Yague , MR , M . Guillen , D . Quilez . 2011 . Effect of covers on swine slurry nitrogen 1 conservation during storage in Mediterranean conditions . Nutrient Cycling in 2

29 Swine slurry (SS) is usually stored in open ponds in Mediterranean conditions before 30 being applied to crop fields. During this storage nitrogen (N) is lost to the atmosphere 31 mainly by ammonia volatilization diminishing the fertilizer value of the slurry and 32 causing environmental problems. Permeable covers made from plant materials are low33 cost alternatives to reduce these losses. This work evaluates the effectiveness of four 34 composite permeable covers to conserve N during SS storage under semi-arid 35 Mediterranean conditions. The covers, supported by a raschel mesh floating over the 36 SS, were 3.5 and 7 cm thickness pine bark (PB3.5 and PB7), 8 cm thickness pruned 37 wood (PW8), and 8 cm thickness cornstalk (CS8) and uncovered treatment (C). In the 38 first four storage months, the pine bark and cornstalk covers conserved ammonium 39 more effectively than the pruned wood and the control treatments (73 to 76% of the 40 initial mass of SS ammonium conserved in the PB3.5, PB7 and CS8 treatments, against 41 51% and 39% in the PW8 and C treatments). In contrast, after ten months of SS storage 42 all treatments behaved similarly (conservation of ammonium below 20%) due to cover’s 43 physical degradation. In general, the nutrient concentrations in SS and their ratios 44 changed during storage and the C/N ratio at the end of the experiment was affected by 45 the type of cover pointing to differential effects between covers. The pine bark and 46 cornstalk covers were more effective than pruned wood to conserve N in SS stored for 47 four months, a period that matches satisfactorily with the spring-summer months of 48 typical SS storage in semi-arid Mediterranean conditions. 49