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Manure acts as a better fertilizer for increasing crop yields than synthetic fertilizer does by improving soil fertility

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Manure acts as a better fertilizer for increasing crop yields than synthetic
fertilizer does by improving soil fertility
Andong Cai
, Minggang Xu
, Boren Wang
, Wenju Zhang
, Guopeng Liang
, Enqing Hou
Yiqi Luo
National Engineering Laboratory for Improving Quality of Arable Land, Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural
Sciences, Beijing, 100081, China
Center for Ecosystem Science and Society, Department of Biological Sciences, Northern Arizona University, Flagsta, AZ, 86011, USA
Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650,
Department of Earth System Science, Tsinghua University, Beijing, China
Synthetic fertilizer
Crop yields
Soil organic carbon
Soil nutrients
Soil pH
Fertilization is an important management strategy for crop yields by mediating soil fertility. However, rare
studies quantitatively assessed the interactions among fertilization, crop yields, and soil fertility. Here, data from
a 25-year fertilization experiment in the humid subtropical region of Southern China were used to evaluate and
quantify the eect of fertilization on crop yields via soil fertility. Seven treatments were chosen: CK (non-
fertilizer); N (synthetic nitrogen); NP (synthetic N and phosphorus); NPK (synthetic N, P and potassium); NPKM
(synthetic NPK with manure); 1.5NPKM
(1.5 times of NPKM
); and M
(manure alone). Overall, the crop yields
of wheat and maize under manure (1.361.58 and 3.85-5.82 Mg ha
) were higher than those under CK (0.34
and 0.25 Mg ha
) and synthetic fertilized treatments (0.270.97 and 0.482.65 Mg ha
), as the averaged of
19912015. Higher SOC stocks were found under the NPKM
, 1.5NPKM
, and M
treatments with a pronounced
increase in SOC over the rst 10 years and stable over the last 15 years. By the boosted regression trees, manure,
synthetic fertilizer and soil properties (SOC storage, soil pH, and soil nutrients) accounted for 39%, 21%, and
40% of the variation of the relative yield, respectively. Path analysis identied a network of inter-relations of
manure, synthetic fertilizer, and soil properties in the relative yields. Compared to synthetic fertilized treat-
ments, manure application strongly and positively aected the relative yield by increasing SOC storage, soil
nutrients, and soil pH (path coecients: 0.90, 0.88, and 0.76). These factors explained 72% of the crop yields'
variance. These results suggest that manure application is a viable strategy for regulating crop yields due to its
improvement in soil fertility.
1. Introduction
Promoting global crop productivity to feed the ever-increasing po-
pulation and high living standards has become a great challenge
(Fischer et al., 2014). The most debating question of recent times is
How to increase the crop yields?(Foley et al., 2011). Technological
progress in eld management has contributed to large increases in crop
yields (Deryng et al., 2011). Among all the management strategies,
fertilization has been suggested as a promising strategy to increase crop
yields. Based on 153 eld experiments in China, Chen et al. (2014)
observed an increase in crop yields of approximately 8.5-14.2 Mg ha
following fertilization with manure without any increase in nitrogen
(N) fertilizer. Using data from 20 eld experiments in Europe, Hijbeek
et al. (2016) reported that crop yields increased by 2.0 Mg ha
due to
synthetic fertilization and had negligible change (an increase of 1.4%)
in response to manure. It is obvious that the eect of dierent fertilizer
types on crop yields is inconsistent via dierent mechanisms. Therefore,
to achieve high crop productivity, it is important to understand the
impact of dierent fertilizer inputs on crop yields.
Exogenous fertilization inuences the crop yields by improving soil
fertility, such as soil carbon, nutrients, and pH. Soil carbon content is
the essential index for dierent yields (Tian et al., 2016). Soil organic
carbon (SOC) sequestration can be enhanced by fertilization such as
incorporation of crop residues or the direct application of manure,
which implies by high carbon inputs (Cai et al., 2016). Synthetic fer-
tilization can also change SOC by the return of crop residues. For
Received 11 February 2018; Received in revised form 17 December 2018; Accepted 26 December 2018
Corresponding author.
E-mail address: (M. Xu).
Soil & Tillage Research 189 (2019) 168–175
0167-1987/ © 2018 Elsevier B.V. All rights reserved.
instance, Zhang et al. (2012) showed that carbon inputs were 2.5-
5.0 Mg ha
by synthetic fertilization in southern China. The
greater amount of carbon inputs by green manure improved the SOC
stock by 1424% and reduced synthetic fertilization of 2551% com-
pared with fallow (Yao et al., 2017). In their meta-analysis, McDaniel
et al. (2014) reported that the rate of SOC sequestration under cover
crop is signicantly higher than SOC sequestration rate under no cover
crop. The application of farmyard manure, rice straw, and fertilizer
nitrogen could maintain SOC almost at the same level as for the un-
cultivated soil for rice-wheat cropping systems in the Indo-Gangetic
plains (Benbi et al., 2012). However, the mechanisms by which dif-
ferent fertilizer inputs aect crop yields by improving SOC remain
Soil nutrients are the major yield-limiting factors. Therefore, to
achieve an ecient and protable crop production relies on the large
inputs of synthetic fertilizers. However, less than half of the total nu-
trients provided by synthetic fertilizers is eectively utilized and left-
over having a range of negative ecological eects (Galloway et al.,
2008). The application of manure could provide not only carbon but
also dierent nutrients for crop uptakes. The residual eect of manure
application was visible after many years, leading to higher nutrient
availability for crop growth (Cai et al., 2018;Demelash et al., 2014).
Soil acidication has received considerable attention in intensive
agricultural systems due to its negative impacts on agricultural pro-
duction and soil fertility (Cai et al., 2014;Guo et al., 2010). The ex-
cessive application of synthetic fertilizer is the main reason for soil
acidication (Zhu et al., 2018). Although China has attained great
achievements in crop yields, the major croplands have still been suf-
fering from signicant acidication since the 1980s (Guo et al., 2010).
