This study was conducted to clarify effects of different row spacings and planting densities on the development, yield, grain quality and NPK (nitrogen, phosphorus and potassium) accumulation of grain-feeding sorghum, and to identify the optimal cultivation mode in agro-pastoral ecozone of Shanxi, so as to provide the theoretical basis for the grain-feeding sorghum cultivation.

A new grain-feeding sorghum variety Liaoxialiang No. 1 was selected for this study. Field experiments were conducted during 2018 and 2019. Three row spacings were set, i.e. 30, 50, and 60 cm, respectively. And there were four planting densities (13.5×10⁴, 16.5×10⁴, 19.5×10⁴ and 22.5×10⁴ plants/hm²) at each row spacing. The plant height and biomass at heading stage, grain yield, NPK accumulation at harvest and grain quality in different row spacings and planting densities were analyzed.

There were significantly effects of row spacing, planting density and their interaction on the grain-feeding sorghum growth, nutrient accumulation, grain yield and quality. As plant density increased, the plant height, biomass and NPK accumulation at heading stage were increased. However, the biomass produced after heading, biomass and NPK accumulation at harvest, along with yield, increased first and then decreased with the increase of density under row spacing with 50 and 60 cm; Actually, the grain yield of feeding sorghum was positively correlated with biomass and N accumulation at harvest and the biomass produced after heading. The average grain yield, N and P accumulation and biomass after heading in row spacing of 50 cm were higher than those of 60 and 30 cm. Among the 12 treatments, the treatment with row spacing of 50 cm, planting density of 16.5×10⁴ plants/hm² had improved biomass and N accumulation at harvest, which were increased by 3.6%-12.8% and 3.6%-18.6%, respectively, relative to the average value of the total 12 treatments. The grain yield with row spacing of 50 cm and planting density of 16.5×10⁴ plants/hm² was the highest among all treatments, and they were 10 814 kg·hm^-2 in 2018 and 12 434 kg·hm^-2 in 2019, respectively. Starch and protein content of grain decreased with planting density increasing, but the influence of row spacing variation on them were less. Grain tannin content was significantly increased with planting density adding, while the row spacing increase also promoted tannin content. The influence of row spacing and planting density on tannin content was obvious, compared with those on starch and protein. Those treatments with row spacing of 50 cm and density of 16.5×10⁴ plants/hm² had similar tannin content with the average value of different treatments.

Both N accumulation and biomass production after heading were important for high grain yield of feeding sorghum. The appropriate plant spacing under different row spacings could improve feeding sorghum grain yield, but affect grain quality, especially the tannin content. Row spacing of 50 cm and density of 16.5×10⁴ plants/hm² was recommended in agro-pastoral ecozone in Shanxi (with variety of Liaoxialiang No.1) in terms of grain yield and quality of feeding sorghum.