Yield and quality properties of silage maize and their influencing factors in China

Abstract

Silage maize (Zea mays L.) is one of the most important forages in the world, and its yield and quality properties are critical parameters for livestock production and assessment of forage values. However, relationships between its yield and quality properties and the controlling factors are not well documented. In this study, we collected 5,663 observations from 196 publications across the country to identify the relationships between yield and quality properties of silage maize and to assess the impact of management practices and climatic factors on its yield and quality in China. The average dry matter yield of silage maize was (19.98±6.93) Mg ha-1, and the average value of crude protein, ether extract, crude ash, crude fiber, acid detergent fiber, neutral detergent fiber, nitrogen-free extract, and relative feed value was 7.86%±1.71%, 2.53%±1.01%, 5.05%±1.66%, 23.97%±6.34%, 27.62%±7.12%, 51.60%±9.85%, 59.68%±7.72%, and 131.17±31.49, respectively. In general, its nutritive value decreased as its yield increased. Increasing planting density could increase the yield but inhibit the nutritive values, while increasing fertilization could benefit the nutritive values. Geographically, the yield increased and the nutritive value decreased from warm (south) to cold (north) regions. The length of growth duration was a major controlling factor for the patterns of these properties. Our findings provide insights for police-makers to make strategy for achieving high yield and good quality of silage maize and help local people to implement better management practices.

Full text

•RESEARCH PAPER•https://doi.org/10.1007/s11427-020-2023-3
...........................................................................................................
Yield and quality properties of silage maize and their influencing
factors in China
Mengying Zhao1,2, Yinping Feng1,2, Yue Shi1,2, Haihua Shen1,2, Huifeng Hu1, Yongkai Luo1,
Longchao Xu1, Jie Kang1,2, Aijun Xing1,2, Shaopeng Wang3& Jingyun Fang1,3*
1State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China;
2University of Chinese Academy of Sciences, Beijing 100049, China;
3College of Urban and Environmental Sciences, and Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking
University, Beijing 100871, China
Received June 8, 2021; accepted November 11, 2021; published online January 27, 2022
Silage maize (Zea mays L.) is one of the most important forages in the world, and its yield and quality properties are critical
parameters for livestock production and assessment of forage values. However, relationships between its yield and quality
properties and the controlling factors are not well documented. In this study, we collected 5,663 observations from 196
publications across the country to identify the relationships between yield and quality properties of silage maize and to assess the
impact of management practices and climatic factors on its yield and quality in China. The average dry matter yield of silage
maize was (19.98±6.93) Mg ha−1, and the average value of crude protein, ether extract, crude ash, crude fiber, acid detergent
fiber, neutral detergent fiber, nitrogen-free extract, and relative feed value was 7.86%±1.71%, 2.53%±1.01%, 5.05%±1.66%,
23.97%±6.34%, 27.62%±7.12%, 51.60%±9.85%, 59.68%±7.72%, and 131.17±31.49, respectively. In general, its nutritive value
decreased as its yield increased. Increasing planting density could increase the yield but inhibit the nutritive values, while
increasing fertilization could benefit the nutritive values. Geographically, the yield increased and the nutritive value decreased
from warm (south) to cold (north) regions. The length of growth duration was a major controlling factor for the patterns of these
properties. Our findings provide insights for police-makers to make strategy for achieving high yield and good quality of silage
maize and help local people to implement better management practices.
silage maize, yield, quality, management practices, climatic factors
Citation: Zhao, M., Feng, Y., Shi, Y., Shen, H., Hu, H., Luo, Y., Xu, L., Kang, J., Xing, A., Wang, S., et al. (2022). Yield and quality properties of silage maize
and their influencing factors in China. Sci China Life Sci 65, https://doi.org/10.1007/s11427-020-2023-3
INTRODUCTION
Silage maize (Zea mays L.), one of the most important
forages worldwide, is the whole plant harvested from the
milk to wax ripening periods and then is chopped or fer-
mented to feed livestock (Fan et al., 2009;Garon et al., 2006;
Kaplan et al., 2016). With the characteristics of low cost,
high yield, abundant nutrition, high palatability, and high
digestibility, it has become an indispensable basic forage for
animal husbandry development (Guyader et al., 2018;Sal-
ama, 2019;Sheaffer et al., 2006). For example, the cultivated
area of silage maize was more than 2.4 million hectares
annually in the United States (Bernard and Tao, 2020) and
reached 1.67 million hectares by 2020 in China (Wang,
2020). The yield and quality properties of silage maize are
important parameters to evaluate forage value and determine
the performance of livestock (Liu et al., 2018;Shi et al.,
2012), and thus research on the yield and quality of silage
maize can provide a theoretical basis for cost-effective for-
age utilization and sustainable animal husbandry production.
© Science China Press and Springer-Verlag GmbH Germany, part of Springer Nature 2022 life.scichina.com link.springer.com
SCIENCE CHINA
Life Sciences
*Corresponding author (email: jyfang@urban.pku.edu.cn)

