Ley-farming and seed dispersal by sheep: Two methods for improving fallow pastures in semiarid Mediterranean environments?

Fallows constitute an important grazing source for livestock in semiarid environments. This work proposes two methods to improve fallow pastures quality in SE Spain consisting of (i) seeding a fallow (seeded fallow, SF) with a mixture of fodder species ( Moricandia arvensis, Vicia ervilia and Medicago sativa cv. Aragón), and (ii) using sheep for introducing these fodder species in a fallow while manuring (“seeded-manured” fallow, SMF), this consisting of fencing sheep for 5 days, after seed ingestion, in a fallow plot. To evaluate the performance of these methods, we compared the yield, fodder quality, and botanical composition of the SF and SMF for two growing seasons (2006 and 2007). Biomass yield in 2006 was greater in the SMF than in the SF, but similar in 2007; additionally, moderate grazing in 2006 did not affect yield in 2007. Crude protein content was greater in SF whereas SMF had a higher lignin content. The species seeded in the SF showed a high self-reseeding ability as indicated by the decrease in weed percentage in 2006 (50%) with respect to 2007 (25%), V. ervilia being the most abundant. In SMF, weeds constituted from 94 (2007) to 99% (2006) of the total biomass, indicating low establishment success of the prescribed species from sheep dung. To assess the potential ability of sheep to introduce fodder species into fallows, we quantified seed recovery after gut passage and potential seedling establishment in greenhouse conditions was also examined. Low seed recovery and low seedling establishment were detected. M. arvensis registered the highest values of seed recovery (2.7%), while M. sativa and the highest seedling-establishment percentages under greenhouse conditions (0.49%). In conclusion, this study suggests that seeding a fallow with a mixture of fodder species, and using sheep for introducing these fodder species in a fallow while manuring may improve fallow pastures quality in semiarid Mediterranean environments. Nevertheless, hardseeded species should be used when introducing new high fodder quality species into pastures by means of livestock dejections.