Research Article
Received: 3 November 2010

Revised: 15 August 2011

Accepted: 22 September 2011

Published online in Wiley Online Library:(wileyonlinelibrary.com) DOI 10.1002/jsfa.4725

Recent trends of nitrogen flow of typicalagro-ecosystems in China – major problems
and potential solutions
Chen Liu,a∗ Qinxue Wang,b Yonghui Yang,c Kelin Wang,d Zhu Ouyang,eYan Li,f Alin Leig and Tetsuzo Yasunaria
Abstract
BACKGROUND: To diagnose problems that threaten regional sustainability and to devise appropriate treatment measures in
China’s agro-ecosystems, a study was carried out to quantify the nitrogen (N) flow in China’s typical agro-ecosystems anddevelop potential solutions to the increasing environmental N load.
RESULTS: The analysis showed that owing to human activity in the agro-ecosystems of Changjiang River Basin the mean
total input of anthropogenic reactive N (i.e. chemical fertiliser, atmospheric deposition and bio-N fixation) increased from
4.41 × 109 kg-N in 1980 to 7.61 × 109 kg-N in 1990 and then to 1.43 × 1010 kg-N in 2000, with chemical fertiliser N being thelargest contributor to N load. Field investigation further showed that changes in human behaviour and rural urbanisation havecaused rural communities to become more dependent on chemical fertilisers. In rural regions, around 4.17 kg-N of per capita
annual potential N load as excrement was returned to farmlands and 1.38 kg-N directly discharged into river systems, whilein urbanised regions, around 1.00 kg-N of per capita annual potential N load as excrement was returned to farmlands and5.62 kg-N discharged into river systems in urban areas.
CONCLUSION: The findings of the study suggest that human activities have significantly altered the N cycle in agro-ecosystemsof China. With high population density and scarce per capita water resources, non-point source pollution from agro-ecosystems
continues to put pressure on aquatic ecosystems. Increasing the rate of organic matter recycling and fertiliser efficiency withlimited reliance on chemical fertilisers might yield tremendous environmental benefits.
c 2011 Society of Chemical Industry

Keywords: agro-ecosystem; nitrogen flow; field investigation; human activity; nitrogen use efficiency

INTRODUCTION
Human activities have caused substantial increases in theamounts of anthropogenic reactive nitrogen (N) in environmental
reservoirs, resulting in severe distortions in the natural N cycleof the Earth.1 The biospheric N boundary has been transgressedbeyond the 3.5 × 1010 kg-N safe limit as human activity currently
releases some 1.21 × 1011 kg-N into the environment, which
is more than three times the safe threshold.2 The highest N
use was once limited to Europe and North America, but thedevelopment of new economies and changes in agricultural
trends have shifted high N uses to Asia and Latin America.3 In
fact, at present, China has the highest fertiliser utilisation in theworld.4
The FAO’s 2006 statistical data4 show that arable lands inrural areas of China account for only 7% of the world total.
China’s arable lands, however, not only account for about
33% of chemical fertilisers used in the world but also support
20% of the world population. This intensive chemical fertiliser
application leads to massive amounts of waste in air, waterand soil systems, with a highly negative environmental impact.
Furthermore, China’s farmlands produce 50 million tons of pork
per annum, accounting for 50% of the world total. Also, because

J Sci Food Agric (2012)www.soci.org∗

Correspondence to: Chen Liu, Graduate School of Environmental Studies,
Nagoya University, D2-1(510) Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan.
E-mail: liu.chen@b.mbox.nagoya-u.ac.jp

