Effect of organic manures and biofertilizers on growth, yield and quality of turmeric (Curcuma longa)

Introduction

Turmeric (Curcuma longa L.) is among the most commercially valuable spice crops, prized for curcumin content that drives culinary and pharmaceutical demand [1] . Global production exceeded 1.2 million tonnes in 2022, with India and China accounting for over 85 % [2] . The crop responds strongly to soil organic matter and microbial rhizosphere activity, making it well suited to organic management [3] . Farmyard manure and vermicompost supply slow-release nitrogen and improve soil structure, while Azospirillum fixes atmospheric nitrogen and PSB solubilizes bound phosphorus [4,5] . Workers have reported 20-40% yield gains when organic manures are combined with biofertilizers [6,7] , attributed to improved nutrient availability and enhanced root colonization [8] . However, most trials were conducted in tropical India, and data from subtropical China remain limited [9] . This research tested nine nutrient combinations to identify the most effective organic-biological package for turmeric under Nanjing conditions.

Material and methods

Research area and material

The field experiment was conducted at the Horticulture Research Station of Nanjing Agricultural University (32.0603°N, 118.8503°E) during April 2022 to January 2023. The site has a humid subtropical climate with mean annual temperature of 15.7°C and rainfall of 1,062 mm. Soil was a yellow-brown earth with pH 6.4, organic carbon 1.87%, available N 186.3 kg/ha, available P 24.7 kg/ha, and available K 148.2 kg/ha [10] . The turmeric variety Nanjing Local was planted using mother rhizome seed pieces of 25-30 g weight at 45 cm × 25 cm spacing.

Methods

Nine treatments in RCBD with three replications: T1-Control, T2-FYM (20 t/ha), T3-Vermicompost (7.5 t/ha), T4-Neem cake (2.5 t/ha), T5-Azospirillum (5 kg/ha), T6-PSB (5 kg/ha), T7-FYM + Azospirillum, T8-VC + PSB, and T9-FYM + VC + Azospirillum + PSB. Plot size was 4 m × 3 m. Organic manures were incorporated 15 days before planting; biofertilizers applied as rhizome dip and soil application at 30 and 60 DAP [11] .

Growth was recorded at 180 DAP. Yields were taken at harvest (270 DAP). Curcumin was estimated by spectrophotometry at 425 nm [12] and oleoresin by Soxhlet extraction. Data were analysed by ANOVA in R 4.3.1 with LSD at P = 0.05 [13] .

Result

Comprehensive interpretation

T9 was clearly superior across all parameters (Table 1). Plant height reached 96.8 cm (57.4% above control). Fresh rhizome yield at 28.3 t/ha was 99.3% above control and 12.7 % above T8. Curcumin peaked at 5.84% and oleoresin at 14.21 % in T9. Among single inputs, vermicompost (T3) outperformed FYM (T2) and neem cake (T4) for both yield and quality. A strong positive linear relationship existed between rhizome yield and curcumin (r = 0.987, p< 0.01) (Figure 1). Treatments improving yield simultaneously enhanced curcumin, indicating that biomass and secondary metabolite pathways aren't competing under these nutrient regimes. Integrated treatments had both the highest medians and tightest spread for plant height and tillers (Figure 2). The control was most limited, while organic-alone fell intermediate between biofertilizer-alone and integrated groups.

Discussion

The 99.3% yield increase under T9 exceeds the 20-40 % gains reported in Indian trials [6,7] , likely because the unfertilized control in Nanjing's lower-organic-matter soils represented a more severe nutrient deficit. T9 outyielded T7 by 17.4 % and T8 by 10.1 %, suggesting the four-component combination captured benefits that two-component mixes missed notably combined Nfixation, P-solubilization, and humus-building [4,8] . The strong yield-curcumin correlation (r = 0.987) is consistent with Sandeep et al. [7] , attributed to enhanced phenylpropanoid pathway activity under improved nutrition. Vermicompost outperformed FYM alone, possibly due to higher humic acid content and more favourable C:N ratio [5] . These results indicate that organic-biological integration is viable for quality turmeric production in subtropical China.

Conclusion

Combined application of FYM, vermicompost, Azospirillum, and PSB (T9) produced the highest turmeric yield (28.3 t/ha) and curcumin content (5.84 %), representing a 99.3% and 71.3 % improvement over the unfertilized control. Rhizome yield and curcumin were strongly correlated (r = 0.987). Among single inputs, vermicompost was superior to FYM and neem cake. The integrated organic-biological approach merits adoption for quality turmeric production in the Nanjing region.

References

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