Field-scale assessment of photosynthetic and reproductive responses of Groundnut (Arachis hypogaea L.) to Deficit Irrigation

Abstract

Groundnut (Arachis hypogaea L.) majorly grown in semi-arid region and productivity highly influenced by drought, particularly during reproductive stages when physiological impairment directly restricts translocation of photosynthates to reproductive sinks. A field experiment was conducted during summer 2025 at the Post Graduate Research Block, UAS Raichur, India in a clay loam soil to quantify the physiological and yield responses of groundnut under different deficit irrigation regimes. The experiment designed in a randomized complete block design with five irrigation treatments based on crop evapotranspiration (ETc): 120% (T1), 100% (T2), 80% (T3), 70% (T4), and 60% (T5), each replicated four times. Physiological parameters including photosynthetic rate (PN), stomatal conductance (GS), and transpiration rate (E) were measured across phenological stages. The results indicate a strong sensitivity of gas exchange attributes to soil moisture availability, particularly during mid-season (90 DAS). The optimal irrigation (T1 and T2) maintained higher PN (maximum 22.81 µmol CO₂ m⁻² s⁻¹), GS (0.2695 mol m⁻² s⁻¹), and E (6.80 µmol H₂O m⁻² s⁻¹), reflecting sustained stomatal aperture, improved mesophyll conductance, and efficient CO₂ diffusion. In contrast, severe deficit treatments (T4 and T5) reduced physiological activity by 15-25%,­ indicating stomatal regulation as a primary drought-avoidance mechanism. Yield responses corresponded closely with physiological trends; T2 recorded superior pod yield (2890 kg ha⁻¹), haulm yield (3592 kg ha⁻¹), and pods per plant (26.10), whereas T5 exhibited a 20-25% reduction in yield, attributable to impaired pod filling and altered source-sink dynamics. Overall, irrigation at 100% ETc optimized physiological efficiency and yield stability, offering a balanced strategy for maximizing productivity and water use efficiency under semi-arid conditions while mitigating drought-induced risks in groundnut cultivation.