and South East; at Brimpton Lake, Karoonda
and Cadgee respectively. The sites all have sandy A horizons with a clay B horizon deeper than 30 cm. A range
of treatments were applied to overcome constraints including water repellence, low water holding capacity and
poor fertility. These treatments included the addition and incorporation of clay, fertiliser and organic matter, and
combinations of these. The aim of this research was to confirm that crop productivity can be substantially improved
when subsoil chemical, physical and biological constraints in sandy soils are treated. The impact of these
treatments on crop production and soil condition has already been monitored for two years and we hope to
continue these trials for several more seasons to measure their ongoing benefits.
Methodology
The Brimpton Lake site is flat to gently undulating and is used for cropping (cereal, canola, and lupins) in rotation
with annual grass and legume-based pastures. The soil profile comprises a grey, sandy, topsoil of 8-10 cm over a
bleached white sand with sodic clay at 30-50 cm deep. Grain yields at the site are generally less than half the
yields of better soils in the district.
The Karoonda site is situated in a Mallee landscape with low dunes and swales. The trial site is located at the base
of a shallow extensive dune, on a grey shallow sand grading to an orange leached sandy layer which overlies an
orange brown clay (20-30 % clay) 30-60 cm below the soil surface. The paddock is in a continuous crop rotation
of cereals and canola.
The Cadgee site is characterised by low rolling dunes and swales with deep sandy soils. The soil profile is
composed predominantly of grey sand (0-15 cm) grading to bleached white sand overlaying a clay horizon (60-65
% clay) 60 – 90 cm below the soil surface. The site has previously been used for grazing of unimproved pasture
and was dominated by silver grass prior to trial establishment.
The trials consist of 12 treatments that were all applied prior to seeding in 2014 (Table 1) with 4 replicates at
Brimpton Lake and 5 replicates at Karoonda and Cadgee; individual treated areas are 25 m x 4 m.
1
Table 1: New Horizons trial treatments applied at all three research sites in 2014. Treatments will not be reimposed in subsequent years.
Un-clayed Treatments
Un-modified Control
“Deep Banded” fertiliser
Spading only
Spading + Nutrition (additional fertiliser applied prior
to spading)
Spading + Organic matter (high rate of OM applied
prior to spading)
Spading + Organic matter + Nutrition (additional
fertiliser and OM applied prior to spading)
Clayed Treatments
Shallow Clay incorporated by tillage
Shallow Clay with “Deep Banded” fertiliser
Spading + Clay (high rate of clay applied prior to
spading)
Spading + Clay + Nutrition (high rate of clay and
additional fertiliser applied prior to spading)
Spading + Clay + Organic Matter (high rate of clay
and OM applied prior to spading)
Spading + Clay + Organic matter + Nutrition (high rate
of clay, OM and additional fertiliser applied prior to
spading)
Average application rates of clay material were 450, 500 and 600 t/ha at the Brimpton Lake, Cadgee and
Karoonda sites respectively. The greater rate applied at Karoonda was due to the lower clay percentage of the
clay rich material compared to the other sites.
Organic matter in the form of lucerne hay at Brimpton Lake and Cadgee and lucerne pellets at Karoonda were
applied at 10 t/ha.
Commercial fertilisers were applied in 2 forms to supply N, P, K, S and trace elements, either surface applied and
spaded in prior to seeding, or deep banded to 20-40 cm at seeding.
Unmodified control treatments were managed as per district practice and were provided with fertilisers matched
to the crops likely potential. Wheat was seeded at all sites in 2014 and 2015 except for Cadgee in 2015 when
barley was used. Commercial varieties suitable for each situation were used with basal NP fertilisers applied at
seeding in all treatments. In-crop nutrition management was matched to the likely potential of each treatment.
Measurements undertaken at the sites included:






Soil sampling conducted post-spading in early May 2014 (but prior to the addition of fertiliser at seeding).
Samples were analysed for nutrition, exchangeable cations, pH (CaCl), EC(1:5), organic carbon and bulk
density. Clay samples were analysed for particle size, clay mineralogy and water retention (2014 only).
