Response of Wheat and Sugar Beet to Different Mineral–Organic Fertilization in a Long-Term Experiment

The effect of cyclic pig slurry (PS) application in long-term crop rotations with alfalfa is poorly recognized, particularly with regard to nitrogen use efficiency (NUE) in crops requiring relatively high nitrogen (N) inputs. A long-term field experiment was established in Prague-Ruzyně, Czechia, in 1955. The experiment evaluated the effects of eight fertilization combinations, involving PS application and various N, phosphorus (P) and potassium (K) rates (N₀P₀K₀; N₁P₁K₁; N₃P₂K₂; and N₄P₂K₂). The effect of fertilization was evaluated in a 9-year crop rotation, in which PS was applied only three times under root crops. Long-term different mineral fertilization treatments and the application of PS significantly affected the yield of the tested crops: winter wheat and sugar beet. The highest wheat yield (8.34 t ha^-1) was observed in the PS+N₃P₂K₂ treatment, while the highest beet yield (86.1 t ha^-1) was recorded in the PS+N₄P₂K₂ treatment. The differences compared with the absolute control (N₀P₀K₀) were 62.3% and 40.5%, respectively. However, statistically significant differences between treatments with different NPK rates were recorded only in plots without PS. With increasing NPK fertilizer rates, the uptake of macronutrients by plants also increased. The only exception was calcium in sugar beet in PS plots. The total N accumulation in plants was proportionally related to the total N input to the soil-plant system (N_in). For winter wheat, this trend was beneficial, as it resulted in higher protein yield, whereas in beet, the sugar yield did not increase significantly when N_in exceeded 250 kg N ha^-1. The obtained results indicate that, in the soil conditions of this experiment, N rates should be primarily balanced with appropriate rates of phosphorus.