Effect of Nano Zinc on growth, yield attributes, yield and quality of groundnut (Arachis hypogaea L.)

Introduction

Groundnut (Arachis hypogaea L.) is an important oilseed legume crop cultivated widely for its edible kernels, high-quality oil and nutritious haulm. It occupies a significant position among oilseed crops because it contributes to human nutrition, edible oil production and livestock feeding. The productivity of groundnut is closely associated with healthy vegetative growth, efficient root development, active nodulation, proper peg penetration and successful pod filling. Since the crop produces flowers above the ground but develops pods below the soil surface, balanced nutrient availability during both vegetative and reproductive stages is essential for obtaining higher yield and better kernel quality. Groundnut is also known for its high nutritional and economic value. The kernels are rich in edible oil, protein, carbohydrates, minerals and vitamins. Generally, groundnut seed contains about 47-50% oil and 25-30% protein, although these values may vary with genotype, season, soil fertility and crop management practices. Groundnut oil is mainly composed of unsaturated fatty acids, particularly oleic and linoleic acids, which contribute to its edible quality, flavour and storage stability. The protein-rich kernels are useful in human diet, while the haulm serves as valuable fodder for livestock. Therefore, improvement in seed yield, oil content, seed index and haulm yield directly enhances both the economic return and nutritional value of the crop. Among the essential micronutrients, zinc plays an important role in the growth and physiological functioning of crop plants. It is involved in enzyme activation, auxin synthesis, chlorophyll formation, membrane stability, pollen viability and carbohydrate translocation. In leguminous crops like groundnut, adequate zinc nutrition also supports root growth and nodule development, which indirectly improves biological nitrogen fixation and overall plant vigour. Deficiency or poor availability of zinc may reduce plant height, leaf area, dry matter accumulation, flowering efficiency, pod development and seed formation, ultimately resulting in lower yield and quality (Noman et al., 2015; Saleem et al., 2022) [6,4] .

In recent years, nano-fertilizers have gained attention as a promising approach for improving nutrient-use efficiency in crop production. Due to their smaller particle size, larger surface area and better contact with plant surfaces, nano forms of nutrients may improve absorption and utilization at comparatively lower concentrations. Foliar application of nano-zinc can be particularly useful because it supplies zinc directly to the growing plant tissues and may reduce nutrient losses caused by soil fixation or limited root-zone availability. This makes nano-zinc important for improving physiological activity, nodulation, dry matter production and reproductive growth in groundnut. Previous studies have indicated that nanoscale zinc oxide can improve germination, seedling vigour, growth and yield of peanut when applied at suitable concentrations (Prasad et al., 2012) [9] . However, the response of nano-fertilizers is generally concentration dependent. An optimum concentration may enhance crop growth, nodulation, assimilate production and pod filling, whereas an excessive concentration may not provide additional benefit and may even reduce performance due to nutrient imbalance or physiological stress. Therefore, identifying the suitable dose of nano-zinc is important for its effective use in groundnut production. Keeping these points in view, the present field experiment was conducted during kharif 2024 to evaluate the effect of different concentrations of nano-zinc on growth, nodulation, yield attributes, yield and quality of groundnut. The study was aimed at identifying the most effective nano-zinc concentration for improving groundnut productivity and quality under the tested field conditions.

Materials and methods:

The field experiment was conducted during the kharif season of 2024 at the Crop Research Farm, Sam Higginbottom University of Agriculture, Technology and Sciences (SHUATS), Prayagraj, Uttar Pradesh, India. The groundnut (Arachis hypogaea L.) variety RG-559-3 was used as the test crop. Although the original field trial comprised phosphogypsum and nano-zinc as treatment factors, the present manuscript is confined specifically to the main-effect response of nano-zinc during 2024. The nano-zinc treatment factor included four levels, namely control, nano-zinc at 750 ppm, nano-zinc at 950 ppm and nanozinc at 1050 ppm. Foliar application of nano-zinc was carried out according to the treatment schedule adopted in the field experiment. All other agronomic and plant-protection practices were followed uniformly in accordance with the recommended package of practices for groundnut, so that the observed variation could be attributed mainly to the imposed nano-zinc treatments. Growth observations, including plant height, number of nodules per plant, number of branches per plant, dry weight and crop growth rate, were recorded before harvest as per standard procedures. Yield attributes and yield-related parameters, such as number of pods per plant, seed yield, haulm yield, shelling percentage, harvest index, seed index and oil content, were recorded at harvest. The data were compiled treatment-wise to assess the comparative performance of different nano-zinc concentrations. The experimental data were subjected to statistical analysis using the standard analysis of variance procedure appropriate for the design of the study. Treatment means were compared with the help of standard error of mean [SEm (±)] and critical difference (CD) at 5% level of probability wherever the treatment effect was found significant. Since the objective of the present article is limited to the nano-zinc component of the experiment, only the nano-zinc main-effect data of 2024 have been presented and discussed.