Forage yield determines the amount of dry matter available
to livestock, and forage quality can influence animal growth
and livestock products by affecting forage digestibility and
energy intake (Coleman and Moore, 2003;Khan et al.,
2012b;Richman et al., 2015). To assess forage quality, re-
searchers have developed a complete set of wet chemistry
parameters in previous studies (Zhang et al., 2018), such as
crude protein (CP), ether extract (EE), crude ash (Ash), crude
fiber (CF), acid detergent fiber (ADF), neutral detergent fiber
(NDF), and nitrogen-free extract (NFE) (Carr et al., 2004;
Grant et al., 2014), which were summarized in Table 1. It was
generally believed that forage with high CP and EE contents
usually had high energy (Zhang et al., 2018), while the CF
content was negatively correlated with forage digestibility
(Ely et al., 1953;Shi et al., 2012). A relatively high forage
ADF content could reduce the digestibility of dry matter, and
a high NDF content could decrease animal dry matter intake
(Oba and Allen, 1999;Rotger et al., 2006). Considering the
divergent results of various quality parameters, integrative
parameters were proposed, such as the relative feed value
(RFV) (Rohweder et al., 1978;Zhang et al., 2004). A rela-
tively high forage RFV represented a high nutritive value
(Grant et al., 2014). Therefore, CP, EE and RFVare treated as
positive quality parameters, while the fiber parameters (e.g.,
CF, ADF and NDF) are treated as negative quality para-
meters in forage quality assessment (Zhang et al., 2018;Zhao
et al., 2008). Understanding the relations among various
quality parameters and their associations with yields are
necessary for optimizing balance between silage maize yield
and nutritive value.
Previous studies have demonstrated that the yield and
quality of forage could be affected by management practices
(Khan et al., 2015;Liu et al., 2018), such as planting density
(Marsalis et al., 2010), fertilization (Aydin and Uzun, 2005),
harvest time (Bumb et al., 2016), irrigation (Karyoti et al.,
2018;Zhang et al., 2019), and weed and insect control
(Bailey et al., 2015). Researchers found that silage maize
yield decreased with increasing planting density (Jia et al.,
2018), while some studies pointed out that a relatively high
planting density was beneficial for yield but not nutritive
value (Ballard et al., 2001;Cox et al., 1998;Subedi et al.,
2006). Likewise, previous studies suggested that increasing
nitrogen (N) fertilizer doses could significantly increase the
yield but decrease the CP content of silage maize (Aydin and
Uzun, 2005), whereas increasing N fertilization could sig-
nificantly increase CP content (Kaplan et al., 2016;Lawr-
ence et al., 2008). These contrasting effects of planting
density and fertilization on silage maize yield and quality
suggested that further investigation was necessary (Salama,
2019). Furthermore, previous attempts to reveal the factors
influencing silage maize yield and quality were based on
single-site or regional analysis synthesizing a few long-term
experiments; thus, the results were context specific (Wang et
al., 2020).
Environmental conditions (e.g., temperature, precipitation,
and sunshine hours) markedly modify physiological pro-
cesses and growth of forage over large spatial scales (Liu et
al., 2013b;Quan et al., 2020), which can affect yield and
quality. Generally, temperature and precipitation are factors
affecting forage yield and quality in most grassland types
across China (Shi et al., 2012), while the growing season
temperature and sunshine hours could influence the growth
and yield of maize crops in the northern China (Liu et al.,
2013a). In addition, temperature affected forage growth rate
and further affected growth duration (Bartholomew and
Williams, 2005;Liu et al., 2013a). As growth duration in-
creased, forage yield, ADF and NDF contents usually in-
creased (Khan et al., 2012a;Khan et al., 2015;Salama,
2019). However, the impact of environmental factors on si-
lage maize yield and quality has not yet been studied across
large spatial scale, and few studies have together evaluated
the effect of management practices and environmental fac-
tors on the yield and quality.
To address this knowledge gap, we compiled a dataset
Table 1 Definition of forage quality parameters
Quality parameter Abbre-viation Unita) Definition Reference
Crude protein CP % Total nitrogenous compounds. Thiex et al., 2002
Ether extract EE % Fat and fat-soluble components. Thiex et al., 2003
Crude ash Ash % Inorganic residue remaining after water and organic matter have been
removed by heating (550°C). Thiex et al., 2012
Crude fiber CF % Organic residue remaining after digesting with weak acid followed by
weak alkaline solubilizes. This residue contains cellulose, lignin and a
portion of hemicellulose. Ely et al., 1953
Acid detergent fiber ADF % The residue remaining after digesting with an acid detergent extraction.
The fiber residues are predominantly cellulose and lignin. Van Soest and Wine, 1968
Neutral detergent fiber NDF % The residue remaining after digesting in a neutral detergent solution. The
fiber residues are predominantly hemicellulose, cellulose, and lignin. Van Soest et al., 1991
Nitrogen-free extract NFE % Water-soluble polysaccharides is calculated by subtracting the sum of
percentages of the CP, EE, Ash and CF from 100. Saura-Calixto et al., 1983
a) The percentages (%) of quality parameters are expressed on a dry matter basis.
2Zhao, M., et al. Sci China Life Sci

