Evaluating the impact combined application of organic amendments and PSB with rock phosphate on soil microbial properties in kharif maize under red lateritic soils of Odisha

Introduction

Among the macronutrients essential to plant growth, phosphorus occupies a central position, shaping processes ranging from root development and seed formation to nutrient uptake, photosynthesis, respiration and the timely completion of the crop cycle (Hinsinger, 2001) [7] . Maize shows vulnerability towards iron toxicity, demanding for proper and sufficient drainage and soil ameliorations. The principal sources of rock phosphorus are considered as the sedimentary rocks which has a lion's contribution of 80% of entire global RP stocks. Flourapatiterich phosphate rocks supposed to have higher reactivity amongst its various forms, considerably most suitable for direct application as a reliable source of phosphorus in agriculture. Use of Organic amendments such as farmyard manure (FYM) and vermicompost not only contribute additional nutrients but also create a conducive environment for microbial activity. Meanwhile, the introduction of phosphate-solubilizing microorganisms (PSMs) plays a key role in mobilizing phosphorus from rock phosphate, thereby improving its uptake by plants (Khan et al., 2010) [8] . Humic acids, as the principal components of soil organic matter, play a vital role in enhancing plant growth and soil health (Nardi et al., 2002) [9] . Empirical studies have shown that humic acids improve soil structure, increase water retention, reduce bulk density, and elevate total porosity and organic matter content. MBC and MBP respond to changes in management practices (organic amendments, fertilization, tillage) much faster than total soil carbon or phosphorus, which changes only over years or decades. It also acts as both a sink and a sources of plant available phosphorus. Since the work focuses on rock phosphates solubilisation using organic amendments and microbial inoculants, MBP directly reflects how effectively the introduced/ native microbial population is mobilizing and cycling phosphorus from the applied rock phosphate.

Higher MBC under organic amendments or PSB treatments indicates a more active, functionally robust microbial community capable of sustaining nutrient availability across the maize growing season.

Materials and Methods

A field experiment was conducted at ARS, Chhatabar farm, IAS, SOADU, Bhubaneswar in kharif season of 2022 and 2023 to determine the impact of combined organic amendments and PSB on solubilisation potential of rock phosphate with Maize crop (Indra 017). The trail was laid out in Randomised Block design with fourteen treatments replicated thrice. The fourteen treatments namely, T 1 -Control; T 2 -100% RP; T 3 -50% RP + 50% SSP; T 4 -100% RP+ PSB; T 5 -100% RP + FYM; T 6 -100% RP+ Humic Acid (HA); T 7 -100% RP + Vermicompost (VC); T 8 -100% RP + Vermicompost +PSB; T 9 -100% RP + FYM + PSB; T 10 -100% RP + Humic Acid +PSB; T 11 -100% RP + FYM + Humic Acid + PSB; T 12 -100% RP + Vermicompost + Humic Acid + PSB; T 13 -100% RP + Vermicompost + FYM + PSB; T 14 -100% RP + Vermicompost+ FYM + Humic Acid+ PSB. Soil samples were collected with proper precautionary measures from maize field at different growth stages (i.e. 30, 60, 90, and at harvest) from 0-15 cm depth at each treatment plot for investigating soil microbial properties such as microbial biomass carbon and microbial biomass phosphorus. Soil microbial biomass carbon is determined by chloroform fumigationextraction method (Vance et al., 1987) [13] and microbial biomass phosphorus was determined by chloroform fumigation-extraction method of Brookes et al., 1982, with modifications by Hedley and Stewart (1982) [6] . Collected soil samples were air-dried lightly, sieved (2mm), and stored moist at 4 °C prior to analysis. The soil of the experimental plot was determined to be sandy loam and moderately acidic (pH-5.68). At harvest the grain and stover yield was recorded and segregated according to treatment plan. All the statistical analysis such as mean, pooled mean, ANOVA and regression studies were carried out using Microsoft Excel at 5% and 1% significance to draw a corroborative result.

Results and Discussion

The data in Table 1 represents grain and stover yield (kg ha⁻¹) of kharif maize as influenced by rock phosphate applied in combination with organic amendments and PSB, pooled over 2022 and 2023. Grain yield ranged from 2297.33 kg ha⁻¹ in the control (T 1 ) to 4419.33 kg ha⁻¹ in T 14 (100% RP + Vermicompost + FYM + Humic acid + PSB), an increase of about 92 per cent over the control. Stover yield followed an identical trend, ranging from 2757.50 kg ha⁻¹ (T 1 ) to 4712.50 kg ha⁻¹ (T 14 ), an increase of about 71 per cent. Treatment T 14 recorded the significantly highest grain and stover yield, remaining statistically at par with T 13 (4115.00 and 4394.67 kg ha⁻¹, respectively) and significantly superior to all remaining treatments. Sole application of RP (T 2 ) produced only a marginal yield improvement over the control, whereas combining RP with a single organic source (T 5 , T 6 , T 7 ) nearly doubled the yield gain, and further inoculation with PSB (T 8 -T 14 ) consistently improved yield over the corresponding noninoculated treatment. The substantial increase in grain and stover yield under integrated nutrient management can be attributed to enhanced phosphorus availability, improved uptake and increased soil biological activities. Application of organic amendments and PSB accelerates its dissolution through the production of organic acids, thereby increasing phosphorus availability throughout the crop growth period. (Ditta et al., 2022; Ali S et al., 2022) [2,1] . Higher phosphorus availability enhances photosynthesis, ATP synthesis, carbohydrate metabolism, and assimilate translocation from source leaves to developing grains. The superior performance of T 14 indicates a strong synergistic interaction among vermicompost, FYM, humic acid and PSB resulting in maximum nutrient use efficiency. at par with T 13 and closely followed by T 12 and T 11. Among the two -component combinations, T 8 (100% RP + Vermicompost +PSB) and T 9 recorded distinctly higher MBP than their respective PSB-uninoculated counterparts T 7 and T 5 , confirming a consistent positive contribution of PSB inoculation across organic carriers. [4] . The synergism observed when a organics and PSB were applied together may be attributed to the organic substrate providing a more favourable microenvironment for survival, multiplication and metabolic activity of the inoculated PSB population, which otherwise faces poor establishment when applied alone with an inorganic carrier such as RP (Elhaissoufi et al., 2022) [3] . [10,11] . The regression of MBP on MBC gave the equation Y = 0.366X -30.890, with a very high coefficient of determination (R² = 0.949), indicating that nearly 94.9 per cent of the variation in microbial biomass phosphorus across treatments and growth stages could be explained by the corresponding variation in microbial biomass carbon alone. Microbial biomass carbon (R² = 0.904) and microbial biomass phosphorus (R² = 0.899) were the strongest predictors of grain yield. The strong anticipatory relationship between MBC and MBP and their respective regression with grain yield shows an evidence that the microbial biomass carbon and phosphorus is closely related to productivity of kharif maize with conjoint application of rock phosphate, organic amendments and PSB.

