Effect of nano-urea, urea and NAA on growth and yield attributes of acid lime (Citrus aurantifolia) cv. Kagzi

Introduction

Acid lime (Citrus aurantifolia Swingle) ranks as India's third most significant citrus crop, following mandarins and sweet oranges. Belonging to the Rutaceae family (chromosome number 2n = 18), this primarily subtropical fruit is also adaptable to tropical cultivation. The fruit is characterized by its small, round or oval shape, polyembryonic nature, greenishyellow flesh, high juice content, pronounced acidity, and distinct aroma. Valued for its nutritional and medicinal properties, acid lime juice is rich in sugars, fruit acids (particularly citric acid), vitamin C, and antioxidants (Thirugnanavel et al., 2007; Prasad and Kumar, 2012) [22,16] . Nutritional analysis indicates that 100 g of juice typically contains approximately 80g water, 26 IU vitamin A (as carotene), 20 mg vitamin B1, 0.1mg riboflavin, 63mg vitamin C, 1.83 mg iron, and 0.16 mg copper, underscoring its health benefits. Acid lime plants exhibit a medium height, bushy and vigorous growth habit with spreading branches. Their dense foliage consists of small, pale green, broadly lanceolate leaves. The trees typically flower three times annually: Ambia/Ambe bahar (January-February), Mrig Bahar (June-July), and Hasta bahar (September-October). Recognized as a nutrientdemanding crop, the productivity and juice quality of acid lime are directly influenced by nutrient supply. While balanced fertilization is essential for enhancing yield and maintaining fruit quality, the excessive and imbalanced use of chemical fertilizers poses risks, including environmental damage, soil degradation, and ultimately, reduced fruit quality and productivity, impacting human health. Consequently, identifying effective nutrient management strategies is crucial to maximize productivity and nutrient use efficiency while safeguarding environmental health. One promising approach involves reducing application rates, especially for highly mobile nutrients like nitrogen, and enhancing their effectiveness.

In this context, nano-fertilizers, particularly nano-urea, have emerged as a viable commercial alternative. Studies report that foliar nano-urea application in fruit crops can reduce conventional urea requirements by up to 50% while boosting use efficiency to approximately 90%. Furthermore, plant growth regulators (PGRs or bioregulators) represent another vital strategy for improving fruit productivity and quality. They achieve this by enhancing flowering, fruit set, fruit size, and shape, while also reducing fruit drop. Considering these factors, the present investigation was undertaken to develop protocols for nitrogen application using both conventional urea and nano-urea-alongside PGR application (specifically NAA), aiming to optimize benefits in acid lime cultivation.

Materials and Methods

A field experiment was conducted during the 2021-2022 growing season at the Fruit Research Station, Imaliya, Department of Horticulture, JNKVV, Maharajpur (Madhya Pradesh), utilizing a well-established orchard of Kagzi acid lime (Citrus aurantifolia Swingle). The study employed 28 uniformly spaced plants (6 × 6 m) in a randomized layout. Seven foliar spray treatments were evaluated: T₁: Control (water spray); T₂: 2.0% urea; T₃: 4.0% urea; T₄: 0.2% nanourea; T₅: 0.4% nano-urea; T₆: 20 ppm NAA (naphthalene acetic acid); T₇: 40 ppm NAA. Treatments were applied twice: first at the 50% flowering stage and second post-fruit set, ensuring precise physiological timing. The experimental soil was characterized as clay-loam with traces of heavy clay, representative of regional growing conditions. The primary objective was to assess the impact of conventional urea, nano-urea, and the growth regulator NAA on growth attributes (e.g., vegetative development, floral metrics) and yield parameters (e.g., fruit set, fruit number, yield efficiency) of Kagzi lime. Data collected throughout the trial were rigorously analyzed using Analysis of Variance (ANOVA). The significance of treatment effects was determined via the F-test at a 5% probability level (p≤0.05).

Where ANOVA indicated significant differences, mean comparisons were made using the Critical Difference (CD) to identify statistically distinct treatments. This design ensured robust evaluation of nano-technology and bioregulators as sustainable alternatives to conventional nitrogen fertilization for enhancing acid lime productivity.

