Agronomic assessment of gibberellic acid and cytokinin plant growth regulators with nitrogen fertiliser application for increasing dry matter production and reducing the environmental footprint


  • A. Ghani
  • S. Ledgard
  • J. Wyatt
  • W. Catto



Abstract Plant growth regulators (PGRs) are increasingly being used in agriculture for a variety of purposes. In pasture systems, the use of PGRs is relatively new and the effects of its application on plant productivity and physiology are poorly understood. A mowing trial was established in Waikato in early spring 2012. Key objectives from this study were: to determine effects of gibberellic acid (GA3) and cytokinin (CPPU) application with and without nitrogen (N) fertiliser application on pasture production, N concentration (%N), root biomass and potential reduction in N leaching from grazed pastures. Treatments (with five replicates) were: control, urea (40 kg N/ha), GA3 at two rates +/- urea, and CPPU at three rates +/- urea. Implications for grazed pasture and N leaching were modelled for a case study dairy farm. Application of GA3 alone showed a significant (P<0.05) rapid increase in dry matter (DM) production compared with the control between 5 and 29 days after application. The DM yields from GA3 alone were similar to those with urea-N alone and the effects of applying GA3 and urea-N together were additive. Application of CPPU showed no significant effect on pasture production. There were no treatment effects from either PGR on root biomass. The %N in herbage was significantly lower in the GA3 treated plots than the control, which would reduce urinary-N excretion under grazing. Preliminary modelling of data for a grazed pasture showed a potential reduction in annual urine-N leaching of 4-29%. Keywords: Gibberellic acid (GA3), cytokinin (CPPU), dry matter yield, total N, root biomass