Summary.The experiments reported show that weed competition throughout growth reduced kale yields by up to 89%. Competition until the 4‐leaf stage reduced yields by about 12%. Application of nitrogen had little effect on the actual loss of yield. The same yield could be obtained by controlling weeds from emergence and giving little nitrogen, or by delaying weed control until the 4‐leaf stage and giving a higher level of nitrogen, but kale crops that had suffered weed competition until the 4‐Ieaf stage appeared to be incapable of achieving the same yield as crops clean‐weeded from emergence. Data on nitrogen percentage and content suggest that competition between weeds and kale was not solely for iEffets du desherbage et du taux de fertilisation azoiée sur le rendement et la teneuren azote du chou