In general, the eect of manure on soil pH is concerned with the ash
alkalinity of manure (Rukshana et al., 2013). The alkalinity of manure
is one of the reasons for the increased pH following the manure ap-
plication to soil, although the nitrogen nitrication can generate pro-
tons for decreased pH (Xu et al., 2006). Therefore, it is of interest to
explore the mechanism how dierent fertilizers aect crop yields by
soil nutrients and soil pH.
The area of subtropical arable land in China is approximately
446,890 km
and 4% of the worlds subtropical arable land surface,
which could support 23% of China's population. Soil acidication and
available nutrients restrict crop growth. Therefore, we tried to answer:
Which is the driving factor of manure, synthetic fertilizer, and soil
property controls over crop yields? How do fertilizer applications aect
overall crop yields in Southern China?
2. Materials and methods
2.1. Study site
The experiment was conducted at the experimental station of the
Chinese Academy of Agricultural Sciences (26°45N, 111°52E),
Southern China. The area receives an average temperature of 18.1 °C,
and the active eective accumulated temperature of 4947 °C. The area
receives an average annual precipitation of 1431 mm. The soil type is
Eutric Cambisol and ferrosols soil based on Chinese soil classication
system. The initial topsoil (020 cm) properties were as follows: soil
organic matter of 13.6 g kg
; total N (TN) of 1.07 g kg
; total P (TP)
of 0.45 g kg
; total K (TK) of 13.7 g kg
; soil bulk density (BD) of
1.19 kg m
; soil pH of 5.70; soil available N, P and K of 79, 14, and
104 mg kg
2.2. Experimental design
This experiment was randomly designed, and seven treatments were
selected for this research (Table 1): (1) CK (no fertilizer); (2) N (syn-
thetic nitrogen); (3) NP (synthetic N and phosphorus); (4) NPK (syn-
thetic N, P and potassium); (5) NPKM
(synthetic NPK and manure); (6)
(1.5 times NPKM
); and (7) manure (M
). Each plot was
replicated twice (20 × 9.8 m) and isolated by 1 m cement bae plates.
The synthetic fertilizers were applied as urea, calcium superphosphate,
and potassium chloride. Manure was pure pig manure (solid manure)
and composed of approximately 75% water with an average content
(during the experiment) of 413, 20.1, 12.9, and 12.5 g kg
for carbon,
nitrogen, phosphorus, and potassium (dry weight). The average content
(during the experiment) of nitrogen and phosphorus was 6.1 and 0.81 g
for wheat residues and 9.5 and 1.3 g kg
for maize residues.
Crop yields and straw were removed and crop residues remained.
Therefore, the amount of nitrogen input was the same under all ferti-
lizer treatments except the 1.5NPKM
treatment. All of the fertilizers
were applied before the sowing, 30% and 70% of fertilization were
assigned to wheat and maize, respectively. Specic fertilization
amounts are shown in Table 1.
2.3. Crop management
The experimental eld was cultivated under a wheat-maize rotation
system. Three years were taken to dispose of the experimental eld to
ensure the same soil physical and chemical property. Annual winter
wheat variety Xiangmai was sown in early November with the rate of
about 160 seeds per m
(63 kg ha
) and harvested in early May of next
year. Summer maize of variety Yedan 13 was sown in early April at a
planting density of 60,000 seeds ha
and was harvested in late July.
No-irrigation was applied for winter wheat and summer maize due to
large amounts of annual precipitation. Omethoate and carbofuran
pesticides were applied to control the wheat aphid population during
the postulation period and maize borers. Glyphosate herbicide was
applied to control grassy weeds after maize harvest. The crop was
harvested manually, the stubble was approximately 6 cm in height, and
the roots were left in the soil. The collected straw and grains were air-
dried and weighed separately for each species.
2.4. Soil sampling and analysis
Soil samples were collected from the cultivated horizon (020 cm)
in September. Each treatment was randomly sampled for ve to ten
cores, which was 0.05 m in diameter. Then, the soil samples were
thoroughly mixed and then stored for later analysis. To measure soil
nutrients, the air-dried soil samples were crushed to pass through a
0.25-mm sieve. The SOC content was measured using the oxidation
method by vitriol acid potassium dichromate oxidation (Page et al.,
1982). Total soil nitrogen, phosphorus, and potassium were measured
with the methods of Black (1965);Murphy and Riley (1962), and
Knudsen et al. (1982), respectively. Available N was measured in ac-
cordance with the methods of Lu (2000), and available P (Olsen-P) and
available K were determined in accordance with the Olsen-P method
(Olsen, 1954) and the methods of Page et al. (1982), respectively. Soil
BD was measured with cutting ring (inner diameter, 50.46 mm; sam-
pling depth, 50 mm; volume, 100cm
) method and three repetitions
(Lu, 2000).
2.5. Calculations
The SOC content was converted to SOC density by the equation (Lal
and Bruce, 1999):
××SOC SOC d BD 10
density content (1)
where SOC
is soil organic carbon density (Mg ha
); SOC
soil organic carbon content (g kg
); d and BD are the depth of the soil
layer (0.20 m) and soil dry BD (kg m
The amounts of C input include plant residues plus returned
manure. The annual C input (C
) was calculated from be-
lowground biomass C (C
) and stubble (C
which was incorporated into the topsoil (as Eqs. (3) and (4)), as well as
A. Cai, et al. Soil & Tillage Research 189 (2019) 168–175
the amount of manure (C
). The method of carbon inputs
was the following:
=++CC C C
input belowground stubbles manure
belowground bg biomass (3)
stubbles stubble s biomass (4)
where R
is the ratio of annual underground carbon from crops to
above-ground biomass carbon, which is estimated as 30% from Kundu
et al. (2007).R
is the ratio of stubble incorporated into the soil to
aboveground biomass.
The relative yields (YR) were used to allow the datasets from the
individual treatments to be more comparable. The relative yield was
calculated as follows:
=−YR Y Y
treatment control
where Y
is the actual yield under the fertilization treatments
(Mg ha
) in a given year and Y
is the yield of the no-fertilization
treatment (Mg ha
) in the same year.
