Effects of Different Nitrogen Regimes on Canopy Structure and Partial Physiological and Agronomic Traits in Summer Maize

Over-fertilized nitrogen leds to irrational crop canopy in summer maize,and thus negatively affected yield production.Therefore,it is important to study the nitrogen application time and level for the construction of efficient crop canopy.A field experiment was conducted using summer maize Zhengdan 958 with four nitrogen application regimes including low basal nitro-gen fertilizer(30 kg ha-1),high basal nitrogen fertilizer(120 kg ha-1),first nitrogen dressing at jointing stage(30 kg ha-1),and zero-nitrogen.The results showed that canopy structure and other indexes were improved by nitrogen input.Slightly reducing of basal nitrogen provided the following advantages:(1) The amount of nitrogen fertilizer was significantly reduced without negative effect to maize seedlings,i.e.90 kg ha-1 nitrogen saved;(2) The canopy structure was improved with high light transmission rate at the bottom of canopy and more compact leaf structure.Compared with the treatment of high basal nitrogen fertilizer,the leaf angel above ear of canopy and mean leaf angel decreased 4.33° and 4.67° respectively in the treatment of low basal nitrogen fer-tilizer.Simultaneously,plant height and ear height were both reduced and the length of the basal stem internodes shortened,which effectively prevented stem from lodging;(3) Under low basal nitrogen fertilizer,canopy SPAD value and nitrogen concentration of the leaf were equivalent with high basal nitrogen treatment;(4) The grain yield was higher under low basal nitrogen fertilizer than under other nitrogen regimes due to the increase of ear number,thousand grain weight,grain number per ear and the decrease of bald tip length of the ear.First nitrogen dressing at jointing stage led to worse nitrogen condition before jointing stage,and thus limited yield formation and crop growth due to runtish seedlings and imbalanced nutrition.