Comparing soil tarping and solarization for early season weed control in vegetable crop systems - a research and demonstration study

Using silage tarps as a method of controlling weeds and conditioning soil in small diversified vegetable farms has enthusiastic adherents; the use is spreading in many areas of the U.S. and Canada. However, most of the research and demonstration of tarping has been in higher rainfall regions of the eastern U.S., with one SARE study as far west as Wisconsin.

We used a two-pronged approach of testing tarping at research farms in Iowa and South Dakota, and demonstrated their efficacy on cooperating farms across a range of soils and climate spanning from eastern Iowa to western South Dakota. The effects of short-term tarping treatments on soil health are largely unknown, so we also are assessing effects of tarping durations of 14, 24, or 42 days on soil temperature, moisture, and microbial activity. Because our cooperating farmers had particular interest in controlling early season weeds, we applied tarps in the spring prior to planting onions. We also compared tarping to early-season solarization, using clear plastic, which warms the soil much more efficiently, leading to germination of warm season weeds so that they can be controlled prior to planting the desired crop.

The demonstration farms used management practices appropriate to their farm; thus we gained information on an array of on-farm practices that may impact tarping efficacy. Because the demonstration farms cover a wide variety of soils and span a range of 18 to 36 inches precipitation per year, we expect that there will also be variation in weed species and their response to tarping. Results are being made available to a wide audience through field days, webinars, videos, reports, and presentations at grower meetings.

Neither year found onion yield differences due to tarping treatments. Patterson outyielded Candy onions, mostly due to undersized Candy bulbing. Clear plastic allowed for early weed germination, with subsequent light tillage before planting, similar to a stale seed bed technique. Analysis of weed and soil results are ongoing.

Project objectives:

Objectives:
1. Compare efficacy of tarps (occlusion) vs. clear plastic (solarization) vs. no plastic for minimizing early season weed pressure under a range of soils and climates
2. Demonstrate on-farm feasibility of using tarps across a range of soils, climates, and management practices
3. Investigate the effect of occlusion or solarization on soil microbes and soil health

4. Investigate whether early season tarping treatments affect onion yield.

Learning outcomes:
+ Participants will learn how to manage tarps or plastic for maximum efficacy and profitability on their farms
Action outcomes:
+ Tillage and/or herbicide use will be reduced on farms using tarps
+ Using recycled tarps reduces landfill waste

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and should not be construed to represent any official USDA or U.S. Government determination or policy.