CHARACTERIZATION OF SPATIAL VARIABILITY STRUCTURE IN 3 SEPARATE FIELDTRIALS ON PESTICIDE DISSIPATION

Experiments were carried out on three Italian farms to assess the degr ee of spatial variation of pesticide field concentration during treatm ent and during dissipation trials. Test pesticides were chloridazon an d metamitron (both sugar-beet herbicides) applied as a tank mix. The c lassical statistical technique and geostatistics were used to summariz e and evaluate variable spatial data. The results show that the actual values of pesticide concentration for application rate and initial co ncentration in all three areas are lower than expected, thus indicatin g that under held 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 fro m 44.1% to 64.2% for application rate and from 40.5% to 99.5% for init ial concentration. The coefficient of variation was similar for both p esticides and ranged from 23.8 to 74.1 for application rate, 24.1 and 58.8 for initial concentration and 11.1 and 110.0 for dissipation half -lives. The high variability in application rate and initial concentra tion could be ascribed to an uneven herbicide distribution, and in dis sipation studies to variation in half-lives for the rate of herbicide loss from soil in different parts of the field. Geostatistic analysis indicated little spatial correlation, probably because the sampling si tes were widely spaced on the held. In all cases, the data were not su fficient to estimate the range of influence, probably because of the s ize of the experimental fields and the sampling strategy.