Phosphorus (P) availability is one of the major constraints in calcareous soils. The soils of Pakistan are mostly calcareous and hence deficient in plant available P. The efficiency of chemical P fertilizers in calcareous soils is around 10 - 25 %. The challenge is how P availability can be increased in calcareous soils and the use of mineral P fertilizers is reduced. A series of pot and lab incubation experiments were therefore undertaken to evaluate the role of phosphate-solubilizing bacteria (PSB) in improving P availability in soil containing varying levels of lime. The 1st pot experiment was conducted to evaluate the integrated effect of PSB and P sources [poultry manure (PM), farm yard manure (FYM), single supper phosphate (SSP) and rock phosphate (RP) each applied at the rate of 45 mg P2O5 kg-1)] on wheat and maize crops in soil under varying levels of lime (4.78, 10, 15 and 20 %). Based on the excellent performance of PM as a sources of P in previous experiment, a 2nd pot experiment was executed to examine the integrated effect of different levels of PM (4, 8 and 12 t ha-1) with PSB on growth of wheat and maize crops in soil with varying levels of lime (4.78, 10, 15 and 20 %). The effect of the same treatments used in pot experiments were evaluated on P availability (during 56 days) and soil respiration (during 10 days) in four laboratory incubation experiments. Three factorial complete randomized design (CRD) with three replications was used for these experiments. The results demonstrated that, PSB inoculation significantly improved wheat tillering (10.7%), plant height (12.7%), grains per spike (10.3%), 100 grains weight (7.0%), grain yield (14.1%), biological yield (16.3%), root dry weight (8.1%), P concentration (7.1%) and uptake (24%) over un-inoculated control in pot experiment one. Moreover, inoculation induced soil acidification over un-inoculated control treatment regardless of P sources. Organic manures (PM and FYM) performed significantly better than mineral sources (SSP and RP) with respect to wheat growth and soil properties after wheat harvest. Furthermore, RP with PSB was as effective as SSP, but in the absence of PSB the performance of SSP was superior to RP. On the basis of performance, P sources could be ranked as PM ≥ FM > SSP >RP. The grain yield and P uptake of wheat gradually reduced with increasing level of lime. Lime application significantly induced soil salinity and alkalinity. In the following season, inoculation with PSB significantly increased the growth and P uptake of maize in pots previously treated with lime and P sources. Interactively, PSB and/or organic manures neutralized the ill effects of lime on crop growth and soil properties. In 2nd pot experiment inoculation considerably improved wheat germination (7%), plant height (14%), grain yield (9%), biological yield (6%), root dry weight (8%), P concentration (5%) and uptake (10%) over un-inoculated control treatment. Inoculation didn‘t affect soil Olsen P, EC, OM and lime after wheat harvest but induced soil acidification over un-inoculated treatments. Application of PM at 4-12 t ha-1 significantly increased wheat yield, P uptake and post harvest soil OM but decreased soil EC, pH and lime. The performance of 8 and 12 t PM ha-1 were however comparable for the most of the parameters. Lime amendment adversely affected the growth of both wheat and subsequent maize crops, and induced soil salinity and alkalinity. However, PSB inoculation and PM significantly nullified the adverse effects of lime on crop growth and soil properties. Additionally, PSB inoculation and previously applied PM levels significantly improved growth and P uptake of maize under varying levels of lime. Soil inoculation with PSB progressively increased Olsen P from all sources compared to control over the course of 56 days; however, this increase was greater from organic sources (PM and FYM) than from mineral P sources (SSP and RP). Initially, P release from inoculated and un-inoculated soils were comparable but later on (at day 56) the net increase in inoculated and un-inoculated soil were 4.22 and 2.20 mg P kg-1 in case of different P sources and 16.96 and 17.43 mg P kg-1 in case of PM levels, respectively. With respect to P release at day 56th the sources could be ranked as PM (12.22 mg kg-1) >FM (11.58 mg kg-1) > SSP (8.42 mg kg-1) >RP (8.02 mg kg-1). Furthermore, P mineralization gradually increased with increasing level of PM but significantly decreased with increasing level of lime at each incubation interval in 56 days. However, with PM rates mineralization/release was similar under control and 10% limed soil. The PSBs were the most viable in inoculated soil amended with organic sources while, addition of lime into soil significantly reduced post incubation (56days) PSB population. Inoculation (PSB) and PM application significantly enhanced soil respiration over control in soil with varying levels of lime during 10 days incubation period. The rate of CO2 evolution increased with increasing level of lime, but decreased with a passage of time in all treatments. The net respiration was statistically similar for inoculated and un-inoculated soils both for P sources and PM rates under varying levels of lime. At day 10, PM emitted significantly higher cumulative CO2 (1.19 g kg-1) followed by FYM (1.16 g kg-1) while, the lowest emission was recorded in RP (1.01 g kg-1) which was comparable to SSP (1.02 g kg-1). Cumulative CO2 released gradually increased both with increasing level of lime and PM. Our findings imply that, organic sources of P performed significantly better than mineral sources. However, the performance of mineral P sources with PSB was similar to sole application of organic manures. Inoculation with PSB counteracted the antagonistic effects of lime over P availability and crop growth, when co-applied with both mineral and organic sources; however, organic sources supported this process more efficiently than do mineral P sources. Therefore, PSB inoculation combined with organic manures appear the best practice for improving P availability under calcareous soils. Application of RP with PSB proved as effective as sole SSP. Thus, PSB has a potential for utilizing RP as alternate to expensive chemical P fertilizers for improving P availability in calcareous soils.