Bacterial inoculants to increase the biomass and nutrient uptake of Tithonia cultivated as hedgerow plants in Ultisols

Ultisols require greater amounts of fertilizer application compared to other soils. Unfortunately, the price of synthetic fertilizers has increased over time during the years, making them unaffordable for most Indonesian farmers. Over the last century, efforts to reduce reliance on synthetic agro-chemicals have recently focused on Tithonia diversifolia as a green manure alternative. Generally known by its common name of tree marigold or Mexican sunflower, this plant has attracted considerable attention for its prolific production of green biomass, rich in nitrogen, phosphorous and potassium (NPK). This outstanding feature and the plant’s capacity to solubilize soil P have recently been capitalized for improving the fertility of highly leached soils in Africa and particularly in Kenya. As microorganisms are expected to play an important role in biomass production and high nutrient uptake of this plant, this issue of importance was pursued further in the following investigation. The aim of this study was to determine the type of bacteria suitable for Tithonia cultivation as hedgerow plants in Ultisols which have higher biomass production and nutrient content. The field experiment was conducted with 5 treatments in a randomized block design (RBD) using 3 replications. The treatments were : without microorganisms inoculation or control (K); phosphate solubilizing bacteria (PSB) (L); Azospirillium (M); PSB + Azospirillium (N); and PSB + Azospirillium + Azotobacter (O). The bacterial substrates were inoculated into the Tithonia rhizosphere in the nursery. The young Tithoniaplants were then planted as hedgerow on Ultisols in the experimental field for 8 months, and pruned once every 2 months. The differences between treatments were statistically significant by HSD test at the 95% level of probability. Treatment L (phosphate solubilizing bacteria) was found to be the most effective, followed by treatment N (PSB +Azospirillum).