Effects of intercropping on the herbage production of a binary grass-legume mixture (Hedysarum coronarium L. and Lolium multiflorum Lam.) under artificial shade in Mediterranean rainfed conditions

Growing perennial legumes in the understory layer in agroforestry systems is a strategy to improve the sustainability of agricultural systems, i.e., by increasing land productivity, fostering carbon sequestration and nutrient cycling and reducing reliance on inorganic nitrogen fertilizers for tree crops. In many parts of Central Italy, sulla, a biennial autochthonous legume, is widely adopted in forage cropping systems for its productivity and nutritive value and it is often intercropped with ryegrass for a better utilization as grazed temporary grassland. To evaluate the agronomic performance of these perennial species grown under different levels of light reduction, an artificial shade plot trial was established in the coastal plain of Pisa, Central Italy, with the aim to simulate the effect of tree presence with different levels of shade intensification in rainfed conditions. The experiment layout complies with a 2-way completely randomized design with four replicates. The two factors tested were the forage species (namely sulla, ryegrass and their intercropping) and the level of shade (no shade, moderate shade - 30% light reduction-, and intense shade - 50% light reduction-). Shading significantly reduced the above ground biomass (AGB) production, especially for the intense shading (on average about - 20% with respect to the full sun). The mixture resulted as the most productive crop, yielding on average about + 30 and + 40% AGB in comparison to sulla and ryegrass pure stands, respectively. The findings about the effect of the shading on AGB production showed that mixture was a suitable sward, especially under moderate shading conditions. Further studies are needed with the purpose to investigate the productive performance of these swards in real agroforestry conditions.