Production of arbuscular mycorrhizal fungi (AMF) inoculum using the on-farm method is an alternative to stimulate the use of microbial inoculant in plant production systems and to reduce the cost associated with purchase of this product. The goal of this study was to evaluate the potential of residues from the forestry industry, pine bark (CP) and pulp sludge (LC), as components of the substrate used to produce on-farm mycorrhizal inoculum. Sorghum plants pre-colonized with the AMFs Claroideoglomus etunicatum RJN101A and Dentiscutata heterogama PNB102A were established in a greenhouse for three months in a substrate of sand:expanded clay:soil (2:2:1). After this period, plants were transplanted to 20 L plastic bags containing a substrate with CP or LC mixed with carbonized rice hulls + soil (1:1:1). The experiment followed a 2 x 2 factorial arrangement, of two fungal isolates and two residues, with five replicates, in a completely randomized design. Plants were grown outdoors for three months and then the substrate was analyzed for AMF spore numbers, mycorrhizal colonization of the host plant, and inoculum potential by the MPN (most probable number) method. The substrate of each bag was divided into three layers (upper, middle, and lower portion) and only the number of spores was analyzed separately for each layer. The type of residue did not affect the number of spores of either AMF, but this number decreased from the upper to the lower layer within each experimental unit. D. heterogama tended to produce more spores than C. etunicatum . Sorghum mycorrhizal colonization by AMF was significantly greater in the LC residue than in the CP residue. The number of AMF infective propagules also tended to be higher in LC (22 to 28 propagules cm-3 substrate) than in CP (2 to 7 propagules cm-3 substrate). The LC residue showed potential for use as a component of the substrate in mycorrhizal inoculum production systems using the on-farm method.
mycorrhiza; mycorrhizal inoculum potential; number of spores; biofertilizers; Claroideoglomus etunicatum; Dentiscutata heterogama