a Graduate School of Environmental Studies, Nagoya University, D2-1(510)
Furo-cho, Chikusa-ku, Nagoya 464-8601, Japanb NationalInstituteforEnvironmentalStudies,16-2Onogawa,Tsukuba305-8506,
Japan
c Institute of Genetics and Developmental Biology, Chinese Academy of Sciences,2863 Huaizhong Road, Shijiazhuang, Hebei 050-021, Chinad Institute of Subtropical Agriculture, Chinese Academy of Sciences, Mapoling,
Changsha 410125, Chinae Institute of Geographical Sciences and Natural Resources Research, Chinese
Academy of Sciences, 11A Datun Road, Chaoyang District, Beijing 100101,
China
f Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, 818
South Beijing Road, Urumqi, Xinjiang 830011, China
g Changjiang Water Resources Protection Institute, Changjiang Water Resources
Commission, Guocikou, Wuhan, Hubei 430051, China

c 2011 Society of Chemical Industry
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wastewater treatment facilities on China’s breeding farms are
inadequate, the chemical oxygen demand (COD) of discharge
waters from livestock facilities is almost equal to that of discharge
waters from industrial facilities in China.5 Moreover, people’s
consumption pattern/diet in China has changed drastically with
rapid economic growth in recent years. The diet system is shiftingfrom a traditional grain-based diet to a meat-based diet moreakin to that in developed countries.6 Increasing animal protein
intake increases the amount of N in human excrement. Hencehuman excrement and other domestic grey water discharge into
water bodies is increasing with the availability of flush toilets
and sewerage systems.6 Also, an insufficiency of septic tanks
and sewage systems means that most domestic wastewater
is discharged untreated into rivers and lakes.7 Such problems
are not only limited to China but also prevail globally. Highproliferation of blue/green algae in lakes and dams and frequent
coastal red tides lead to severe health and environmental
issues.8,9 To quantitatively evaluate the impact of human activities
on the environment, it is important to understand real timechanges in China’s farmlands. Analysing the changes in humanactivities not only clarifies the related environmental problems
but also facilitates the development of sustainable on-sitecountermeasures.
Previous studies have investigated N flow in different agroregions of Changjiang River Basin using a county-level agrostatistical database.10,11 Liu et al.6 also investigated N flow
pertaining to human food consumption and lifestyle (i.e. daily
life activities related to diet intake, waste disposal and farming).
Liu et al.12 took the study further by quantitatively analysing
and comparing representative regions for the impact of humanbehavioural changes on N flow using integrated statistical andsurvey data. The present study adds new results to the previous
findings with the overall aim of pinpointing the main issues of
N flow in China’s agro-ecosystems. The study focuses on N flowchanges in farmlands and suggests potential solutions to reducing
the reactive N load and maintaining a sustainable/balanced N flowin China’s agro-ecosystems. As the N problem is not unique toChina, the proposed solutions in this study could be applicable toother regions of the world.

C Liu et al.

MATERIALS AND METHOD
We used data from 801 counties in Changjiang River Basin todevelop sufficient insight into not only spatiotemporal changes
in farmland N budget (including N source, e.g. atmospheric
wet/dry deposition, chemical fertiliser N use, N fixation by legume
crops, green manure and non-symbiotic crops, N recycling inhuman/animal excrement, crop residue/manure and N emission
from crop residue combustion; N sink, e.g. N in harvested
grain/straw biomass, denitrification, volatilisation and N flow into
water bodies by leaching/run-off; and soil N storage) but also N use
efficiency in the basin.11 We also used field data from different agroecosystems to isolate human activities such as daily diet intake,domestic wastewater discharge route, chemical fertiliser type andapplication method, human/animal excrement N discharge into
soil/water systems and N from agro-by-product utilisation.6
Field investigation was first conducted in 2006 in collaboration
with the Integrated Environmental Monitoring (IEM) Networkof the Asia-Pacific Environmental Innovation Strategy Project(APEIS). This was followed by data collection via questionnaire
and/or personal interview in six typical ecosystems – urban areasof Shijiazhuang (SJZ) in Hebei Province and Wuhan (WH) in Hubei
Province and urban city/town and rural township/village areas of
Fukang (FK) in Xinjiang Uygur Autonomous Region, Yucheng (YC)in Shandong Province, Taihe (TH) in Jiangxi Province and Taoyuan(TY) in Hunan Province – of China (Fig. 1) in April–June 2006.
Feedback was obtained from a total of 1650 people: 200 in SJZ,
150 in WH, 100 in urban FK, 100 in rural FK, 150 in urban YC, 200 inrural YC, 120 in urban TH, 180 in rural TH, 250 in urban TY and 200
in rural TY. To further enhance the survey data, the investigationsite was expanded to cover Hanjiang River Basin (HJ), an upper
reach sub-basin of Changjiang River Basin, in February–April 2008
and to Shanghai (SH) in September–December of 2009. A totalof 800 (350 in urban and 450 in rural areas of HJ) and 450 (300
in urban and 150 in rural areas of SH) people were interviewed(Fig. 1).
The questionnaire comprised four main parts. The first partcontained basic information about the respondents, including
sex, age, height, weight, occupation, income, registration type,educational level and intensity of daily activities. The second part

