A Study of the Effects of Black Woven Polypropylene on Soil Biota

NOTE: FARMER GRANTEE UNABLE TO COMPLETE OBJECTIVES OF THE GRANT WITHIN THE TIME ALLOTTED. GRANT PROJECT CLOSED OUT. 1/27/2020

Commodities

• Vegetables: cabbages, cucurbits, eggplant, greens (leafy), greens (lettuces), peppers, sweet potatoes, tomatoes

Practices

• Soil Management: composting, earthworms, soil microbiology

Over the last decade, black woven polypropylene has grown increasingly popular among organic farmers. Its easy installation and relatively low cost have made it a convenient way to suppress weeds and reduce labor hours, saving both time and labor costs. But while studies have been conducted to test crop yields generated through the use of black woven polypropylene, little research has been done to determine the effects, if any, that using black woven polypropylene may have on soil biota, specifically soil microbes and earthworms. Concerns over a lack of soil aeration and high sustained soil temperatures generated have been voiced in relation to using black woven polypropylene, but have not been thoroughly studied. Both of these issues could possibly have a negative impact on soil biota, but the high sustainable soil temperatures generated by black woven polypropylene could be particularly problematic for farms in the South, due to the already high temperatures so regularly experienced.

Soil microbes and earthworms are necessary to humus formation by breaking down organic matter. They also aid plants in the absorption of nutrients, by making nutrients more readily available. Because growing a rich humus is an important goal to most organic farmers, it is a problem that no studies have been conducted to determine whether or not black woven polypropylene has a negative effect, a positive effect, or a neutral effect on soil biota. A negative effect on soil biota could translate to lowered yields, lowered crop defenses to pests, increased input costs and increased amounts of inputs added, lowered nutrients in produce, and a loss of soil organic matter -- all indicators of an unsustainable farming practice.

In order to address the problem of a lack of research into the effects of black woven polypropylene on soil biota, a study must be conducted to ascertain if black woven polypropylene has a positive effect, a negative effect, or has no effect on soil biota. By creating a small-scale garden research study in which the only variable is different methods of mulching, any loss, gain, or constancy of soil microbes and earthworms will be able to be easily measured.

In the instance that black woven polypropylene is determined to have a negative effect on soil biota, it is not sufficient to simply relay to farmers that the convenient and cost-effective weed suppressing material they have been using is not beneficial to the soil. Instead, the findings must be relayed along with the option of another, cost-effective mulch replacement that has either a neutral or positive impact on soil biota and could be applied on a small scale. Therefore, the study should also test the effects of another, natural mulch that could be used in the event that black woven polypropylene is deemed to have a negative effect on soil biota. Thus, the proposed solution is to have a study that not only analyzes the effects of black woven polypropylene on soil biota, but also analyzes the effects of wood chip mulch on soil biota.

Seventy-five garden beds, each 50 feet in length and 30 inches wide will be created to total an approximately half-acre garden plot designated to the Southern SARE grant study. The garden plot will be divided evenly: Three columns of 25 beds with a 5-foot wide pathway between each column. Because tilling often results in a lowered earthworm population, the beds will be created using no-till methods to result in a more accurate earthworm assessment.

Prior to any application of woodchips or black woven polypropylene, soil samples will be collected and analyzed to determine the microbe density for all three columns. Earthworm population assessments would also be made on all three columns prior to the start of the farming season.

Prior to the first planting the of the farming season, mulches will be acquired and applied. New black woven polypropylene will be obtained as a donation from a neighboring farm that has recently decided to stop using the weed suppressor. Wood chips will also be obtained free of charge from a local tree removal service. Black woven polypropylene will be installed entirely on the beds in one column. A mulching of wood chips will be spread entirely over the beds in another column, to equal an approximate application of 4 inches. The third column of garden beds will remain bare.

The crop varieties will include, but would not be limited to tomatoes, eggplant, peppers, kale, winter squash, head lettuces, Swiss chard, kohlrabi, sweet potatoes, melons and cabbage.

After a complete farming season, soil samples will again be collected from each bed and analyzed to determine if a change in microbe density occurred. Another earthworm population assessment will be administered for all three columns to determine if any change in earthworm populations occurred.