A study on the spatial difference of farmland nitrogen nutrient budget in the Bohai Rim region, China

The Bohai Rim region is one the most important bases for commodity grain production in China. With the rapid pace of agricultural industrialization, nitrogenous fertilizer has been used at an ever increasing rate, which resulted in the trace of accumulative nitrogen in the soil and caused serious environmental problems. In this study we made use of the farmland nitrogen balance model to assess the spatial difference of farmland nitrogen nutrient budget in the Bohai Rim region in 2008 with the assistance of GIS. Our results indicated that: 1) Farmland in this region has a nitrogen surplus totaling 5.0822 million tons, or an average of 288.54 kg/ha. 2) In the Bohai Rim region, farmland nitrogen input and farmland nitrogen budget both show a spatial differentiation. Major grain-producing areas have a higher nitrogen input than that of the grazing-farming areas. The main sources of nitrogen input include chemical fertilizer, organic fertilizer, deposition from atmospheric drying and wetting, and biological fixation, which account for 79.47%, 9.53%, 4.62%, and 3.58% of the total input, respectively. Therefore, chemical fertilizer is the predominant source of nitrogen input to farmland. 3) A total of 3.3398 million tons of nitrogen were output from the farmland via harvested crops and it accounts for 52.36% of the total nitrogen output from farmland in this region. On average, the amount of nitrogen output from unit farmland is equal to 176.65kg/ha. This study has shed light on farmland nitrogen budget and its spatial variation in the study area, may provide scientific evidences for rationalizing the use of chemical fertilizer and managing agricultural operation on the regional scale and is also valuable for improving the economic and ecological efficiency of fertilizer use at the regional scale