During the summer of 2012–13 Andrew Hall, SLTEC Fertilizers’ agronomist for Tasmania and southern Victoria, collaborated Rob Jones from Roberts Irrigation to set up a fertilizer injection trial at a ‘Janefield’ dairy located at Meander in Tasmania.

The aim of the trial was to further investigate the replacement of traditional broadcast urea post grazing with fertigated UAN nitrogen. The trial sought to establish if dividing
the total quantity of applied N (40kg/Ha) over 4-6 split fertigations during the summer pasture recovery phase (approx 20 days) could be more efficient and provide the same
pasture growth response as one single application of broadcast urea.

The theory is that split fertigations have the potential to reduce total N units applied due to reduction in losses and better plant uptake. Rather than using straight UAN, SLTEC’s
NitrologiCAL PLUS TE™ was chosen as it contains calcium and essential trace for pasture growth including Cu, Zn and boron.

Grundfos’ Area Manager, Tony Hourigan, arranged for the loan of a Grunfos Alldos injection unit which was matched to the desired injection rate per hour for the pivot. This unit is extremely easy to use and can be wired back from the pump shed to the pivot centre for automatic operation. It is also capable of handling a wide range of liquid products.

The general findings were that a larger, up-front hit of N was required to kick start pasture post grazing. This gave a better immediate growth response than split applications. Anecdotally, this is the experience that dairy farmers have based their usual urea application on, ie applying monthly budget in one application.

A more appropriate approach may have been to apply the full amount of NitrologiCAL PLUS TE™ up-front to stimulate root development and regrowth. The literature supports the application of N as ammonium for root development in pasture as after grazing there is significant reduction in root mass as plant top removal is balanced by root death. Later regrowth of leaf would be expected to benefit directly from the nitrate nitrogen component of the applications.

Tissue samples have shown that the level of N and subsequent dry matter production tends to fall off in the latter half of the regrowth period and that a follow-up foliar application of NitrologiCAL PLUS TE™ at 30-40L/Ha could boost final dry matter production and improve plant tissue levels of nutrients important for animal health.

SLTEC Fertilizers and Roberts Irrigation would like to thank Grundfos for their assistance and anticipate revisiting this work and encouraging dairy farmers to look at the installation of fertilizer injection units on new pivots and fertigation of nitrogen as a serious option for managing summer nitrogen inputs.