Fukang(the oasis agricultural system in the temperate continental
desertification zone)
Shijiazhuang(northern urban city)

Yucheng(the irrigated agricultural
Systems in the
Huang-Huai-Hai Plain)
Shanghai(a mega-city in the
Chanjiang River Delta)
Wuhan(southern urban city)
Hanjiang RiverBasin(an upper reach sub-basin of
Changjiang River Basin)
Taoyuan
Taihe(the decentralized paddy-field agricultural(the forest/hill terrains
system around Dongting Lake)in the middle Changjiang River Basin)

Figure 1. Locations of investigation sites in China.

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c 2011 Society of Chemical IndustryJ Sci Food Agric (2012)

Nitrogen flow in China’s agro-ecosystems

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N in harvested Crops
1980

Recycled organic N
4.28

2.71
Deposition
Bio-N fixation

Chemical fertiliser

1.00

1.98

0.92

1.28

Farmland

2.49

N in harvested Crops

Bio-N fixation
Chemical fertiliser

3.03

0.90

2.49

Farmland

5.74

Bio-N fixation
Chemical fertiliser

2.15

1.73

NH3 volatilization

Leaching & runoff
Denitrification
NH3 volatilization

Recycled organic N

4.64
Deposition

Denitrification

5.80

0.97

N in harvested Crops

2000

Leaching & runoff

Recycled organic N

4.01
Deposition

1.26

1.45

1990

(Unit: 109 kg-N)

5.57

0.90

4.50

1.12

Farmland

4.47

12.23

2.97

3.25

Leaching & runoff
Denitrification
NH3 volatilization

Figure 2. N budget in farmlands of Changjiang River Basin.

included the current state and trend of dietary lifestyle. Herefood products were categorised into 47 items in nine groupsin accordance with the China Food Composition database.13,14
The respondents filled in forms based on what and how much
was eaten in the last 24 h as breakfast, lunch, dinner andanything in between these main meals. The third part consistedof questions about human waste disposal, including sewage
situations, home toilet specifications, discharge routes and user
satisfaction. The fourth section comprised questions relating toactual farming methods implemented in the region, i.e. application
rates/methods of various chemical fertilisers and recycling of agrolivestock excreta.

RESULTS AND DISCUSSION
Trends in farmland N budget and fertiliser use efficiency
The trend in farmland N budget in Changjiang River Basin for
1980–2000 is shown in Fig. 2. The estimated anthropogenic newreactive N (wet/dry deposition, biological N fixation and chemicalfertiliser) input is 1.43 × 1010 kg-N in 2000, which is 1.9 times
that in 1990 and 3.2 times that in 1980. Recycled N (from animal
excrement, rural human excrement, crop residue, irrigation andseeds) increases slightly from 4.28 × 109 kg-N (1.50 × 109 kgN from animal excrement and 1.63 × 109 kg-N from rural humanexcrement) in 1980 to 5.80×109 kg-N (2.16×109 kg-N from animal
excrement and 2.03 × 109 kg-N from rural human excrement) in
1990, but because of a declining rural population it decreases
slightly to 5.57×109 kg-N (2.18×109 kg-N from animal excrement
and 1.53 × 109 kg-N from rural human excrement) in 2000. Humanand animal excrement accounts for 67–73% of total recycled N
in the region. Recycled organic N in 1980 is 1.7 times higher thanchemical fertiliser N, implying that crop production in the region ismainly supported by recycled organic N. However, released N fromchemical fertilisers increases drastically to 1.22×1010 kg-N in 2000.

