Crop density and fertilization effects on weed suppression in spring oilseed rape

Field experiments were conducted in 2008 and 2009 at the Experimental Station of the Lithuanian University of Agriculture on a Calc(ar)i-Epihypogleyic Luvisol (LVg-n-w-cc). The objective of the current study was to determine the effect of crop density and fertilization on photosynthetically active radiation (PAR) interception and weed suppression in spring oilseed rape (Brassica napus L.) 'Sponsor'. Treatments of the investigations: factor A fertilization: 1) without fertilization, 2) fertilization before rape sowing N68P68K68 and at the budding stage N-70; factor B - crop density: 1) 2 kg ha(-1) (50.1-100 plants m(-2)), 2) 4 kg ha(-1) (100.1-150 plants m(-2)), 3) 6 kg ha(-1) (150.1-200 plants m(-2)), 4) 8 kg ha(-1) (200.1-250 plants m(-2)), 5) 10 kg ha(-1) (250.1-300 plants m(-2)), 6) 12 kg ha(-1) (300.1-350 plants m(-2)), 7) 14 kg ha(-1) (350.1-400 plants m(-2)), 8) 16 kg ha(-1) (400.1-450 plants m(-2)). With the increasing spring rape crop density the PAR reaching the soil surface, 1/4 and 1/2 height of the crop stand decreased in the crops without and with fertilization. Intensive fertilization of rape crop, in comparison with that without fertilization, significantly reduced the PAR reaching the soil surface, 1/4 height of the crop stand and 1/2 height of the crop stand in 2008. In the spring rape crop without fertilization dry matter weight of weeds was influenced by crop density and PAR reaching the soil surface and 1/4 height of the crop stand, whereas in the spring rape crop with fertilization it depended on crop density, PAR reaching the soil surface, 1/4 and 1/2 height of the crop stand.