1 Introduction

Rice (Oryza sativa L.) is the backbone of the rural population and the food security of the maximum residents worldwide which is considered as one of the most important food grains of the world’s population. In rice production, India ranks first in area (45 million ha) and also secures the second-highest position in production by producing about 118 Mt of milled rice with a productivity of 3.96 t ha−1 (FAOSTAT 2020). Application of chemical nitrogenous fertilizer maintains a vital function in improvement of rice yield. Fertilizer N use efficiency generally varies from 30 to 40% in rice soils, because maximum nitrogen losses are found due to volatilization of ammonia, denitrification, leaching, runoff etc. which result in negative effect on yield and moreover pollute the environment simultaneously. Intensive cropping with inorganic fertilizers results in continuous soil fertility exhaustion which leads to a net negative balance of soil nutrients, which will suppose major restraints in the future for sustainable crop production. A part of applied organic manure is left in the soil after harvesting of preceding crop which is advantageous to succeeding crops in a good proportion. Thus, partial substitution of chemical fertilizers with organic manure is a reliable way not only to obtain fairly high productivity of rice but also to nourish soil health and fertility.

Application of fertilizers releasing N, P and K nutrients is a routine practice by Indian farmers, but use of micronutrients is unusual. The occurrence of micronutrient deficiency is because of continuous cultivation, destruction of productive topsoil and leaching loss of nutrients. Among the micronutrients, zinc plays an important role for the growth of plant, particularly for rice cultivated in submerged conditions (Fageria et al. 2002; Quijano-Guerta et al. 2002). It is also an integral component of many enzyme structures like oxidoreductases, isomerases, hydrolases, ligases, transferases and lyases (Auld 2001). The important role of zinc for plant growth can be adjudicated as it controls synthesis of indole acetic acid which regulates the plant growth (Tarafdar et al. 2014), synthesis of chlorophyll and formation of carbohydrate (Vitosh et al. 1994). The nutrient use efficiency of zinc as fertilizer generally varies between 2 and 5%. So, to mitigate zinc-deficient disorder, an efficient technique should be adopted for proper application of zinc fertilizer without hampering the plant growth and yield. To enhance the use efficiency as well as to reduce the rate of application, the nanosized zinc particle as fertilizer was proposed due to its penetrating capacity and large surface area. Foliar application of zinc in rice was found beneficial to improve concentration of zinc in grain rather than soil application due to avoidance of chemical interactions that obstruct uptake of zinc through plant’s root (Mabesa et al. 2013).

Nanotechnology has been found as an innovative technique to meet the challenges related with agriculture in a much better way than regular conventional methods (Verma et al. 2018). It is associated with the transformation of materials into nanoscale (1 to 100 nm) for creating functional materials, sensors and devices (Verma et al. 2019, 2022). Nanofertilizers are synthesized or modified forms of traditional fertilizers. Less particle size causes expansion of specific surface area and more numbers of particles per unit area of a fertilizer which results in maximum chance of contact of nanofertilizers with the applied surface material. Fertilizers enclosed in nanoparticles increase the nutrient availability and uptake by the crops (Tarafdar et al. 2012a). Application of nanoparticles as foliar spray of fertilizer remarkably boosts the crop yield (Tarafdar et al. 2012b). Effective supply of zinc to plants from zinc oxide nanoparticle (ZnO NP) application is expected due to their tiny size, easy dissolvability and diffusible qualities that make quick absorption by the plant serving the nutritional requirements and insufficiencies in the crop plant (Raliya and Tarafdar 2013). Thus, it was found to improve the vegetative as well as physiological characteristics of rice crop (Bala et al. 2019; Wu et al. 2020; Yan et al. 2021).

Considering the above facts, this experiment was initiated with integrated nutrient management and foliar spray of zinc in nanoform with a target to observe better nutrient use efficiency without hampering soil health and for profitable performance of Kharif rice in Inceptisols.

2 Materials and Methods

2.1 Experimental Site and Material

The field trial was carried on for 2 consecutive years at the ‘D’ Block Farm of Bidhan Chandra Krishi Viswavidyalaya, Kalyani, Nadia, West Bengal (India), situated at 22° 58′ 8″ N latitude and 88° 25′ 5″ E longitude with an altitude of 9.75 m above mean sea level (AMSL) during Kharif season of 2018 and 2019. The experiment was conducted on a low-land, well-drained alluvial soil (order — Inceptisol) that belonged to the textural class of sandy loam and alkaline in reaction (pH 7.4) containing 0.55% organic carbon content, 208.70 kg available N ha−1, 26.5 kg available P2O5 ha−1, 232.6 kg available K2O ha−1 and 1.2 mg available Zn kg−1.

