Topsoil pH stratification impacts on pulse production in SE Australia

Take home messages

  • Acidic layers below 5cm adversely affect root growth and architecture, nodulation, plant vigour and N fixation potential of acid-sensitive pulses.
  • Moderately (pHCa 4.6-5.0) and severely (pHCa <4.5) acidic layers in the 5-20cm soil profile are not detected using soil samples collected at standard depths of 0-10cm and 10-20cm — finer sampling at 5cm intervals is recommended to detect pH stratification.
  • The current standard industry practice of spreading lime with no incorporation under no-till or zero till systems confines the lime effect to the surface layers.
  • If severe pH stratification is detected, incorporate lime to a depth of 10cm with a full cultivation operation at least 6-12 months before sowing acid-sensitive species.
  • Use appropriate lime rates to maintain pHCa > 5.5 in the entire top 10cm layer.
  • The effect of pH stratification on more acid-tolerant species including canola, lucerne and cereals should be monitored.

Background

While faba beans and lentils are generally acknowledged as being sensitive to soil acidity, they are successfully grown on slightly acidic soils (pHCa >5.0-6.0) in the high and medium rainfall zones of south eastern Australia, albeit with somewhat inconsistent yields. This paper focuses on the preliminary findings of a New South Wales Department of Primary Industries (NSW DPI) project, supported by GRDC, aimed at identifying factors limiting the production and N fixation of pulse crops grown on acidic soils in the grain production regions of south eastern Australia with a long term average annual rainfall > 500mm.

Consultation with growers indicates that faba bean is the pulse crop best adapted to soils prone to waterlogging and is the pulse of choice in the acid soil regions of south west Victoria (SW VIC), Gippsland and South Australia (SA). However, widespread adoption of acid-sensitive species, such as faba beans and lentils, is limited by inconsistency of yield and perceived high production risk. While field peas show intermediate sensitivity to soil acidity, susceptibility to disease and frost limits  potential in the high rainfall zone (HRZ) (E Armstrong pers. comm.).

Very little detailed agronomic research has been reported that examined the response of pulses to soil acidity. Guidelines for tolerance of pulses and rhizobia to soil acidity are inconsistent and vague, for example:

  • Anon (2015) proposes the ideal pHCa for faba beans is 6.0-8.0, but also indicates that pHCa > 5.2 is suitable.
  • However, Drew et al. (2012) indicate the optimal pHCa range for Rhizobium spp. used for faba beans, lentils and field peas is > 6.0, although these rhizobia species are sensitive to pHCa < 5.0.

The environment to which the rhizobia and host plant are exposed influences the success of the complex nodulation process (Cregan and Scott 1998). Effective nodulation is essential to optimise the early growth, vigour and production potential of pulses sown into nitrogen (N) depleted soils. Consultation with growers indicates that while the inoculation process and use of the appropriate rhizobium strain are well understood, the management required to avoid biotic and abiotic stresses that compromise plant and rhizobial function during the nodulation process is not.

Numerous studies (such as Conyers and Scott 1989; Paul et al. 2003) report the presence of acidic layers at 5-15cm (to 20cm in sandy soils) in both agricultural and non-agricultural systems. The work was taken a step further with the investigation of the effect of soil acidity below 5cm depth on nodulation and plant growth. Pulse crop and soil data collected from commercial paddocks in 2015 and 2016 have shown the detrimental effect of moderately (pHCa 4.6-5.0) to severely (pHCa <4.5) acidic layers below 5cm on root growth, nodulation and crop vigour. It was concluded that even at sites where lime application has increased soil pH sufficiently to enable acceptable production from canola crops, pH stratification and moderately and severely acidic layers below 5cm depth may still be present and limit pulse crop growth, production and N fixation.

The findings are likely to be relevant to acid-sensitive pulses grown on acid soils across all rainfall zones. Furthermore, the severity of the acidity below 5cm depth at a number of sites is sufficient to be affecting the productivity of the main crop and pasture species, including cereals and canola.

