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Students research the restoration of salinised soils using halophytes

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There were problems with salinisation in the Netherlands last summer. Due to extreme drought and the very low water levels in the major rivers, salinisation of the soil and water in the west of the Netherlands increased. Salinisation is a huge problem for farmers and is harmful for the environment. How can we prevent salinisation, or perhaps even use it? Three second-year Horticulture and Business Management (HBM) students researched these questions.

Sustainable, creative and good for the environment

HBM students Kimberly van der Vegt, Ronald Vreugdenhil and Kate McCollum have worked on projects together before. “We are all interested in soil quality and increasing the sustainability of food production,” explains Kimberly enthusiastically. Kate adds, “We are committed to sustainable arable farming which is also good for the environment.” “And we really wanted a project where we had to think out-of-the-box,” continues Ronald. Lecturer Erno Bouma had the perfect project for them: ‘The restoration of salinised soils using halophytes.’

A global problem with major implications for agriculture and horticulture

Salinisation is a global problem that arises due to water shortage and particularly affects areas such as North Africa, Australia and the Mediterranean. Last summer we even experienced this problem in the Netherlands when the drought evaporated the water, leaving salts behind. ‘Normal’ plants, called glycophytes, cannot grow in salty soils and this has major implications for agriculture and horticulture. Ronald explains, “You can use chemicals to prevent salinisation, but that is expensive and bad for the environment. You also need water for this too and salinisation occurs primarily during a water shortage. We wanted to look for a sustainable solution to salinisation which is good for the environment.” A natural solution could be the cultivation of halophytes on salinised soils. A halophyte, or salt-tolerant plant, is a plant which can grow in soils with a high salt content. The halophyte absorbs the salt in the soil, desalinating it and, over time, possibly making it suitable again for normal plants.

A project full of challenges

The students tested their research with two plants which can cope with a high concentration of salt: glasswort and ice plant. Glasswort is well-known and can be grown without tides and even with very little water, making it ideal for this research. The ice plant is a less familiar plant which is not used for consumption. “We learnt a lot,” says Ronald. “We had to sow everything ourselves because we couldn’t buy the plants. That was a real challenge as there was no previous research we could fall back on. Eventually 50% of the glasswort germinated.” Kimberly continues, “Unfortunately we couldn’t use any real salinised soil, so we had to simulate it, which was difficult. It was hard to take a good EC-measurement (to measure the concentration of salt). We took a measurement each week for eight weeks, but we didn’t get any information. The salts in the top of the bucket were gone, but at the bottom there was a lot of salt.” “We also wanted to know if the salt content had increased in the plants,” continues Ronald. “So, we dried the plant matter of each pot in a drying oven and measured the weight. The dry weight was attained with the drying oven at 105 degrees Celsius, and the ash was heated to 600 degrees Celsius. The remaining ash was therefore the remaining salt. Later in the research we also added organic matter such as moulds. Moulds work together with the roots enabling the plant to absorb more nutrients, and therefore also more salt, from the soil.”

A promising method needing more research

The plants did actually absorb salt from the salinised soil, but exactly how much and what the precise influence of the added moulds was, is not entirely clear. Kimberly explains, “It is a promising method, but it definitely needs more research before it can be applied practically.” Ronald adds, “We now know the plants absorbed salts from the soil, but we don’t yet know how much would need to be removed before salinised soil could actually be used again for normal plants.”

Researching, experiencing and solving things yourself

All three students agree that you learn more if you can immediately put the theory into practice. “Especially for the Statistics and Cultivation & Research subjects,” says Ronald, “and it is also great that you’re free to do your own research in your own area of interest.” “The theory helps you during your research,” adds Kimberly, “but you must keep thinking for yourself, which is good.” Having to come up with their own solutions was experienced by the students as extremely positive. “A farmer discouraged us from using glasswort, but we still wanted to try, so that we could really research, experience and solve it ourselves,” according to the enterprising students. They concluded the project before the summer holidays with a report, a presentation for fellow students and a vlog.

Passing on the baton

Kimberly, Ronald and Kate are inviting Horticulture and Business Management and Horticulture & Arable Farming students to take over the baton and continue their project. The global problem of salinised soils will, unfortunately, probably increase in the future and this research could find an answer.