2.2 Procurement and Characterization of Zinc Nanoparticles

The nanosized particles of zinc were obtained from ICAR-Central Arid Zone Research Institute, Jodhpur, India. The particles were characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and electron-dispersive X-ray (EDX) spectroscopy measurements (Fig. 1) to determine the nature and size of the particle. Scanning electron micrograph (Fig. 1c) shows zinc nanoparticles range from 5 to 70 nm and possess an average size 20 nm at least in one dimension. EDX (Fig. 1d) shows the purity of the particle used for the study.

Fig. 1
figure 1

Characterization of zinc nanoparticles using a Fourier transform infrared (FTIR) spectroscope image, b X-ray diffraction (XRD) analysis image, c scanning electron microscopy (SEM) image, d electron-dispersive X-ray (EDX) spectroscopy image

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2.3 Experimental Design and Nutrient Application

The experiment was laid out in a randomized block design with three replications possessing eight treatments viz. T1 — control (N0P0K0), T2 — 100% RDN (recommended dose of nitrogen) from commercial chemical fertilizer, T3 — 75% RDN from commercial chemical fertilizer + 25% RDN from FYM, T4 — 50% RDN from commercial chemical fertilizer + 50% RDN from FYM, T5 — N0P0K0 + nano zinc spray, T6 — 100% RDN from commercial chemical fertilizer + nano zinc spray, T7 — 75% RDN from commercial chemical fertilizer + 25% RDN from FYM + nano zinc spray and T8 — 50% RDN from commercial chemical fertilizer + 50% RDN from FYM + nano zinc spray, wherein the dimensions of every experimental plot were 9 m × 3 m. The rice variety taken was Shatabdi (IET 4786) and sown at the rate of 50 kg ha−1. Rice seedlings of 22 days and 21 days of age were transplanted in the main field on 26 July and 30 July during 2018 and 2019 respectively by maintaining a proper distance of 20 cm × 10 cm. The recommended dose of fertilizers was 60:30:30 kg (N/P2O5/K2O) ha−1. Urea, single super phosphate (SSP) and muriate of potash (MOP) were used as inorganic source of nitrogen, phosphorus and potassium respectively, and for organic purpose, farmyard manure was applied. Half of the needed quantity of inorganic nitrogen and a complete dose of phosphorus and potassium were applied by broadcasting method before transplanting of rice, and the remaining amount of the required nitrogen was applied at 21 DAT and 42 DAT by dividing into 2 equal splits. Application of total amount of FYM was done during the course of land preparation. Applied FYM contained 0.53% N, 0.17% P, 0.56% K and 1.81 µg g−1 Zn. Two sprays of nano zinc with a dose of 10 mg L−1 each were given at all respective treatments 2 weeks after transplanting and 5 weeks after transplanting of rice seedlings (Tarafdar et al. 2014).

2.4 Intercultural Operation and Recording of Data

Hand weeding was made twice at 20 and 40 days after sowing. Irrigations were given as and when required. One spray of imidacloprid 200 SL (17.8%, w/w) was applied to control the sucking insect pest during the tillering stage of the crop. Growth parameters, yield attributes and yield of rice were measured, and chemical analyses of plant and soil samples were conducted, and economic analysis was done. Five plants from each experimental plot were selected indiscriminately and tagged for measuring vegetative parameters during the crop growth period. The growth parameters were started recording 30 days after sowing, and successive observations were taken at a discontinuity of 30 days till harvest of the crop. Standard procedures were used to ascertain yield-contributing characters and yield. Ultimately, the yield was calculated in t ha−1.

