Responses of winter wheat genotypes to reduced rainfall, nitrogen fertilization and pre-crops in Switzerland

Problem: Wheat (Triticum aestivum L.) yields may be reduced by projected rainfall decline due to climate change as well as environmental protection demands for less nitrogen (N) fertilizer inputs. Research question: Therefore, our study aims to determine how projected decreases in rainfall due to climate change and the reduction of N fertilizer inputs might impact the production of different wheat genotypes. Methods: A field experiment was carried out in a warm-summer humid continental climate in Switzerland with two water treatments: rainfed and rainout shelters to reduce rainfall during grain filling. This was overlaid with two N treatments (non-fertilized and enough N supply to reach 180 kg N ha⁻¹), four winter wheat genotypes, and three pre-crops (barley, Hordeum vulgare L.; oilseed rape, Brassica napus L.; winter pea, Pisum sativum L.) across three field seasons. Grain yield and protein content, yield related components, water-soluble carbohydrates (WSC), N use efficiency (NUE) and N associated traits, were among the assessed variables. Additionally, soil mineral N (Nmin) was measured at beginning of tillering. The three seasons encompassed both average and above average precipitation. The rainout shelter extended the rainfall range to low rainfall during grain filling, compared to the last 30 years. Results: The reduced rainfall during grain filling had no impact on yield, regardless of crop season, N fertilizer application, pre-crop, initial Nmin, or genotype. N fertilizer applications had no impact on wheat yield when fields had an initial Nmin > 50 kg N ha⁻¹, nor after a poor crop establishment caused by a wet autumn. During a wet season with initial Nmin ≤ 50 kg N ha⁻¹, wheat responded to N fertilizer after a brassica pre-crop, but less so after a legume or a cereal crop. The genotype with a mean of 29% more grains per unit area, yielded up to 8.2 t ha⁻¹ in one plot and, on average, about 25% higher than the mean of the other genotypes. Conclusions: In the short term, wheat production in warm-summer humid continental climates appears resilient to projected rainfall decline from climate change and reductions of N fertilizer inputs, but excessive rainfall during sowing causing poor crop establishment might be much more devastating. The impact on wheat yields observed only on the third year of consecutive cultivation without N fertilizer, suggests the potential for decreasing N supply over a few years. Implications or significance: This study underscores wheat's short-term resilience to drought and reduced N use, bolstering food security efforts.