Supporting information

for

Enhanced acidification in Chinese croplands as derived from element budgets in

the period 1980-2010

Qichao Zhu1, Wim de Vries2,3, Xuejun Liu1,*, Tianxiang Hao1, Mufan Zeng1, Jianbo

Shen1 and Fusuo Zhang1

1 College of Resources and Environmental Sciences, Centre for Resources,

Environment and Food Security, Key Lab of Plant-Soil Interactions, MOE, China

Agricultural University, Beijing 100193, China

2 Environmental Systems Analysis Group, Wageningen University, PO Box 47, 6700

AA Wageningen, The Netherlands

3 Alterra-Wageningen UR, Soil Science Centre, P.O. Box 47, 6700 AA Wageningen,

The Netherlands

* Corresponding author: Xuejun Liu (liu310@cau.edu.cn)

Telephone: +86 10 62733459; Fax: +86 10 62731016

S1

Summary of supporting information:

Method S1. Assessment of element inputs and outputs budgets assessment.

Table A.1 Calculations of elements (ions) from kg/ha/yr to keq/ha/yr

Table A.2 Available data sources used to assess element inputs and outputs for the period 1980-2010

Table A.3 Element concentrations in urine and dejection (%)

Table A.4 Parameters used in the calculation of animal excretion

Table A.5 Element concentrations in crop harvest, crop residues and related parameters in crop

removal calculation

Table A.6 Average annual element budgets in China in 1980 and 2010

Fig. A.1 Trends in various N fertilizer types used in the period 1980-2010, given as a fraction of the

total N fertilizer use.

Fig. A.2 Trends in various P fertilizer types in the period 1980-2010, given as a fraction of the total P

fertilizer use. FMP denotes fused calcium-magnesium phosphate.

Fig. A.3 Ratios of crop residues return of major crops during the period 1980-2010.

Fig. A.4 Annual inputs and outputs of Cl (a,b) and HCO3- (c,d) in Chinese cropland during 1980 and

2010.

Fig. A.5 Provincial scale N inputs (top), N removals (middle) and N surpluses (bottom) in 1980 (left)

and 2010 (right).

Fig. A.6 Provincial scale BC input (top), BC removal (middle) and BC surplus (bottom) in 1980

(left) and 2010 (right).

Fig. A.7 Provincial scale P inputs (top), P removals (middle) and P surpluses (bottom) in 1980 (left)

and 2010 (right).

Fig. A.8 Provincial scale S inputs (top), S removals (bottom) and S surpluses (bottom) in 1980 (left)

and 2010 (right).

References used in Methods S1

References used in crop residue return assessment (Fig. A.3)

S2

Method S1. Assessment of element inputs and outputs

All element inputs and outputs were derived from total flows at provincial level and

divided by the arable land area in each province (Taiwan, Hong Kong and Macao

were not included due to the data limitation). An overview of the data sources that

were used to assess the budgets at province level are given in Table A.2. The details

with respect to the assessment of inputs and outputs are given below.

1.1 Assessment of element inputs

1.1.1 Chemical fertilizer (Xchem)

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Provincial chemical fertilizer consumption rates of nitrogen (N), phosphorous (P)

and potassium (K) during period 1980-2010 were accessed from the National Bureau

of Statistics of China (NBSC, http://data.stats.gov.cn/), splitting NPK compound

fertilizers into N, P2O5, K2O using a ratio of 1:1:1 (Liu, 2017). The average

composition of the various N and P fertilizers at national scale was derived from

Zhang and Zhang (2013). This is especially crucial for the different forms of N (i.e.

NH4+ and NO3

-), considering their different roles in soil acidification (see Eq. S1), but

also with respect to other cations or anions as these elements affect the acidity

balance. Detailed information on fractions of various types of N and P fertilizers are

given in Fig. A.1 and A.2, respectively (see also in Supplementary Material). Sulphate

(SO42-), calcium (Ca2+), magnesium (Mg2+), bicarbonate (HCO3

-) and chloride (Cl-)

inputs were calculated from the rates of N and P and K fertilizers in fertilizer types

containing those elements. For K fertilizers, we assumed that all K was applied as

potassium chloride (KCl), which accounts for more than 95% of the total K

consumption (Wang, 2009). SO42-, HCO3

- and Cl- inputs by chemical fertilizer were

derived from fractions of (NH4)2SO4, NH4HCO3, NH4Cl and KCl combined with the

total N and K consumption. The same approach was used for Ca and Mg in P

fertilizer. Sodium input from chemical fertilizer was assumed to be negligible.

In the acidification calculation, the NH4+-N and NO3

--N inputs by fertilizer were

based on the total N consumption and the proportion of NH4+-N and NO3

--N in those

N fertilizers. Because the acidification induced by organic nitrogen (e.g. N in Urea,

manure, biologically N fixation and seeds) is only 1 proton, that equivalent to

NH4NO3, so we split organic N into 50% NH4+-N and 50% NO3

--N (Zeng et al.,

2017). The NH4+-N and NO3

--N input from N fertilizer consumption were thus

estimated as:

S4

N NH 4 , i=f NH 4 ,i × Nchem ,i+0.5× NORG , i (S1)

N NO3 ,i=f NO3 ,i× N chem, i+0.5× N ORG ,i (S2)

NORG ,i=(1−f NH 4 ,i−f NO3 , i )× N chem, i (S3)

Where, NNH4, NNO3 and NORG denote the N application of NH4+-N, NO3

--N and

organic N, f denotes the fraction of total N, Nchem represents total chemical N fertilizer

consumption and i denotes the year.

Proton input was assessed by considering the charge balance of all elements in

chemical fertilizer, as:

H ¿=Anions¿−Cations¿ (S4)

Where, Anions denote SO42-, NO3

-, H2PO4-, HCO3

- and Cl-, while the Cations denote

NH4+, K+, Na+, Ca2+ and Mg2+, with all ions given in equivalents per hectare. The same

method was used to assess the proton input in manure, irrigation, seed and deposition.

1.1.2 Manure (Xmanu)

Main sources of manure in China are human and animal excretion with additional

small amounts of straw compost, cake manure and green manure (Li & Jin, 2011). In

our calculation, only human excretion and livestock excretion were considered

because straw compost was included by assessing net straw removal in the output

calculation (see below). Nutrient inputs by cake manure and green manure were

negligible (Li & Jin, 2011). Total manure application was thus calculated as：

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X manu,i=X HE,i+X AE, i (S5)

Where, XHE and XAE denote the nutrients (i.e. N, P, K, Ca, Mg, Na, and S) applied in

agriculture by human excretion and animal excretion, respectively, and i denotes the

year.

