Abstract. A Nationwide Nitrogen Deposition Monitoring Network (NNDMN) containing 43 monitoring sites was established in China to measure gaseous NH3, NO2, and HNO3 and particulate NH4+ and NO3− in air and/or precipitation from 2010 to 2014. Wet/bulk deposition fluxes of Nr species were collected by precipitation gauge method and measured by continuous-flow analyzer; dry deposition fluxes were estimated using airborne concentration measurements and inferential models. Our observations reveal large spatial variations of atmospheric Nr concentrations and dry and wet/bulk Nr deposition. On a national basis, the annual average concentrations (1.3–47.0 μg N m−3) and dry plus wet/bulk deposition fluxes (2.9–83.3 kg N ha−1 yr−1) of inorganic Nr species are ranked by land use as urban > rural > background sites and by regions as north China > southeast China > southwest China > northeast China > northwest China > Tibetan Plateau, reflecting the impact of anthropogenic Nr emission. Average dry and wet/bulk N deposition fluxes were 20.6 ± 11.2 (mean ± standard deviation) and 19.3 ± 9.2 kg N ha−1 yr−1 across China, with reduced N deposition dominating both dry and wet/bulk deposition. Our results suggest atmospheric dry N deposition is equally important to wet/bulk N deposition at the national scale. Therefore, both deposition forms should be included when considering the impacts of N deposition on environment and ecosystem health.

Abstract. Soil carbon sequestration is a complex process influenced by agricultural practices, climate and soil conditions. This paper reports a study of long-term fertilization impacts on soil organic carbon (SOC) dynamic from six long-term experiments. The experiment sites are located from warm-temperate zone with a double-cropping system of corn (Zea mays L.) -wheat (Triticum Aestivium L.) rotation, to mild-temperate zones with mono-cropping systems of continuous corn, or a three-year rotation of corn-wheatwheat. Mineral fertilizer applications result in an increasing trend in SOC except in the arid and semi-arid areas with the mono-cropping systems. Additional manure application is important to maintain SOC level in the arid and semi-arid areas. Carbon conversion rate is significant lower in the warmtemperate zone with double cropping system (6.8%-7.7%) than that in the mild-temperate areas with mono-cropping systems (15.8%-31.0%). The conversion rate is significantly correlated with annual precipitation and active accumulative temperature, i.e., higher conversion rate under lower precipitation and/or temperature conditions. Moreover, soil high in clay content has higher conversion rate than soils low in clay content. Soil carbon sequestration rate ranges from 0.07 to 1.461 t ha −1 year −1 in the upland of northern China. There is significantly linear correlation between soil carbon sequestration and carbon input at most sites, indicating that these soils are not carbon-saturated thus have potential to migrate more CO 2 from atmosphere.

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Predictive models for the accumulation of available phosphorus (Olsen-P, extracted with 0·5 mol/l sodium bicarbonate (NaHCO 3 ) at pH 8·5) in the north-western arid areas of China, especially in Xinjiang, are essential for the improved management of phosphorus (P) fertilizers. In the present study, an accumulation model for Olsen-P in grey desert soil (Calcaric Cambisol) was developed using the data for initial Olsen-P in soil, P fertilizer application rate (organic and inorganic P), crop yields, and soil pH from a 22-year long-term experiment (1990-2011) with 3-year rotation of wheat (Triticum aestivum L.), maize (Zea mays L.) and cotton (Gossypium spp.). The model was also validated independently using previously published data from the literature. The results indicated an average net accumulation of Olsen-P in the plough layer (0-200 mm) of 0·36 mg/kg/year (from 0·083 to 0·47 mg/kg/year) when P fertilizer was applied, while an average net Olsen-P loss of 0·12 mg/kg/year (from 0·067 to 0·26 mg/kg/ year) was observed without P fertilization in the soil. For target yields of wheat, maize and cotton at 5, 6 and 6 tonne/ha (t/ha), respectively, in soil with pH 8, the rates of Olsen-P increase in the soil as estimated by the model were 0·11, 0·24, 0·36, 0·49 and 0·61 mg/kg/year when P application rates were 60, 70, 80, 90 and 100 kg P/ha per 3-year period, respectively. For every 100 kg/ha of P surplus, Olsen-P increased by 1·1 mg/kg in Xinjiang grey desert soil. This Olsen-P accumulation model was valuable for the management of soil P in agricultural production and environmental protection in north-western China and other arid areas planted with a yearly rotation of wheat, maize or cotton.