Nitrogen Utilization by Grain Sorghum as Affected by Rate of Nitrogen Fertilization and Plant Density: A Preliminary Study

Grain sorghum ( Sorghum bicolor (L.) Moench ) has become a popular alternative to maize in drought‐stricken areas of Hungary. A three‐factorial small plot field experiment was conducted in Keszthely (Hungary) in order to examine the effects of plant density (D1 = 240,000, D2 = 280,000 plants ha −1 ) and nitrogen (N) application (N0–N5 = 0−40−80−120−160−200 kg ha −1 ) on the N utilization characteristics and grain content indicators of four commercial grain sorghum cultivars (G1 = KWS Nemesis, G2 = RTG Huggo, G3 = GK Erzsébet, G4 = ES Foehn). The results revealed that the utilization of applied N was better in D2, which also resulted in a significant increase in most quantitative parameters. This can be verified based on generally higher total N uptake, nitrogen harvest index (HI N% ), nitrogen utilization efficiency (NUtE), and agronomic N use efficiency (AE N ) values. Plant density treatment did not have a significant effect on grain N content ( p = 0.096), but compared to D1, the densification of grain sorghum significantly reduced crude protein ( p < 0.001) and starch ( p < 0.001) contents. An inverse proportional relationship between the evolution of grain protein and starch contents was also found. Optimum N rates varied between 120 and 160 kg N ha −1 for G1 and G2, both in D1 and D2, 40–80 kg N ha −1 for G3 in D1 and 80–120 kg N ha −1 in D2 and 120–160 kg N ha −1 for G4 in D1 and 160–200 kg N ha −1 in D2. In conclusion, a genotype‐specific approach in the optimization of Hungarian grain sorghum cultivation technology is required to ensure potential performance and to reduce N loss.