Influence of plant spacing and nutritional regimes on quantitative fruit traits of water chestnut (Trapa natans var. bispinosa Roxb.)

Introduction

Water chestnut (Trapa natans var. bispinosa Roxb.) is an important aquatic fruit crop in India belonging to the family Trapaceae. It is popularly known as Singhara in Hindi and is considered to have originated in India, China and Eurasia. It is a free-floating annual aquatic plant cultivated in shallow fields, ponds and swampy lands. The crop thrives in nutrient-rich water with a pH ranging from 6.7 to 8.2 (Anonymous, 2002; Bhatiwal et al., 2012) [2,3] . In India, it is extensively cultivated in Madhya Pradesh, Uttar Pradesh, Bihar, Odisha, West Bengal, Jharkhand, Karnataka and Jammu & Kashmir. It is also grown in several tropical regions including Pakistan, Sri Lanka, Indonesia and Africa, and is prevalent in Southeast Asia, southern China, Japan, Italy and tropical America. Furthermore, it has naturalized in certain regions of the eastern United States (Takano and Kadono, 2005) [16] . The fruit is used as a substitute for cereal in Indian subcontinent during fast days especially during Navratri and other sacred days when consumption of wheat flour is avoided. Chestnut flour is made by drying chestnut fruits in hot air, shelling them, picking out discolored chestnuts, and crushing them with a stone mill (Alary et al., 2007) [1] . Chestnut flour can be used in gluten-free breads for its nutritional and health benefits. Traditionally, cookies are created with wheat flour. Additional grain flours or starches can enhance the flavor and structure of the finished product. Water chestnut grows for commercial cultivation, heavy muddy soils rich in organic matter are preferred. Application of oil cakes, poultry manure and FYM/compost @ 8 t ha⁻¹ is recommended for crop growth and development (Chowdhury et al., 2003) [4] . Phosphorus and potassium are essential for optimum crop performance. In West Bengal, 30-40 kg urea ha⁻¹ is recommended at transplanting followed by an additional 20 kg ha⁻¹ after 25-30 days (Jana, 2016a) [9] . Soils rich in zinc and boron improve fruit number and fruit weight. For newly cultivated fields, fertilizer application may be increased from NPK 60:20:20 kg ha⁻¹ to60:40:30 kg ha⁻¹, while maintaining a spacing of 1 m × 2 m with a plant population of 4500-5000 plants ha⁻¹ (Jana et al., 2019) [8] .

Nano-fertilizers possess nanoscale dimensions and a high surface area-to-volume ratio, which facilitate efficient nutrient absorption, translocation and utilization within plants. Consequently, they improve nutrient use efficiency and reduce nutrient losses through leaching, volatilization and fixation, thereby enhancing crop productivity and sustainability (Raliya et al., 2018) [15] . Nano-Urea enhances nitrogen use efficiency through improved nitrogen availability and uptake, resulting in increased chlorophyll synthesis, photosynthetic activity, protein formation, vegetative growth and crop productivity (Kumar et al., 2021) [12] . Nano-Zinc plays an essential role in enzyme activation, auxin biosynthesis, chlorophyll formation and carbohydrate metabolism. Adequate zinc nutrition enhances physiological processes, photosynthetic efficiency, growth, yield attributes and quality characteristics of crops by improving nutrient utilization and metabolic activities (Tarafdar et al., 2014; Raliya et al., 2018) [17,15] . Silver nanoparticles have been reported to enhance physiological and biochemical activities, stimulate antioxidant defense systems and improve plant tolerance to environmental stresses, thereby contributing to improved growth, development and productivity in various crops (Khan et al., 2023; El-Saadony et al., 2021) [10,7] . Application of Jeevamrut has been shown to increase microbial population, soil biological activity, and nutrient availability in the rhizosphere, resulting in increased plant growth and yield performance. Nano-fertilizers improve nutrient delivery and nutrient usage efficiency, whereas organic nutrient sources promote nutrient cycling and soil biology. As a result, combining nano-nutrients with organic nutrient sources may increase nutrient availability, absorption efficiency, and crop yield while reducing nutrient losses (Dimkpa and Bindraban, 2018; Raliya et al., 2018) [5,15] .

Materials and Methods

Experimental site

Experiment was conducted during the Kharif seasons of 2023 and 2024 at Horticulture Farm No. 1, Department of Horticulture, School of Agricultural Sciences and Technology, Babasaheb Bhimrao Ambedkar University, Lucknow, Uttar Pradesh, India. The experimental farm was geographically situated at 26.769559° N latitude and 80.927135° E longitude, with an elevation of approximately 121 m above mean sea level.