Nutrient inputs by human excretion were calculated as:

X HE, i=Pi× f h × ( XUE ×U h+X FE × Dh ) (S6)

Where. P denotes the population in the province or in China as a whole (See Table

A. 2), XUE and XFE denote the nutrient concentrations in urine and faeces, respectively,

Uh and Dh denote the urination rate (liquid manure) and defecation rate (solid manure)

per person per year and fh is the fraction of human manure that is applied to the

cropland. Data on nutrient concentrations in urine and faeces of humans are given in

Table A. 3. Values used for Uh and Dh were 550 kg and 51 kg, respectively, based on

Jönsson et al. (2004). We set fh equal to 0.3 for all provinces and municipalities of

China, based on Sun et al. (2008), except for the sparsely populated Tibet, Inner

Mongolia, Qinghai and Xinjiang provinces where we used a value of 0.1.

The nutrient inputs from livestock excretion were adapted from previous study (Jia,

2014, Li & Jin, 2011) and calculated as:

X AE , i=∑ f a × L j × ( XUE× U a , j ×T j+X FE× Da, j× T j ) (S7)

S6

Where, fa is the fraction of animal manure that is applied into cropland, L is the

number of livestock, j denotes the animal type (e.g. pig, sheep, poultry, beef cattle and

dairy/farm cattle), Ua and Da denote the amount of urine and faeces per animal type

per day, respectively, T is breeding days per cycle and XUE and XFE are the nutrient

concentrations in urine and faeces, respectively. Slaughter rates of each animal were

used to assess the livestock numbers, except for dairy/farm cattle, whose amount was

assumed to equal to the cattle stock at the end of the year (See Table A.2 for the data

sources). Data of breeding cycles, element concentrations and urine, dejection rates

are given in Table A.3 and A.4 in the supplementary material.

1.1.3 Biological N fixation (Xfix)

Based on literature data, N fixation rates (FR) of soybean and peanuts were set at

80 kg/ha/yr (Li & Jin, 2011, Smil, 1999), paddy rice at 25 kg/ha/yr (Giller, 2001,

Herridge et al., 2008, Smil, 1999) and the remaining upland crops at 5 kg/ha/yr (Smil,

1999). N fixation rates were multiplied by the corresponding sown area of the crop to

assess annual provincial and national N inputs by biological N fixation according to:

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X fix ,i=∑ FR k × A i ,k (S8)

Where, i and k denote the years and crop types, respectively and A represent the

cultivated area of the crop obtained from NBSC.

1.1.4 Seeding (Xseeds)

Annual inputs by seeds at provincial and national scale were calculated as:

X seeds ,i=∑ SRi , k × XSk × A i ,k (S9)

Where, SR denotes the seeding rates of the crop and XS denotes the element

concentrations in seeds, as given in Table A. 5. National averaged seeding rates for

each crop were obtained from the Yearbook of National Agricultural Products Cost

and Benefit Compilation (Price Office of National Development and Reform

Commission, 1981-2011).

1.1.5 Irrigation (Xirr)

Nutrient inputs by irrigation were only included for N, P and K, while Ca, Mg and

S were neglected due to data limitation. Element inputs by irrigation were based on Li

and Jin (2011), where N inputs by irrigation in 2008 varied from 2.7 to 4.8 kg

N/ha/yr, and P and K varied from 0.13 to 0.26 kg P/ha/yr and 2.7 to 5.0 kg K/ha/yr

across provinces. The inputs by irrigation in the period 1980-2010 were assumed to

follow the trends of the irrigated area in China, which was derived from NBSC.

1.1.6 Deposition (Xdep)

Annual total NH4+-N and NO3

--N deposition at provincial level in the period 1980-

2010 were obtained from provincial NH4+ and NO3

- deposition in the year 2000 from

Dentener et al. (2006) in combination with trends in N bulk deposition in the period

S8

1980-2010 presented by Liu et al. (2013). S deposition was assessed by a similar

method, using total deposition of 2000 from Dentener et al. (2006) combined with

trends in SO2 emission, since SO2 deposition trends are lacking (Xin, 2009). SO2

emissions after 1990 were available from the National Environment Bulletin

(Ministry of Environmental Protection of China, 1990-2014). Lacking emissions in

the period 1980-1989 were assumed to have the same trends as in the period 1990-

2002 by considering the linear increase in coal combustion in the period 1980-2002.

Ca and Mg deposition at 14 sites for the year 2009 from EANET

(http://www.eanet.asia/) and Lu et al. (unpublished) were allocated to regions based

on the geographic location. The trends in Ca and Mg deposition were set equal to the

trends in Ca and Mg emission in 1990-2005, taken from Lei et al. (2011), while the

lacking emission in the periods 1980-1989 and 2006-2010 were assumed to equal

those of 1990 and 2005, respectively. Because a trend in K deposition or emission is

lacking during 1980-2010, K deposition was estimated as one-sixth of the total Ca

deposition in equivalents, according to Huang et al. (1993) and Zhu et al. (2016b).

The assessment by a fraction of Ca deposition was considered acceptable since the

rate was very low compared to the K inputs from fertilizer and manure. As with Ca

and Mg, Na and Cl deposition during 2000-2014 were collected from EANET and

were allocated to regions based on their geographic locations. Values thus derived for

Na deposition were 0.06 keq/ha/yr for Southwest China, 0.16 keq/ha/yr for Northeast

China, 0.24 keq/ha/yr for North China and 0.57 keq/ha/yr for East and South China.

Values thus derived for Cl deposition were 0.15 keq/ha/yr for Southwest China, 0.43

keq/ha/yr for North China, 0.30 keq/ha/yr for North China and 0.62 keq/ha/yr for East

and South China. The temporal trends of Na and Cl deposition were neglected,

S9

because both elements are mainly emitted from natural sources. P deposition input

was assumed to be constant in time, at 0.62 kg/ha/yr (Du et al., 2016).

1.2 Assessment of element outputs

1.2.1 Crop removal (Xrem)

Element removal was calculated separately for the harvested crop and crop residues

removal.

X rem=XRH +X RR (S10)

X RH ,i=∑ HY i ,k × XH k ×W %k (S11)

X RR ,i=∑ HY i , k × W %k × RRH ,k ×(1−f CR, i ,k )× XRk (S12)

Where, XRH and XRR denote the elements removed by the harvested parts and

residues, respectively, HY denotes the yield production, XH and XR denote the

element concentrations in harvested parts and residues, respectively, W% denote the

water content in harvest part, RRH denotes the ratio of crop residue to harvested part

and fCR denotes the fraction of crop residue return to cropland.

Data on annual yield production at provincial level were derived from NBSC.

Ratios of crop residues to harvested part, water content in harvested part and element

concentrations in harvested part and residues of different crops are given in Table A.

5, including the various sources. Straw return ratios of rice, wheat and maize were

gathered from published papers, assuming a linear increase in the period 1980-2010

based on these data (Fig. A.3). The averaged fraction from wheat and maize was used

for the rest of upland crops.