Pre-seeding (2014 and 2015) and post-harvest gravimetric soil moisture in 2014 only. No data collected
post-harvest 2015 due to rainfall just prior to harvest at the sites.
Plant establishment counts and dry matter cuts near flowering (2014 and 2015).
Soil mineral nitrogen pre-seeding (2014 and 2015).
Soil samples for root DNA analysis (some in 2014 and all sites and treatments in 2015).
Grain yield (t/ha), protein and screenings at harvest (2014 and 2015).
Economic analysis of treatments including internal rate of return has also been conducted using 2014 results.
2
Results and discussion
Both the 2014 and 2015 growing seasons were climatically challenging with very much below average spring
rainfall received at the Karoonda and Cadgee sites in both years; the sites were also affected to varying degrees
by frost. The Brimpton Lake site suffered early waterlogging in 2014 followed by a dry spring; however, except for
a dry October, the 2015 growing season was nearly ideal from a rainfall perspective. As a result, grain yields were
affected at most sites, with poor conversion of biomass to grain for many of the treatments. A summary of the
results for each year is presented below, along with biomass and grain yields for each of the sites (Table 2 and
Figures 1 - 6).
Table 2. Grain yield expressed as a % increase or decrease of the unmodified control. Figures in bold are
significantly different to the control at 5% level.
Brimpton Lake
Karoonda
Cadgee
Treatment
2014
2015
2014
2015
2014
2015
unmodified (control)
deep nutrition
shallow clay
shallow clay + deep nutrition
spading
spading + nutrition
spading + clay
spading + clay + nutrition
spading + OM
spading + OM + nutrition
spading + clay + OM
spading + clay + OM +
nutrition
0%
33%
44%
8%
64%
11%
77%
21%
111%
104%
87%
0%
15%
45%
8%
43%
42%
50%
31%
95%
102%
81%
0%
220%
-22%
194%
200%
133%
118%
114%
318%
308%
220%
0%
99%
-35%
118%
99%
32%
86%
44%
205%
202%
226%
0%
53%
-10%
14%
69%
134%
42%
27%
102%
108%
69%
0%
-25%
14%
0%
-19%
-31%
29%
26%
45%
30%
68%
101%
78%
190%
213%
80%
74%
Summary: 2014 season










3
Water repellence appeared to affect plant numbers at Cadgee with treatments involving clay application
and/or soil mixing recording higher plant numbers than the unmodified control and deep nutrition
treatments (data not shown here).
Mineral nitrogen pre-seeding increased from 50-70 kg N/ha in the top 50-60 cm in unmodified controls to
150-200 kg N/ha in treatments with incorporated organic matter across all sites.
High rates of clay with poor incorporation reduced plant numbers at Cadgee and Karoonda.
Deep incorporated clay treatments (spaded) delivered greater early vigour than non-clayed treatments.
Biomass (shoot dry matter) of best treatments was 100 to 220 % higher than the unmodified control
(Figures 1, 3 and 5).
Treatments that included organic matter delivered highest biomass at all sites.
Additional fertiliser treatments generally delivered higher dry matter yields than the unmodified controls,
but results were mixed and varied across the three sites.
Spading alone provided large increases in biomass at Karoonda and Cadgee, but not at Brimpton Lake.
Grain yields of the best treatments on all sites were at least 100% greater than the unmodified control
(Table 2 and Figures 2, 4 and 6). Organic matter treatments delivered the highest grain yields. Spading and
the incorporation of deep mineral nutrients delivered yield increases, but results of these treatments varied
between sites. Clay addition delivered mixed results both within and between sites.
Conversion of dry matter to grain yield varied, with clayed treatments generally providing slightly lower
conversion than unclayed treatments.
Summary: 2015 season









Mineral nitrogen pre-seeding increased from 60-80 kg N/ha in the top 50-60 cm in unmodified controls to
100-150 kg N/ha in treatments with incorporated organic matter across all sites.
Water repellence appeared to be a bigger issue at Karoonda and Cadgee in 2015 than in 2014, with plant
numbers higher on clayed treatments than unclayed treatments. Unlike 2014, lower plant numbers were
also recorded on spaded treatments without organic matter (data not shown here).
