Suppressive soils have been identified as soils that can inhibit the growth of naturally occurring soil-borne diseases. These soils contain microbial communities that are capable of suppressing or controlling disease-causing organisms, including fungi (e.g. Fusarium virguliforme (cause of sudden death syndrome, SDS), Macrophomina phaseolina (cause of charcoal rot), Phytophthora root rot (Phytophthora sojae) and nematodes (e.g., soybean cyst nematode, Heterodera glycines). How the native soil microbial communities reduce disease is not known. Knowledge of factors that contribute to and support these beneficial microbial communities is also unknown.
One example of this natural improvement in soil microbial community reducing disease was demonstrated in our previous research (sponsored by the Kansas Soybean Commission) that demonstrated that a high-glucosinolate mustard (Brassica juncea) reduced fungal populations that caused charcoal rot in soil and in soybean plants. The research proposed here builds on those results by exploring the interaction between soil health and disease pressure. Management practices will be tested in field studies to determine the impact on soil health, fungal pathogen presence, and soybean growth and yield.
Impact of soil health on soybean disease.
Crop plants that are disease hosts increase the number of disease-causing organisms in the soil. We have previously shown the increase in colony forming units (CFU) of M. phaseolina in the soil after soybean production (Sassenrath et al., 2019). Other factors reduce soil-borne disease, include high-glucosinolate mustard as a cover crop (Sassenrath et al., 2017, 2019) and increasing the soil temperature (e.g., "solarization"). Use of animal manures greatly increases the diversity of the soil microbial community, and beneficial microorganisms in particular. In addition to improving the soil nutrient balance, manure may contribute to reduced disease pressure (Graham et al., 2014) and soybean cyst nematode populations (Bao et al., 2013).

1. Measure the impact of soil health on soybean diseases;
2. Assess soil health for different growing environments and management practices;
3. Assess the efficacy of alternative management practices on controlling soil-borne diseases

1. Presence of soil-borne diseases from soils under different management
2. Link between soil health and disease pressure in soybean
3. Alternative management protocols to reduce or control soil-borne diseases

Updated May 16, 2023:
Preliminary soil samples have been collected from research plots and production fields. Soils will be analyzed for a range of nutrient factors and disease presence. Treatments have been implemented in research test plots to stimulate or reduce soil-borne diseases.

Diseases are primary factors reducing the yield and quality of soybeans in Kansas and throughout the world. Soil-borne diseases are highly prevalent in eastern Kansas crop fields. Certain plants have been shown to produce chemicals that act as biofumigants that control or reduce harmful soil fungi. Animal manures have also been used to alter the soil microbiome to improve control of disease organisms. Our working hypothesis is that improving the overall soil health by supporting healthy soil microbial communities can reduce disease pressure, i.e. creating suppressive soils by altering management practices will reduce disease pressure. This research will explore the relationship between soil health and disease pressure. The research outlined here will test the ability of cover crops, animal manure, and solarization to control charcoal rot in soybean production through improved soil microbial communities. The research will also work to develop a rapid, accurate test to assess the disease organisms in the soil microbiome.