2.6. Statistical analyses
To assess the dierent fertilization treatment eects on the relative
crop yields; three periods were analyzed (19912000, 20012005 and
20062015) by one-way ANOVA as implemented with the SPSS 19.0
software package. We also explored the trends of SOC under the dif-
ferent fertilization treatments. Dierent equations were selected and
performed by SigmaPlot 10.0. Boosted regression tree (BRT) was con-
structed using the recommended parameter values (Elith et al., 2008).
The procedure of boosted regression tree was applied using the gbm
package in R version 3.3.3. Structural equation model (SEM) was used
to quantify the relationships among relative yields, soil fertility, and
dierent fertilizations as conducted with the Amos package. All of the
graphs were prepared with SigmaPlot 10.0 software.
3. Results
3.1. Crop yields
Crop yields in each treatment exhibited similar changes among
years, which increased over time in NPKM
, 1.5NPKM
and M
decreased in CK, N, NP, and NPK despite some uctuations in some
years (Fig. 1). There was no crop yield in the N treatment after 12-year
fertilization. The crop yields varied from 0.34 (CK) to 1.58 Mg ha
) and from 0.25 (CK) to 5.82 Mg ha
), respec-
tively, as averaged over 19912015 (Table 2). Signicantly higher
yields were observed in the NPKM
, 1.5NPKM
, and M
during the period 20012005. Compared with the period of
19912000, CK caused 10% to 41% decrease of wheat yield while
maize yield showed 45% to 56% during the period of 20012005. The
largest decrease (26100%) of crop yields was found in N, NP, and NPK
treatments. However, 265% increases in crop yields were found in
and M
treatments during 20062015, whereas 1.5NPKM
creased wheat and maize yields by 1223% during 20062015.
3.2. Dynamic changes of SOC and responses to fertilization treatment
The average annual carbon inputs in the CK treatment were 0.17
(wheat) and 0.13 Mg ha
(maize), respectively, each year from crop
residue (Fig. 2). The applications of NP and NPK signicantly increased
carbon biomass, with 0.36-0.61 Mg ha
. Carbon inputs under
and 1.5NPKM
treatments were 1.721.87 times for the wheat
and 1.982.31 times for the maize under the NPK treatment. SOC was
unchanged under the CK treatment and slightly decreased under the N
treatment (Fig. 3). Higher SOC values were observed under the NPKM
, and M
treatments, depicting a pronounced increase over
the rst 10 years and then a high stable level over the last 15 years. The
relationship between annual SOC sequestered and duration was de-
scribed with y = 0.80e
and y = 3.16e
under the synthetic
fertilizer and manure treatments (Appendix 4a and b). A signicant and
positive relationship was found between carbon inputs and annual SOC
sequestered (Fig. 4). The estimated decomposition rate of SOC was
0.17 Mg ha
each year (when carbon inputs were zero), and the
minimum rate of carbon inputs necessary to maintain SOC content was
0.36 Mg ha
each year (when soil carbon sequestration rate was zero).
3.3. Soil nutrients changes
Soil nutrients, pH, and BD were displayed in Table 3. Soil TN,
available N, and K showed no signicant dierences among CK, N, and
NP during 19912000, 20012005 and 20062015 periods. Compared
with CK, NPK treatment signicantly increased soil TN and available K
during both 20012005 and 20052015 periods but did not sig-
nicantly aect soil TN, available N, and available K during 19912000
periods. Soil TP and available P did not signicantly dier between the
CK and N treatments but were signicantly increased in NP and NPK
treatments relative to CK treatment in all three fertilization periods. Soil
TK did not dier among the fertilizer treatments. Compared with CK,
the synthetic fertilizers (N, NP, and NPK) signicantly decreased soil
pH. Compared with their initial values, soil TN, available K, pH, and BD
decreased on average by 9, 9, 19, and 1%; available N, TP, available P
and TK increased on average by 20, 50, 81, and 1%, respectively, under
the synthetic fertilizer treatments. Soil TN, AN, TP, AP, TK, AK, pH, and
BD increased by 24, 54, 208, 815, 3, 180, 8, and 13%, respectively,
under manure treatments.
3.4. Mechanisms of relative yield
The result of BRT suggested that manure was the most inuential
trigger on relative yields among the studied 11 variables (39%, Fig. 5a).
Table 1
Annual rate (kg ha
) of synthetic nitrogen (Sy-N), phosphorus (Sy-P), and potassium (Sy-K) fertilizer addition and organic nitrogen (Or-N), phosphorus (Or-P), and
potassium (Or-K) fertilizer applied in the various fertilization treatments. Notes: CK, no fertilizer; N, synthetic nitrogen; NP, synthetic N, and phosphorus; NPK,
synthetic N, P, and potassium; NPKM
, synthetic NPK, and manure; 1.5NPKM
, 1.5 times NPKM
; and M
manure. Synthetic N fertilizer is urea; P added as calcium
superphosphate; K added as KCl.
Fertilizations Wheat Maize
Sy-N Sy-P Sy-K Or-N Or-P Or-K Sy-N Sy-P Sy-K Or-N Or-P Or-K
CK 000000000000
N 90 0 0 0 0 0 210 0 0 0 0 0
NP 90 16 0 0 0 0 210 37 0 0 0 0
NPK 90 16 30 0 0 0 210 37 70 0 0 0
27 16 30 63 40 39 63 37 70 147 94 91
40 24 45 94 61 59 95 55 105 220 141 137
0 0 0 90 58 56 0 0 0 210 135 131
A. Cai, et al. Soil & Tillage Research 189 (2019) 168–175
The synthetic N, P, and K accounted for 21% of the relative yields. The
relative individual inuence of soil properties was small. The BRT
model driven by these variables explained 98% of the relative yields
(Fig. 5b). In the SEM analysis, dierent pathways were constructed to
examine the eect of the dierent variables on the variation of crop
yields (Fig. 6). These variables were grouped to two latent variables
(synthetic fertilizers and soil nutrients) and three factors (manure, soil
pH, and SOC storage) in the path analysis. The loading scores suggested
that synthetic phosphorus application and soil available phosphorus
were more powerful indicators of synthetic fertilizer and soil nutrients,
respectively, than were synthetic N application and soil available N.