consisting of 5,663 observations of silage maize yield and
quality from 177 sites across the country (Figure 1). Our
study aims to (i) elucidate the relationship between yield and
quality properties of silage maize, (ii) examine the effects of
management practices and climate factors on yield and
quality, and (iii) reveal the regional patterns of yield and
quality across China.
RESULTS
Yield and quality properties
The national average yield of silage maize was (19.98±
6.93) Mg ha−1 in China (Table 2; Figure S1 in Supporting
Information). The average contents of CP, EE, Ash, CF,
ADF, NDF, and NFE were 7.86%±1.71%, 2.53%±1.01%,
5.05%±1.66%, 23.97%±6.34%, 27.62%±7.12%, 51.60%
±9.85% and 59.68%±7.72%, respectively, and the average
RFV value was 131.17±31.49 (Table 2; Figure S1 in Sup-
porting Information).
Silage maize yield was negatively correlated with positive
quality parameters (CP, EE and RFV) but was positively
correlated with NFE content (Figure 2). CP content was
positively correlated with EE content, and both CP and EE
content showed positive correlations with RFV (Figure 2).
Positive quality parameters had a negative relationship with
Ash, CF, ADF, NDF and NFE contents (Figure 2). Negative
quality parameters (CF, ADF and NDF) were positively
correlated with Ash content but negatively correlated with
EE and NFE contents and RFV (Figure 2).
Effects of management practices on yield and quality
Planting density was positively correlated with Ash, ADF,
NDF contents and the yield, but was negatively correlated
with EE, NFE contents and RFV (Figure 3). We only found a
positive correlation between phosphorus (P) fertilizer
amount and yield (Figure 3). N fertilizer amount was posi-
tively correlated with CP and Ash contents but was nega-
tively correlated with CF, ADF, and NFE contents (Figure 3).
A positive correlation was found between P fertilizer amount
and RFV (or NFE content), but negative relationships be-
tween P fertilizer amount and negative quality parameters
(CF, ADF, and NDF) were observed (Figure 3). Potassium
(K) fertilizer amount was strongly correlated with most
quality parameters, which had positive correlations with CP,
EE, NFE contents and RFV, but negative correlations with
fiber parameters (CF, ADF, and NDF) (Figure 3).
Figure 1 Sampling sites of silage maize from selected researches in this study. We divide the country into six maize regions: Northeast, North, East, South
Central, Northwest, and Southwest China. This map was reviewed by Ministry of Natural Resources of the People’s Republic of China (GS (2021) 8687).
3
Zhao, M., et al. Sci China Life Sci

