Monday, April 22, 2024

Results trickle through from Gabrielle silt trials

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Plant & Food Research testing various seeds to gauge recovery of land blanketed during cyclone.
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Trials to gain a better understanding of how key vegetable crops respond when grown in silt-affected areas are underway in Hawke’s Bay.

Flooding during Cyclone Gabrielle resulted in several million cubic metres of silt being dumped on orchards, farms, roads and properties. 

These extensive layers of silt, or alluvium, have adversely affected soil conditions, posing challenges to cultivation. In Hawke’s Bay, some vegetable growers have retired plots of land while they weigh up the viability of resuming farming in these areas.

Plant & Food Research launched a project in October called Promoting Crop Resilience in Silt-Affected Landscapes, designed to help address these challenges faced by growers and industry. The work is being funded by Plant & Food Research, with the first stage of the project expected to be completed by June.

“Cyclone Gabrielle has had a significant impact on horticulture, arable, and vegetable crop farmers in affected areas, resulting in extensive damage to cropping lands and significant financial losses,” said project leader, crop eco-physiologist Dr Eduardo Dias de Oliveira.

The research is being conducted on a commercial farm in Hawke’s Bay that was impacted by alluvium in the 2023 cyclone event. One hectare of land with varying silt depths was planted in four different vegetable crops — carrot (small seeds), peas (medium seeds), maize (large seeds), and transplanted broccoli. 

These crops are economically significant in the region and have diverse seed sizes and root structures.

“Silt has no defined structure, and we know very little about the dynamics of water and nutrients in the silt,” Dias de Oliveira said. 

“Also, despite varying texture, silt is usually extremely fine, and that may reduce soil oxygen, and reduce root ability to grow and reach the original soil below the silt. That’s why we are doing this work, to understand how varying silt depths affect the performance of these crops.”

Crop eco-physiologist Dr Eduardo Dias de Oliveira says we know very little about the dynamics of water and nutrients in the silt.

The trial site is being regularly monitored to evaluate growth and yield and test the interactions of plant roots with the silt. Alongside this work, trials are also being undertaken in a greenhouse at Plant & Food Research’s Hawke’s Bay research centre, using different ratios of alluvium to soil to better understand how crops perform in these different conditions.

“Our initial findings indicate that small-seed crops may struggle to establish in the silt as their roots may have less vigorous growth early on. This may reduce their ability to explore the silt, absorb nutrients in the silt or reach the original fertile soil beneath,” said Dias de Oliveira.

The research project will aim at understanding different management practices could enhance the resilience of the farms. 

Some of the questions Dias de Oliveira hopes to answer through the project include: Should silt be stripped off immediately? Can crops grow into silt? Can the silt be incorporated into the original soil? What is the optimal depth for silt incorporation? And, depending on the chosen practice, what is the timeline for full farm recovery?

“These questions will guide our investigation into enhancing the overall performance and adaptability of these crops.”

The ultimate goal is to develop industry-specific resources that not only aid decision-making and facilitate a swift recovery from the aftermath of Cyclone Gabrielle but also contribute to future recovery efforts in the face of similar events. 

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