. The Evaluation of N Quantity, Time of N Application, and Herbicide Usage on Spatial Distribution of Lambsquarters Seed Banks of Corn Field. Narges Poortoosi1, Mohammad Hasan Rashed Mohasel1, Elmira Mohammadvand 1, Mahdi Nasiri Mahalati1; 1Ferdowsi University of Mashhad, Mashhad, Khorasan Razavi, Iran In order to evaluate the effect of different management on composition, density and distribution patterns, an experiment was conducted in a grain corn field at the Agricultural Research Station, Ferdowsi University of Mashhad 2006 growing season.The treatments consisted of: Application of 25 kg/ha nitrogen fertilizer at the time of corn planting with 2.4.D+MCPA herbicide (533 g. ai./ha 2.4.D+467 g. ai./ha MCPA), Application of 25 kg/ha nitrogen fertilizer at the time of corn planting without herbicide, Application of 25 kg/ha nitrogen fertilizer at the time of corn planting and six-leaf stage with herbicide, Application of 25 kg/ha nitrogen fertilizer at the time of corn planting and six-leaf stage without herbicide, Application of 120 kg/ha nitrogen fertilizer at the time of corn planting with herbicide, Application of 120 kg/ha nitrogen fertilizer at the time of corn planting without herbicide, Application of 120 kg/ha nitrogen fertilizer at the time of corn planting and six-leaf stage with herbicide, Application of 120 kg/ha nitrogen fertilizer at the time of corn planting and six-leaf stage without herbicide.The percentage of weed seed free spaces was zero throughout the season. Application of herbicide was useful in reducing the amount of Lambsquaters seed bank. Semivariograms of seeds were fitted with spherical and exponential models.Semivariogram analysis in the levels of treatments indicated a range of influence of 0.88 m to 45.12 m . The highest spatial correlation was 0.093% and the lowest one was 28.81%. Weed seed bank patches was obvious in maps.Although the nitrogen fertilizer did not have a strong effect on reducing the amount of seed bank but the application of herbicide was a useful factor in reducing weed seed bank.

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