Abstract
Five field experiments were conducted during 2007–2009 to investigate the effects of cultural practices (planting density, date of planting and harvest, urea and GA₃ foliar spray, and shoot clipping) on morphological and growth characters of canopy to increase leaf and biomass yield in two Indigofera spp. viz., I. tinctoria and I. suffruticosa. Each of the five experiments was carried out in two consecutive years. Seeds of the two species were sown on six consecutive planting dates (PDs) viz., 15–Jan, 15–Mar, 15–May, 15–Jul, 15–Sep and 15–Nov. Seeds sown on 15–Jan, 15–Mar and 15–May produced higher leaf fresh biomass (11.16 t ha⁻¹, average over the above three PDs compared to 2.62 t ha⁻¹, average over rest of the PDs). Total dry mass (TDM) yield followed a trend similar to that of fresh leaf biomass (5.80 vs 2.05 t ha⁻¹). Density effect on morphological characters of canopy was investigated using 16, 20, 27, 40, 60, 80, 100 and 120 plants m⁻². Optimum planting density for leaf biomass yield was not obtained but higher planting density (80–120 plants m⁻²) produced increased leaf fresh biomass yield (16.15, 18.98 and 18.01 t ha⁻¹ for 80, 100 and 120 plants m⁻² compared to 10.25 t ha⁻¹ for the rest of densities). Biomass yield was also increased by promoting leaf growth using urea and GA₃ foliar spray. Five concentrations of urea (0.00, 0.25, 0.50, 1.00 and 1.50%) and six GA₃ (0, 25, 50, 75, 100 and 125 mg L⁻¹) concentrations were employed. It was observed that 1% urea and 100 mg L⁻¹ GA₃ appeared better and increased leaf fresh biomass (8.57 and 6.33 t ha⁻¹ for 1% urea and 100 mg L⁻¹ GA₃, respectively compared to 7.50 and 5.45 t ha⁻¹ for the rest of urea and GA₃ doses, respectively). Increased leaf biomass yield was also obtained by clipping the mainstem apex at 30 cm height from the ground following 1% urea spray (9.95 t ha⁻¹ for 1% urea, average over two years vs 6.70 t ha⁻¹ for control, average over two years). Indigo content was determined by extracting shoot harvested at 2, 3, 4, 5 and 6 months old plant from sowing, and results indicated that 4 to 5 months old plant yielded higher Indigo content. It appeared that all the canopy characters viz., branch and leaf production, LAI and other morphological attributes were increased at densities 80–120 plants m⁻² grown from seeds sown between 15–Jan and 15–May, leading to increased leaf fresh biomass and TDM yield. Fresh leaf biomass yield was also increased by foliar spraying 1% urea on clipped shoot at 30 cm height and allowing regrowth afterwards. Indigo extracted using fresh leaves and shoot from 4 to 5–month old plants were higher (5.73 g kg⁻¹ fresh weight) than that obtained from other aged plants (3.42 g kg⁻¹ fresh leaf weight, average over ages and years). Higher indigo dye yield was obtained when the shoots were harvested after 4 to 5 months from sowing. It might be concluded that proper cultural practices improved canopy characters, biomass and dye yield in Indigofera spp.