J Sci Food Agric (2012)

This is the equivalent of a fivefold increase over 1980, becoming
the largest N contributor in the basin in 2000. On the other hand,
harvested crop N (including straw N) is estimated at 2.71 × 109 kgN in 1980, 4.01 × 109 kg-N in 1990 and 4.64 × 109 kg-N in 2000.
This is a 1.71-fold increase in 2000 over the value for 1980. N use
efficiency (i.e. the proportion of N input, including anthropogenic
new reactive N and recycled organic N, exported via harvested
crop N) decreases from 31% in 1980 to 30% in 1990 and then to
23% in 2000 (Fig. 3). The proportion of N in harvested crops to total
N input decreased, while that lost by denitrification, volatilisation
and riverine N transport and the proportion stored in soil increased
2.5-fold between 1980 and 2000 (Fig. 2). Table 1 details theprevailing agricultural conditions for 1980, 1990 and 2000 withregard to the parameter factors of cultivated land area, cropped
land area, multi-cropping index (cropped land area/cultivatedland area), crop yield (including straw) and fertiliser application
rate. Whereas cultivated land area decreases, cropped land area
increases. This implies that agricultural lands in Changjiang River
Basin intensified substantially, especially in 1990–2000. Comparedwith the world’s average N fertiliser application rate (FAOSTAT,
102–117 kg-N ha−1 ), N fertiliser application rate (225 kg-N ha−1 in2000) is almost two-times higher in Changjiang River Basin. Crop
yield increases from 82 kg-N ha−1 of cropped land area in 1980
to 117 kg-N ha−1 of cropped land area in 1990, but it decreases
to 86 kg-N ha−1 of cropped land area in 2000. In terms of N, thistrend implies that crop production increases by 35 kg-N ha−1 ofcropped land area with the addition of 92 kg-N ha−1 of chemicalfertiliser in 1980–1990. Contrarily, crop production decreases by
31 kg-N ha−1 of cropped land area for every 58 kg-N ha−1 additionof chemical fertiliser in 1990–2000. The drop in crop production
could be caused by (1) decreasing fertiliser use efficiency due toincreasing chemical fertiliser application (this is simply the lawof diminishing returns, which states that, holding all other inputs
constant, the marginal product of each unit of input declines as thec 2011 Society of Chemical Industry


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C Liu et al.

eutrophication, global warming gas emission, etc.) in the study
area. Note that the ratios of N discharge in soils or rivers from waste
and livestock excreta are set constant in the above estimates at
40% of rural human excrement for recycled N in soils and 60%
of rural human excrement for discharged N to surface waters
and at 40% of cattle/sheep excrement and 100% of pig/poultry
excrement for recycled N in farmlands.

Figure 3. Relationship between total farmland N input and harvested
crop N.

Table 1.

Variations in studied parameters during 1980–2000

Parameter

1980

1990

2000

Cultivated land (106 ha)a
Cropped land (106 ha)a
Multi-cropping index (%)
Crop yield (kg-N ha−1 of cropped land area)a
N fertiliser (kg-N ha−1 of cropped land area)a

26.6
33.2
125
82
75

25.5
34.3
135
117
167

24.0
54.2
226
86
225

a

Data from 1981, 1991 and 2001 China Rural Statistics Yearbooks.15 – 17amount of that input increases), (2) effective utilisation of recycledorganic fertiliser in the agro-ecosystems in 1980, as against limited
utilisation in 2000, and (3) decreasing fertiliser use efficiency due
to multiple cropping and intensive farming.
The high fertiliser application rate and low N use efficiency are
the most important factors of environmental degradation (e.g.

