Grain yield and grain protein of old and modern durum wheat cultivars grown under different cropping systems

A five-year field trial was performed in a typical Mediterranean environment to compare grain yield (GY) and GY stability, grain protein percentage (GP) and GP stability resulting from different cropping systems: two based on 14 old durum wheat landraces/cultivars grown in low-fertility soils; and one based on 14 modern cultivars grown in high-fertility soils. Cropping systems were also differentiated in terms of sowing date, sowing rate (250 vs. 350 viable seeds m−2 for the modern cultivars only) and nitrogen rate (36, 76 and 112 kg N ha-1 on average for the ‘OLDlow’, ‘OLDmedium’ and ‘MODERN’ cropping systems, respectively). Depending on the year, the GY of the OLDlow system ranged from 22% (2017) to 74% (2016) of that obtained in the MODERN system. The maximum GY obtained in the OLDlow system was 4.18 t ha-1. The average GY obtained with modern cultivars varied from 5.6 to 6.6 t ha-1; with the exception of that obtained in 2016 (only 3.37 t ha-1). The higher GY of the modern cultivars was the main cause of higher rainfall productivity, reaching a maximum value of 23 kg ha- 1mm-1. In all the systems, the between-year variation in GY was associated with the corresponding variation in grain number m−2 (GNO), but anthesis date was only negatively associated with GY for the old cultivars, while GP was negatively associated with GY and GNO only in the modern cultivars. GP was always higher in the OLDlow (11.9–14.0 %) and OLDmedium (13.4–15.7%) systems compared with the MODERN one (10.5–12.1 %) in spite of the lower nitrogen fertilization rate, which also assured a higher nitrogen fertilizer recovery efficiency. The three systems were comparable in terms of GY stability, in spite of the later anthesis of old cultivars, which was expected to exacerbate the impact of the terminal drought typical of Mediterranean environments. With regard to GP stability, the old cultivars were less stable than the modern ones. The greatest GxY interaction was generated by the more favourable years, whereas the least interaction occurred in the year with the most severe drought stress. Rainfall, during post-anthesis in particular, but also after sowing, was the main driver of GxY interaction for GY and GP, either directly or via its interaction with nitrogen availability.