Effect of crop rotations of rain-fed and irrigated autumn-sown and spring-sown forage on milk feed unit and soil traits in the European Mediterranean environment

The aim of this study is to assess the agronomic effect of a threeyear continuous intensive double-crop cultivation of different varieties of legumes and grasses sown in autumn and grasses sown in spring under irrigated and rain-fed conditions in the European Union (EU) Mediterranean environment. Our experiment aimed to compare the dry matter (DM, t ha–1) and the milk feed unit (MFU, kg (DM)–1) from silage production and soil characteristics of popular autumn-sown Italian ryegrass (Lolium multiflorum Lam.) and spring-sown maize (Zea mays L.) compared with other crop system legume and grass varieties. The autumn and spring legume and grass varieties were grown under either rain-fed or irrigated conditions. The investigated traits, i.e. DM, MFU and organic carbon (OC, g kg–1), were influenced by the cropping system, the sowing time and the irrigation treatments. The mean total number of MFU ha–1, derived from the potential silage yield of legume and grass autumn varieties, ranged from 4297 to 5895 MFU ha–1 under rain-fed conditions and from 5778 to 7871 MFU ha–1 with irrigation, respectively. The MFU ha–1 observed in varieties sown in spring under rain-fed conditions was 8926 for grain sorghum (Sorghum bicolor L. (Moench)), 12,459 for silage sorghum; and 15,148, 24,004, 20,323 and 13,521 for lucerne (Medicago sativa L.), maize, silage and grain sorghum grown with irrigation respectively. Furthermore, the mean MFU ha–1 of autumn and spring legume and grass varieties used for grain consumption, in comparison to those of silage, was reduced by 67.6% under rain-fed conditions and 53.4% with irrigation. Three years of continuous rotations of irrigated autumn and spring grass varieties reduced the initial experimental content of OC by 2.49 g kg–1 in the autumn grass and 1.50 g kg–1 in legumes, while under rain-fed conditions the decrease was 0.81 g kg–1 and 1.86 g kg–1 in autumn legumes and grass respectively.