2.5 Estimation of Total Chlorophyll Content

The chlorophyll content in the rice leaf samples collected from each of the treatment plot was estimated as per Arnon (1949). One hundred milligrams of fresh leaf sample was finely chopped and taken in a stoppered test tube. Then, 10 ml of 80% acetone was added to the tube, and it was allowed to stand at room temperature for 7 days under dark. Then, the green liquid was collected in a separate test tube, and the colourless leaf particles were discarded. Absorbance was read at 645- and 663-nm wavelengths in Systronics-105 spectrophotometer against a blank containing only 80% acetone.

$$\mathrm{mg}\;\mathrm{of}\;\mathrm{total}\;\mathrm{chlorophyll}\;\mathrm g^{-1}\mathrm{of}\;\mathrm{fresh}\;\mathrm{tissue}=\left[\left(20.2\times\mathrm A645\right)+\left(8.02\times\mathrm A663\right)\right]\times\frac V{1000\times W}$$

where V = volume of the extract (ml), W = fresh weight of leaf tissue (g), A = absorbance

2.6 Analysis of Plant Samples for Nutrient Concentration in Plant

The analysis of N in plant samples was performed by micro-Kjeldahl method (AOAC 1995). For this analysis, 1 g of plant sample (mix of stem and leaf sample) was taken in 800 ml Kjeldahl flask in which 20 ml of conc. H2SO4 and 2–3 g of Hibbard’s mixture were added. After shaking it properly, the Kjeldahl flask was placed on the heater of the digestion operator and allowed to heat for 40–45 min until white flume appeared throughout the inside portion of the Kjeldahl flask. After cooling of the Kjeldahl flask, 150 ml distilled water and 100 ml 40% NaOH solution were added, and it was properly placed on the heater of the distillation operator. Twenty-five millilitres of 4% H3BO3 was taken to a 50-ml conical flask, and it was set with the corresponding tube of the Kjeldahl. One hundred millilitre of distillate was collected in the conical flask. After cooling of the distillate, titration was done by 0.1 (N) H2SO4 solution. During titration, the colour of the solution changed from greenish to deep orange. The analysis of P and K in plant samples was performed by the vanadate-molybdate acid yellow colour method (Piper 1966) and flame photometer method (Jackson 1973) respectively. For this analysis, 1 g of plant sample was taken in a 100-ml conical flask, and 5 ml of conc. HNO3 was added in it and placed in digestion box. It was allowed 3 h 30 min to 4 h for digestion maintaining 180–200 heat unit. Change of colour of the solution to white indicated completion of digestion. The next day, taking the digested sample from the digestion box, 5 ml of the triacid mixture was added to it and was shaken properly and placed into the digestion box for the second digestion. When the solution turned into a white colour, the conical flask was taken from the digestion box and was allowed to cool. Ten millilitres of conc. HCl was added into the conical flask; it was washed properly and poured in to a 100-ml volumetric flask. Ten millilitres of 6 (N) of HCl was added into the conical flask, washed properly and again poured into the previous 100-ml volumetric flask. Then, distilled water was taken into that conical flask, washed properly and again poured into that 100-ml conical flask and was made the volume up to 100 ml. After that, the solution was allowed to filtrate with the help of funnel and filtrate paper. For analysis of P, 1 ml of filtrate solution was taken into a 50-ml volumetric flask with the measuring cylinder. Then, 15 ml of distilled water, 4–5 drops of 2,4-D solution and 4 (N) HCl were added in sequence to the filtrate solution until HCl neutralized the solution showing a colour less sample. Then, 5 ml of (NH4)6Mo7O24 solution and 6–7 drops of 5% SnCl2 were added to the solution. The volume of the solution was made up to 50 ml with the distilled water. Reading of sample was taken with the help of a spectrophotometer. For analysis of K, 1 ml of filtrate solution was taken into the 50-ml volumetric flask with the measuring cylinder and was made up the 50-ml volume with the help of distilled water. Reading of the sample was taken with the help of a flame photometer. Analysis of Zn content in plant samples was done after dry ashing in a muffle furnace, by an atomic absorption spectrophotometer (PerkinElmer made Pinaacle 900H) where 0.5 g of plant sample was taken in crucible, and the crucible was kept in the muffle furnace at 550 °C for 5 h. Next day, 10 ml of 6 (N) HCl was added in the crucible. The solution was filtrated in a 50-ml volumetric flask by using filter paper 1. The volume of the volumetric flask was made up with double-distilled water and kept in a container, and reading was taken by AAS.

