Abstract
Rice production in Asia is a cornerstone of global food security. Implementing innovative crop establishment practices and utilizing nano fertilizers can enhance rice yields and mitigate environmental concerns, thereby contributing to a resilient and sustainable food system. Therefore, a field experiment was conducted over 2020 and 2021 that included various methods of application (seed treatment, root dipping, soil and foliar application) of nano fertilizers (nano nitrogen and nano zinc) under different rice establishment methods (conventional paddy and SRI). Statistical analysis was performed using Fisher’s analysis of variance and Duncan’s multiple range test (p ≤ 0.05). The findings showed that the application of 75% N and two foliar sprays of nano-nitrogen and nano-zinc at 25 to 30 and 45 to 50 days after transplanting under System of Rice Intensification method (Treatment T14) was statistically superior in improving growth and yield parameters, grain and straw yield, and in enhancing the quality of rice over other treatments. Studies revealed strong positive correlations between all the measures, with the exception of the proportion of chaffiness and unfilled grains. The results of the stepwise regression analysis revealed the percentage dependence of grain and straw yield on growth, yield, and quality factors.
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Nano Fertilizer Application Under Different Establishment Techniques for Sustainable Paddy (Oryza sativa L.) Production
Thangamuthu Theerthana 
,a,* Shivalli Boregowda Yogananda ,a Salekoppal Sannegowda Prakash ,b Matadadoddi Nanjundegowda Thimmegowda ,c Hadivappa Marulappa Jayadeva ,c Avverahalli Puttegowda Mallikarjuna Gowda ,c and Rampura Shivappa Ramanji d
Rice production in Asia is a cornerstone of global food security. Implementing innovative crop establishment practices and utilizing nano fertilizers can enhance rice yields and mitigate environmental concerns, thereby contributing to a resilient and sustainable food system. Therefore, a field experiment was conducted over 2020 and 2021 that included various methods of application (seed treatment, root dipping, soil and foliar application) of nano fertilizers (nano nitrogen and nano zinc) under different rice establishment methods (conventional paddy and SRI). Statistical analysis was performed using Fisher’s analysis of variance and Duncan’s multiple range test (p ≤ 0.05). The findings showed that the application of 75% N and two foliar sprays of nano-nitrogen and nano-zinc at 25 to 30 and 45 to 50 days after transplanting under System of Rice Intensification method (Treatment T14) was statistically superior in improving growth and yield parameters, grain and straw yield, and in enhancing the quality of rice over other treatments. Studies revealed strong positive correlations between all the measures, with the exception of the proportion of chaffiness and unfilled grains. The results of the stepwise regression analysis revealed the percentage dependence of grain and straw yield on growth, yield, and quality factors.
DOI: 10.15376/biores.20.1.1136-1160
Keywords: Sustainable agriculture; Paddy; SRI; Nano fertilizers; Quality; Yield; Correlation; Regression
Contact information: a: Department of Agronomy, College of Agriculture, V. C. Farm, Mandya, 571405, University of Agricultural Sciences, Bangalore, Karnataka, India; b: Department of Soil Science and Agricultural Chemistry, College of Agriculture, V. C. Farm, Mandya, 571405, University of Agricultural Sciences, Bangalore, Karnataka, India; c: College of Agriculture, GKVK, University of Agricultural Sciences, Bangalore-560065, Karnataka, India; d: Department of Agricultural Statistics, College of Agriculture, V. C. Farm, Mandya, University of Agricultural Sciences, Bangalore-560065, Karnataka, India; *Corresponding author: theerthumuthu@gmail.com
INTRODUCTION
The world’s population is predicted to surpass 9.7 billion by 2050, necessitating a 60% increase in food production (United Nations Department for Economic and Social Affairs 2019). The most contributing cereal crops, namely maize, rice, wheat, and their products in world, account for 140.43, 516.25 and 535.49 kcal/capita/day, respectively (FAO 2022). With 197 g/day and 71.9 kg/year, rice has the highest net availability per person of all the cereals in 2020 to 2021 (Directorate of Economics and Statistics 2021). Rice provides about 700 calories day-1 person-1 for about 3000 million people living mostly in developing countries (Sangeetha and Baskar 2015).
The success of rice production in Asia will determine the future stability of the world’s food supply. In addition to using between 24% and 30% of the global freshwater, rice consumes between 34% and 43% of the irrigation water on the global scale (Surendran et al. 2021). According to predictions, Asia’s 17 to 22 million hectares of irrigated rice land will experience water scarcity by 2025 (Tuong and Bouman 2002), prompting widespread use of water-saving techniques. While the total employment in agriculture dropped in India from 63.32% in 1991 to 42.6% in 2019 as a result of rapid economic growth in non-agricultural sectors and rising labor wages, manual rice transplanting requires 25 to 50 man-days ha-1 (Zhang et al. 2011; Singh and Sharma 2012).
