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.