Results and discussion: Growth response:

The growth parameters of groundnut responded clearly to foliar application of nano-zinc during kharif 2024 (Table 1). Among the four treatment levels, nano-zinc at 950 ppm consistently recorded the highest numerical values for plant height, nodulation, branching, dry matter accumulation and crop growth rate. The response declined at 1050 ppm, indicating that the beneficial effect of nano-zinc was concentration dependent and that 950 ppm was the most effective level under the tested field conditions.

Plant height:

The effect of nano-zinc on plant height was marked. Foliar application of nano-zinc at 950 ppm recorded the maximum plant height (47.725 cm) and was significantly higher than the control (38.775 cm), nano-zinc at 750 ppm (40.668 cm) and nano-zinc at 1050 ppm (41.277 cm). Nano-zinc at 1050 ppm was significantly higher than the control but remained statistically at par with 750 ppm, while 750 ppm was statistically at par with the control. The increase in plant height at 950 ppm may be ascribed to optimum zinc availability, which supports enzyme activation, auxin biosynthesis and cell elongation, thereby improving vegetative growth in groundnut (Prasad et al., 2012; Saleem et al., 2022) [4,9] .

Number of nodules per plant:

The number of nodules per plant also showed a significant response to nano-zinc application. Nano-zinc at 950 ppm recorded the highest nodules per plant (43.35) and was significantly superior to the control (35.27), nano-zinc at 750 ppm (36.98) and nano-zinc at 1050 ppm (37.49). Nano-zinc at 1050 ppm was significantly higher than the control and statistically at par with 750 ppm, whereas 750 ppm remained statistically at par with the control. The higher nodulation at 950 ppm may be attributed to better root growth and zinc-supported nodule development, which favour biological nitrogen fixation and overall plant vigour in legumes (Noman et al., 2015; León-Mediavilla et al., 2018) [6] .

Number of branches per plant:

The maximum number of branches per plant was recorded with nano-zinc at 950 ppm (10.199). This treatment was significantly higher than the control (9.148) and nano-zinc at 750 ppm (9.263), while it remained statistically at par with nano-zinc at 1050 ppm (9.703). The 1050 ppm treatment was also statistically at par with 750 ppm and the control. The improvement in branching at 950 ppm may be due to adequate zinc nutrition, which enhances chlorophyll formation, metabolic activity and auxin-regulated shoot development (Saleem et al., 2022) [4] .

Dry weight: Dry matter accumulation was significantly influenced by nano-zinc treatments. Nano-zinc at 950 ppm recorded the highest dry weight (29.923 g), which was significantly higher than the control (24.312 g), nano-zinc at 750 ppm (25.498 g) and nano-zinc at 1050 ppm (25.879 g). Nano-zinc at 1050 ppm was significantly higher than the control and statistically at par with 750 ppm, whereas 750 ppm remained statistically at par with the control. The greater dry matter accumulation at 950 ppm may be explained by improved photosynthetic efficiency, enzyme activity and translocation of assimilates towards actively growing plant parts under optimum zinc supply (Prasad et al., 2012; Saleem et al., 2022) [9,4] .

Crop growth rate: Crop growth rate followed a similar trend. Nano-zinc at 950 ppm recorded the highest CGR value (0.299) and was significantly higher than the control (0.243), nano-zinc at 750 ppm (0.255) and nano-zinc at 1050 ppm (0.258). The control, 750 ppm and 1050 ppm treatments were statistically at par with each other. The higher CGR at 950 ppm may be due to greater leaf activity, improved nutrient uptake and increased biomass production under an optimum nano-zinc concentration (Prasad et al., 2012; Noman et al., 2015) [9,6] .

Overall interpretation: Overall, the growth data clearly indicated that nano-zinc at 950 ppm was the most effective treatment for improving pre-harvest growth characters of groundnut during 2024. The superiority of 950 ppm over the control and other nano-zinc levels suggests that adequate nanozinc supply improved plant vigour, nodulation and biomass accumulation. However, the reduced performance at 1050 ppm shows that increasing the concentration beyond the optimum level did not provide additional benefit. Thus, nano-zinc at 950 ppm may be considered the optimum concentration among the tested levels for improving growth performance of groundnut under the present experimental conditions.

Yield attributes, yield and quality response

The data on yield attributes, yield and quality characters of groundnut showed a clear response to foliar application of nanozinc during kharif 2024. Among the evaluated concentrations, nano-zinc at 950 ppm recorded the highest values for pods per plant, seed yield, haulm yield, shelling percentage, harvest index, seed index and oil content. The response declined at 1050 ppm, indicating that the beneficial effect of nano-zinc was concentration dependent and that 950 ppm was the most effective concentration under the tested field conditions. The data on yield attributes, yield and quality characters of groundnut showed a clear response to foliar application of nanozinc during kharif 2024. Among the evaluated concentrations, nano-zinc at 950 ppm recorded the highest values for pods per plant, seed yield, haulm yield, shelling percentage, harvest index, seed index and oil content. The response declined at 1050 ppm, indicating that the beneficial effect of nano-zinc was concentration dependent and that 950 ppm was the most effective concentration under the tested field conditions.