Method

In 2015 and 2016, a total of 39 commercial pulse crops were monitored in NSW, VIC, SA and Tasmania (TAS) (Figure 1). The 2015 sites were chosen to achieve geographical spread across acidic soil regions of the target zones and included 12 paddocks of faba beans, two of narrow-leaf lupins and one of field peas. Sodosols were the dominant soil type at these sites. In 2016, an additional five growers were engaged in order to investigate a broader range of pulses and soil types — Sodosols, Chromosol and Rudosols (alluvial). Sites monitored in 2016 were sown to faba beans (14), narrow-leaf lupins (2), chickpeas (3) and lentils (3).

Map showing the acidic soil region of the high rainfall cropping zone of south eastern Australia showing the location of paddocks monitored in 2015 and 2016.

Figure 1. The acidic soil region of the high rainfall cropping zone of south eastern Australia showing the location of paddocks monitored in 2015 and 2016.

A uniform, one hectare area of crop was selected at each site. Soils were sampled at depths of 0-10cm and 10-20cm, with pH measured using the calcium chloride method through Nutrient Advantage® Laboratories.

Crop plants were assessed two to three months post-emergence for effectiveness of nodulation each year. Plants with intact root systems were collected at random from the designated areas and scored for nodulation using the Columbia protocol (Anon 1991). Scoring was done for (1) plant growth and vigour, (2) nodule number, (3) nodule position, (4) nodule colour, and (5) nodule appearance with all parameters of equal weighting and ‘25’ the maximum possible total score.

In 2015, crops with low nodulation scores (< 18) were investigated further. Root growth was assessed in situ and soil samples were collected at 2.5cm intervals to a depth of 15cm and tested for pH using a Manutec® Soil pH Test Kit.

Late in the growing season (October 2015), one of the collaborating growers at Lake Bolac, VIC requested that two additional, adjoining faba bean crops be investigated. Paddock 1 had 2.5t/ha of lime topdressed, but not incorporated, in February, 2015, while the neighbouring Paddock 2 had been treated with 2.5t/ha of lime in 2012, with the lime incorporated to a depth of 10cm as part of a slug management strategy. These paired paddocks provided the project with an opportunity to compare the impact of lime incorporation on faba bean response.

In 2016, root growth was assessed in situ and soil cores were collected from all monitored sites and divided into increments of 2.5cm to a depth of 10cm, and 5cm increments from 10-20cm. Soil pH was measured in the NSW DPI Wagga Wagga laboratory.

Results and discussion

Faba bean was the most commonly grown pulse species in this study, enabling us to identify common constraints across NSW, SA and VIC environments, which are also likely to be relevant to other acid-sensitive legume species. Nodulation of faba beans was found to be adversely affected by low soil pH in 2015 and 2016.

Soil acidity and nodulation

Analysis of the nodulation scores for faba bean crops and pHCa of 0-10cm soil samples from the monitored paddocks (Figure 2) showed a strong correlation (R2=0.89) between soil acidity and nodulation scores (0 = nil nodules present, to a maximum of 25 = all plants with effective nodules). The form of inoculant used (peat slurry, freeze dried or granular) did not have a significant effect on nodulation score.

The monitored crops fell into two distinct categories: (1) vigorous, well nodulated crops; and (2) those with a nodulation score below 18, which included extremely variable crops that showed symptoms of N deficiency within two to three months of emergence, particularly at the Holbrook (Hb) and Kybybolite (Ky) sites, which recorded nodulation scores of 17 and 15, respectively.

Although percentage exchangeable aluminium at the Holbrook site was 8% in the 0-10cm and 35% at 10-20cm, the percentage exchangeable aluminium at both Kybybolite and Lismore was < 2%. Therefore, it appears that low pH affected the nodulation process and reduced nodulation, irrespective of aluminium level.

