Effect of Flowering Shading on Grain Yield and Quality of Durum Wheat in a Mediterranean Environment

The phenomenon known as "dimming" or shading, caused by the increase in aerosols, air pollutants, and population density, is reducing global radiation, including both direct solar radiation and radiation scattered by the atmosphere. This phenomenon poses a significant challenge for agricultural production in many regions worldwide, with a global radiation decrease estimated between 1.4% and 2.7% per decade in areas between 25° N and 45° N. In particular, in Mediterranean regions, the production of durum wheat (Triticum turgidum L. subsp. Durum) is increasingly constrained by abiotic factors, such as spring/summer heat stress and drought, as well as reductions in solar radiation. Field experiments were conducted in Mosciano Sant'Angelo, Italy, over two cropping seasons (2016-2017 and 2017-2018) to evaluate the effects of photosynthetically active radiation (PAR) availability and nitrogen (N) fertilization on durum wheat. A split-plot design was used with two PAR levels (100% and 20% PAR) and three N rates (0, 100, and 250 kg ha^-1). Results highlighted that full sunlight (NoSh) significantly increased grain yield (+25%), thousand kernel weight (+46%), and total gluten fractions (+16%) compared to shaded conditions (Sh). Chlorophyll content and NDVI values were highest under Sh combined with 250 kg N ha^-1. Rainfall patterns strongly influenced productivity, with better vegetative growth in 2016-2017 and improved grain filling in 2017-2018. Nitrogen application significantly enhanced grain protein content, particularly under arid conditions. These findings emphasize the interaction between light availability and nitrogen management, suggesting that optimizing these factors can improve yield and quality in durum wheat under Mediterranean conditions.