Root development and soil carbon stocks of tropical pastures managed under different grazing intensities

Abstract

Grasslands may act as a carbon (C) sink or C source depending on how they are managed. Soil C stocks, root biomass, root length, root length density and soil organic C concentrations were assessed on pastures of elephant grass ( Pennisetum purpureum ) managed under different post-grazing stubble heights and signal grass ( Brachiaria decumbens ) managed under different stocking rates. Soil samples were collected in 20-cm layers down to 1-m soil depth. Neither stubble height nor stocking rate had any significant effects on root parameters. Both the root system and C stocks declined in both pastures with increasing soil depth. Root biomass in the 0–20 cm layer contained 2.84 and 2.04 t C/ha, declining to 0.39 and 0.64 t C/ha at 80–100 cm for elephant grass and signal grass, respectively. Signal grass had greater root development deeper in the soil than elephant grass pastures, possibly due to its greater tolerance of Al toxicity and acidity. Total soil C stocks were greater for signal grass than for elephant grass (358 vs. 214 t C/ha, respectively). Keywords: Carbon sequestration, nutrient cycling, soil nutrients, stocking rate, tropical grass. DOI: 10.17138/TGFT(2)254-261