Abstract: 【Objective】The purpose of this study is to elucidate morphological and physiological mutual beneficial mechanism for compact type maize hybrid under nitrogen and density interaction, for further raise overall productivity of density tolerant maize hybrid.【Method】Plant morphological trait, ear leaf photosynthetic ability and yield were determined under field experimental condition in 2014 and 2015. Split-split plot design, 2 plant type hybrids (compact plant type and flat plant type) as the main plot, 3 nitrogen treatments (N1: 0, N2: 90 kg N·hm^-2 and N3: 180 kg N·hm^-2) as the split plot, 3 plant densities (D1: 45 000 plant/hm², D2: 60 000 plant/hm² and D3: 75 000 plant/hm²) as the sub-split plot. 【Result】The effects of nitrogen on internode length, leaf angle, SPAD value, kernel weight per ear and yield were stronger than that of density on those parameters. Stem diameter, Pn and kernel number per ear was sensitive to density increasing. Compared with flat type hybrid, decreased range of stem diameter was small, and response sensitivity from 1 to 3 internode length was slowness with plant density increased for compact type hybrid. However, the 1-3 internode length was shortened significantly with nitrogen input amount increased (P_N2→N3=0.004-0.028), negative response range of 4-5 internode length for compact type hybrid (10.9%) was higher than positive response range of 4-5 internode length for flat type hybrid (3.3%). Leaf angle of compact type hybrid was down to 2.9°±1.1° with nitrogen input. The leaf angle of leaf below ear leaf changed to a relatively lower with plant density increased. Response peak value of SPAD to nitrogen for compact type hybrid (N₃) was higher than that for flat type hybrid (N₂). The negative effect of Pn caused by density increasing was relatively small for compact type hybrid. SPAD and Pn of ear leaf for compact type hybrid were higher than that for flat type hybrid in N₃ and D₃ treatment. Altogether, the effect of nitrogen and density interaction on kernel number and kernel weight per ear for compact type hybrid was smaller than that for flat type hybrid. Harvest index of compact type hybrid was relatively high, which the difference between N×D interaction treatment (P _N1→N3 =0.16，P_D1→D3 =0.12) was no significant, however, that the difference between that (P _N1→N3 =0.03，P _D1→D3＜0.01) of flat type hybrid was very significant. The highest yield record was obtained in N₃D₃ and N₃D₁ treatments for compact and flat type hybrid, respectively. And their yield gain ratio for density and nitrogen was 1﹕2.3 and 1﹕4.0, respectively. 【Conclusion】 Compared with flat type hybrid, compact type hybrid had a more adaptable ability of regulating cross and longitudinal growth of basal part of stem. Nitrogen application could reduce leaf angle of leaf above ear leaf, ear leaf and leaf below ear leaf, which could enhance ear leaf light use efficiency. Proper morphophysiological coordinate ability keeps a higher dry matter transfer rate for the compact type hybrid under higher density and higher nitrogen fertilizer condition at kernel weight formation stage, thus achieving a higher population yield.

Key words: maize, plant type, nitrogen, plant density, morphology, photosynthetic property, yield