Objective of this research were to decrease the weed biomass and find the weed control methods in seed production field of grasses and legumes.
The species of grasses and legumes selected from species evaluation experiment as a Medicago varia (native), Elymus dahuricus (IM), Agropyron mongolicum (IM) and Stipa sibirica (native) were sown in irrigated and non irrigated plots of forest steppe zone (Tuv, Bornuur) and tested weed control methods as a control; cleaning cut, cleaning by hand, spray herbicide and harrow between rows.
The perennials were sown in beginning of June.  In 2007 planted in spring ploughing plots and in 2008 in fallow between rows was 45 cm.
The following characteristicshave been measured or scored:Field germination; Weed biomass; Summer survive; Spring regrowth and winter survive; Perennials biomass  and height;
Data was analyzed with SPSS 16.0.
The  2007and2008 was good year for perennials by air temperature and precipitation. However, in May of 2007 air temperature was at 4.4-7oC lower than in MMY.
In irrigated condition of forest steppe zone in 2007 the field germination of grasses and legumes was 36.9-69.6% and 50.8-83.0% of them leaved to first autumn and 17.2-48.3% of leaved plants overwintered to next spring. In non irrigated experiment of 2008 the perennials germinated at 17.0-54.0% and 31.5-85.0% of them leaved to first autumn.
In seed multiplication field of  perennials able to decrease weeds to 62.8-100% using the methods as a cleaning cut, cleaning by hand and spraying herbicide 1 time for summer.
However, by harrowing between rows able to decrease weeds just in 57.3-64.7% depended from that during the harrowing the weeds between rows deleted well, but weeds in the rows leaved and growing intensively. 
In the plots of alfalfa were cleaned by cut weeds every July gave more green and seed yield and it shown that the alfalfa able to dislodge the weeds from 2nd year of life, however, the Agropyron mongolicum is not resistant for weeds it shown by low yield.