Compost Science Complete scientific data on compost process control and end product quality

Choosing a Mixture Ratio for the On-Farm Production of AM Fungus Inoculum

Compost Science & Utilization, (2008), Vol. 16, No. 1, 52-60

Choosing a Mixture Ratio for the On-Farm Production of AM Fungus Inoculum In Mixtures of Compost and Vermiculite

David D. Douds, Jr. (1), Gerald Nagahashi (1), Carolyn Reider (2) and Paul R. Hepperly (2)

(1) U.S. Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, Wyndmoor, Pennsylvania
(2) The Rodale Institute, Kutztown, Pennsylvania

Arbuscular mycorrhizal [AM] fungi are potentially important tools in sustainable agriculture due to their roles in crop nutrient uptake, disease resistance, and water relations and in stabilizing soil aggregates. Inocula of these fungi can be effectively produced on-farm in mixtures of compost and vermiculite with a suitable plant host, such as bahiagrass (Paspalum notatum Flugge). Success of this method, however, depends upon utilizing the optimal compost and vermiculite mixture ratio. Experiments were conducted over two years utilizing a complete factorial design with three composts, four mixture ratios, and three AM fungi with the objective of producing regression equations to predict optimal mixture ratios using routine measures of compost nutrient analyses as independent variables. Growth of colonized P. notatum in yard clippings and dairy manure + leaf composts; which were high in N, low in P, with moderate K levels; produced more spores of AM fungi at mixture ratios of 1:2 to 1:4 [v/v compost: vermiculite] relative to higher dilutions. Dilution ratios of 1:19 and 1:49 were best for controlled microbial compost, which was high in P, low in N, and moderately high in K. Simple equations were developed which predict the optimal fraction of compost in the mixture for each of the three AM fungi studied (Glomus intraradices, Glomus mosseae, and Gigaspora rosea). Percent N, P, and K and N:P ratio were the significant independent variables. These equations allow a farmer to choose a mixture ratio for the on-farm propagation of AM fungi knowing only the nutrient analysis of the compost to be used.