The impact of precipitations and air temperatures on winter wheat yields was evaluated in a 34-year long-<br /> term field trial with mineral and organic fertilization established at two experimental sites with different soil-climatic conditions: Ivanovice na Hané with well fertile soils (degraded Chernozem), higher average year temperatures and lower precipitations; Lukavec situated in Bohemian-Moravian highlands with less fertile soils (Cambisol), lower temperatures and higher precipitations. At both sites, a significant positive effect of used fertilizers was noted from the dose of 80 kg N/ha; the best yields were generally obtained at 120 kg N/ha and 160 kg N/ha. The wheat yields at the Ivanovice site were negatively affected by the decrease of precipitations, namely in more fertilized treatments, particularly farmyard manure + mineral nitrogen, from the dose of 80 kg N/ha. A different trend was obtained at the Lukavec site where better winter wheat yields were obtained under lower precipitations. The air temperatures played a positive role at the Lukavec site, but no significant effect of temperature was observed at the Ivanovice site. The less productive areas in highlands can become more interesting for agriculture production with changing climate. However, the soils generally having lower quality and nutrient content can be a limiting factor for obtaining high yields.

The climate changes and increased drought frequency still more frequent in recent periods bring challenges to management with wheat straw remaining in the field after harvest and to its decomposition. The field experiment carried out in 2017–2019 in the Czech Republic aimed to evaluate winter wheat straw decomposition under different organic and mineral nitrogen fertilizing (urea, pig slurry and digestate with and without inhibitors of nitrification (IN)). Treatment Straw 1 with fertilizers was incorporated in soil each year the first day of experiment. The Straw 2 was placed on soil surface at the same day as Straw 1 and incorporated together with fertilizers after 3 weeks. The Straw 1 decomposition in N treatments varied between 25.8–40.1% and in controls between 21.5–33.1% in 2017–2019. The Straw 2 decomposition varied between 26.3–51.3% in N treatments and in controls between 22.4–40.6%. Higher straw decomposition in 2019 was related to more rainy weather. The drought observed mainly in 2018 led to the decrease of straw decomposition and to the highest contents of residual mineral nitrogen in soils. The limited efficiency of N fertilisers on straw decomposition under drought showed a necessity of revision of current strategy of N treatments and reduction of N doses adequately according the actual weather conditions.

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The effects of organic and mineral nitrogen fertilization on nitrogen leaching and nitrate concentration in percolated water were simulated using the CANDY model. In a long-term IOSDV field experiment carried out from 1983 to the present in Lukavec, Czech Republic, increasing nitrogen rates from 0 kg to 200 kg N*ha-1 in mineral fertilizers were combined with the application of farmyard manure or straw, the control treatment was without organic fertilization. The simulation results of four rotations in the years 1996-2007 are presented. In the treatments, the average simulated nitrogen leaching ranged from 2 kg to 71 kg N*ha-1 y-1 , the average nitrate concentrations were between 5 mg and 191 mg*l-1. The average year concentration of nitrate about 40 mg*l-1 indicated increasing occurrence of concentrations above 50 mg*l-1 at daily basis. Nitrogen leaching and nitrate concentrations were non-linearly related to the total nitrogen inputs (R 2 = 0.98), the organic fertilizer treatments only negligibly altered the form of the relationship. The average nitrate concentration exceeded 50 mg*l-1 at a total nitrogen input level about 150 kg N*ha-1 ; this corresponding to an average leaching of 20 kg N*ha-1 y-1 .

The yields of winter wheat, winter barley, and potatoes in a long-term field experiment on one of the international IOSDV network sites, were evaluated. The experiment was set up in 1983 in Lukavec, Czech Republic, within a potato growing region on a sandy-loam soil. The experiment includes three systems of organic fertilization: Without manure; manure added for the potatoes; and cereal straw ploughed-down, in combination with increasing nitrogen (N) rates from 0-160 kg N ha 71 or 0-200 kg N ha 71 , for cereals and potatoes, respectively. The results of two rotations, during the years 2002-2007, were analyzed. Nitrogen rates had a strong effect on the yields of all crops (p 5 0.001). The highest average yields of the cereals 7.2-7.4 t ha 71 (wheat), and 5.2-5.5 t ha 71 (barley) were attained with nitrogen rates of 120 or 160 kg ha 71 . With potatoes the highest yields of 46-54 t ha 71 were observed with 150 or 200 kg N ha 71 . The yield differences between the two highest N levels were small and not significant. Organic fertilizers had a positive impact on the yields of all crops (p 5 0.001), with increasing N rates the effect diminished. Manure and straw yield effects for the most part can be attributed to the nitrogen in the manure and the extra N added for better decomposition of the straw. The strong effects of the year conditions upon the yields of all crops (p 5 0.001) were moderated by the N level. The coefficient of variability decreased with increasing N levels from 37-22% (wheat), from 33-16% (barley), and from 32-20% (potatoes).