Effect of integrated phosphorus management on yield and biochemical activities in rice under saline conditions

Introduction

Rice (Oryza sativa) is one of the most important staple foods in the world, serving as a primary source of nourishment for over half of the global population. It is estimated that rice provides approximately 20% of the world's caloric intake, underscoring its importance in global food security and agricultural economy. Salinity is a major soil and water-related constraint in coastal areas, severely affecting agricultural productivity and ecological stability. It is the major abiotic stress limiting rice productivity as it adversely affects soil properties, nutrient availability and absorption by the plant. Salinity further impairs photosynthesis through stomatal closure, chlorophyll degradation drastically reducing carbohydrate production and biomass accumulation Mrudhla et al. (2025) [9] . At the cellular level, overproduction of reactive oxygen species (ROS) causes oxidative damage to membranes, proteins, and DNA, overwhelming the plant's natural antioxidant defences. To overcome the limitations of salinity, biofertilizers were applied in combination with inorganic fertilizers to improve the soil rhizosphere activity and thereby improving the nutrient uptake by plants under salt stress conditions.

Materials and Methods

A field experiment was conducted at OFT farm, Saline Water Scheme Bapatla, Andhra Pradesh during kharif, 2025. The soil of the experimental field was clay in texture, neutral in reaction with pH 7.52, electrical conductivity 6.4 dS m -1 , saline, medium in organic carbon, low in available nitrogen, medium in available phosphorus and medium in available potassium. Average mean maximum temperature was 32.0 0 C and minimum temperature was 22.0 0 C during the crop growth period. The total amount of rainfall received was 903.9 mm with 31 rainy days. The experiment was laid out in Randomized Block Design with 9 treatments replicated thrice. The treatments include, T 1: Control (no P); T 2: 100% RDP (60 kg P 2 O 5 ha -1 ); T 3: 100% RDP + PSB; T 4: 100% RDP + VAM; T 5: 100% RDP + PSB + VAM; T 6: 75% RDP; T 7: 75% RDP + PSB; T 8: 75%RDP + VAM; and T 9: 75% RDP + PSB + VAM. Nutrient NPK was applied in the form of urea, Single Super Phosphate (SSP) and Muriate of Potash (MOP) respectively. Nitrogen was applied in three equal splits i.e., as basal, 30 DAT and 60 DAT and entire dose of phosphorus was applied as basal, for treatments receiving 100% RDP, 60 kg P₂O₅ ha⁻¹ was applied, while for treatments receiving 75% RDP, 45 kg P₂O₅ ha⁻¹ was applied. In case of biofertilizers i.e. PSB (Phosphate solubilizing bacteria), and VAM (vesicular arbuscular mycorrhizae) were thoroughly mixed with vermicompost and applied in experimental plots as per the treatments. Potassium was applied in two splits at i.e. basal and at 30 DAT. Gap filling, weeding, irrigation and other necessary intercultural operations were done in proper time. Harvesting was done plot wise, five hills were selected randomly from each unit plot for taking yield component data at harvest. One m 2 area from each plot was selected from the central portion and was cut manually from the ground level to take grain and straw yields. The harvested crop of each plot was separately bundled, properly tagged and then brought to the threshing floor. The harvested crops were threshed manually. The grain was cleaned and dried to a moisture content of 14 per cent. Straws were sun dried properly. Data recorded for yield parameters were compiled and tabulated in proper form for statistical analysis (Gomez and Gomez 1984) [4] .Total chlorophyll content in leaves was estimated colorimetrically by dimethyl sulphoxide (DMSO) method as described by Hiscox and Israelstam, (1979) [6] .The proline content was estimated by following the method of Bates et al. (1973) [1] .The peroxidase content is estimated by following the method of Malik and Singh et al., (1980) [7] .The phenols content is estimated by following the method of Malik and Singh (1980) [7] .The method used for Na + /K + determination is by flame photometry given by Tandon (1993) [19] .

