Belowground carbon stocks of 21-year-old Grevillea robusta stand in the humid tropics of Keralawca2014-1148 Samritika Thakur 1,*Kunhamu T. K. 1Mohan Kumar B. 2Sudhakara K. 1 1Silviculture and Agroforestry, Kerala Agricultural University, Thrissur, Thrissur, 2Agronomy and Agroforestry, ICAR, New Delhi, India
Tree root biomass production and turnover play key role in improving soil productivity in land use systems involving woody perennials. Also, tree roots provide substantial contribution to the soil carbon pool which however varies with tree species and management regimes. A field study was conducted at Vellanikkara, Kerala, India in a 21-year-old Grevillea robusta stand (460 trees ha-1) to quantify the extent of belowground biomass production and carbon sequestration along with soil carbon stocks. A total of 18 trees were excavated using destructive sampling. The study also explored the distribution of C in the various root size fractions and at various soil depths up to one meter. Mean tree root biomass production based on diameter class ranged from 12.94 to 59.81 kg tree-1 with a mean annual increment (MAI) varying from 0.62 to 2.85 kg tree-1 yr-1 while root biomass production at the stand level was 18.45 Mg ha-1 with a MAI of 0.88 Mg ha-1 yr-1. Based on the diameter class elemental carbon storage in the belowground root biomass of a mean tree varied from 5.58 to 23.58 kg tree-1. Grevillea robusta stand sequestered 8.04 Mg C ha-1 and 77.45 Mg C ha-1 in the root system and soil respectively. On the whole, the net belowground carbon sequestration (soil + roots) was 80.28 Mg C ha-1. The high root biomass and C sequestration suggest the potential to enrich the soil nutrient status of polyculture systems involving Grevillea robusta. Tree tap roots by virtue of their higher biomass and longer soil residence time may greatly contribute to belowground C sequestration.