ABSTRACT Crop and tree compartments cohabit side by side within agroforestry and thus it can possibly induce inherent environmental spatial heterogeneity of soil organic carbon (SOC) and nutrient stocks. Although previous studies largely focused on elucidating agroforestry effects on SOC stocks on spatial scales, its effect on the spatial heterogeneity of nutrient stocks is lacking. Furthermore, little is known about the contrasting effects of short‐ (≤ 10 years) and long‐rotation (≥ 20 years) agroforestry trees on CO 2 sequestration rate, and SOC and nutrient stocks accrual, nor is there any robust comparison. This study evaluated four contrasting AFS (IG‐AF, IJ‐AF, MN‐AF, and TK‐AF‐based) and one adjacent conventional cropland (CL) without trees to elucidate the spatial heterogeneity of SOC concentration, phyto‐availability of nutrients and their stocks, and to quantify SOC stocks in the tree biomass, CO 2 equivalent sequestration rate in soil and biomass. We also propose the measurement of net carbon sequestration of a given AFS. Random cores were collected from topsoil (0–15 cm) and subsoil (15–30 cm) in quintuples from RS and CS of the AFS along with sampling from CL. Allometrics were used for measuring C stocks in the tree biomass. The magnitude of the measured soil properties (pH, POX‐C, SOC, and nutrient concentration) and SOC and nutrient stocks were generally higher ( p < 0.05) at RS than CS. Long‐rotation TK‐AF registered significantly ( p < 0.001) the highest concentration of SOC (9.4 and 8.2 g kg −1 ), POX‐C (315.2 and 241.8 mg kg −1 ), and N (166.1 and 129.4 kg ha −1 ), P (21.0 and 17.4 kg ha −1 ), and K (253.0 and 250.2 kg ha −1 ) availability at RS and CS, respectively, and it also showed the highest TBCS (91.9 Mg ha −1 ) and NCS (109.1 Mg ha −1 ). Conversely, short‐rotation MN‐AF registered significantly the highest CO 2 – e t both in soil (5.4 Mg CO 2 ha −1 y −1 ) and biomass (41.6 Mg CO 2 ha −1 y −1 ). The SOC stock gain over the cropland (Δ SOC ) increased with stand age, with the highest gain noticed at IG‐AF (17.8 Mg ha −1 ) followed by TK‐AF (17.1 Mg ha −1 ). Our results warrant long‐term experimental agroforestry for a higher elevation of SOC stocks with possibly a steady CO 2 sequestration rate to restore the degraded lands in a semiarid environment.
Debnath et al. (Mon,) studied this question.