Different Responses of Soil Environmental Factors, Soil Bacterial Community, and Root Performance to Reductive Soil Disinfestation and Soil Fumigant Chloropicrin

Reductive soil disinfestation (RSD) and soil fumigant chloropicrin (SFC) are two common agricultural strategies for the elimination of soil-borne pathogens. However, the differences in soil environmental factors, soil bacterial microbiome, and root performance between SFC and RSD are poorly understood. In this study, three soil treatments, untreated control (CK), SFC with 0.5 t⋅ha–1 chloropicrin, and RSD with 15 t⋅ha–1 animal feces, were compared. We evaluated their effects on soil environmental factors, bacterial community structure, and root activity using chemical analysis and high-throughput sequencing. RSD treatment improved soil composition structure, bacterial diversity, and root performance to a greater extent. Carbon source utilization preference and bacterial community structure were strikingly altered by SFC and RSD practices. Bacterial richness, diversity, and evenness were notably lowered in the SFC- and RSD-treated soil compared with the CK-treated soil. However, RSD-treated soil harbored distinct unique and core microbiomes that were composed of more abundant and diverse potentially disease-suppressive and organic-decomposable agents. Also, soil bacterial diversity and composition were closely related to soil physicochemical properties and enzyme activity, of which pH, available Na (ANa), available Mg (AMg), available Mn (AMn), total Na (TNa), total Ca (TCa), total Cu (TCu), total Sr (TSr), urease (S-UE), acid phosphatase (S-ACP), and sucrase (S-SC) were the main drivers. Moreover, RSD treatment also significantly increased ginseng root activity. Collectively, these results suggest that RSD practices could considerably restore soil nutrient structure and bacterial diversity and improve root performance, which can be applied as a potential agricultural practice for the development of disease-suppressive soil.

In vivo mutagenicity evaluation of the soil fumigant 1,3-dichloropropene

1,3-Dichloropropene (1,3-D; CAS No. 542-75-6) is a soil fumigant used for the control of nematodes in agriculture. There is an extensive database on the genotoxicity of 1,3-D and many of the published studies are confounded by the presence of mutagenic stabilisers in the test substance. Mixed results were obtained in the in vitro assays, often due to the purity of the 1,3-D sample tested. In order to get further clarity, the mutagenic potential of 1,3-D was investigated in vivo in the transgenic Big Blue rodent models. Inhalation exposure of 150 ppm 1,3-D (×2.5 tumourigenic dose) to transgenic male B6C3F1 mice did not induce lacI mutations in either the lung (tumour target tissue) or liver. Similarly, dietary administration of 1,3-D up to 50 mg/kg/day to transgenic male Fischer 344 rats did not increase the cII mutant frequency in either the liver (tumour target) or kidney. These results, along with other available in vivo data, including the absence of DNA adducts and clastogenic/aneugenic potential, support the conclusion that 1,3-D is efficiently detoxified in vivo and, as such, does not pose a mutagenic hazard or risk.

Determination of optimum metam-potassium rate for weed, tomato, and pepper termination

Metam potassium (metam-K) is a soil fumigant used commonly in Florida at the end of the tomato and pepper production season. The fumigant essentially cleans a field by killing the established weeds and crops after harvest. The goal of this project was to determine the optimal rate of metam-K for the effective termination of tomato, pepper, and established weeds such as purple nutsedge, goosegrass, and dogfennel. Tomato, pepper, and purple nutsedge at bed center were effectively terminated with the metam-K rate of 65 kg ha−1. Optimal rates required for the termination of goosegrass and dogfennel were 91 and 156 kg ha−1, respectively. In contrast, metam-K at 500 to 680 kg ha−1 was required to terminate purple nutsedge on bed edges. The reduced efficacy of metam-K at bed edge might be related to the limited movement of metam-K in soil.

Economics of fumigation in tomato production: the impact of methyl bromide phase-out on the Florida tomato industry

The Florida tomato industry is facing challenges of increased production costs and decreased yields resulting from the methyl bromide (MBr) phase-out under the Montreal Protocol for environmental concerns. MBr and several accepted alternative soil fumigant systems are analyzed in this study from an economic perspective. This article focuses on identifying optimal fumigant systems by analyzing the cost effectiveness and economic risk associated with MBr and several other commercially available soil fumigant systems using data collected from scientific field trials. The results obtained show that a 67:33 formulation of MBr: chloropicrin is the most cost-effective treatment, and no alternative fumigant systems investigated can substitute MBr cost-effectively in Florida tomato production. The analysis indicated that switching from MBr (67:33) to the new industry standard PicChlor 60 approximately resulted in a loss of $3,569 per acre in gross revenue and $1,656 per acre in profit using market prices in the 2013/14 season. Higher market prices would further increase the loss.