Models are tools in which knowledge about agricultural systems is integrated. The process of model building and the application of completed models are important. This applies to all crops in general but, for relatively new crops such as hemp, is particularly relevant.   The use of a hemp simulation model to complement the more traditional agronomic field trials offers a number of potential advantages. A simulation models can capture the growth and development processes of hemp in response to a number of conditions and scenarios and has the potential to improve research efficiency. This paper traces the outline of a model for growth, development and yield in response to climatic, nitrogen and management input. It is essentially composed by two sub-models: phenological and growth and development. The model challenges innovative solutions and state of the art knowledge to simulate all processes by means of mechanistic approaches.
For hemp, early flowering has been recognized as one of the major factors limiting yield because it generally stops stalk growth (Meijer et al., 1995). Extensive literature highlighting the joint role of photoperiod and air temperature in modulating development in both short-day and long-day plants has since followed, and many models simulating plant phenology have been based on these two factors (Summerfield and Roberts, 1987; Yan and Wallace, 1998).
Based on the general scheme from Major (1980) and the criteria of Carberry et al. (1992) for kenaf (Hybiscus cannabinus L.), a short-day plant similar to hemp, Lisson et al. (2000a, b) developed a modelling approach of hemp’s response to both photoperiod and air temperature. Detailed and systematic information on the effects of air temperature on the phenological development of hemp is needed to be able to understand its widespread distribution-growth capacity at different latitudes. The same information is essential for the development of a mechanistic model. To provide biological information for modelling purposes, we put particular emphasis on the characterisation of the phenological development of hemp in response to variations in air temperature and photoperiod by determining the duration of the juvenile phase and the effects of temperature and photoperiod on reproductive development. The amount of field data collected under various air temperature-photoperiod combinations offered a unique opportunity to identify key parameters and relationships to build a model of hemp phenology, taking multiple environmental interactions into account.
The growth model is based on transport-resistance model described by Thornley (1998) for shoot:root partitioning in relation to the availability of C and N.  In this approach substrates sources are connected with transport resistances to substrate sinks where chemical/biochemical conversion take place.
The scalarity of nodes formation is responsible of a relatively high heterogeneity of growth pattern along the stem. For this reason, a hemp growth model aiming at fibre quality forecasting would be unrealistic if it treated the stem as a single growth unit. With the goal to build a realistic representation of stem growth and fibre deposition we decided to model stem growth taking the single node formation and ontogenesis into account. This approach gives the opportunity to model fibre production at level of single node disclosing encouraging perspectives to forecast fibre quality along the stem.