Responses of yield, nutrient uptake, and quality of hybrid sorghum varieties with different shoot heights to nitrogen fertilizer in China

Objectives Hybrid sorghum varieties are quite different in height to meeting specific purpose. We studied their yield and nutrient utilization response to nitrogen fertilizer, to provide technical supports for high efficient sorghum production.

Methods Field experiments were carried out in 2020 and 2021. Forty hybrids were collected across China, and were classified into three groups based on shoot height: short (<1.3 m), moderate (1.3–1.6 m), and tall (>1.6 m) respectively. All varieties were subjected to no N application (N0) and N 150 kg/hm² (N150) treatment. At harvest, sorghum grain yield, grain number per ear (GPE) and 1000-grain weight (TGW), aboveground biomass were investigated. The contents of NPK in both shoot and grain were determined. Grain starch, protein and tannic content were analyzed as well. The N uptake efficiency and N use efficiency (grain yield/N absorption) were calculated.

Results Grain yield and aboveground biomass increased significantly with sorghum shoot height; whereas the harvest index did not vary among varieties. Tall and moderate varieties had similar grain yield and GPE. N150 increased GPE whereas decreased TGW of tall and moderate varieties but had no significant effect on those of short varieties. The aboveground N, P, and K accumulations of sorghum increased linearly with shoot height. Tall and moderate varieties had similar N accumulation. The three variety groups had similar N uptake efficiency, 25.5%–30.4%, whereas tall and moderate varieties had significantly higher grain N use efficiency than short varieties. Plant height had significant and positive correlation with grain starch content, but negative correlation with protein content. Compared to N0, N150 decreased starch content but increased protein content, however, tannic content for all the three variety groups was not affected.

Conclusions The tested hybrid sorghum varieties have similar harvest index and N uptake efficiency. Tall and moderate sorghum varieties have higher grain number per ear, yield, grain starch content and nitrogen grain use efficiency, and are more sensitive than short varieties in response to nitrogen fertilizer. Moderate varieties require lower NPK rate than tall varieties. Comprehensively considering yield and fertilizer efficiency, and the demand of mechanized harvest, hybrid sorghum varieties with shoot height of 1.3–1.6 m are recommended for adoption.