Synthetic fertilizer was signicantly and positively associated with re-
lative soil nutrients (0.27), while its associations with relative soil pH
(-0.36) and SOC storage (-0.12) were signicantly negatively corre-
lated. Manure application strongly and positively aected the soil nu-
trients, soil pH, and SOC storage (path coecients: 0.90, 0.76, and
0.88). The soil nutrients, soil pH and SOC storage directly inuenced
the relative yields (path coecients: 0.23, 0.44, and 0.25). The path
analysis explained 72% of the variance of relative yields (R
= 0.72).
4. Discussion
Crop yields increased over time in the NPKM
, 1.5NPKM
and M
and decreased over time in CK, N, NP, and NPK, although there were
some uctuations in some years (Fig. 1 and Table 2). These results
could be attributed to the residual eect of manure application (Shen
et al., 2007). The residual eect could maintain crop yields for several
years after manure application ceases (Demelash et al., 2014). A posi-
tive residual eect on crop yields is observed with improvements in
plant dry matter production. Another reason is the indiscriminate use of
synthetic fertilizer, which has caused soil acidication, particularly in
the south of China (Cai et al., 2014;Guo et al., 2010). The extent and
intensity of soil acidication are the main factors that contribute to the
dramatic yield reduction (Zhu et al., 2018). Accordingly, there was no
yield in the N treatment after 12 years with the lower soil pH (Fig. 1 and
Table 3). N fertilization acidies the soil by the oxidation of dry-de-
posited compounds, loss of basic cations through ion exchange, and
plant uptake and nitrication of ammonium. The lower pH not only
Fig. 1. Annual wheat (a) and maize (b) grain
yields under various fertilization treatments of
a long-term experiment in a wheat-maize
system. Notes: CK, no fertilizer; N, synthetic
nitrogen; NP, synthetic N, and phosphorus;
NPK, synthetic N, P, and potassium; NPKM
synthetic NPK, and manure; 1.5NPKM
, 1.5
times NPKM1; and M
Table 2
Wheat and maize grain yields for the periods 19912015, 19912000,
20012005 and 20062015 under various fertilization treatments in a long-
term experiment in a wheat-maize system. Notes: CK, no fertilizer; N, synthetic
nitrogen; NP, synthetic N, and phosphorus; NPK, synthetic N, P, and potassium;
, synthetic NPK, and manure; 1.5NPKM
, 1.5 times NPKM
; and M
manure. Dierent letters in the same column indicate signicant dierences
(P< 0.05) among treatments.
Crops Treatments 1991-
Mg ha
Change (%)
Wheat CK 0.34 d 0.42 c 0.38 d 0.25 d 10 41
N 0.27 d 0.64 c 0.06 e 0.00 e 91 100
NP 0.79 c 1.32 ab 0.68 cd 0.31 cd 49 76
NPK 0.97 bc 1.46 ab 1.08 b 0.42 c 26 71
1.58 a 1.58 a 1.85 a 1.44 a 17 9
1.57 a 1.71 a 1.80 a 1.32 ab 5 23
1.36 ab 1.16 b 1.90 a 1.25 b 65 8
Maize CK 0.25 e 0.36 d 0.20 e 0.16 d 45 56
N 0.48 e 1.15 d 0.11 e 0.00 d 91 100
NP 1.66 d 3.02 c 1.12 c 0.57 d 63 81
NPK 2.65 c 4.02 bc 2.72 b 1.24 c 32 69
5.19 a 4.61 b 6.11 a 5.30 a 33 15
5.82 a 5.91 a 6.86 a 5.21 a 16 12
3.89 b 3.70 bc 3.79 b 4.08 b 2 10
Fig. 2. Average annual carbon input from crop
and manure under various fertilization treat-
ments in wheat (a) and maize (b) system.
Notes: Dierent lower-case letters (annual
carbon input from crops) and upper-case let-
ters (total annual carbon input) indicate sig-
nicant dierences at the P< 0.05 level for
each treatment. CK, no fertilizer; N, synthetic
nitrogen; NP, synthetic N, and phosphorus;
NPK, synthetic N, P, and potassium; NPKM
synthetic NPK and manure; 1.5NPKM
, 1.5
times NPKM1; and M
A. Cai, et al. Soil & Tillage Research 189 (2019) 168–175
increases the availability of potentially toxic heavy metals but also
contribute to the severe reduction of the microbial community that
promotes the root functions (Stevens et al., 2009). A combination of
manure and synthetic fertilizers could improve nutrient availability for
plant uptake with a positive eect on crop yields (Diacono and
Montemurro, 2010). The results of our study showed that wheat yield
was signicantly higher under manure than NPK treatment (Table 2).
The application of manure alone has a vibrant increasing eect on
maize yield but a weaker increasing eect than NPK on wheat yield.
One potential reason for this nding was that the manure was applied
before the wheat was sown. Another potential reason is that the higher
soil temperatures and precipitation in summer increase nutrient mi-
neralization (Agehara and Warncke, 2005). Meanwhile, the eect of
manure on crop yields is crucial by improving soil pH (Fig. 6c). Overall,
the crop yields were signicantly higher under manure than synthetic
fertilizer treatments.
