The Potential of Arbuscular Mycorrhizal Fungi as Biofertilizer to Reduce Chemical Fertilizer Use in Calcareous Soil

Abstract Arbuscular mycorrhizal fungi (AMF) are beneficial soil fungi with potential as a biofertilizer. Since calcareous soil in the Timor dryland is infertile and has capacity to fix phosphorus (P), the application of AMF could be an alternative to improve plant productivity in the region. A field experiment was conducted on calcareous soil to evaluate the potential of AMF to reduce NPK fertilizer and its effect on green gram growth and yield in calcareous soil. The trial was arranged in a split-plot design, with AMF inoculation as the main plot factor and NPK fertilizer as the sub-plot factor. The main plots included two levels: without AMF inoculation (M0) and AMF inoculation (M1), while the sub-plots consisted of four NPK rates: P1 (25%), P2 (50%), P3 (75%) and P4 (100%) of the recommended rate (200 kg NPK ha −1 ). The results revealed a significant interaction between AMF application and NPK fertilizer dose on plant fresh biomass, number of pods, seed dry weight, soil available P, AMF spores density and AMF colonization. Plants inoculated with AMF combined with a low dose of NPK fertilizer, particularly 25% NPK, had higher plant fresh biomass, number of pods and seed dry weight compared to plants supplied with a high level of inorganic fertilizer alone. Under AMF inoculation combined with 25% NPK fertilizer, the highest seed dry weight was 17.97 g plant −1 , while under the highest NPK regime alone (100% NPK), the seed dry weight only 10.1 g plant −1 , representing a 77% increase. AMF inoculation combined with NPK fertilizer increased P availability more effectively than NPK fertilizer alone. High levels of inorganic fertilizer combined with AMF reduced plant growth and yield, AMF spore density and colonization. Further studies on a larger scale are needed to confirm these findings.