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Climate Smart Agriculture starts with soil, Tongan scientist tells farmers

Nadi, Fiji

Siosiua Halavatau

By Finau Fonua

Tongan scientist, Siosiua Halavatau, is encouraging farmers to be “soil smart” when cultivating crops; to not overplough the land and to avoid using fertilizers.

Currently attending a soil conference in Fiji, he told Matangi Tonga that the well-managed cultivation of crops would not only cause less disturbance to the organic matter of soils but would also reduce the greenhouse emissions that contribute to climate change.

“The science says that if your soil is high in organic carbon, you will grow better crops and it will resist climate change. That is a scientific fact”, he stated.

“When the soil is high in organic carbon there’s a process of fixing the carbon in the soil so they don’t get converted to Carbon Dioxide. When we plough we expose the land to the sunlight, this sunlight oxidizes the carbon into Carbon Dioxide, which is emitted. In Tonga, we tend to keep ploughing the land.”

“Normal soil should have 5% organic matter, so our approach is, how do we maintain that 5% of organic matter in the soil. If we find a way to maintain these organic soils, then we can make sure that they don’t oxidize and contribute to climate change.”

Planting yams

Halavatau stated that the intensive plouging of the land was unnecessary and destructive to the organic composition of soil. He said that research he conducted on intensively ploughed land severely reduced the organic composition.

“I analysed the organic matter of these soils that, it is surprizing that the Tongan soil, if you plough intensively three or four times a year to grow your crops, it takes three years to drop the organic carbon from 10% to 1%. See how fast it comes down,” he stated.

“A lot of farmers in Tonga think that you have plough twice. You don’t need that, you just plough once and then you turn the weeds upside down and then it is killed by the sun. And then you dig your soils and plant your yams.”

Let weeds rot

Halavatau also encourages farmers to not remove dead weeds from land. He said that allowing dead weeds to rot on farmlands maintained the organic matter of soils, contributing to better crops.

“While you do your cultivation, don’t get rid of organic matter but let it recycle back into the system. A lot of farmers in Tonga often take the weeds and burn it on the side. You shouldn’t be harvesting the roots (of weeds) and burning it on the side. Let the roots remain there and let them rot back into the soil.”

“There are certain weeds they you should remove such Kaningi, these can regrow within two days or less.”

“I also recommend to our farmers not to use fertilizers, that’s a fast way of reducing organic matter because fertilizers don’t have anything. Farmers tend to look at a taro growing well from fertilizers and they throw away the weeds.”

At a soil conference in Fiji, Halavatau said that he hoped local scientific evidence and conclusions would be accepted as a government policy to guide Tongan farmers.

“We have all the evidence from our scientists in Tonga. All we need to turn this evidence into policy to guide agriculture in Tonga.”

“I call it smart soil. How you can manage your soil so you can produce your crop and maintain the organic carbon, how can you seed smart, finding the right growing material so that everything you grow is precise. Climate Smart Agriculture, how can we turn a village to be climate smart?"

Halavatau works with the South Pacific Forum is currently sharing his research with other agriculturalists and soil scientists from around the region.