Results and Discussion

Floral bud initiation

The data pertaining to floral bud initiation is presented in Table 4.1. The data revealed that the flower bud initiation ranged from 5 th January to 15 th January and it was recorded that earlier (5 th January) flower bud initiation took place under T 6 , while it was delayed (15 th January) in T 1 (control).

Days to 50% flowering

The data representing days to 50% flowering is presented in Table 1. The data revealed that days to 50% flowering ranged from 27 to 35 days and it was observed that among the different treatments, minimum (27) days were required under T 6 to attain 50% flowering while maximum (35 days) number of days were recorded in T 1 (control).

Number of flowers shoot -1

Data clearly showed that number of flowers shoot -1 was significantly influenced by the treatments. Maximum numbers of flowers shoot -1 (50.93) was obtained under treatment T 5 (spray of 0.4% Nano-urea) over rest of the treatments excluding T 2 (46.95), T 3 (49.67) and T 4 (48.21) which were statistically at par with treatment T 5 . However, the minimum number of flowers shoot -1 (43.15) was recorded under control having no applied nutrients.

Number of flowers tree -1

It is clear from the data that the maximum number of flowers tree -1 (1986) was observed with application of Nano-urea (0.4%) over all the treatments including control which was found to be at par with treatment T 3 (1887) and T 4 (1832). However, the minimum number of flowers tree -1 (1553) was found under control (T 1 ).

The results revealed that the hermaphrodite flower (%) was influenced significantly by the treatments. It was observed that the higher hermaphrodite flower% (88.93%) was recorded in T 5 with application of Nano-urea (0.4%) while, the minimum percentage of hermaphrodite flower was recorded in T 1 (Control) i.e., 76.39%.

The minimum male flower% (11.07%) was recorded with application of Nano-urea (0.4%) which was found to be at par with T 3 (12.75%). However maximum male flower percentage (23.61%) was recorded under control (T 1 ).

Hermaphrodite: Male ratio

The higher ratio of Hermaphrodite (8.03) was recorded under the foliar application of Nano-Urea (0.4%) and lower ratio (3.24) was recorded under control.

Days to initial fruit set

It is clear from the data that the minimum number of days (5.87) to initial fruit set from 50% flowering was observed under treatment T 5 (foliar spray of Nano-urea @ 0.4%) followed by T 3 (6.02) whereas the maximum days (8.15) to initial fruit set was found under control T 1 .

Yield parameters Fruit set%

It is clear from the data that the fruit set% was significantly influenced by different treatments. The result revealed that the maximum number of fruit set% (59.81%) was observed under the treatment T 6 with the application of 20 ppm NAA which was found to be significantly at par with treatment T 5 (57.95%) and T 7 (54.67%).The minimum number of fruits set% (45.13%) was noted under control T 1 .

Fruit drop%

It was observed that fruit drop was significantly influenced by the spray of plant growth regulators. The result thus obtained showed that minimum (40.19%) fruit drop was recorded under the treatment T 6 (foliar application of 20 ppm NAA) while the maximum (54.87%) fruit drop% was recorded under control (T 1 ).

Number of fruit shoot -1

The data indicate that the number of fruits shoot -1 was significantly influenced by different treatments. The result revealed that the maximum number of fruit shoot -1 (29.51) was observed under the treatment T 5 with the application of Nano-urea (0.4%) which was found to be at par with T 6 (28.83). The minimum number of fruits per shoot (18.81) found under control (T 1 ).

Number of fruits tree -1

It is cleared from the data that with the application of Nanourea (0.4%), maximum number of fruit tree -1 (1151.04) was recorded in treatment T 5 which was found to be at par with treatment T 6 (1095.71) with foliar application of NAA 20 ppm. However, the minimum number of fruits per plant (677.00) was recorded under control (T 1 ).

Average fruit weight

The average fruit weight was recorded to be significant among different treatments. Maximum average weight of the fruit was observed in treatment T 3 (49.37 g) with foliar application of urea 4% followed by the treatment T 4 (47.55 g) and the minimum average fruit weight was found in treatment T 7 (41.77 g).

The results revealed that the maximum fruit yield tree -1 (49.17) was recorded with the foliar spray of urea 2% under the treatment T 2 followed by treatment T 5 (48.79), T 6 (47.70) which were found to be at par with T 2 . However, the minimum fruit yield tree -1 (29.73) was recorded under control.