Actual biomass (t/ha) was greater than in 2014, however the biomass of the unmodified controls at each
site were also considerably greater than in 2014, resulting in an overall lower percentage increase in
biomass of best treatments when compared to the control (Table 2 and Figures 1, 3 and 5).
There was an increase in biomass from spading alone, but not as great as the response was in 2014.
At Cadgee and Brimpton Lake, surface clay addition increased biomass and grain yield in 2015, but reduced
biomass at Karoonda (this may be due to poor incorporation at Karoonda or issues connected with the
type of clay applied – note clay used at Karoonda had lower clay % than other sites and higher pH).
Spading + Clay + Organic Matter + Nutrition recorded the highest biomass at all sites in 2015.
The four best performing treatments at the three sites all contained spading and organic matter.
Grain yields increased by >78 % over the unmodified control in the four treatments that contained OM at
Brimpton Lake, whereas three of the four OM treatments at Cadgee returned 45 to 74 % increases in grain
yield over the unmodified control (Table 2).
Karoonda was the only site to record consistently lower grain yields for all treatments in 2015 than 2014
(Figure 4), reflecting the very poor winter and spring conditions at the site in 2015. Despite this, the four
best treatments still returned an average 211% increase in yield over the unmodified control (Table 2).
Economic assessment of the trial treatments is problematic because the treatments imposed in these trials were
to test principles, not to investigate least cost options. Nevertheless, an economic assessment has been
undertaken by external agronomic advisers using modelled farms in four locations (Upper Eyre Peninsula, Lower
Eyre Peninsula, South Australian Murray Mallee and the South-East) based on 2014 results.
In general, it is the more moderately priced treatments (less than $500 per hectare) that deliver the highest internal
rate of return (IRR) even though they generate the lesser increases in yield. However, where organic matter can
be sourced at a cost of $500/ha or less, this may be a more viable option to add value to other treatments.
Farmers in both the Murray Mallee and Eyre Peninsula have started trialling the incorporation of organic matter at
rates that are more economically attractive and are still seeing spectacular increases in grain yield.
2014
2015
Biomass tha-1
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
Figure 1. Comparison of biomass (t/ha) at Brimpton Lake in 2014 and 2015. Biomass production was
considerably higher in 2015 than 2014 (115 to 350 % higher), reflecting the better winter conditions of that year.
The four treatments that include spading (S) plus organic matter (OM) performed the best in both years.
(UN = Unmodified control, DN= Deep banded nutrition, SHC= Shallow clay, S= Spading, N= nutrition, C = clay,
OM= Organic Matter).
4
2014
2015
4.5
Yield tha-1
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Figure 2. Comparison of grain yield (t/ha) at Brimpton Lake for the 2014 and 2015 seasons. The four treatments
that contain spading and organic matter had significantly higher yields (average 101% in 2014 and 89% in 2015)
than the unmodified control in both years (see Table 2 for significance). Despite the large increase in biomass
in 2015 (Figure 1), grain yields were only 15 to 70 % greater in 2015 than 2014 for the same treatments.
(UN = Unmodified control, DN= Deep banded nutrition, SHC= Shallow clay, S= Spading, N= nutrition, C = clay,
OM= Organic Matter).
2014
2015
Biomass tha-1
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Figure 3. Comparison of biomass (t/ha) at Karoonda in 2014 and 2015. Biomass production was higher in 2015
than 2014, consistent with trends seen at Brimpton Lake (Figure 1) and Cadgee (Figure 5).
(UN = Unmodified control, DN= Deep banded nutrition, SHC= Shallow clay, S= Spading, N= nutrition, C = clay,
OM= Organic Matter).
5
2014
2015
Yield tha-1
2.5
2.0
1.5
1.0
0.5
0.0
Figure 4. Comparison of grain yield (t/ha) at Karoonda in 2014 and 2015. The four treatments containing spading
and organic matter again returned the highest grain yields in 2015 (average 211 % > than control), despite not
always having the highest biomass in that year (Figure 3). The two treatments containing deep banded nutrition
performed exceptionally well at this site compared to the other two sites in both years (Figures 2 and 6); the
reasons for this are not yet known but there appears to be an interaction with the form and depth of physical
disturbance and fertiliser incorporation.
