Effect of treated and untreated sewage water irrigation on soil properties, nutrient uptake and performance of China aster (Callistephus Chinensis L.)

Introduction

Increasing scarcity of freshwater resources and growing demand for irrigation water have encouraged the reuse of wastewater in agriculture. Sewage water contains appreciable quantities of plant nutrients and organic matter and therefore has potential as an alternative source of irrigation water. However, its quality varies considerably depending on its origin and degree of treatment. Application of untreated or inadequately treated sewage water may increase soil salinity and nutrient loading and may also introduce potentially toxic elements and microbial contaminants into the soil-plant system. Therefore, proper assessment of wastewater quality and its effects on crop and soil properties is essential for safe and sustainable agricultural reuse (Ayers and Westcot, 1985; who, 1989; Jaramillo and Restrepo, 2017) [1,2] . Several studies have reported beneficial effects of wastewater irrigation on crop growth and soil fertility due to the additional supply of nitrogen, phosphorus, potassium and other nutrients. Al-Suhaibani et al. (2021) [3] reported that treated wastewater influenced plant growth and nutrient uptake, while Alvarez-Holguin et al. (2022) [4] observed improved chlorophyll content and biomass production under treated wastewater irrigation. Gatta et al. (2016) [5] demonstrated the potential of treated municipal wastewater for irrigation of globe artichoke without adverse effects on crop production under the conditions studied. These findings indicate that suitably treated wastewater can provide both irrigation water and supplementary nutrients to horticultural crops. Despite these benefits, repeated application of wastewater can alter soil properties. Mapanda et al. (2005) [6] reported increased concentrations of heavy metals in soils receiving wastewater irrigation, while Mohammad et al. (2003) [7] observed changes in soil and crop properties following long-term wastewater application.

Thus, wastewater reuse requires a balance between its agronomic benefits and the possible risks associated with salts, nutrients and trace elements. China aster (Callistephus chinensis L.) is an important annual floricultural crop cultivated for loose flowers, cut flowers, garlands and ornamental purposes. Since the harvested produce is not directly consumed as food, floricultural crops provide a suitable system for evaluating wastewater reuse. However, information on the comparative effects of untreated and treated sewage water on the growth, flowering, flower yield, nutrient accumulation and postharvest soil properties of China aster under field conditions is limited. This is particularly relevant in water-scarce regions where alternative irrigation sources are required.

Therefore, the present study was undertaken to evaluate the effects of treated and untreated sewage water irrigation on water quality, growth, flowering, flower yield and quality, plant nutrient accumulation and postharvest soil properties of China aster variety Arka Archana under field conditions. The study also aimed to identify a suitable sewage-water irrigation regime for maintaining crop productivity while minimizing potential adverse effects on soil quality.

Materials and Methods

Experimental site and crop

The experiment was conducted at the College of Horticulture, Tamaka, Kolar, Karnataka (13°12′ N latitude and 78°17′ E longitude), during the summer season of 2023-24. The site falls in the eastern dry zone (Zone 5) of Karnataka. The soil was red sandy loam, initially slightly alkaline (pH 7.64) with EC 0.75 dS m -1 and low organic carbon (0.42%), available N (146.85 kg ha -1 ) and available K 2 O (132.86 kg ha -1 ). China aster variety Arka Archana was procured from ICAR-IIHR Bengaluru.

Experimental design and treatments

The experiment was laid out in randomized complete block design with seven treatments and three replications. Each plot measured 2.4 × 2.4 m (5.76 m²), with plants spaced at 30 × 30 cm. Seedlings were transplanted during March 2024. Alternate borewell water + treated sewage water All treatments received 20 t FYM ha -1 and 180:120:60 kg ha -1 N:P 2 O 5 :K 2 O according to the UHS Bagalkot package of practices.

Raw sewage was collected from the inlet and treated sewage from the outlet of the sewage treatment plant at the College of Horticulture, Kolar.