Scatter plot showingThe effect of topsoil pH (0-10cm) on nodulation of faba beans across the south eastern Australian HRZ in 2015. Sites of sampling include Kybybolite, SA (Ky), Holbrook, NSW (Hb), Lismore, VIC (Li), Inverleigh, VIC (Iv), Frances, SA (F), Darlington, VIC (D), Willaura, VIC (W) and Henty, NSW (H). W* = after wheat, W# = after canola.

Figure 2. The effect of topsoil pH (0-10cm) on nodulation of faba beans across the south eastern Australian HRZ in 2015. Sites of sampling include Kybybolite, SA (Ky), Holbrook, NSW (Hb), Lismore, VIC (Li), Inverleigh, VIC (Iv), Frances, SA (F), Darlington, VIC (D), Willaura, VIC (W) and Henty, NSW (H). W* = after wheat, W# = after canola.

All 2015 sites, with the exception of Kybybolite, had received applications of lime within the past five years. Lime had been applied at the Holbrook site in 2010 and again in 2015 at a rate of 2t/ha. A Speedtiller® was used in 2015 to mix the lime into the surface layers.

The association between nodulation score and soil pHCa was also evident in crops assessed in 2016. The sites at Holbrook, Kybybolite, Paddocks 1 and 2 at Lake Bolac and  two sites at Junee, NSW, which grew faba beans (shown as the stars labelled J1 and J2 in Figure 3), are discussed in detail in this paper.

Sites J1 and J2 are within the same paddock that had received a blanket lime application in 2011 at a rate of 1.13t/ha, which was not incorporated.

Scatter plot showing the effect of topsoil pH (0-10cm) on nodulation of faba beans across the SE Australian HRZ in 2015 with two sites added in 2016. Stars marked J1 and J2 represent sites at Junee (NSW) growing faba beans.

Figure 3. The effect of topsoil pH (0-10cm) on nodulation of faba beans across the SE Australian HRZ in 2015 with two sites added in 2016. Stars marked J1 and J2 represent sites at Junee (NSW) growing faba beans.

Soil pH stratification

The observations and soil test results that are discussed in detail in this paper are those relating to the 2015 faba bean crops at Holbrook, NSW (Hb), Kybybolite, SA (Ky), the adjoining faba bean crops at Lake Bolac, as well as the 2016 sites at Junee, NSW (J1 and J2). The Hb, Ky and Lake Bolac (LB) crops grew on Sodosols. The Sodosols at Ky and LB had a light sandy loam topsoil overlying a sodic layer at 20-30cm. The Hb crop grew on a Sodosol with heavier textured loam topsoil. The J1 and J2 crops grew on a red Chromosol (clay loam topsoil).

The responses of crops to soil pH at these sites are consistent with the observations made on all monitored crops growing in acidic soils, across the range of soil types and seasonal conditions experienced in 2015 and 2016.

The results from composite soil samples taken at depths of 0-10cm and 10-20cm at the Holbrook and Junee sites (Table 1 and 2), which are traditionally used by growers and advisers to guide decisions on acid soil management, failed to detect significant variation in soil pH down the profile at the Holbrook or Junee sites.

Table 1. The pHCa measurements of 0-10cm and 10-20cm depths underestimate the pH stratification in the soil profile at the Holbrook, Kybybolite and Junee sites, compared with tests from finer sampling increments. Soil conditions at each site are reflected in the appearance of faba bean plants.

