Investigating Soil, Nutrient Impact on Organic Leafy Greens in Unheated, Greenhouse-like High Tunnel System

Dec 31, 2024

By Jane Cerza

A recent study by scientists at the University of Florida sheds light on how soil and nutrient management practices significantly influence the productivity and quality of leafy green crops grown in high tunnel organic systems. The research provides valuable insights for organic farmers seeking to optimize crop yields while maintaining soil health and meeting market demands for high-quality produce.

Leafy greens, rich in essential vitamins and minerals, are increasingly in demand in the United States, with organic sales growing by over 24% between 2016 and 2021. Florida, a key producer of organic leafy greens, faces challenges in maintaining productivity due to subtropical conditions like temperature extremes, humidity fluctuations, and frequent rainfall. These challenges are compounded by sandy soils with low organic matter content, making water and nutrient management difficult. As high tunnel systems gain popularity among Florida growers, research is needed to evaluate their effectiveness in improving crop yields and quality under these conditions.

High tunnels, which are unheated greenhouse-like structures, are increasingly used in organic farming to extend growing seasons and protect crops from adverse weather conditions. Despite this growing interest in high tunnel organic vegetable production, limited information is available regarding optimizing nutrient management for organic leafy greens in Florida sandy soils.

In this 3-year study, the cowpea cover crop as well as a range of soil amendments, nutrient inputs, and management techniques were examined to determine their impact on crop performance in high tunnels, within the context of crop rotation as required by organic vegetable production. The work is published in the journal HortScience.

Results revealed that tailored and integrated nutrient management not only improved crop yields but also helped maintain the overall nutritional quality of organically-grown leafy greens, key factors for consumer satisfaction and marketability. It also pointed out the need to tackle the interactions of soil fertility management practices along with environmental conditions on vegetable mineral and phytochemical compositions while promoting crop productivity.

This study underscores the importance of balancing soil fertility and plant nutrient requirements, especially in high tunnel systems with sandy soils. Effective management strategies, the research suggests, can help mitigate challenges such as nutrient leaching and soil degradation, ensuring sustainable production for organic farmers.

These findings contribute to a growing body of knowledge aimed at supporting the organic agriculture sector, offering actionable recommendations for farmers and agricultural advisors. The high tunnel organic vegetable systems research was part of a recently completed multi-institutional project led by Dr. Xin Zhao.

Dr. Zhao is a Professor in the of Horticultural Sciences Department at the University of Florida, Gainesville. Her research program focuses on high tunnel vegetable systems, organic and integrated vegetable cropping systems and innovative technologies for improving crop resilience, soil health, and food quality in vegetable and strawberry production.

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Video: Can Gene Editing Give Seeds a Stronger Start?

Reagan Reed has a way of describing his research that might make a plant breeder pause.

“I’m the sort of person who likes to break things to understand them,” he says.

What he breaks are genes involved in seed germination. Reed, a Ph.D. candidate at the University of California, Davis, is investigating whether changing those genes can help seeds establish healthy plants under a wider range of conditions.

Reed recently attended the National Association for Plant Breeding meeting in College Station, Texas, as an NAPB Borlaug Scholar. His work speaks to a question that matters well beyond a research lab: what does it take for a seed to get a crop off to a strong start?

A seed that germinates quickly, alongside the others planted with it, spends less time vulnerable to stresses before seedlings become established.

“If you’re able to bridge that gap between germination to stand establishment, then that’s going to give you the highest probability of having a solid yield that year,” Reed says. “There’s a bunch that can go wrong after that, but it maximises your yield from the start, at least.”

Reed works in Dr. Imtiyaz Khanday’s lab at UC Davis, where his research focuses on seed quality in tomatoes and potatoes. He brings an unusual academic background to the work: at Skidmore College, he studied both biology and Latin.

Reed believes that combination prepared him for research. Translating an ancient text means studying each word, weighing its possible meanings and using context to reach the best interpretation. There is rarely a way to know with complete certainty what an author intended. Science, he says, requires a similar willingness to work through uncertainty.

“Attention to detail and comfortability working with uncertainty,” is how he sums up what Latin taught him.

In the lab, uncertainty can produce a surprise. Reed describes changing one gene and seeing little effect. Changing a second gene also appears to do little. Put both changes in the same genetic background, though, and the result can be substantial.

“I break this gene, nothing really happens. I break this other gene, nothing really happens. I combine them into the same genetic background, and now there’s a massive effect,” he says.

Those interactions matter as researchers gain the ability to edit multiple genes at once. They also complicate any simple account of how a trait works: improving a seed may depend on understanding what several genes do together.

For Reed, the question is whether that knowledge could help seeds germinate reliably when conditions are difficult. Some of the genes he studies prevent germination under certain conditions. That response may serve a plant well in one setting while limiting its usefulness in agriculture. He wants to learn what happens when those genes are changed, and whether the result improves establishment.

Yet a discovery that works in a lab still has a long way to travel before it reaches a field. Reed argues that agricultural biotechnology faces an economic challenge as well as a scientific one. New tools can create value for farmers, he says, but developing them requires a way to support the work in an industry where margins can be thin.

His fellowship with Flagship Pioneering gave him a view across AI, agriculture-related work and human health research. It also reinforced the importance of bringing people with different expertise into the same conversation—a benefit of gatherings such as the NAPB meeting.

“You need to have a team of people with different backgrounds who are willing to work together and approach the same problem in different perspectives and different ways,” he says.

That thinking connects the different parts of Reed’s path. Latin taught him to examine details without expecting a perfect answer. Gene editing lets him test what individual genes do—and what happens when their effects combine. Working with people beyond his own field helps him ask what those findings could become.

He came to agriculture because of its reach: the possibility that work by a small group of researchers could eventually make a difference on a much larger scale. His immediate focus is smaller and more precise. He wants to understand what helps a seed get through its first days and become a healthy plant.