Spatial Relationships between Soil Seed Bank and Seedling Populations of Hordeum spontaneum and Cardaria draba in Saffron Fields H. Makarian, M. H. Rashed Mohassel, M. Bannayan, M. Nassiri Ferdowsi University of Mashhad Department of Agronomy Faculty of Agriculture P. O. Box: 91775-1163 Mashhad Iran. Keywords: Crocus sativus, geostatistics, spatial dependence, spatial pattern, weeds map Abstract Geostatistical techniques were used to characterize the spatial relationship between Hordeum spontaneum and Cardaria draba seedling and soil seed bank over the entire growing season of 2004-2005 in three saffron (Crocus sativus L.) fields, located in Southern Khorasan (33° North latitude, 57° East longitude), Iran. The maps of H. spontaneum seed bank density corresponded moderately to those seedling density in a and strongly to those in b and c fields. The emergence percentage of Cardaria draba was higher than for H. spontaneum in all fields. Semivariograms showed spatial autocorrelation in seed bank and seedling populations of H. spontaneum and C. draba in all fields. Grey-scale field maps of C. draba seed banks corresponded visually to maps of seedling populations and could have been used to target control efforts, but visual correspondence between H. spontaneum seed bank and seedling maps was poor. INTRODUCTION Understanding the spatial and temporal dynamics of weed populations and the rate of their spread within fields is increasingly important as methods are being developed for the site-specific management of weeds (Zhang and Wang, 2002). Several studies have shown that weeds are not randomly distributed but are aggregated at one or more spatial scales (Cardina et al., 1995; Mortensen et al., 1998; González-Andújar and Saavedra, 2003; Jurado-Expósito et al., 2004). The cause of the patchy nature of weed distribution has been attributed to interacting influences of innate weed biology, local microenvironmental conditions, and agricultural practices (Bigwood and Inouye, 1988; Chavel et al., 1989). A weed patch is considered stable if it is consistent with density and location over time (Wyse, 1996; Gerhards et al., 1997). Stability is important from the perspective of patch management, so that a patch map from one year can be used to direct weed control in subsequent years (Mortensen et al., 1998). Knowledge of spatial variability helps to improve weed management efficiency (Moloney, 1988; Wiles et al., 1992a; Colbach et al., 2000). Currently, yield loss is usually overestimated (Brain and Cousens, 1990) as patchiness of weeds may result in incorrect evaluation of control measures (Wiles et al., 1992a). An approach to the analysis of weed spatial distribution has been described for emerged populations of common lambsquarters (Chenopodium album L.) in soybean (Glycine max (L.) Merr)