ADVANCE STUDY FOR ESTIMATION OF YIELD LOSS DUE TO WEEDS IN CORN FIELDS.ý

Because of no accurate information on the damage of weeds to seed corn fields this experiment was performed in cold temperature areas of Kermanshah province. In this way 30 seed corn fields were chosen by stratified random-sampling method and appropriate number of samples to every stratum was regarded. In this method region was considered as primary and field size as secondary stratum. At every field sampling was performed using ten 1.5 m2 quadrates (two rows of cultivation with 1 m length). The distance between quadrates was 20 meters and the pattern of sampling was reverse W. At every quadrate the number of weeds based on individual species were counted and registered. Sampling was carried out when the corn plants were at 5-6 leaved stage. During sampling the surface was exactly marked and at harvest time the yield of that place was measured. Similarly at every field ten 1.5 m2 quadrates (two rows of cultivation with 1 m length) from parts of the field without any kind of weeds which represented the normal condition of the field was chosen and at harvest time seed yield at every quadrate was measured and registered as mentioned above. Afterwards using the data coming from every seed corn field, the amount of damage resulting from weeds was evaluated. The obtained data were adapted with oblong hyperbolic method of weed compaction (Kozens equation) and quantities of a and I factors were calculated. These adapted equations have evaluated the damage of weeds to seed corn fields in Kermanshah province. Based on these results the yield shortage of seed corn caused by weeds in Kermanshah province was estimated as 17.32 percent. Regarding 252566 tons of seed corn during the crop year 2009-2010 and 450 tomans for every kg of seed corn it is distinguished that without appropriate management of weeds in this fields we have nearly 19 billion tomans annual loss to seed corn crop in Kermanshah province.