Integrated phosphorus management in Rice (Oryza sativa L.): Effect on soil properties, nutrient dynamics, yield and economic returns in Telangana

Introduction

Rice (Oryza sativa L.) is the staple cereal crop of Telangana, cultivated across approximately 1.8 million hectares annually across kharif and yasangi seasons. In the Northern Telangana Zone (NTZ), irrigated rice under the yasangi season occupies a dominant position in the cropping calendar, supported by canal and reservoir irrigation. Sustaining productivity of this system demands balanced and site-specific nutrient management. Phosphorus (P), the second most critical macronutrient for rice after nitrogen, plays central roles in energy transfer (ATP), root development, tillering and grain filling. Phosphorus deficiency markedly restricts yield in alkaline-calcareous soils where P fixation is prevalent (Dobermann and Fairhurst, 2000) [7] . In Telangana soils, a significant proportion of irrigated rice areas are characterised by low to medium available P status with 61% of Indian soils reported to be low in P (Bhatta et al., 2021) [3] yet farmers eepersistently apply P at uniform rates without soil testing, resulting in both economic loss and environmental loading (Srinivasarao et al., 2014) [16] . Studies have demonstrated that SHC-based fertilizer management can sustain crop yields while reducing excess P application by 15-25% compared to blanket recommendations (Vanlauwe et al., 2010; Kishore et al., 2021) [18,11] . However, adoption of SHC recommendations at the farmer level remains partial, with surveys indicating that only 41% of SHC recipients actually follow the prescribed practices, with education, gender and market access being key determinants (Pandit et al., 2025) [15] . Integrated nutrient management (INM) approaches, combining inorganic fertilizers with organic manures, further improve P use efficiency through enhanced microbial activity and organic acid production that solubilise soil-fixed P (Bhattacharyya et al., 2008; Anantha et al., 2024) [4,1] . Meta-analyses of site-specific nutrient management (SSNM) across Asia and Africa have demonstrated that SSNM consistently increases rice grain yield by approximately 12% and profitability by 15% relative to farmer practice, with 10% less fertilizer nitrogen applied, thereby improving nutrient use efficiency (Chivenge et al., 2021) [5] . Farmyard manure (FYM) application is particularly beneficial in low-P soils by reducing phosphate sorption and increasing P concentration in the soil solution. Long-term INM studies in rice systems have further confirmed that combined NPK and FYM application yields the highest benefit-cost ratio and improves soil carbon status over time (Das et al., 2024) [6] . Despite their agronomic and economic merits, SHC-guided integrated phosphorus management (IPM) practices remain underutilised at the farmer level in Telangana due to limited awareness, knowledge gaps, and perceived risk of yield reduction. On-farm demonstrations that compare IPM with existing farmer practice under actual field conditions are essential to build evidence and farmer confidence. The present study was therefore undertaken during the yasangi (rabi) season 2020-21 at Arpelli village, Sarangapoor mandal, Jagtial district, Telangana, with the objectives of: (i) Evaluating the effect of Integrated Phosphorus management versus farmer practice on crop nutrient content and uptake at panicle initiation and harvest stages; (ii) comparing grain and straw yield; and (iii) assessing the economic returns through benefit-cost analysis.

Materials and Methods

Study Site and Farmer Selection

The study was conducted during the yasangi (rabi irrigated) season, October 2020 to February 2021, at Arpelli village, Sarangapoor mandal, Jagtial district, Telangana (approximately 18°52'N, 78°56'E; altitude ~280 m amsl). The region has a semi-arid tropical climate with mean annual rainfall of 900-950 mm, predominantly received during the kharif season. Ten farmers (Table 1) with comparable field sizes and similar management history were selected through purposive sampling in consultation with local agricultural extension staff.

Initial Soil Sampling and Analysis

Prior to transplanting, composite soil samples (0-20 cm depth) were collected from each farmer's field using a soil sampling auger. Each composite sample comprised 10-12 sub-samples collected in a zig-zag pattern across the plot. Samples were airdried, ground, and passed through a 2-mm sieve. Standard laboratory procedures were followed: soil pH and EC were measured in 1:2.5 soil-water suspension using a digital pH metre and conductivity metre, respectively (Jackson, 1973) [10] ; organic carbon (OC) by the Walkley-Black wet oxidation method (Walkley.A, 1947) [20] ; available nitrogen (N) by the alkaline permanganate method (Subbiah and Asija, 1956) [17] ; available phosphorus (P) by the Olsen method using NaHCO₃ extractant (Olsen et al., 1954) [14] ; and available potassium (K) by flame photometry after ammonium acetate extraction (Jackson, 1973) [10] . Soil organic carbon was rated according to the critical limits established for Indian soils, and available P and K were interpreted using criteria validated for Telangana soils (Krishnamurthy et al., 2024) [12] .

