There has been a steady increase in plants grown in plastic greenhouses over the last two decades.
For example, in the grocery stores now you can find tomatoes that are grown greenhouses. These tomatoes will be usually marked on the plastic container.
Plastic greenhouses in China are estimated to be more than 3.3 million hectares.
Just how big is that? That is 8,154,477 acres or a square that has 113 miles on each side.
A recent study published in the Journal of Agricultural and Food Chemistry reported how the soil changes inside a greenhouse over 20 years.
This research determined how the pH of soil changes, the bacteria and fungal composition changes, and the determined if plastic is present in the soil.
Here are the details of the study
Study design: Case study of a site in Weifang, Shandong Province China.
Sample collection: The surface soil in each greenhouse was sampled at five sites to a depth of 20 cm (following a serpentine pattern) and then mixed together to represent one greenhouse cultivation soil.
Plants typically grown included watermelon and peppers
The bacteria community (i.e. microbial community) was determined
Plastic greenhouses decreased the diversity of fungal species in the soil, but not bacteria.
Soil bacteria and fungal community structures were changed with plastic greenhouses.
Here are the main results
– Soil pH: A significant decrease in soil pH occurred over the years. Specifically, soil pH value decreased after 15 years from 7.8 to 6.9). –
– Phthalate esters (PAEs). – Presence of plastic phthalate esters was higher in soil grown in plastic greenhouses. 16 phthalate esters were detected.
– The most abundant phthalate was bis(2-n-butoyethyl) phthalate (DEHP)
– Highest phthalates were detected at 15 years. At year 20 a decreasing trend was observed.
Here is what the authors had to say
The sources of PAEs in the soil could be mainly ascribed to the use of plastic films over the soils and the application of chicken manure. It has been reported that the PAE concentrations in plastic film and chicken manure could reach 119 and 6.84 mg/kg, respectively.
And
A decreasing trend of PAE residue concentrations in soil after 15 years of PGVC was observed, which could be ascribed to the microbial degradation and downward leaching of PAEs with high solubility
And
Therefore, the decreased pH in soil could still be explained by the excessive addition of N fertilizer even though large amounts of organic fertilizers were also added to the soil studied.
And
Therefore, the ratio of fungal richness to bacterial richness was significantly decreased in soils under PGVC, which indicates that the stability of the soil ecosystem is decreased
Take away message
This 20 year case study from a site in China suggests that plastic greenhouses can change the soil pH, plastic content (i.e. phthalates) and microbial community. One area of concern is the present of plasticizers in soil that has the potentially to be taken up by plants grown in this soil. This study did not answer that question if plants take up plasticizers. However, it is well known that plants can pick up nutrients and minerals from the soil as well as environmental contaminants through a process called phytoremediation.
Hopefully, future studies will determine if phthalates (i.e. plasticizers) are present in vegetables and fruits grown in plastic greenhouses.
References
Long-Term Plastic Greenhouse Cultivation Changes Soil Microbial Community Structures: A Case Study. Journal of Agricultural and Food Chemistry. 2018 August 29; Volume 66 (Issue 34): Pages 8941-8948.
His research on plant medicine has led to more than 45 publications and abstracts.This research has been presented at international meetings in the USA, France, Turkey, Peru, Israel, Austria, and Italy.
Categories: Antioxidant, Growing conditions, Plant Medicine