2.7 Soil Sample Analysis for Organic Carbon Content and Available Nutrients in Soil

The organic carbon content of soil was determined by Walkley and Black (1934)’s method. In this method, 1.0 g of soil was wet oxidized by 10 ml of 1(N) K2Cr2O7 and 20 ml conc. H2SO4. The digested material was kept in a dark place for 30 min followed by titration with 0.5 (N) (NH4)2Fe(SO4)2(H2O)6 after the addition of 200 ml of water and 10 ml of H3PO4 and expressed as percentage (%). The available soil nitrogen was estimated by a Kjeldahl flask using the alkaline permanganate method (Subbiah and Asija 1956) following titration with H2SO4. Available phosphorus of soil was determined following Olsen’s (Olsen et al. 1954) method using 0.5 (M) NaHCO3 (pH 8.5) extractant as the reaction of the soil samples was in the range of neutral to slightly alkaline (pH 6.7–8.1). Neutral normal ammonium acetate was used to estimate available potassium of soil by using flame photometer (Jackson 1973). Available zinc content of the soil was determined by extracting the soils with 0.005 (M) DTPA solution adjusted to pH 7.3 (soil/extractant = 1:2) following the method of Lindsay and Norvell (1978).

2.8 Microbial Analysis in Soil Samples

The serial dilution and pour plate method (Zubere 1994) was used to estimate the total microbial population (bacteria, actinomycetes and fungi) of soil. Nutrient agar, rose Bengal agar and actinomycete isolation agar were used as growth media for culturing and counting bacteria, fungi and actinomycetes respectively.

2.9 Dehydrogenase Enzyme Activity in Soil Samples

The soil dehydrogenase enzyme activity was measured by following the methods described by Klein et al. (1971), where 1 g of air-dried soil was taken in an air-tight screw-capped test tube of 15-ml capacity, and 0.2 ml of 3% 2,3,5-triphenyl tetrazolium chloride solution and 0.5 ml of 1% glucose solution were added. After incubation of the tubes at 28 ± 0.5 °C for 24 h, 10 ml of methanol was added into the tubes and was allowed to stand for 6 h. Clear pink-coloured supernatant liquid was withdrawn, absorbance was read at a wavelength of 485 nm, and the outcomes were mentioned in μg TPF g−1 h−1.

2.10 Experimental Design and Statistical Analysis

The analysis of variance (ANOVA) was accomplished to visualize the impacts of various nutrient management practices on rice in a randomized block design, by using SPSS (IBM® SPSS Statistics, Ver. 24, USA). Comparison among the treatments (mean ± SE) was performed by Duncan’s multiple range test (DMRT) (Duncun 1955) (p = 0.05).

3 Results

3.1 Characterization of Zinc Nanoparticles

The nanoparticles obtained from the above-mentioned source were successfully characterized using FTIR, XRD, SEM and EDX methods. These experiments confirmed the nature, size, shape and quality of zinc nanoparticles.

3.2 Effect on Vegetative Growth Parameters of Rice

Results showed that application of 75% RDN from commercial chemical fertilizer + 25% RDN from FYM + nano zinc spray produced significantly tall plants (104.26 cm) which was at par with all other treatments except control and only nano zinc sprayed plot at harvest stage. The highest number of productive tillers per m2 (322.75) was found at 60 DAT by using 75% RDN from commercial chemical fertilizer + 25% RDN from FYM + nano zinc spray. Accumulation of dry matter increased with the advancement of crop growth and was obtained maximum (805.08 g m−2) at harvest stage by application of 75% RDN from commercial chemical fertilizer + 25% RDN from FYM + nano zinc spray and that was at par with 100% RDN from commercial chemical fertilizer + nano zinc spray treated plot. Plant height, number of productive tillers per m2 and accumulation of dry matter were increased by 1.12, 3.50 and 6.53%, respectively, compared to that of 100% RDN from inorganic fertilizer application (Table 1).

