California researchers mixed discarded tomato waste into soil and covered it for biosolarization. The decomposing food waste raised temperatures by about 2°C and created conditions that could help kill soil pests

What if discarded tomato waste could do more than end up as food-processing waste? A study by researchers at the University of California explored whether tomato pomace, the solid material left after tomatoes are processed, could be mixed into soil and used as part of a technique called biosolarization. The laboratory experiments found that tomato pomace could raise soil temperatures by up to 2°C for about four days under aerobic conditions while also triggering chemical changes associated with soil-pest inactivation.

What is biosolarization and how does it work?

Biosolarization combines the heat of solarization with organic material that decomposes in the soil. In conventional soil solarization, moist soil is covered, allowing sunlight to heat the ground. Biosolarization adds an organic amendment, creating biological and chemical changes that can make the soil less favorable to certain pests and pathogens.

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The California researchers wanted to know whether food-processing residues could provide an additional source of biological activity and heat. Their experiment focused on tomato pomace as well as white and red wine-grape pomaces.

The tomato waste raised soil temperature by up to 2°C

The headline result involved tomato pomace and soil temperature. Under aerobic conditions, adding tomato pomace produced a temperature increase of up to 2°C that lasted for four days compared with the control. Researchers linked the heating to microbial activity as the organic material decomposed.

Interestingly, the absolute highest temperature increase recorded across the tested amendments was 2.32°C, and that peak came from white wine-grape pomace rather than tomato pomace. The tomato treatment, however, produced the reported sustained increase of up to 2°C for four days.

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Why would a small temperature increase matter?

Soil temperature is important in solarization and soil pest management because heat can affect the survival of organisms living in the soil. The researchers noted that temperatures in roughly the 40°C to 60°C range can be effective against some soil pests, although the effect depends on the organism and how long it is exposed.

The study therefore examined temperature changes as one indicator of conditions that could contribute to soil disinfestation. It did not suggest that a 2°C increase by itself would eliminate every soil pest.

Decomposing tomato pomace changed the soil chemistry

Heat was only part of the story. As microorganisms broke down the organic material, they produced gases and altered the chemistry of the soil.

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Under anaerobic conditions, the tomato-pomace treatment reduced soil pH from 6.5 to 4.68. The researchers considered this acidification another condition associated with potential pest inactivation. Under aerobic conditions, tomato pomace also generated substantial carbon dioxide, which the researchers used as an indicator of microbial activity and organic-matter utilization.

Researchers tested tomato waste in controlled laboratory conditions

There is an important detail behind the experiment: the researchers were not simply dumping leftover tomatoes onto farmland.

The tomato pomace came from a commercial tomato-paste production facility in California. Researchers dried and ground the material before incorporating it into their experimental soil. The amended soil contained 5% tomato pomace by dry weight along with 2% green-waste compost. The experiments were conducted in controlled laboratory bioreactors using soil collected from the University of California's Kearney Agricultural Research and Extension Center.

That distinction matters because the study was designed as a screening experiment to determine whether food-processing residues showed enough potential to justify more resource-intensive field testing.

Tomato waste could give agricultural waste a second life

California produces large quantities of tomato-processing residues. Much of this material consists of skins and seeds, or pomace, left behind after tomatoes are processed.

Instead of viewing the material only as waste, researchers explored whether its organic compounds could be useful to agriculture. Because the pomace contains carbohydrates that microorganisms can consume, it can stimulate biological activity when incorporated into soil.

That creates an intriguing connection between food waste recycling, sustainable agriculture and soil pest management.

The study did not prove tomato waste can replace pesticides

Despite the promising findings, the research should not be interpreted as proof that farmers can simply add tomato waste to fields and eliminate the need for pest control.

The study was a simulated biosolarization experiment, rather than a demonstration that tomato pomace alone can control pests under commercial field conditions. The researchers described the results as evidence that tomato and other fruit-processing residues deserved further investigation, particularly through field-scale studies.

Later research has continued investigating tomato residues for biosolarization. A field study published in ACS Agricultural Science & Technology found that combining tomato crop residues or pomace with solarization could enhance weed-seed mortality, with temperature, soil pH and volatile fatty acids contributing to the effect.

A surprising idea for turning food waste into a farming tool

The California experiment offers a simple but potentially powerful idea: some agricultural waste streams may have another job after their original purpose is over.

Instead of treating tomato-processing residues solely as waste, biosolarization research explores how their decomposition could generate heat, alter soil chemistry and contribute to conditions that suppress unwanted organisms. The 2015 study did not provide a ready-made replacement for conventional pest control, but it opened another avenue for combining waste reduction with sustainable soil management.