Crop establishment procedures can be changed to provide solutions to all of the aforementioned issues. However, transplanting machines are expensive, so poor farmers cannot afford them. Non-availability of herbicides, compulsory land leveling, and more quantity of seeds (8 to 10 kg acre-1) makes direct seeded rice disadvantageous. Aerobic rice is not appropriate for higher rainfall areas where water cannot be controlled and also requires relatively extra weed management (Alam et al. 2014; Alam et al. 2016; Chakraborty et al. 2017). System of Rice Intensification (SRI) is a renowned methodology that greatly enhances rice yield without requiring additional seeds, chemical fertilizer, or other external inputs (Devi and Ponnarasi 2009).
The efficiency of nitrogen fertilizers in Asia is only 20% to 30%, compared to 45% globally. A proper and effective nutrient management could achieve 75% to 80% of potential yield (Sapkota et al. 2021). Management of nutrients helps to lower fertilizer losses and increase production (Ye et al. 2019). Most rice growing areas are nitrogen-poor, necessitating a strong concentration on nitrogen nutrition (Fageria and Baligar 2003). Consumption of nitrogenous fertilizers in India during 2019 to 2020 was 19,100 thousand tons while it was only 16,735 thousand tons during 2016 to 2017 (Department of Fertilizers, Ministry of Chemicals and Fertilizers 2020).
Zinc deficiency is prevalent in many rice-growing regions (Impa and Johnson-Beebout 2012), with ca. 50% of soils in these areas exhibiting low zinc levels (Singh 2008). Submergence of the soil, which is prevalent in rice production, causes a Zn shortage. Zinc deficiency is also common in alkaline or calcareous soils (Prasad et al. 2014). Field studies have shown that seed treatment, foliar application, or a combination can effectively enhance zinc uptake and accumulation in grains (Nair et al. 2010).
Nanotechnology is a strategy to enhance nutrient use efficiency. Nano fertilizers can be alternatives to conventional fertilizers for gradual and controlled supply of nutrients in the soil (Kottegoda et al. 2011; Shang et al. 2019). They could be a crucial development in the protection of the environment because they can be applied in smaller quantities compared to traditional fertilizers (Adisa et al. 2019), hence reducing leaching, runoff, and gas emissions to the atmosphere (Manjunatha et al. 2016). Given the recognized significance of these nano nitrogen and nano zinc in plant development and their common deficiencies in agricultural soils, this investigation was undertaken to explore their potential benefits on growth, yield, and quality parameters of rice.
EXPERIMENTAL
Experimental Site
The field experimentation was conducted at the A-block, College of Agriculture, Vishweshwaraiah Canal Farm, Mandya, situated in the Agro-Climatic Zone VI (Southern Dry Zone) of Karnataka at 12º 57′ N latitude and 76º 83′ E longitude at an altitude of 678 m above mean sea level.
The details of the weather parameters recorded during the crop growth period are depicted in Fig. 1. The soil at the experiment site was sandy clay loam in texture with 57.3%, 14.0%, and 28.6% sand, silt, and clay, respectively. The soil was alkaline in reaction (pH 8.1) and low in soluble salts (0.45 dS m-1).
a)
b)
Fig. 1. Meteorological data of the experimental area at College of Agriculture, V. C. Farm, Mandya during a) 2020 and b) 2021
The soil was in the medium range in organic carbon (0.52%), available nitrogen (318 kg ha-1), P2O5 (33.5 kg ha-1), K2O (226 kg ha-1), and S (15.3 mg kg-1). The exchangeable calcium and magnesium content of soil was 8.86 and 2.91 cmol (p+) kg-1, respectively. The DTPA extractable iron, zinc, manganese, copper, and hot water-soluble boron content was 34.9, 1.53, 11.2, and 3.11 mg kg-1, respectively. Bacterial, fungal, and actinomycetes population was 14.2 cfu × 105 g-1 of soil, 12.2 cfu × 104 g-1 of soil, and 5.28 cfu × 103 g-1 of soil, respectively. The dehydrogenase activity was 129 μg TPF g-1 soil hr-1, urease activity was 10.7 μg NH4+-N g-1 hr-1, acid and alkaline phosphatase activity was 17.9 and 13.0 μmol g-1 hr-1, respectively.
Treatments and Layout
The experiments were conducted during kharif 2020 and 2021. Considering the nature of factors under study and the convenience of agricultural operation, the experiment was laid out in randomized complete block design. The whole field was divided into three blocks each representing a replication. The experiment consisted of 14 treatments and was randomly allocated within the replications. A distance of 0.3 m between treatments and 0.50 m between replications was provided. Bunds with the height of 30 cm were raised in the space available between replications and treatments.
