Sowing date and nitrogen fertilisation effects on dry matter and nitrogen dynamics for durum wheat: An experimental and simulation study

The effects of sowing date and nitrogen (N) fertilisation on the dynamics of dry matter (DM) and N accumulation during grain filling and on final grain yield and protein concentration for durum wheat were studied in two field experiments. In addition, the ability of the wheat simulation model SiriusQuality1 to simulate grain yield and protein concentration for durum wheat was evaluated. The model simulated the anthesis date and the grain filling duration with a root mean square error of 1.7 and 2.2 days, respectively. The model simulated reasonably well the changes in the dynamics of leaf, stem and grain DM and N in response to sowing date and N fertilisation. Harvest grain yield and protein concentration were simulated with a root mean square error of 0.045 kg DM m(-2) and 1.25%, respectively. The longer vegetative period with autumn sowing compared with winter sowing resulted in higher crop DM and N at anthesis, which was associated with higher final grain yield. Independently of the sowing date or N fertilisation, post-anthesis DM accumulation contributed 70% to final grain yield. Post-anthesis N accumulation contributed between 25% and 40% to final grain N yield depending on the sowing date and N fertilisation. The efficiency of vegetative DM and N remobilisation was not modified by the sowing date or N fertilisation, averaging 21% and 74%, respectively. Sowing date had larger effects on grain DM yield than on grain N yield and grain protein concentration was significantly higher for the late sowing date than for the normal sowing date. N treatments did not affect crop phenology, but N fertilisation allowed the crops accumulating more DM and N during the vegetative period. In addition, high-N crops, because of their larger canopy, accumulated more DM and N during grain filling than low-N crops, resulting in higher grain yield and protein concentration at harvest. Both grain number per unit ground area and grain yield were closely correlated with crop DM and N at anthesis. Single grain DM was not modified by N availability. Averaged across N treatments, single grain DM varied from 44.2 to 57.3 mg DM grain(-1). These variations were almost entirely accounted for by the mean daily maximum temperature calculated for the 15 days prior to anthesis, suggesting that the temperature during the period of active cell division in the ovary is a major determinant of the final size of durum wheat grains.