Supplemental Material
Nitrogen use efficiencies in Chinese agricultural systems and implications for food security and environmental protection
Baojing Gu,1,2,a Xiaotang Ju,3,a Scott X. Chang,4 Ying Ge,5 and Jie Chang5*
1Deparment of Land Management, Zhejiang University, Hangzhou 310058, PR China
2Policy Simulation Laboratory, Zhejiang University, Hangzhou 310058, PR China
3College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, PR China
4Department of Renewable Resources, University of Alberta, Edmonton, Alberta, Canada T6G 2E3
5College of Life Sciences, Zhejiang University, Hangzhou 310058, PR China
a Both authors contributed equally to this work
*Corresponding Author:
College of Life Sciences, Zhejiang University, 866 Yuhangtang Road, Hangzhou 310058, PR China. Tel & Fax: +86 571 8820 6465. E-mail:
SM Materials and Methods
Source-sink-flux and the mass balance approach. Source-sink-flux analysis uses a series of calculations to determine the sources, internal flows and fates of N within a system. N mass balance is calculated by quantifying N inputs and outputs, then determining if the system is a N source (input < output) or sink (output < input). Internal cycling processes then can be analyzed further. The calculations of N budgets of the three agricultural subsystems were listed as followed:
Cropland subsystem (CL)
CLIN=CLINFer+CLINBNF+i=12CLINExc,i+CLINDep+CLINIrr 1.1
CLOUT=i=14CLOUTCrop,i+i=14CLOUTStr,i+i=16CLOUTLoss,i (1.2)
where CLIN and CLOUT are the total N input to and output from cropland; CLINFer is synthetic fertilizer application; CLINBNF is the BNF, including symbiotic and non-symbiotic N fixation; CLINExc,i is excretion recycled to cropland from both livestock and human; CLINDep is N deposition, including both dry and wet depositions; CLINIrr is Nr input to cropland from irrigation; CLINStr is the straw recycled to cropland (Because straw was harvested first, then part of the harvested straw was chopped up and applied to the soil as organic fertilizer, we considered this as part of input); CLOUTCrop,i is crop production, including crop used as human food, livestock feed, aquaculture feed and industrial materials; CLOUTStr,i is straw production, including straw used as feed, biofuel and industrial materials, and burning in the field; CLOUTLoss,i is Nr loss during crop production, including NH3 volatilization, NO emission, riverine runoff, denitrification (both N2 and N2O) and leaching to groundwater. Nitrogen accumulation is calculated as the difference between CLIN and CLOUT.
Grassland subsystem (GL)
GLIN=GLINFer+GLINBNF+GLINDep 2.1
GLOUT=GLOUTProduct,i+i=15GLOUTLoss,i (2.2)
where GLIN and GLOUT are the total N input to and output from the grassland subsystem; GLINFer is N fertilizer applied to managed grassland; GLINBNF is BNF, symbiotic and non-symbiotic N fixation; GLINDep is N deposition, including both dry and wet depositions; GLOUTProduct is the animal products from grazing livestock; GLOUTLoss is Nr loss from grassland, including burning of livestock excretion, NH3 volatilization, NO emission, leaching and denitrification (both N2 and N2O). Nitrogen accumulation is calculated as the difference between GLIN and GLOUT.
Livestock subsystem (LS)
LSIN=i=12LSINCrop+LSINFer+LSINStr+LSINAqu 3.1
LSOUT=i=12LSOUTMeat,i+LSOUTIndu+i=16LSOUTExc,i (3.2)
where LSIN and LSOUT are the total N input to and output from the livestock subsystem; LSINCrop is crop used as livestock feed both from domestic production and import; LSINFer is the urea input for straw ammoniation to produce feed; LSINStr is the straw used as feed; LSINAqu is the fishmeal used as livestock feed; LSOUTMeat,i is livestock product, including meat and milk, which are transferred to the human subsystem or exported; LSOUTIndu is the livestock product that is not used as food, such products include cocoon, leather, wool, etc.; LSOUTExc,i is livestock excretion, which is recycled to cropland or grassland, lost through riverine runoff, leaching to groundwater or NH3 volatilization, or treated through artificial facilities. N accumulation in the livestock subsystem is calculated as the difference in livestock biomass N stock between the current year and the previous year.
