Efficiency of nitrogen fertilization in spring wheat

An assessment of the nitrogen fertilization efficiency should not only include quantitative and qualitative yield changes, but also an analysis of formation some indicators such as: N harvest index (NHI), N use efficiency (NUE), N utilization efficiency (NUtE), N agronomic efficiency (NAE), N physiological efficiency (NPE) and N apparent recovery fraction (NRF). The objective of the study was the evaluation of spring wheat N fertilization efficiency under soil conditions of Luvic Chernozem. Factors of the experiment were: cultivar (Bombona and Tybalt) and level of N fertilization (0, 60, 90, 120 and 150 kg N ha-1). The application of increasing N rates in the wheat crop raised the grain N from 56 to 92 kg N ha-1 and the aboveground biomass N from 70 to 123 kg N ha-1 and it decreased most of the efficiency indicators. The highest NHI value of 84%, PFNUE of 139.5 kg kg-1, NAE of 32.7 kg kg-1, NPE of 72.2 kg kg-1 and an NRF of 47% were observed for the lowest N rate of 60 kg N ha-1. The NUtE of 92.8 kg kg-1, was at the highest level on the control plot. Every increase on N rate resulted in a significant decrease in the efficiency indicators. The cultivar factor significantly affected the grain and aboveground biomass N and the NAE, NPE and NRF values. Low rainfall depths during the vegetative period favorably affected the NHI, NUtE, NAE and NPE indicators. On the other hand, excessive rainfall depths limited PFNUE, NAE, NPE and NRF.