Optimizing Organic Hemp Production: The Role of Colored Plastic Mulches in Enhancing Soil Microbial Diversity and Plant Health
Gwendolyn Englebach, MS Seminar
Monday, March 18, 2024, 10:00 am
(Under the direction of Dr. Jeanine Davis, Chair)

Location: Mtn Hort Crops Research & Extension Center / Hybrid
Join Zoom Meeting: https://ncsu.zoom.us/j/91831050573?pwd=bmNWNWd6RmROOFFRMkNCWmFoYjRVZz09
Meeting ID: 918 3105 0573
Passcode: 805643

 Englebach.Abstr.pdf

Abstract:
Cannabinoids are recognized for their therapeutic benefits in managing conditions like epilepsy, anxiety, depression, and chronic pain. Hemp grown for cannabidiol (CBD) production experienced an upsurge in the last decade due to rising consumer demand. However, hemp cultivators in the Southeastern United States face challenges due to hot and humid conditions and a lack of EPA-approved herbicides. Many organic growers turned to plasticulture systems to mitigate the effects of heavy rainfall and competition from weeds. Colored plastic mulches reflect different patterns of solar radiation into the plant canopy, affecting both photosynthetic and photomorphogenic processes such as secondary metabolite activation. The targeted application of colored mulches could promote cannabinoid profiles most suitable for CBD production and improve yields. However, long-term plastic mulching may result in negative outcomes for soil health that outweigh these short-term productivity gains. Colored mulches alter soil temperature and moisture, with likely downstream effects on carbon cycling, nitrogen mineralization, and soil microbial activity. Darkly colored mulches such as black, red, and green tend to warm soils more than lighter mulches such as white and silver, resulting in early yield gains. However, darkly colored mulches may also accelerate carbon loss or increase soil temperature above optimal levels for microbial activity. Strategic selection of mulch color in relation to hemp cultivar requirements and local climatic conditions could optimize plant-microbial interactions.

Our study measured soil temperature and moisture conditions under five plastic colors at seven on-farm locations over two years. We found that green, red, and black mulches produced higher average and maximum soil temperatures than white or silver, especially during summer. Soil moisture conditions varied seasonally but not between mulch colors. Secondly, we sought to determine whether colored mulches affected plant growth or cannabinoid profiles. We found no effect on total cannabinoids, cannabigerol, tetrahydrocannabinol or CBD content. However, the interaction of days after transplant and mulch color significantly affected plant height. Lastly, we investigated the microbial community beneath the colored mulches. We found that mulch color had no impact on soil carbon levels or microbial community composition. However, the effect of collection date on microbial community composition varied with soil depth. Additionally, microbial species richness depended on the interaction between mulch color and environment and between season and environment. Soil microbial communities play a pivotal role in driving numerous biogeochemical processes, yet we lack a comprehensive understanding of how these communities will respond to global temperature rise. Based on our findings, researchers might forecast some of the effects of future climate warming on soil microbial communities.