Table 1 Effect of integrated nutrient management along with foliar spray of nano zinc on vegetative growth parameters of rice
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3.3 Effect on Leaf Area Index and Total Chlorophyll Content of Rice

Leaves are important organs that have an active role in photosynthesis, and net photosynthesis is indicated by total chlorophyll content of leaves. The leaf area index of rice plants starts increasing from initial growth stage and reaches maximum at 60 DAT, then it slightly decreases at the harvesting stage due to the drying and withering of lower leaves. Seventy-five per cent RDN from chemical fertilizer + 25% RDN from FYM + nano zinc spray–treated plot recorded the highest LAI both at 60 DAT and harvest stage (4.71 and 3.56 respectively). LAI increased by 11.46, 8.53 and 11.60% in rice at 30 DAT, 60 DAT and at harvest respectively in 75% RDN from commercial chemical fertilizer + 25% RDN from FYM + nano zinc spray–treated plot compared with those in 100% RDN from inorganic fertilizer application. Maximum total chlorophyll content was obtained from 100% RDN from inorganic fertilizer + foliar spray of nano zinc and 75% RDN from chemical fertilizer + 25% RDN from FYM + nano zinc spray–treated plots at 30 DAT and 60 DAT respectively (Table 2).

Table 2 Effect of integrated nutrient management along with foliar spray of nano zinc on leaf area index and total chlorophyll content of rice
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3.4 Effect on CGR and NAR of Rice

Crop growth rate (CGR) is the dry matter production rate of a crop in per unit area, and net photosynthesis rate is specified by net assimilation rate (NAR). The highest crop growth rate was attained from 75% RDN from inorganic fertilizer + 25% RDN from FYM + nano zinc spray–treated plot both during 30–60 DAT and 60 DAT–AH stages (9.98 and 9.69 g m−2 day−1 respectively). Among the various nutrient management practices, the maximum NAR value between 30 and 60 DAT was obtained with the application of 75% RDN from inorganic fertilizer + 25% RDN from FYM (1.42 g m−2 day−1) and during the period of 60 DAT–harvest of rice, it was observed in 100% RDN from inorganic fertilizer + foliar spray of nano zinc (1.04 g m−2 day−1)–treated plot (Fig. 2).

Fig. 2
figure 2

Effect of integrated nutrient management along with foliar spray of nano zinc on crop growth rate (CGR) and net assimilation rate (NAR) of rice. RDN from commercial chemical fertilizer + 25% RDN from FYM, T4 50% RDN from commercial chemical fertilizer + 50% RDN from FYM, T5 N0P0K0 + nano zinc spray, T6 100% RDN from commercial chemical fertilizer + nano zinc spray, T7 75% RDN from commercial chemical fertilizer + 25% RDN from FYM + nano zinc spray, T8 50% RDN from commercial chemical fertilizer + 50% RDN from FYM + nano zinc spray. Data represent mean ± standard error. Data for each column with different lowercase letters are significantly different according to Duncan’s multiple range test (DMRT) (Duncun 1955) at P = 0.05

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3.5 Effect on Root Growth of Rice

A considerable effect of varying treatment combinations was noticed in root length, dry weight of root per hill and root length density of Kharif rice, and these were varied significantly at all of crop growth stages (Table 3). The highest root length of rice was observed in 50% RDN from chemical fertilizer + 50% RDN from FYM applied plot at 30 DAT (19.53 cm) and in 50% RDN from inorganic fertilizer + 50% RDN from FYM + nano zinc–treated plot at both 60 DAT and harvest stages (26.37 and 26.23 cm respectively). The highest root dry weight (g) per hill was obtained from 50% RDN from chemical fertilizer + 50% RDN from FYM, 50% RDN from chemical fertilizer + 50% RDN from FYM + nano zinc spray and 75% RDN from inorganic fertilizer + 25% RDN from FYM + nano zinc spray–treated plot respectively at 30 DAT, 60 DAT and harvest stage (4.64, 10.30 and 11.34 g respectively). Amidst the various nutrient combination applications, 50% RDN from chemical fertilizer + 50% RDN from FYM + nano zinc spray recorded maximum root length density both at 30 DAT and at harvest stage (1.20 and 2.29 cm cm−3 respectively). At 60 DAT, it was found highest in 50% RDN from chemical fertilizer + 50% RDN from FYM treated plot (2.15 cm cm−3).

