Internal Efficiency of Macronutrients in Barley Depending on Nitrogen Nutrition

Bulgarian barley varieties Emon, Obzor, Krami, Kristi and Kaskadior were studied at three levels of nitrogen nutrition 0, 200 400 mg N.kg⁻¹ soil in a pot experiment. The nitrogen levels were created by adding NH4NO3 dissolved in water. Each experimental treatment was studied in four replicates. Ten plants of each variety were grown in plastic pots filled with 5 kg alluvial-meadow soil under greenhouse conditions. The Internal efficiency (IE) of the absorbed nitrogen (N), phosphorus (P2O5), potassium (K2O), calcium (CaO) and magnesium (MgO) was studied in relation to the grain (IEg) and biomass (IEb) formation. The internal efficiency was calculated as the ratio of the grain yield or biomass yield to the total absorbed nutrient at maturity (g.g⁻¹). It was established that the internal efficiency of macronutrients proven decreased in parallel with increased nitrogen input into the soil. Higher reduction of the internal efficiency of nitrogen by 25.5% for grain and by 29.4% for biomass was found at N400 level, compare to N0. The studied barley varieties did not show proven differences in the internal efficiency of nitrogen, phosphorus and potassium for grain and biomass formation. A trend was found indicating the Kristi variety as more efficiently using the accumulated nitrogen for both grain (NIEg=43.9 g.g⁻¹ N) and biomass formation (NIEb=106.7 g.g⁻¹ N), regardless of the soil nitrogen. The Kaskadior variety could be referred to as less efficient. A strong negative relationship was found between the soil nitrogen level and the internal efficiency of nitrogen, phosphorus and potassium for grain and biomass formation, as well as a significant negative relationship (r=-0.536*) with the internal efficiency of magnesium for grain. Index of NIEg was in a strong positive correlation with the internal efficiency of phosphorus, potassium and magnesium for grain and biomass formation.