Table 2.

Human N intake via diet and discharge route of human waste
Based on field investigations, per capita daily protein intake by foodgroup in the region is detailed in Table 2. Per capita average daily
protein intake is 113.4 g in urban areas and 95.1 g in rural areas,
and the difference between the two is significant at P < 0.05.
A difference in diet in terms of economic status determines
the differences in prevailing characteristics/habits among theecosystems. For instance, Fukang is known for sheep pasture,
where economically developed urban dwellers consume moremeat protein (especially mutton and dairy products such as
cheese) than those in other regions of the country. Shanghai
is known for freshwater/seawater farming, and Shanghai dwellers
consume more fish protein than those in other regions. One
possible reason for high fish consumption in Taihe is proximity to
the dam, where extensive fish farming ensures ready availability
and affordability. The insignificant difference between urban andrural areas of Yucheng and Taoyuan is because the region is
primarily an agricultural county. On average, urban dwellers
consume more meat, egg, fish, milk and legume products andfewer grain, vegetable and fruit products than rural dwellers.
There is a significant difference between urban and rural regionsin terms of potential N load from human waste. While the rate of
returned human waste to soils via septic tank, manure store andbiogas plant decreases, that discharged in rivers via drainage andsewage increases (Fig. 4). Assuming that N intake is proportional
to N content in adult excrement, per capita annual N discharge
into the environment is estimated and detailed in Table 3. Per
capita potential annual N load in human waste that is returned

Daily amount of protein intake (g day−1 per person) by food group at investigation site

Location/type

Cropa

Meata

Egga

Fisha

Legumea

Milka

Tuber/starcha

Vegetable/fruita

Othersa

TotalaMeat-basedc (%)

SJZ
FKb

34.7
39.4
39.5
44.5
52.6
25.1
33.4
26.3
30.0
28.3
29.3
33.1
25.4
26.6
32.7
34.4

28.7
29.2
16.4
28.6
19.0
22.2
27.2
23.0
27.2
31.1
24.7
13.4
29.8
15.5
27.2
19.7

6.7
7.8
8.1
6.5
6.8
7.6
5.5
6.3
6.2
6.7
13.5
6.8
9.6
5.0
7.9
6.6

12.3
11.2
4.8
10.1
4.1
13.0
14.9
18.3
11.9
12.5
17.8
8.5
23.0
15.9
14.3
10.7

11.8
12.7
15.2
8.1
12.4
19.2
14.4
9.5
15.8
10.0
17.5
12.5
12.1
14.4
14.0
12.3

6.8
7.9
2.5
4.0
1.0
6.8
2.4
0.1
4.4
1.7
2.3
0.7
5.6
0.9
5.0
1.1

1.3
1.9
2.3
0.7
0.6
1.4
0.5
0.5
1.1
0.8
1.3
0.8
0.8
0.3
1.1
0.9

5.4
3.1
2.6
3.4
5.5
2.8
5.4
6.6
4.6
4.6
3.6
3.4
3.7
3.6
4.0
4.4

8.7
8.7
6.0
6.5
3.9
10.6
2.8
5.9
7.2
7.7
7.0
3.8
6.7
1.8
7.3
4.8

116.5
121.8
97.4
111.6
106.1
108.6
106.5
96.3
108.3
103.3
117.0
83.2
116.8
84.1
113.4
95.1

47
46
33
44
29
46
47
49
46
50
50
35
58
44
48
40

YC
WH
THb
TY
HJb
SHb
Totalb
a

Urban
Urban
Rural
Urban
Rural
Urban
Urban
Rural
Urban
Rural
Urban
Rural
Urban
Rural
Urban
Rural

Difference in per capita daily amount of protein intake by food group significant at P ≤ 0.05 (Kruskal–Wallis test) among sites.

b Difference in per capita total protein intake per day significant at P ≤ 0.05 (Mann–Whitney test) between urban and rural residents.
c Percentage protein intake from meat-based food (meat, egg, fish, milk) in total ingested protein.