Details about data sources and main parameters used for the calculations can be found in Tables S1-S7.
Table S1 Data sources and main parameters used in the nitrogen balance calculation
Data/Parameters / Description / Unit / Value / ReferencesFor cropland
D1 / Fertilizer applied / Tg N yr-1 / 28.9 (9.4)* / 1
D2 / Crop yield / Tg yr-1 / 546.5 (320.5) / 1
D3 / Irrigation / 109 m3 / 362.0 (269.3) / 1
P1 / Symbiotic N fixation rate / kg N ha-1 yr-1 / 115 / 2
P2 / Non-symbiotic N fixation rate / kg N ha-1 yr-1 / Paddy field: 33; Other: 15 / 2, 3
P3 / Livestock excretion recycled ratio / % / 40-50 / 4, 5
P4 / Human excretion recycled ratio / % / Table S8 / Table S8
P5 / N deposition / kg N ha-1 yr-1 / 21.8 (7.7) / 6
P6 / N concentration of irrigation / mg N L-1 / 1.6 (0.2) / 7
P7 / Grain N concentration / % / Table S3 / Table S3
P8 / Straw N concentration / % / Table S3 / Table S3
P9 / Harvest index / - / Table S3 / Table S3
P10 / Fate of straw / % / Table S4 / Table S4
P11 / N loss ratio / % / Table S5 / Table S5
For grassland
P12 / Fertilization rate on artificial grassland / kg N ha-1 yr-1 / 100 / 8
P13 / Non-symbiotic N fixation rate / kg N ha-1 yr-1 / 3 / 9
P14 / Grass N concentration / % / 2.4 / 10
P15 / Volatilization rate of manure input / % / 21.3 / 11-13
P16 / Burning rate of dry manure / % / 14 (20) / 14, 15
P17 / N leaching rate of N input / % / 5 / 15
P18 / Denitrification rate of N input / % / 20 / 16
P19 / N2O emission rate of N input / % / 1.3 / 11, 12
P20 / NO emission rate of N input / % / 0.7 / 3
For Livestock
D4 / Livestock production / Tg yr-1 / 146.8 (20.7) / 17
P21 / N concentration of livestock products / % / Table S6 / Table S6
P22 / N excreta rate for animal / kg N capita-1 yr-1 / Table S7 / Table S7
P23 / NH3 emission factor for animal / kg N capita-1 yr-1 / Table S7 / Table S7
P24 / Nr leaching rate of excreta / % / 5 / 15
P25 / Nr runoff rate of excreta / % / 35 / 15
* The value outside the parentheses represents the data in 2010; the value in the parentheses represents the data in 1980.
Table S2 Nitrogen concentration of grain and straw, and the harvest index
Crop / Grain N concentration (%) / Straw N concentration (%) / Harvest indexRice / 1.14 / 0.75 / 0.43
Wheat / 2.10 / 0.52 / 0.37
Corn / 1.60 / 0.58 / 0.44
Millet / 1.92 / 0.73 / 0.37
Broomcorn / 1.75 / 0.72 / 0.40
Beans / 5.99 / 1.93 / 0.43
Potatoes / 0.26 / 3.00 / 0.67
Cotton / 0.21 / 1.59 / 0.38
Peanut / 4.00 / 1.80 / 0.43
Rape / 3.48 / 0.67 / 0.25
Sesame / 3.48 / 0.67 / 0.15
Hemp / 0.75 / 0.34 / 0.36
Sugarcane / 0.59 / 0.67 / 0.91
Sugarbeet / 0.24 / 0.67 / 0.91
Tobacco / 1.53 / 0.75 / 0.49
Note, ref. 16-25
Table S3 Proportions of straw utilization in China over the past three decades
Utilization / Proportion1980 / 1990 / 2000 / 2010
Recycle to cropland / 0.07 / 0.13 / 0.22 / 0.28
Livestock feed / 0.27 / 0.25 / 0.23 / 0.24
Domestic energy / 0.56 / 0.39 / 0.31 / 0.26
Industrial materials / 0.01 / 0.02 / 0.04 / 0.06
Burning in field / 0.10 / 0.21 / 0.19 / 0.16
Total / 1.00 / 1.00 / 1.00 / 1.00
Note, ref. 1, 19, 20, 24, 26
Table S4 The loss rate (%) of nitrogen applied as fertilizer and manure in China’s cropland, divided into the south and north regions
