Technical note: A comparison of methods to determine pH in silages

摘要

The techniques used to assess pH in silages varygreatly. The aim of this study was to evaluate the effectsof water-to-sample ratio, extraction procedure,and standing time on pH determination. Silage samples(n = 20 for each silage) were chosen to represent diversecrops (corn, elephant grass, sugarcane, and foragepeanut) to have a varied ensilability index and thus awide range in final pH. Three water-to-sample ratiosand 2 extraction procedures were used to measure pHat 0, 5, 10, 15, 30, 60, and 120 min of standing time.The ratios (undried silage to water) were 9:60, 25:100,and 30:270. The samples with the first 2 ratios weremanually extracted, using a glass beaker and a glassstirring rod. The samples with the 30:270 ratio wereextracted by using a stomacher blender for 4 min at200 rpm. An electrode was used to perform pH readings.Dry matter (DM), water-soluble carbohydrates,and lactic acid concentrations were determined. Theexperimental design was completely randomized usinga mixed repeated-measures model. Mean separationwas performed using the Tukey test at P < 0.10 usingthe MIXED procedure of SAS (SAS Institute Inc.,Cary, NC). The DM concentrations ranged from 24.5to 40.2, 15.8 to 25.9, 26.9 to 30.6, and 17.8 to 21.4%for corn, elephant grass, sugarcane, and forage peanutsilages, respectively. The lactic acid concentrationsranged from 2.9 to 10.1, 1.8 to 4.4, 0.7 to 11.4, and 0.3to 1.4% of DM for corn, elephant grass, sugarcane, andforage peanut silages, respectively. The pH values measuredby the 9:60 method were greater than other techniquesat any standing times. The pH values from the25:100 and 30:270 methods did not differ for elephantgrass and forage peanut silages at any standing times.However, the 30:270 method had greater pH values forcorn and sugarcane silages than the 25:100 techniqueat any standing times. The pH values measured by the30:270 method did not vary for any of the silages accordingto standing time. Nevertheless, the pH valuesof the 25:100 method were greater from 0 to 10 minthan for other standing times for all silages. Thus, forthis method, there was pH stabilization from 15 minof standing time on. Overall, the 25:100 and 30:270methods are recommended for assessment of silage pH.Fifteen minutes of standing time should be used for the25:100 method but the pH reading can be performedimmediately after mixing for the 30:270 technique.