Effect of LCO-fortified biofertilizer and nano nitrogen on growth and nutrient use efficiency of rice (Oryza sativa L.)

Introduction

Rice (Oryza sativa L.) is one of the most important staple food crops in the world and serves as the primary source of calories for nearly half of the global population. Globally, rice is cultivated over approximately 162.06 million hectares with a production of about 496.40 million tonnes (Anon., 2021) [2] . Asia accounts for nearly 90 per cent of global rice production and consumption, while India ranks second in rice production with an area of 46.28 million hectares and a production of 129.47 million tonnes (Anon., 2022) [4] . In Karnataka, rice occupies about 13.85 lakh hectares with an average productivity of 3089 kg ha -1 (Anon., 2022) [3] . With the global population projected to exceed eight billion, sustaining rice productivity under limited land, water and nutrient resources remains a major challenge. Nitrogen is the most crucial nutrient determining rice growth and yield as it plays a vital role in chlorophyll formation, photosynthesis, tillering, leaf area development, grain formation and protein synthesis. However, nitrogen use efficiency (NUE) in rice ecosystems is relatively low due to losses through volatilization, denitrification, leaching and runoff. Excessive and imbalanced use of nitrogen fertilizers not only increases production costs but also contributes to environmental pollution and soil degradation. Nanotechnology has emerged as a promising approach to improve fertilizer efficiency. Nano-fertilizers with particle sizes ranging from 1-100 nm possess unique physicochemical properties such as high surface area and enhanced reactivity, enabling controlled and targeted nutrient release synchronized with crop demand (Giraldo et al., 2014) [9] . Recent studies have reported that nano urea improves nitrogen use efficiency, plant growth and yield in rice (Patel et al., 2024) [16] ; Gondwal et al., 2024 [10] .

In addition to advanced fertilizer technologies, biofertilizers play an important role in sustainable nutrient management. Arbuscular mycorrhizal fungi enhance the uptake of relatively immobile nutrients such as phosphorus and micronutrients by extending the effective root surface area (Lehmann et al.,2014) [13] ; (Wu et al.,2024) [20] . Lipo-chitooligosaccharides (LCOs), also known as Myc factors, are signaling molecules produced by rhizobacteria and mycorrhizal fungi that regulate root development, microbial colonization and nutrient acquisition (Aamir et al., 2020) [1] . LCO-fortified biofertilizers stimulate root hair proliferation and improve plant-microbe interactions, thereby enhancing nutrient use efficiency. However, limited information is available on the combined application of LCOfortified biofertilizers and nano nitrogen in rice under field conditions. Therefore, the present study was undertaken to evaluate their effect on growth, yield attributes and nutrient uptake of rice with the aim of improving nutrient use efficiency and promoting sustainable nutrient management.

Materials and Methods

The field experiment on the "Effect of LCO-fortified biofertilizer and nano nitrogen on growth and nutrient use efficiency of rice (Oryza sativa L.)" was conducted during Kharif 2022 at L-block, Integrated Farming System (IFS) demo unit, Zonal Agricultural Research Station, University of Agricultural Sciences, Gandhi Krishi Vignana Kendra, Bengaluru. The experimental site belongs to Eastern Dry Zone (Zone-V) of Karnataka and is located at 13°08' N latitude, 77°58' E longitude at an altitude of 930 m above mean sea level. The soil was red sandy loam (pH 5.92; EC 0.28 dS m -1 ) with low organic carbon (0.46%), low nitrogen (263.5 kg ha -1 ), high phosphorus (61.4 kg ha -1 ) and medium potassium (225.4 kg ha - 1 ). The experiment was laid out in a Randomized Complete Block Design (RCBD) with seven treatments and three replications using paddy hybrid KRH-4 at a spacing of 30 × 10 cm and seed rate of 15 kg ha -1 . Treatments included 100% recommended NPK, 75% recommended NPK, Mycorrhiza, LCO-fortified biofertilizer @ 10 kg ha -1 , and foliar sprays of nano urea @ 0.2% at 30 and 60 DAT. LCO-fortified biofertilizers contain Bradyrhizobium strains enriched with lipo-chitooligosaccharides (LCOs) to enhance root growth, nutrient signaling and physiological efficiency, while nano nitrogen (nano urea) provides nitrogen in nanoparticle form for rapid foliar absorption and improved nitrogen use efficiency. Farmyard manure @ 10 t ha -1 was applied before transplanting, and fertilizers were applied as per treatment schedule with 50% basal nitrogen and full P and K, and remaining nitrogen top-dressed at 30 DAT. Standard crop management practices including irrigation, gap filling, manual weeding, and nutrient management were followed. Growth parameters were recorded from five tagged plants at different growth stages, and soil and plant samples were analyzed for N, P, and K to determine nutrient use efficiency, and agronomic efficiency.

