The effects of soil type and organic material quality on the microbial biomass and functional diversity of cropland soils were studied in a transplant experiment in the same climate during a 1-year field experiment. Six organic materials (WS: wheat straw, CS: corn straw, WR: wheat root, CR: corn root, PM: pig manure, CM: cattle manure), and three contrasting soils (Ferralic Cambisol, Calcaric Cambisol and Luvic Phaeozem) were chosen. At two time points (at the end of the 1st and 12th months), soil microbial biomass carbon (C) and nitrogen (N) (MBC and MBN) and Biolog Ecoplate substrate use patterns were determined, and the average well color development and the microbial functional diversity indices (Shannon, Simpson and McIntosh indices) were calculated. Organic material quality explained 29.5–50.9% of the variance in MBC and MBN when compared with the minor role of soil type (1.4–9.3%) at the end of the 1st and 12th months, and C/N ratio and total N of organic material were the main parameters. Soil properties, e.g., organic C and clay content were the predominant influence on microbial functional diversity in particular at the end of the 12th month (61.8–82.8% of the variance explained). The treatments of WS and CS significantly improved the MBC and microbial functional diversity indices over the control in the three soils in both sampling periods (P < 0.05). These results suggest that the application of crop straw is a long-term effective measure to increase microbial biomass, and can further induce the changes of soil properties to regulate soil microbial community.

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The present study was carried out to investigate the potential of AM (Arbuscular mycorrhiza) fungi alone and in combination with bioinoculants i.e., Rhizobium to find out the best combination on dry biomass, nodulation, colonization, and yield, along with their biocontrol against groundnut foot and root rot caused by Sclerotium rolfsii. The study was carried out under pot culture conditions in the net house of the Soil Science Division, Bangladesh Agricultural Research Institute, Joydebpur, Gazipur in 2020 and 2021. The experiment was designed in RCBD with eight treatments and four replications. Peat-based rhizobial inoculum (BARI RAh-801) was used @ 1.5 kg ha-1 in this experiment. Soil-based AM inoculum containing approximately 252 spores and infected root pieces of the host plant was used in pot-1. The treatments were Arbuscular mycorrhiza (AM), Rhizobium, AM+Rhizobium, Sclerotium rolfsii, Sclerotium rolfsii+AM, Sclerotium rolfsii+Rhizobium, Sclerotium rolfsii+AM+Rhizobium and Control. Dual inoculation (AM+Rhizobium) significantly increased dry biomass, nodulation, colonization, yield, and yield attributes of groundnut compared to single inoculation or other treatments. The result showed that dual inoculation (AMF+Rhizobium) increased nut yield (59.61% in 2020 and 26.32% in 2021) and stover yield (23.21% in 2020 and 33.74% in 2021) compared to control. On the contrary, Sclerotium rolfsii+AMF+Rhizobium increased nut yield (65.50% in 2020 and 52.94% in 2021) and stover yield (36.45% in 2020 and 99.35% in 2021) compared to only Sclerotium rolfsii treatment. The plant dry biomass, nodulation, colonization, nutrient concentration and uptake were increased by dual inoculation under pathogenic and non-pathogenic conditions leading to an improved yield of groundnut. Therefore, AMF species and its combination with rhizobial inoculum were significant in the formation and effectiveness of AM fungi symbiosis. They also increased yield and reduced the incidence of foot and root rot disease in groundnut plants.

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