Forages for Reduced Nitrate Leaching, Ngai Tahu (Canterbury)

Reducing nitrogen (N) fertiliser, cow numbers and imported supplements, and growing fodder beet on the platform.

Significant farm system changes occurred between 2014/15 and 2015/16 seasons. These included:

• Reducing N fertiliser from 344 kg N/ha to 227 kg N/ha.
  • The farm was originally converted from forestry and has historically used significant amounts of N to assist with carbon breakdown during the development phase.
• Imported supplementary feed decreased from 863 to 234 kg DM/cow.
• Reducing cow numbers from 1278 to 1110, stocking rate from 3.6 cows/ha to 3.1 cows/ha.
• Fodder beet was planted in a paddock on the milking platform to feed to lactating cows in autumn to extend the lactation and transition cows for wintering.

This resulted in milk production decreasing from 1660 to 1397 kg MS/ha, a 32% decrease in N leaching and farm working expenses decreased from $4.71/kg MS to $3.97/kg MS.

Decreasing stocking rate, increasing imported supplements, and continuing to establish plantain as part of a mixed sward and undersowing into existing pasture.

This season was largely about refining systems after the large change that occurred in 2015/16.

• Stocking rate decreased by a further 0.1 cows/ha.
• N use increased slightly from 2015/16 by 10 kg N/ha to 237 kg N/ha.
• The amount of imported supplement eaten increased from 234 to 599 kg DM/cow of low-N feeds (lifted fodder beet and maize silage).
• Pasture harvested decreased to 13.2 t DM/ha.
• Production was 1405 kg MS/ha, similar to the 1397 in 2015/16 and less than the 1660 in 2014/15. It was a disappointing end to the season as the farm had been tracking well ahead until wet weather struck in April.
• 17 ha (5% of platform) of pasture, including plantain, was renewed during the season, half of this area was the ex-fodder beet paddock from autumn 2015/16.
• About 60 ha (17% of platform) was undersown with a mix including plantain.

Compared to 2015/16, the 2016/17 season saw a slight increase in nitrate leaching from 56 to 61 kg N/ha, as estimated by Overseer, after a significant reduction from 88 kg N/ha in 2014/15. Purchased N surplus also increased from 141 in 2015/16 to 185 kg N/ha in 2016/17 after having reduced from 302 in 2014/15. The purchased N surplus of 185 kg N/ha was still the lowest of the five dairy monitor farms.

The increase in purchased N surplus and N leaching between 2015/16 and 2016/17 was driven by increases in N fertiliser and imported supplement, without a corresponding increase in output.

Fodderbeet

After success in 2014/15 and 2015/16, another fodder beet crop was sown on the milking platform for use as autumn feed and transitioning.

Effluent was applied to the paddock prior to cultivation.

The fodder beet was grazed in April and May. Crop yield was approximately 23 t DM/ha.

Cows were grazing the fodder beet for 2-3 hours, without supplement before going to their paddocks. Before dry-off they were being offered up to 7 kg DM/cow.

Plantain

It will be difficult to achieve the levels of plantain needed to reduce N leaching through pasture renewal alone. A trial was run to investigate the cost-effectiveness of 12 different methods of establishing plantain into existing pastures on Paritea and two other monitor farms.

On Paritea three establishment methods were tested in one paddock:

• Broadcast pre-grazing,
• Broadcast post grazing, and
• Direct drill post grazing.

Sowing occurred in the second week of February at a rate of 8 kg/ha of plantain seed.

The paddock was mown before being grazed at 30 days after sowing.

At the end of October 2017 little plantain (0-5%) had established in the sward, mostly in areas with low competition (poor pasture).

Better success was seen with direct drilling in late December on one of the other monitor farms.

Based on this result we concluded February was too late to try and establish plantain into an existing pasture.

Introducing catch crop, increase in N fertiliser use, decrease in imported supplement, continued to grow fodder beet on the platform.

The farm system in 2017/18 was similar to 2016/17. Changes include:

• N fertiliser use increased from 237 to 281 kg N/ha
• The amount of imported supplement decreased slightly from 599 to 543 kg DM/cow
• A catch crop of oats and Italian ryegrass was grown following last year’s autumn fodder beet

Fodder beet continued to be used on the milking platform and plantain continued to be sown in pasture.

Milk production decreased by 120 kg MS/ha, which combined with the changes in inputs led to an increase in purchased N surplus from 185 kg N/ha in 2016/17 to 230 kg N/ha for 2017/18. Estimated N leaching also increased from 61 kg N/ha to 70 kg N/ha.

Catch Crops

Paritea took part in a oats/Italian ryegrass catch crop trial, with oats and Italian ryegrass being sown immediately after the fodder beet had finished being grazed (mid-June).

Fallow areas were left to allow a soil mineral N comparison with areas where catch-crop had been sown.

Results

• The oat/Italian ryegrass crop was harvested early in December, yielding 9.3 t DM/ha, at a quality of 12.1 MJ ME/kg DM.
• The soil under the catch crop contained 33 kg mineral N/ha, 35% less than the fallow land at 51 kg N/ha. This indicates the catch crop reduced the risk of N leaching.

Similar to 2016/17 with less N fertiliser and imported supplement, fodder beet still grown on the platform, catch crop grown.

The farm system in 2018/19 was similar to 2016/17 but less N fertiliser was used and slightly more imported supplement.

• An oats and Italian ryegrass catch crop was again grown following last autumn’s fodder beet and this was harvested in December.
• The Italian ryegrass continued to grow during the season and was not regrassed. This was weedy at times and the oats disappeared after harvest.
• N fertiliser use decreased from 281 kg N/ha in 2017/18 to 235 kg N/ha.
• The amount of imported supplement decreased slightly from 543 kg DM/cow in 2017/18 to 494 kg DM/cow.

The purchased N surplus was lower than 2017/18 at 187 kg N/ha, and N leaching reduced to 60 kg N/ha. This was mainly driven by the lower N fertiliser use.

“Toitū te Marae o Tāne, Toitū te Marae o Tangaroa, Toitū te Iwi

When land and water are sustained the people will prosper.

Ngāi Tahu Farming’s purpose is to produce sustainable products from our environment in a way which is in line with Ngāi Tahu values; contributes to achieving Ngāi Tahu aspirations such as upholding the tribe’s role as a kaitiaki (custodian) of the environment, creating employment opportunities for Ngāi Tahu people, and running a successful business. Furthermore, we hope to encourage industry change for better farming practices throughout Aotearoa – New Zealand.

One of Ngāi Tahu Farming’s’ key sustainability goals is to use less water and leach fewer nitrates. We want to push the boundaries of best practices. Being involved in the FRNL programme has enabled us to report back results and outcomes to Mana whenua (local iwi who are guardians of the whenua/land).” 

Footnote: The potential effects on N leaching of the FRNL options implemented on the farm (plantain, fodder beet and catch crops) are not yet reflected in Overseer. FRNL researchers and Overseer are working together on updating the model and providing the necessary background information to users and other stakeholders, such as policy makers and regulators.