Pestic. Sci. 1997, 50, 175È182 Characterization of Spatial Variabilit y Structure in Three Separate Field Trials on Pesticide Dissipation* Costantino Vischetti,1” Mario Businelli,2 Mauro Marini,2 Ettore Capri,3 Marco Trevisan,3 Attilio A. M. Del Re,3 Lucia Donnarumma,4 Elisa Conte4 & Giancarlo Imbroglini4 1 Centro di Studio sulla Chimica e Biochimica dei Fitofarmaci C. N. R, Borgo XX Giugno 72, 06121 Perugia, Italy 2 Istituto di Chimica Agraria dellÏUniversita` Borgo XX Giugno 72, 06121 Perugia, Italy 3 Istituto di Chimica Agraria ed Ambientale, Universita` Cattolica del Sacro Cuore, 29100 Piacenza, Italy 4 Istituto Sperimentale per la Patologia Vegetale, via Bertero 22, 00156 Roma, Italy (Received 28 October 1996 ; revised version received 30 January 1997 ; accepted 25 February 1997) Abstract : Experiments were carried out on three Italian farms to assess the degree of spatial variation of pesticide Ðeld concentration during treatment and during dissipation trials. Test pesticides were chloridazon and metamitron (both sugar-beet herbicides) applied as a tank mix. The classical statistical technique and geostatistics were used to summarize and evaluate variable spatial data. The results show that the actual values of pesticide concentration for applica- tion rate and initial concentration in all three areas are lower than expected, thus indicating that under Ðeld conditions only a part of the pesticide reaches the soil during the distribution. The actual values for both herbicides in all three areas expressed as percentage of expected values ranged from 44É1% to 64É2% for application rate and from 40É5% to 99É5% for initial concentration. The coeffi- cient of variation was similar for both pesticides and ranged from 23É8 to 74É1 for application rate, 24É1 and 58É8 for initial concentration and 11É1 and 110É0 for dissipation half-lives. The high variability in application rate and initial concen- tration could be ascribed to an uneven herbicide distribution, and in dissipation studies to variation in half-lives for the rate of herbicide loss from soil in di†erent parts of the Ðeld. Geostatistic analysis indicated little spatial correlation, probably because the sampling sites were widely spaced on the Ðeld. In all cases, the data were not sufficient to estimate the range of inÑuence, probably because of the size of the experimental Ðelds and the sampling strategy. Pestic Sci., 50, 175È182, 1997 No. of Figures : 4. No. of Tables : 3. No. of Refs : 19 Key words : spatial variability, pesticide dissipation, metamitron, chloridazon, geostatistics * Based on a paper presented at the 6th International COST ACTION 66 Workshop “Pesticides in the Soil and the EnvironmentÏ held on 13È15 May 1996 at Stratford-on-Avon, UK. ” To whom correspondence should be addressed. 175 1997 SCI. Pestic. Sci. 0031-613X/97/$17.50. Printed in Great Britain (