Ecosystem services of wheat-maize cropland systems in the North China Plain

Field investigations were conducted at Luancheng Agro-Ecosystem Experimental Station of Chinese Academy of Sciences in Hebei Province for the period from 2006 to 2007. The field data were then used to evaluate ecosystem services of wheat-maize croplands in the North China Plain. Ecosystem services analyzed in the study included primary products, gas regulation, soil organic matter (SOM) accumulation, water regulation and nitrogen transformation. The results showed that primary products from croplands accounted for 5.04~5.71 t·hm^-2·a^-1 of wheat grain, 6.69~8.24 t·hm^-2·a^-1 of maize grain, 8.58~9.72 t·hm^-2·a^-1 of wheat straw and 6.97~8.58 t·hm^-2·a^-1 of maize straw. As for cropland gas regulation, O₂ and N₂O emissions were 24.99~28.64 t·hm^-2·a^-1 and 0.72~1.13 kg·hm^-2·a^-1, whereas CO₂ and CH₄ assimilations were 34.23~39.22 t·hm^-2·a^-1 and 3.39~5.70 kg·hm^-2·a^-1, respectively. While cropland SOM accumulation was calculated at 1.13~2.39 t·hm^-2·a^-1, that of water consumption was 2 890~3 830 m³·hm^-2·a^-1. Soil nitrogen content dropped considerably at the rate of -107.73~5.33 kg(N)·hm^-2·a^-1 after one crop rotation. Total economic value of cropland ecosystem services was estimated at 5.48×104~6.25×104 Yuan·hm^-2·a^-1, which was three times the value of food production. Based on the results, effects of nitrogen fertilizer on the welfare of cropland ecosystem services was complicated. Nitrogen application led to economic loss due to increasing nitrogen transformation, simultaneously, increased economic value of primary production, gas regulation, CO₂ fixation, and O₂ releasing. Most ecosystem services studies have focused on the positive effects of ecosystems on human welfare. But a balanced and reasonable approach was to analyze both the positive and negative effects of cropland ecosystem services on human welfare.