利用SPAD和Dualex快速、无损诊断玉米氮素营养状况

Evaluation of SPAD and Dualex for In-Season Corn Nitrogen Status Estimation

为了探讨玉米生长过程中适宜的施氮量，以加拿大玉米品种Pioneer 38B84为试验材料，在底施氮为45 kg hm^-2和基本苗7.9万株 hm^-2条件下，研究追氮量0、34、68、101、135、169和203 kg hm^-2以及氮饱和参考小区等8个处理对吐丝后玉米穗位叶SPAD值、Dualex值、地上部生物量及产量的影响。结果表明，SPAD值、地上部生物量以及产量均随追氮量增加而增加，Dualex值随追氮量增加而降低。追氮101、135、169和203 kg hm^-2处理的SPAD-氮饱和指数（SPAD-NSI）在各测定日期均大于0.95。追氮101 kg hm^-2处理的Dualex-NSI在吐丝后18~46 d大于0.95；追氮135、169和203 kg hm^-2各处理的Dualex-NSI在各测定日期均大于0.95。SPAD 值、Dualex 值、SPAD-NSI和Dulaex-NSI均与追氮量显著相关。在拔节期追氮101 kg hm^-2 或135 kg hm^-2即可满足玉米生长对氮素的需求，获得最大的经济产量。当超过最大产量施肥量时，氮肥用量的增加对SPAD值、Dualex值、地上部生物量以及产量均无显著影响。追肥不仅可达到与氮饱和参考小区同样的产量效果，而且还可减少氮肥的施用量，减少种植者的经济投入。在本试验条件下，基施氮45 kg hm^-2，在拔节期适宜的追氮量为101 kg hm^-2或135 kg hm^-2。SPAD叶绿素仪与Dualex仪均可用来诊断玉米的氮素营养状况。

Nitrogen （N） is one of the most important nutrients influencing both yield and grain quality, and N supply is one of the few production factors that can be controlled and which is known to effectively influence crop performance. Both SPAD reading and Dualex reading are shown to be highly correlated with leaf N concentration, and crop N status can be assessed through the SPAD reading and Dualex reading. The purpose of this study was to evaluate the suitable N rate at topdressing time. In order to evaluate the N application rates on SPAD reading and Dualex reading of corn after silking, corn field experiment was conducted with application of 45 kg N ha^-1 at sowing and planting density of 79 000 plants ha^-1 in 2008 on the L’Acadie experimental farm （Quebec, Canada）. Topdressing N was performed with 0, 34, 68, 101, 135, 169 and 203 kg N ha^-1 at jointing stage. N-saturated reference plots with topdressing of 180 kg N ha^-1 at 10 days after sowing, besides 45 kg N ha^-1 at sowing, was established. With increasing topdressing N rates, SPAD reading, aboveground dry biomass and corn grain yield increased, and Dualex reading decreased. The SPAD-NSI of topdressing N treatments with 101, 135, 169 and 203 kg N ha^-1 was always higher than 0.95 at all samplings dates. The Dualex-NSI of topdressing N treatments with 101 kg N ha^-1 was higher than 0.95 from 18 d to 46 d; the Dualex-NSI of topdressing N treatments with 135, 169 and 203 kg N ha^-1 was also higher than 0.95 at all samplings dates. SPAD reading, Dualex reading, SPAD-NSI and Dualex-NSI were strongly correlated with topdressing N rates. The maximum yield was reached when topdressing N was 101 or 135 kg N ha^-1 at jointing stage. When maximum yield was reached, any additional N was no significant effect on SPAD reading, Dualex reading, aboveground dry biomass and corn grain yield. Topdressing N rate of 101 or 135 kg N ha^-1 was enough for corn growth after silking and getting maximum grain yield. There was no significant difference between splitting the N into two applications and N-saturated application on grain yield; however, splitting the N into two applications significantly decreased the total N application rate and growers’ inputs. In the present study, the suitable topdressing N rate was 101 or 135 kg N ha^-1 with 45 kg N ha^-1 at sowing. SPAD and Dualex could be integrated to evaluate in-season N status of corn.