Development of a model to predict drying rates of cut ryegrass

A mathematical model was developed to describe the rates of drying of peren nial ryegrass across a number of different treatments at mowing and after m owing and different weights of grass per unit area. In the experiment, weig ht change of grass in wire-mesh trays was measured in the field over 2 d (3 2 h). Weight change was used to assess water loss and hence drying rate of the grass. The effects on drying rate of five weights of grass per unit are a (1.5, 3, 6, 12 and 24kg [fresh material] m(-2)), three treatments at mowi ng (no treatment, mower-conditioned, flail-treated) and three treatments af ter mowing (no treatment, inverted, mixed) were examined in a 5 x 3 x 3 fac torial experimental design. The experiment was replicated twice on each of 16 occasions in 1992 at the Agricultural Research Institute of Northern Ire land. This gave a total of 32 replicates per treatment. The trays were weig hed at 2-h intervals from 09.00 to 17.00h each day. Three potential evapora tion parameters (net/solar radiation, the Penman equation) were compared fo r use in a final empirical model. Drying rate parameters were calculated fo r each of the individual treatments. Relationships were developed between d rying parameters and weight of grass per unit area for each of the treatmen ts at and after mowing. Inclusion of a rainfall correction factor made the prediction of grass dry matter concentration more complex. The final empiri cal model reliably predicted dry matter concentration of grass in trays in the field over 32 h across the wide range of weather conditions and mechani cal treatments that were studied. This final model which incorporated a sin gle evaporation parameter (solar radiation) was shown to describe the patte rn of grass drying in the field as accurately as a final model based on the Penman equation. However, further work is required to establish the extent of any differences between grass drying rates in the wire-mesh trays used in the current work and grass drying rates from commercial-type swaths. (C) 2001 Silsoe Research Institute.