Results and Discussion

Growth parameters

Growth parameters of rice were significantly influenced by the application of LCO-fortified biofertilizer and nano nitrogen management, and the results are presented in Table 1. Among the treatments, T 4 (100% recommended NPK + LCOfortified biofertilizer @ 10 kg ha -1 + foliar spray of nano urea @ 0.2% at 30 and 60 DAT) recorded significantly higher plant height (77.1 cm), number of tillers (35.8 plant -1 ) and number of leaves (71.5 plant -1 ) compared with T 1 (100% recommended NPK as per PoP) which recorded 56.9 cm plant height, 30.2 tillers plant -1 and 58.3 leaves plant -1 . However, T 4 was statistically on par with T 7 (75% recommended NPK + LCOfortified biofertilizer @ 10 kg ha -1 + nano urea spray). The improved growth parameters under T 4 may be attributed to the synergistic effect of recommended fertilizers, LCO-fortified biofertilizer and foliar application of nano nitrogen. Lipochitooligosaccharides act as signaling molecules that stimulate root development, microbial activity and phytohormone regulation, thereby enhancing vegetative growth (Khan et al., 2011) [12] ; (Minami et al., 1996) [15] . In addition, foliar application of nano nitrogen improves nitrogen availability and nitrogen use efficiency, resulting in enhanced photosynthetic activity, enzyme function and tiller production (Changmei et al., 2002) [8] ; Hong et al., 2005) [11] . Similar improvements in growth and tillering of rice due to nano fertilizer application were reported by Benzon et al., (2015) [6] and Rathnayaka et al., (2018) [18] .

Soil Dehydrogenase Activity

Soil dehydrogenase activity differed significantly among treatments (Table 1). The higher activity (67.05 µg TPF g -1 soil day -1 ) was recorded with T 6 (75% recommended NPK + LCOfortified biofertilizer), which was on par with T 5 (75% recommended NPK + mycorrhiza). The lowest activity was observed in T 1 (100% recommended NPK). Increased enzyme activity under LCO-based treatments may be attributed to enhanced microbial proliferation and rhizosphere activity. Dehydrogenase enzymes are indicators of microbial oxidative metabolism and soil biological activity (Bolton et al., 1985) [6] . Reduced chemical fertilizer levels combined with biofertilizers may stimulate microbial respiration and enzyme synthesis in soil. ---Note: Rec. NPK-Recommended dose of nitrogen, phosphorus and potassium-125: 62.5: 50 kg N: P2O5: K2O ha -1, PoP-Package of practice, LCO-Lipo-chito oligosaccharides, NS-Non-Significant, 0-2: 0% lodging; 3-4: 25% lodging; 5-6: 50% lodging; 7-8: 75% lodging; 9-10: 100% lodging

Days to fifty per cent flowering and physiological maturity

The number of days required to attain 50% flowering and physiological maturity of rice as influenced by LCO-fortified biofertilizer and nano nitrogen management is presented in Table 2. The treatments did not significantly influence the days to 50% flowering and physiological maturity as indicated by the non-significant F-test. However, numerically fewer days to 50% flowering (90.1 days) and physiological maturity (130.8 days) were recorded with T 4 (100% recommended NPK + LCOfortified biofertilizer @ 10 kg ha⁻¹ + foliar spray of nano urea @ 0.2% at 30 and 60 DAT) compared with T 1 (100% recommended NPK as per POP), which recorded 93.5 and 133.7 days, respectively. A similar trend was observed with T₇ (75% recommended NPK + LCO-fortified biofertilizer + nano urea spray). The relatively earlier flowering and maturity observed under treatments receiving LCO-fortified biofertilizer and nano nitrogen may be attributed to improved root growth, enhanced nutrient uptake and better physiological activity. Lipochitooligosaccharides (LCOs) act as signaling molecules that stimulate root development and plant-microbe interactions, thereby enhancing nutrient absorption and plant growth (Supanjani et al., 2009) [19] . In addition, foliar application of nano nitrogen improves nitrogen use efficiency and metabolic processes, which may accelerate crop growth and development. Similar observations were reported by Midde et al. (2022) [14] .

