Fertigation proves its worth in trial

16 Apr, 2019 04:00 AM
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Precision is paramount and it is important that the irrigation system is operating at optimum ...

A fertigation trial in south-east Queensland for the past two years has shown it produces more pasture and cuts labour and fuel costs.

The trial compared a fertigation system — injecting water-soluble fertiliser through the farm's centre pivot irrigation system — with a broadcast nitrogen application system.

The project was undertaken in the 2017 and 2018 ryegrass seasons at McInnes Brothers 500-hectare dairy farm at Harrisville, Qld.

A centre pivot irrigation system was used to compare fertigation against traditional broadcast methods of applying nitrogen fertiliser to a grazed and irrigated annual ryegrass pasture.

One-quarter of the pivot area was fertilised after each grazing with Easy N liquid fertiliser and one quarter was fertilised with broadcasted urea for a comparison.

The Easy N was bought in 1000-litre shuttles for the trial and applied using an EcoDose fertigation system injector pump. Irrigation agronomist Pat Daley, from Daley's Water Service Pty Ltd, provided the advice and support for the purchase, installation and use of the fertigation system.

Soil moisture monitoring equipment (EnviroPro SDI 12 unit with a tipping bucket) was installed in each quarter to monitor irrigation and rainfall.

Pasture dry matter yield was measured before and after grazing, and results indicated that the fertigation quarter produced slightly more feed on offer.

Fertiliser, irrigation and rainfall events were recorded.

Benefits of the fertigation system included labour and fuel savings, in addition to savings on repairs and maintenance of machinery.

The liquid fertiliser was immediately available to the plants and could be distributed more evenly (provided the irrigation system had an even distribution uniformity) compared with granular fertilisers.

Applying smaller amounts more often enabled a more optimum growth rate, and liquid fertilisers aren't as volatile, reducing potential losses to the atmosphere.

Related reading

  • ">Methods of fertigation

  • In times of extended wet weather, a spreader might still be required to avoid unnecessary irrigation applications (and for application of nutrients other than nitrogen).

    Observations made during the project included:

  • The EcoDose fertigation pump was relatively inexpensive to purchase.
  • The fertigation quarter was less labour intensive than the broadcasted quarter.
  • Managing the soil moisture profile with the assistance of soil probes was effective.
  • Grazing management is a key factor of a cost-effective ryegrass season.
  • Getting the right advice upfront when considering fertigation should ensure that the right size injector unit is purchased.
  • Soil testing before planting highlighted potassium deficiencies, if not corrected there may have been an adverse effect on pasture growth.
  • No detrimental effects were observed to applying nitrogen through the pivot, smaller amounts of nitrogen were applied regularly as opposed to one big application.
  • A comparison of the true cost of each option demonstrates that buying in bulk (setting up a bulk storage tank holding 19,000-litre) will generally be more labour efficient (and more cost effective in years when the bulk purchase price of Easy N is significantly cheaper compared to the shuttle price).
  • About the McInnes farm

    The McInnes farm comprises mostly irrigated crops and pastures. The dairy herd, which supports 500 milkers, is split into two herds, the "fresh herd" and "stale herd".

    The fresh herd is fed a partial mixed ration on a feedpad. The PMR comprises silage, grain mixes, cotton seed, brewers grain and hay. The herd also grazes ryegrass during the cooler months, and if seasons are favourable, grazes summer pastures or legumes.

    The stale herd grazes pastures throughout the year and is supplemented with a mixed ration once or twice per day, depending on the season and herd numbers.

    Pasture production is mainly ryegrass in the winter months. A range of pastures and crops are grown as conserved feed to supply the PMR ration, including corn, barley and lucerne, in addition to some ryegrass silage. Other legume crops are grown in the summer to be grazed such as cow pea.

    Irrigation comprises of two centre pivots on the home block, with areas of 18ha and 12ha, with the remaining blocks irrigated by soft hose travellers. Water is sourced from Warrill Creek.

    About the trial

    The 18ha annual ryegrass grazing paddock allocated to the fresh herd with a 56-metre centre pivot was used for the trial.

