Spatial variation in soil carbon stocks under a miscanthus crop

Soils play an important role in the sequestration of soil carbon. Land management uses such as afforestation, grassland management etc can play a vital role in the mitigation of carbon from the atmosphere. Bioenergy crops are not only considered carbon neutral but may enhance the amount of C sequestered in the soils over time. In Ireland, field trials conducted using Miscanthus grass have estimated the soil organic carbon sequestration rate to be 0.6 t C ha-1.This study aims to investigate the spatial and depth variability of soil carbon stocks under a bioenergy crop and the potential to detect changes in soil carbon stocks using direct sampling techniques There is a need to develop sampling strategies that will enable soil C changes to be detected with repeat soil inventories. The study site is located in Cahir Co. Tipperary where Miscanthus x giganteus grass has been grown since March 2009. In order to determine the variability of carbon stocks, soil organic carbon concentration (SOC) and bulk density (BD) samples were taken up to a depth of 30 cm at 5 cm intervals. Sampling points were selected using GPS and GIS. A 20 × 20 m grid was set up with a total of 60 sample points selected. Patterns of spatial variation of soil organic carbon concentration and bulk density were observed using geostatistical methods. Means for both variables were 3.36 % and 1.09 g/cm-3 respectively. There were significant differences (i.e. p<0.05) between depth intervals. Soil organic carbon concentration was determined to be the variable which had the most influence on the spatial pattern of carbon stocks. Mean carbon stocks were found to be ~ 17.09 t C ha-1. A baseline for carbon stocks was discovered to be 104 t C ha-1. A power analysis using the variance of both bulk density and soil organic carbon concentration was used to determine the optimal sampling plan for a subsequent inventory. This was found to be 1.5 :1. Use of Pedo Transfer Functions showed that carbon stocks would be overestimated by 8 %. Results found in this study give a baseline for carbon stocks in mineral soils under a Miscanthus crop. Although the values are site specific there are a number of aspects of this study that should be considered when developing a baseline for other soil types