Comparacion de acido formico con formiato de sodio y metabisulfito de sodio como aditivos para ensilaje de alfalfa (Medicago sativa L.).

The effect of formic acid and sodium formate, with and without sodium metabisulphite, as silage additives for ensiling direct cut (CD) and 24 hour wilted (PM) alfalfa (Medicago sativa L.) was studied in a time course experiment. The herbage composition for CD and PM, respectively, was 148 and 228 g DM kg-1; 39 and 34 g TN kg-1 DM and 45 and 57 g non-structural carbohydrates (CNE) Kg-1 DM. The treatments were formic acid (AF; 2 l tonne-1 herbage), sodium formate (FS; 3.44 Kg tonne-1 herbage), sodium formate and sodium metabisulphite (FSM; 3.44 and 0.17 Kg tonne-1 herbage, respectively) and a control without additive (C). Seventy-two 10 kg silos were stored at 20-24 deg C, until opened at 0.25, 0.5, 1, 1.5, 3, 9, 27, 90 and 180 days of fermentation. Results for pH, CNE, soluble nitrogen (NS), ammonia-N (N-NH3) and buffering capacity (CT) were adjusted by regression analysis to quadratic or single exponential models, which successfully represented the processes involved. AF treated silages had significant differences of change rate and final value for pH, CNE, NS, N-NH3 and CT compared to C, indicating the need of an efficient additive for preserving the nutritive value of alfalfa. In the case of CD and for silages treated with AF, FS, FSM and C, respectively, the values after 180 days of fermentation for pH were 4.6, 5.0, 5.0 and 5.0; for CNE were 22, 15, 13 and 11 g Kg-1 DM; for NS were 734, 828, 805 and 824 g Kg-1 TN; for N=-NH3 were 113, 187, 189 and 205 g kg-1 TN; and for CT were 70, 39, 33 and 49 meq. 100 g-1 DM. In the case of the silages made with PM the results for pH were 4.2, 4.5, 4.4 and 4.9; for CNE were 23, 16, 19 and 12 g kg-1 DM; for NS were 733, 786, 790 and 791 g kg-1; for N-NH3 were 100, 125, 113 and 193 g kg-1 TN; and for CT were 70, 55, 54 and 45 meq. 100 g-1 DM. The efficacy of FS and FSM depend upon D.M. content, results being similar to C for CD and similar to AF for PM. The use of sodium metabisulphite did not improve preservation, except for CNE. It was concluded that FS could be used as silage additive for alfalfa, taking into account that it is less effective than formic acid and its efficacy depends on DM content of the herbage.