Soil Nutrient Dynamics under Horse Gram Intercropping in Melia dubia–Based Agroforestry in the Central Dry Zone of Karnataka

Agroforestry is a sustainable land-use system that integrates trees and crops, enhancing soil fertility and productivity, particularly in semi-arid regions. This study evaluated the impact of intercropping Macrotyloma uniflorum (horse gram) in Melia dubia (Malabar neem)-based agroforestry on soil nutrient status in the central dry zone of Karnataka. Soil samples were collected from five depths (0-20 cm, 20-40 cm, 40-60 cm, 60-80 cm, and 80-100 cm) before and after harvesting, and analyzed for key soil parameters using a response index approach. The intercropping significantly reduce soil pH (from 7.2 to 6.8), with a response index of -4.8%, due to organic acid release from decomposed litter. Electrical conductivity (EC) decreased from 0.42 dS m⁻¹ to 0.35 dS m⁻¹, with a response index of -16.6%, indicating improved soil structure. Soil organic carbon (SOC) increased from 0.48% to 0.62%, with a response index of +29.2%, attributed to organic matter accumulation. Available nitrogen (N) improved from 215 kg ha⁻¹ to 265 kg ha⁻¹, showing a response index of +23.2%. Similarly, available phosphorus (P₂O₅) and potassium (K₂O) increased from 16.8 to 22.5 kg ha⁻¹ and 240 to 280 kg ha⁻¹, with response indices of +33.9% and +16.7%, respectively, largely due to nutrient cycling and organic matter decomposition. Statistical analysis indicated improvements in soil fertility under intercropped conditions compared to sole cropping. These findings highlight that M. dubia-based agroforestry with horse gram enhances soil nutrient retention and fertility, offering a viable strategy for sustainable agriculture in resource-limited dryland agriculture