Treatment Details

Each participating farmer implemented both treatments on comparable, adjacent plots within their holding. Integrated Phosphorus Management (IPM): Phosphorus fertilizer dose was determined individually for each field based on Soil Health Card (SHC) recommendations, with P rates adjusted according to initial available P status. All fields received farmyard manure (FYM) at 5 t ha⁻¹ as basal application to improve organic matter and enhance P availability. FYM application has been shown to substantially reduce P sorption in calcareous soils, increasing P concentration in the soil solution and improving P use efficiency, particularly in fields with low initial P status. Nitrogen and potassium were applied uniformly at recommended rates (120 kg N ha -1 and 60 kg K₂O ha⁻¹) across all IPM plots, with N split into three equal doses (basal, active tillering, panicle initiation).

Farmer Practice (FP)

Farmers applied fertilizers according to their customary practice without soil test guidance. The FP plots received no organic manure. Fertilizer quantities and splitting patterns were recorded for each farmer.

Plant Sampling and Nutrient Analysis

Plant samples (whole tillers) were collected at panicle initiation (PI) stage and at harvest from five representative spots per plot. At harvest, grain and straw fractions were separated. All samples were oven-dried at 65°C to constant weight and ground to fine powder. Plant nutrient content (N, P, K) was determined after tri-acid (HNO₃:H₂SO₄: HClO₄) wet digestion. Nitrogen was estimated by micro-Kjeldahl distillation, phosphorus by the vanado-molybdate yellow colour method spectrophotometrically, and potassium by flame photometry (AOAC, 2000) [2] . Nutrient uptake (kg ha⁻¹) was calculated as the product of dry matter yield and nutrient content (Irfan et al., 2020) [9] .

Yield and Economic Analysis

Grain and straw yields (kg ha⁻¹) were recorded at physiological maturity from a 5 m × 5 m area per plot. The benefit-cost (B:C) ratio was calculated using prevailing market prices during 2020-21: paddy grain at ₹1,868 per quintal (MSP, GoI), urea at ₹266.50 per bag (45 kg), SSP at ₹350 per bag (50 kg), MOP at ₹850 per bag (50 kg), and FYM at ₹1,500 per tonne. Total input costs included seed, irrigation, plant protection, labour and fertilizer/manure costs.

Statistical Analysis

Data from the ten paired farmer fields were analysed using a paired-samples t-test to compare IPM and farmer practice within each field (treatment as within-subject factor).

Results and Discussion

Initial Soil Physico-Chemical Properties

The initial soil chemical analysis of the ten participating fields is presented in Table 2. Soil pH ranged from 7.38 to 7.91 with a mean of 7.69, indicating slightly alkaline reaction, which is characteristic of the black cotton (Vertisol) and mixed red-andblack soils of Northern Telangana. Electrical conductivity ranged from 0.28 to 0.52 dS m⁻¹ (mean 0.40 dS m⁻¹), well below the salinity threshold for rice (4 dS m⁻¹) and posing no salinity constraint. Organic carbon content ranged from 0.38 to 0.62% (mean 0.50%), falling in the medium category (0.50-0.75%) as per the Walkley-Black scale. Low OC in intensively cropped rice fields of Telangana has been widely documented and is attributed to rapid mineralisation of crop residues under warm, humid conditions, stubble removal, and intensive tillage (Srinivasarao et al., 2014) [16] . Farming scenario studies on Vertisol-based rice systems have further confirmed that conventional tillage without organic inputs significantly depresses soil OC, available N, P, and K compared to integrated nutrient management (Mishra et al., 2024) [13] . Soil organic matter level directly influences P availability through competition between humic acids and phosphate ions for sorption sites, and through stimulation of Psolubilising microbial communities (Bhattacharyya et al., 2008; Dutta et al., 2024) [4,8] . Available nitrogen ranged from 136 to 205 kg ha⁻¹ (mean 167 kg ha⁻¹), placing most fields in the low to medium N category. Available phosphorus ranged from 29.0 to 82.0 kg ha⁻¹ (mean 53 kg ha⁻¹), spanning low (fields 1, 8), medium (fields 2, 3, 4, 6, 7), and high (field 5) categories according to the critical limits established for Telangana soils (Velayutham et al., 1999) [19] . This spatial variability in soil P status across neighbouring fields underscores the inadequacy of blanket P recommendations and validates the SHC-based field-specific IPM approach. Nationally, over 61% of Indian agricultural soils have been reported to be deficient in available P, reinforcing the need for routine soil testing as the basis for fertilizer decisions (Bhatta et al., 2021) [3] . Available potassium ranged from 186 to 326 kg ha⁻¹ (mean 245 kg ha⁻¹), indicating medium to high K status, consistent with the K-rich nature of black soils in the region.