Experimental design and treatments

The experiment was conducted in a Factorial Randomized Block Design involving two experimental factors with three replications. Factor A comprised two plant spacing levels, namely S₁ = 1.0 m × 1.0 m and S₂ = 2.0 m × 1.0 m. Factor B consisted of thirteen nutritional regimes (T₁-T₁₃) comprising conventional fertilizer practices, reduced fertilizer doses, recommended fertilizer application, nano-fertilizers and organic nutrient sources. The factorial combination of the two spacing levels and thirteen nutritional regimes resulted in 26 treatment combinations (2 × 13). Each treatment combination was replicated three times, resulting in a total of 78 experimental units. The treatments were randomly assigned within each replication to minimize experimental variability and obtain reliable estimates of treatment effects. The factorial design enabled the evaluation of the main effects of plant spacing and nutritional regimes, as well as their interaction (S × T) on the growth, yield and quality performance of water chestnut.

Nutritional treatments

A total of thirteen nutritional regimes were evaluated during the study. These treatments included control, farmer's fertilizer practice, reduced fertilizer doses, recommended dose of fertilizer (RDF), nano-fertilizers, Jeevamrut and nano-fertilizer-fortified organic nutrient sources. The details of the nutritional treatments are presented in Table 1.

Treatment combinations and field layout

Each of the thirteen nutritional regimes was combined with both plant spacing levels, resulting in 26 factorial treatment combinations, designated as S₁T₁ to S₁T₁₃ and S₂T₁ to S₂T₁₃. Under S₁, plants were maintained at a spacing of 1.0 m × 1.0 m, whereas under S₂, a spacing of 2.0 m × 1.0 m was maintained. The experimental units consisted of individual ponds measuring 2.0 m × 1.0 m. A border space of approximately 0.5 m was maintained, wherever required, to minimize the influence of adjacent experimental units. Water chestnut plants were established during the third week of July, and the water depth was maintained at approximately 60-70 cm throughout the crop period. All other recommended cultural practices were kept uniform across the experimental units, except for the respective nutritional treatments imposed according to the experimental design.

Results and Discussion

Fruit characteristics are important indicators of productivity, marketable quality and overall performance of water chestnut. In the present investigation, plant spacing and nutritional regimes produced noticeable variations in different fruit attributes during both years of experimentation. The response of fruit characters varied with the availability of growing space, nutrient supply and their combined effects. The influence of plant spacing, nutritional regimes and their interaction on individual fruit parameters is presented and discussed in the following sections.

Number of fruits per rosette

The data presented in Table 2 revealed that the number of fruits per rosette was significantly influenced by plant spacing and nutrient management treatments during both years of experimentation. However, the interaction between spacing and nutrient management treatments was statistically significant during the year 2023, whereas a significant interaction was observed during the year 2024. Plant spacing significantly affected the number of fruits per rosette during both years. The wider spacing (S₂) recorded a significantly higher number of fruits per rosette, with 6.18 fruits during the year 2023 and 6.31 fruits during the year 2024, compared with 5.41 and 5.62 fruits per rosette, respectively, under closer spacing (S₁). The better performance under wider spacing may be attributed to reduced inter-plant competition for light, nutrients and space, which favoured reproductive growth and fruit initiation. Similar variation in reproductive characteristics of Trapa natans has been reported by Palm et al., (2024) [13] , who observed considerable variation in rosette development and fruit production among Trapa populations and emphasized the role of plant growth conditions in determining reproductive performance. Nutrient management treatments significantly influenced the number of fruits per rosette in both years. During the year 2023, the maximum number of fruits per rosette (7.83) was recorded under T₁₀ (Nano zinc fortified Jeevamrut), followed by T₁₂ (Nano zinc fortified FYM) with 7.17 fruits, T₇ (RDF) and T₁₃ (Nano silver fortified FYM) with 6.34 fruits each. The lowest value (4.00 fruits per rosette) was recorded under T₁ (Control). A similar trend was observed during the year 2024. T₁₀ again recorded the maximum number of fruits per rosette (7.83), followed by T₁₂ (7.17), while the minimum value (4.50) was recorded under the control treatment. The superior response of T₁₀ and T₁₂ may be associated with the combined availability of macro-and micronutrients along with organic nutrient sources. Zinc plays an important role in several physiological and reproductive processes, while organic nutrient sources can improve nutrient availability and overall plant growth. Puste et al., (2005) [14] reported that balanced management of nitrogen and other nutrients through integrated organic and inorganic sources substantially influenced the production and quality of water chestnut under wetland conditions. The interaction between spacing and nutrient management treatments was non-significant during the year 2023, indicating that the effect of nutrient treatments on fruit number was statistically similar across the two spacings. In contrast, the interaction was significant during the year 2024, indicating that the response of nutrient management treatments varied according to plant spacing.

