Coarse root biomass, carbon, and nutrient stock dynamics of different stem and crown classes of silver oak (Grevillea robusta A. Cunn. ex. R. Br.) plantation in Central Kerala, India

• Published in: Agroforestry systems 2015-10, Vol.89 (5), p.869-883
• Main Authors: Thakur, Samritika, Kumar, B. Mohan, Kunhamu, T. K.
• Format: Article
• Language: English
• Subjects: Agriculture; Agroforestry; Biogeochemistry; Biomass; Biomass energy; Biomedical and Life Sciences; Carbon sequestration; Forestry; Grevillea robusta; Life Sciences; Nutrient cycles; Nutrient dynamics; Organic carbon; Roots; Soil profiles; Trees
• ISSN: 0167-4366; 1572-9680
• DOI: 10.1007/s10457-015-9821-y

Belowground biomass production is a vital process that contributes to carbon sequestration. The relative proportion of belowground carbon allocation, however, varies with species, age, ecoclimatic conditions and crown dominance categories of trees. Here we compare the coarse root biomass and nutrient stocks of different stem size/crown class categories of 21-year-old Grevillea robusta stand in Kerala, India and the soil carbon/nutrient stocks of the G. robusta stand with an adjoining unplanted site. Root systems of 18 trees of three stem diameter/crown classes (5–15, 15–25, and >25 cm: suppressed + intermediate, co-dominant and dominant crown classes, respectively) were excavated and their coarse root biomass estimated. Mean coarse root biomass ranged from 12.94 to 59.81 kg tree −1 with production of 18.45 Mg ha −1 (mean annual increment = 0.88 Mg ha −1  year −1 ). Medium sized trees (co-dominant) had the highest root:shoot ratio, followed by intermediate and suppressed crown classes and the dominant trees had the least values, implying persistence strategies of the suppressed, intermediate and co-dominant trees under conditions of resource limitation. Coarse roots accounted for 8.04 Mg ha −1 C while soil organic carbon pool (0–100 cm) was 77.56 Mg ha −1 C, as against 66.04 Mg ha −1 for contiguous treeless plots. Coarse roots accrued 24.87 kg N, 1.66 kg P and 21.06 kg K per ha. G. robusta stand exhibited higher NPK stocks in the lower soil layers, compared to treeless controls. Deep rooted G. robusta trees (>1.0 m) thus have the potential to enrich lower layers of the soil profile through plant cycling of nutrients, which is important for on-site nutrient conservation and resource sharing with associated field crops.