Climate change

How are coastal farmers responding to salty soils?

When most people think about agricultural fields, they envision vast landscapes of crops as far as the eye can see. Although that may be true for parts of the Midwest, it’s a very different story on the Eastern Shore in Maryland.

Here, the line is blurred between farmland and marshland. What was once land where corn grew along the edges of agricultural fields is now home to wetlands with plants like salt marsh hay.

What have these changes taken place – at the whim of Mother Nature? Why is the marsh migrating onto coastal farmlands? The short answer – saltwater intrusion.

drone shot high above a farm field also showing some forest, marsh and a stream
Salt-intruded farm field in Somerset County, Maryland. This farm is next to a marsh and brackish tributary; both provide unwanted salts to the farm field. Photo credit: Jarrod Miller

Saltwater intrusion, the movement of sea salts from coasts to inland locations, is driven by several things:

  1. Well-known rising sea levels.
  2. Withdrawal of water from coastal aquifers for human use.
  3. The increased frequency and duration of droughts.
  4. The connections among agricultural water ditches.
  5. The frequency of storms and tides.

Although soil salinization is not a new issue facing farmlands, saltwater intrusion is. This unique phenomenon is comprised of high salinity levels and long periods of saturation. This causes problems for farmers in coastal areas.

In front, long grass, middle of photo bare sandy soil, back is a green weed, then trees
An actively managed farm field, which is growing soybean this season, in Somerset County, Maryland that is experiencing saltwater intrusion. In the foreground, salt marsh hay is growing and in the background an invasive weed species growing. The extensive bare area where nothing is growing has some of the highest salt concentrations on the field. Photo credit: Elizabeth de la Reguera

High soil salinity does not allow a productive and profitable rotation of corn, soy, and wheat, common crops along the Eastern Shore of Maryland. These crops can only tolerate salty soils up to a point – and that point was reached years ago. Currently, there is about 5 times more salt in the soils than corn, soy or wheat can tolerate!

Salt stress can reduce a plant’s ability to absorb water. So, even though water might be present, the crops can’t easily access it – it’s like they are experiencing a drought. Saline soils also can cause ion imbalances. You might be familiar with electrolyte solutions used for long-distance runners. The balance in these solutions is important – the correct amount of sodium, magnesium and calcium is important for athletes, and even “regular” humans.

It’s the same for plants, too. These ion imbalances can suppress growth and limit productivity. The worse-case scenario is plant death. Farmers face a tough decision – try to continue farming, restore the land to wetland, or abandon their fields and way of life.

corn stalks and leaves about two feet high in standing water
Corn attempting to grow on a salt-intruded farm field there is currently inundated with saltwater. Photo credit: Kate Tully

Farmers who wish to continue farming have started replacing crops with salt-tolerant species. For example, farmers have switched to sorghum because corn is no longer producing profitable yields. Farmers have also switched varieties of soy, because some are more salt-tolerant than others. Some types of barley can grow in our region, too.

Part of my research is determining the correct rotations of these new crops for farmers.  Our preliminary data shows that salt-tolerant soybean has a higher percent germination compared to sorghum on salt-intruded farm fields.

When we investigated reasons why the sorghum wasn’t doing well, we found some interesting things. The sorghum wasn’t germinating well. Most likely, sorghum is more sensitive to sodium and chloride toxicity. We found other reasons that affected the salt-tolerant soy. This helps us make recommendations to farmers. However, the differences in each crops’ sensitivity to different stressors associated with saltwater intrusion highlights the complexity and challenges for these farmers, and the scientists who support them.

In some cases, the only decision for a coastal farmer is to abandon their farm fields and put them into different uses. When a farmer stops planting crops, we have found a unique community of agricultural weeds and wetland species takes over the land. This suggests that abandoned fields may facilitate marsh migration.

So, whether a farmer chooses to switch to a salt-tolerant cropping system or abandon their field, the marsh is still going to encroach onto the fields.

drone shot showing strips of green and brown on a farm trial field
University of Maryland field trial on a salt-intruded field. Investigating sorghum, salt-tolerant soybean, salt marsh hay, and switchgrass for salt tolerance. Photo credit: Jarrod Miller

Further, as weather conditions become variable (i.e. frequency in storms and droughts) and sea level continues to rise, saltwater intrusion will only move further inland. But what if a farmer decided to restore their salt-intruded field to a tidal wetland instead of surrendering to nature? Farmers can enroll in the Conservation Reserve Enhancement Program (CREP) to take their farmland out of production for at least a decade and establish wetlands. This provides farmers with an income and provides ecosystem services. For example, agricultural soils are very low in carbon compared to tidal wetland soils. Thus, converting the land to a tidal wetland has the potential to store carbon now and sequester more carbon in the future, which can help mitigate climate change.

At the end of the day, a farmer needs to decide what the best course of action is for them. The unfortunate reality is that we can’t stop saltwater intrusion. In a decade or two, these farmlands will more closely resemble a tidal wetland than an agricultural field. H

Answered by Elizabeth de la Reguera, University of Maryland

About us: This blog is sponsored and written by members of the American Society of Agronomy and Crop Science Society of America. Our members are researchers and trained, certified, professionals in the areas of growing our world’s food supply while protecting our environment. We work at universities, government research facilities, and private businesses across the United States and the world.

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