3.4 Nitrate accumulation in soil profiles
Nitrate contents in soil profiles of orchards were significantly higher than those in cereal fields. The average nitrate contents in 0-2 m soil profiles of kiwifruit orchards of Meixian County was higher than that in cereal fields of Wugong and Meixian counties (Fig. 5). The nitrate accumulation in the 0-2 m soil profiles significantly increased with the increase in stand ages of kiwi orchards. The average nitrate accumulation in 0-2 m soil profiles of 1-10-yr and 11-20-yr kiwi orchards were 591 and 909 kg N ha-1, which were greater than the cereal fields (308 and 194 kg N ha-1in Wugong and Meixian County). The nitrate accumulation in the 0-5 m soil profiles of kiwi orchards with 11-20-yr was as high as 3071 kg N ha-1.