SPATIAL VARIABILITY OF SOIL ORGANIC C, INORGANIC N AND EXTRACTABLE P IN A MEDITERRANEAN GRAZED AREA

In this paper, we studied the spatial variability of soil organic C (SOC), inorganic N (SIN) and extractable P (P-extr) in a grazed Mediterranean-type vegetation formation. Sampling was conducted from a gently sloping area in northern Greece.. The grazing pressure was evenly distributed over the experimental area with the exception of an overgrazed passage zone 200-300m from steeper foothills. Soil samples, from the upper 10cm, were collected every 10m along four replicate lines (400m length with a distance of 10m between lines). Sampling took place twice (October and February). Data were analysed by geostatistical tools, and spherical models were significantly fitted to the semivariograms. SOC in both samplings and SIN in the first one displayed moderate spatial dependence which indicates the non-random distribution of their concentration. On the contrary, P-extr and SIN in winter exhibited weak spatial dependence, whereas P-extr in autumn showed spatial independence. For the parameters exhibiting spatial pattern, two scales of dependence were revealed: a fine scale within distances shorter than 10m and a coarse scale varying between 80 and 130m. The coarse distribution of SOC, SIN and P-extr invoked interplay among more predictable (composition of vegetation) and unpredictable (leaching, runoff) extrinsic factors, occurring at the landscape level. Specifically, SOC as a storage agent exhibited uniform spatial pattern in both samplings. By contrast, SIN by being susceptible to leaching exhibited time-specific dependence, whereas P-extr which was affected by surface runoff displayed limited or even spatial independence. Copyright (c) 2012 John Wiley & Sons, Ltd.