Phosphorus (P) is the second most essential macronutrient after nitrogen. Phosphorus limitation in acidic soils is well known and the P-use and - recovery efficiencies (PUE and PRE) in these soils are notoriously low. Though the rhizosphere-based P management approaches are considered as useful methods for
enhancing PUE in acidic rice soils, some fundamental questions still need to be addressed. This study determined the dynamics of soil available-P (AvlP), P-content and -uptake in rice under the potted condition of different P sources [rock phosphate (RP), single supper phosphate (SSP), compost, phosphate solubilizing bacteria (PSB), PSB+RP, PSB+compost, and compost+PSB+RP]. The critical limits of P-dose and incubation duration for the root-dip-SSP soil slurry method of P application were
determined using incubation study. Effects on grain yield, P-content and –uptake, PUE and PRE, soil AvlP in rice were studied under P source-cum-method combinations (basal application of RP and SSP separately, root-dipping in PSB alone and in combination with RP, SSP-root-dip, and SSP-root-dip+PSB+RP in micro-plot field experiment. The soil used in all these experiments was strongly acidic (pH 4.31) Inceptisols and the crop was sali rice variety Shahsarang. The dynamics of soil AvlP and pH at l0days interval, acid-phosphomonoesterases activity (PHA), P-content and – uptake in biomass at 30 days interval till harvest of rice crop were determined. Results indicated that soil AvlP was the highest at 20 days after transplanting (DAT) and gradually decline till harvest. The application of compost+PSB+RP could maintain consistently higher soil AvlP throughout the crop growing period, which was significantly higher from the rest of the P sources (as evident by repeated measures- ANOVA). Changes in soil pH during crop growth period showed an asymptotic trend. Barring few exception, soil pH increased at 30, 50, 90 and 110 DATs. The increase in soil pH, values of PHA and root volume were the highest under compost+PSB+RP compared to other P sources. Phosphorus content and uptake in biomass (straw+root)
of rice reached the highest peak at 60DAT and then gradually declined till harvest. Effects of SSP and compost+PSB+RP to rice crop found to be comparable on grain yield, chlorophyll concentration index, P content and uptake in grain, PUE and PRE. Results from the incubation experiment indicated that the critical limits for P-dose and incubation duration for root-dip in SSP amended soil slurry method of P application were found to be 112.5 mg kg-1 soil and 10 h, respectively. In micro-plot field experiment, the combination of source cum method of P applications i.e. SSP (basal), SSP-root-dip, and SSP-root dip+PSB+RP were found to be comparable in terms of the number of effective tiller, grain yield, biological yield and harvest index. However, SSProot- dip+PSB+RP method produced significant higher root volume, P-content and uptake, PUE and PRE compared to other P source cum methods, but were
comparable to that in SSP basal application. Results from the micro-plot field experiment clearly revealed that rice yield enhancement over control was 52.9%, 32.5%, 47.8%, and 55.4% due to application of SSP alone, PSB+RP, SSP-root-dip, and SSP-root-dip+PSB+RP, respectively. In conclusion, this study clearly demonstrated that the application of PSB+RP+Compost could maintain higher soil AvlP throughout the rice growth period compared to SSP basal practice. The critical limits of P dose and incubation duration for root-dip SSP-soil slurry method were 112.5 mg kg- 1soil and10 h, respectively. The SSP-root-dip+PSB+RP was found to be superior management practice in acidic rice soils, which needs to be validated through multilocational trial in farmers’ fields.