Influence of Organo-Mineral Briquette-Based Nutrient Management on NPK Uptake and Grain Nutritional Quality of Lowland Rice

Introduction

Rice (Oryza sativa L.) is an important cereal crop and requires substantial nutrient inputs to sustain productivity. Fertilizer management is an important component of rice production, while incomplete recovery of applied nutrients can occur through processes such as volatilization, leaching, runoff and fixation. Consequently, balanced fertilization, improved placement and synchronization of nutrient supply with crop demand are important for improving nutrient recovery in rice (Bijay-Singh and Vinod, 2017; Dobermann and Cassman, 2002; Nayak et al., 2018) [4,7,15] . Integrated nutrient management provides an approach for combining organic and inorganic nutrient sources. In lowland rice, deep placement of fertilizer briquettes places nutrients below the soil surface and has been reported in the thesis literature as a strategy for reducing nitrogen loss and improving nutrient-use efficiency (FAO, 2000; Mikkelsen et al., 1978; Rahman et al., 2016) [14,18] . Deep placement of urea and NPK briquettes has also been associated with greater nitrogen uptake than broadcast application of prilled urea (Sharna et al., 2021) [21] . Nutrient management can also influence grain nutritional characteristics. Previous work cited in the thesis indicates that integrated nutrient management may improve grain protein content, while responses of proximate composition and lysine can vary with genotype and nutrient management (Sharma et al., 2015; Bharali and Baruah, 2022; Karikatti, 2018; Verma and Srivastav, 2017; Umon et al., 2018) [14,3,13,23] . The present study therefore focused specifically on the response of N, P and K uptake an d selected grain nutritional quality attributes-protein, starch, lysine, fat, fibre, moisture and ash-to different fertilizer sources, doses and placement approaches in lowland rice.

Materials and Methods

Experimental site and soil

The experiment was conducted during kharif 2025-26 at the Research Farm, Anand Niketan College of Agriculture, Anandwan, Warora, District Chandrapur, Maharashtra. The experimental soil was a fairly uniform clay-loam Inceptisol. The initial soil was slightly alkaline, with low available N and P, high available K and medium organic carbon. The initial soil pH was 7.62, electrical conductivity 0.21 dS m⁻¹, organic carbon 5.1 g kg⁻¹, available N 187.6 kg ha⁻¹, available P 14.10 kg ha⁻¹ and available K 291.5 kg ha⁻¹.

Experimental design and treatments

The experiment was laid out in a randomized block design with eight treatments, each replicated three times, giving 24 plots. Rice variety PDKV Tilak was transplanted at 20 × 15 cm spacing. The recommended fertilizer dose was 100:50:50 kg N:P₂O₅:K₂O ha⁻¹. In T₁, 50% N along with the full P, K and supplemental nutrients was applied at puddling and the remaining 50% N after 30 days of transplanting. In T₂-T₇, treatment-wise quantities of organo-mineral or urea-DAP briquettes were placed at 5-7 cm depth within four hills after transplanting. The organo-mineral briquette was prepared using vermicompost, gliricidia leaves, DAP, urea, MOP, elemental sulphur, zinc sulphate and borax; the briquette size was 2.5-2.7 g.

Plant sampling and NPK uptake

Grain and straw samples were collected after harvest and chemically analysed. Total N in plant material was estimated by Kjeldahl's method (Piper, 1966) [17] . For P and K determination, plant samples were digested using a nitric acid-perchloric acid di-acid mixture in a 9:4 ratio; total P was determined by the vanadomolybdate phosphoric yellow colour method and total K by flame photometry (Jackson, 1973) [12] . Nutrient uptake was calculated from nutrient concentration and corresponding yield data.

Grain quality analysis

Protein content was determined by Kjeldahl's method (AOAC, 2000), starch by the colorimetric method of Dubois et al. (1956) [8] , lysine by the spectrophotometric method of Tsai et al. (1972) [22] , and fat by the Soxhlet method (AOAC, 1998). Fibre was determined using 1.25% H₂SO₄ and 1.25% NaOH as extraction reagents according to AOAC (2000). Moisture was determined by the oven-dry method of Oxley et al. (1960) [16] , and ash by the ignition method described by Jackson (1973) [12] .

Statistical analysis

Experimental data were analysed using Fisher's analysis of variance for randomized block design following Gomez and Gomez (1984) [11] , Significance was tested at p = 0.05, and critical difference (CD) values were calculated where the Ftest was significant. [21] , who reported higher N uptake with deep placement of urea and NPK briquettes than with broadcast prilled urea. The response is also consistent with Sharma et al. (2015) [19] , who reported that nutrient management practices affecting N nutrition were reflected in rice protein content.

