An approach to modelling the effect of environmental and physiological factors upon biomass accumulation in winter wheat

Six sites of variable soil type and environments in England and Scotland we re sown with winter wheat (Triticum aestivum L. cv. Mercia) in the autumns of 1992 and 1993 with optimum inputs for growth. Crop monitoring between Fe bruary and grain maturity provided data to investigate environmental and ph ysiological factors important in controlling biomass accumulation. With increasing use of crop modelling as a tool for interpreting experiment s and as crop management decision support systems, it is important that all influences on crop productivity are understood. The 'radiation use efficie ncy' or radiation conversion coefficient provides a convenient basis to stu dy these influences. Significant differences in seasonal radiation conversion coefficients were observed between sites (P < 0.001), ranging from 2.82 to 3.87 g total dry m atter/MJ absorbed photosynthetically active radiation. A series of simple d ry matter models were developed to help explain biomass accumulation in rel ation to a number of environmental variables (using the measured green area index as an input) with correlation coefficients <greater than or equal to > 0.98 obtained across all sites. Apart from sunlight. differences in the c anopy's ability to accumulate nitrogen and maintenance respiration costs we re the most significant factors (P < 0.001). The nitrogen effect suggests c hanges in the conversion of assimilates with nitrogen availability, despite relatively high nutrition levels (<greater than or equal to> 180 kg N/ha). Over all sites the canopy extinction coefficient could be described as a li near function of the site spring time plant population (P < 0.01). A more d etailed model considered canopy light attenuation to vary between sites acc ording to sowing date and autumn/winter plant establishment and environment .