Environmental N leaching - Everest Family (Canterbury)

Flemington Farm, 10km south of Ashburton (Hinds Catchment), is 273ha of flat terrain, with a milking platform of 217ha and 38ha used for winter/feed crops and young stock. The balance, 18ha, is in trees, laneways and buildings. No cows are wintered on milking platform and young stock are grazed off from weaning.

Two options for reducing environmental footprint were modelled for this farm, from the 2018/19 season:

1. The first scenario focuses on reducing N fertiliser use, reducing the cropping area on farm, and replacement rate of young stock, while maintaining production. This resulted in reduced N loss, and emissions, and increased profitability.
   
   
2. The second option builds on the first option and aims to reduce N loss by a further 12% through further reducing N fertiliser and substituting pasture grown with low-N supplements. This results in further reductions in N loss and emissions and a decrease in profitability.

“We care for the environment but need a balance between social, economic, environment – we can’t go broke individually or as an industry/country.  Being involved in DairyNZ’s Selwyn/Hinds project has given us the opportunity to carefully review options.  We are prepared to give things a go. For example by spreading plantain out of the fertiliser bulk spreader truck, using duals on pivots to reduce ruts, focusing on labour/time efficiency as our team only milk once a day with the automation in the dairy shed.”

 – Phill Everest, Flemington Farm.

Challenges

The Everest’s have chosen their low input system based on the challenges they have to work with at Flemington. Phill says that by choosing to have a lower stocking rate, they are working with rather than against the farm characteristics.

• Flemington is a farm that has heavy soils and a high-water table, with drains throughout. By sticking to cow numbers in the 650-750 range, there is the added bonus that they are able to have their team milk only once per person, per day. At this stocking rate they are also able to have a low amount of feed brought onto the farm – and with the high-water table and wet soils, they can stick to feeding this as grain the shed. 
• Using fodder beet in autumn has taken the pressure off in that part of the season, as pasture damage in wet weather is a challenge. By using the beet, it also reduces the transition pressure at winter grazing as the cows are adjusted to 5kgDM beet before they leave the milking platform.
• Because the farm is already operating efficiently in terms of irrigation on heavier soils, and with a low stocking rate and low feed input, they don’t have a lot of room to improve to further reduce both N loss and GHG significantly – further reductions will rely on additional fine tuning.

N loss mitigations

Irrigation

The Everest’s have invested in a centre pivot with VRI, which means irrigation efficiency can be achieved to a high degree of precision. It also allows a low application rate of effluent, which is injected into pivots over 50% of milking platform.

Farm system choice

Flemington have adopted a low intensity system, with only 5% imported feed used on the milking platform.

Drainage

Flemington’s tile drains are very effective in reducing N loss on this farm, as the N is in the whole of the soil profile and is not lost when water drains, as it is through preferential flow.  N loss is by matrix flow i.e. when water flows out of the 0-60 cm root zone from the soil pores.  However, if high rates of effluent are applied, (greater than 5-10 mm depth) this can lead to high loss of effluent direct to water ways through preferential flow. Flemington farm have avoided this by applying effluent at a depth of 1-2 mm via pivots.

Fencing waterways

Flemington Farm have had all their drains fenced off for at least 20 years, and have planted on the north side of the drains to provide shade to encourage biodiversity in the  drains - in keeping with Mahinga Kai principles. Phill says they are currently looking into whether they can plant the south side of the drains in a way which allows them to be maintained as needed.

Greenhouse gas mitigations

Flemington in the 2018/19 season produced a total of 14.8 t CO₂ equivalent/ha/yr, and 11 kg CO₂ eq/kgMS. Phill says while there is no one silver bullet available to dramatically reduce their GHG losses, there are a number of small practices they can adopt now that will make a difference. Flemington have implemented a number of these, and have had a case study done to look at future options.

Current greenhouse gas mitigations

• Low application rates of effluent (1-2mm), utilising the variable rate irrigation (VRI) technology on the pivots and storage capacity of over 50 days to ensure effluent is applied at a time when it can be fully used for pasture growth and not lost to water or the atmosphere
• Not applying N fertiliser in the shoulder season to reduce N surplus and therefore N₂O emissions
• Sowing alternate pasture species such as Italian ryegrass and plantain for over five years
• Using fodder beet as a low N feed instead of kale to reduce N content in cow urine
• Increasing MS production per cow to lower the feed needed for maintenance of cows as opposed to milk production
• Planting shelter and riparian strips – a total of 22km has been done on farm to date.

Case study on options for future greenhouse gas reductions

Flemington were a case study farm in the Greenhouse Gas project, and six scenarios were modelled for Greenhouse Gas reduction in Overseer and Farmax. Of these scenarios, the Everests chose to focus on Scenario 5 and 6, as described below.

• Scenario 5: N fertiliser use reduced from 349 kgN per effective ha (313 kgN/total ha) to 203 kgN per effective ha (187 kgN/total ha). Effluent blocks are treated separately to account for the N content in the effluent. The crop area (wheat, barley and fodder beet) is reduced from 23.3 to 18.9 ha, and stock replacement rate is reduced to 20%. It is assumed that there is enough potential to increase feed efficiency so that milk production can be maintained.
• Scenario 6: As above in scenario 5, plus further reduction of N fertiliser to 134 kgN per total ha. Milk production is maintained, and to fill the modelled drop in pasture production from the reduced N fertiliser, additional barley grain will be bought in.

Modelling outcomes

The main opportunity for the Everest’s to drop N loss further is to reduce their N surplus, as they have already optimised their irrigation efficiency. Scenarios 5 and 6 show that there is potential to drop from their Baseline by 28% and 40% respectively, mostly by reducing their N surplus.

Scenario 5 improves the profitability of the farm by 11%, while scenario 6 reduces profitability due to the expense of bringing in the barley to replace the pasture not grown. GHG outputs are improved in both cases, with a drop of 8% and 11% - this gain comes predominantly from the reduction in N²O and CO₂ from lowered N fertiliser use.