(UN = Unmodified control, DN= Deep banded nutrition, SHC= Shallow clay, S= Spading, N= nutrition, C = clay,
OM= Organic Matter).
2014
2015
Biomass tha-1
6.0
5.0
4.0
3.0
2.0
1.0
0.0
Figure 5. Comparison of biomass (t/ha) at Cadgee in 2014 and 2015. Biomass production was considerably
higher in 2015 than 2014 (80 to 350 % higher) reflecting the better establishment at the site in 2015 and that
barley was used in 2015. The four treatments that involve spading (S) plus organic matter (OM) performed the
best in 2014, with the shallow clay and spading plus clay treatments performing better in 2015.
(UN = Unmodified control, DN= Deep banded nutrition, SHC= Shallow clay, S= Spading, N= nutrition, C = clay,
OM= Organic Matter).
6
2014
2015
Yield tha-1
2.5
2.0
1.5
1.0
0.5
0.0
Figure 6. Comparison of grain yield (t/ha) at Cadgee in 2014 and 2015. Grain yields overall (wheat in 2014 and
barley in 2015) were considerably higher in 2015 than 2014. The shallow clay treatments performed better in
2015 than 2014, owing to the re-incorporation of clay in that year. The four treatments containing spading and
organic matter once again performed the best in 2015 (see Table 2 for significance), albeit only the S+C+OM+N
treatment returned a yield increase greater than 70% over the unmodified control.
(UN = Unmodified control, DN= Deep banded nutrition, SHC= Shallow clay, S= Spading, N= nutrition, C = clay,
OM= Organic Matter).
Conclusions
Crop biomass and grain yield data generated at the three New Horizons research sites in both 2014 and 2015
confirm that productivity can be substantially improved on infertile sandy soils when subsoil chemical, physical and
biological constraints are treated. Despite the challenging climatic conditions observed, crop yields of the best
treatments at each site exceeded the yields of the unmodified control by 110 – >300 % in 2014 and 70 – >200 %
in 2015.
The best treatments at all sites in both years included spading and the incorporation of organic matter to depth,
with or without the inclusion of clay and additional fertiliser. The operation of spading aids with overcoming water
repellence, mixes the often chemically hostile bleached A2 horizon with organic matter and organic carbon that is
otherwise stratified at the surface and can overcome compaction issues by reducing the bulk density. The
incorporation of organic matter undoubtedly provides additional nutrition, but we also suspect it contributes to
increasing cation exchange capacity, water holding capacity, biological activity and the stabilisation of soil
aggregates; further monitoring and analysis of the soil chemical, physical, hydrological and biological
characteristics of the New Horizons sites is required to confirm these hypotheses.
We hope to continue the trials in 2016, however there is some degree of uncertainty regarding funding. Continuing
the trials will give us greater certainty about the potential benefits and longevity of each of the applied treatments;
this will enable further economic analysis to be conducted which will improve confidence in applying the
recommended treatments. A new site is also being established at the Struan Research Centre to demonstrate and
assess the effectiveness and economic feasibility of applying different types of organic matter (all at a cost of
$500/ha).
Useful resources
http://pir.sa.gov.au/major_programs/new_horizons
Disclaimer
PIRSA and its employees do not warrant or make any representation regarding the use, or results of the use, of
the information contained herein as regards to its correctness, accuracy, reliability and currency or otherwise.
PIRSA and its employees expressly disclaim all liability or responsibility to any person using the information or
advice
NEW HORIZONS: THE NEXT REVOLUTION IN AGRICULTURAL PRODUCTION
Information current as of 11 02 2016
© Government of South Australia 2016
7
All enquiries
Brett Bartel
Director Service Delivery, Rural Solutions SA
Primary Industries and Regions SA (PIRSA)
GPO Box 1671, Adelaide SA 5001
Ph: 8226 9771
E: [email protected]
8