Tuesday, March 19, 2024

Effluent management key to kaitiakitanga

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A Bay of Plenty farm in a high-risk area has implemented environmental initiatives to mitigate their footprint. Anne Boswell reports.
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CREATING a positive example of kaitiakitanga, or guardianship, is a major motivation behind the environmental initiatives undertaken by the Taumanu Lands Trust dairy farm – which include a state-of-the-art nutrient containment system and cow barn.

With the farm situated south of Lake Rotoehu in the Bay of Plenty, farm staff and trustees have worked with their farm consultant and local council to create a strategic plan to minimise nitrogen (N) leaching into the nearby lake.

The 230-hectare farm is governed by the Taumanu Lands Trust, and its appointed trustees – Sam Emery, Fred Whata, Eniz White and Wiremu Keepa – oversee the farm for the benefit of the Maori shareholders, members of the Ngati Pikiao tribe.

Three generations of the Wright family have sharemilked and run the day-to-day operation of the farm for almost 30 years.

Today, Phil Wright is the overseer of the farm and his daughter Samantha and her brother Karl are farm manager and 2IC respectively.

Their 560-strong herd is outstanding: it has a PW of 262, the fifth highest of 11,000 national herds, and a BW of 230, the eighth highest in herds of 500 or more cows. 

With the sensitive catchment of Lake Rotoehu lying at the northern end of the farm, the Trust has always known the importance of paying particular attention to environmental issues.

Rotoehu, which translates to muddy water, is prone to thermal stratification, where lake waters divide into different layers of density due to differing temperatures, causing multiple algal blooms every year.

With this natural process and a lack of outlet already contributing to a reduction in water quality in the lake, Taumanu Lands Trust and a neighbouring agricultural operation completed nutrient reduction agreements with the council.

With the guidance of their farm consultant Mark Macintosh, the Trust applied to the Bay of Plenty Regional Council for a funding grant that would allow the stock to be off the pasture daily – one of the key methods they saw to reduce N leaching. From that, the barn concept was born and construction was completed in 2017.

In terms of nutrient containment the dairy shed has a fairly standard system; wash water is diverted directly to the effluent pond, which is applied to around 37ha with a travelling irrigator.

But the barn is “where the magic happens” according to Mark and is a further commitment to mitigating leaching.

“February to May is a critical nitrogen loss time,” he says.

“The more the stock is on the pasture, the more nitrogen is built up and stored in the soil and flushed out by winter rains.

“With the barn, cows are taken off the pasture over the summer-autumn period in particular, thereby reducing the nitrogen content in the soil and consequent leaching to the lake.”

The barn is 5322m², designed to hold a maximum of 550 cows at 5m² per cow, plus 450m of feed bins.

The barn is not high usage, but it is used strategically. The herd is split into two – one herd moves to once-a-day milking by Christmas, and the second herd moves to once-a-day in around February. Both herds are fed in the barn for one-and-a-half hours prior to milking. The once-a-day herd in the morning, and the twice-a-day herd in the afternoon.

The nutrient containment system underneath the barn incorporates a concrete internal structure lined with a full effluent pond liner, with a layer of sand and pumice underneath the wood chip surface. 

The key benefit of the system is its enormous N leaching mitigation capability. 

The wood chips soak up almost 100% of the effluent, and it is cultivated every day with a rototiller to keep it aerated. The 9.5m apex has ventilation to ensure adequate airflow, while the roof pitch ensures minimal condensation in the barn, critical for the composting process. The litter is recycled annually with the used wood chips applied to new grass pastures in the autumn. This provides a slow-release form of N. 

Over the past four years, staff has fine-tuned a number of operational features as required.  

“There’s no rule book,” Phil says.

“In the first two seasons, we cleaned out the litter every year, but for the past two seasons we have brought new (wood) chips in as required and let it pile up. It is still free flowing and looks and smells great.

“There is a large cost to pulling it out so we are saving money by not doing that every year,” he says.

“The only part of the barn that is scraped is the concrete apron outside, straight into the effluent trap.”

They have also piled the calf chip at the end of the barn to easily push inside as required, instead of carting it from a stack beside the barn.

The team has found the barn has benefits over and above its excellent N leaching mitigation – it doubles as a feed pad, used as a management tool to avoid feed wastage, and is outstanding for both calving and calf rearing.

This spring, they calved 565 cows and had no stock losses.

“The litter is extremely comfortable for cows to calve on,” Samantha says.

“We can flick on the light in the middle of the night and keep an eye on everything. Stock recording is effortless, and we can set up the calf pens so they are close to the cows. It is very peaceful.”

Staff also enjoy calving inside, especially on a cold and windy night.

The Trust has also reduced cow numbers over the past few years as part of the strategy to lower its environmental footprint. It went from 720 cows to 570, then 560, and it plans to further reduce numbers by 50 cows. By fully feeding fewer cows, they expect to maintain milk production. 

Trust chair Sam Emery says the commitment of the Wright family to do the best for the land resonates with the culture of the Trust.

“We have a great team on the ground,” he says. 

“It is important for us to model this to other trusts to demonstrate what they can achieve.

“The combined work of the Trust team, the Wright team and the AgFirst consultant has taken marginal land and turned it into profitable land.”

The Trust hopes its work will help bring Lake Rotoehu back to an historic level of trophic level index (TLI), which indicates the health of a lake based on its degree of nutrient enrichment. 

“The barn has given us real confidence going forward,” Phil says.

“The Trust has a real desire to improve the lake.”

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