3.5 Nutrient balances and the fates of surplus nutrient
Over 25 years, the combined total N inputs at the county scale were much higher in Meixian (16881 kg ha-1) than in Wugong (9880 kg ha-1) (Fig. 6). N fertilizer input in Wugong County is 6279 kg ha-1, while the N input in Meixian County was 13452 kg ha-1, resulting in a higher N surplus in Meixian than in Wugong County. Regarding the fate of N inputs, N outputs by harvesting crops were 5256 kg ha-1 (53.2% of the total N inputs) in Wugong and 4236 (25.1%) kg ha-1 in Meixian. This resulted in the accumulation of 40.7% and 9.9% of the total N surplus as nitrate in 0-2 m soil profiles in Wugong and Meixian, respectively, and 34.7% of the total N surplus accumulation in 0-5 m soil profiles in Meixian County. N stored in kiwi vines in Meixian County was 2.4% of the total N surplus. About 59.3% and 62.9% of the total N surplus was lost through NH3, N2, and N2O emissions and into deeper soil and groundwater in Wugong and Meixian counties, respectively.
Total P inputs over 25 years in Wugong and Meixian counties were 2788 and 3456 kg ha-1, including synthetic fertilizers (2182 and 2954 kg ha-1), manure (546 and 447 kg ha-1), straw return (27 and 23 kg ha-1), irrigation (22 and 22 kg ha-1) and wet atmospheric deposition (11 and 12 kg ha-1). P surplus was 57.8 % and 72.4 % of the total P inputs, and crop uptake was 42.2 % and 27.6 % of the total P inputs in Wugong and Meixian counties, respectively.
Total K input over 25 years in Wugong and Meixian counties were 4300 and 7416 kg ha-1. Regarding the fate of K inputs, 92.8% and 46.3% of the total K inputs were removed by harvested crops. Unlike the N and P balance, the K surplus was 7.2% of input in Wugong County, but Meixian County K surplus was 53.7%.