The treatments included were as follows: T1: TP with recommended practice; T2: SRI with recommended practice; T3: TP with 50% RDN + ST; TP4 with 50% RDN + RD; T5: TP with 50% RDN + FS; T6: SRI with 50% RDN + ST; T7: SRI with 50% RDN + RD; T8: SRI with 50% RDN + FS; T9: TP with 75% RDN + ST; T10: TP with 75% RDN + RD; T11: TP with 75% RDN + FS; T12: SRI with 75% RDN + ST; T13: SRI with 75% RDN + RD; T14: SRI with 75% RDN + FS (Note: TP: Transplanted paddy; SRI: System of Rice Intensification; RP: Recommended practice; ST: Seed treatment; RD: Root dipping; FS: Foliar sprays of both Nnano and Znnano; Recommended FYM, 100% P and K is common to all the treatments; Recommendations are as per package of practice of University of Agricultural Sciences, GKVK, Bangalore).
ST: Seed treatment involved immersing the seeds in a nano-nutrient solution at a concentration of 1000 milliliters per hectare of seed material. This treatment involved soaking the seeds in a solution containing the nano-nutrients prior to sowing. This treatment aimed to enhance seed germination, early seedling vigor, and overall plant growth by delivering essential micronutrients directly to the germinating seeds.
RD: Seedlings were dipped in a 1000 mL/ha nano nutrient solution to facilitate root uptake of nutrients. This technique is commonly used to enhance early plant growth and nutrient acquisition, particularly for micronutrients like zinc.
FS: Two foliar applications of both Nnano and Znnano solutions were administered at two critical growth stages: 25-30 and 45-50 days after transplanting i.e. with 20 days interval. Each application utilized a 0.4% concentration solution, ensuring optimal nutrient delivery to the plants.
A commercial nano-nitrogen and a nano-zinc product were sourced from IFFCO, a public sector company.
Seeds were sown in the nursery beds and trays for manual transplanted paddy and SRI method, respectively. Fifteen days prior to transplanting, 10 t ha-1 FYM was applied to the experimental plots. The recommended doses of 100 kg N ha-1, 50 kg P2O5 ha-1, 50 kg K2O ha-1, and 20 kg ZnSO4 ha-1 fertilizers were applied for specific treatments through urea, single super phosphate (SSP), muriate of potash (MOP), and zinc sulphate (ZnSO4), respectively. A full dose of recommended phosphorus and potassium were applied at the time of transplanting to all the treatments along with 50% N as a basal dose. The remaining 50% N was applied in two splits at 30 and 60 DAT as top dressing according to the treatments.
Methods of Application of Nano Fertilizers
Nano fertilizers were applied as seed treatment (before sowing), root dipping (before transplanting), soil application (mixing nano fertilizers with sand and applied as top dressing), and foliar application (sprayed directly onto the leaves). These are shown in Fig. 2.
Fig. 2. Methods of nano fertilizers application: a) Seed treatment; b) Root dipping; c) Soil application; d) Foliar application
Characterization of Nano Particles
Dynamic light scattering (Zeta Sizer) for particle size analysis
The average particle diameters of nano nitrogen and nano zinc particles were characterized from the intensity distribution analysis by using Zeta Sizer. The average particle diameters of nano nitrogen and nano zinc particles were found to be 57.45 nm and 65.2 nm, respectively. Similar results were confirmed with Gazulla et al. (2013) and Wazid et al. (2018).
Scanning electron microscopy for surface morphology analysis
The morphological features of nano nitrogen and nano zinc particles were characterized by scanning electron microscopy (SEM; EVO 18; Carle Zeiss India Pvt Ltd., Germany) and are shown in Fig. 3. The nano nitrogen particles formed were spherical shaped and zinc showed a spherical shape as well. The results are in agreement with the findings of Gazulla et al. (2013) and Alamdari et al. (2020). The SEM images of nano nitrogen and nano zinc particles on the nano fertilizer sprayed paddy leaves are shown in Fig. 4.
Energy dispersive X-ray spectroscopy for elemental content
Energy dispersive X-ray spectroscopy (EDX) (Oxford 80; Carle Zeiss India Pvt Ltd., Germany) is an elemental analysis technique, which is used in combination with SEM to determine the chemical composition in the sample and is shown in Fig. 3. The nano nitrogen particles formed were 45.4% weight basis N content in the sample whereas, nano zinc particles formed were 67.2% weight basis Zn content in the sample. Similar results were confirmed with (Gazulla et al. 2013).