1.2.2 Ammonia Emission losses (X NH3)

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Ammonia emissions from croplands were estimated following the method from

Yan et al. (2003) that use emission factors multiplied with N inputs by fertilizer,

manure and N fixation. Emissions from irrigation, deposition and seeds were

neglected. NH3 volatilization induced by chemical N fertilizer to cropland strongly

depends on the nitrogen fertilizer type, timing and method of fertilizer application,

soil moisture and properties of the soil (Yan et al., 2003). In China, urea and

ammonium bicarbonate are the dominant N fertilizers, which accounted for

approximately 85% of the overall N fertilizer consumption during 1980-2010 (Zhang

& Zhang, 2013). Average NH3 emission factors for urea were set at 22% and 13.7%

for paddy rice and upland crops, respectively, and at 33% and 20.5% for ammonium

bicarbonate based on a comprehensive compilation of field experiments.

The allocations of N fertilizer rates on paddy rice and other upland crops were

calculated as:

N rice=CFN total × f NA /∑ (Ak × RN , k) (S13)

N k=N rice× RN , k (S14)

Where, Nrice and Nk denote the N fertilizer rate on rice and upland crops, CFNtotal is

the provincial or national chemical N fertilizer consumption, fNA is the ratio of N

fertilizer consumed by the considered 19 crops to total N consumption, A denotes the

sown area and RN,k denotes the ratios of the N fertilizer rate of each of the 18 upland

crops as compared to rice.

S11

The total chemical fertilizer application rates on paddy rice (CFNrice) and on all

upland crops (CFNupland) were calculated as:

CFN rice=N rice∗¿ (S15)

CFN upland=CFN total× f NA−CFNrice (S16)

Ratios of upland crops N rates to rice (RNk) are shown in Table A. 5, based on a

farmer survey of N application (Price Office of National Development and Reform

Commission, 2005-2006). The ratio of N fertilizer consumption by the 19 crops

compared to total N consumption (fNA) has been set equal to the ratio of the sown area

of these crops to the total sown area of crops in China, being 0.88.

Average NH3 emission factors from human and animal excretion were set at 20%

for human, cattle, pigs and poultry and 10% for sheep, while biologically fixed N was

set at 1% being volatilized (Yan et al., 2003).

The total NH3 emission (XNH3) for each province was aggregated as:

X NH 3=∑ ( f ¿¿k , l× N k ,l × Ak )+∑( f ¿¿ j × N M , j)+1 %× N fix¿¿¿¿ (S17)

Where, f denotes the emission factors of the different N sources (N fertilizers (l),

manure N types (j) and biologically fixed N), Nk was the amount of chemical N

applied on the crop type and NM is the amount of human and animal manure

application.

1.2.3 Denitrification losses (Xden)

Denitrification losses include the emissions of nitric oxide (NO), nitrous oxide

(N2O) and dinitrogen gas (N2) induced by nitrification and denitrification processes.

An assessment was made for each gas as described below.

1.2.3.1 NO and N2O emission

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Separate NO and N2O emission fractions for N fertilizer application were used for

upland crops and paddy rice due to their apparent differences in water management

and soil oxidation-reduction status. The NO emission factors were set at 0.66% and

0.13% for upland crops and paddy rice, while the N2O emission factors were set at

1.25% and 0.25%, respectively (Bouwman, 1996, Yan et al., 2003). Emissions by

manure and other N sources were included as a background emission of 0.57 kg

N/ha/yr for NO and 1.22 kg N/ha/yr for N2O, respectively (Yan et al., 2003).

1.2.3.2 N2 emission

N2 emission can be an important loss in terms of N surplus from agroecosystems,

but very limited understanding still exists on how much nitrate is denitrified to N2 and

emitted to the air (Galloway et al., 2004). In our study, we assumed that soil N pool

changes and N losses by soil erosion were negligible and N2 emission was thus

assessed on the basis of an N input-output balance. The N2 emission was set equal to

the difference between the total N input and the N output by crop removal, NH3

emission, N discharge and the denitrification losses by NO and N2O, according to:

N 2=N ¿−(N rem+N NH3+N dis+NO+N 2O) (S18)

1.2.4 Discharge losses to water (Xdis)

Nutrient discharge losses from the soil system, Xdis, were derived by using various

assumptions for the different elements involved. With respect to N, we assumed that

the change in N pool is negligible (no net mineralization or immobilization, nor any

adsorption of either NH4+ or NO3

-), and that ammonium is fully nitrified to nitrate,

implying that all N losses to water occur in the form of nitrate. N losses by discharge

were estimated as 50% of the Nrest (Nrest = Nin – Nrem – NNH3) from the root zone. This

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estimation was based on (i) relationships with N fertilizer rates from field experiment

for wheat, maize and rice (Liu et al., unpublished) and (ii) model (expert judgement)

based leaching fractions at 24.8% of Nrest in 100cm soil depth, independent of crop

type from Ma et al. (2012). Results were corrected for the difference between

discharge at 30 cm (where root mostly distributed) using data from Li & Li, (2000).

Thus, N losses by discharge were calculated as:

N dis=(N ¿−N rem−NNH 3)×50 % (S19)

HCO3- discharge strongly depends on the soil CO2 pressure and pH (Kindler et al.,

2011). The discharge can be calculated as the product of water flux times the HCO3-

concentration in soil solution, which is determined by the dissociation of CO2. Based

on De Vries et al. (1989) and Tarkalson et al. (2006), we calculated the discharge of

HCO3- (HCO3

-,dis, keq/ha/yr) as:

HCO3 , dis−¿=¿¿ (S20)

Where, KCO2 is the product of Henry's law constant for the equilibrium between

CO2 in soil water and soil air, and the first dissociation constant (10-7.8), PC02 is the

partial pressure of CO2 in the soil solution (in atm, 0.005), [H+] is the H+ concentration

in soil solution derived from soil pH and Vdis is the precipitation surplus or water

discharge rate (mm/yr). Data of soil pH in each province were derived from the

National Data Center of Soil Testing and Formulated Fertilization of China, and data

for Vdis in Northeast, Northwest, North Plain, South Central, Southwest and South

were set at 70, 50, 150, 300, 300 and 400mm/yr, based on Zhu et al. (accepted).

Phosphate losses to water were neglected due to the strong H2PO4- adsorption to the

soil, while inversely adsorption of Cl- was assumed to be negligible, implying that Cl-

discharge was equal to Cl- input. We also assumed that discharge by SO42- is equal to

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the SO42- surplus (the difference between total input and crop removal), which implies

that no SO42- adsorption occurred in soil.

