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

Distribution and stability of purple nutsedge (Cyperus rotundus) populationwithin four fields under corn- fallow rotation were analyzed over two growingseasons in 2005 and 2006 at the Agricultural Research Station of FerdowsiUniversity, Mashhad, Iran. In 2005, N-fertilizer (urea) was applied at twodifferent application methods (whole and split application). As a result ofapplying or not applying herbicide (a mixture of 2,4-0 and MCPA) on thefields under the same N-fertilizer management, four treatments includingN(whole)-herb, N(whole)- no herb, N(split)-herb and N(split)- no herb wereassigned 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 rn grids)and dates (three times). Geostatistical techniques were used to examine thedata. Purple nutsedge density was higher in corn fields than the fallowcondition, with average densities of51.73 and 19.61 plants m, respectively. In both years, the mean density of purple nutsedge was higher in fields withwhole application ofN-fertilizer compared with split application. Spherical andExponentialmodels indicated strong or moderate spatial autocorrelation.Spatial distributions were found to be heterogeneous, with high-density patchesand areas at lower density. The distribution pattern of purple nutsedge densitiesindicated that patch-level ʹspatial aggregationʹ existed. Despite fluctuation inmargins, spatial stability was observed tor purple nutsedge patches. Thissuggests that purple nutsedge would be a good candidate for site-specificapplication; however more practical experiments are needed to confirm thisissue.