Chemical composition of clamped and baled grass silages harvested in England and Wales and relationships between dry matter contest, pH and volatile N

The paper reports a study of the chemical composition of 25400 grass silage s produced in England and Wales, of which 1040 were from the period 1961-63 , 17 900 (15 480 clamped and 2420 baled) were from 1982-88 and 6460 (5640 c lamped and 820 baled) were from 1992-93. A sample of each silage had been a nalysed for dry matter (DM), pH, crude protein (CP) and volatile N and in m ost cases for ash. The baled silages were drier on average than the clamped silages, with a wi der spread of DM contents. The clamped silages with the lowest pH on averag e were those with a DM content of c. 240 g/kg; clamped silages wetter than this were progressively higher in pH with reduction in DM content; clamped and baled silages drier than 240 g/kg were progressively higher in pH with increase in DM content, up to pH 5.9 in baled silages of 580 g DM/kg. At a given DM content pH was on average 0 6 units higher in baled than in clampe d silages. The ash content of baled silages was similar to that of clamped silages. There was an increase in the mean CP content of clamped silages be tween 1961-63 and 1992-93 and a reduction in the proportion of CP which was volatile. The relationship between DM and volatile N as a proportion of to tal N was a curve rather than a straight line, with the steepest part of th e curve at the lower end of the DM range. The wet silages harvested in 1961 -63 were particularly high in volatile N. At a given DM content in the rang e 170-320 g/kg, volatile N was rather higher in baled than in clamped silag es in both 1982--88 and 1992-93. Clamped silages with a DM content of at le ast 250 g/kg and baled silages with a DM content of at least 310 g/kg were typically well preserved in the sense of having < 100 g volatile N/kg total N.