Table 3 Effect of integrated nutrient management along with foliar spray of nano zinc on root growth of rice
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3.6 Effect on Yield Attributing Characters and Yield of Rice

The yield-attributing and associated characteristics of rice like the number of panicles per m2, panicle length, no. of filled grains per panicle and test weight were measured at maturity of the rice. The highest number of panicles per m2 (300.28) was produced by 75% RDN from chemical fertilizer + 25% RDN from FYM + nano zinc spray treatment whereas application of 100% RDN from inorganic fertilizer + foliar spray of nano zinc recorded the highest number of filled grains per panicle (121.11) and maximum test weight (19.96). Maximum grain and straw yield were recorded with the application of 75% RDN from chemical fertilizer + 25% RDN from FYM + nano zinc spray which is recorded as an 8.82% and 11.85% increase in grain and straw yield respectively compared to that from 100% RDN from chemical fertilizer–treated plot. It was also found that application of nano zinc over 100% inorganic fertilizer increased the grain yield of rice by 5.59% in comparison with the application of only 100% inorganic fertilizer, and application of only nano zinc recorded the rice grain yield of 4.01 t ha−1, and it increased by 17.60% over control (Table 4; Fig. 3).

Table 4 Effect of integrated nutrient management along with foliar spray of nano zinc on yield attributes and yield of rice
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Fig. 3
figure 3

Effect of different nutrient management practices along with foliar spray of nano zinc on rice. T1 control (N0P0K0), T2 100% RDN (recommended dose of nitrogen) from commercial chemical fertilizer, T3 75% RDN from commercial chemical fertilizer + 25% RDN from FYM, T4 50% RDN from commercial chemical fertilizer + 50% RDN from FYM, T5 N0P0K0 + nano zinc spray, T6 100% RDN from commercial chemical fertilizer + nano zinc spray, T7 75% RDN from commercial chemical fertilizer + 25% RDN from FYM + nano zinc spray, T8 50% RDN from commercial chemical fertilizer + 50% RDN from FYM + nano zinc spray

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3.7 Effect on Soil Chemical Properties and Total Nutrient Uptake by Rice

Significant variations regarding soil organic carbon content, available nitrogen, available phosphorus and available zinc were found in the residual soil samples after the harvest of rice (Table 5). Higher soil organic carbon (%) was obtained in integrated nutrient management treated plots. Significantly highest soil available nitrogen and potassium (165.68 and 177.92 kg ha−1 respectively) was obtained with the application of 50% RDN from chemical fertilizer + 50% RDN from FYM + nano zinc spray, and it was increased by 9.49 and 2.71% respectively than solely chemically treated plot. An evaluation of the data revealed that available phosphorus in soil increased significantly in 50% RDN from chemical fertilizer + 50% RDN from FYM-treated plot (25.51 kg ha−1), which was increased by 17.61% than 100% RDN from inorganic fertilizer applied plot. Soil-available zinc was found to increase by 9.89% after harvest of rice in 50% RDN from commercial inorganic fertilizer + 50% RDN from FYM + nano zinc applied plots (1.00 mg kg−1) than solely chemically treated plots.

Table 5 Effect of integrated nutrient management along with foliar spray nano zinc on chemical properties of post-harvest soil of rice and total nutrients uptake by rice
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Both grain and straw samples of rice from individual treatment were collected at maturity. The uptake of nutrients by grain and straw was then computed by multiplying grain and straw yield with respective nutrient contents (Figs. 4 and 5). Total uptake of nutrients varied significantly by different nutrient management practices (Table 5). Results revealed that 75% RDN from chemical fertilizer + 25% RDN from FYM + nano zinc spray–treated plot registered 14.24 and 18.19% increase in total nitrogen and potassium uptake respectively than 100% chemically treated plot. Significantly highest total phosphorus uptake was found with the application of 75% RDN from chemical fertilizer + 25% RDN from FYM in rice, resulting in 1.33% higher total phosphorus uptake than 100% RDN from chemical fertilizer–treated plot. Maximum zinc concentration in brown rice was found in 75% RDN from chemical fertilizer + 25% RDN from FYM + nano zinc spray–treated plot which was at par with 100% RDN from chemical fertilizer + nano zinc spray–treated plot and 50% RDN from chemical fertilizer + 50% RDN from FYM + nano zinc spray–treated plot.

