Intercropping two or more crops under similar micro environmental conditions can increase the agricultural productivity. A field study was conducted in three-year period 2003-2005 at experimental field of Maize Research Institute, Belgrade on chernozem soil type. This examination included three experimental hybrids of maize from various FAO groups of ripening (500,600 and 700) and the type of soya bean from II group of ripening (Nena). Maize and soybean was grown in pure stands and three combinations of intercrops (alternate-row and in strip intercropping).

The effect of different densities of Italian ryegrass (Lolium italicum L.: G₁- 5 kg/ha seeds, 60 cm row spacing; G₂- 5 kg/ha seeds, 20 cm row spacing; G₃- 20 kg/ha seeds, 60 cm row spacing, and G₄- 20 kg/ha seeds, 20 cm row spacing) and different rates of applied nitrogen fertilizer (N₁- 0 kg N/ha; N₂ - 50 kg N/ha; N₃- 100 kg N/ha and N₄-150 kg N/ha) on SPAD values under interaction between the crop and cleavers (Galium aparine L) was investigated.