Carbon sequestration and nutrient removal by some tree species in an agrisilviculture system in Punjab, India

Trees have a significant potential to mitigate climate change by sequestering atmospheric carbon in the biomass and underneath soil. An investigation was conducted to quantify the biomass production, C and CO₂ storage in the biomass, nutrient content (N, P and K) and their removal by five tree species (5 x 4 m spacing) namely toon (Toona ciliata), maharukh (Ailanthus excelsa), dek (Melia azedarach), poplar (Populus deltoides) and eucalyptus (Eucalyptus tereticornis) after seven years of growth in an agrisilviculture system (trees intercropped with pearlmillet -wheat rotation) in Punjab. Depthwise (015, 15–30 and 30–45 cm) status of soil organic carbon (OC) and available N, P and K in the surface soil (0–15 cm) were also determined before planting and at the time of harvesting of the trees. The DBH and height of poplar and eucalyptus were significantly higher than the other species after seven years of age. The aboveground (stem, branches and leaves) and belowground (roots) fresh biomass was the lowest (100 and 23 t/ha, respectively) in toon and the highest in eucalyptus (255 and 72 t/ha, respectively), whereas the dry biomass was the lowest (49 and 11.2 t/ha, respectively) in toon and the highest in poplar (134 and 33.2 t/ha, respectively). Carbon sequestration by poplar, eucalyptus, dek, maharukh and toon was 54.9, 48.0, 43.3, 20.8 and 19.1 t/ha, respectively. Similarly, CO₂ storage by these species was 201, 176, 159, 77 and 70 t/ha, respectively. The removal of N by different tree species was in the order of poplar (839 kg/ha)>eucalyptus>dek>maharukh>toon (365 kg/ha). Similarly, the removal of P and K from soil was the lowest (P: 30.3 kg/ha, K: 223 kg/ha) by toon and the highest (P: 107 kg/ha, K: 609 kg/ha) by poplar. Soil OC stock seven years after planting was highest under poplar (7.50 t/ha in 0–15 cm depth) and it was higher by 15.6% over its initial level (6.49 t/ha). Available N, P and K were highest under poplar (137.4 kg/ha), dek (15.29 kg/ha) and toon (189.1 kg/ha), respectively at the end of the experiment. Poplar, eucalyptus and dek had higher biomass production and thus more C and CO₂ sequestration than maharukh and toon.