Two cultivars of soybean from each of three maturity groups (early IV, late IV and V) most commonly planted in Southeast Kansas will be planted in research plots at the Southeast Ag Research Center experiment fields outside of Columbus, KS. Cultivars from each maturity group will be selected as resistant (R) or susceptible (S) to charcoal rot, for a total of six cultivars tested. Fungal treatments will be:
1) no fungicide control
2) complete chemical control (seed treatment plus in-season fungicide application)
3) biological control
4) chemical and biological control
Biological control will be attained using a high-glucosinolate mustard with known biofumigant properties (Larkin et al., 2011). The mustard will be planted in the fall of the previous year, terminated in the spring with herbicide, and tilled into the soil prior to planting soybeans. All plots will be tilled to remove tillage as a variable. Weed and insect infestations in each treatment will be noted weekly during the growing season and controlled according to standard practices.
Production measurements will include in-season assessment of plant development and growth stage. Charcoal rot disease severity will be determined by randomly selecting ten plants per plot at the R7-R8 growth stage for root and stem severity rating. The plants will be scored by splitting the stem and taproot of each plant and rating the degree of gray discoloration and microsclerotia in the vascular and cortical tissues on a scale of 1-5. M. phaseolina root population levels will be estimated by grinding the split roots after the severity evaluation. The ground plant tissue will be plated on microbiological medium and incubated. Colony forming units (CFUs) of M. phaseolina will be counted and transformed to CFUs per gram of root tissue.
Sections of each plot will be hand-harvested at maturity to determine yield components of soybean (plants/acre; pods/plant; seed/pod; number of seed/acre; average seed weight and total seed weight/acre). Total plot yield will be taken with a plot combine and seed samples will be analyzed for seed size and quality. Economic analysis will be performed by developing partial budgets for each treatment from harvested yield and total input expenses.
Soil analysis will be performed to determine total biological activity of soils before planting cover crops and again after soybean harvest. Soil microbial activity will be measured with the Solvita respiration test system.