Abstract: Four spring maize cuhivars, two density-resistant hybrids （Huameil, Zhengdan958） and two non-density resistant hybrids （Nongdal08, Kehe8） were used as expm＇iment materials to study the effects of different planting densities （PD8.25,PD10.5） and nitrogen rates （0N,150N,300N） on yield and physiological characteristics of different density toleranet spring maize varieties. The resuhs showed the yield-enhancing potential of the density-resistant hybrid Huameil was exerted after the densifieation, the yield increased signifcantly and was greater than that of the non-density resistant hybrids, while the non-density resistant hybrids showed a decrease in yield. Under the conditions of PD10.5, yield did not significantly increase with the increase of nitrogen fertilizer, and even a decrease in production oeemTed. As the density increases, the leaf area index increases, while the net photosynthetic rate （Pn）, relative chlorophyll content （SPAD）, and maximum photochemical eflleieney （Fv/Fm） all deereased. Nitrogen application eased the pressure from densifieation and improved photosynthetic performance under high density conditions. Compared with weaker and denser varieties, density- resistant hybrids can maintain high photosynthetic capacity in the later growth period.

Key words: Maize;Increased density and reduced N rates;Yield;Physiological characteristics