Balance of field nitrogen nutrient input/output using GIS technology in China

This study presents a detailed investigation of the supply and demand status of nitrogen for more than 2000 counties across the country. In the study, statistic data, field survey results, graphic data and a number of datasets published in the literature were analyzed and the spatial distribution of nitrogen balance was presented with GIS technology. Results show that the total national input of nitrogen for cropland is 34.22×10⁶ t, but only 31.57×10⁶ t of which has been used, inducing a net excess supply of 2.65×10⁶ t. Despite this overall excess, the number of counties with a deficit supply of nitrogen is 37.68% of the total and the cropland of these counties is 43.1% of national total cropland. These counties are located in each province. At national scale, chemical nitrogenous fertilizer, organic nitrogenous fertilizer, biological nitrogen fixation and other nitrogen supply occupy 76.54%, 16.26%, 3.10% and 4.09% of the total nitrogen supply, respectively. While the contribution of chemical nitrogenous fertilizer plays a dominant role in the overall supply, the excrement and urine of human and animals are the main sources in organic nitrogen supply. The biological output of nitrogen from national cropland amounts to 19.87×10⁶ t, weighting 62.85% of the total expenditure. Among provinces, the weight of the biological output of nitrogen in Heilongjiang Province is the highest, nearly 85%.