Direct weed suppression by cover crops and residual effects on grain maize and sunflower

We investigated the weed suppression potential of different winter cover crops grown alone or in mixtures during the cover crop growing cycle and in subsequent grain maize and sunflower. A plot trial was conducted in 2005-06 and 2006-07 at CIRAA (University of Pisa, Italy). The experiment was laid out as an RCB design. Data were subjected to ANOVA and subsequent LSD test at P ≤ 0.05 for mean separation. In both years there were significant differences between treatments in terms of cover crop and weed biomass. Leguminous cover crops produced the highest biomass, especially Vicia villosa when grown alone (5.3 and 5.7 t ha-1 in 2006 and 2007 respectively). In 2007 also cover crop mixtures gave good results with a mean biomass of 6.9 t ha-1. Mixtures were the most weed suppressive cover crops in both years, yielding on average 0.3 and 0.2 t ha-1 total weed biomass compared to an overall mean of 0.9 and 1.1 t ha-1 in 2006 and 2007 respectively. In both years, we registered the highest cash crop grain yield when maize or sunflower followed V. villosa or the mixtures including a leguminous cover crop. There were significant differences among treatments in terms of total weed biomass in the subsequent cash crops in 2006 but not in 2007. In sunflower, the lowest total final weed biomass was observed after the Avena sativa cover crop (0.4 t ha-1) whereas in maize the lowest weed biomass was observed after V. villosa (0.3 t ha-1).