Symposium no. 48 Paper no. 1314 Presentation: poster Spatial variability of nutrients in successive years

fertility on an acid soil of the subtropical area in Sao Paulo State, Brazil. A case study of soil chemical properties (pH, organic matter content, Ca, Mg, K, Al, CEC and Base Saturation (V)) in a field (160 m x 120 m) is used to explore sampling issues. Soil samples were taken, first, in a recently tilled soil, just after the land had been abandoned for a long time, and later on in the same soil managed according to minimum tillage practices for successive years. A regular sampling grid scheme (20 m x 20 m) with 63 sites was used to identify the magnitude and scale of spatial variation of selected nutrients and soil properties. Data sets were collected from two depths within this single field and for three different times, 1985, 1987 and 1988 in a long-term experience. The statistical results indicate that the initial soil condition was found to be more diverse, providing evidence that in the studied Ferralsol, clearing and long-term cultivation tend to increase soil heterogeneity at both studied depths. Experimental variograms of individual variables were computed and modelled by a nugget component plus a spherical structure. The nugget effect were important, generally higher than 50% for most of the studied variables, at the first sampling date and tended to decrease at successive sampling dates. Thus, the effect of agricultural soil use was to improve the continuity of the studied attributes at close distances. The autocorrelation ranges for most of the studied soil properties varied between 40 and 80 m. Semivariograms provided a description of nutrients spatial structure and some insight into possible processes affecting their distribution. Kriging maps allowed the identification of small regions with distinct nutrient concentrations and illustrate the diversity of..