Characterizing Distribution and Stability of Purple NutsedgePopulation Using Geostatistics over two Growing Seasons

Distribution and stability of purple nutsedge (Cyperus rotundus) population within four fields under corn-fallow rotation were analyzed over two growing seasons in 2005 and 2006 at the Agricultural Research Station of Ferdowsi University, Mashhad, Iran. In 2005, N-fertilizer (urea) was applied at two different application methods (whole and split application). As a result of applying or not applying herbicide (a mixture of 2,4-D and MCPA) on the fields under the same N-fertilizer management, four treatments including N(whole)-herb, N(whole)- no herb, N(split)-herb and N(split)- no herb were assigned to four fields. In 2006, the field was kept under fallow. In both years, samplings were conducted at the same points (intersections of 2.5 m-2 grids) and dates (three times). Geostatistical techniques were used to examine the data. Purple nutsedge density was higher in corn fields than the fallow condition, with average densities of 51.73 and 19.61 plants m-2, respectively. In Correspondence to: E. Mohammadvand; E-mail: el_mo19@stu-mail.um.ac.ir both years, the mean density of purple nutsedge was higher in fields with whole application of N-fertilizer compared with split application. Spherical and Exponentialmodels indicated strong or moderate spatial autocorrelation. Spatial distributions were found to be heterogeneous, with high-density patches and areas at lower density. The distribution pattern of purple nutsedge densities indicated that patch-level ‘spatial aggregation’ existed. Despite fluctuation in margins, spatial stability was observed for purple nutsedge patches. This suggests that purple nutsedge would be a good candidate for site-specific application; however more practical experiments are needed to confirm this issue.