The effect of split application of mineral nitrogen on biomass yield and nitrogen content, uptake, use efficiency and harvest index in spring rye

The spring form of rye can be grown on soil with relatively low utility value and in areas where winter rye becomes damaged during the winter. Under conditions of soil with low sorption complexes, it is important to adopt the right nitrogen application strategy to achieve high fertilizer efficiency (high yield). This study determined the weight of the separated parts of spring rye, productivity of 1 kg of nitrogen introduced into the soil with mineral fertilizer (E), N content (Nc), N uptake (Nup), N uptake per day (Nup/day), nitrogen use efficiency (NUE), nitrogen utilization efficiency for yield (NutEY), and the nitrogen harvest index (NHI) in six stages of development: BBCH 22, BBCH 33, BBCH 51, BBCH 65, BBCH 75 and BBCH 91. NutEY and NHI were calculated in two ways, with and without including the N accumulated in the roots, and were designated NutEY_1 and NutEY_2 and NHI_1 and NHI_2, respectively. Rye was fertilized once before sowing with 120 kg N ha^-1 (N1) and with the same amount split into two portions, i.e. 60 + 60 kg N ha^-1 (N2), and into three portions: 40 + 40 + 40 kg N ha^-1 (N3). There was also a control treatment without nitrogen application (N0). The first portion was always applied before sowing, and the second and third as top dressing. In most cases, both the stage of development and the nitrogen treatments significantly influenced the values of the spring rye parameters. Split application of nitrogen in two or three portions increased the weight of the whole ears, including the grain, and the whole biomass of spring rye harvested at the fully ripe stage, without significantly altering the weight of the roots or straw. At this development stage, split application of nitrogen did not significantly affect the Nc value in any of the separated parts of the plant. Following the application of nitrogen in three portions, the NutEY_2 values were lower than after application in two portions, while values for NutEY_1, NHI_1, NHI_2, grain yield, whole biomass of spring rye, and Nc and NUE for the grain and whole plant were similar, and the Nup value was lower. On average for the entire growing period, the E value for the grain were not significantly altered by splitting nitrogen application into two or three portions, but the values for the whole spring rye biomass were higher following N application in two or three portions than after a single application. During the growth and development of spring rye, there was an increase in total biomass, total Nup, and NUE, and a decrease in average Nc in the whole plant and in Nup/day. In most cases, the inclusion of the roots in the calculation of NutEY and NHI did not result in statistical differences compared to their calculation without the roots.