Abstract: The Northern Yin Mountain is the main productive area of potato in Inner Mongolia. Recently, large amounts of chemical N fertilizers were applied to potato fields with the extension of tertigation in the local area. The applied N in excess of potato requirement probably leads to potential environmental risk. In the current study, through on-site investigation, sampling and combining previous resuhs, the N input and output, N residuals and N balance of potato fields in the Northern Yin Mountain were analyzed and N optimum management on a regional scale was evaluated. The results indicated that the total applied N rate as chemical and organic fertilizer ranged between 114.6 and 1 029.5 kg/hm^2, with an average of 440.7 kg/hm^2 in irrigated potato fields. The total nitrogen input was 158.5-1 076.1 kg/hm^2, with an average of 496.4 kg/hm^2 and total N output was 134.4-335.7 kg/hm^2, with an average of 249.5 kg/hm^2. Thus, the N in irrigated potato fields occurred in surplus. The amount of N surplus changed fi＇om 18.6 to 742.9 kg/hm^2, with an average of 249.5 kg/hm^2, which caused high N residual in the soil （227.0 kg/hm^2）. The nitrate content of groundwater achieved 5-74 mg/L, with an average of 22.4 mg/L. It is concluded, in Northern Yin Mountain, that the N input in irrigated potato fields greatly exceeds potato demand and maintains a surplus. Technologies and methods tor eflective N tertilizer managenlent are urgently needed in this area. Otherwise, environmental risks will rise, which influence local production and the livelihoods of farmers and herdsmen.

Key words: Irrigated potato;Nitrogen input;Nitrogen output;Nitrogen balance;Nitrogen loss;Nitrate