During the year 2024, the maximum number of fruits per rosette (8.33) was recorded under S₂ × T₁₀, followed by S₂ × T₁₂ (7.67) and S₂ × T₇ (7.00). The minimum value (4.33 fruits per rosette) was observed under S₁ × T₁. The higher reproductive performance under wider spacing combined with nutrient supplementation suggests that adequate growing space together with balanced nutrient availability favoured fruit initiation and development. Palm et al., (2024) [13] reported that nutrient availability, particularly nitrogen, can influence rosette and leaf development in Trapa natans, while nutrient acquisition may occur from both the sediment and water column. Overall, the results indicated that wider spacing (S₂) and integrated nutrient management, particularly T₁₀, were favourable for increasing the number of fruits produced per rosette in water chestnut.

The data presented in Table 3 indicated that average fruit length was significantly influenced by plant spacing and nutrient management treatments during both years of experimentation. The interaction between spacing and nutrient management was also significant during both years, indicating that fruit length was influenced by the combined effect of spacing and nutrient regime. [14] demonstrated that integrated organic and inorganic nutrient management significantly influenced the productivity and quality of water chestnut under wetland conditions, supporting the beneficial role of balanced nutrient management in this crop.

The interaction between spacing and nutrient management treatments was significant during both years. The highest fruit length was recorded under S₂ × T₁₂, with 41.94 mm in the year 2023 and 42.27 mm in the year 2024, followed by S₂ × T₁₀ with 41.91 and 42.24 mm, respectively. The minimum fruit length was recorded under S₁ × T₁, with 38.30 mm in the year 2023 and 38.23 mm in the year 2024. The consistently higher fruit length under wider spacing combined with nutrient supplementation indicates that adequate plant space and improved nutrient availability jointly favoured fruit development. Dwivedi et al., (2010) [6] reported considerable variability in fruit length, breadth, weight and volume among water chestnut germplasm, demonstrating that these physical attributes are important and variable characteristics of Trapa natans var. bispinosa. Thus, S₂ × T₁₂ emerged as the most favourable treatment combination for improving fruit length under the present experimental conditions.

The results presented in Table 4 showed that average fruit width was significantly influenced by plant spacing, nutrient management treatments and their interaction during both years of experimentation. [14] reported that appropriate combinations of organic and inorganic nutrient sources enhanced production and quality attributes of water chestnut, indicating the importance of balanced nutrient availability in aquatic food crops. The interaction between spacing and nutrient management treatments was significant during both years. [6] , who reported substantial variation in fruit breadth and other physical fruit characteristics among water chestnut germplasm. Their observations confirm that fruit dimensions are important measurable attributes of Trapa natans var. bispinosa.

The results therefore suggest that wider spacing combined with efficient nutrient management, particularly S₂ × T₁₂, was most favourable for improving fruit width.

The data presented in Table 5 revealed that average fruit weight was significantly influenced by plant spacing and nutrient management treatments during both years of experimentation. The interaction between spacing and nutrient management was significant during the year 2023, whereas it was non-significant during the year 2024. Plant spacing significantly affected average fruit weight during both years. Wider spacing (S₂) produced significantly heavier fruits, with an average weight of 22.08 g in the year 2023 and 22.05 g in the year 2024, compared with 20.80 g and 20.77 g, respectively, under closer spacing (S₁). The greater fruit weight under wider spacing may be associated with reduced competition among plants and improved availability of assimilates for fruit growth and filling. The importance of fruit weight as a major physical yield component in water chestnut has also been demonstrated by Dwivedi et al., (2010) [6] , who reported substantial variation in fruit weight among water chestnut genotypes under central Uttar Pradesh conditions. Nutrient management treatments significantly influenced fruit weight during both years. In the year 2023, T₁₂ recorded the maximum average fruit weight (24.00 g), followed by T₁₀ (23.34 g) and T₇ (22.84 g), whereas the minimum value (16.67 g) was observed under T₁.