Nitrogen loss / Fertilizer / ManureUpland / Paddy field
North / South / North / South
NH3 emission / 21.3 / 11.0 / 16.0 / 16.0 / 23.0
Denitrification / 3.2 / 25.3 / 33.0 / 36.4 / 15.0
Leaching / 7.3 / 3.2 / 0.5 / 1.2 / 4.0
Runoff / 3.5 / 11.0 / 5.2 / 5.2 / 5.0
N2O emission / 1.1 / 1.1 / 0.4 / 0.4 / 1.0
NO emission / 0.7 / 0.7 / 0.1 / 0.1 / 0.7
Note, ref. 11, 12, 27, 28, 29
Table S5 Nitrogen concentration of livestock products
Product / N concentration (%) / Product / N concentration (%)Pork / 2.1 / Egg / 2.1
Beef / 3.2 / Duck egg / 2.0
Lamb / 3.0 / Goose / 1.8
Donkey / 3.4 / Milk / 0.5
Horsemeat / 3.2 / Goat's milk / 0.2
Rabbit / 3.2 / Honey / 0.1
Chicken / 3.1 / Silkworm cocoon / 3.4
Duck / 2.5 / Sheepskin / 8.4
Goose / 2.9 / Leather / 12.6
Game meat / 2.9 / Wool / 12.2
Turkey / 3.2
Note, ref. 23, 30, 31
Table S6 Livestock nitrogen excretion rate (kg N capita-1 yr-1)
Livestock / Total Excretion / Total NH3 / NH3 (Storage) / NH3 (Manure) / NH3 (Grazing)Dairy cow / 74.40 / 26.36 / 12.48 / 12.98 / 1.8
Draft cow / 50.00 / 21.02 / 10.48 / 10.55
Beef cattle / 45.87 / 18.60 / 8.69 / 9.91
Horse / 68.64 / 18.60 / 6.11 / 7.50 / 5.0
Donkey/mule / 68.64 / 18.60 / 6.11 / 7.50 / 5.0
Sheep/Goat / 11.23 / 4.18 / 0.63 / 2.95 / 0.6
Pig / 4.87 / 2.33 / 1.43 / 0.90
Layers / 0.82 / 0.41 / 0.24 / 0.17
Rabbits / 0.45 / 0.20 / 0.10 / 0.09
Ducks/Geese / 0.47 / 0.25 / 0.16 / 0.08
Chicken / 0.09 / 0.04 / 0.03 / 0.02
Camel / 55 / 10.5
Buffalo / 45 / 8.7
Note, ref. 5, 32, 33
Table S7 Excretion utilization (%) in China’s urban and rural area
Fate of excretion / 1980 / 1990 / 2000 / 2010Urban sewage treatment / 5.0 / 14.9 / 34.3 / 75.0
Urban excretion recycled / 90.0 / 69.4 / 41.2 / 5.0
Urban excretion discharged / 5.0 / 15.8 / 24.6 / 20.0
Urban excretion leached / 9.0 / 9.0 / 9.0 / 9.0
Rural sewage treatment / 0.0 / 1.5 / 4.2 / 7.2
Rural excretion recycled / 95.0 / 93.8 / 77.1 / 53.4
Rural excretion discharged / 5.0 / 4.7 / 18.7 / 39.4
Rural excretion leached / 9.0 / 9.0 / 9.0 / 9.0
Note, ref. 7, 33-35
Table S8 Coefficients of variations (CVs) for selected activity data (D), parameters (P) and EFs (F)
Description / Distribution / CVs (%) / RefFor Cropland
D1 / Fertilizer applied / normal / 5 / 1
D2 / Crop yield / normal / 5 / 1
D3 / Cultivated areas / normal / 10 / 1
D4 / Irrigation areas / normal / 10 / 1
D5 / Human population / normal / 5 / 1
D6 / Aquaculture production / normal / 5 / 1
D7 / Food consumption / normal / 5 / 36
D8 / Areas of N-fixing crops / normal / 5 / 1
P1 / Ratio of fertilizer to fishery / uniform / 30 / 36
P2 / Daily excrement rate / normal / 25 / 37
P3 / Human excretion recycled ratio / uniform / 25 / 36
P4 / Livestock excretion recycled ratio / uniform / 25 / 36
P5 / Proportion of rural population / uniform / 5 / 36
P6 / Fraction of tatty latrine / - / 25 / 37
P7 / Symbiotic N fixation rate / normal / 50 / 38
P8 / Non-symbiotic N fixation rate / normal / 50 / 38
P9 / N concentration of irrigation / normal / 25 / 36
P10 / N deposition rate / normal / 50 / 36
P11 / Grain N content / normal / 25 / 36
P12 / Straw N content / normal / 25 / 36
P13 / Harvest index / uniform / 50 / 38
P14 / Fate of crop / uniform / 30 / Estimated