Results and Discussion

Phosphorus uptake

Total P uptake varied from 8.15 kg ha⁻¹ in T₈ to 16.78 kg ha⁻¹ in T₃. Under T₃, P uptake by straw and grain was 6.83 and 9.95 kg ha⁻¹, respectively. T₄ and T₇ recorded 15.86 and 15.89 kg ha⁻¹, respectively, whereas T₁ recorded 14.06 kg ha⁻¹. The total P uptake under T₃ was 19.35% higher than conventional RDF. The higher P uptake with the organo-mineral briquette treatment indicates that the combination of nutrient sources and placement used in the experiment supported greater crop acquisition of P. The thesis attributes the response to continued nutrient availability within the reduced soil zone and improved soil conditions around the placed briquette. Darade and Bankar (2009) [6] similarly reported higher N, P and K uptake with deeply placed urea-DAP briquettes in hybrid rice.

Potassium uptake

Total K uptake was highest under T₃ (97.96 kg ha⁻¹), followed by T₄ (91.73 kg ha⁻¹) and T₇ (88.70 kg ha⁻¹), while the lowest value was recorded in T₈ (55.09 kg ha⁻¹). Conventional RDF (T₁) resulted in 79.68 kg ha⁻¹. Straw and grain K uptake under T₃ were 77.78 and 20.18 kg ha⁻¹, respectively. The total K uptake under T₃ was 22.94% higher than T₁. The greater K uptake under T₃ is consistent with the overall NPK uptake response of the crop to organomineral briquette placement. The thesis associates higher uptake under briquette treatments with balanced nutrient supply, steady nutrient availability and placement in the reduced soil zone. Similar improvement in NPK uptake under briquette-based nutrient management has been reported by Darade and Bankar (2009) [6] .

Grain protein

Grain protein content ranged from 7.21% in T₈ to 7.88% in T₃. Treatments T₂, T₃, T₄, T₆ and T₇ were significantly higher than the absolute control, while T₁ and T₅ were statistically at par with the control. T₃, T₄ and T₇ were mutually at par. The highest protein content under T₃ corresponded with its highest total N uptake, supporting the treatment relationship described in the thesis between N nutrition and grain protein accumulation. Sharma et al.

(2015) [19] similarly reported a trend in rice protein content corresponding to N uptake, while Chauhan (2023) reported improved grain protein under integrated application of organic and inorganic nutrient sources.

Grain starch

Starch content varied from 77.04 to 78.24%. The highest value (78.24%) was recorded under T₄, while the lowest (77.04%) occurred under T₃. The treatment effect was statistically significant. Thus, the treatment producing the highest NPK uptake and protein content did not produce the highest starch content. The observed range was narrow compared with the treatment differences in NPK uptake, indicating that the response of starch was distinct from the response of nutrient uptake.

Grain lysine

Lysine content ranged from 0.26% in T₈ to 0.37% in T₇. All fertilized treatments recorded numerically higher lysine than the absolute control. T₇ and T₆, both receiving supplemental S, Zn and B, recorded significantly higher lysine than T₁, T₂, T₃, T₄ and T₅ and were statistically at par with each other. Karikatti (2018) [13] , as cited in the thesis, reported only a small influence of nutrient management on rice grain lysine concentration, indicating that lysine may show a comparatively limited response to fertilizer regime.

Grain fat and fibre

Grain fat content ranged from 0.63% in T₇ to 0.83% in T₅, and the treatment effect was non-significant. Fibre content ranged from 0.42 to 0.48%, with the highest numerical value under T₃; however, the differences among treatments were non-significant. Therefore, neither fat nor fibre showed a statistically reliable response to the nutrient management treatments in the present experiment. The thesis literature similarly reports that grain proximate composition can vary among rice genotypes and that responses to nutrient management are parameter-dependent (Verma and Srivastav, 2017; Ekanayake et al., 2026) [23] .

Grain moisture and ash

Moisture content ranged from 11.33% under T₄ to 12.33% under T₁, T₃, T₆ and T₈. The treatment effect was nonsignificant. Ash content ranged from 1.43 to 1.53% and was also not significantly influenced by the treatments. The thesis attributes the lack of a consistent treatment response in moisture partly to sampling and environmental variability. The observed moisture range falls within the range reported for Indian rice accessions by Verma and Srivastav (2017) [23] , although the present study concerns a single rice variety.

Conclusion

Under the conditions of the present kharif 2025-26 field experiment, application of 100% RDF through an INMbased organo-mineral briquette (T3) was the most effective treatment for increasing total N, P and K uptake and grain protein content of lowland rice. Total N, P and K uptake under T 3 reached 84.71, 16.78 and 97.96 kg ha⁻¹, respectively, while grain protein reached 7.88%. The 80% RDF briquette treatment produced the highest starch content (78.24%), whereas the treatment combining urea-DAP briquette, potash and S, Zn and B supplementation (T 7 ) produced the highest lysine content (0.37%). Fat, fibre, moisture and ash were not significantly affected. Thus, within the scope of the present experiment, organo-mineral

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