Abstract
Crop type and management practices during rotation influence the spatial distribution and dynamics of weeds. The present study was conducted in order to evaluate the spatial distribution pattern and weed dynamics in Astane Ghodse Razavi experimental field. One hectare size field with Alfalfa- Fallow- Wheat rotation was selected, sampling was carried out by discrete systematic method in which the samples were taken from the intersection of 7 m* 7m grids using 0.5 * 0.5 m quadrates in three stages, pre chemical control, post chemical control and pre harvesting. Totally 24 species were collected and identified from 195 sampling points. At the beginning of the growth season Fumaria vaillantti and Polygonum aviculare were dominant species but gradually perennials such as Convovulus arvensis and Circium arvensis dominated. Meanwhile, the importance of some dominant annual species of the early season such as Fumaria vaillantti were reduced. In order to describe the spatial distribution of weeds within the farm, the species variogram in each stage was calculated. Variogram parameters were differed from each other due to the diversity of species and the stages of sampling. The minimum and maximum of nugget effect for current species in first and second stages of sampling was 0.6 and 1.001, respectively. The range of weeds in the field varied between 3.6 – 93.48m. The variogram parameters were used in Kriging and weeds' spatial distribution maps were drawn. Generally it could be conclude that the type of crops in rotation and cultural operation affects dynamics of the weeds. On the other hand, the maps showed the patch distribution, lead us toward using site specific weed management.

Keywords: Spatial distribution, Discrete sampling, Variogram, Weed mapping