Effects of Field and Greenhouse Solarization on Soil Microbiota and Weed Seeds in the Northeast USA

Abstract

Soil solarization using clear plastic is a promising weed management strategy for organic farms in the Northeast USA. Based on grower concerns that the practice might negatively affect beneficial soil microbiota, we conducted experiments to measure the effects of 2 and 4 weeks of solarization in a field and a closed greenhouse. Soil microbial communities were assayed by dilution plating on semi-selective agar media. Populations of general bacteria, general fungi, bacilli, and florescent pseudomonads were unaffected by field solarization, but fluorescent pseudomonads were reduced following greenhouse solarization. At plastic removal, soil biological activity was reduced non-significantly in the field and by 45% in the greenhouse. Soil biological activity fluctuated following field solarization, being significantly suppressed at 5 but not 14 days after plastic removal. In the greenhouse, biological activity remained suppressed up to 28 days after plastic removal. Solarization increased available nitrogen in the field and greenhouse. Four weeks of solarization reduced viability of buried weed seeds by 64% in the field and 98% in the greenhouse, indicating that the practice can cause substantial weed seed mortality. Maximum soil temperatures, measured at 10 cm depth under solarization, were 44 • C in the field and 50 • C in the greenhouse; temperatures were theoretically sufficient for the reduction of some soil borne pathogens. A subsequent experiment measured the effects of solarization and tarping (black plastic) on soil biological activity. During mulching, biological activity was unaffected by treatment, but 14 days after plastic removal, biological activity was reduced in the solarized treatment as compared with the control. Overall, these results suggest that solarization can deplete the weed seedbank. Although soil biological activity was reduced by solarization, it may bounce back after a period. Greenhouse solarization achieved higher temperatures and was more lethal to weed seeds and some microbiota than field solarization.

A Review of Non-Chemical Management of Couch Grass (Elymus repens)

“…A farmer in Maine successfully killed his E. repens rhizomes by covering a field with two layers of clear plastic for a whole season (personal communication of Birthisel). Conducting solarization within a greenhouse [145,146] or covering fields with multiple plastic layers [147], particularly when separated by an airspace of at least a couple of inches typically results in higher soil temperatures than single-layer solarization, and can improve pest control efficacy [148][149][150].…”

“…Although solarization is considered a 'mild' (i.e., low temperature) soil treatment in comparison to other disinfestation techniques including steaming [151], it nonetheless affects the soil ecosystem beyond the control of target pests particularly depending on soil temperatures reached during solarization. Solarization often increases dissolved organic matter [152] and plant available nutrients including inorganic nitrogen and can alter microbial community composition during treatment [150,153].…”

A review of soil pollution from LDPE mulching films and the consequences of the substitute biodegradable plastic on soil health

“…Sofi et al (2014) inferred that due to solarization, the percentage of moisture content is also raised, which again stimulates the decomposition of organic matter and the formation of toxic volatile chemicals that are hazardous to many phytopathogens (Oka et al, 2007). Moreover, during and following soil solarization, available nitrogen concentrations in the form of NO3 and NH4 are increased (Birthisel et al, 2019). A higher temperature in the topsoil layer was noted after covering it with both mulching films.…”

Tarping and mulching effects on crop yields, profitability, and soil nutrients in a continuous no-till organic vegetable production system

“…Tarps can be applied in a range of field applications, prior to both transplanted and direct-seeded crops, and with duration extending several months (overwinter periods or over sod) depending on field conditions and management goals. They are commonly applied after tillage, warming soils and moderating soil moisture, to create a stale seedbed and reduce weed emergence in the following crop (Birthisel et al, 2019; Birthisel and Gallandt, 2019; Kinnebrew et al, 2022). Tarps can also be used in NT applications to overcome some of the common barriers to NT adoption.…”