Discussion

Effect of Nano-urea, Urea and NAA on growth and development attributes of Acid lime.

It is evident from the data and the result presented in previous chapter that various treatments of different concentrations had significant effect on growth and development parameters such as number of flowers shoot -1 , total number of flower tree -1 , hermaphrodite flowers (%) and hermaphrodite: male ratio and days to initial fruit set. It might be because urea and Nano-urea play an important function in encouraging plant growth as nitrogen is a constituent of chlorophyll, the substance that allows plants to use sunlight energy to convert CO 2 to carbohydrates through the process of photosynthesis. Similar findings were done by Chermahini et al. 2011 [2] and Syamal et al., 2008 [21] who revealed that the increase in number of flowers and hermaphrodite flowers may be due to the nitrogen which is major component of protoplasm which increase photosynthesis. The nitrogen supplied through Nano-urea helps in chlorophyll synthesis which increases photosynthesis as a result of which there is more accumulation of carbohydrates leading to flower initiation and profuse flowering. Similar findings also in conformity reported by Etehadnejad and Aboutalebi (2014) [5] , Lovatt (1994) [10] , Stiles (1999) [20] . Maximum number of fruits shoot -1 (29.51) was observed by the foliar spray of Nano-urea (0.4%) which was found to be at par with foliar spray of 20 ppm NAA (28.83). The minimum number of fruits per shoot (18.81) was found under control. The results revealed that with the application of Nano-urea (0.4%), maximum number of fruit tree -1 (1151.04) was recorded which was found to be at par with the foliar spray of 20 ppm NAA (1095.71). However, the minimum number of fruits tree -1 (677.00) was recorded under control. Same findings were done by Lovatt (1994) [10] , Stiles (1999) [20] . They reported that the increase in number of fruits may be due to foliar application of nitrogen fertilizer. The metabolic and physiological roles of nitrogen includes supply of carbohydrates which are important and necessary for growth of flower bud, initiation of flower and its development, along with effective pollination and fertility.

The foliar application of NAA had a significant effect on the retention of fruit which may be due to balancing the internal status of auxin which prevents the formation of abscission layer which leads to produce more numbers of fruits. Similar findings were also obtained by Singh and Rajput (1988) [18] in mango. Maximum average fruit weight (49.37 g) was observed with foliar application of urea 4% followed by the foliar spray of nano-urea @ 0.2% (47.55 g) and the minimum weight of fruit was found by the foliar spray of 30 ppm NAA (41.77 g). The increase in fruit weight by urea may be due to accumulation of sugars and high percentage of pulp. This finding was in accordance with the Mazumdar and Bhatt (1976) [12] in sweet orange. Similar findings were done by Parmar et al. (2014) [15] in guava. It was also observed that the maximum fruit yield tree -1 (49.17) was noted by the foliar spray of urea 2% followed by foliar spray of 0.4% Nano-urea (48.79), foliar spray of 20ppm NAA (47.70) which were statistically at par with T 2 . Whereas, the minimum fruit yield tree -1 (29.73) was obtained under control. This may be due to the cumulative effects of nitrogen on photosynthetic and metabolic activities which resulted in increase in fruit size and weight and therefore increasing yield of Acid lime (Jat and Kacha, 2014).

Conclusion

On the basis of result obtained in present experiment, it can be concluded that treatment T 5 (foliar spray of 0.4% nanourea) was found significantly superior as compared to other treatments for growth and development parameter. Maximum fruit set% and minimum fruit drop% was observed with the foliar application of 20 ppm NAA. Maximum yield and yield attributing characters were found recorded under foliar spray of 4% urea and 0.4%nano urea

Acknowledgement

AcknowledgementThe author wishes to acknowledge the support and facilities provided by the Head of the Department of Horticulture at the College of agriculture Jabalpur to carry out the present investigation.

