3.1 Nutrient inputs, outputs and surpluses
Nutrient inputs to croplands of the two counties have increased gradually since 1992 (Fig. 2), with a greater increase in Meixian than in Wugong County. In Wugong County, total N, P, and K increased from 303, 77, and 118 kg ha-1 in 1992 to 526, 136 and 240 kg ha-1 in 2017, with growth rates of 74, 77, and 103%, respectively. Whereas in Meixian County, total N, P, and K increased from 464, 71, and 118 kg ha-1 to 887, 216, and 552 kg ha-1, with growth rates of 91, 204, and 368%. Among various input sources, nutrients from synthetic fertilizers are the main contributors. Nutrient outputs in the two counties over the years remained relatively stable, resulting in high nutrient surpluses, especially in Meixian County.