Tree spacings and nutrient sources effect on turmeric yield, quality, bio-economics and soil fertility in a poplar-based agroforestry system in Indian Himalayas

The tree-based farming system is one of the finest options for crop diversification, ecological stabilisation and economic upliftment in the Indian Himalayan regions. Keeping this scenario in mind, an on-field experiment was conducted to assess the effect of Populus deltoides ‘G-48’ tree spacings (S₁:6 m × 4 m, S₂:4 m × 4 m) with open-field condition (S₀) and different nutrient sources [T₁:Control; T₂:100% RDN (recommended dose of nitrogen); T₃:75% RDN + 25% FYM (farmyard manure); T₄:50% RDN + 50% FYM; T₅:25% RDN + 75% FYM; T₆:100% FYM; T₇:100% Vermicompost); T₈:Jeevamrut (10%), each replicated thrice] on agronomic performance of Curcuma longa at Solan, India during 2019–2021. The results revealed that C. longa grown under tree spacing S₁ coupled with the application of T₃ treatment showed marked enhancement in growth, quality attributes of C. longa and post-harvest soil nutrient status whereas, yield attributes were better in S₀. The yield of C. longa was curtailed by 22.5 and 31.6%, whereas curcumin content was enhanced by 13.4% and 12.2% under S₁ and S₂, respectively over S₀. The vegetation carbon density (66.38 Mg ha⁻¹), total ecosystem carbon density (119.04 Mg ha⁻¹), and total carbon sequestered (436.47 Mg ha⁻¹) was found to be higher under S₁, whereas soil carbon density (55.68 Mg ha⁻¹) was maximum under S₂ being at par with S₁. Maximum net returns (14,693 US$ ha⁻¹ yr⁻¹) were realised under S₁ tree spacing and T₃ treatment. Overall, the study concluded that in P. deltoids–C. longa system, application of 75% RDN + 25% FYM at 6 m × 4 m spacing of poplar have demonstrated efficacy in getting a better quality of turmeric, maintaining soil fertility, and combating climate change.