Fig. 4
figure 4

Effect of integrated nutrient management along with foliar spray of nano zinc on nutrients concentration of rice. T1 control (N0P0K0), T2 100% RDN (recommended dose of nitrogen) from commercial chemical fertilizer, T3 75% RDN from commercial chemical fertilizer + 25% RDN from FYM, T4 50% RDN from commercial chemical fertilizer + 50% RDN from FYM, T5 N0P0K0 + nano zinc spray, T6 100% RDN from commercial chemical fertilizer + nano zinc spray, T7 75% RDN from commercial chemical fertilizer + 25% RDN from FYM + nano zinc spray, T8 50% RDN from commercial chemical fertilizer + 50% RDN from FYM + nano zinc spray Data represent mean ± standard error. Data for each column with different lowercase letters are significantly different according to Duncan’s multiple range test (DMRT) (Duncun 1955) at P = 0.05

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Fig. 5
figure 5

Effect of integrated nutrient management along with foliar spray of nano zinc on nutrients uptake by rice. T1 control (N0P0K0), T2 100% RDN (recommended dose of nitrogen) from commercial chemical fertilizer, T3 75% RDN from commercial chemical fertilizer + 25% RDN from FYM, T4 50% RDN from commercial chemical fertilizer + 50% RDN from FYM, T5 N0P0K0 + nano zinc spray, T6 100% RDN from commercial chemical fertilizer + nano zinc spray, T7 75% RDN from commercial chemical fertilizer + 25% RDN from FYM + nano zinc spray, T8 50% RDN from commercial chemical fertilizer + 50% RDN from FYM + nano zinc spray. Data represent mean ± standard error. Data for each column with different lowercase letters are significantly different according to Duncan’s multiple range test (DMRT) (Duncun 1955) at P = 0.05

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3.8 Effect on Soil Microbial Population Count

Different nutrient combinations had a notable impact on the soil microbial population at all growth stages of rice (Table 6). The total number of microbial populations was found higher at 60 DAT than 30 DAT and at harvest stages. Application of 50% RDN from inorganic fertilizer + 50% RDN from FYM + nano zinc spray recorded the highest microbial population at 60 DAT which was increased by 32.16, 47.13 and 46.09% in bacterial, fungal and actinomycete population count respectively than 100% inorganic fertilizer treated plot.

Table 6 Effect of integrated nutrient management along with foliar spray of nano zinc on microbial population count of soil
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3.9 Effect on soil Dehydrogenase Enzyme Estimation

Highest dehydrogenase enzyme activity in soil was found at 60 DAT due to abundance of microbial population (Table 7). It was found that at 60 DAT dehydrogenase enzyme activity increased by 5.85 and 8.44% in 50% RDN from chemical fertilizer + 50% RDN from FYM + nano zinc–treated plot than 100% RDN from chemical fertilizer + nano zinc–treated plot and 100% RDN from chemical fertilizer–treated plot respectively.

Table 7 Effect of integrated nutrient management along with foliar spray of nano zinc on dehydrogenase enzyme estimation of soil
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4 Discussion