Soil depth (cm)

Holbrook site - 2015

Kybybolite site – 2015No history of lime

Lake Bolac Paddock 1 – 2015
Lime applied 2015, not incorporated

Lake Bolac Paddock 2 - 2015 Lime applied 2012, incorporated to 10cm

Soil pHCa#

Soil pHCa#

Soil pHCa#

Soil pHCa#

Nodulation score – 17

Nodulation score - 15

Assessed nodulation – poor

Assessed nodulation – satisfactory

Assessed nodulation – good

Composite sample

Sub samples*

Composite sample

Sub samples*

Lime missa

Lime strip

 

0-2.5

4.6

(Grower’s paddock soil test - 5.2)

6.5

4.5

4.2

5.3

7.3

6.5

2.5-5.0

5.6

Not tested

Not tested

Not tested

Not tested

5.0-7.5

4.4

Not tested

3.8

4.8

5.3

7.5-10.0

4.2

4.0

Not tested

Not tested

Not tested

10.0-15.0

4.1

4.1

5.7

Not tested

3.8

4.3

4.8

15.0-20.0

4.1

Not tested

Not tested

Not tested

Not tested

Plant appearance

Plants yellow, stunted. Roots were concentrated in top 6cm— stunted, thickened and distorted, typical of aluminium toxicity. Roots of <10% of plants extend below 10cm. Dark colouration of roots due to disease — likely due to multiple stresses.

Very poorly nodulated, stunted, yellow plants. Root growth confined to top 10cm.Roots are stunted, thickened and distorted despite soil testing <2% aluminium. Minimal root hair development.

Plants yellow, N deficient. Root growth concentrated in top 10cm.Tap roots appeared to hit a physical barrier and did not extend below 10cm, although soil was friable sandy loam at that depth.

Plant colour good, height nodulation adequate, plant height approx. 1m. Roots concentrated in top 10cm, but some roots grew to depth 30cm.

Excellent crop colour, height approx. 1.3m. Roots more fibrous and dense than in Paddock 1, extended to subsoil moisture below 30cm.

# pHCa for Hb, Ky and Lake Bolac sub-samples was estimated using Manutec® Soil pH Test Kit; pHwater was converted pHCa using the relationship:  pHCa =1.012pHW – 0.768 (Conyers and Davey 1988).

*Sub-samples were not collected from same location as composite samples.

a The low pH results and distinct strips across Paddock 1 suggest poor lime distribution during the spreading operation.

As shown in Table 1, the intense pH stratification identified by testing finer layers at Holbrook and Paddock 1 at Lake Bolac demonstrated that lime incorporation was ineffective under the no-till systems adopted by the majority of participating growers. The lime was concentrated in the shallow surface layers (0-2.5cm) with little movement of the lime effect below these at Holbrook (pHCa at 0-2.5cm of 6.5 to pHCa 4.4 at 5.0-7.5cm) and Paddock 1 at Lake Bolac (pHCa at 0-2.5cm of 7.3 to pHCa 4.8 at 5.0-7.5cm). Clearly, under no-till systems, lime topdressing with no incorporation is ineffective in neutralising acidity below approx. 5cm depth.

In comparison, the pH assessments from Paddock 2 at Lake Bolac indicate that incorporation increased the lime effect and raised pH to a depth of at least 10cm. It is also probable that the lime effect will have moved down the profile and passed the depth of incorporation in the three years since it was applied.

Table 2. The pHCa measurements of test strips at Junee highlight soil variability within a paddock. Nodulation scores and plant appearance reflect the different soil conditions.

Soil depth (cm)

Junee 1 site – 2016

Lower slope

Junee 2 site – 2016

Upper slope

Soil pHCa

Soil pHCa

Nodulation score – 20.6

Nodulation score – 16.6

Composite sample

Sub-samples

Composite sample

Sub-samples

0-2.5

5.19

5.53

4.43

4.86

2.5-5.0

5.44

4.55

5.0-7.5

5.15

4.22

7.5-10.0

4.63

4.07

10.0-15.0

4.81

4.60

4.37

4.19

15.0-20.0

5.02

4.55

Plant appearance

Healthy, vigorous plants with good nodulation, approx. 35cm tall at first node growth stage (Sept.). Healthy and dense roots, including finer root hairs superior to plants from J2 site. Roots restricted to top 10cm.