Results and Discussion

Grain Yield (kg ha -1 ) Grain yield of rice was significantly influenced by different phosphorus levels. Significantly the highest grain yield (5140 kg ha -1 ) was obtained with (T 5 ) 100% RDP + PSB + VAM highlighting the effectiveness of nutrient application along with biofertilizers in realizing higher productivity. This treatment was statistically at par with (T 3 ) 100% RDP + PSB (4947 kg ha -1 ), (T 4 ) 100% RDP + VAM (4917 kg ha -1 ), (T 9 ) 75% RDP+ PSB+ VAM (4900 kg ha -1 ) (T 7 ) 75% RDP+ PSB (4783 kg ha -1 ) and (T 8 ) 75% RDP + VAM (4753 kg ha -1 ). Significantly lowest grain yield (3617 kg ha -1 ) was recorded with (T 1 ) control treatment. Pratibha Rawat et al. (2020) [12] revealed that these assimilates were subsequently translocated to the developing grains, resulting in improved grain filling and higher yield. Furthermore, sufficient nutrient supply during the early growth stages supports better plant growth and development, which ultimately contributes to increased productivity. Similar findings have been reported by Gudarankaiah et al. (2021) [5] , Tejaswini et al. (2017) [20] , Bhavani et al. (2013) [2] and Verma et al. (2017) [23] .

Straw yield recorded at harvest in different treatments of rice were found comparable with each other and significant difference was observed in straw yield tested under study Significantly the highest straw yield (5383 kg ha -1 ) was obtained with (T 5 ) 100% RDP + PSB + VAM this treatment was statistically at par with (T 3 ) 100% RDP + PSB (5150 kg ha -1 ), (T 4 ) 100% RDP + VAM (5033 kg ha -1 ), (T 9 ) 75% RDP+ PSB+ VAM (4917 kg ha -1 ) (T 7 ) 75% RDP+ PSB (4900 kg ha -1 ) and (T 8 ) 75% RDP + VAM (4833 kg ha -1 ). Significantly lowest straw yield (4400 kg ha -1 ) was recorded with (T 1 ) control treatment. The increased straw yield may be attributed to the synergistic effect of phosphorus fertilization along with PSB and VAM, which enhanced phosphorus availability and uptake, leading to improved root growth, nutrient absorption, and vegetative development. Prasanthnaik et al. (2020) [11] reported that enhanced phosphorus nutrition promotes cell division and photosynthetic efficiency resulting in greater dry matter production and straw yield.

Total chlorophyll content at flowering and maturity

The total chlorophyll content at flowering and maturity were significantly influenced by the application of different levels of phosphorus and biofertilizers tested under study. At flowering, significantly the highest total chlorophyll content (2.8 mg g -1 ) was recorded in the treatment 100% RDP+PSB+VAM, which was at par with (T 3 ) 100% RDP+PSB whereas, significantly the lowest total chlorophyll content (1.7 mg g -1 ) was recorded at control treatment. Rajasekaran et al. (2015) [13] reported that phosphorus plays a vital role in energy transfer, photosynthesis, and chlorophyll synthesis. PSB enhances the solubilization of fixed phosphorus, while VAM improves nutrient and water absorption through an extensive hyphal network. At maturity, significantly the highest total chlorophyll content (2.2 mg g -1 ) was observed in the treatment (T 5 )100% RDP+PSB+VAM and it was found to be at par with (T 3 ) 100%RDP +PSB (2.2 mg g -1 ) and (T 4 ) 100% RDP +VAM (2.1 mg g -1 ) treatments. The lowest total chlorophyll content (1.6 mg g -1 ) was recorded at control treatment, respectively. Shanaz Parvin et al. (2020) [10] reported that the higher chlorophyll content in treatments with biofertilizers indicate delayed senescence and sustained photosynthetic activity owing to better phosphorus nutrition and improved plant health under saline conditions.

Proline content at flowering and maturity

Proline content at harvest and flowering were significantly influenced by the different levels of phosphorus and biofertilizers tested under study. At flowering, significantly the highest proline content (26 µg g -1 ) was recorded in the treatment (T 1 ) control, which was at par with (T 2 ) 100% RDP (24 µg g -1 ) and (T 6 ) 75% RDP(25 µg g -1 ), whereas, significantly the lowest proline content (12 µg g -1 ) was recorded in the (T 5 )100% RDP+PSB+VAM treatment. Shi et al. (2007) [16] revealed that increased accumulation of proline in the control treatment indicates greater stress perception and cellular damage due to nutrient deficiency and salt stress. In contrast, the lower proline content in treatments inoculated with PSB and VAM suggests that these biofertilizers improved phosphorus availability, nutrient uptake, water relations, and ionic balance, thereby reducing stress intensity and the need for osmotic adjustment through proline accumulation. Significantly the highest proline content (34 µg g -1 ) at maturity was recorded in the treatment (T 1 ) control, same as at flowering which was at par with (T 2 ) and (T 6 ), whereas, significantly the lowest proline content (12 µg g -1 ) was recorded in the (T 5 ) treatment. (15 µg g -1 ). Higher proline content was observed at maturity than at flowering. Under, salt and drought stress conditions, large accumulation of intracellular soluble sugar and proline improves the cell sap concentration, maintains normal cell turgor, prevents excessive water loss and enhances the resistance of plants as reported by Stewart and Lee (1974) [18] .

