Note to readers, attached is the complete final report for FNE06-578
Pre-warming spring soil with used greenhouse plastic proved quite effective at raising soil temperatures. The technique could be beneficial to small-scale, intensive vegetable farms whose market offers a premium for early spring crops. The significantly higher soil temperatures (an average of 20 degrees at 5” depth after 3 weeks under plastic) gives an early germination boost to these crops. Of course, it does the same for weeds, and so the weed management strategy must be modified accordingly.
The technique appears to offer no benefit to long season, heat-loving crops, whether grown under mulch (plastic or straw) or on bare soil. However, in our trials we did not attempt to set plants earlier on the pre-heated soil, as this would have required frost protection. In our climate and market frost protection for these crops (primarily peppers and eggplants) does not pay. The one exception here is in pre-warming greenhouse tomato beds; by covering the soil with used greenhouse plastic for 2-3 weeks before spring startup, the soil pre-heating time is reduced from 4-5 days to approximately 2 days. This offers some fuel savings.
An ancillary benefit to the technique is that in a wet spring, the covered soil becomes workable earlier, as it is protected from spring rains.
A significant drawback is that in long-season crops, pest pressure seemed heavier in the covered areas than in uncovered areas. Oddly, this increase did not appear in spring crops, where it would seem more likely. A second drawback is the earlier weed pressure. Of course, this could also be seen as a benefit, as weed management can begin earlier.