BC losses were estimated from a charge balance in leachate that equal to the molar

equivalent of all anions:

BC¿=SO 42−¿+NO3

−¿+Cl−¿+HCO 3

−¿ ¿¿¿ ¿ (S21)

Considering the uncertainty in dominant leaching of NO3- with chemical N

fertilizer application (Vieira et al., 2008; Tarkalson et al., 2006), we considered the

input of RCOO- to be negligible.

1.2.5 Soil accumulation (Xacc)

Accumulation of N, S, Cl and HCO3- were assumed to be negligible, because of

their weak immobilization capacity. Inversely, P accumulation was set equal to the P

surplus by considering negligible P discharge. Finally, BC accumulation (or release)

was calculated as:

BCacc=BC i n−BC rem−BC dis (S22)

Annual average input and output fluxes were given both in kilogram and in kilo

equivalent per hectare, the first being used as the common standard for nutrient

balances and the latter giving a more direct impression and easier understanding of

the acidity calculations.

Results of all calculations for China as a whole in the years of 1980 and 2010 are

given in Table A.6.

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Table A.1 Calculations of elements (ions) from kg/ha/yr to keq/ha/yrElement/ions kg/ha/yr keq/ha/yrNH4

+-N 1 1/14NO3

--N 1 1/14H2PO4

--P 1 1/31K 1 1/39Ca 1 1/40×2Mg 1 1/24×2Na 1 1/23S 1 1/32×2Cl 1 1/35.5HCO3

--C 1 1/12

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Table A.2 Available data sources used to assess element inputs and outputs for the period 1980-2010

Data Data sourceArea cropland per province Ministry of Environmental Protection of China (1999)N, P, K fertilizer input data per province

National Bureau of Statistics of China (NBSC, http://data.stats.gov.cn/ )

Fertilizer composition (N, P, K, Ca, Mg, S, Cl) content

Zhang and Zhang (2013)

Human population and livestock number per province

NBSC (http://data.stats.gov.cn/)China Compendium of Agricultural Statistics 1949-2008

Slaughter and herds at the end of the year per province

NBSC (http://data.stats.gov.cn/);China Compendium of Agricultural Statistics 1949-2008

Excretion rates per human (capita) for whole of China

Jönsson et al. (2004)

Excretion rates per animal category for whole of China

Li and Jin (2011); Jia (2014)

N fixation rates per crop for whole of China

Li and Jin (2011); Smil (1999); Giller (2001); Herridge et al. (2008)

Seeding rates per crop for whole of China

Price Office of National Development and Reform Commission (1981-2011)

N,P and K inputs by Irrigation per province

Li and Jin (2011)

Area of effective irrigation per province

NBSC (http://data.stats.gov.cn/)

Deposition per province Dentener et al. (2006); Du et al. (2016); Huang et al. (1993); Lei et al. (2011);Liu et al. (2013); Zhu et al. (2016); Ministry of Environmental Protection of China, 1990-2014; EANET (http://www.eanet.asia/)

Crop sown area and crop yields per province

National Bureau of Statistics of China (http://data.stats.gov.cn/ )

Element contents N, P, Ca, Mg, K, S in grains (also used for seeds) and straw per crop for whole of China

Center for Disease Control and Prevention and Food Security of China (2009); U.S. and International Nutrient Databases (http://www.foodhealth.info/); National Agricultural Technical Extension and Service Center (1999)

Ratio of harvest to residue per crop for whole of China

Bi (2010)

Straw return for cereal crops for whole of China

Publications, see below in supplementary materials

NH3 emission fractions per N fertilizer type, manure type and land use for whole of China

Yan et al. (2003); Bouwman (1996)

N2O and NOx emission fractions from N fertilizer per land use for whole of China

Yan et al. (2003)

N leaching fractions for whole of China

Ma et al. (2012); Li and Li (2000); Liu et al. (Unpublished)

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Table A.3 Element concentrations in urine and faeces (%)Items Element Human Pig Sheep Poultry Cattle

Urine

N 0.526 0.166 0.592 - 0.501P 0.038 0.022 0.021 - 0.017K 0.136 0.157 0.695 - 0.906Ca 0.101 0.011 0.689 - 0.056Mg 0.034 0.011 0.181 - 0.049Na 0.233 0.052 0.017 - 0.062S 0.036 0.016 0.240 - 0.035

Faeces

N 1.159 0.547 1.014 0.76 0.383P 0.261 0.245 0.216 0.33 0.095K 0.304 0.294 0.532 0.59 0.231Ca 0.304 0.494 1.305 1.66 0.434Mg 0.133 0.222 0.254 0.24 0.106Na 0.197 0.080 0.062 0.20 0.037S 0.110 0.103 0.149 0.15 0.073

Data from National Agricultural Technical Extension and Service Center (NATESC), 1999

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Table A.4 Parameters used in the calculation of animal excretion

Animals Breeding days per cycle (d)

Urination rate kg/d

Defecation rate Kg/d

Pig 198.5 3 2Dairy Cattle/Farm cattle 365 8.53 36.6

Beef cattle 300 4.67 18Sheep 243 0.5 1.5

Poultry 210 0 0.13Data from Li and Jin, 2011; Jia 2014.

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Table A.5 Element concentrations in crop harvest, crop residues and related parameters in crop removal calculation

cropsElement concentration in harvested part a

g/kgElement concentration in crop residues a

g/kgRRH

b

-

W% c

%RN,k

d

-N P K Ca Mg Na S N P K Ca Mg Na S

Rice 11.8 1.1 1.03 0.13 0.34 0.04 0.3 9.1 1.3 18.9 6.1 2.24 0.12 1.38 0.95 14 1.0Wheat 19 3.25 2.89 0.34 0.04 0.07 0.9 6.5 0.8 10.5 5.2 1.65 0.29 0.96 1.3 12.5 0.95Maize 13.9 2.18 3 0.14 0.96 0.03 0.83 9.2 1.52 11.8 5.4 2.24 0.39 0.94 1.1 14 1.09

Chinese sorghum 16.6 3.29 2.81 0.22 1.29 0.06 1.0 12.5 1.46 14.3 4.6 1.9 0.39 0.94 1.6 14 0.74

Millet 14.4 2.29 2.84 0.41 1.07 0.04 2.01 8.2 1.01 17.5 4.76 4.5 0.3 1.06 1.4 14 0.50potato 3.2 0.4 3.42 0.08 0.23 0.03 0.26 26.5 2.72 39.6 30.3 5.8 1.0 3.7 0.96 75 0.74