- Energy-dispersive X-ray spectroscopy of nano nitrogen
a) Energy-dispersive X-ray spectroscopy of nano zinc
b) Scanning electron microscope image of nano nitrogen
c) Scanning electron microscope image of nano zinc
Fig. 3. Characteristics of nano nitrogen and nano zinc particles: a) EDX of nano-N; b) EDX of nano-Zn; c) SEM of nano-N; d) SEM of nano-Zn
Fig. 4. SEM images of nano fertilizers on paddy leaves (nano N and nano Zn sprayed): a) SEM image of paddy leaves with nano-N; b) SEM image of paddy leaves with nano-Zn; c) SEM image of paddy leaves with nano-N and nano-Zn
Biochemical Analysis
Carbohydrates
The total carbohydrate content was estimated by the method of Hedge and Hofreiter (1962). Carbohydrate was first hydrolyzed into simple sugars using dilute hydrochloric acid. In hot acidic medium, glucose was dehydrated to hydroxmethyl furfural. This compound formed with anthrone a green-colored product with absorption maximum at 630 nm.
Protein
Total protein was estimated by modified Lowry’s method given by Hartree (1972). Determination of protein concentration by ultraviolet absorption depends on the presence of aromatic amino acids in the proteins. To the extracted samples, alkaline CuSO4 reagent was added and incubated at room temperature for 10 min followed by 0.5 mL of Folin’s phenol reagent. The contents were mixed well, and the absorbance was measured at 650 nm after 15 min in a spectrophotometer (Cary 60 UV-Vis; Agilent Technologies, India). From the standard graph, the amount of protein in the given unknown solution was calculated.
Tryptophan content
The tryptophan content in grain sample was estimated by colorimetric method (Sadasivam and Manickam 1992). The protein in the grain sample was hydrolyzed with a proteolytic enzyme, papain. Then, the hydrolyzed sample was incubated at 65 °C overnight. A total of 1.0 mL supernatant was taken after centrifugation. To this, 4 mL of ferric chloride was added and kept for incubation at 65 °C for 15 min. The indole ring of tryptophan gives an orange red color with ferric chloride under strongly acidic condition. The intensity was measured at 545 nm. The tryptophan content in sample was estimated by comparing with standard curve:
Statistical Analysis
Observations recorded during different phenological phases of rice crop were analyzed statistically to find out the result and to draw a conclusion of the experiment conducted. Fisher’s method of analysis of variance (ANOVA) was used in the analysis, as given by Gomez and Gomez (1984). Significance between the treatments was tested by Duncan’s multiple range test at a significance level of p ≤ 0.05. The analysis was performed using IBM SPSS, version 22. Correlation and regression analysis were conducted using R4.2.0 software package.
RESULTS AND DISCUSSION
Plant Vegetative Growth Parameters
Different growth parameters, such as plant height, number of tillers per hill, dry matter accumulation in leaves, stem, and panicles, were statistically influenced by the application of 75% N and two foliar sprays of nano nitrogen and nano zinc at 25 to 30 and 45 to 50 DAT under SRI method over rest of the treatments. Data pertaining to growth parameters are presented in Table 1.
Benzon et al. (2015) revealed that plant height was more enhanced when nano fertilizer was combined with conventional fertilizers because nano fertilizer can either provide nutrients for the plant or aid in the transport or absorption of available nutrients, thereby resulting in better crop growth. The transplanting of younger seedlings with wider spacing helped for both direction weeding and the application of nano nitrogen and nano zinc as foliar spray improved the availability of nutrients throughout the crop growth period influencing the number of tillers per hill under the SRI method (Geethalakshmi et al. 2011; Ghafari and Jamshid 2013).
The increase in dry matter accumulation may be due to the high reactivity of nano fertilizers, especially when they are applied as foliar spray because of more specific surface area in plant leaves (Dhoke et al. 2013). Large root volume, profuse tillering, and wider spacing of 25 cm × 25 cm sustained minimum injury while transplanting and established quickly due to the availability of nutrients (Hossain et al. 2003; Sathyanarayana and Babu 2004). Further, optimum utilization of resources leads to early tillering in SRI, which made the plants have more time for accumulation of photosynthates in panicles. Nano nitrogen and nano zinc fertilizers applied to the rice crop were readily available to the crop and that made the crop physiologically more active. As a result of better uptake and efficient utilization of nutrients, increased mobilization and accumulation of photosynthates in the reproductive parts of rice were observed. These results are in line with the findings of Armin et al. (2014) and Kumar et al. (2015a). The positive effect on plant growth of nano fertilizers was reported by Hassan et al. (2011), Morteza et al. (2013), Kannan et al. (2012), Prasad et al. (2012), Hedait and Salama (2012), and Tapan et al. (2013).
Table 1. Influence of Different Methods of Nano Nitrogen and Nano Zinc Applications on Growth Parameters of Paddy at Harvest During Kharif 2020 and 2021