Water, plant and soil analysis

Borewell, treated sewage and untreated sewage waters were analyzed for suspended solids, dissolved solids, BOD, COD, E. coli, pH, EC, TDS, carbonate, bicarbonate, chloride, nitrate, sulphate, Ca, Mg, Na, K, micronutrients and selected heavy metals. Irrigation suitability was assessed using EC, TDS, potential salinity, residual sodium carbonate, residual sodium bicarbonate, sodium percentage, sodium ratio, sodium adsorption ratio, permeability index and magnesium adsorption ratio. Growth observations included plant height and SPAD chlorophyll at 30, 60 and 90 days after transplanting, primary and secondary branches, plant spread and total dry matter. Flowering observations included days to first bud appearance and 50% flowering. Yield observations included average flower diameter, 100-flower fresh weight, flower yield plant -1 and hectare -1 , shelf life and vase life. Plant samples were analyzed for N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu and B. Postharvest soil samples (0-15 cm) were analyzed for bulk density, maximum water-holding capacity, pH, EC, organic carbon, available N, P 2 O 5 , K 2 O, exchangeable Ca and Mg, available S, DTPA-extractable Fe, Mn, Zn and Cu, hot-water-soluble B, and total bacterial, fungal and actinobacterial populations.

Statistical analysis

The experimental data were analysed using Microsoft Excel and OPSTAT statistical software. The experiment was conducted with three replications. Treatment means were compared using the critical difference (CD) at the 5% level of probability.

Results and Discussion

Characteristics and irrigation quality of water sources

Untreated sewage water had the highest suspended solids (23 mg L -1 ), dissolved solids (868 mg L -1 ), BOD (4 mg L -1 ), COD (30 mg L -1

), E. coli (10 MPN 100 mL -1 ), pH (8.24), EC (378 µmhos cm -1 ) and TDS (242 mg L -1 ). Treated sewage water showed intermediate values, including 17 mg L -1 suspended solids, 776 mg L -1 dissolved solids, BOD 2 mg L -1 , COD 10 mg L -1 , E. coli 2 MPN 100 mL -1 , pH 7.80, EC 279 µmhos cm -1 and TDS 179 mg L -1 . Borewell water recorded the lowest values for most of these parameters (Table 2). Sewage waters also contained higher concentrations of Ca, Mg, Na and K and higher concentrations of Fe, Mn, Zn and Cu than borewell water. Pb, Ni, Cd and Cr were not detected in borewell water but were detected in treated and untreated sewage water. Thus, treatment reduced several quality indicators relative to raw sewage, but did not eliminate the presence of all trace elements. The irrigation indices showed that EC classified borewell water as low-salinity and treated and untreated sewage water as medium-salinity water, while SP, SR, SAR, PI and MAR were within the ranges. The study consequently identified treated sewage water as the more balanced wastewater source for irrigation. plant spread. Total dry matter was 32.07 g plant -1 under raw sewage and 27.17 g plant -1 under treated sewage compared with 17.10 g plant -1 under borewell water. These results are in agreement with the findings of Alvarez-Holguin et al. (2022) [4] in barley and Kumar et al. (2023) [8] in Datura innoxia.

Flower yield and quality

Raw sewage irrigation produced the highest 100-flower fresh weight (168.03 g), flower yield per plant (66.98 g) and flower yield per hectare (6.44 t ha -1 ). Treated sewage irrigation produced 155.19 g, 59.75 g plant -1 and 5.28 t ha -1 , respectively. Borewell irrigation recorded 125.38 g, 42.13 g plant -1 and 2.76 t ha -1 . Average flower diameter did not differ significantly. Shelf life differed significantly and was highest under raw sewage water (3.17 days), followed by treated sewage water (2.83 days), while borewell water recorded 2.17 days. Vase life did not differ significantly and ranged from 6.33 to 7.67 days. The increased yield under sewage irrigation is consistent with the greater nutrient supply and vegetative growth observed in the sewage water treatments. These results are in line with results obtained by Rinu et al. (2024) [9] in China aster. Al-Huqail et al. (2023) [10] found that sewage sludge amendments enhanced the marigold flower yield, supporting the role of wastewater nutrients in floriculture.

