Geostatistical techniques were used to describe the spatial distribution of weeds, under conventional management conditions and theirs effect on wheat biomass production over the course of one growing season (2008-2009), in a wheat (Triticum aestivum L.) field at Research Station of Shahrood University, Iran. Weeds Seedling were identified and counted at 121 points of field based on two intervals including prior to and after post-emergence control. Wheat biomass dry weight was determined at the same places of weeds. In the field, 12 weed species were identified. The semi-variogram analysis indicated that 67.4% to 99.8% of the variation of sample density was due to spatial dependence, which suggests that most of the weed species were patchy. Wheat biomass dry weight showed spatial patterns on the field. Cross-semivariograms analysis showed strong (89 and 87.4% in the first and second stages of sampling respectively) spatial continuity between wheat biomass dry weight and weed density patterns on the field. The maps of total weed species corresponded visually to map of wheat biomass. As a result, patchy distribution of weeds can cause spatial heterogeneity in crop biomass production.
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