Optimizing crop geometry (spacing) and nutrient inputs for sustainable cultivation and conservation of black turmeric (Curcuma caesia Roxb.)

Abstract

A field experiment was conducted to evaluate the influence of crop geometry and nutrient management on the growth, yield, and rhizome traits of black turmeric (Curcuma caesia Roxb.). The study involved three spacing levels (45 × 30 cm, 30 × 30 cm, and 45 × 45 cm) and four nutrient regimes (no NPK, 25 t FYM + 75% NPK, 25 t FYM + 100% NPK, and 125% NPK). Growth attributes were measured at 210 days after sowing, while rhizome yield and its components were assessed at harvest. Spacing and nutrient levels significantly interacted to influence both vegetative performance and rhizome yield. Wider spacing (45 × 45 cm) combined with higher nutrient input enhanced plant stature and leaf traits, whereas closer spacing (45 × 30 cm) with 25 t FYM and 100% NPK (150:125:250 kg NPK ha⁻¹) produced the highest fresh rhizome yield. This treatment also improved mother, primary, and secondary rhizome production. Root tuber weight was greatest under wider spacing, but the highest tuber number occurred under nutrient omission. Overall, a spacing of 45 × 30 cm with integrated application of FYM and balanced NPK fertilization proved most effective for optimizing fresh rhizome yield and improving rhizome quality. These results highlight the importance of combining appropriate crop geometry with integrated nutrient management to enhance the sustainable cultivation and conservation of black turmeric, a valuable medicinal crop.