Abstract: Under field condition,this paper studied the effects of shading on the growth,development,and grain yield of summer maize varieties ND108 and YD13.The results showed that shading decreased maize yield significantly,and the effect was differed with different shading period and intensity.With a shading intensity of 50% and 90%,the grain yield of ND108 and YD13 was decreased by 67.5% and 79.4%,and 82.9% and 86.7% when shading at flowering-maturing stage,and by 34.1% and 55.3%,and 47.2%,65.7% when shading at joining-flowering stage,respectively.Shading at seedling-joining stage had a relatively smaller effect,with the grain yield decreased by 16.9% and 24.5%,and 18.9% and 24.3%,respectively.Shading had a larger effect on YD13 than on ND108,and the effect of shading period was larger than that of shading intensity.Under shading,the growth and development of maize was retarded,and the effect was increased with increasing shading intensity.Shading at joining-flowering stage affected spike differentiation significantly,reflecting in the marked decrease of the numbers of silks and tassels,and the effect was also larger on YD13 than on ND108.The leaf and plant growth was restrained significantly when shading at seedling stage and at flowering-maturing stage.

Key words: rice, long-term experiment, biomass, C and N contents, fertilization