Potential of an alkaline-stabilized biosolid to manage nematodes: case studies on soybean cyst and root-knot nematodes

The use of treated biosolids for pest management and soil nutrient augmentation is not a new practice, but it has increased in the last two decades, primarily in the United States (22). In the late 1970s, the first land application regulations were formulated by the U.S. Environmental Protection Agency (USEPA) in response to the Clean Water Act (44). Land application of sewage sludge for soil amendment and land reclamation has increased over time as a result of the ban on ocean dumping of wastewater residuals (Ocean Disposal Ban Act of 1988). The Act also minimizes other disposal options, such as land-filling or incineration. In 1993, the Standards for the Use or Disposal of Sewage Sludge (Code of Federal Regulations Title 40, Part 503) was created (45,46). Part 503 (as it is commonly called) set pollutant limits, operational standards for human/animal pathogen and vector-attraction reduction, management practices, and other provisions intended to protect public health and the environment from any reasonably anticipated adverse effects from chemical pollutants and pathogenic organisms. In 1995, the EPA promoted the terminology “biosolids” rather than “sewage sludge” and defined biosolids as “the primarily organic solid product yielded by municipal wastewater treatment processes that can be beneficially recycled as soil amendments and meets the standards of Part 503”. Although the term is sometimes controversial (33), we will use biosolid in reference to the product tested in this research

Characterizing microbial communities associated with northern root-knot nematode (Meloidogyne hapla) occurrence and soil health

The northern root-knot nematode (Meloidogyne hapla) causes extensive damage to agricultural crops globally. In addition, M. hapla populations with no known genetic or morphological differences exhibit parasitic variability (PV) or reproductive potential based on soil type. However, why M. hapla populations from mineral soil with degraded soil health conditions have a higher PV than populations from muck soil is unknown. To improve our understanding of soil bio-physicochemical conditions in the environment where M. hapla populations exhibited PV, this study characterized the soil microbial community and core- and indicator-species structure associated with M. hapla occurrence and soil health conditions in 15 Michigan mineral and muck vegetable production fields. Bacterial and fungal communities in soils from where nematodes were isolated were characterized with high throughput sequencing of 16S and internal transcribed spacer (ITS) rDNA. Our results showed that M. hapla-infested, as well as disturbed and degraded muck fields, had lower bacterial diversity (observed richness and Shannon) compared to corresponding mineral soil fields or non-infested mineral fields. Bacterial and fungal community abundance varied by soil group, soil health conditions, and/or M. hapla occurrence. A core microbial community was found to consist of 39 bacterial and 44 fungal sub-operational taxonomic units (OTUs) across all fields. In addition, 25 bacteria were resolved as indicator OTUs associated with M. hapla presence or absence, and 1,065 bacteria as indicator OTUs associated with soil health conditions. Out of the 1,065 bacterial OTUs, 73.9% indicated stable soil health, 8.4% disturbed, and 0.4% degraded condition; no indicators were common to the three categories. Collectively, these results provide a foundation for an in-depth understanding of the environment where M. hapla exists and conditions associated with parasitic variability