Plant nutrient concentration

Raw sewage irrigation has the highest concentrations of the major nutrients (Fig. 1) N (6.47%), P (0.86%) and K (4.26%), compared with 3.21, 0.43 and 2.23%, respectively, under borewell water. It also produced the highest Ca (1.43%), Mg (1.01%) and S (0.51%). Among micronutrients, Mn, Zn, Cu and B reached 135.58, 53.88, 20.31 and 78.59 ppm, respectively, under raw sewage irrigation. Treated sewage generally produced intermediate concentrations. Iron did not differ significantly among treatments. The results indicate that sewage water supplied appreciable nutrients to the crop. At the same time, the greater accumulation of micronutrients and trace metals in sewagewater-irrigated systems supports the need for periodic monitoring when sewage water is used repeatedly, even for non-food crops. These results are corroborated with findings from previous studies that have observed increased micronutrients concentration in plants irrigated with sewage water, highlighting the potential of sewage effluents as a source of trace elements essential for plant growth (Rodrigues et al., 2024) [11] .

Postharvest soil properties influenced by different sewage irrigation levels

Bulk density and maximum water-holding capacity did not differ significantly among treatments, although raw sewage irrigation reduced bulk density to 1.34 Mg m -3 and increased maximum water-holding capacity to 43.56% (Table 5). Soil pH was also not significantly affected and ranged from 6.74 to 7.79. Raw sewage irrigation resulted in the highest EC (1.45 dS m -1

) and organic carbon (0.72%), while borewell water resulted in 0.84 dS m -1 and 0.54%, respectively. Available N, P 2 O 5 and K 2 O were also highest under raw sewage water (412.74, 66.95 and 263.45 kg ha -1 ), with treated sewage giving more moderate values (238.83, 38.69 and 147.89 kg ha -1 ). Exchangeable Ca and Mg and available S were enhanced by sewage irrigation. Raw sewage produced 6.16 cmol(p + ) kg -1 Ca, 3.41 cmol(p + ) kg -1 Mg and 28.63 ppm S compared with 0.64, 0.40 and 14.94, respectively, under borewell irrigation. DTPA-extractable Fe, Mn, Zn and Cu and hot-water-soluble B were also significantly higher under raw sewage irrigation. Treatments with treated sewage water and mixed irrigation maintained moderate enrichment, indicating that sewage water acts as a rich source of micronutrients in addition to macronutrients (Mapanda et al., 2005; Sharma et al., 2007) [6,12] .

Soil microbial populations

Sewage water irrigation increased postharvest microbial populations. Raw sewage produced 432 × 10 7 CFU g -1 bacteria, 17 × 10 4 CFU g -1 fungi and 71 × 10 5 CFU g -1 actinobacteria, compared with 39 × 10 7

, 9 × 10 4 and 9 × 10 5 CFU g -1 , respectively (Table 6), under borewell water. Treated sewage water also increased microbial counts (368 × 10 7 bacteria, 15 × 10 4 fungi and 54 × 10 5 actinobacteria), although values were lower than those under raw sewage. This suggests that organic matter and nutrient inputs associated with sewage stimu-lated soil microbial activity during the experimental period. Biological parameters such as bacteria, fungi, and actinobacteria populations were strongly influenced by sewage water treatments. Application of 100 per cent untreated sewage water irrigation supported significantly higher microbial counts compared to borewell water, reflecting the contribution of organic matter and nutrients to microbial growth. However, treated sewage water and mixed irrigations also enhanced microbial activity, though to a lesser extent than raw sewage water. These results suggested that sewage water irrigation promotes a more biologically active soil environment, which could improve nutrients cycling and soil health (Mohammad et al., 2003) [7] .

Conclusion

Treated and untreated sewage water significantly altered China aster growth, flowering, yield, plant nutrient concentration and postharvest soil fertility compared with borewell irrigation. Raw sewage water produced the maximum plant growth and flower yield, reaching 6.44 t ha -1 , but also resulted in the greatest accumulation of salts, organic carbon, available nutrients and micronutrients in the soil. Treated sewage water produced a substantial yield of 5.28 t ha -1 while maintaining lower contaminant and salinity-related loads than raw sewage water. Treated sewage water therefore shows potential as a supplementary irrigation source for China aster. Long-term field studies are required before recommending continuous use, with particular emphasis on salinity, heavy-metal accumulation and microbiological safety.

Acknowledgement

AcknowledgmentsThe authors sincerely acknowledge the support and facilities provided by the College of Horticulture, Bengaluru and College of Horticulture, Kolar for conducting the present study.

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