Gardeners and farmers know the frustration of buying seeds and looking forward to a bountiful harvest, only to have a lot of seeds fail to germinate. When you hear plasma you probably think of plasma TVs or the aurora borealis (Northern Lights) caused by solar plasma interacting with the atmosphere. It turns out plasmas can also be useful for treating seeds to increase their germination rate and subsequent growth.

Agricultural seeds are sold as commodities yet seed quality can be non-uniform. Despite the extensive literature showing that plasma treatments of seeds provides advantages for many crops, lettuce studies, particularly in indoor farming systems, are limited. A new study provides a systematic investigation of the impacts of non-thermal plasma treatments with various feed gases (N 2 , O 2 , dry air, and wet air) on the germination and growth characteristics of four lettuce cultivars (Red Oakleaf (RO), Black Simpson (BS), Valley Heart Romaine (VHR), and Paris Romaine (PR)) under controlled cultivation conditions in an agrivoltaic agrotunnel .

Results of Treating Seeds with Plasma: It Depends on the Plasma and the Lettuce

Although the germination time was not conclusively affected by the treatments, the results show a complex interaction between germination rate and yield across the different cultivars and plasma treatments. All tests were run in a well-documented vertical farm system. Except for Paris Romaine seeds (77.8% vs. 65.8% control), wet air plasma treatments increased germination rates by 18.7–100% over controls for all other cultivars. In yield analysis, wet air treatment had the strongest effect, especially for VHR (51.7 vs. 42.5 g/pot). Treatments did not notably affect Red Oakleaf. For Black Simpson, N 2 treatment gave the highest increase (54.2 vs. 48.1 g/pot), while Paris Romaine responded best to O 2 treatment (58.4 vs. 51.8 g/pot).

Does Plasma Treating Seeds Make Sense?

The energy consumption of plasma treatments was negligible for all treatments, while labor costs for small batches of seeds accounted for the largest share of secondary operating costs (839, 622, and 659 h/year, respectively for BS, VHR, and PR). Despite additional expenses, including labor, O&M, and degradation costs, the reduced seed requirements from higher germination rates and higher yield increased net profit by 12.0% compared to untreated cultivation in the most impacted (Valley Heart Romaine) lettuce. There is an opportunity for further cost optimization of the non-thermal plasma treatment for each type of lettuce seed. Future work could also look at using the plasma-treated seeds for other types of farming including agrivoltaics . To really drop future costs someone should consider developing an open source plasma supply that farmers could use themselves to treat seeds on site.