Most plants were yellow, less vigorous, with less root hair development than plants from J1. Height 15-25cm. Root growth concentrated in the top 4cm, with minimal root growth below 4cm. Root disease evident on most plants.

The effect of acidic layers on root development and nodulation of faba beans

Despite the Holbrook site receiving 4t/ha of lime since 2010, incorporation with a Speedtiller® was ineffective in mixing the lime below 5cm. Finer sampling of the topsoil indicated that at a sowing depth of approx. 6cm, the faba bean seedlings and rhizobia were exposed to a hostile environment (pHCa <4.4), two pH units more acid than the surface soil (pHCa 6.5). Nodulation was poor and the crop was showing symptoms of severe N deficiency within three months of emergence. Root growth was restricted to the surface 6cm and did not penetrate into the severely acidic soil below 5cm.

The results and observations from the Kybybolite site are included to highlight the impact of low pH on faba bean growth and nodulation. Root hair development was poor and plant roots were stunted, thickened and distorted — all symptoms typical of aluminium toxicity. However, with exchangeable aluminium levels of < 2%, it is likely that low pH at this site is primarily responsible for the restricted root growth, reduced rhizobial activity and inefficiency of the nodulation process as reported by Cregan and Scott (1998).

The observations at Lake Bolac tell a similar story, with root development and nodulation of plants in Paddock 1 apparently adversely affected by an acidic layer at the approximate sowing depth of 5.0-7.5cm (pHCa of 3.8in the strip missed by the spreader and pHCa of 4.8 in the lime strip) and rooting depth restricted to the top 10cm by severe acidity, pHCa < 4.5 below 10cm. By comparison, the higher pHCa of 5.3 at 5.0-7.5cm in Paddock 2 resulted in improved root density and nodulation. Plants in Paddock 1 were severely moisture stressed compared to those in Paddock 2, which had grown into subsoil moisture below 30cm.

Yield maps from Paddocks 1 and 2 confirmed improved crop growth with Paddock 1 yielding an average of 1.14t/ha for a gross margin of $130/ha. The average yield for Paddock 2 was 1.99t/ha, which returned a gross margin of $458/ha.

The Junee sites were from lower slope (J1) and mid slope (J2) areas within the same paddock. The soil tests from J1 indicate slight acidity (pHCa > 5.0) from 0-7.5cm, tending toward moderately acid (pHCa > 4.6) from 7.5-15.0cm. Plant roots from this area appeared healthy and were well nodulated (nodulation score of 20.6), but root growth was restricted to the top 10cm. The moderately acidic layers at 7.5 to 15cm (pHCa of approx. 4.6) may be responsible for the shallow rooting depth, but the intermittent waterlogging experienced during July to September of 2016 was likely to have compounded the stress caused by the acidic layers.

The J2 soil tests indicated moderate acidity in the surface 0-2.5cm (pHCa of 4.86), tending to severe acidity from 5.0-15.0cm, with pHCa ranging from 4.55 at 2.5-5cm, to as low as 4.07 at 7.5-10cm. In contrast with plants from the J1 site, J2 plants were stunted and showed symptoms of severe N deficiency two months after sowing. Root growth was restricted to the surface layers (0-4cm), root hair development was considerably less than J2 plants, and plants were not as well nodulated.

The majority of plants collected from the J2 site showed symptoms of root disease, in contrast with the relatively healthy J1 plants. It is likely the disease infection was a secondary, physiological response to the more ‘hostile’ soil conditions (acidityand waterlogging) at J2. The lower incidence of infection observed in plants from J1 suggests that the higher pH in the root zone may have improved the ‘health’ of those plants and made them less susceptible to damage and infection. The plants were not screened for specific root diseases, but there are likely to be many different species present, such as Pythium, Rhizoctonia, Fusarium and Phytophthora (K Lindbeck pers. comm.).

