Effect of different planting densities on the biological characteristics and yields of photoperiod-sensitive sorghum-sudan hybrids in arid land of east Gansu

In the present study, two photoperiod-sensitive (Sorghum bicolor×S. sudanense), ‘Big Kahuna’ and ‘Monster’, were planted in the rainfed region of the loess plateau at three different planting densities (83 300, 125 000, and 166 700 plants per hectare) by dibbling with plastic film. The growth and development indices and yields of each hybrid were measured and compared. The results showed that for the growth duration, there was a significant difference between the two hybrids after the booting stage. For the agronomic characters, the numbers of tiller and whole plant leaves of ‘Monster’ were higher than that of ‘Big Kahuna’, whereas the other characters of ‘Big Kahun’ were higher than that of ‘Monster’. Stem diameter, tiller number, whole plant leaf number, internode number, and leaves and stem weights per plant of the two hybrids decreased under increasing planting density over the 2 years with a negative correlation. The leaf number of the main culm showed a trend of first increasing and then decreasing with increased density. The fresh grass and dry matter yields of ‘Big Kahuna’ were higher than that of ‘Monster’ over the 2 years and the fresh yield in the 83 000 plants per hectare density was the highest of the three densities and tended to decrease with an increase in density. The dry matter yield in the 166 700 plants per hectare density was higher than that of the other densities during 2014, which experienced abundant rainfall, whereas the yield in the 125 000 plants per hectare density was higher than that of the other densities during the 2015 drought. In conclusion, when photoperiod-sensitive S. sudangrass hybrid are planted in a rainfed region of the loess plateau by dibbling with plastic film, ‘Big Kahuna’ should be chosen at a density of 166 700 plants per hectare in an area with good irrigation conditions or precipitation, otherwise a density of 125 000 plants per hectare should be planted.