Interplanting ryegrass in winter leek: effect on weed control, crop yield and allocation of N-fertiliser

abonos nitrogenados allium ampeloprasum allium porrum bulbous vegetables chemical control control cultural crop yield cultivo mixto cultural control date de semis fecha de siembra fitotoxicidad herbicidas herbicide herbicides hortalizas de bulbo integrated control interplanting leeks lolium perenne lucha integrada lutte chimique lutte culturale lutte physique malezas mauvaise herbe mechanization mixed cropping nitrogen balance nitrogen fertilizers nitrogen metabolism physical control phytotoxicity poireau puerro rendement des cultures rendimiento de cultivos sowing date suisse suiza switzerland weeds