Effect of IPM on Grain and Straw Yield, and Benefit-Cost Ratio

The grain yield, straw yield, and B:C ratio under IPM and FP are presented in Table 3. Mean grain yield and stover yield under IPM (5733 kg ha⁻¹) (6125 kg ha -1 ) was not significantly different from FP (5832 kg ha⁻ 1 ; p = 0.299) (6348 kg ha -1 ), indicating that the SHC-guided P management, despite using lower or more precisely calibrated P doses, maintained yield parity with conventional over-application. This finding is consistent with earlier on-farm studies across Andhra Pradesh and Telangana demonstrating that balanced, site-specific fertilizer management sustains yields without sacrificing productivity (Bhattacharyya et al., 2008; Srinivasarao et al., 2014) [4,16] . Straw yield, however higher under FP (6348 kg ha⁻¹) compared to IPM (6125 kg ha -1 ). The higher straw biomass under FP is likely attributable to the generally higher P applications promoting vegetative tissue development. Excess P availability can stimulate shoot growth through enhanced photosynthate allocation to straw (Dobermann and Fairhurst, 2000) [7] . Nevertheless, the higher straw yield under FP did not translate into significantly higher grain yield, suggesting differential assimilate partitioning rather than greater total productivity. The B:C ratio was higher under IPM (mean 1.97) than under FP (mean 1.82). This economic advantage accrued principally because IPM plots required lower expenditure on P fertilizers (SSP/DAP), since soil test-based doses were often lower for medium-to high-P fields, while grain yield was sustained. Longterm INM studies in rice systems have confirmed that combined NPK and FYM application consistently achieves B:C ratios above 2.0, outperforming mineral fertilizer alone in economic terms (Das et al., 2024) [6] . Similarly, Chivenge et al. (2021) [5] reported a global average 15% improvement in profitability under SSNM relative to farmer practice across rice, wheat and maize cropping systems. The economic advantage of IPM is particularly relevant in the Telangana context, where input costs are a key constraint for small and marginal farmers.

Plant Nutrient Content and Uptake at Panicle Initiation Stage

Plant nutrient content (N, P, K) and uptake at the panicle initiation (PI) stage are presented in Tables 4 and5, respectively. Mean N content was 0.89% under IPM and 0.88% under FP (p = 0.249, NS). Similarly, K content (IPM: 1.41%; FP: 1.42%) was statistically similar (p = 0.411, NS). Plant P content at PI was comparable between IPM (0.14%) and FP (0.15%), with a nearsignificant trend (p = 0.062). Mean N uptake at PI was 31.37 kg ha⁻¹ under IPM and 31.70 kg ha⁻¹ under FP (p = 0.432, NS). Phosphorus uptake at PI tended to be lower under IPM (4.78 kg ha⁻¹) than FP (5.32 kg ha⁻¹; p = 0.056, NS). Potassium uptake was statistically similar (IPM: 49.7; FP: 51.3 kg ha⁻¹; p = 0.262, NS).

These results indicate that P nutrition at the critical panicle initiation stage was adequately maintained under IPM despite lower P fertilizer inputs. Adequate P nutrition at PI is critical for panicle emergence, spikelet differentiation, and grain filling (Dobermann and Fairhurst, 2000) [7] . The comparable P uptake between IPM and FP at PI suggests that FYM application under IPM enhanced P availability sufficiently to compensate for lower inorganic P input, consistent with the documented role of organic manure in reducing P sorption in alkaline soils and improving P recovery by the crop. The beneficial effect of FYM on P nutrition under SSNM has also been demonstrated through enhanced lowland paddy P use efficiency when Azolla and straw are combined with balanced mineral fertilisation. 6 and7. Mean grain N content was virtually identical between IPM (1.02%) and FP (1.03%; p = 0.303, NS). Grain P content was similarly comparable (IPM: 0.19%; FP: 0.20%; p = 0.303, NS). Grain K content showed no significant difference (IPM: 0.39%; FP: 0.41%; p = 0.135, NS). These data confirm that IPM plots achieved equivalent grain nutrient quality to FP, which is agronomically important from both a crop productivity and nutritional quality perspective. [9,3] . The current data suggest that the SHC-guided IPM approach, by avoiding P over-supply, elicited a similar response at the agronomy level: plants under IPM were more efficient in utilising absorbed P for grain development rather than accumulating excess P in straw tissue. Furthermore, soil P dynamics in alkaline soils are strongly influenced by organic matter content. Long-term INM studies have shown that combined organic-inorganic P management improves the bioavailable P pool in alkaline Fluvisols and Vertisols, reducing P fixation and sustaining crop P nutrition across seasons (Dutta et al., 2024) [8] . The P dynamics reported here are thus consistent with a system where FYM-driven improvements in OC and microbial activity under IPM compensate for lower inorganic P inputs, sustaining crop P nutrition while reducing total P removal in straw.