P15 / Fate of straw / uniform / 30 / Estimated
P16 / Nr loss during crop production / - / 50 / Estimated
F1 / Synthetic fertilizer / normal / 50 / 38
F2 / N-Fixing Crop / normal / 50 / 38
F3 / Agriculture soil / normal / 50 / 38
F4 / Straw returning / normal / 50 / 36
F5 / Livestock manure spreading / normal / 50 / 36
F6 / Crop residues field burning / normal / 50 / 36
For Livestock
D9 / Livestock production / normal / 5 / 1
D10 / Animal population / normal / 5 / 1
P17 / Fate of livestock products / normal / 25 / Estimated
P18 / Fate of livestock excretion / normal / 25 / Estimated
P19 / Nr loss from livestock / - / 50 / Estimated
P20 / N excreta rate for animal / normal / 25 / 38
F7 / EFs for livestock / normal / 50 / 37
For Grassland
D11 / Area of grassland / normal / 5 / 1
D12 / The grassland area affected by fires / normal / 10 / 1
D13 / Population of grazing animals / normal / 5 / 1
D14 / Animal products / normal / 5 / 1
D15 / N deposition to grassland / normal / 50 / 36
P21 / Fertilization rate on artificial grassland / normal / 10 / 36
P22 / Grass N content / uniform / 10 / 36
P23 / Biomass density / normal / 25 / 36
P24 / Volatilization rate of manure / normal / 25 / 36
P25 / Combustion efficiency / - / 25 / 37
P26 / Nr loss from grasslands / - / 50 / Estimated
Note：Fate of crop, includes crops used as human food, livestock feed, aquaculture feed and industrial materials; Fate of straw, includes straw used as feed, fuel in rural areas and industrial materials, recycled to cropland, and burned in the field; Fate of livestock products, includes food, cocoons, leather, wool and so on; Fate of livestock excretion, includes recycled to cropland, lost through riverine runoff, leached to groundwater or NH3 volatilization; Nr loss during crop production, including NH3, N2, N2O and NOx emissions, riverine runoff, and leaching to groundwater; Nr loss from livestock, includes lost through riverine runoff, leached to groundwater or NH3 volatilization; Nr loss from grasslands, includes burning of livestock excreta, NH3, N2, N2O and NOx emissions, and leaching.
Figure S1 Source appointments of nitrogen input and fates of nitrogen output to cropland, livestock and grassland across provinces in China in 2010. (a) Nitrogen input to cropland; (b) Nitrogen output from cropland; (c) Nitrogen input to livestock; (d) Nitrogen output from livestock; (e) Nitrogen input to grassland; (f) Nitrogen output from grassland. “Fertilizer” for livestock nitrogen input is mainly used for ammoniated feed. “Treated” for livestock nitrogen output represents the livestock wastewater that was treated via artificial facilities in China. The minus sign in import represents feed (or grass) export. Abbreviations of provinces: Anhui (AH), Beijing (BJ), Chongqing (CQ), Fujian (FJ), Gansu (GS), Guangdong (GD), Guangxi (GX), Guizhou (GZ), Hainan (HaN), Hebei (HB), Heilongjiang (HL), Henan (HN), Hubei (HuB), Hunan (HuN), Inner Mongolia (IM), Jiangsu (JS), Jiangxi (JX), Jilin (JL), Liaoning (LN), Ningxia (NX), Qinghai (QH), Shaanxi (SaX), Shandong (SD), Shanghai (SH), Shanxi (SX), Sichuan (SC), Tianjin (TJ), Tibet (Ti), Xinjiang (XJ), Yunnan (YN), Zhejiang (ZJ).