Sweet Potato 2.0 0.43 1.52 0.24 0.15 0.43 0.26 23.7 2.83 30.5 21.1 4.6 1.0 3.0 0.63 75 0.74Soybean 56 4.65 15 1.91 1.99 0.02 0.3 18.1 1.96 11.7 17.1 4.8 1.0 2.1 1.6 13 0.26Peanut 38.4 3.24 5.87 0.39 1.78 0.04 1.7 18.2 1.63 10.9 17.6 5.6 1.0 1.4 1.5 15 0.49

sunflower 38.4 2.38 5.62 0.72 2.64 0.06 2.0 8.2 1.12 17.7 15.8 3.1 1.0 1.7 2.8 12 0.70Rape seeds 45.8 5.6 7.2 3.35 2.87 0.37 6.43 8.7 1.44 19.4 15.2 2.5 1.0 4.4 2.7 8.0 0.70

cotton 24.1 3.31 11.7 2.17 1.55 0.23 0.8 12.4 1.5 10.2 8.5 2.8 1.0 1.7 5.0 12 1.25Hemp 6.0 0.5 7.0 6.0 1.5 0.25 0.5 13.1 0.6 5.0 30.6 4.5 1.0 0.5 1.9 14 1.55

sugar cane 15.5 1.4 16 3.27 1.83 0.14 0.35 11.0 1.4 11 8.8 2.1 0.4 0.63 0.1 70 2.19Sugar beet 14 1.0 16.1 2.56 3.94 3.9 0.85 10.0 2.93 12.1 9.35 7.74 17.4 2.6 0.1 75 1.09

tobacco 20.8 2.3 16.2 22.7 2.8 0.26 4.5 14.4 1.69 18.5 14.9 1.9 1.0 2.7 1.6 17 0.72vegetables 1.74 0.79 1.48 0.29 0.14 0.32 0.32 29.8 3.79 27.7 14.5 4.99 0.0 3.2 0.1 90 1.77

water melons 0.96 0.09 0.87 0.08 0.08 0.03 0.09 25.8 2.29 19.7 46.4 8.3 1.0 2.4 0.1 95 1.77other melons 0.77 0.13 1.43 0.13 0.13 0.11 0.09 23.5 4.76 21.6 46.4 8.3 1.0 2.4 0.1 95 1.77

Tea 54.7 1.91 16.6 3.25 1.96 0.28 4.5 - - - - - - - - 0.84Apple 0.32 0.12 1.19 0.04 0.04 0.02 0.0 - - - - - - - - - 2.93Pear 0.64 0.14 0.92 0.09 0.08 0.02 0.04 - - - - - - - - - 2.93

Banana 2.24 0.28 2.56 0.07 0.43 0.01 2.06 - - - - - - - - - 2.93Orange 1.12 0.18 1.54 0.35 0.11 0.01 0.08 - - - - - - - - - 2.93Grape 0.8 0.13 1.04 0.05 0.08 0.01 0.75 - - - - - - - - - 2.93

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a The concentration in harvested parts for different crops are fresh weight based, while the concentration in crop residues are dry weighed based. Data from the Center for Disease Control and Prevention and Food Security of China (2009); U.S. and International Nutrient Databases (http://www.foodhealth.info/); b RRH denotes the ratio of crop residue to harvested part and c w% denotes water concentration in harvested parts (%), data from Bi, 2010. d denotes the ratio of N fertilizer rate on the crop to on rice, data adapted from the Price Office of National Development and Reform Commission (2005 and 2006).

Table A.6 Average annual element budgets in China in 1980 and 2010¡¡

Source Element budgets in China in 1980 and 2010 (kg/ha/yr and in keq/ ha/yr in brackets)N NH4

+-N NO3--N H2PO4

--P BC-K SO42--S HCO3

--C Cl--Cl H+-HInput to land 1980 2010 1980 2010 1980 2010 1980 2010 1980 2010 1980 2010 1980 2010 1980 2010 1980 2010Mineral fertilizer 72.5 227 56.0 133 16.6 93.7 9.5 47.2 32.3 106 1.2 0.0 32.0 21.7 5.1 105 -0.45 0.76

(5.18) (16.2) (4.00) (9.53) (1.18) (6.69) (0.31) (1.52) (0.83) (2.71) (0.08) (0) (2.66) (1.81) (0.14) (2.97) (-0.45) (0.76)Manure 21.8 43.1 10.9 21.5 10.9 21.5 3.9 9.4 63.9 147.1 2.8 6.2 0.0 0.0 0.0 0.0 -1.34 -3.08

(1.56) (3.08) (0.78) (1.54) (0.78) (1.54) (0.13) (0.3) (1.64) (3.77) (0.18) (0.39) (0) (0) (0) (0) (-1.34) (-3.08)Biological fixation

16.4 18.3 8.2 9.1 8.2 9.1 - - - - - - - - - - - -(1.17) (1.31) (0.58) (0.65) (0.58) (0.65) - - - - - - - - - - - -

Atmospheric deposition

5.9 18.2 4.2 12.9 1.7 5.3 0.6 0.6 14.3 38.8 11.0 21.5 0.0 0.0 14.2 14.2 0.56 0.22(0.42) (1.3) (0.3) (0.92) (0.12) (0.38) (0.02) (0.02) (0.37) (0.99) (0.68) (1.34) (0) (0) (0.4) (0.4) (0.56) (0.22)

Irrigation 1.4 1.9 0.7 1.0 0.7 1.0 0.1 0.1 1.4 1.9 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0(0.1) (0.13) (0.05) (0.07) (0.05) (0.07) (0) (0) (0.04) (0.05) (0) (0) (0) (0) (0) (0) (0) (0)

Seeds 2.3 2.1 1.1 1.0 1.1 1.0 0.3 0.3 0.5 0.8 0.1 0.2 0.0 0.0 0.0 0.0 0.0 0.0(0.16) (0.15) (0.08) (0.07) (0.08) (0.07) (0.01) (0.01) (0.01) (0.02) (0.01) (0.01) (0) (0) (0) (0) (0) (0)

Total input 120 311 81.1 179 39.2 132 14.4 57.5 113 295 15.1 27.9 32.0 21.7 19.3 120 -1.27 -2.16(8.59) (22.2) (5.79) (12.8) (2.8) (9.4) (0.46) (1.86) (2.89) (7.56) (0.95) (1.74) (2.66) (1.81) (0.54) (3.37) (-1.27) (-2.12)

Output from landHarvest removal 51.2 108 0.0 0.0 51.2 108 6.2 16.7 65.0 130 3.5 8.2 0.0 0.0 0.0 0.0 2.41 5.39

(3.66) (7.68) (0) (0) (3.66) (7.68) (0.2) (0.54) (1.67) (3.34) (0.22) (0.52) (0) (0) (0) (0) (2.41) (5.39)Surplus 69.0 203 69.0 203 8.2 40.8 47.8 164 11.6 19.7 32.0 21.7 19.3 120 -3.68 -7.56

(4.93) (14.5) (4.93) (14.51) (0.26) (1.32) (1.23) (4.22) (0.73) (1.23) (2.66) (1.81) (0.54) (3.37) (-3.68) (-7.56)NH3 21.7 55.8 21.7 55.8 - - - - - - - - - - - - - -

