1Inner Mongolia Agricultural University，Hohhot 010018，Inner Mongolia，China；2Inner Mongolia Academy of Agricultural and Animal Husbandry Sciences，Hohhot 010031，Inner Mongolia，China；3Wuchuan Observing and Experimental Station of National Soil Quality，Hohhot 011705，Inner Mongolia，China
Abstract：In view of the low nitrogen use efficiency in the main potato producing areas in Inner Mongolia，two typical ecological areas，namely，the southern foothills of Yinshan Mountain（Chahar Right Wing Front Banner，Wulanchabu City）and the northern foothills of Yinshan Mountain（Wuchuan County,Hohhot City），were selected to study the changes of SPAD value of high-yield potato leaves under different
nitrogen application rates，and the relationship between SPAD value and nitrogen application rates and potato yield．The results showed that the SPAD value of high-yield potato leaves under different nitrogen treatments decreased gradually with the advancement of growth period；With the increase of nitrogen application rate，the SPAD value of potato leaves increased linearly，and the yield of potato increased first and then decreased，which indicated that the relationship between SPAD value of potato leaves and yield was quadratic function．When SPAD value of potato leaves exceeded a certain value，the yield increase of potato was no longer significant．In Wuchuan，the nitrogen application rate was 225 kg·hm-2，and the highest yield was 46.2 t·hm-2；Nitrogen application rate was 350 kg·hm-2 in Qianqi，and the highest yield was 61.7 t·hm-2；The critical SPAD values were 43.4，41.5，40.7，34.6，32.0 at the northern foot of Yinshan，49.3，49.1，44.9，37.8，35.6 at the southern foot of Yinshan，respectively at seedling stage，tuber formation stage，early tuber expansion stage，late tuber expansion stage and starch accumulation stage；Based on the SPAD value of potato leaves，the topdressing model of nitrogen fertilizer in main growth stages of high-yield potato in two ecological regions was established．
