Abstract:
The ability of soils to store large quantities of carbon (C) makes them an important factor in the global C cycle. Small changes within soil C can lead to large changes in atmospheric C. Land management practices can influence the amount of C that is stored within the soil and rates of C accumulation or loss. The Purukohukohu Experimental Basin in New Zealand provides a great opportunity to analyze C and nitrogen (N) differences in soils as it contains three catchments with different land use practices; native forest, pasture, plantation pine with Pinus radiata. By using Sequential Density Fractionation I could examine differences in pools of C and N in each land use type. Sequential Density Fractionation allows the soil organic matter to be analyzed based upon the stability of the C and N in each of the density fractions, with heavier density fractions generally corresponding to more stable C and N. The results showed a loss of C from converting native forest to pasture and a gain of C from converting pasture to plantation pine. The amount of C in the plantation pine was also larger than was the C in the native forest. There was an increase in N from the native forest to the pasture and the plantation pine had the highest N levels. The losses and gains of C in the plots are attributed to stable C inputs from the forested sites. More stable C inputs results in more C stored. The N increases were due to the planting of white clover in the pasture site, which resulted in high N in the plantation as it was planted on a pasture site.
