Effects of Drought Stress, Apera spica-venti (L.) Beauv. Competition, and Biostimulants on Morphological and Nutritional Traits of Winter Wheat—Part 1

Agroecosystems are perpetually subjected to environmental factors. Driven by a shifting global climate, soil moisture deficits represent an increasingly frequent threat to crop productivity. In farming, however, these abiotic stressors seldom occur in isolation, as fields are invariably compounded by biotic weed pressure. Consequently, investigating plant responses to such combinatorial, multi-faceted stress is paramount to evaluating the realistic efficacy of modern agrotechnical interventions. A 2-year, three-factor pot experiment was conducted at the Research and Education Station in Swojczyce, belonging to the Wrocław University of Environmental and Life Sciences. The aim of the study was to examine the response of winter wheat (Triticum aestivum L., cv. Agil) to drought stress during the period when cereal plants were at the 51–65 BBCH developmental stages. Additionally, in some pots with winter wheat, Apera spica-venti (L.) Beauv. was sown as a weed to evaluate the effects of biotic stress. To observe the mitigation of stressors, three different types of biostimulants were used—a silicon-based preparation and two seaweed-based preparations derived from Ecklonia maxima (Osbeck) Papenfuss and Ascophyllum nodosum (L.) Le Jolis, respectively, representing structural, morphological, and biochemical defense strategies. Drought stress significantly and negatively affected the length of the wheat main stem, lateral tillers, and lateral spikes, as well as the weight of the main wheat spike. The simultaneous occurrence of drought stress and A. spica-venti competition resulted in the greatest cumulative reduction in main spike weight. Furthermore, drought stress was associated with an increase in nitrogen/protein content and potassium content in wheat straw. The presence of A. spica-venti significantly reduced both the weight of the main wheat spike and the number of non-productive tillers. The limited effectiveness of biostimulants may be associated with the severity and timing of stress exposure during reproductive development.