Zinc Adsorption–Desorption Behavior and Sequential Extractable Pools in Sugarcane-Based Cropping Systems of Western Indo-Gangetic Plain

The fractionation of Zn and its adsorption at soil matrix are crucial for careful management to attain the sustainability in Western Indo-Gangetic Plain region. To fulfil the objectives, the soil at the three depths (15, 30 and 45 cm) was collected from the farmers field in 2021–2022 from five different cropping systems (sugarcane–ratoon–wheat, sugarcane–ratoon–wheat–rice, sugarcane–mustard–ratoon–rice, sugarcane–cucumber–ratoon, and sugarcane–ratoon–potato) which are practicing the same cropping sequence since from 12 years and a reference soil which remains uncultivated from last 50 years. The soil was sandy loam to sandy clay loam in texture with BD 1.33 gm/cc and 22% water holding capacity. The pH and EC revealed neutral-to-moderate alkaline, low-to-medium organic carbon (0.59 mg/kg), medium-to-high Olsen’s phosphorous (30.14 mg/kg) and low to sufficient DTPA-Zn (1.82 mg/kg). Sugarcane–ratoon–wheat among cropping system revealed highest total (86.94 mg/kg), residual (67.95 mg/kg) and sequentially extractable Zn (19 mg/kg) fractions which implies that Zn is retained and released for longer duration. The retention of Zn at the soil matrix was further clarified by sorption mechanism which invoked maximum %Zn sorption occurred at S₁ (49.17%). The sorption phenomena of Zn on soils are spontaneous (ΔG is negative) and are physically adsorbed (E < 8 kJ/mol). Monolayered-Zn sorption depicted from Langmuir Isotherm constants (Q_o = 8.67 µg/gm, K_L = 0.25 ml/µg) occurs at silt (r² = 0.813*) and calcium carbonate surface (r² = 0.943*) of top soil, while at subsurface multilayered sorption from Freundlich isotherm constant (K_F = 3.07 µg/gm, n = 6.27 gm/ml) is pH-dependent (r² = 0.910*) and occurs at clay surface (r² = 0.812*).