Evidence of nutrient, not soil pH, stratification in pasture soils in the Australian Capital Territory

Susan Orgill 1, 2, Sally McIntosh 3, Belinda Hackney 1, 2 and Anna van Dugteren 3

1 NSW Department of Primary Industries, PMB, Pine Gully Rd, Wagga Wagga, NSW 2650

2 Graham Centre for Agricultural Innovation, Charles Sturt University and NSW Department of Primary Industries, Pugsley Place, Wagga Wagga, NSW, 2650

3 ACT NRM, Environment, Planning and Sustainable Development, ACT Government, GPO Box 158 Canberra, ACT, 2601

Abstract:

There has been an increasing interest in the stratification of soil nutrients and pH, and the need to revise sampling depths to better diagnose soil surface and subsurface constraints to crop and pasture production. Twenty-three commercial paddocks were sampled in the Australian Capital Territory (ACT) to diagnose soil chemical constraints to 30 cm. There was little evidence of pH stratification, but strong evidence of phosphorus (P), sulfur (S) and potassium (K) accumulation in the surface (0-5 cm) soil. Nutrient concentrations were highest at 0-5 cm and declined significantly with depth, consistent with the trend in soil organic matter (indicated by total carbon and nitrogen concentration). Sixty six percent of paddocks had available P (0-10 cm) in excess of the critical value, while 61% were deficient in S (0-10 cm). There was no evidence of S accumulation in subsurface soil layers to 30 cm and overall 61% of paddocks were deficient in S in the 0-30 cm profile sampled. Therefore, even if S has accumulated deeper in the profile (>30 cm) it is likely to be below the root zone of most annual species until late in the growing season. Our results indicate nutrient stratification may limit pasture production more than pH stratification in the ACT.

Effect of rate and placement of phosphorus on vetch performance

Brian Dzoma1, Nigel Wilhelm2, Peter Telfer3 and Kym Zeppel1

1SARDI Loxton Research Centre. P O Box 411, Loxton SA, 5333

2SARDI Waite Research Precinct. Building 11A Hartley Grove, Urrbrae, SA 5064

3Turretfield Research Centre. Holland Road, Rosedale, SA 5350

Abstract:

Phosphorus (P) is an essential nutrient which influences plant growth. Inadequate P restricts root and shoot growth and other functions that reduce N fixation by legumes. Vetch (Vicia sativa), a versatile pasture legume crop that can be used for grain, pasture, hay/silage or green manure, is being grown on naturally infertile Mallee soils which are often quite deficient in P. Consequently, it struggles to achieve optimum productivity and hence less fixed nitrogen is returned to the system. This project evaluated the impact of P on vetch productivity and nodulation and also investigated placement of P at sowing on nodulation, root and shoot dry matter (DM) production. Results showed that there are productivity gains to be realised from applying P fertilisers when sowing vetch on soils with low P reserves. Application of 32 units of P resulted in shoot DM increases of 239% and 45% at Loxton and Peebinga respectively. Results also showed that deep placement of P is beneficial to early and late DM production, but can set back nodulation as the plants need the P upfront. P applications, however, need to be matched against expected productivity gains for different soil types and rainfall regions to make sure that the fertiliser applications are economically justifiable

Banded application improves the recovery of phosphorus fertiliser in a temperate pasture sward containing red clover

Jonathan W. McLachlan1, Chris N. Guppy1, Richard J. Flavel1

1University of New England, School of Environmental and Rural Science, Armidale, NSW, 2351, jmclach7@une.edu.au

Abstract:

Phosphorus (P) fertiliser is commonly broadcast onto existing pasture swards for ease and cost of application. However, improvements in P acquisition efficiency may be achieved by banding fertiliser. Micro-swards of red clover (Trifolium pratense L.) were grown in intact sandy loam soil cores with a 33P-labelled fertiliser source. Dissolved P fertiliser was applied either to the surface or at a depth of 30 mm, to either small or large volumes of soil. Growth rates were modest and significant differences were not observed for shoot yield among treatments. However, shoot P content and P recovery were 37% and 35% higher, respectively, when P fertiliser was distributed across a larger soil volume when compared to concentrated points. Similarly, banded treatments increased recovery by 40% compared to surface-applied fertiliser. The results suggested that banded application of a low concentration liquid P fertiliser may improve the recovery of P fertiliser by pasture legumes grown in soil with a low phosphorus buffering index (PBI).