    In the cooler months, it is planted to a straight ryegrass sward. One-quarter of the pivot area (Q3) was used for fertigation (Easy N) and one quarter (Q4) used for broadcasted granular urea. Each quarter was 4.52ha in area.

    It was important that the irrigation system had a good distribution uniformity (DU) so as to ensure the evenness of water and nutrient application. An irrigation systems check was preformed prior to the project, and the DU was deemed to be greater than 90 per cent.

    The farmers opted for a liquid fertigation system (as opposed to a soluble system) due to convenience and ease of use. The EcoDose injector pump fertigation unit was purchased, at a cost of $2900 (excl GST), and installed at the centre pivot site.

    This unit uses a positive displacement plunger pump with variable speed motor to give precise doses of nutrients proportional to the flow rate. A controller allows the operator to easily dial up the required flow rate (litres per hour) and it will immediately adjust the speed of the pump.

    As part of the trial a reference guide of injection rate per hour was developed for different application rates, which allowed for injection rates to be altered as per irrigation scheduling needs.

    Results of the trial

    A comparison of weather data for the two years of the trial indicated average rainfall and a milder winter in 2017 compared with 2018.

    In 2018, less rainfall was received, and minimum temperatures were noticeably lower, particularly during the winter months, where there were many more mornings below zero as compared with the previous year.

    Interestingly, in spring and early summer, minimum and maximum temperatures were much higher in 2018, which contributed to an earlier finish to the ryegrass season, with the final recorded grazing occurring in mid-October, a month earlier than in 2017.

    A total of eight ryegrass grazings were recorded in 2017 compared with seven grazings in 2018. The initial grazing in each year was in June. Days between grazings varied from 18 to 26 days.

    A comparison of dry matter production showed that the fertigation quarter provided more feed on offer than the broadcasted quarter.

    In 2018 this difference was 970 kilograms of dry matter/ha and in 2017 the difference was 186 kg DM/ha. Interestingly, the cumulative DM growth for the season was exactly the same for the fertigation quarter in both 2017 and 2018. For the broadcasted quarter, a difference of 39kg DM/ha was recorded for cumulative DM growth when comparing the two years.

    Utilisation was higher in 2018, at 47 per cent and 45pc respectively for Q3 and Q4. In comparison, utilisation in 2017 was 33pc and 37pc respectively. While not significant, the fertigation quarter had higher daily growth rates (not including the first grazing) in both years.

    A greater volume of irrigation water was applied to the trial site in 2018, reflecting the drier winter conditions experienced. A comparison of the fertigation and broadcasted quarters indicated that a greater volume of water was applied to the fertigation quarter in each year. Fertiliser costs varied; in 2017 the bulk Easy N price was noticeably lower than the following year.

    See Table 1 for a summary of pasture yields.

    Set-up costs for the fertigation system are summarised in Table 2. Although more expensive to set up, use of the bulk storage system was found to be more cost effective over time.

    A record was kept of the labour utilised to fertilise both the fertigation and broadcasted quarters. This information is detailed in Table 3. Fertigation saved labour resources in both years of the trial. This labour saving would be reduced even further with a bulk tank setup.

    The trial showed that there were no detrimental effects to pivot hardware by applying nitrogen fertiliser through the system. Also, managing the soil moisture profile with the assistance of soil moisture probes was shown to be an effective means to manage irrigation.

    The importance of obtaining specialist advice before installing a fertigation system to maximise the benefits derived from improved nitrogen use efficiency was a key outcome of the trial. Precision is paramount and it is important that the irrigation system is operating at optimum water use efficiency. The initial set up of dosing systems requires somewhat complex calculations but once established, the system is very easy to use.

    The results of the fertigation on-farm demonstration highlighted in a practical sense the on-farm and off-farm benefits of improved nitrogen use efficiency. Such benefits warrant further scientific investigation with more replications over a longer trial period.

    In 2017 the project was funded through the Australian Government's National Landcare Programme, and in 2018 was funded through the Dairy and Fodder Water for Profit program. The project was delivered by the Dairying Better 'n Better program, a joint initiative of Queensland Dairyfarmers' Organisation and Subtropical Dairy, with support from the Dairy and Fodder Water for Profit program.

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