Uptake of weed-borne nitrogen by maize was tested with ¹⁵N in field experiments on silty loam (haplic phaeozem) after common growth of maize and Chenopodium album L. and incorporating the weeds at the 4- to 6-leaf stage of maize. Maize took up 22–23% of the weed-borne N in the year of incorporating and residual 7–32% in the following year. Uptake of weed-borne N was higher in comparable pot experiments. Different soil humidity after different water supply was mainly reasonable for these differences. Weed-borne nitrogen contributed 7–16% to total N of maize in the year of incorporating and 4–11% in the following year. Yield and N uptake between weeded and unweeded maize differed partly significant.