Optimum plant density and nitrogen level for the efficient accumulationand transportation of dry matter and nitrogen in waxy sorghum

Objectives Planting density and nitrogen application level affect the efficient accumulation and transportation of dry matter and nitrogen. Here, we studied the optimum plant density and nitrogen levels of waxy sorghum to provide technical support for Guizhou’s green and efficient sorghum industry.

Methods Field experiments were conducted in Huairen City of Guizhou Province in 2017 and 2018; the waxy sorghum cultivar ‘Hongyingzi’ was used as test material. We used a split-plot design for the experiment, with low, medium and high planting densities: 9×10⁴ plants/hm², 11.25×10⁴ plants/hm², and 13.5×10⁴ plants/hm² assigned to the main plot, and four N application rates: 0, 120, 240 and 360 kg/hm² were allotted to the subplot. Plant samples were collected at the anthesis and maturing stages to determine biomass and N content. Yield and yield components were investigated at harvest.

Results The yield of waxy sorghum reached the maximum under medium plant density (4805 kg/hm²) and N application rate (4768 kg/hm²). The effective panicles per unit area were increased by 24.93% and 51.13% in the medium and high planting densities than in low density. N application increased the effective panicle number per unit area, 1000-grain weight, and panicle length. The total dry matter (nitrogen) accumulation, ratio, and its proportional contribution to translocation in the grain of waxy sorghum (P<0.05) increased with increasing planting density and nitrogen application. Nitrogen recovery efficiency, apparent recovery rate, agricultural efficiency, partial productivity, and nitrogen physiological efficiency of waxy sorghum were (P<0.05) higher at medium and high density than under low density. However, these parameters decreased with increasing N application. The relationship among planting density (D), N rate (N) and yield (Y) was Y=2169.72D+7.14N–94.52D²–0.016N²+0.059DN–8198.737. The maximum yield reached 7720.92 kg/hm² when the planting density and N application rate were 11.53×10⁴ plants/hm² and 234.29 kg/hm², respectively.

Conclusions The optimum planting density and N application rate can promote dry matter, nitrogen accumulation and translocation, and improve nitrogen use efficiency and waxy sorghum yield. Under the test conditions, the optimal density and N application rate were 11.53×10⁴ plants/hm² and 234 kg/hm².