播期与施氮量互作对甜菜光合特性及氮素利用效率的影响

为探明播期与施氮量互作对甜菜光合特性、氮素利用效率及产量的影响，设3个播期：4月14日（早播）、4月21日（适播）和4月28日（晚播），4个施氮量：纯氮0 kg·hm^-2、120 kg·hm^-2、150 kg·hm^-2及180 kg·hm^-2。结果表明，播期和施氮量对甜菜光合特性影响的互作效应显著，同一施氮量下，不同播期之间光合作用指标及氮素利用效率差异显著，早播较适播与晚播更有利于提高甜菜叶绿体色素含量、净光合速率、RuBP羧化酶活性、光系统 Ⅱ 最大光能转换效率、实际光化学量子产量、光化学淬灭系数、光保护能力、氮素利用效率，降低胞间CO₂浓度。同一播期中，随施氮量的提高，相关指标及产质量变化不同，早播条件下，随着施氮量的提高，甜菜光合特性、产量、产糖量、氮素利用效率也随之提高，施氮量为180 kg·hm^-2时，产量和产糖量分别为67 055.33 kg·hm^-2和11 780.83 kg·hm^-2， 氮肥利用率、氮肥农学利用率分别为 43.88%和80.45%，显著高于其他处理(P＜0.05)；适播和晚播条件下，施氮量分别超过150 kg·hm^-2和120 kg·hm^-2时，不利于提高甜菜光合特性、氮素利用效率。综上，播期与施氮量互作通过改善甜菜光合特性及提高氮素利用效率来影响产量，不同播期适宜的施氮量不同，在本试验条件下，早播且施氮量为180 kg·hm^-2更利于提高甜菜光合特性及氮素利用效率，可获得更高的产质量，若播期后移，则可适当减少施氮量，以达到减氮增产的效果。

Effects of Sowing Date and Nitrogen Fertilizer Interaction on Photosynthetic Characteristics and Nitrogen Use Efficiency in Sugar Beet

In order to investigate the effects of interaction between sowing date and nitrogen application rate on sugar beet’s photosynthetic characteristics,nitrogen utilization efficiency,and yield,three sowing dates were set:April 14th(early sowing),April 21st(optimal sowing),and April 28th(late sowing). Four nitrogen application rates were implemented:pure nitrogen 0 kg·hm^-2,120 kg·hm^-2,150 kg·hm^-2,and 180 kg·hm^-2. The results showed a significant interaction effect of sowing date and nitrogen application rate on the photosynthetic characteristics of sugar beet. Under the same nitrogen application rate,significant differences in photosynthetic indexes and nitrogen use efficiency were observed among different sowing dates. Early sowing was more conducive to improving the chloroplast pigment content,net photosynthetic rate,RuBP carboxylase activity,maximum light energy conversion efficiency of photosystem Ⅱ,actual photochemical quantum yield,photochemical quenching coefficient,photoprotection capacity nitrogen utilization efficiency,there by reducing intercellular CO₂concentration. During the same sowing period,the changes in relevant indicators,yield and quality were showed with the increase of nitrogen application rate. Under early sowing conditions,the photosynthetic characteristics,yield,sugar yield,and nitrogen utilization efficiency of sugar beet also increased with the increasing nitrogen application rates. At the nitrogen application rate of 180 kg·hm^-2,the yield and sugar yield reached 67 055.33 kg·hm^-2 and 11 780.83 kg·hm^-2,respectively. The nitrogen fertilizer utilization efficiency and nitrogen fertilizer agronomic utilization efficiency were 43.88% and 80.45%,respectively,significantly higher than other treatments (P<0.05)；under suitable and late sowing conditions,nitrogen application rates exceeding 150 kg·hm^-2 and 120 kg·hm^-2,respectively,were found to be unfavorable for enhancing the photosynthetic characteristics and nitrogen utilization efficiency of sugar beet. In summary,the interaction between sowing date and nitrogen application rate affects the yield of sugar beet by improving their photosynthetic characteristics and increasing nitrogen utilization efficiency. The appropriate nitrogen application rate varies at different sowing dates. Under the conditions of this experiment,early sowing with a nitrogen application rate of 180 kg·hm^-2 is more conducive to improving the photosynthetic characteristics and nitrogen utilization efficiency of sugar beet,resulting in higher yield and quality. For later sowing date,the nitrogen application rate can be appropriately reduced to achieve desired effect of reducing nitrogen and increasing yield.