References

1. Anantha KC, Penjarla R, Challa VR, Bairi R, Kurella CS, Gokenapally S, et al. Phosphorus transformation and balancing under a long-term rice-rice cropping system in an inceptisol of India. Journal of Plant Nutrition. 2024;47(18):3035-3050.
2. AOAC. Official methods of analysis of AOAC International. 17th ed. Gaithersburg, MD: AOAC International; 2000.
3. Bhatta BB, Panda RK, Anandan A, Pradhan NSN, Mahender A, Rout KK, et al. Improvement of phosphorus use efficiency in rice by adopting image-based phenotyping and tolerant indices. Frontiers in Plant Science. 2021;12:717107.
4. Bhattacharyya R, Kundu S, Prakash V, Gupta HS. Sustainability under combined application of mineral and organic fertilizers in a rainfed soybean-wheat system of the Indian Himalayas. European Journal of Agronomy. 2008;28(1):33-46.
5. Chivenge P, Saito K, Bunquin MA, Sharma S, Dobermann A. Co-benefits of nutrient management tailored to smallholder agriculture. Global Food Security. 2021;30:100570.
6. Das B, Bhattacharyya R, Bhatt R, Yadav B, Singh AK, Bisht JK, et al. Long-term assessment of diverse nutrient management strategies in a rice-rice cropping system: analysing yield trends, resource use efficiency and economic viability over a sixteen-year period. Journal of Plant Nutrition. 2024;47(6):905-925.
7. Dobermann A, Fairhurst TH. Rice: nutrient disorders and nutrient management. Manila: International Rice Research Institute; 2000.
8. Dutta A, Hazra KK, Nath CP, Kumar N, Singh SS, Praharaj CS. Long-term impact of legume-inclusive diversification and nutrient management practices on phosphorus dynamics in alkaline Fluvisol. Scientific Reports. 2024;14:65.
9. Irfan M, Aziz T, Maqsood MA, Bilal HM, Siddique KHM, Xu M. Phosphorus use efficiency in rice is linked to tissuespecific biomass and P allocation patterns. Scientific Reports. 2020;10:4278.
10. Jackson ML. Soil chemical analysis. New Delhi: Prentice Hall of India Pvt. Ltd.; 1973.
11. Kishore A, Alvi M, Krupnik TJ. Development of balanced nutrient management innovations in South Asia: perspectives from Bangladesh, India, Nepal, and Sri Lanka. Global Food Security. 2021;28:100464.
12. Krishnamurthy R, Bhavya N, Govinda K, Basavaraja PK, Uday Kumar SN, Mohamed Saqueebulla H, et al. Soil test crop response nutrient prescription equations for improving soil health and yield sustainability: a long-term study under Alfisols of southern India. Frontiers in Plant Science. 2024;15:1439523.
13. Mishra AK, Maurya PK, Sharma S. Impact of different farming scenarios on key soil sustainability indicators driving soil carbon and system productivity of rice-based cropping systems. Frontiers in Plant Science. 2024;15:1408515.
14. Olsen SR, Cole CV, Watanabe FS, Dean LA. Estimation of available phosphorus in soils by extraction with sodium bicarbonate. USDA Circular 939. Washington, DC: United States Department of Agriculture; 1954.
15. Pandit NR, Thapa G, Gaihre YK, Choudhary D, Rusinamhodzi L. Farmers' response to soil health card recommendations: input usage and crop yield. Nutrient Cycling in Agroecosystems. 2025;131:473-486.
16. Srinivasarao C, Venkateswarlu B, Lal R, Singh AK, Kundu S, Vittal KPR, et al. Long-term manuring and fertilizer effects on depletion of soil organic carbon stocks under pearl millet-cluster bean-castor rotation in Western India. Land Degradation and Development. 2014;25(2):173-183.
17. Subbiah BV, Asija GL. A rapid procedure for the estimation of available nitrogen in soils. Current Science. 1956;25:259260.
18. Vanlauwe B, Bationo A, Chianu J, Giller KE, Merckx R, Mokwunye U, et al. Integrated soil fertility management: operational definition and consequences for implementation and dissemination. Outlook on Agriculture. 2010;39(1):1724.