The effects of plant density and nitrogen dose on the quantitative indicators and weed infestation of grain sorghum

The replacement of maize with grain sorghum is a promising practice for enhancing climate change adaptation strategies in the drought-prone areas of Central Europe. The refinement of the agrotechnics of commercial hybrids contributes to the development of sustainable agriculture. A field experiment was conducted between 24 May 2023 and 27 September 2023 in Keszthely (Hungary) in order to evaluate the effects of plant density (D1 = 240,000 plants ha–1, D2 = 280,000 plants ha–1) and equidistantly increasing N doses (0–40–80–120–160–200 kg N ha–1) on the grain yield, biomass weight and leaf area index (LAI) of 4 grain sorghum cultivars (G1 = KWS Nemesis, G2 = RTG Huggo, G3 = GK Erzsébet, G4 = ES Foehn). Another aim was to examine the effect of treatments on weed coverage. According to the results, plant density and N treatment had a general significant effect on grain yield (p < 0.05), biomass weight (p < 0.05) and LAI (p < 0.05; p = 0.015), regardless of the applied cultivar. Positive correlations were observed between biological and grain yield (D1: r = 0.9, p = 0.02; D2: r = 0.91, p = 0.01) as well as between LAI and grain yield (D1: r = 0.89, p = 0.6; D2: r = 0.91, p = 0.07). Significant differences were also observed between the grain yield (p < 0.05), biomass weight (p < 0.05) and LAI (p < 0.05) of the cultivars. In general, grain yields peaked around 120 kg N ha–1 at the plant density of 240,000 plants ha–1 and around 160 kg N ha–1 at the plant density of 280,000 plants ha–1. Among the experimental conditions RTG Huggo yielded the best results. In general, weed coverage was significantly lower (p = 0.002) in denser stands. The enhancing effect of N on weed coverage could not be detected (p = 0.318). In conclusion, a plant density of 280,000 plants ha–1, a N dose of 120–160 kg N ha–1 and RTG Huggo cultivar proved to be the best under the experimental conditions.