Project Overview
Organic vegetable growers rely on a suite of weed management practices to limited unwanted vegetation in their production systems. Plastic mulches have become a popular foundation for an integrated weed management program, because they generally provide excellent weed control while providing other benefits (e.g., soil warming, moisture conservation) to the crop. However, plastic mulches create significant plastic waste.
Biobased plastic mulches would provide many of the same benefits as a conventional plastic mulch in a similar format, but without relying on single-use, petroleum-based plastic. Multi-layer biobased fabrics have been created out of polylactic acid (PLA), a biodegradable plastic material that can be manufactured from vegetable starch.
Importantly, researchers had previously identified that crop roots could penetrate the PLA mulches. Based on this information, a vegetable planting system was developed where seeds are planted directly into a compost layer on top of the PLA mulch, without additional planting holes. Researchers at the University of Nebraska and 3M created a set of field experiments to determine how PLA mulch could be deployed as a plastic mulch in organic carrot production systems, including comparisons of different PLA mulch thicknesses and different compost planting substrate materials.
Farmer Takeaways
- PLA mulch reduced weed emergence by 90% compared to bare soil.
- Yields between carrots grown under different thicknesses of PLA mulch and composts were similar to yields grown on bare ground and under compost alone, when all treatments were hand weeded weekly.
- PLA mulch reduced soil nitrate levels by nearly half, as the high carbon content of PLA mulch immobilized nitrogen.
Project Objectives and Approach
Adapt PLA mulches for field use by developing techniques to direct seed vegetable crops into compost on top of the PLA mulch.
- Researchers created a small plot field experiment in Nebraska to test PLA mulch topdressed with compost with organic carrot production practices.
- Carrot beds were established by rototilling, fertilizing with organic soybean meal, and forming beds in a previously fallow field. PLA mulches were laid onto the bed tops in experimental plots, before composts were applied with a drop spreader at a thickness of ~0.5”.
- Carrot seeds were planted into the compost with six-row Jang seeder. To facilitate this planting, the researchers did not test PLA mulch without a layer of compost. Drip irrigation was installed over top of the planted beds.
Evaluate different PLA much and compost combinations on weed suppression, crop establishment and yield, and nutrient availability.
- In the experimental production system described above, the researchers tested six different treatments against a nontreated control that had neither compost nor PLA mulch. The six treatments included three levels of PLA plastic (none, 80 gsm PLA, and 120 gsm PLA) crossed with two kinds of compost (yard waste compost and mixed source compost).
- Weed emergence was counted weekly for the first five weeks of the experiment, until the carrot canopy closed. After each monitoring, plots were hand weeded to eliminate weed competition.
- Carrot emergence was counted two weeks after planting, and carrots were harvested after about 10 weeks. Carrot yield was measured at harvest.
- The researchers used PRS brand ion exchange soil probes to monitor plant available N, P, and K. They also used electronic soil moisture and temperature probes throughout the experiment.
Key Findings
The PLA mulch system is a viable alternative to conventional plastic mulches and results in excellent weed suppression.
- Weed emergence under PLA mulch was reduced around 90% compared to bare soil and compost treatments. Weekly hand weeding in this study limited the effect of weeds on crop growth, but PLA mulch reduced the labor involved in hand weeding.
- Weed emergence did not differ between compost treatments nor different thicknesses of PLA mulch. Both types of compost seemed to be compatible with the production system, and both thicknesses of PLA mulch stopped weed germination while allowing the carrot roots to establish, even without planting holes in the mulch.
- Carrot emergence increased under PLA mulch, with plant stand counts nearly doubling in the treatments that included PLA mulch. Carrot yields were unaffected by any treatment in the study.
- Soil nitrate was significantly reduced by the PLA mulch, even though compost was applied over the top. Soil P did not differ between treatments, and there was no consistent relationship between PLA mulch and soil K (one of the composts had more K).
Resources
Wehrbein, C. D., Kadoma, I., & Wortman, S. E. (2024). First Field Evaluation of a Polylactic Acid-based Weed Barrier with Compost for Carrot Production. HortTechnology, 34(2), 204–210.
Read MoreLocation
NebraskaCollaborators
Caleb Wehrbein, University of Nebraska, Lincoln
Ignatius Kadoma, 3M Company
Region
Plains
Topic
Weed Management, Cropping Systems
Category
Vegetables/Fruits
Year Published
2024