(1.55) (3.99) (1.55) (3.99) - - - - - - - - - - - - - -N2O 1.9 4.0 - - 1.9 4.0 - - - - - - - - - - - -

(0.14) (0.29) - - (0.14) (0.29) - - - - - - - - - - - -NO 0.9 2.0 - - 0.9 2.0 - - - - - - - - - - - -

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(0.07) (0.14) - - (0.07) (0.14) - - - - - - - - - - - -N2 20.8 67.6 20.6 68.1 - - - - - - - - - - - -

(1.49) (4.83) (1.49) (4.83) - - - - - - - - - - - -Discharge to water

23.7§ 73.7§ - - 23.7 73.7 0.0 0.0 139£ 408£ 11.6 19.7 7.1 7.1 19.3 120 - -(1.69) (5.26) - - (1.69) (5.26) (0) (0) (3.56) (10.5) (0.73) (1.23) (0.6) (0.6) (0.54) (3.37) - -

Accumulation/consumption¢

0.0 0.0 0.0 0.0 0.0 0.0 8.2 40.8 -91§ -244§ 0.0 0.0 0.0 0.0 0.0 0.0 -3.68 -7.56(0) (0) (0) (0) (0) (0) (0.26) (1.32) (-2.3) (-6.2) (0) (0) (0) (0) (0) (0) (-3.68) (-7.56)

Number in brackets denote the items in unit of keq/ha/yr. - and 0 denote the items were irrelevant with the elements and were assumed as 0, respectively. ¢we assume no changes in soil N, S, C, and Cl pool, due to their weak immobilization. £ Calculated as the charge balance in leachate. § derived from mass balance of the element. ψ Calculated as mass balance, N2= surplus-discharge-NH3-N2O-NO ¡¡ Note that total fluxes for China can be derived by multiplying with a crop area of 1.3×108 ha;

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Fig. A.1 Trends in various N fertilizer types used in the period 1980-2010, given as a fraction of the

total N fertilizer use.

S23

Fig. A.2 Trends in various P fertilizer types in the period 1980-2010, given as a fraction of the total P

fertilizer use. FMP denotes fused calcium-magnesium phosphate.

S24

Fig. A.3 Percentages of crop residue return of major crops during the period 1980-2010.

S25

Fig. A.4 Annual inputs and outputs of Cl- (a,b) and HCO3- (c,d) in Chinese cropland during 1980 and

2010.

S26

Fig. A.5 Provincial scale N inputs (top), N removals (middle) and N surpluses (bottom) in 1980 (left)

and 2010 (right).

S27

Fig. A.6 Provincial scale BC input (top), BC removal (middle) and BC surplus (bottom) in 1980

(left) and 2010 (right).

S28

Fig. A.7 Provincial scale P inputs (top), P removals (middle) and P surpluses (bottom) in 1980 (left)

and 2010 (right).

S29

Fig. A.8 Provincial scale S input (top), S removals (middle) and S surpluses (bottom) in 1980 (left)

and 2010 (right).

S30

References used in Methods S1:

Agricultural Technology Promotion and Service Center of China, 1999. Nutrients of Chinese

organic fertilizer. China Agricultural Press, Beijing, China.

Bouwman, A., 1996. Direct emission of nitrous oxide from agricultural soils. Nutr. Cycling

Agroecosyst. 46, 53-70.

Center for Disease Control and Prevention and Food Security of China, 2009. China food

composition, 2nd edition. Peking University Medical Press, Beijing, China.

Dentener, F., Drevet, J., Lamarque, J., Bey, I., Eickhout, B., Fiore, A., Hauglustaine, D.,

Horowitz, L., Krol, M., Kulshrestha, U., 2006. Nitrogen and sulfur deposition on regional

and global scales: a multimodel evaluation. Global Biogeochem. Cycles 20, 1-21.

Du, E., De Vries, W., Han, W., Liu, X., Yan, Z., Jiang, Y., 2016. Imbalanced phosphorus and

nitrogen deposition in China’s forests. Atmos. Chem. Phys. Discuss. 16, 8517-8579.

Galloway, J.N., Dentener, F.J., Capone, D.G., Boyer, E.W., Howarth, R.W., Seitzinger, S.P.,

Asner, G.P., Cleveland, C., Green, P., Holland, E., 2004. Nitrogen cycles: Past, present,

and future. Biogeochemistry 70, 153-226.

Giller, K.E., 2001. Nitrogen fixation in tropical cropping systems. CABI publishing, Wallingford,

U.K.

Herridge, D.F., Peoples, M.B., Boddey, R.M., 2008. Global inputs of biological nitrogen fixation

in agricultural systems. Plant Soil 311, 1-18.

Huang, M., Hiromasa, U., Liu, S., 1993. Comparison and analysis of the chemical characteristics

of precipitation in China and Japan. Sci. Atmos. Sin. 17, 27-38.

Jönsson, H., Stintzing, A.R., Vinnerås, B., Salomon, E., 2004. Guidelines on the use of urine and

faeces in crop production. EcoSanRes Programme, Stockholm, Sweden.

S31

Jia, W., 2014. Studies on the evaluation of nutrient resources derived from manure and optimized

utilization in arable land of China. College of Resources and Environmental Sciences.

China Agricultural University, Beijing, China.

Lei, Y., Zhang, Q., He, K., Streets, D., 2011. Primary anthropogenic aerosol emission trends for

China, 1990-2005. Atmos. Chem. Phys. 11, 931-954.

Li, S., Jin, J., 2011. Characteristics of nutrient input-output and nutrient balance in different

regions of China. Sci. Agric. Sin 44, 4207-4229.

Li, S., Li, S., 2000. Leaching loss of nitrate from semiarid area agroecosystem. Chin. J. Appl.

Ecol. 11, 240-242.

Liu, Q., 2017. Spatio-temporal changes of fertilization intensity and environmental safety

threshold in China. Transactions of the CSAE 33, 214-221.

Liu, X., Zhang, Y., Han, W., Tang, A., Shen, J., Cui, Z., Vitousek, P., Erisman, J.W., Goulding,

K., Christie, P., 2013. Enhanced nitrogen deposition over China. Nature 494, 459-462.

Ma, L., Velthof, G., Wang, F., Qin, W., Zhang, W., Liu, Z., Zhang, Y., Wei, J., Lesschen, J., Ma,

W., 2012. Nitrogen and phosphorus use efficiencies and losses in the food chain in China

at regional scales in 1980 and 2005. Sci. Total Environ. 434, 51-61.

Ministry of Agriculture of China, 2009. China Compendium of Agricultural Statistics 1949-2008.

China Agricultural Publisher, Beijing, China.

Ministry of Environmental Protection of China, 1990-2014. China Statistical Yearbook on

Environment. Environmental Year Publisher of China, Beijing, China.