Apparently, manure treatments can increase SOC and soil nutrients
over long-term cropping. Manure not only directly increases carbon
inputs into the soil but also inuences crop residues, which determine
the benets of agricultural SOC sequestration and nutrient release
(Fig. 2 and Appendix 2) (Kuzyakov and Blagodatskaya, 2015;Lal,
2008). The observed non-linear relationship between SOC sequestration
and carbon inputs indicated that SOC was approaching an equilibrium
level. This result agrees with many previous studies (Cong et al., 2012;
Stewart et al., 2007;Zhang et al., 2012), but diers from other re-
searches (Kong et al., 2005;Majumder et al., 2007) that reported linear
relationships. The contrasting ndings may be partially due to dier-
ences in the ranges of carbon inputs and carbon stabilization. Our
carbon inputs rate showed a much wider range than observed in pre-
vious studies, being 0.30-9.36 Mg ha
. Another long-term ex-
periment is being performed to examine the relationship between SOC
sequestration and carbon inputs (Fig. 4 and Appendix 5). In contrast,
Majumder et al. (2007) reported a carbon input of only 1.96-4.10 Mg
each year. We estimated that the minimum rate of carbon inputs
required maintaining SOC content was 0.36 Mg ha
each year. The
value is slightly higher than N treatment (0.26 Mg ha
each year),
resulting in a signicantly decreasing trend. The minimum carbon in-
puts under NPK treatment (1.06 Mg ha
each year) were signicantly
higher than the minimum rate of carbon inputs (0.26 Mg ha
year), contributing to the increasing trend in SOC. These results de-
monstrated that balanced fertilization (NPK) could maintain or even
improve SOC via the return of crop residues.
Exogenous application of synthetic fertilizer accelerated soil acid-
ication, whereas manure or interactive application of manure with
synthetic fertilizer prevented this process (Table 3). Plants generally
extrude net excess of H
; conversely, they extrude net excess of OH
or consume H
when anion uptake exceeds cation uptake
(Tang et al., 2010). NH
-fed plants are characterized by a high cation/
anion uptake ratio, while NO
-fed plants have a low cation/anion
uptake ratio (Tang et al., 2010). Synthetic N application signicantly
reduced the exchangeable base cations in soils, which lead to declined
soil pH. Additionally, synthetic N application has shifted soils into the
buering stage. Al is released into solution at a pH below 5 by the
hydrolysis of both Al-hydroxides and silicates on clay mineral surfaces.
A number of other heavy metals behave in a manner similar to Al. A
decline in base saturation is symptomatic of soil acidication (Stevens
et al., 2009). Accordingly, many studies reported that synthetic ferti-
lizer application could signicantly decrease soil pH (Cai et al., 2014;
Zhu et al., 2018). In general, the ash alkalinity of manure is associated
with soil acidication with protons to neutralize soil acidity (Rukshana
et al., 2013). The alkalinity of organic materials following the dec-
arboxylation of organic anions and the ammonication of organic N are
the major causes of increases in soil pH, although nitrication of mi-
neralized N can generate protons for the decrease of soil pH to some
degree (Xu et al., 2006). Following long-term manure application, soil
Fig. 3. Trends in soil organic carbon under various fertilization treatments in a long-term experiment in a wheat and maize system. Notes: CK, no fertilizer; N,
synthetic nitrogen; NP, synthetic N, and phosphorus; NPK, synthetic N, P, and potassium; NPKM
, synthetic NPK, and manure; 1.5NPKM
, 1.5 times NPKM1; and M
Fig. 4. Correlation between soil organic carbon storage and annual carbon
input in a long-term experiment in a wheat-maize system. Notes: Experiment
points come from our study site and test points come from Cai et al. (2018)
reported site.
A. Cai, et al. Soil & Tillage Research 189 (2019) 168–175
pH increased due to manure residues.
As expected, manure signicantly aected crop yields, compared to
other variables including synthetic fertilizer and soil fertility (Fig. 5).
Manure mainly plays an important role in regulating plant growth,
potential nutrient input, and microbial decomposition activity. This
role can largely mediate the soil nutrient and soil micro-environment,
which have a strong impact on crop growth. In addition, manure could
also result in increased microbial biomass and changes in community
structure, which provide a better environment for the growth of the
crop (Peacock et al., 2001). Manure application to cropland can aect
soil properties, but the eects may not be apparent over a short time
period. We identied a network of correlations among synthetic ferti-
lizer, manure, and soil fertility in determining crop yields (Fig. 6c). The
application of manure strongly and positively aected crop yields by
increasing SOC storage, soil nutrients, and soil pH. Synthetic fertilizer
aected crop yields by weakly increasing soil nutrients and decreasing
SOC storage and soil pH. SOC, soil nutrients, and soil pH directly in-
uenced crop yields, and soil pH played a more important role in in-
creasing crop yields than did soil nutrients and SOC in this experimental
eld in the south of China. Increased soil acidication can reduce the
availability of soil nutrients to plants in the soil and it thereby reduced
crop yields (Wright, 1989). Soil pH-induced changes in soil enzyme
activity and microbial composition might be important mechanisms for
alleviating acid stress on crop yields by various ameliorants. In
addition, the total eect of soil pH, the SOC and soil nutrients on crop
yield were also identied. Cai et al. (2018) reported that manure in-
uenced crop yields via aecting soil TN and available N and P (soil
pH) based on an 8-year eld experiment. Our results showed further
evidence that the interplay of dierent fertilization, soil pH, SOC and
soil nutrients and their interaction jointly inuenced crop yields
(Fig. 6). These results suggest that manure is a better fertilizer than
synthetic fertilizer for regulating crop yields by improving soil fertility
for Chinese subtropical arable soils.
5. Conclusions
Signicant dierences in soil fertility and crop yields among dif-
ferent fertilization treatments were found in this study. The manure or
combined with synthetic fertilizer signicantly increased crop yields,
SOC, soil nutrients and soil pH compared with CK. The crop yields in-
creased with increasing amount of added manure. Manure inputs ac-
counted for 39% of the relative inuence on relative yield, followed by
synthetic fertilizer of 21% and soil fertility of 40%. Synthetic fertilizers
indirectly aected crop yields by weakly increasing soil nutrients and
decreasing SOC storage and soil pH. Manure indirectly aected crop
yields by strongly and positively increasing soil nutrients, SOC storage
and soil pH. Our results suggest that manure acts as a better fertilizer
than synthetic fertilizer in increasing crop yields by improving soil
Table 3
Contents of soil nutrients of dry soil for the period of 19912015, 19912000, 20012005 and 20062015 under various fertilizations of long-term experiments in
wheat-maize systems. Notes: CK, no fertilizer; N, synthetic nitrogen; NP, synthetic N, and phosphorus; NPK, synthetic N, P, and potassium; NPKM
, synthetic NPK and
manure; 1.5NPKM
, 1.5 times NPKM
; and M
manure. Dierent letters in the same column during year indicate that there are signicant dierences (P< 0.05)
among the dierent treatments.
