Elsevier

Pedosphere

Volume 32, Issue 4, August 2022, Pages 521-531
Pedosphere

Biofumigation effects of brassicaceous cover crops on soil health in cucurbit agroecosystems in Hawaii, USA

https://doi.org/10.1016/S1002-0160(21)60054-1Get rights and content

ABSTRACT

Brassicaceous cover crops, such as brown mustard (Brassica juncea) and oil radish (Raphanus sativus), are commonly used for biofumigation, a process that utilizes isothiocyanates (ITCs) generated from the hydrolysis of glucosinolates in Brassica plants to suppress soil-borne pathogens, including plant-parasitic nematodes. Given the biocidal nature of ITCs, limited information is available on the non-target effects of biofumigation on free-living nematodes, which are reliable soil health indicators. The objectives of this study were to determine if biofumigation methods effective against plant-parasitic nematodes would have non-target effects on free-living nematodes, and to examine the relationships between biofumigation indicators and nematode communities. Three field trials were conducted to examine whether different biofumigation methods would affect free-living nematodes. Tissue maceration of biofumigant crops, soil tillage, and black plastic mulching were adopted singly or in combination to generate different regimes of biofumigation efficacy. Termination of biofumigant crops by tissue maceration and soil tillage followed by black plastic mulching for one week was most effective in suppressing plant-parasitic nematodes and enhancing bacterial decomposition. However, these effects did not last through the subsequent zucchini (Cucurbita pepo) crop cycle. When comparing changes in soil glucose and sulfate concentrations as indicators of biofumigation efficacy, we found that soil sulfate was a better indicator of biofumigation efficacy than soil glucose, owing to the more stable state of sulfate in soil. Canonical correspondence analysis between soil sulfate as a biofumigation indicator and nematode soil health indicators revealed strong positive correlations of sulfate level with the abundances of bacterivorous and carnivorous nematodes, enrichment index, brown mustard biomass, and soil temperature. However, biofumigation did not affect the nematode community structure. This study demonstrated that biofumigation can suppress plant-parasitic nematodes without compromising soil health.

Section snippets

INTRODUCTION

Biofumigation is an agronomic practice that utilizes isothiocyanates (ITCs) generated from the breakdown of glucosinolates (GLs) present in brassicaceous crops to manage soil-borne pests and pathogens in agroecosystems (Kirkegaard et al., 1993). Glucosinolates are stored in the vacuoles of brassicaceous plant cells. Upon tissue maceration, GLs get in contact with the endogenous enzyme myrosinase in the cell wall or cytoplasm and undergo hydrolysis to release glucose and aglycone moieties.

Trial I

A field trial was initiated on November 17, 2016, at the Poamoho Experiment Station, Waialua, Hawaii, USA (21°32′14.7″ N, 158°5′20.2″ W; 166–215 m above sea level). The soil at the experimental site was a well-drained silty clay Oxisol (Wahiawa series, very fine, kaolinitic, isohyperthermic, Rhodic Haplustox), with a pH of 6–7 and organic matter content of 9 g kg-1. The soil was naturally infested with reniform (Rotylenchulus reniformis) and root-knot (Meloidogyne incognita and Meloidogyne

RESULTS

The nematode genera present in all three field trials are presented in Table I, and the abundance of each nematode genus in every trial is presented in Tables SI–SVI (see Supplementary Material for Tables SI–SVI).

Effects of oil radish and brown mustard biofumigation on nematode communities

Based on the nematode community analysis, oil radish was better for soil health improvement than brown mustard especially when it was terminated by MTBP. This termination method suppressed plant-parasitic nematodes, increased nematode diversity and bacterivore abundance, and reduced the F/(F + B) ratio and CI, indicating higher bacterial decomposition than fungal decomposition in the soil. In addition, oil radish terminated by MTBP increased EI, indicative of soil nutrient enrichment. All of

CONCLUSIONS

This study demonstrated that biofumigation can be effective against plant-parasitic nematodes without compromising soil health or changing the nematode community structure. Oil radish or brown mustard as a biofumigant crop, if terminated by the MTBP method for one week, suppressed the abundance of plant-parasitic nematodes. Bacterial decomposition was enhanced in the MTBP treatment, which led to nutrient enrichment. However, sometimes these effects did not last throughout the subsequent

ACKNOWLEDGEMENTS

This work was funded in part by the University of Hawaii College of Tropical Agriculture and Human Resources (Nos. 9034R, 9048H, and POW 16-964), the Natural Resources Conservation Services-Conservation Innovation Grants (Nos. NR 1892510002G004 and 69-9251-15-957), and the Western Sustainable Agriculture Research and Education Graduate Student Grant (No. GW18-026) of USA. The authors thank Ms. Donna Meyer, Mr. Josiah Marquez, Ms. Shelby Ching, Ms. Shova Mishra, and Dr. Xiaodong You for their

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