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By Darius Koreis 8 August 2019 6 min read

Image: Flickr / Ryan and Nada

TARO – or Colocasia esculenta – holds a big place in the cultures of the Pacific Islands but the starchy, edible corms that grow underground are getting smaller in size.

Mr Khem Chand, one of one the biggest taro farmers on the Fijian island of Taveuni, says he used to harvest taro with corms as large as 5-6 kilos.

“This time we are harvesting taro little over one kilo or even below, some with good ‘bell’ shape corm and some with deformed shape,” Mr Chand says.

He explains that the rejection rate of taro for the export market has also substantially increased since the industry’s glory years, when only three-to-five per cent of taro corms were rejected.

“As of now, that number has really increased from five to 40 per cent,” he says.

Taro corms have reduced in size, leading to loss of food production and economic impacts.

The reason for this decline – widely seen across the Pacific - might seem puzzling. At first sight, the volcanic soils typically found in Fiji, Samoa and Tonga might not seem like they have a lot in common with the coarse coral soils found on low-lying coral atolls on Tuvalu or Kiribati.

Despite being on opposite ends of the soil spectrum, these islands do share similarities. They are used to grow similar crops, and they inhabit a similar tropical climate.

However, for farmers like Mr Chand, who has seen radical changes since commercial production started on his island in 1993, the reason for the decline in taro yields is obvious.

“The reject rate has increased due to overuse of soil,” he says.

The Pacific Community (SPC) recognises taro as a traditional staple throughout the region, and it is a key source for vital fibre, vitamins and minerals in a healthy diet.

Pacific Island countries are banding together to address the need to grow enough food, sustainably, and help retain the cultural role of taro.

Multi-year projects funded by the Australian Centre for International Agricultural Research (ACIAR) are seeing CSIRO soils and farming systems scientists collaboratively work with Pacific Island nations to respond to this challenge. Critical to the project is that it brings together key institutions, ministries responsible for agriculture in Tonga, Fiji, Kiribati, Tuvalu and Samoa, Manaaki Whenua Landcare Research NZ, Secretariat of the Pacific Community, and CSIRO to tackle the problem on farmer’s fields and unravel barriers within market and policy domain.

Economic and food security risks

Mr Siua Halavatau has been involved in Tongan agriculture since the 1980s and has a vision for a thriving sector that is resilient to climate change, and environmentally sustainable.

Now working as a private consultant and Pacific panel member on the UN Food and Agriculture Organization’s Intergovernmental Technical Panel on Soils, he has seen a great change overcome his country’s agricultural fortunes.

“I have seen nutrient deficiencies in Tonga since the 1980s on cool vegetables, corn, squash pumpkin and water melons as well as root crops,” Mr Halavatau says.

These deficiencies are resulting in yield gaps (the difference between theoretical crop harvests, and actual results), which are putting a strain on the subsistence farming that many rural areas rely on.

Halavatau says climate change will only exacerbate the problem, with farmers already feeling the effects. For instance, international demand for Tongan squash has increased in recent years. But a poor dry season hampered efforts to grow crops.

Coral atolls naturally suffer from poor soil fertility. However, Mr Halavatau says perceptions are hampering efforts to improve farming practices on the volcanic islands as well.

“Because of the notion among farmers that we have very fertile soils and do not need external sources of nutrients – this is the worry, and national production is stagnating,” he says.

CSIRO soil scientist Dr Ben Macdonald is overseeing a far-reaching project that’s looking to turn this around across Tonga, Fiji, Tuvalu, Kiribati, and Samoa.

Field trials in Tuveuni. This work aims to lift average corm size to 2-3kg.

“With agricultural intensification and a move towards cash exports – the systems haven’t been well maintained. Yields are actually coming down, risking the futures of communities,” Dr Macdonald says.

“We’re using taro – a root crop that’s common to all the islands and is important culturally – as a model crop to better understand the dynamics at play across these different areas.”

The choice of taro is particularly pertinent, as it is one of the crops to have suffered worst from the long-term decline in soil health.

Soil impacts felt at the farm and societal level

The impact of this situation is having a significant impact on the livelihoods of the farmers, who are finding it difficult to cope compared to times when 80 per cent of the taro harvested was exported.

To tackle this, Dr Macdonald’s research team is working with farmers to design nitrogen and nutrient management recommendations for the region’s different soils, while building in-country capability.

While farmers can apply fertilisers to reverse the decline in soil nutrients and increase their yields, the researchers are also looking at implementing other strategies such as crop rotations to improve soil health.

“There’s a complex interplay between how crops interact with various types of soil – what they take out and put back in. When that’s combined with other factors such as fertilisers, pests, weeds and weather, it doesn’t become as simple as saying ‘apply more nutrients’ to fix the problem,” Dr Macdonald says.

Samoa fallow management taro trial. This work is investigating the use of legumes to improve soil nutrients and taro yields.

At the same time, the cost of getting Pacific agriculture wrong goes beyond putting food on the table – it can also impact the very water on the dining table and the wider environment.

One reason why farmers may be hesitant to fertilise their crops comes from past experiences of fertilisers leaching into the groundwater.

In some cases, groundwater is only 60cm below the surface, with taro roots extending to that depth. Fertilisers were known to escape into the waterways, resulting in algal blooms in waterways and contaminating domestic water supply.

A separate CSIRO project using the Chameleon Soil Water Sensor system is providing farmers with an affordable way to measure whether their crops need watering. This is looking to reduce instances of over-watering (which also reduces crop yields) as well as preventing rogue fertilisers from escaping into the environment.

However, Dr Macdonald is convinced that better understanding the soil itself is the key to raise the Pacific’s crop yields. For a problem spanning multiple countries, how can that knowledge be built in a timely and cost-efficient manner?

Historic data holds the answer

Plans are currently underway to salvage historic soil data, digitise this information, and make it available for policymakers and land managers via a data portal. This effort is being led by with Manaaki Whenua Landcare Research NZ.

It is expected that this solution of using existing knowledge of soil classification could save between AU$20-30 million.

“There are still gaps in the soil knowledge – the blanks will need to be filled in. However, much of the information already exists, and making this information available will open the region to big data responses to many soil problems,” he says.

CSIRO is working with Pacific agricultural sectors in utilising new sensing technology, in the lab and in the field, to identify production constraints arising from soil nutrient deficiencies. This technology enables near real time and in-country diagnosis of nutrient limitations, soil condition and organic carbon levels. A game changer.

The end goal is to tie together the soil data with field trial data and provide Pacific farmers with precision agriculture tools to herald a new era in regional farming.

Improved agricultural decision making informed by a scientific-led response could lead to a sustainable and resilient sector that can stand up to the other challenges facing the region. At the same time, the resulting increased yields could see a return of the strong export industries that originally drove so much economic growth in the Pacific region.

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