Differences in subsoil P acquisition by two subterranean clover cultivars in a P deficient soil

Jonathan W. McLachlan1,2, Richard J. Flavel1, Chris N. Guppy1, Richard J. Simpson2, Rebecca E. Haling2

1 University of New England, School of Environmental and Rural Science, Armidale, NSW, 2351, jmclach7@une.edu.au

2 CSIRO Agriculture and Food, GPO Box 1700, Canberra, ACT, 2601

Abstract:

Phosphorus (P) is usually concentrated in the uppermost layers of the soil profile under pasture, hence topsoil root allocation is important for maximising P acquisition. However, total root length was recently found to be a marginally better predictor of variation in P uptake among twenty-six genotypes of subterranean clover (Trifolium subterraneum L.) when compared to topsoil root length alone. This result prompted a preliminary assessment of P acquisition by subsoil roots. Micro-swards of two cultivars were grown with a topsoil layer that was either P-deficient or amended with P for improved plant growth, overlying a low-P subsoil that contained 32P-labelled phosphate. Both cultivars produced less shoot dry mass under P constraint, and the cultivar that allocated more root length to the subsoil layer produced a larger shoot dry mass in the P-deficient soil. This cultivar also recovered more 32P-labelled phosphate from the subsoil layer in both P treatments. Therefore, variation exists for subsoil P acquisition and this trait may be important for determining shoot yield in P-deficient soil.

Flowering time responses of serradella cultivars

Suzanne Boschma1, Daniel Kidd2, Matthew Newell3, Adam Stefanski4, Rebecca Haling4, Richard Hayes5, Megan Ryan2, Richard Simpson4

1 NSW Department of Primary Industries, 4 Marsden Park Rd, Calala, NSW, 2340, www.dpi.nsw.gov.au, suzanne.boschma@dpi.nsw.gov.au

2 University of Western Australia, School of Agriculture & Environment, M090, Perth, WA, 6009

3 NSW Department of Primary Industries, PO Box 129, Cowra, NSW, 2794

4 CSIRO Agriculture & Food, GPO Box 1700, Canberra, ACT, 2601

5 NSW Department of Primary Industries, PMB, Wagga Wagga, NSW, 2650

Abstract:

Serradellas (Ornithopus spp.) are alternative temperate annual pasture legumes, until recently grown mainly on deep sandy soils where their deep rooting habit and tolerance of low soil fertility/acidity confer an advantage over subterranean clover (Trifolium subterraneum).  Expansion of serradella use requires cultivars with appropriate maturity type and hardseededness to underpin persistence in a wider range of growing seasons and climates. In 2018, a national experiment was conducted to determine the maturity types of a range of serradella cultivars that are potentially available in Australia. Thirteen cultivars of serradella (six O. compressus, six O. sativus, one O. pinnatus) and five cultivars of subterranean clover were sown in Perth, Canberra, Cowra and Tamworth to examine flowering times and duration in these environments. The results indicated a wide range in maturity types among serradella cultivars, but with significant gaps in the maturity types available for hardseeded O. sativus cultivars.  A number of the serradellas had unstable flowering times indicating inadequate germination-date flexibility and will flower too early (during severe frost periods) after germinating on an early break to the growing season in eastern Australia.

Identifying the causes of unreliable nitrogen fixation by strand medic (Medicago littoralis) based pastures

Fiona Tomney1, Brian Dzoma2, Ross Ballard3 and Nigel Wilhelm3

1SARDI, Minnipa Agricultural Centre, 226 McKenzie Rd, Minnipa SA 5654 fiona.tomney@sa.gov.au

2SARDI, Loxton Research Centre, Loxton SA 5333

3SARDI, Waite Research Precinct, Urrbrae SA 5064

Abstract

Following grower reports of low soil nitrogen (N) following vigorous medic-based pastures on the upper Eyre Peninsula of South Australia, management practices including herbicides and fertilisers were investigated for their effect on the N fixation of strand medic pastures at six field sites on the upper Eyre Peninsula. Applying phosphorus to soils with low P reserves at medic pasture establishment increased medic shoot dry matter and improved N fixation. The addition of urea at seeding reduced N fixation by the medics at some sites. Soil residues of the herbicide Logran reduced medic growth at one site. The application of a full label rate of Agritone 750 Herbicide (applied late when the medic plants were 5-7 cm in diameter) decreased pasture production and N fixation.

Host

The Australian Society of Agronomy is the professional body for agronomists in Australia. It has approximately 500 active members drawn from government, universities, research organisations and the private sector.

Photo Credits

David Marland Photography david_marland@hotmail.com Graham Centre for Agricultural Innovation, Charles Sturt University

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