(Harish, M.N et al., 2022) [5] .

Conclusion

Present investigation clearly suggests that the confluence in application of rock phosphate, organic amendments and PSB considerably enhanced both grain and stover yield and biological activities in red lateritic soils of Odisha under a kharif Maize cropping system evaluated over two years. MBP and MBC of soil collected at different growth stages of Maize followed and identical trend with slight increase at 30DAS reaching peak at 69 DAS and then gradually decreasing toward physiological maturity of crop. A strong regression equation developed between MBP and MBC (R² = 0.949) clarifying that the soil microbial biomass maintained a stable carbonto-phosphorus ration across the treatments. Further it was also observed that grain yield and MBC (R² = 0.904) and MBP (R² = 0.899) holds a strong relationship. The multicomponent holds a higher value over sole application or two component application as conjoint application played a major role in solubilisation of rock phosphate for increasing P in soil P pool.

References

1. Ali S, et al. Comparative efficacy of phosphorous supplements with phosphate solubilizing bacteria for optimizing wheat yield in calcareous soils. Sci Rep. 2022;12:12274. doi:10.1038/s41598-022-16035-3.
2. Ditta A, Muhammad J, Imtiaz M, Mehmood S, Qian Z, Tu S, et al. Coupling phosphate-solubilizing bacteria (PSB) with inorganic phosphorus fertilizer improves mungbean phosphorus acquisition, nitrogen fixation, and yield in alkaline-calcareous soil. Front Plant Sci. 2022;13:900579. doi:10.3389/fpls.2022.900579.
3. Elhaissoufi W, Ghoulam C, Barakat A, Zeroual Y, Bargaz A. Phosphate bacterial solubilization: a key rhizosphere driving force enabling higher P use efficiency and crop productivity. J Adv Res. 2022;38:13-28. doi:10.1016/j.jare.2021.08.014.
4. Fei C, Bertrand I, Abalos D, Zhang L, Pistocchi C. Organic amendments as a major driver for improving the microbial recycling of soil P: a global meta-analysis. SSRN. 2024. doi:10.2139/ssrn.4865126.
5. Harish MN, Choudhary AK, Kumar S, et al. Double zero tillage and foliar phosphorus fertilization coupled with microbial inoculants enhance maize productivity and quality in a maize-wheat rotation. Sci Rep. 2022;12:3161. doi:10.1038/s41598-022-07148-w.
6. Hedley MJ, Stewart JWB. Method to measure microbial phosphate in soils. Soil Biol Biochem. 1982;14(4):377-385. doi:10.1016/0038-0717(82)90009-8.
7. Hinsinger P. Bioavailability of soil inorganic P in the rhizosphere as affected by root-induced chemical changes: a review. Plant Soil. 2001;237(2):173-195. doi:10.1023/A:1013351617532.
8. Khan MS, Zaidi A, Ahemad M, Oves M, Wani PA. Plant growth promotion by phosphate solubilizing fungi: current perspective. Arch Agron Soil Sci. 2010;56(1):73-98. doi:10.1080/03650340902806469.
9. Nardi S, Pizzeghello D, Muscolo A, Vianello A. Physiological effects of humic substances on higher plants. Soil Biol Biochem. 2002;34(11):1527-1536. doi:10.1016/S0038-0717(02)00174-8.
10. Niedeggen D, Rüger L, Oburger E, Santangeli M, Ahmed MA, Vetterlein D, et al. Microbial utilisation of maize rhizodeposits applied to agricultural soil at a range of concentrations. Eur J Soil Sci. 2024;75(4):e13530. doi:10.1111/ejss.13530.
11. Pausch J, Kuzyakov Y. Carbon input by roots into the soil: quantification of rhizodeposition from root to ecosystem scale. Glob Change Biol. 2018;24(1):1-12. doi:10.1111/gcb.13850.
12. Rodríguez H, Fraga R. Phosphate solubilizing bacteria and their role in plant growth promotion. Biotechnol Adv. 1999;17(4-5):319-339. doi:10.1016/S0734-9750(99)000142.
13. Vance ED, Brookes PC, Jenkinson DS. An extraction method for measuring soil microbial biomass C. Soil Biol Biochem. 1987;19(6):703-707. doi:10.1016/0038-0717(87)90052-6.