Ministry of Environmental Protection of China, 1999. China Statistical Yearbook on

Environment. Environmental Year Publisher of China, Beijing, China.

National Data Center of Soil Testing and Formulated Fertilization,

http://m.soildbc.com/webstation//main/mainlogin.aspx

S32

Price Office of National Development and Reform Commission, 1981-2011. Yearbook of

National Agricultural Products Cost and Benefit Compilation, China Statistics Press,

Beijing, China.

Price Office of National Development and Reform Commission, 2005-2006. Yearbook of

National Agricultural Products Cost and Benefit Compilation, China Statistics Press,

Beijing, China.

Smil, V., 1999. Nitrogen in crop production: An account of global flows. Global Biogeochem.

Cycles 13, 647-662.

Sun, B., Shen, R., Bouwman, A., 2008. Surface N balances in agricultural crop production

systems in China for the period 1980-2015. Pedosphere 18, 304-315.

Tarkalson, D.D., Payero, J.O., Hergert, G.W., Cassman, K.G., 2006. Acidification of soil in a dry

land winter wheat-sorghum/corn-fallow rotation in the semiarid US Great Plains. Plant

Soil 283, 367-379.

Vieira, F., Bayer, C., Mielniczuk, J., Zanatta, J., Bissani, C., 2008. Long-term acidification of a

Brazilian Acrisol as affected by no till cropping systems and nitrogen fertiliser. Soil Res.

46, 17-26.

Wang, J., 2009. Supply and demand status and market forecast of potassium in China. Chem.

Enterprise Manage. 9, 17-23.

Xin, Y., 2009. Forecast of acidification of typical forest soil in south China. Tsinghua University,

Beijing, China.

Yan, X., Akimoto, H., Ohara, T., 2003. Estimation of nitrous oxide, nitric oxide and ammonia

emissions from croplands in East, Southeast and South Asia. Global Change Biol. 9,

1080-1096.

Zeng, M., De Vries, W., Bonten, L.T.C., Zhu, Q., Hao, T., Liu, X., Xu, M., Shi, X., Zhang, F.,

Shen, J., 2017. Model-based analysis of the long-term effects of fertilization management

on cropland soil acidification. Environ. Sci. Technol. 51, 3843-3851.

S33

Zhang, W., Zhang, F., 2013. Research report on fertilizer development of China. China

Agricultural University Press, Beijing, China.

Zhu, Q., De Vries, W., Liu, X., Zeng, M., Hao, T., Du, E., Zhang, F., Shen, J., 2016b. The

contribution of atmospheric deposition and forest harvesting to forest soil acidification in

China since 1980. Atmos. Environ. 146, 215-222.

Zhu, Q., Liu, X., Hao, T., Zeng, M., Shen, J., Zhang, F., De Vries, W. Modelling soil

acidification in typical Chinese cropping systems. Sci. Total Environ., accepted

S34

References used in crop residue return assessment (Fig. A.3)

1. Bi Y, Wang Y, Gao C, System constitution and general trend of straw resource comprehensive

utilization in China. Chinese Journal of Agricultural Resources and Regional Planning 2010, 31, (4),

35-38.

2. Cao S, Wu Y, Situation and Prospects of straw return in Anhui Province. Anhui Agricultural

Science Bulletin 1995, 1, (1), 42-43.

3. Chen D, Gai Z, Chen Y, You N, Situation and future direction of straw utilization. Shanghai

Agricultural Sciences and Technology 2006, (5), 32-33.

4. Chen S, Zhang D, Middle-long-term developing problem of mechanization in Qingyundian

Village of Daxing County. Journal of Beijing Agriculture Engineering University 1989, 9, (3), 1-10.

5. Dong Y, Hou F, Study on the industrialized development for integrated utilization of the straw of

crops. Transactions of the Chinese Society of Agricultural Engineering 2003, 19, (Supp), 192-195.

6. Fan P, Li S, Wang S, Xu X, Preliminary research on the comprehensive utilization, problems and

solutions of crop straw. Anhui Agricultural Science Bulletin 2009, 15, (12), 62-63.

7. Feng J. Researches on soil organic carbon density and carbon sequestration effects in the

farmland of Yangtze Delta. Nanjing Agricultural University, Nanjing, China, 2005.

8. Feng X, Hao H, Li J, A survey on straw utilization of maize in Anyang City. Farm Machinery

2003, 46, (5), 38-39.

9. Gao L, Ma L, Zhang W, Wang F, Ma W, Zhang F, Analysis on the quantities and utilization of

crop straw and its nutrient in Huang-Huai-Hai Region. Chinese Agricultural Science Bulletin 2009,

25, (11), 186-193.

10. Gao L, Ma L, Zhang W, Wang F, Ma W, Zhang F, Estimation of nutrient resource quantity of

crop straw and its utilization situation in China. Transactions of the Chinese Society of Agricultural

Engineering 2009, 25, (7), 173-179.

11. Gao X, Ma W, Ma C, Zhang F, Wang Y, Analysis on the current status of utilization of crop

straw in China. Journal of Huazhong Agricultural University 2002, 21, (3), 242-247.

S35

12. Hao J. The research of the problems exist in crops' straw utilization and countermeasure in

agriculture production in Linyi Area. China Agricultural University China Agricultural University,

Beijing, China, 2004.

13. Hang Q, Wang X, Wang G, Cui B, The utilization of stalk resources in Yuncheng Area and its

effect on sustainable agriculture. Journal of Shanxi Agricultural Sciences 1998, 26, (2), 89-91.

14. Liu F. The analysis of the straw comprehensive utilization status and development

countermeasures in Luoyang City. Henan University of Science & Technology, Luoyang, China,

2012.

15. Liu H, Zhou J, Zhou P, Xiao A, Wu J, Analyze regional characteristics and influencing factors of

different crop straw treatment in South Central of China. Quaternary Sciences 2014, 34, (4), 848-855.

16. Liu J. Analyses on the distribution pattern of the crop-straw resources and the status quo of its

application in China. China Agricultural University, Beijing, China, 2005.

17. Liu J, The comprehensive utilization of straws. Feed Industry 1987, 8, (1), 45-46.

18. Liu L. Greenhouse gases emissions from agriculture residues burning- A case study of Jiangsu

Province. Nanjing Agricultural University, Nanjing, China, 2011.

19. Liu X. A study on comprehensive utilization of crop straws in Jingzhou. Yangtze University,

Jingzhou, China, 2013.

20. Liu Y, Wei M, Li H In Analysis and recommendations on comprehensive utilization of straw

resource in Henan Province, Coordinated development of science, technology, engineering, economic

and society - The Fourth Henan Youth Annual Conference Proceedings (Volume II), 2004;

Association of Henan Science and Technology, Ed. Science and Technology Press of China: 2004; pp

1374-1377.