Total phenols at flowering and maturity

The total phenolic content in rice at flowering and maturity were significantly influenced by the different phosphorus levels and biofertilizers tested under the study. At flowering, significantly the highest phenolic content (42 mg/100 g) was recorded in the treatment (T 1 ) control, which was at par with (T 6 ) 75% RDP (38 mg/100 g), whereas, significantly the lowest phenolic content (27 mg/100 g) was recorded in the (T 5 )100% RDP+PSB+VAM treatment. Sharma et al. (2009) [15] reported that phenolic compounds are important secondary metabolites that accumulate in plants under stress conditions and play a crucial role in protecting cells against oxidative damage caused by reactive oxygen species (ROS) Mrudhula et al., (2025) [8] . The higher phenolic content in the control treatment indicates greater oxidative stress induced by salinity and inadequate nutrient availability. At maturity, significantly the highest phenolic content (53 mg/100 g) was recorded in the treatment (T 1 ) control, which was at par with (T 6 ) 75% RDP (49 mg/100 g) and (T 2 ) 100% RDP (47 mg/100 g) whereas, significantly the lowest phenolic content (29 mg/100 g) was recorded in the (T 5 )100% RDP+PSB+VAM treatment. Higher phenolic content was observed at maturity than at flowering. The higher phenolic content at maturity compared to flowering may be attributed to prolonged exposure to salinity stress and age-related physiological changes that enhance the synthesis and accumulation of phenolic compounds as reported by Kumar et al.

Peroxidase activity at flowering and maturity

The peroxidase activity in soil was significantly influenced by the different phosphorus levels and biofertilizers tested under the study. At flowering, significantly the highest peroxidase activity (4.96min -1 g -1 ) was recorded in the treatment (T 1 ) control, which was at par with (T 6 ) 75% RDP (4.48 min -1 g -1 ) and (T 2 ) 100% RDP (3.97 min -1 g -1 ) whereas, significantly the lowest peroxidase activity (1.72 min -1 g -1 ) was recorded in the (T 5 )100% RDP+PSB+VAM treatment. Velazahan et al. (2006) [22] revealed thatunder saline conditions, excessive production of reactive oxygen species (ROS) induces higher peroxidase activity as a protective mechanism to detoxify harmful free radicals. Therefore, the elevated peroxidase activity observed in the control treatment which indicates greater oxidative damage and stress. Significantly the highest peroxidase activity (6.24 min -1 g -1 ) was recorded at maturity in the treatment (T 1 ) control, which was at par with (T 6 ) 75% RDP (5.91 min -1 g -1 ), (T 2 ) 100% RDP (5.32 min - 1 g -1 ) and (T 7 ) 75% RDP+ PSB (5.91 min -1 g -1 ) whereas, significantly the lowest peroxidase activity (2.32 min -1 g -1 ) was recorded in the (T 5 )100% RDP+PSB+VAM treatment. Sharma et al. (2012) [14] reported that the increase in peroxidase activity at maturity compared to flowering may be attributed to prolonged exposure to salinity stress and enhanced oxidative stress during the later stages of crop growth.

Na + /K + ratio at flowering and maturity

The Na + /K + ratio in rice was significantly influenced by different phosphorus levels and biofertiliers tested under study. At flowering significantly the highest Na+ /K+ ratio (0.54) was recorded in the control treatment, which was at par with (T 6 ) 75% RDP(0.49), (T 2 ) 100% RDP (0.46), (T 8 ) 75% RDP+ VAM (0.41) and (T 7 ) 75% RDP +PSB (0.37) whereas, the lowest Na+ /K+ ratio (0.21) was recorded in the treatment (T 5 ) 100% RDP+PSB+VAM. Mamta et al. (2008) [8] reported thatat flowering stage, a low Na⁺/K⁺ ratio helps maintain reproductive development, pollen viability, spikelet fertility, and photosynthetic efficiency, thereby reducing yield losses caused by salinity. At maturity stage significantly the highest Na+ /K+ ratio (0.68) was recorded in the control treatment, which was at par with (T 6 ) 75% RDP(0.61), (T 2 ) 100% RDP (0.56) and (T 8 ) 75% RDP+ VAM (0.49). The significantly lowest value was recorded by the treatment (T 5 ) 100% RDP+PSB+VAM (0.32). Tester and Davenport (2003) [21] revealed that at maturity stage, maintaining a favorable Na⁺/K⁺ ratio supports efficient grain filling, nutrient balance, and overall plant health under prolonged salt stress.