Lodging percentage at harvest

Lodging incidence at harvest as influenced by LCO-fortified biofertilizer and nano nitrogen management is presented in Table 2. Lodging was minimal across all treatments, with lodging scores ranging from 0 to 2 on the standard lodging scale. Slightly higher lodging scores (scale value of 2) were observed in T 4 (100% recommended NPK + LCO-fortified biofertilizer + nano urea spray) and T 7 (75% recommended NPK + LCOfortified biofertilizer + nano urea spray) compared to other treatments. This may be attributed to increased plant height and vigorous vegetative growth resulting from improved nutrient availability and enhanced physiological activity. Greater biomass accumulation and plant stature may slightly increase susceptibility to lodging under field conditions. However, the overall lodging incidence remained negligible and did not adversely affect crop performance.

Nutrient use efficiency

Nutrient use efficiency of rice as influenced by LCO-fortified biofertilizer and nano nitrogen management is presented in Table 3 and Fig. 1. The results indicated that nutrient use efficiency of nitrogen, phosphorus and potassium improved with the combined application of LCO-fortified biofertilizer and nano nitrogen.

Among the treatments, T 7 (75% recommended NPK + LCOfortified biofertilizer @ 10 kg ha -1 + foliar spray of nano urea @ 0.2% at 30 and 60 DAT) recorded the higher nitrogen use efficiency (72.63 kg kg -1 ), phosphorus use efficiency (145.38 kg kg -1 ) and potassium use efficiency (181.71 kg kg -1 ). This was followed by T 6 (75% recommended NPK + LCO-fortified biofertilizer @ 10 kg ha [17] . 4 and Fig. 2. Among the treatments, T 7 (75% recommended NPK + LCOfortified biofertilizer @ 10 kg ha -1 + foliar spray of nano urea @ 0.2% at 30 and 60 DAT) recorded the higher agronomic use efficiency of nitrogen (18.99 kg kg -1 ), followed by T 4 (100% recommended NPK + LCO-fortified biofertilizer + nano urea spray) (16.18 kg kg -1 ), whereas the lower value (4.71 kg kg -1 ) was observed in T 5 (75% recommended NPK + mycorrhiza @ 10 kg ha -1 ).

Similarly, the higher agronomic use efficiency of phosphorus (38.02 kg kg -1 ) and potassium (47.52 kg kg -1 ) was recorded under T 7 , followed by T 4 , which recorded 32.38 and 40.48 kg kg -1 for phosphorus and potassium, respectively. The lower agronomic use efficiency of phosphorus (9.43 kg kg -1 ) and potassium (11.78 kg kg -1 ) was recorded in T₅. The higher agronomic use efficiency observed under treatments receiving LCO-fortified biofertilizer and nano nitrogen may be attributed to improved root growth, enhanced nutrient uptake and better synchronization between nutrient availability and crop demand. LCO molecules stimulate root development and microbial activity in the rhizosphere, thereby improving nutrient absorption efficiency. In addition, foliar application of nano nitrogen provides nitrogen in a readily available form and reduces nutrient losses, ensuring sustained nutrient supply during critical growth stages. These factors improve source-sink relationships and ultimately enhance grain yield, resulting in higher agronomic use efficiency. Similar findings were reported by Chandana et al. (2021) [7] .

Conclusion

The present study demonstrated that integration of LCO-fortified biofertilizer with nano nitrogen significantly improved growth attributes and nutrient use efficiency of rice. Application of 100% recommended NPK with LCO-fortified biofertilizer and nano urea spray enhanced plant growth, while 75% recommended NPK combined with LCO-fortified biofertilizer and nano nitrogen resulted in higher nutrient use efficiency. The results suggest that nano nitrogen and LCO-based biofertilizers can reduce chemical fertilizer requirement while maintaining crop productivity, thereby contributing to sustainable rice production.

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