Modelling non-structural carbohydrates in forage grasses with weather data

A weather-based dynamic model was formulated to simulate the concentration of water-soluble carbohydrates (WSC) in harvestable dry matter of forage gr asses. The main aim of the model development was to describe and quantify t he response of photoperiod (daylength), incoming shortwave radiation, air t emperature and plant-available soil water on WSC content in a simple functi onal approach with widely available weather data. In co-operation with a re gional or national agrometeorological service, farmers can, in the future, get information about the WSC content of their herbage in order to optimize the cutting date for pastures and temporary grassland due to the demands o f animal nutrition and silage management. The response of meteorological fa ctors on WSC content was modelled in two steps. Firstly, the general trend of WSC content was calculated, describing indirect weather effects on WSC c ontent concerning phenological development of the plants. Secondly, direct influences of weather factors on WSC content were added, reflecting photosy nthesis and respiration processes on a short time scale. The modelling appr oach was parameterized on a set of data from northern Germany, which were c ollected daily in different growing periods in the years 1990, 1991 and 199 4 in stands of Lolium perenne L. The model fitted the WSC content of the pr esented data with a mean root mean square error of 2.74% units (cv: 11.3%). The potential of the model is discussed in relation to weather sensitivity and adaptability to different genotypes, sward types and nitrogen fertiliz ation levels. (C) 1999 Published by Elsevier Science Ltd. All rights reserv ed.