Treatments Treatments TN AN TP AP TK AK pH BD
Initial year 1.07 79 0.45 14 13.7 104 5.7 1.19
1991-2000 CK 0.80 e 96 c 0.46 d 5 d 14.63 a 82 c 5.75 b 1.15 ab
N 0.94 de 120 bc 0.45 d 4 d 15.76 a 70 c 4.98 c 1.11 b
NP 0.95 de 101 bc 0.69 c 20 c 14.61 a 89 c 5.05 c 1.12 b
NPK 1.06 cd 112 bc 0.77 c 21 c 15.32 a 128 c 4.90 c 1.22 ab
1.23 ab 114 bc 1.00 b 49 b 14.54 a 198 b 6.04 ab 1.32 a
1.31 a 130 bc 1.30 a 74 a 16.88 a 288 a 6.05 ab 1.23 ab
1.13 bc 142 ab 0.82 c 37 b 12.76 a 200 b 6.48 a 1.30 a
2001-2005 CK 0.81 c 64 c 0.44 e 5 e 13.64 a 56 d 5.63 a 1.17 d
N 0.90 c 90 bc 0.41 e 4 e 11.66 a 47 d 4.30 b 1.15 d
NP 0.87 c 81 c 0.70 d 37 d 12.92 a 51 d 4.53 b 1.17 d
NPK 1.03 b 85 c 0.79 d 43 d 12.13 a 136 c 4.59 b 1.30 c
1.36 a 119 ab 1.35 b 148 b 12.85 a 283 b 5.77 a 1.48 a
1.44 a 133 a 1.74 a 226 a 12.74 a 404 a 5.68 a 1.42 b
1.22 a 91 bc 1.05 c 100 c 12.11 a 190 c 6.58 a 1.40 b
2006-2015 CK 0.86 d 60 c 0.45 e 4 d 14.72 a 59 e 5.75 c 1.23 b
N 0.86 d 86 c 0.45 e 4 d 13.54 a 50 e 4.04 e 1.16 c
NP 0.96 cd 85 c 0.86 d 51 c 13.72 a 64 e 4.30 d 1.19 c
NPK 1.05 c 86 c 0.98 d 48 c 14.79 a 201 d 4.35 d 1.18 c
1.34 b 115 b 1.69 b 170 b 14.62 a 350 b 5.88 bc 1.36 a
1.55 a 138 a 2.32 a 245 a 14.43 a 484 a 5.94 b 1.33 a
1.49 a 119 b 1.50 c 147 b 14.22 a 253 c 6.66 a 1.39 a
Fig. 5. The relative contributions (%) of pre-
dictor variables for the boosted regression tree
model of relative yield (a). Observed and pre-
dicted relative crop yield by the boosted re-
gression tree model using predictors shown in
Fig. 5b. The dashed line shows the 1:1 line.
Notes: SOC, soil organic carbon; Manure,
amounts of manure input; Synthetic N, P, and
K, amounts of synthetic N, P, and K input.
A. Cai, et al. Soil & Tillage Research 189 (2019) 168–175
fertility for Chinese subtropical arable soils.
Financial support from the National Natural Science Foundation of
China (41620104006) and National Key Research and Development
Program of China (2016YFE0112700) is gratefully acknowledged. The
authors are very grateful for revisions to the manuscript by Muhammad
Nadeem Malik. We are thankful to all of our colleagues who were in-
volved in these long-term trials for their unremitting eorts to maintain
these unique experiments. We are also grateful to the anonymous re-
viewers for their comments.
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Purpose Soil microbial biomass and extracellular enzymes are involved in the decomposition of soil organic matter, a temporary nutrient pool for plants. This study was conducted to evaluate the mineralization potentials of carbon (CMP) and nitrogen (NMP), and the relationship of CMP and NMP with microbial biomass and extracellular enzymes in soil fertilized with mineral and manure amendments for 3 decades. Materials and methods A long-term experiment (37 years) consisted of seven fertilizer treatments, including unfertilized control (CK); nitrogen, phosphorus, and potassium (NPK); manure (M); manure plus phosphorus and potassium (PKM); nitrogen and potassium plus manure (NKM); nitrogen and phosphorus plus manure (NPM); and NPK plus manure (NPKM), was selected. Results and discussion Compared to the CK treatment, the long-term mineral fertilizer (NPK) and combined manure plus mineral fertilization (e.g., M, PKM, NKM, NPM, and NPKM) significantly increased soil microbial biomass carbon (SMBC) by 58% and 131% and nitrogen (SMBN) by 66% and 161%, respectively. Similarly, soil microbial biomass phosphorus (SMBP) also significantly increased by 67–156% in combined manure and mineral fertilizer treatments than the CK and NPK treatment. Higher values of β-glucosidase and cellobiohydrolase activities were observed with the application of PKM. In comparison with CK, the application of combined manure and mineral fertilization significantly increased the leucine aminopeptidase and N-acetyl-glucosaminidase enzyme by 129% and 175%, respectively. Soil CMP and NMP significantly increased by 231–307% and 176–289% in combined treatments than the CK. A significant positive correlation was also observed between the microbial biomass, extracellular enzymes, and the CMP and NMP (R² = 0.66–0.84, 0.44–0.76, P < 0.0001). Conclusions This study suggested that long-term manure application greatly increased the microbial biomass and enzyme activities, playing an important role in co-mineralization potentials of organic carbon and nitrogen for improving soil fertility.
