DissertationMaize is a primary staple crop for over 80% of Tanzanians, accounting for more than 70% of the country's starch requirements. Small-scale farmers produce the majority of the crop, with production unpredictable and inconsistent with agricultural requirements. Despite the fact that total maize production has increased over the last decade, owing primarily to extensification, yields per unit area remain low, averaging around 1.6 Mg/ha and translating to just 17.8 to 26.7 percent of the feasible yield. In order to fulfill the demands of the country's fast rising population, maize production must be increased. Low soil fertility, which has been related to inadequate fertilization and poor soil fertility management practices, is one of the reasons for low maize production. Soil phosphorus (P) insufficiency is one of the most critical soil fertility concerns in most Tanzanian soils, owing to the preponderance of soils with high Phosphorus-fixing capacity. Water-soluble P fertilizers (WSF) and local rock phosphates (RP) have been advised to ease the P deficit problem. While WSF are agronomically very effective, their application is limited due to their expensive cost, whereas directly applied RP are associated with delayed agronomic effectiveness and low plant phosphorus consumption efficiency. A potent solution to the low reactivity of RP is its co-application with phosphate- solubilising microorganisms (PSMs) in an appropriate carrier or carbon source. PSMs are soil microorganisms, capable of converting the insoluble P sources into its plant available forms. When co-applied with RP, PSMs could help solubilize the insoluble P in RP. However, there is limited knowledge on PSMs characterized and selected based on their ability to solubilize local phosphate rocks while utilizing locally available, naturally occurring organic carbon sources. To evaluate potentials of PSB-RP combination of maize productivity, the first specific objective was set to characterize phosphate solubilising bacterial (PSB). Forty (40) PSBs were previously isolated from various agricultural fields in eastern and southern highlands of Tanzania. Eleven (11) Isolates were selected, molecularly identified, screened for plant-growth promoting traits such as (1) ability to solubilize three P-sources namely ferric-, tricalcium-, and hard Minjingu rock phosphate, (2) Indole Acetic Acid (IAA) production, (3) Siderophore production, (4) Ammonia gas production, (5) Hydrogen cyanide (HCN) gas production, and (6) Activity against phytopathogenic fungi. The second objective was to examine the influence of organic carbon sources and fertilizer- grade nitrogen sources on phosphate solubilising abilities of PSBs. Three organic carbon sources namely Molasses (ML), sunflower seedcake (SC), and filter mud (FM) were initially evaluated for their physicochemical properties according their comparative potentials to enhance solubilisation of Tri-calcium phosphate (TCP) and Ferric phosphate (FP) by ten PSB isolates. In place of glucose, 20 g per liter of either ML, SSC or FM were added in Pikovskaya Agar (PVK) broth. Accordingly, a double-modified synthetic minimal media (dSMM) was prepared which contained all components of the Pikovskaya broth, except the carbon and Nitrogen source. The third objective focused on evaluating the influence of organic carbon sources and fertilizer-grade nitrogen sources on antifungal efficiencies of PSB isolates against phytopathogenic fungi. Each of the PSB isolate was grown in the modified synthetic minimal agar medium supplemented separately with either ML, SSC, FM, or glucose as the sole source of carbon. Accordingly, agar plates were spot-inoculated with different PSB isolates on one end of the 9 cm diameter Petri dish and test fungi on the other end. Antifungal efficiency (AE) of each PSB under each treatment was determined. Lastly, influence of co-application of MPR and PSBs in a molasses-based carrier was evaluated for enhancing maize yield and phosphorus use efficiency. Field experiments were laid out in randomized complete block design in quadruplicates under two sites, Madaba and Magadu, respectively located in the southern highlands and eastern zones of Tanzania. The soils of each study area were characterized for soil fertility parameters. Experimental treatments were PSB inoculum co-applied with varying P rates (0, 20, 40, 60, and 80 kg P /ha) from MPR. Two P rates without PSB inoculum (0 and 40 kg P /ha) were set respectively as absolute and positive control. Soil available P, maize grain yield, biomass yield, phosphorus uptake, and use efficiency for each treatment were evaluate at harvest maturity. The results indicated that six bacterial isolates had the highest homology with the known strains of the genus Klebsiella, two isolates related to the strains of genus Burkholderia, while one isolate is still unidentified. All PSB isolates were positive for ammonia production test with highest amount being 168.3 ug/ mL produced by Klebsilla sp.- NA19a while none of the isolates exhibited ability to produce hydrogen cyanide gas. The highest amount of IAA produced was 24.32 ug/ mL by Klebsilla sp.- SI-SP1. Similarly, Klebsilla sp-NA5 showed a significantly (P≤ 0.05) bigger solubilisation index on ferric phosphate agar plate while K. variicola spp.-MdG1 showed highest solubilisation index on ZnCO 3 agar plates. All the eleven isolates inhibited growth of F. proliferatum on agar plates with the highest inhibition of 47.7% by Burkholderia sp.-MK10. Among organic carbon sources tested, molasses significantly (P ≤ 0.05) enhanced solubilisation of both tri-calcium and ferric-Phosphates compared to filter mud or sunflower seedcake while urea-containing media resulted into a significantly (P ≤ 0.05) lower amount of P-solubilized as compared to fertilizer-grade or laboratory-grade ammonium sulfate (SA) as N source. The evaluation of antifungal activity showed that the use of molasses as carbon source retains most of antifungal activity of isolates but filter mud and sunflower seedcake do not. Fertilizer-grade SA enhanced the antifungal activity of most bacterial isolates than urea. Furthermore, the bacterial isolates under study retained their antifungal efficiencies whether yeast extract is included in the growth media. A study on field evaluation of RP-PSB co-application revealed the following. The characterized soils of both study sites were acidic and deficient of nitrogen, phosphorus, and potassium. The data collected at harvest time indicated that soil available P of both sites responded positively to increasing P rates from Minjingu rock phosphate + phosphate solubilising bacteria (Bio-rock). Unlike Magadu soil, sole application of PSB inoculum in soils of Madaba increased soil available P to values statistically comparable to applying either sole MPR at 40 kg P /ha or 20 kg P /ha + PSB inoculum. Compared to applying sole MPR at 40 kg P /ha, maize grain yield, P uptake and phosphorus use efficiency (PUE) were improved by inoculation of PSB combined with either 20 kg P /ha or 40 kg P /ha. It is recommended, for enhanced maize productivity and efficient use of phosphorus, co-application of PSB inoculum and Minjingu RP at 20 kg P /ha for the soils of Madaba and 40 kg P /ha for the soils of Magadu.Tanzania Commission of Science and Technology (COSTECH)