Acid phosphatase enzyme activity

The acid phosphatase activity in soil at harvest was significantly influenced by the different phosphorus levels and biofertilizers tested under the study. At harvest, the acid phosphatase activity in soil recorded significantly the highest (45.4 µg pNP g⁻¹ hr⁻¹) in the treatment (T 5 ) 100% RDP+PSB+VAM, which was at par with (T 3 ) 100% RDP+PSB (42.7µg pNP g⁻¹ hr⁻¹), (T 4 ) 100% RDP+VAM (39.2µg pNP g⁻¹ hr⁻¹) and (T 9 ) 75% RDP+PSB+VAM (37.4µg pNP g⁻¹ hr⁻¹) whereas, significantly the lowest acid phosphatase activity (17.2 µg pNP g⁻¹ hr⁻¹) was recorded at control treatment. Srilatha et al. (2013) [17] reported that the increased acid phosphatase activity in treatments inoculated with PSB and VAM may be attributed to enhanced microbial activity and greater root exudation in the rhizosphere.

Alkaline phosphatase enzyme activity

Alakaline phosphatase activity in soil at harvest shown significant difference among the different levels of phosphorus and biofertilizers tested under the study. At harvest, the alkaline phosphatase activity in soil recorded significantly the highest (37.2 µg pNP g⁻¹ hr⁻¹) in the treatment (T 5 ) 100% RDP+PSB+VAM, which was at par with (T 3 ) 100% RDP+PSB (34.3µg pNP g⁻¹ hr⁻¹), (T 4 ) 100% RDP+VAM (31.4µg pNP g⁻¹ hr⁻¹), (T 9 ) 75% RDP+PSB+VAM (29.4µg pNP g⁻¹ hr⁻¹) and (T 7 ) 75% RDP+PSB (26.3 µg pNP g⁻¹ hr⁻¹) whereas, significantly the lowest alkaline phosphatase activity (12.2 µg pNP g⁻¹hr⁻¹) was recorded at control treatment. Ghosh et al. (2023) [3] revealed that the enhanced alkaline phosphatase activity in PSB and VAM treated plots may be attributed to increased microbial population, greater root proliferation, and higher secretion of phosphatase enzymes in the rhizosphere.

Conclusion

Based on the findings, it can be concluded that application of inorganic nutrients along with biofertilizers had significantly improved the yield and reduced the adverse effects of salinity stress in T 5 (100% RDP+PSB+VAM)followed by T 3 (100% RDP+PSB) and T 4 (100% RDP+VAM) thereby, improving the nutrient uptake and soil microbial activity. The application of inorganic nutrients alone in the control treatment showed increased biochemical activity which indicates the plants response towards the salt stress to improve crop growth and productivity.