Number of pods per plant:

Nano-zinc at 950 ppm recorded the maximum number of pods per plant (19.50) and was significantly higher than control (16.63), nano-zinc at 750 ppm (17.45) and nano-zinc at 1050 ppm (17.71). Nano-zinc at 1050 ppm was significantly superior to control and statistically at par with 750 ppm, while 750 ppm remained statistically at par with control. The higher pod number under nano-zinc at 950 ppm may be due to improved vegetative growth, better nodulation and greater assimilate supply towards peg development and pod formation (Prasad et al., 2012; Noman et al., 2015) [9,6] .

Seed yield

The highest seed yield was recorded with nano-zinc at 950 ppm (2769.8 kg/ha), which was significantly higher than control (2362.6 kg/ha), 750 ppm (2478.0 kg/ha) and 1050 ppm (2514.7 kg/ha). Nano-zinc at 1050 ppm was significantly higher than control and statistically at par with 750 ppm, whereas 750 ppm was statistically at par with control. In comparison with control, nano-zinc at 950 ppm increased seed yield by about 17.24%. The improvement in seed yield may be attributed to zincmediated enhancement in enzyme activity, photosynthesis, pollen function and translocation of carbohydrates from source to sink, resulting in better pod filling and kernel development (Saleem et al., 2022; Prasad et al., 2012) [4,9] .

Haulm yield

Nano-zinc at 950 ppm produced the highest haulm yield (6482.2 kg/ha) and was significantly superior to control (5529.1 kg/ha), 750 ppm (5799.1 kg/ha) and 1050 ppm (5885.0 kg/ha). Nano-zinc at 1050 ppm was significantly higher than control but remained statistically at par with 750 ppm; 750 ppm was statistically at par with control. The increase in haulm yield at 950 ppm over control was about 17.24%. Higher haulm yield may be due to better canopy development, increased dry matter accumulation and improved nutrient-use efficiency under optimum nano-zinc application (Prasad et al., 2012; Saleem et al., 2022).

Shelling percentage

The effect of nano-zinc on shelling percentage was nonsignificant. However, the highest numerical shelling percentage was recorded with nano-zinc at 950 ppm (59.231%), followed by 1050 ppm (57.318%), 750 ppm (57.308%) and control (55.623%). All nano-zinc treatments were statistically at par with each other for this character. The numerical improvement in shelling percentage may be associated with better seed filling and kernel development due to improved zinc nutrition, although the variation was not large enough to become statistically distinct (Noman et al., 2020; Saleem et al., 2022) [8,4] .

Harvest index: Harvest index was not significantly influenced by nano-zinc levels. Numerically, nano-zinc at 950 ppm recorded the highest harvest index (34.35%), followed by 750 ppm (33.40%), 1050 ppm (33.24%) and control (32.42%). The treatments remained statistically at par, indicating that nano-zinc improved economic yield and biological yield in a relatively proportional manner.

The non-significant variation in harvest index suggests that the yield increase was mainly due to overall biomass improvement and pod development rather than a marked shift in dry matter partitioning (Saleem et al., 2022) [4] .

Seed index

The seed index was also not significantly affected by nano-zinc application. [9,4] .

Oil content

Oil content followed a trend similar to seed index. Nano-zinc at 950 ppm recorded the highest numerical oil content (39.16%), followed by 1050 ppm (37.90%), 750 ppm (37.89%) and control (36.78%). However, the differences among treatments were statistically at par, showing that nano-zinc did not significantly alter oil content in the present season. The marginal improvement in oil content may be related to better seed metabolic activity and improved seed development under zinc nutrition, but the effect on oil accumulation remained statistically non-significant under the supplied 2024 data (Noman et al., 2020; Saleem et al., 2022) [8,4] . Overall, nano-zinc at 950 ppm was the most effective treatment for improving yield attributes, seed yield and haulm yield of groundnut during 2024. The lower performance at 1050 ppm indicates that increasing the concentration beyond the optimum level did not provide additional advantage. Therefore, the response pattern confirms that nano-zinc application in groundnut is dose dependent, with 950 ppm emerging as the best concentration among the tested levels.

Overall interpretation

The 2024 data clearly indicated that nano zinc at 950 ppm was the most effective level among the tested treatments. The treatment improved growth, nodulation, dry matter production, pods per plant, seed yield and haulm yield. The 1050 ppm treatment did not maintain the same level of response, which shows that higher concentration alone is not always beneficial. From a practical agronomic view, 950 ppm may be considered the optimum nanozinc concentration under the tested field conditions. However, because this manuscript uses only one year of nano-zinc data, multi-season validation and economic analysis would be useful before making a wider recommendation. The response declined at 1050 ppm, indicating that 950 ppm was the optimum concentration among the tested nano-zinc levels. Therefore, nano zinc at 950 ppm can be considered a promising treatment for improving groundnut productivity under the experimental conditions of Prayagraj, Uttar Pradesh.

Acknowledgement

AcknowledgementThe authors are thankful to the Department of Agronomy, Sam Higginbottom University of Agriculture, Technology and Sciences, Prayagraj, Uttar Pradesh, for providing field and laboratory support during the experiment

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