The Junee paddock is gently undulating and has a history of lucerne pasture, canola and wheat production. A 2013 soil pHCa test result from this paddock of 5.4 for the 0-10cm soil depth failed to detect the variability in soil acidity across the paddock. The blanket lime rate of 1.3t/ha, applied in 2011, but not incorporated (all subsequent crops being direct drilled with a knife point press wheel seeder), was inadequate to ameliorate the severe acidity at 5-15cm at the J2 site.

Other factors affecting nodulation and early growth of pulses

Management practices that caused severe damage to pulse crops monitored in 2015 and 2016 included:

  • Crop damage caused by sulfonyl urea (SU) herbicides applied in the previous 12 months. Ineffective incorporation of lime produces an elevated pH in the surface soil layers and delays the breakdown of sulfonyl urea herbicides such as triasulfuron.
  • Addition of zinc to inoculant slurries during the inoculation process. Zinc is toxic to rhizobia and when mixed with the inoculant resulted in extremely poor nodulation. If zinc is to be used on pulses, ensure it is not placed in close proximity to the rhizobia at time of sowing (applied in fertiliser mix or separated from seed) or apply to the crop as a foliar application.

Conclusion

Effective nodulation underpins productive and profitable pulse crops. When detailed soil pH data were aligned to root growth and nodulation of pulse crops, it was concluded that the presence of previously undetected, but severely acidic layers was likely to be a major factor responsible for inconsistent production of acid-sensitive pulses on slightly (pHCa >5.0) and moderately acidic soils (pHCa 4.6 to 5.0) of the medium and HRZs.

The impact of acidic layers on root hair development was apparent in all reported crops. As discussed by Drew et al. (2012), the main pathway for rhizobial infection of commonly grown temperate legume species is via root hairs. The exception is lupin. At all sites with poor nodulation (Hb, Ky, LBP1 and J2), the seed and rhizobia encountered an acidic layer (pHCa of 4.4, 4.5, 4.8 and 4.2, respectively) at 5.0-7.5cm in the profile, which appears to have been sufficient to disrupt the infection process. Optimal nodulation requires pH conditions favourable to both the rhizobia and host plant. These results suggest that although management strategies, such as lime pelleting of seed to raise pH in the immediate vicinity of the seed, may improve rhizobial activity in the short term, pelleting is unlikely to improve soil pH sufficiently to improve root hair development and significantly improve nodulation.

While most growers are effectively managing disease and weeds in pulse crops and are sowing recommended varieties, these findings highlight the need to review basic agronomic principles and management practices. Management of pulses sown in acidic soils must focus on promoting the nodulation process and minimising or avoiding environmental stresses. The results from this project, reinforced by grower experience, indicate that well nodulated, vigorous pulse crops have the ability to withstand multiple stresses, including infection by root diseases and transient waterlogging. The 2015 and 2016 experiences indicate that timely sowing, early in the recommended sowing window, allows plants and nodules to establish before cold temperatures slow growth and rhizobial function. Quoting one of the collaborating growers:
‘Variety is not as important as agronomy… it’s clear from what we are seeing we need to pay more attention to soils and agronomy’.

Faba beans are proving to be ‘the canary in the coal mine’ for detecting acidic layers. The dramatic clinical symptoms expressed by faba bean plants exposed to acidic layers has helped highlight the extent and severity of pH stratification, even in soils with a long history of lime application. From observations at other sites not reported here, shoot growth of other acid-sensitive species such as chickpeas (and we suspect lentils, canola and lucerne) does not demonstrate the dramatic response to acidic layers or obvious clinical symptoms exhibited by faba beans. For these crops, close inspection of the roots is recommended, in conjunction with finer soil sampling to check for the presence of acidic subsurface layers.

The traditional 0-10cm soil sampling procedure is not detecting pH stratification. Finer sampling at 5cm intervals to a depth of 20cm is needed to verify the presence and depth of acidic layers. It is important to test representative paddocks and soil types in order to monitor change in pH over time for each farming system and operation.