Conjunctive use of organic and inorganic sources of nutrients resulted in significant increase in growth parameters. Accessibility of nutrients during the whole crop growth period because of steady release of nutrients from organic source helps to improve accumulation of dry matter and production of fertile tillers from which higher number of panicles per unit area was achieved that finally converts into yield. Efficacy of organic manure with inorganic fertilizer application in growth and yield of rice was also reported by Mondal et al. (2015), Karki et al. (2018) Moe et al. (2019), Ram et al. (2020) and Mangaraj et al. (2022). In an experiment, Ullah et al. (2019) found better results in yield components like number of panicles per plant, length of panicle, 1000-grain weight with the application of 50% RDN from inorganic fertilizer + 50% in the form of FYM whereas Borah et al. (2016) reported 75% RDN in the form of FYM or vermicompost with 25% recommended rate of fertilizers produced rice plant with greater growth and yield attributes which accelerate to increase grain yield by 89.6% over control. In a research, Islam et al. (2019) specified that balanced supply of nutrients increased chlorophyll content of leaf, LAI and NAR which eventually led to more accumulation of dry matter and yield of rice. Higher leaf area index might be due to an adequate supply of nutrients and also higher nutrient absorption through the foliar spray of zinc by the plants. Related findings were noticed by Torabian et al. (2015). Application of nano zinc as foliar treatment significantly increases total chlorophyll concentration per unit of leaf area which was supported by the conclusions of Kheir et al. (2019), Bala et al. (2019) and Yan et al. (2021). In the present study, application of zinc in nanoform was proven to be quite effective in order to enhance plant growth parameters. The zinc nanoparticles were characterized by FTIR, XRD, SEM and EDX methods before they were applied. Use of these methods (FTIR, XRD, SEM and EDX) to identify and characterize zinc nanoparticles was reported by several other researchers as well (Hall et al. 2007; Mourdikoudis et al. 2018; Modena et al. 2019). Integrated nutrient management practices ameliorated the physicochemical properties of soil which encouraged prolific root attributes like length of root, dry weight of root and root volume that ultimately helped plants in better uptake of water and nutrients from lower layers of soil. Betterment of root morphological characteristics of rice plant for incorporation of organic manure into soil was also observed by Yang et al. (2004), Ullah et al. (2019) and Ajaykumar and Sivakumar (2020). Kheyri et al. (2019) reported that slow release of nutrients by nano-ZnO application during the crop growth period increases rice growth as well as yield. A significant impact of foliar application of ZnO NPs on the yield-contributing characteristics of rice, i.e., number of panicles per m2, number of grains per panicle, in comparison with the non-sprayed treatment was noticed by Bala et al. (2019) and Kheir et al. (2019). Nutrients from chemical fertilizer are immediately utilizable to plants because of quick solubility in soil solution whereas organic manures help in enhancing the availability of nutrients for a longer period due to the slow decomposition of manures. As a result, improved organic carbon content, soil-available nutrients after the harvest of rice and uptake of nutrients by the plant were observed in the combined use of inorganic and organic fertilizer–treated plots. The beneficial effect of conjoint use of organic manure along with inorganic fertilizer in improving soil chemical properties was supported by Naher and Paul (2017), Abid et al. (2020), Rollon et al. (2021) and Urmi et al. (2022). Ghoneim (2016) observed that zinc as foliar spray increased zinc concentration in soil as compared to control. Bala et al. (2019) also observed that the application of ZnO NPs as foliar treatment significantly affected soil zinc content. Better uptake of nutrients by the plant due to integrated nutrient management was also observed by Banik and Sharma (2009), Mitra and Mandal (2012), Mondal et al. (2016) and Ram et al. (2020). The decrease in phosphorus content at harvest stage both in grain and straw and total phosphorus uptake was found with the application of zinc because of the antagonistic effect of zinc on P absorption. This result was also supported by Fageria et al. (2011) and Ghoneim (2016). More zinc concentration in rice grain due to foliar spray of nano zinc was also reported by Adhikary et al. (2020). A profound increase in microbial population was observed in organic manure addition with inorganic fertilizer and foliar spray of nano zinc-applied plots as compared to the only chemical fertilizer application because organic matter serves as a source of the nourishment and also as a substance for decomposition and mineralization of nutrients which creates a favourable condition for the growth of microbes in the soil. Similar findings were also observed by Bahadur et al. (2012), Kumari et al. (2017) and Kumar et al. (2018). Raliya and Tarafdar (2013) had noticed an increment in the microbial population after using of nano zinc oxide particles. Dehydrogenase enzyme activity acts as a measure of comprehensive microbial activity in soil. Greater dehydrogenase enzyme activity was noticed in integrated nutrient management treatments because degradation of added organic material supposed to provide intra- and extra-cellular enzymes that eventually increase microbial activity in the soil. This result finds conformity with the discussions of Kumari et al. (2017), Patra et al. (2020) and Kumar et al. (2021).

5 Conclusion

Addition of good quality organic matter in soil improves soil biological properties which are regarded as an indicator of high-quality soil. In spite of providing good amount of nutrients required by the plants for growth and development, inorganic fertilizers also cause numerous menaces to the soil and environment. Modern agro-techniques like nanotechnology particularly nanofertilizers play vital role in reducing problems connected with nutrient and fertilizer management in the field of agriculture. The effect of nano zinc application was found more pronounced under integrated nutrient management system as compared to sole application of chemical fertilizers in terms of yield of rice crop though they were found statistically at par. These effects may be more distinct under long-term INM practice. Therefore, it may be concluded that integrated nutrient management practice with foliar application of nutrients is a tool which aims to minimize the dose of chemical fertilizer in soil that creates favourable soil physiochemical properties and healthy environment and helps to attain desired crop productivity with proper maintaining of soil fertility by protecting soil nutrient balance in the long run as a whole for sustainability in agricultural production.