During the year 2024, T₁₂ again recorded the highest average fruit weight (23.84 g), followed by T₁₀ (23.34 g) and T₇ (22.67 g). The minimum fruit weight (16.34 g) was recorded under T₁. The superior performance of T₁₂ may be attributed to the combined contribution of FYM and zinc, which provided a more favourable nutrient environment for fruit growth. Puste et al., (2005) [14] reported that integrated nutrient management involving organic and inorganic nutrient sources significantly improved the production of water chestnut. Their findings support the importance of balanced nutrient supply for improving productivity in aquatic food crops.

The interaction effect was significant during the year 2023 but non-significant during the year 2024. In the year 2023, the maximum fruit weight (24.33 g) was recorded under S₂ × T₁₂, followed by S₂ × T₁₀ (23.67 g), while the minimum value (16.00 g) occurred under S₁ × T₁. During the year 2024, although numerical differences were observed among treatment combinations, the interaction was statistically non-significant; therefore, these differences should not be interpreted as statistically superior treatment combinations. The overall response nevertheless showed that wider spacing and improved nutrient management were associated with greater fruit weight. Palm et al., (2024) [13] also emphasized that fruit size and reproductive performance vary substantially in Trapa, and larger-fruited types can contribute substantially to productivity. Hence, wider spacing (S₂) and nutrient treatment T₁₂ were individually favourable for increasing fruit weight, while their interaction was statistically important only during the year 2023.

The data presented in [6] , who observed considerable variation in fruit volume among water chestnut germplasm under central Uttar Pradesh conditions. Nutrient management treatments significantly influenced average fruit volume during both years. During the year 2023, the maximum fruit volume (20.95 ml) was recorded under T₁₂ (Nano zinc fortified FYM), followed by T₁₀ (20.45 ml), T₇ (20.10 ml) and T₉ (19.55 ml). The minimum fruit volume (14.00 ml) was recorded under T₁ (Control).

During the year 2024, T₁₂ again recorded the maximum fruit volume (20.80 ml), followed by T₁₀ (19.90 ml), T₇ (19.20 ml) and T₉ (19.10 ml), whereas the minimum value (14.43 ml) was recorded under T₁.

The higher fruit volume under T₁₂ and T₁₀ may be attributed to improved nutrient availability and enhanced physiological activity during fruit development. Organic nutrient sources can contribute to improved nutrient availability and soil fertility, while micronutrients such as zinc are important for enzyme activity, growth regulation and reproductive development. Puste et al., (2005) [14] demonstrated that integrated organic and inorganic nutrient management significantly influenced water chestnut productivity and associated quality characteristics.

The interaction between spacing and nutrient management treatments was significant during both years. In the year 2023, the highest fruit volume (21.20 ml) was recorded under S₂ × T₁₂, followed by S₂ × T₁₀ (20.80 ml), whereas the lowest value (13.50 ml) was recorded under S₁ × T₁. During the year 2024, S₂ × T₁₂ again recorded the maximum fruit volume (21.00 ml), followed by S₂ × T₁₀ (19.80 ml), while the minimum value (12.67 ml) was recorded under S₁ × T₁. The consistent superiority of S₂ × T₁₂ indicates that wider spacing combined with nano-zinc-fortified FYM provided a favourable environment for fruit enlargement. This response is consistent with the broader evidence that fruit size and physical characteristics of Trapa vary with growing conditions and genotype. Palm et al., (2024) [13] documented substantial variation in fruit dimensions and fresh fruit weight across Trapa populations, while Dwivedi et al., (2010) [6] reported marked variation in fruit volume among T. natans var. bispinosa germplasm. Thus, wider spacing (S₂), particularly in combination with T₁₂, was most favourable for increasing fruit volume under the conditions of the present investigation.

Conclusion

The results of the present investigation demonstrated that plant spacing and nutrient management played important roles in improving the fruit characteristics of water chestnut (Trapa natans var. bispinosa Roxb.). Across the evaluated fruit parameters, wider spacing (S₂) generally resulted in superior fruit development compared with closer spacing (S₁), as reflected by higher number of fruits per rosette, fruit length, fruit width, fruit weight and fruit volume. Among the nutrient management treatments, nano zinc fortified FYM (T₁₂) and nano zinc fortified Jeevamrut (T₁₀) consistently performed better than the control and other nutrient regimes, particularly for fruit size, weight and volume. The control treatment (T₁) generally recorded the lowest values for the studied fruit attributes, indicating the beneficial effect of adequate and balanced nutrient availability on reproductive growth and fruit development. The interaction of spacing and nutrient management further indicated that wider spacing combined with improved nutrient regimes, particularly S₂ × T₁₂ and S₂ × T₁₀, provided favourable conditions for enhanced fruit development. Overall, the findings suggest that wider plant spacing in combination with nano zinc-enriched organic nutrient sources can be considered a promising management strategy for improving the quality-related fruit attributes of water chestnut under the conditions of the present study.

