In vitro digestibility of green lamina of cocksfoot (Dactylis glomerata L.) in relation to water deficit

The effect of water deficit on in vitro dry-matter digestibility (IVDMD) of green lamina of cocksfoot (Dactylis glomerata) was investigated over a 6-week period following a cut. Two levels of water deficit were compared with a well-irrigated sward. The leaf water potentials were -10.3, -7.6, -1.9 bars, respectively, for the three treatments. For the last 25 d of the regrowth period, the IVDMD of green laminae decreased significantly faster on the well-watered (-0.11) than on the treatments that were subjected to a water deficit (from -0.036 to -0.068). This difference was associated with a smaller drop in the leaf appearance rate and a greater increase in the length of the successively emerging leaves on the well-watered than on the two water-stressed treatments. Overall, the IVDMD showed greater correlation with the average leaf insertion level on a tiller than the sampling date. In the range of water stress observed, the IVDMD increased in relation to a delay of the normal ontogenetical drift.