Manure nutrient management can affect soil carbon (C) and nitrogen (N) fractions. The objective of this study was to determine the effects of long term manure and mineral fertilizer applications on C and N fractions. This study was conducted for 11 years under corn and soybean rotation. The study rates included low manure (LM (4,194 kg ha−1), based on the crop’s phosphorus (P) requirement), medium manure (MM (8,081 kg ha−1), based on the crop’s N requirement), high manure (HM (16,162 kg ha−1), two times the rate of MM), medium fertilizer (MF (204 kg N ha−1), recommended), high fertilizer (HF (224 kg N ha−1), high), and control. Soil samples were collected to measure C and N fractions. HM recorded higher particulate C (8%) at 0–10 cm and higher dissolved C (26%) at 10–20 cm compared to LM. All manure rates had higher permanganate oxidizable C compared to mineral fertilizer rates. Carbon management index was higher under MM compared to the HF (17%) and MF (33%). This study suggests that manure application (16,162 kg ha−1 rate and even 8,081 kg ha−1 and 4,194 kg ha−1 rates in some cases) can enhance C and N pools compared to mineral fertilizer application.
El principal reto que enfrenta la agricultura es satisfacer la creciente demanda mundial de alimentos y al mismo tiempo reducir el impacto agrícola ambiental negativo. La nutrición de los cultivos depende principalmente de los fertilizantes minerales, lo cual es una amenaza para el medio ambiente y para la salud humana. Una alternativa para solventar esta problemática es el manejo nutricional integrado con fertilizantes minerales y abonos orgánicos para disminuir el uso de los fertilizantes minerales al tiempo que se favorece la productividad de los cultivos, así como la calidad de los productos agrícolas y del medio ambiente. La presente revisión recopila resultados de investigaciones enfocadas al manejo nutricional integrado, como parte del funcionamiento holístico de los agroecosistemas, en varios ámbitos: a) calidad del suelo; b) productividad y rentabilidad de los cultivos; c) calidad de los productos agrícolas; d) emisión de gases de efecto invernadero; y e) transferencia de nitrógeno al agua.
Las ventajas de incorporar abonos orgánicos (AO) disminuyen cuando sus propiedades físicas, químicas y microbiológicas no son las adecuadas. El objetivo de la presente investigación fue caracterizar abonos orgánicos destinados a suelos florícolas y analizar las repercusiones de su aplicación. Se determinaron las propiedades de 10 AO: potencial de hidrógeno (pH), conductividad eléctrica (CE), materia orgánica (MO), contenido de nitrógeno, fósforo, potasio y nitratos. Se utilizó un diseño completo al azar y análisis de varianza (P ≤ 0.05) para evaluar el índice germinativo (IG) en semillas de rábano y maíz, con lixiviados de AO al 5 %, así como la actividad microbiana de tres AO incorporados al suelo en incubaciones aerobias. El pH promedio fue de 8.2 ± 0.81, y el intervalo de la CE en AO fue de 0.15 dS/m a 6.7 dS/m, mientras que el de la MO fue de 28.8 % a 80 %. El IG fue diferente estadísticamente (P < 0.05) en cada especie de semilla. Asimismo, la incorporación de AO incrementó significativamente (P < 0.05) la actividad microbiana del suelo. Se concluye que la heterogeneidad de la materia prima genera una gran variabilidad en las características de los AO, sin embargo, en todos los casos, su aplicación mejoró las propiedades de los suelos florícolas.
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In agro-ecosystems, the relationship between soil fertility and crop yield is mediated by manure application. In this study, an 8-year field experiment was performed with four fertilizer treatments (NPK, NPKM1, NPKM2, and NPKM3), where NPK refers to chemical fertilizer and M1, M2, and M3 refer to manure application rates of 15, 30, and 45 Mg ha⁻¹ year⁻¹, respectively. The results showed that the NPKM (NPKM1, NPKM2, and NPKM3) treatments produced greater and more stable yields (4.95–5.45 Mg ha⁻¹ and 0.59–0.75) than the NPK treatment (4.01 Mg ha⁻¹ and 0.50). Crop yields under the NPKM treatments showed two trends, with a rate of decrease of 0.48–0.83 Mg ha⁻¹ year⁻¹ during the first 4 years and a rate of increase of 0.10–0.25 Mg ha⁻¹ year⁻¹ during the last 4 years. The soil organic carbon (SOC) significantly increased under all treatments. The estimated annual SOC decomposition rate was 0.35 Mg ha⁻¹ year⁻¹ and the equilibrium SOC level was 6.22 Mg ha⁻¹. Soil total nitrogen (N), available N, total phosphorus (P) and available P under the NPKM treatments increased by 0.15–0.26, 15–33, 0.17–0.66 and 45–159 g kg⁻¹, respectively, compared with the NPK treatment. Manure application mainly influenced crop yield by affecting the soil TN, available N, and available P, which accounted for up to 64% of the crop yield variation. Taken together, applying manure can determine or at least improve the effects of soil fertility on crop yield in acidic soils in South China.
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Organic inputs have a positive effect on the soil organic matter balance. They are therefore an important asset for soil fertility and crop growth. This study quantifies the additional yield effect due to organic inputs for arable crops in Europe when macro-nutrients are not a limiting factor. A meta-analysis was performed using data from 20 long-term experiments in Europe. Maxima of yield response curves to nitrogen were compared, with and without organic inputs, under abundant P and K supply. We were surprised to find that, across all experiments, the mean additional yield effect of organic inputs was not significant (+ 1.4 % ± 1.6 (95 % confidence interval)). In specific cases however, especially for root and tuber crops, spring sown cereals, or for very sandy soils or wet climates, organic inputs did increase attainable yields. A significant correlation was found between increase in attainable yields and increase in soil organic matter content. Aggregating data from 20 long-term experiments in Europe, this study shows that organic inputs and/or soil organic matter do not necessarily increase yields, given sufficient nutrients are supplied by mineral fertilisers. Results show the relevance of some environmental factors for additional yield effect of organic inputs, but no simple relation between organic inputs and crop growth.