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Figure 5. Future consumption trend. Note that 100% here represents total
choices available and not total number of respondents.

Figure 4. Discharge routes of human waste.

to farmland in urban areas is around 1.00 kg-N, while 5.62 kg-N
is discharged into rivers. For rural regions, around 4.17 kg-N isreturned to farmland and 1.38 kg-N directly discharged into rivers.
The study further shows that even human wastes stored in septic
tanks, manure stores and biogas plants (normally considered asorganic fertiliser) are gathered in outdoor heaps and therefore
hardly recycled as organic fertiliser in farmlands. This is because
there exists manpower shortage in rural areas. In recent years,
most youngsters have given up farming and left for cities/towns
in search of their fortune. Hence only elderly people over 60 yearsof age live in rural areas, who cannot do heavy-lifting farming
jobs. Much labour and manpower are needed for composting andtransporting of excrements on farmlands. Compared with organic
fertiliser, chemical fertiliser not only saves labour and manpower
but is also very effective.
The future trend in (multi-choice) food consumption in the
study area is shown in Fig. 5. There is a preference for highintake of animal-derived foodstuffs, vegetables and fruits. A
large proportion of the respondents express a positive attitude
towards balanced nutrition; willing to consume nutritional

Table 3.

YC
WH
TH
TY
HJ
SH
Total

Potential river/soil N load via farming method
The investigation shows that the most commonly used chemicalfertilisers are urea and mixed fertilisers. Fertiliser diversification
occurs widely in agricultural lands with sufficient irrigation systems
and in paddy-field plains. Potassium use is relatively low inYucheng and Shanghai (Fig. 6(a)). In the irrigated agro-systemsof Yucheng, fertiliser application is mainly by fertigation becauseof the ease of adding chemical fertiliser to irrigation water whennecessary. Whole-layer application is very common in (the hilly
areas of) Taihe because it is reported to prevent N loss via soil
erosion. Surface application is common in Shanghai as it highly
labour-saving (Fig. 6(b)). In the irrigated agro-systems of Yucheng,over 75% of agro-by-products such as wheat straw are recycled
into livestock feed. Almost 80% of agro-by-products are recycled
as cooking fuel in Shanghai rural areas. In other regions, mostof the agro-by-products such as straw are generally burned or
mixed with base fertiliser and returned to the soil (Fig. 6(c)).
In most instances, livestock excreta are reduced over time in

Potential environmental N load originating from human waste

Location/type
SJZ
FK

supplements not only in urban areas but in rural areas as
well.

Urban
Urban
Rural
Urban
Rural
Urban
Urban
Rural
Urban
Rural
Urban
Rural
Urban
Rural
Urban
Rural

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Amount (kg-N year−1 per person)

Human waste released
to environment(kg-N year−1 per person)

Rate (%)
Returned to soil

Discharged in rivers/pipes

Returned to soil

Discharged in rivers/pipes

6.80
7.11
5.69
6.52
6.20
6.34
6.22
5.63
6.32
6.03
6.83
4.86
6.82
4.91
6.62
5.55

6
9
70
32
80
25
24
95
6
47
15
85
3
73
15
75

94
91
30
68
20
75
76
5
94
53
85
15
97
27
85
25

0.44
0.62
4.01
2.09
4.97
1.59
1.52
5.35
0.35
2.85
1.02
4.13
0.20
3.58
1.00
4.17

6.36
6.49
1.68
4.43
1.22
4.76
4.70
0.27
5.97
3.18
5.81
0.73
6.62
1.33
5.62
1.38

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(a)

(b)

(c)

(d)

C Liu et al.

