CO2, H2O and energy fluxes from chickpea crop grown under residual soil moisture condition in rainfed peninsular India using eddy covariance techniques

Present study is the first to report the ecosystem CO₂, H₂O and energy exchanges (at diurnal, daily and seasonal-scale) from rainfed winter chickpea crop (Cicer arietinum L.), grown under residual soil moisture over semi-arid peninsular India, using eddy covariance system. The available energy to the ecosystem was found to be predominantly partitioned into sensible heat flux (H), except during the peak vegetative stage. Asymmetric response of the daytime (forenoon and afternoon) CO₂ and energy fluxes were observed due to limited soil moisture condition. The peak vegetative stage of the crop i.e., 40–60 Days after Sowing (DAS) showed highest rate of Net Ecosystem CO₂ Exchange (NEE; −9 to −11 μmol m⁻² s⁻¹) and Latent Heat Flux (LE; ∼ 300 W m⁻²). The response of daytime Gross Primary Production (GPP) to light intensity was found to be poor during 1–16 DAS, improved steadily in 17−34 DAS, remained high in 35–69 DAS, and deteriorated thereafter till harvesting (70–106 DAS). The chickpea crop was net CO₂ sink on daily basis during 17–69 DAS. Peak daily NEE of −2.52 gC m⁻² day⁻¹, GPP of 4.2 gC m⁻² day⁻¹ and Evapotranspiration (ET) of 2.38 mm day⁻¹ were observed during the growing season. Over the entire season, rainfed chickpea was found to be a weak carbon sink with cumulative NEE of -32.39 ± 4.21 gC m⁻²; GPP of 163.03 ± 15.04 gC m⁻²; Ecosystem Respiration (Rₑcₒ) of 127.45 ± 12.85 gC m⁻²; ET of 177 ± 18.13 mm. The maximum ecosystem water use efficiency (GPP/ET) and crop coefficient were found to be 1.7 gC m⁻² mm⁻¹ and 0.6 respectively at peak vegetative stage, which are sub-optimal compared to well managed chickpea crop. The results help us to understand the ecosystem processes and exchanges from rainfed winter legume-based cropping system, which intern would significantly contribute in global carbon and moisture budget.