References

1. Bal JS, Randhawa JS, Singh SN. Effect of NAA on fruit characters and quality of ber cv. 'Umran'. Haryana J Hortic Sci. 1998;1(1-2):20-23.
2. Chermahini SA, Moallemi N, Nabati DA, Shafieizargar AR. Winter application of foliar urea can promote some quantitative and qualitative characters of flower and fruit set of Valencia orange trees. J Food Agric Environ. 2011;9(1):252-255.
3. Debaje PP, Shinde Ekta D, Ingale HV. Effect of plant growth regulator and nutrients on quality of acid lime. Asian J Agric Hortic Res. 2011;6(1):253-255.
4. Debaje PP, Shinde Ekta D, Ingale HV. Effect of plant growth regulator and nutrients on quality of acid lime. Asian J Hortic. 2011;6(1):253-255.
5. Etehadnejad F, Aboutalebi A. Evaluating the effects of foliar application of nitrogen and zinc on yield increasing and quality improvement of apple cv. 'Golab Kohanz'. Indian J Fundam Appl Life Sci. 2014;4:125129.
6. Ilyas A, Yasin AM, Mumtaz H, Muhammad A, Aashid A, Ali K. Effect of micronutrients (Zn, Cu and B) on photosynthetic and fruit yield attributes of Citrus reticulata Blanco var. Kinnow. Pak J Bot. 2015;47(4):1241-1247.
7. Jain MC, Choudhary HD, Sharma MK, Singh B. Yield and quality attributes of Nagpur Mandarin as affected by use of different plant growth regulators. Environ Ecol. 2014;32(3):1141-1145.
8. Jat G, Kacha HL. Response of guava to foliar application of urea and zinc on fruit set, yield and quality. J Agric Res. 2014;1(2):86-91.
9. Kumar J, Kumar R, Rai R, Mishra S. Response of 'Pant Prabhat' guava trees to foliar sprays of zinc, boron, calcium and potassium at different plant growth stages. Bioscan. 2015;10(2):495-498.
10. Lovatt CJ. Improving fruit set and yield of 'Hass' avocado with a spring application of boron and/or urea to the bloom. Calif Avocado Soc Yearb. 1994;78:167173.
11. Makhija M, Chandra A, Yamdagni R. Note on quality improvement by nutrients spray in ber cv. 'Gola'. Cuff Agril. 1990;14:73-74.
12. Mazumdar BC, Bhatt DNV. Effect of pre-harvest application of GA and ethrel on sweet orange (Citrus sinensis Osbeck) fruits. Prog Hortic. 1976;8(2):89-91.
13. Pandey V. Effect of NAA and GA3 spray on fruit retention, growth, yield and quality of ber (Zizyphus mauritiana L. amk.) cv. Banarasi Karaka. Orissa J Hortic. 1999;27(1):69-73.
14. Pandey V. Effect of NAA and GA3 spray on fruit retention, growth, yield and quality of ber (Zizyphus mauritiana L. amk.) cv. Banarasi Karaka. Orissa J Hortic. 1999;27(1):69-73.
15. Parmar JM, Karetha KM, Rathod PJ. Effect of foliar spray of urea and zinc on growth and flowering attributes of guava (Psidium guajava) cv. Bhavnagar Red. Adv Res J Crop Improv. 2014;5(2):140-143.
16. Prasad S, Kumar U. A handbook of fruit production. Agrobios; 2012. p.654-659.
17. Sandhu S. Improving lemon [Citrus limon (L.) Burm.] quality using growth regulators. J Hortic Sci. 2013;8(1):88-90.
18. Singh AK, Rajput CBS. Effect of GA3, BA and calcium on the chemical properties of fruit in mango (Mangifera indica L.). Punjab Hortic J. 1988;28(34):159-163.
19. Singh K, Sandhu AS. Berry thinning in Perlette grapes through pre-bloom application of Planofix (NAA) and GA3. Punjab Hortic J. 1987;27(1-2):34-36.
20. Stiles WC. Effects of nutritional factors on regular cropping of apple. Hortic Technol. 1999;9:328-331.
21. Syamal MM, Singh SK, Singh BP. Effect of urea and zinc on growth flowering fruiting and fruit quality of Kagzi lime. Environ Ecol. 2008;26(3):1036-1038.
22. Thirugnanavel A, Amutha R, Baby Rani W, Indira K, Mareeswari S, Muthulaksmi S. Studies on regulation of flowering in acid lime (Citrus aurantifolia Swingle). Res J Agric Biol Sci. 2007;3(4):239-241.