Figure 6. Farming methods: (a) chemical fertiliser type; (b) chemical fertiliser application method; (c) agro-by-product utilisation; (d) livestock excreta
utilisation.

pastures/farmlands in the case of traditional small-scale household
livestock breeding (Fig. 6(d)). Although farmers have raised three
to five pigs per household in the past, such practice is declining
with time. This is not only because pig raising is difficult in termsof technical knowhow, manpower and time, but also because ofhigh instability of meat market prices, cost of processed feed andavailability of low-priced alternative meat. On the other hand, thenumber of large-scale livestock breeding centres introduced via
external financing is steadily increasing. This study, however, did
not identify waste discharge routes of these externally financed
livestock breeding centres as they were not included in the field
investigation.
Potential solutions for decreasing N loads and sustained
N balance
As demonstrated in this study, the changes in human activities
due to economic growth and urbanisation are as follows:(1) increased consumption of animal-based products, leading toincreasing demand for such products over crop-based products;(2) increasing use of flush toilets, reducing human/animal waste
recycling in agricultural lands; (3) increasing dependence ofrural communities on chemical fertilisers; (4) functional shifts inhuman/animal excrement from soil nutrient to environmental
load; and (5) increasing environmental N load from both thesurplus application of chemical fertilisers and the abandoned
human/animal excrement. Urbanisation of rural areas is expectedto accelerate further. According to the Prime Minister Wen
Jiabao, the strategy of constructing socialist new farms is steadily
promoted and emphasised in the 2006 report of the government

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activity. In China’s rural region with 800 million people, finding
better ways of producing, consuming and delivering N without
further environmental stress constitutes a tremendous challenge.
In 2008, China’s central government released the ‘mid/longterm plan for ensured food security in the country’. The plan target
is to produce over 500 billion kg of grain by 2010, 540 billion
kg by 2020 and 640–702 billion kg by 2030.18 In China (where
33% of the world’s chemical fertiliser is consumed by 20% of
the world population) it is important to improve fertiliser use
efficiency for sustainable increase in crop production. Finding waysof increasing crop N use efficiency is also critical for decreasing N
loss to the environment. With highly intensified cropping systems
in China, further improvements in fertiliser use efficiency remaina daunting challenge.19 Nevertheless, advances in fertilisationrelated sciences and technologies raise the possibility of meeting
this challenge. For example, Ju et al.20 reported that current
agricultural N practice with 550–600 kg-N ha−1 year−1 cannot
significantly increase crop yield. It could, however, increase N losses
to the environment twofold. Hence knowledge-based optimum N
fertilisation could save 30–60% of N fertiliser.20
Developing an efficient soil/fertiliser strategy management
system is also critical. For example, the law of diminishing returns
necessitates the development of different fertilisation strategies
that reflect the nutrient state of soils. This implies that nutrientdeficient soils require high fertilisation to build soil fertility andincrease yield, nutrient-sufficient soils need limited fertilisation tomaintain soil fertility, and nutrient-abundant soils need cultivation
to deplete soil nutrient. Improper use of fertilisers is anotherfactor for low N efficiency in China. In extreme cases, farmers