References

1. Bates L, Waldren RP, Teare ID. Rapid determination of free proline for water stress studies. Plant Soil. 1973;39(1):205207.
2. Bhavani G, Martin Luther M, Chandra Sekhar K, Ravindra Babu P. Biological mining of soil reserve phosphorus in lowland rice (Oryza sativa L.). The Andhra Agricultural Journal. 2013;60(1):1-5.
3. Ghosh A, Biswas DR, Bhattacharyya R, Das S, Das TK, Lal K, et al. Rice residue promotes mobilisation and plant acquisition of soil phosphorus under wheat (Triticum aestivum)-rice (Oryza sativa L.) cropping sequence in a semi-arid Inceptisol. Scientific Reports. 2023;13(1):17545.
4. Gomez MA, Gomez AA. Statistical procedures for agricultural research. New York: John Wiley and Sons; 1984. p. 97-129, 207-215.
5. Gudarankaiah U, Bhargava Rami Reddy C, Sujani Rao C, Martin Luther M. Effect of phosphorus management on yield of direct sown rice. The Andhra Agricultural Journal. 2021;68(1):86-95.
6. Hiscox JD, Israelstam GF. A method for the extraction of chlorophyll from leaf tissue without maceration. Can J Bot. 1979;57(12):1332-1334.
7. Malik CP, Singh MB. Plant enzymology and histoenzymology. New Delhi: Kalyani Publishers; 1980. p. 53.
8. Mamta JB, Ashish D, Patel PMB, Amar NP. Effect of soil salinity on growth, water status and nutrient accumulation in seedlings of Ziziphus mauritiana (Rhamnaceae). Journal of Fruit and Ornamental Plant Research. 2008;16:383-401.
9. Mrudhula KA, Madhu Vani P, Sunil Kumar M, Suvarna Latha A. Effect of foliar application of salicylic acid on enhancing salinity tolerance in sorghum. Journal of the Indian Society of Soil Salinity and Water Quality. 2025:228235.
10. Mrudhula KA, Madhu Vani P, Prasuni Rani P. Effect of saline irrigation on maize productivity, resource use efficiency and soil dynamics under drip fertigation system. Journal of Soil Salinity and Water Quality. 2025;17(2):155162.
11. Parvin S, Van Geel M, Yeasmin T, Verbruggen E, Honnay O. Effects of single and multiple species inocula of arbuscular mycorrhizal fungi on the salinity tolerance of a Bangladeshi rice (Oryza sativa L.) cultivar. Mycorrhiza. 2020;30(4):431-444.
12. Prasanth Naik B, Lalitha Kumari A, Venkata Subbaiah P, Martin Luther M. Effect of liquid biofertilizers on growth and yield of direct sown rice. The Andhra Agricultural Journal. 2020;67(3):194-196.
13. Rawat P, Shankhdhar D, Shankhdhar SC. Plant growth promoting potential and biocontrol efficiency of phosphate solubilizing bacteria in rice (Oryza sativa L.). Int J Curr Microbiol App Sci. 2020;9(9):2145-2152.
14. Rajasekaran S, Sundaramoorthy P, Sankar Ganesh K. Effect of FYM, N, P fertilizers and biofertilizers on germination and growth of paddy (Oryza sativa L.). International Letters of Natural Sciences. 2015;35:59-65.
15. Sharma N, Kaur C, Singh J, Gupta AK. Biochemical responses associated with bacterial blight of rice (Oryza sativa L.). Archives of Phytopathology and Plant Protection. 2012;45(1):47-61.
16. Sharma AK, Singh T, Patel A, Yadav RA. Influence of integrated nutrient management practices on scented rice (Oryza sativa L.) pertaining to eastern Uttar Pradesh. Journal of Pharmacognosy and Phytochemistry. 2018;7(5):14481453.
17. Shi YW, Wang YL, Li WB. Effects of water stress on soluble protein, soluble sugar and proline content in Tamarix hispida. Journal of Xinjiang Agricultural University. 2007;30(2):5-8.
18. Srilatha M, Rao PC, Sharma SHK, Bhanu Rekha K. Influence of long-term fertilizer application on soil phosphatase enzyme activity and nutrient availability in rice-rice cropping system. Journal of Rice Research. 2013;6(2):45-52.
19. Stewart GR, Lee JA. The role of proline accumulation in halophytes. Planta. 1974;120:279-289.
20. Tandon HLS. Methods of analysis of soils, plants, waters and fertilizers. New Delhi: Fertilizer Development and Consultation Organization; 1999. p. 144.
21. Tejaswini M, Sreedevi B, Akula B, Kumar BA, Singh A. Effect of cultivars and biofertilizers on growth, yield and nutrient content of aerobic rice (Oryza sativa L.). Environment and Ecology. 2017;35(4C):3022-3027.
22. Tester M, Davenport R. Na+ tolerance and Na+ transport in higher plants. Ann Bot. 2003;91:503-539.
23. Velazhahan R, Jayaraj J, Khabbaz. Xanthomonas oryzae pv. oryzae infection triggers accumulation of phenolics, defenserelated enzymes and thaumatin-like proteins in rice leaves. Archives of Phytopathology and Plant Protection. 2006;39:329-339.
24. Verma P, Singh Y, Anil C, Manish A, Chaudhary C. Root parameters and grain quality of lowland rice as affected by different nutrient management practices and microbial inoculants. Journal of Pharmacognosy and Phytochemistry. 2017;6:2392-2394.