Changes in soil total C and N contents at three chronosequences after conversion from plantation pine forest to dairy pasture on a New Zealand Pumice soil

Abstract

The large amounts of carbon (C) and nitrogen (N) sequestered as organic matter in soils have implications for global and national C and N balances and greenhouse gas emissions. Changes in soil management can affect the amount of C and N stored in soil. We investigated the change in land use from radiata pine plantation to ryegrass-white clover dairy pasture on the total C and N content of Taupo Pumice Soil. Samples were taken at three study sites (Atiamuri, Tokoroa and Wairakei) in North Island, New Zealand. Soils were cored to 60cm depth and subsampled by soil horizon, and bulk density cores were taken from soil pits. A chronosequence of sites was obtained after conversion from pines to pasture. Long-term pastures (40-80 years) and mature pine plantations were included for further comparison. Regression analyses were completed after logarithmic transformation of the time data. The data were highly variable, but significant (P<0.05) increases in total C and N were found at the Atiamuri and Wairakei sites. However, there was no significant change in the total C content of the profile at the Tokoroa site. Increases in total C and N were greatest in the Ap horizon and were most rapid 1-5 years after conversion. Overall rates of increase in the first 10 years after conversion were 0.167kg C m-2 year-1 for total C and 0.032kg N m-2 year-1 for total N, dropping to 0.027kg C and 0.005kg N m-2 year-1 for the 10-50-year period. The change in land use from plantation forest to dairy pasture has resulted in a moderate increase or no change in soil storage of C. Compared with total C, increases in total N storage were proportionately greater in all three examples of this Taupo Pumice Soil. © CSIRO 2014.