References

1. Alary R, Buissonade C, Joudrier P, Gautier MF. Detection and discrimination of cereal and leguminous species in chestnut flour by duplex PCR. European Food Research and Technology. 2007;225(3):427-434.
2. Anonymous. Addressing water chestnut in CNY. Oneida Lake and Watershed Management Plan Project News (Central New York Regional Planning and Development Board, Syracuse, NY). 2002;Fall:3-4.
3. Bhatiwal S, Jain A, Chaudhary J. Trapa natans L. (water chestnut): an overview. International Journal of Research in Pharmacy and Science. 2012;3:31-32.
4. Chowdhury SR, Sahoo N, Verma HN. Growth behaviour and yield of five water chestnut varieties under waterlogged condition. 2003.
5. Dimkpa CO, Bindraban PS. Nanofertilizers: New products for the industry? Journal of Agricultural and Food Chemistry. 2018;66(26):6462-6473.
6. Dwivedi DH, Babu M, Lata R, Shringar R. Genetic variability studies in water chestnut (Trapa natans var. bispinosa Roxb.) under Central Uttar Pradesh conditions. In: XXVIII International Horticultural Congress on Science and Horticulture for People (IHC2010): III International Symposium; 2010. p. 433440.
7. El-Saadony MT, ALmoshadak AS, Shafi ME, Albaqami NM, Saad AM, El-Tahan AM, et al. Vital roles of sustainable nano-fertilizers in improving plant quality and quantity-an updated review. Saudi Journal of Biological Sciences. 2021;28(12):7349-7359.
8. Jana BR, Bhatt BP, Singh IS, Idris M. A study on commercial cultivation and storage of water chestnut (Trapa natans L.) under wetland ecosystem of North Bihar, India. Journal of Applied and Natural Science. 2019;11(2):528.
9. Jana H. Water Caltrop: A potential crop of waterbodies. Rastriya Krishi. 2016;11(2):7-11.
10. Khan S, Zahoor M, Khan RS, Ikram M, Islam NU. The impact of silver nanoparticles on the growth of plants: The agriculture applications. Heliyon. 2023;9(6).
11. El-Saadony MT, Saad AM, Soliman SM, et al. The role of nano-fertilizers in improving plant quality and productivity. Saudi Journal of Biological Sciences. 2021;28(12):7349-7366.
12. Kumar Y, Tiwari KN, Singh T, Latare AM, Kumar O, Singh SK, et al. Nano fertilizers for sustainable crop production, higher nutrient use efficiency and enhanced profitability. Indian Journal of Fertilisers. 2021;17(11):1209-1225.
13. Palm N, Franzaring J, Schweiger AH. International Biological Flora: Trapa natans: No. 5. Journal of Ecology. 2024;112(10):2386-2420.
14. Puste AM, Sarkar PK, Das DK. Balanced nitrogen economy as a flexible strategy on yield stabilizing and quality of aquatic food crops in wetland ecosystem. Science in China Series C: Life Sciences. 2005;48(Suppl 2):980-987.
15. Raliya R, Saharan V, Dimkpa C, Biswas P. Nanofertilizer for precision and sustainable agriculture: Current state and future perspectives. Journal of Agricultural and Food Chemistry. 2018;66(26):64876503.
16. Takano A, Kadono Y. Allozyme variations and classification of Trapa (Trapaceae) in Japan. Aquatic Botany. 2005;83(2):108-118.
17. Tarafdar JC, Raliya R, Mahawar H, Rathore I. Development of zinc nano-fertilizer to enhance crop production in pearl millet (Pennisetum americanum). Agricultural Research. 2014;3(3):257-262.
18. Tsuchiya T, Iwakuma T. Growth and leaf life-span of a floating-leaved plant, Trapa natans L., as influenced by nitrogen flux. Aquatic Botany. 1993;46(3-4):317-324.