The efficient use of radiation, water, and nitrogen uptake by low-nitrogen-tolerant broomcorn millet (Panicum miliaceum L.) increased grain yield in the Loess Plateau, China

•Low N input decreased broomcorn millet grain yield by poor resource use efficiency.•Low-N-tolerant cultivars performed better than low-N-sensitive cultivars at low N.•Low-N-tolerant cultivars had increased photosynthesis and dry matter transport.•Low-N-tolerant cultivars had high productivity under field conditions.