Growth and yield response of soybean (Glycine max (L.) Merr.) varieties to Rhizobium and arbuscular mycorrhizal fungi inoculation in Lagawe, Ifugao, Philippines

Abstract

Soybean productivity in upland agroecosystems is influenced by genotype and the effectiveness of beneficial microbial inoculants, yet information on suitable variety–inoculant combinations remain limited in the Cordillera, Philippines. This study evaluated the effects of Rhizobium and arbuscular mycorrhizal fungi (AMF) inoculation on the growth, nodulation, root colonisation and yield of three soybean varieties under upland conditions in Lagawe, Ifugao, Philippines. The experiment employed a 3 × 4 split-plot arrangement in a randomised complete block design (RCBD) with 3 replications. Soybean varieties (Tiwala 6, Select Manchuria and Select Tudela Black) were assigned to the main plots, while microbial treatments (uninoculated control, Rhizobium, AMF and Rhizobium + AMF) were assigned to the subplots. Microbial inoculation significantly affected plant growth, nodulation, AMF root colonisation and computed seed yield. Rhizobium inoculation, either alone or in combination with AMF, increased nodulation and seed yield compared with the uninoculated control. Co-inoculation resulted in greater AMF root colonisation than sole AMF inoculation but provided no additional yield advantage over sole Rhizobium inoculation. Soybean variety significantly influenced several growth and yield components, with Tiwala 6 producing the highest seed yield (5.43 t ha-1), although statistically comparable with Select Manchuria. Overall, Rhizobium inoculation showed greater potential for improving soybean productivity than AMF co-inoculation under the conditions evaluated. The findings support the use of Rhizobium inoculation with high-performing soybean varieties such as Tiwala 6 under similar upland conditions, while further multi-environment studies are needed to determine the consistency of these responses.