Author: Reily Menhenett – Technical Agronomist, Incitec Pivot Fertilisers

With dry conditions across much of South-Eastern Australia, and cold winter conditions imminent, growers may be wondering what they can do to maximise the productivity of their pastures to feed hungry livestock.

Irrespective of the seasonal challenges, the fundamentals of managing a high-performance pasture remain the same – grazing strategies and nitrogen (N) applications are key for success. In support, IPF trials have demonstrated additional benefits from incorporating gibberellic acid (formulated as ProGibb®) into an N program.

Augmenting pastures with gibberellic acid

Gibberellic acid is a plant growth hormone which boosts pasture growth, particularly over the winter months when growth rates naturally slow (Agriculture Victoria, 2021). Gibberellic acid can promote growth of grass-based pastures, with annual Phalaris particularly responsive to applications (Biddiscombe et al., 1962). Annual Ryegrass and Cocksfoot are also likely to benefit from applications.

With dwindling feed reserves and dry conditions, it may be tempting to apply gibberellic acid to promote leaf elongation and increase dry matter production. Whilst this is a logical plan, it is worth noting sufficient soil moisture is required to ensure plants can make use of any application of gibberellic acid.

Equally, to support the increased growth rates, plants must be adequately fertilised to maximise the benefits of application. By rapidly increasing the leaf area and growth rate of grasses, gibberellic acid can dilute N within the plant. Therefore, if the pasture system is N limited, the full benefit of increased dry matter will not be realised. Figure 1 highlights the need to coapply ProGibb with an N product. As shown in the graph, solo applications of ProGibb or N were significantly less effective than when applied together.

Figure 1: Phalaris response to nitrogen and ProGibb.

Source: IPF Winter Phalaris Trial Site, Tatong 2016.

Right product, right time

To gain operational efficiencies, EASY N® is the recommended mixing partner for ProGibb, allowing growers to conduct one pass with both products in the tank. Applying at least 60L/ha, and up to 120L/ha of EASY N with ProGibb can boost fodder production and help to support the pasture’s rapid growth rate, with positive effects also seen on crude protein (Lemus et al 2020).

Timing is also important. N should be applied as soon as possible after a grazing to maximise the response (Agriculture Victoria, 2022), and to minimise the risk of phytotoxicity if EASY N is used (Incitec Pivot, 2023).

Grazing management

Using ProGibb with EASY N is a trade-off to maximise the benefits of both products. For gibberellic acid, grazing is recommended to recommence after 28 days, however, to realise the maximum benefit of the N application, waiting 40-60 days (allowing the pasture to reach 2.5-3 leaf reemerged) is the ideal period (Incitec Pivot, 2024).

Figure 2 highlights the cumulative benefits of a longer spell after grazing. Here, where plots were grazed at 28 days, and again 24 days later, cumulative dry matter was inferior in all treatments when compared to 1 cut at 52 days. In ideal conditions, allowing pastures to reach canopy closure before restocking will give the best chance for full assimilation of an N application.

Figure 2: Effect of resting pastures on dry matter (2 grazes vs long spell).

Source: IPF Winter Phalaris Trial Site, Tatong 2016.

Given the direction of the season, and the need to keep feed levels up to stock, it may not be possible for growers to follow a ‘best practice’ approach to pasture management. To balance practicality with profitability, apply a lower rate of EASY N + ProGibb (60L/ha) if the paddock can only be spelled for 28 days before re-entering. This will also allow nitrate levels in new tissue to return to acceptable levels, reducing the risk of nitrate poisoning in stock.

Where pastures can be rested until the optimal window for regrowth, higher rates of EASY N are recommended, which will continue to pay dividends as the season progresses.

Summary

Ultimately, ProGibb and EASY N are both tried and tested products for boosting pasture growth, with a co-application promoting additive effects from the two products.

Incitec Pivot plans to conduct further trial work into both ProGibb and EASY N applications for pastures, to provide further data and confidence to growers.

Further information

For more information on the winter pasture management and nitrogen strategies, feel free to email me at reily.menhenett@incitecpivot.com.au, or call on 0474 093 167.

References

Agriculture Victoria (2021) Driving winter pasture growth rates. Agriculture Victoria https://agriculture.vic.gov.au/farm-management/land-and-pasture-management/driving-winter-pasture-growth-rates

Agriculture Victoria (2022) Pushing for Fodder. Agriculture Victoria Pushing for fodder | Agriculture Victoria

Biddiscombe EF, Arnold GW Scurfield G (1962) Effects of Gibberellic acid on pasture and animal production in winter. Australian Journal of Agricultural Research 13, 400-413.

Incitec Pivot Fertilisers (2023) EASY N. Incitec Pivot https://www.incitecpivotfertilisers.com.au/siteassets/assets/documents/use-directions/18401—use-direction—easy-n.pdf

Lemus R, White JA, Morrison JI. Effect of gibberellic acid and nitrogen application on biomass and nutritive value of annual ryegrass. Crop, Forage & Turfgrass Mgmt. 2021; 7:e20089. https://doi.org/10.1002/cft2.20089

Menhenett L (2024) The wonders of nitrogen use in pasture. Smart Fertilisers smartfertilisers.com.au/the-wonders-of-nitrogen-use-in-pasture/