evaluation of multi-species weed competition and weeds population dynamic in corn )zea mays l.) field

in order to examine the multi-species weed competition in corn field an experiment as an interval mapping was carried out at the agricultural research field of ferdowsi university of mashhad during growing season 2009-2010. at 3-4 leafy stages of corn, 20 non-destructive quadrates determine and the density of weeds was counted separately. at the same time, 20 destructive quadrates determine and in addition of counting number of plants, leaf area index and dry weight of each species were recorded separately. by using data from previous section, hyperbolic functions were fitted. in these functions number of species serve as the independent variable, weight or leaf area was considered as the dependent variable. with the help of these functions and leaf dry weight of each species was determined for non-destructive quadrates at this stage. relative leaf area at early season as independent variables and natural logarithm of individual plant weight at later season as dependent variable in a multiple linear regression was fitted to obtain the interspecies competition coefficients. based on ln of weight of single plant equation the weed interference effects on the corn yield can be divided into two groups: inhibition (negative sign) and stimulation (positive sign). among all weeds, night shade (solanum nigrum l.), redroot pigweed (amaranthus retroflexus l.) and lambsquarter (chenopodium album l.) had positive effects on corn yield, respectively. in fact, these weeds had competition and negative impacts on other weeds and reduced their competition power with corn and caused facilitation role on corn yield. at the end of growing season of corn, population of lambsquarter and common purslane (portulaca oleracea l.) decreased while population of barnyard grass(echinochloa crus-galli l.), redroot pigweed and night shade increased.