The intensity of soil pH stratification identified by testing finer layers demonstrates that lime was concentrated in the shallow surface layers (0-5cm) under the no-till systems adopted by the majority of participating growers. This study indicates that current acidic soil management and liming programs are ineffective in neutralising subsurface acidity or counteracting acidification below the shallow surface layers. Lime rates, frequency and method of lime application need to be reviewed in order to improve productivity of acid-sensitive species on acidic soils. The effectiveness of lime in raising pH and movement of the lime effect down the profile varies with management practices, such as rate and incorporation, as well as lime quality, soil type and rainfall.

The negative impact on agricultural production of shallow subsurface acidic soil layers is well documented. The presence of these layers effectively places a ceiling on production potential and reduces efficiencies in water and nutrient use. The severity of the acidic layers identified in this study suggests that less acid-sensitive species, including barley, canola, lucerne and many wheat varieties are probably suffering a yield penalty at pHCa < 4.7 in the top 15cm.

A rapid solution to severely or moderately acidic layers at 5-15cm (5-20cm in sandy loam soils) requires an aggressive approach, including lime incorporation to 10cm with full cultivation. For erosion prone, sandy loam soils where cultivation is not appropriate, it may be necessary to delay sowing acid-sensitive species until the lime effect moves down the profile. In the longer term, for all soil types, it is essential that appropriate lime rates are used to maintain pHCa > 5.5 in the entire surface 10cm. This will facilitate movement of the lime effect into the acidic layers at 10-20cm and avoid further acidification of the 10-20cm layers.

Useful resources

GRDC Ground Cover Issue 120 Jan-Feb 2016: Soil acidity holds back pulse potential

Upjohn B, Fenton G, Conyers M (2005) Soil acidity and liming. Agfact AC.19 NSW Department of Primary Industries, Orange.

References

Anon (1991). Field Guide to Nodulation and Nitrogen Fixation Assessment, British Columbia Ministry of Forests.

Anon (2015). Pulse Australia, 2015 Southern Faba & Broad bean – Best Management Practices Training Course Manual.

Conyers, M.K. and Davey, B.G. (1988). Observations on some routine methods for soil pH determination. Soil Science 145, 29-36.

Conyers MK and Scott BJ (1989). The influence of surface incorporated lime on subsurface acidity. Australian Journal of Experimental Agriculture 29, 201-207.

Cregan P and Scott B (1998). Soil Acidification - An Agricultural and Environmental Problem. In ‘Agriculture and the environmental imperative’. (Eds JE Pratley, A Robertson). pp. 98-128. (CSIRO Publishing: Melbourne).

Drew E, Herridge D, Ballard R, O’Hara G, Deaker R, Denton M, Yates R, Gemell G, Hartley E, Phillips L, Seymour N, Howieson J and Ballard N (2012). Inoculating Legumes: a practical guide. Grains Research and Development Corporation.

Paul KI, Black S and Conyers MK (2003). Development of acidic subsurface layers of soil under various management systems. Advances in Agronomy 78, 187-213.

Richards M, Gaynor L (2016). Southern NSW Pulse Survey 2015-16. NSW Department of Primary Industries, Wagga Wagga.

Robertson M, Kirkegaard J, Peake A, Creelman Z, Bell L, Lilley J, Zhang H, Kleven S, Duff C, Lawes R and Riffkin P (2016). Trends in grain production and yield gaps in the high-rainfall zone of southern Australia. Crop & Pasture Science 67, 921-937.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC — the author would like to thank them for their continued support.

The contribution of the 21 growers participating in this project and their willingness to share their experience is greatly appreciated.

Contact details

Helen Burns, NSW Department of Primary Industries, Wagga Wagga Agricultural Institute
Pine Gully Road, Wagga Wagga 2650
(02) 6938 1947
helen.burns@dpi.nsw.gov.au

GRDC Project code: DAN00191