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Long-term manure application is recognized as an efficient management practice to enhance soil organic carbon (SOC) accumulation and nitrogen (N) mineralization capacity. A field study was established in 1979 to understand the impact of long-term manure and/or chemical fertilizer application on soil fertility in a continuous maize cropping system. Soil samples were collected from field plots in 2012 from 9 fertilization treatments (M0CK, M0N, M0NPK, M30CK, M30N, M30NPK, M60CK, M60N, and M60NPK) where M0, M30, and M60 refer to manure applied at rates of 0, 30, and 60 t ha-1 yr-1, respectively; CK indicates no fertilizer; N and NPK refer to chemical fertilizer in the forms of either N or N plus phosphorus (P) and potassium (K). Soils were separated into three particle-size fractions (2000-250, 250-53, and <53 μm) by dry- and wet-sieving. A laboratory incubation study of these separated particle-size fractions was used to evaluate the effect of long-term manure, in combination with/without chemical fertilization application, on the accumulation and mineralization of SOC and total N in each fraction. Results showed that long-term manure application significantly increased SOC and total N content and enhanced C and N mineralization in the three particle-size fractions. The content of SOC and total N followed the order 2000-250 μm > 250-53μm > 53 μm fraction, whereas the amount of C and N mineralization followed the reverse order. In the <53 μm fraction, the M60NPK treatment significantly increased the amount of C and N mineralized (7.0 and 10.1 times, respectively) compared to the M0CK treatment. Long-term manure application, especially when combined with chemical fertilizers, resulted in increased soil microbial biomass C and N, and a decreased microbial metabolic quotient. Consequently, long-term manure fertilization was beneficial to both soil C and N turnover and microbial activity, and had significant effect on the microbial metabolic quotient.
We applied the adapted model VSD+ to assess cropland acidification in four typical Chinese cropping systems (single Maize (M), Wheat-Maize (W-M), Wheat-Rice (W-R) and Rice-Rice (R-R)) on dominant soils in view of its potential threat to grain production. By considering the current situation and possible improvements in field (nutrient) management, five scenarios were designed: i) Business as usual (BAU); ii) No nitrogen (N) fertilizer increase after 2020 (N2020); iii) 100% crop residues return to cropland (100%RR); iv) manure N was applied to replace 30% of chemical N fertilizer (30%MR) and v) Integrated N2020 and 30%MR with 100%RR after 2020 (INMR). Results illustrated that in the investigated calcareous soils, the calcium carbonate buffering system can keep pH at a high level for >150years. In non-calcareous soils, a moderate to strong decline in both base saturation and pH is predicted for the coming decades in the BAU scenario. We predicted that approximately 13% of the considered croplands may suffer from Al toxicity in 2050 following the BAU scenario. The N2020, 100%RR and 30%MR scenarios reduce the acidification rates by 16%, 47% and 99%, respectively, compared to BAU. INMR is the most effective strategy on reducing acidification and leads to no Al toxicity in croplands in 2050. Both improved manure and field management are required to manage acidification in wheat-maize cropping system.
Reducing the carbon footprint (CF) of crop production is an efficient way to mitigate climate change. Growing legume green manure (LGM) instead of summer fallow may achieve this goal by lowering synthetic nitrogen (N) fertilizer needs and replenishing the depleted soil carbon (C) pool. The Rothamsted Carbon (RothC) model was incorporated into the Life-Cycle Assessment (LCA) to evaluate the present and projected CFs of green manure-based wheat production systems in dryland agriculture on the Loess Plateau of China. The field study included four main treatments (Huai bean, soybean and mung bean grown as green manure in summer and fallow as control) and four synthetic N rates (0, 108, 135 and 162kgNha(-1)) applied at wheat sowing. Soybean as LGM increased averaged wheat yield over 4 synthetic N rates by 8% compared with fallow (P<0.05), and synthetic N requirement was reduced by 33% without compromising the wheat yield for all the main treatments. Although LGM treatments had higher greenhouse gas (GHG) emissions from agricultural inputs, the greater amount of C inputs elevated the corresponding SOC stocks (SOCS) by 14-24% after 8years, thus significantly reducing the CF by 25-51% compared with fallow. The modelled SOCS equilibrium indicates that the CF for cropping systems with LGM will be 53-62% lower than fallow and 23-37% lower compared with their current level. In conclusion, introducing legume green manure instead of summer fallow is a highly efficient measure for persistent CF reduction, and coupling the RothC model and LCA is an alternative method to predict the long-term impact of different cropping systems on GHG emissions.
Subsoil compaction at 15–30 cm depths due to the increase of bulk density or decrease in porosity after long-term no tillage or reduced tillage (e.g. rotary tillage or harrow tillage) is of growing concern. Deep tillage is generally regarded as an important method to reduce subsoil compaction due to long-term conservation tillage and thereby improve crop production and soil conditions. We compared the responses of crop yield and soil carbon (C) among 10-year no tillage (NT), rotary tillage (RT), and harrow tillage (HT) treatments, and their conversions to deep tillage (DT) for 4 years involving NT-DT, RT-DT and HT-DT treatments. The soil organic carbon (SOC) pool under the NT treatment was 29 and 91% higher than the SOC pools of the HT and RT treatments, respectively, whereas the NT annual yield decreased by 0.6 Mg ha−1 yr−1 over 10 years. The NT-DT, RT-DT and HT-DT treatments increased crop yield by 35, 24 and 24% and altered the SOC pool by −1.5, 15.6 and 13.2 Mg ha−1 over the 4 years of deep tillage compared with the corresponding values for NT, RT, and HT, respectively. Therefore, conversion to DT after long-term NT, RT, and HT use can benefit crop yield and play an important role in improving soil carbon sequestration following the long-term adoption of RT and HT systems in North China.
A single solution reagent is described for the determination of phosphorus in sea water. It consists of an acidified solution of ammonium molybdate containing ascorbic acid and a small amount of antimony. This reagent reacts rapidly with phosphate ion yielding a blue-purple compound which contains antimony and phosphorus in a 1:1 atomic ratio. The complex is very stable and obeys Beer's law up to a phosphate concentration of at least 2 μg/ml.The sensitivity of the procedure is comparable with that of the stannous chloride method. The salt error is less than 1 %.