A prediction model for field drying of hay using a heat balance method

A hay drying model with a multi-layer representation has been developed. This model, based on a heat balance method, was designed to compute hay drying dynamics in the field. It was implemented for hay spread over a field or in windrows. The necessary inputs are: (1) meteorological data (temperature, humidity, wind speed, solar and atmospheric radiation); (2) biological characteristics of the plant; (3) hay physical parameters (depth, leaf area index). The output provides time-dependent cumulative water losses and changes in water content and temperature in the different layers. The model was tested against data measured under experimental conditions with different kinds of grass (ryegrass, permanent pasture and alfalfa). It was shown that agreement between the simulated and measured parameters was fairly good. Further, the model was used to study the sensitivity of water loss to changes in input variables and plant characteristics.