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continue intensive fertilisation to further increase productivity
even under sufficiently fertile soil conditions. NPK balance isalso very important for crop growth – a factor that farmers still
remain unfamiliar with. The establishment of information systems
to strengthen technological transfer to farmers is equally an
important factor.
Next to chemical fertilisation, N from human waste is thesecond largest source of increasing N load from farmlands tothe environment (Fig. 2). China plans to enlarge facilities forurban pipe water and sewage treatment systems. With theproliferation of flush toilets, the rate of human excreta returned
to soils is decreasing, as most of such wastes are discharged
via pipe systems. Because N removal rate by sewage treatment
systems is less than 20% in China, most of the N in humanwaste is discharged into water bodies. This causes widespreadwater pollution problems in the country. Over a period of 1 year
the average person disposes through pipe water and sewage
treatment systems 400 L of harmless urine (containing 4 kg-N
and 0.4 kg-P, directly usable as farmland fertiliser) and 50 L ofharmless faeces flushed by 1.5 × 104 L of pure water.21 Removalof N and P in wastewaters requires the construction of costly
sewage treatment plants at the end of the pipe systems. Thisimplies that dealing with only 50 L of harmless faeces wastes not
only 300 times that volume of pure water but also leads to losing
valuable urine fertiliser. In European counties, ecological sanitation
systems are prevalent, which are clean and economical. Urine andcompost can also be used as fertiliser, limiting chemical fertiliser
application. Water issues (e.g. shortages of water resources anddrinking water in terms of quantity and quality and degeneration ofwater environments) are closely linked to organic waste disposal.
China faces myriad hydrological issues (including a lack of aquatic
resources, quantitative/qualitative issues of drinking water anddeterioration of water environment) that are intricately relatedwith excrement and organic waste problems. There is therefore adire need to construct systems that support waste circulation andrecycling needs of China.
Environmental N load originating from livestock excreta is alsoa serious problem. While small-scale livestock breeding is on the
decline in the study area, intensive large-scale livestock breeding
is increasing. This trend is spurred by huge economic benefits andmanpower shortage in rural areas. Most of the livestock breeding
centres are, however, not equipped with wastewater processing
systems, raising concerns about possible excessive livestock
excreta pollution of water systems. The increased N load fromlarge-scale livestock breeding without wastewater treatments istherefore a potential environmental problem. Improved animal
management strategies and methods/technologies of livestock
excreta recycling are therefore needed for reducing the N load tothe environment.
Recycling-based agriculture has gradually taken root in Japanin recent years. For instance, technology is now available forconverting all sorts of organic matter (excrement, straw, waste,etc.) to organic carbon fertiliser, which drastically improves soil
conditions. As shown in Fig. 1 and Table 1, efficiently reusing
recycled N could cut down chemical fertiliser application byalmost half. Relying entirely on pipe-borne systems could
spur environmental N load from both chemical fertilisers andrecycled N.
Given the complexities of N use, its environmental mobility
and differences among regions, no single and definite strategy
suffices. This is especially true for China, a large country withdiverse agro-ecosystems and stages of economic development.

J Sci Food Agric (2012)

With the notion of ‘creating a harmonious society’, the governmentof the People’s Republic of China has proposed large-scale
environmental technologies and improvement projects. It is
important to incorporate suitable N management systems withinthese strategies/projects.

CONCLUSIONS
The findings of this study suggest that human activities havesignificantly altered the N cycle in agro-ecosystems of China. Withhigh population density and scarce per capita water resources,
non-point source pollution from agro-ecosystems continues toput pressure on water environment. Increasing the rate of organic
matter recycling and fertiliser efficiency with limited relianceon chemical fertilisers might yield tremendous environmental
benefits. Thus technology, management, education, etc. are
required for increasing fertiliser use efficiency and the rate oforganic matter recycling. This study provides not only a baseline
N cycle but also a useful case-study for sustainable development
and management of rural communities.
The present study reveals new issues that are not supported by
the current designed questionnaire/personal interview but will be
examined in future studies. For instance, besides the traditional
small-scale household livestock breeding, waste discharge ofthe externally financed livestock breeding centres is anotherpotential factor of increasing N load in the region. This requires
adequate redressing for sustainable environmental managementin the study area. Detailed data collection is also need tomore adequately isolate regional differences. More specifically, atimeline investigation with fixed respondents could be necessary
in determining the dynamics of human behaviour in the region.
Hence studies will continue in basic and clinical environmental
research with the aim of not only diagnosing problems thatthreaten the sustainability of the relationship between humansociety and the natural world but also developing appropriate
prevention/treatment measures and predicting the avoidance ofpotential side effects of such treatment measures.22

ACKNOWLEDGEMENTS
This study was supported by the Nagoya University Global COE(Center of Excellence) programme ‘From Earth System Scienceto Basic and Clinical Environmental Studies’ (FY2009-2013), the‘Development of Environmental Management Techniques overthe Yangtze River Delta for Conservation of the Environment of East
China Sea’ (2009–2011) programme sponsored by the Ministry ofEnvironment, Japan, and the international collaborative project
supported by the Ministry of Science and Technology, China(2009DFA21690).

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