21. Liu Y, Yu Z, Zhang F, Song C, Liu Y, Dynamic change of soil organic matter and its affecting

factors at county level. Plant Nutrition and Fertilizer Science 2005, 11, (3), 294-301.

22. Mu C, Yan G, The situation and recommendation on the utilization of straw in Jiangyan City.

Shanghai Agricultural Sciences and Technology 2008, 2, (2), 25-26.

S36

23. Qiu L, Guo S, The situation and rational development on straw utilization in Shaanxi Province.

Resource Development & Market 1989, 5, (3), 171-177.

24. Quan Y, Yang P, Guo H, Survey and analysis on the general situation of comprehensive

utilization of straw in Huanghe-Huaihe Plain Region. Journal of Anhui Agricultural Sciences 2010,

38, (28), 15814-15817.

25. Rui W, Zhou B, Zhang W, Affecting factors of farm household behavior for crop residue

recycling: a case study in Jiangsu province, China. Ecology and Environmental Sciences 2009, 18, (5),

1971-1975.

26. Song J, Research on the straw resources and its quality in Zhejiang Province. Soils and

Fertilizers 1995, 32, (2), 23-26.

27. Sun H, Chen J, Wang C, Problems and solutions in soil nutrient cycling in Qing County, Hebei

Province- Analysis with multivariate statistical analysis method. Rural Eco-Environment 1986, 1, 1-8.

28. Sun Z, The application and development of reduced tillage and non-tillage in State Farm in

Anhui Province. Journal of Anhui Agricultural Sciences 1987, 5, (3), 20-26.

29. Tian F, Gou Z, Chen Y, Investigation and analysis of re-utilization of maize straw in Qianzhong

and Qianbei Areas. Guizhou Agricultural Sciences 2007, 35, (3), 58-60.

30. Tian T, Chen X, The recognition on straw utilization in Shaanxi. Agro-Environment & Develop

2010, 27, (5), 25-28.

31. Wang G, The situation and utilization of straw resources of main crops in Anhui Province. China

Resources Comprehensive Utilization 2010, 28, (1), 13-17.

32. Wang R, Zhang J, Dong S, Liu P, Present situation of maize straw resource utilization and its

effect in main maize production regions of China. Chinese Journal of Applied Ecology 2011, 22, (6),

1504-1510.

33. Wang S. A system study on efficiency and profitability of major uses of crop straw in Hebei

Plain. Agricultural University of Hebei, Baoding, China, 2011.

34. Wang S. Research on rural householders' comprehensive utilization in Jiangsu Province. Nanjing

Agricultural University, Nanjing, China, 2012.

S37

35. Wang S, Cai R, Economic analysis of the straw disposal behaviour of farmers: Based on the

survey of rice & wheat farmers in Jiangsu. China Population, Resources and Environment 2014, 24,

(8), 162-167.

36. Wang Y, Zhao Y, Ding M, Ji C, Wang C, The situation and comprehensive utilization of straw

resources in Jiangsu Province. Jiangsu Agricultural Sciences 2010, 38, (4), 393-396.

37. Wang Z, Yang J, Hu C, Ways and technical measures for high efficient utilization of straw

resources in Taihang Piedmont. Resources Science 2001, 23, (5), 67-72.

38. Wei Y, Xue J, The situation and recommendations on the comprehensive utilization of straw

resources in Weiyang Distric, Xi’an. Agricultural Technology & Equipment 2004, 40, (1), 24-25.

39. Wu Y, Zhang L, Cui G, Investigation and thoughts on the comprehensive utilization of crop stalk

resources in Henan Province. Journal of Henan Agricultural University 2010, 44, (3), 352-359.

40. Wu J, Song X, Research on resources and qualities of the straw resources in Henan Province.

Journal of Henan Agricultural Sciences 1995, 24, (11), 30-31.

41. Xia S, The resources and technology of straw utilization in Nantong City. Shanghai Agricultural

Sciences and Technology 1997, 25, (4), 2-3.

42. Xie Y, Gui Z, Research on straw utilization and straw return in Fanchang County. Journal of

Anhui Agricultural Sciences 1999, 27, (2), 146-147.

43. Xiong D, Zhang J, Hu Z, Status of crop straw utilization and preliminary analysis on its

comprehensive utilization ways in Huanggang City. Hubei Agricultural Sciences 2011, 50, (21), 4370-

4373.

44. Xu X, Wu W, Crop straw resources and their utilization in Anhui Province. Journal of

Agricultural Science and Technology 2009, 11, (2), 39-43.

45. Yan G, Wang Y, Qian C, Xue A, The situation and development of straw utilization in Jiangyan

City. Shanghai Agricultural Sciences and Technology 1999, 29, (3), 7-8.

46. Yan W, Chen Y, Discussion on the comprehensive utilization of maize straw. Chinese

Agricultural Mechanization 2003, 3, (3), 12-13.

S38

47. Yang G, Huang F, Li L, Yang Z, Liu Z, The situation and trend of straw return in intensive

cropland around Dongting Lake. Hunan Agricultural Sciences 1998, 5, 28-30.

48. Yang G, Shang Y, Li D, Primary discussion on resources and utilization of straw in Qinghai

Province. Chinese Qinghai Journal of Animal and Veterinary Sciences 1994, 24, (2), 33-34.

49. Yang L, Yan C, Discussion and Thinking on straw resources. Agro-Environmental Protection

1993, 12, (6), 271-273.

50. Yang L, Fan C, Qin S, The comprehensive utilization status and countermeasures of the straw

resources in Guizhou. Guizhou Agricultural Sciences 2012, 40, (5), 109-112.

51. Yu Z, The developing trend of resources treatment of crop stalk in Fuzhou City. Fujian

Environment 2003, 20, (5), 31-32.

52. Zhang M, Survey on straw return by mechanization in wheat-maize interplanting system in

Huantai County. Crops 1999, 15, (6), 33-34.

53. Zhang N. Comprehensive utilization of crops straw ecological research in Shandong District.

Northwest A&F University, Yangling, China, 2013.

54. Zhao C, Utilization status of crop straws and sustainable development in Beijing. Journal of

Agriculture 2015, 5, (2), 42-46.

55. Zheng J, Shi J, Utilization of crop straw, current situation, dilemma of micro-economics and

ways out: Taking Shandong Province as example. Research of Agricultural Modernization 2012, 33,

(3), 354-358.

56. Zhu Q, Huang D, Liu S, Zhang W, Su Y, Wu J, Status and prospects of crop straw

comprehensive utilization in hilly red soil region. Chinese Journal of Ecology 2005, 24, (12), 1482-

1486.

57. Zou S, Sun J, Wang Q, Utilizing saturation and developing countermeasure of organic manures

resources in Jiangxi Province. Chinese Agricultural Science Bulletin 2004, 20, (5), 170-173.

S39