Gibberellic acid in vetch

BCG have established a trial at Pyramid Hill in North Central Victoria with funding from the GRDC and Agriculture Victoria, investigating Gibberellic Acid (GA) applications on two vetch varieties, Morava and Popany at two application timings.

GA is a plant hormone that promotes cell elongation and consequently increases plant growth. It is commonly used in the horticulture industry and also has a role in intensive grazing systems such as dairy farming. The use of GA in broadacre farming is uncommon and any benefits it may or may not provide are poorly understood. BCG established this trial to identify if GA can be used to improve vetch hay yields in the Victorian North central region.

The product utilised in this trial was GALA applied at a rate of 80ml/ha. The application timings were an early application during the middle of winter (31 July) where there is not a lot of natural growth occurring and a later application 4 weeks prior to expected hay cut timing (1 September). This later timing is what many growers are targeting in order to improve harvestability of the vetch hay crop.

The application of GA did not result in any significant differences in hay yield, regardless of timing of application. There was a yield difference between varieties with Popany yielding 1t/ha more than Morava (Var P<0.001, LSD 0.7t/ha) (table 1.)

Table 1. Hay yield (t/ha) of Morava and Popany at different spray timings. Spray timing x Var P=0.618, NS

Variety Spray timing Hay yield (t/ha)
Morava Early application 3.68
Late application 3.66
x 2 application 3.70
Nil 3.93
Popany Early application 5.20
Late application 4.45
x 2 application 4.75
Nil 4.59

While no yield improvements were achieved by spraying GA on vetch, differences in canopy height were observed fortnightly throughout the season. Two weeks after the early spray application there was a significant increase in height of both varieties from applying GA (P<0.001, LSD=2.4cm). This was not a long-lasting result, with no differences in crop height observed between treatments six weeks after the spray (P=0.798, NS) (Figures 1 & 2). These observations were repeated following the late GA application timing, at the time of hay cutting the canopy height of the early sprayed treatments was significantly lower than all other treatments. This is likely due to growing taller earlier and increasing lodging susceptibility.

Figure 1. Crop height (cm) every two weeks following spray applications of Morava.

Figure 2. Crop height (cm) every two weeks following spray applications of Popany.

Biomass yields and crop canopy height results from this trial suggest the use of GA in vetch crops will not improve hay yield results. Further investigation is required to determine if GA has a role in vetch hay in seasons with different conditions.  

Final results will be published in the 2020 BCG season research results publication and presented at the BCG trials review day.

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