Regional differences in yield and quality properties
The yield and CF content increased, but CP and EE contents
and RFV decreased from south to north, while Ash, ADF,
NDF and NFE contents did not exhibit significant patterns
along the latitudinal gradient (Figure 4). Accordingly, these
trends were in line with the observed patterns between cli-
mate factors and yield (or quality parameters) (Figure 5). The
yield and CF content decreased with increasing MAT, and the
yield decreased with increasing mean annual precipitation
(MAP) (Figure 5). In contrast, positive quality parameters
(CP, EE and RFV) showed increasing trends with increasing
mean annual temperature (MAT) and MAP. Ash, ADF and
NDF contents were not significantly affected by climate
Table 2 Statistical characteristics of silage maize yield and quality in Chinaa)
Parameter nMean SD CV 95%CI
Yield (Mg ha−1) 1,612 19.98 6.93 0.35 19.65–20.32
CP (%) 1,125 7.86 1.71 0.22 7.76–7.96
EE (%) 607 2.53 1.01 0.40 2.45–2.61
Ash (%) 435 5.05 1.66 0.33 4.90–5.21
CF (%) 364 23.97 6.34 0.26 23.32–24.62
ADF (%) 604 27.62 7.12 0.26 27.05–28.18
NDF (%) 612 51.60 9.85 0.19 50.82–52.38
NFE (%) 304 59.68 7.72 0.13 58.81–60.55
RFV 576 131.37 31.49 0.24 128.62–134.12
a) The percentages (%) of quality parameters are expressed on a dry matter basis. Yield, dry matter yield; n, sample size; Mean, arithmetical mean; SD,
standard deviation; CV, coefficient of variation; 95%CI, 95% confidence interval.
Figure 2 Correlation matrix of silage maize yield and quality. Yield, dry matter yield (Mg ha−1); CP (%); EE (%); Ash (%); CF (%); ADF (%); NDF (%);
NFE (%). The number on the upper panel represents Pearson correlation coefficient between the two parameters. The blue figure on the lower panel
represents the number of observations. The symbols “*”, “**” and “***” represent the significance levels of P<0.05, P<0.01 and P<0.001, respectively.
4Zhao, M., et al. Sci China Life Sci

factors (Figure 5). In addition, growth duration increased
with increasing latitude and decreasing MAT and MAP
(Figure S2 in Supporting Information). As a result, the yield
and CF content increased with increasing growth duration,
while CP and Ash contents decreased (Figure 6).
One-way ANOVA showed that silage maize yield and
quality differed significantly among different regions (Figure
7; Table S1 in Supporting Information). The yields in the
northern regions were significantly higher than those in the
southern regions (Figure 7; Table S1 in Supporting In-
formation). The CP and EE contents and RFV of the north-
west and northeast regions were significantly lower, while
Figure 3 Correlation between silage maize yield (or quality) and management practices. Yield, dry matter yield (Mg ha−1); CP (%); EE (%); Ash (%); CF
(%); ADF (%); NDF (%); NFE (%). Density represents planting density (plants per hectare). N, P2O5and K2O represent the consumption of nitrogen,
phosphate and potash fertilizer in kg ha−1, respectively. The black number represents correlation coefficient between the two parameters with a significance
level of 0.05. The blue figures represent the number of observations.
Figure 4 Latitude pattern of silage maize yield and quality. (a) Yield, dry matter yield; (b) CP; (c) EE; (d) Ash; (e) CF; (f) ADF; (g) NDF; (h) NFE; (i) RFV.
The red and blue lines represent significant positive and negative relationship, and n is the number of observations.
5
Zhao, M., et al. Sci China Life Sci

Figure 5 Bivariate relationships between yield or quality of silage maize and climatic factors. (a and b) Yield, dry matter yield; (c and d) CP; (e and f) EE; (g and h) Ash; (I and j) CF; (k and l) ADF; (m and n)
NDF; (o and p) NFE; (q and r) RFV. The red and blue lines represent significant positive and negative relationship, and nis the number of observations.
6Zhao, M., et al. Sci China Life Sci

the ADF content was higher than those of the other regions
(Table S1 in Supporting Information). Although the CP and
EE contents were lower in the northwest and northeast re-
gions than in other regions, their CP and EE yields were
higher (Figure 7; Table S2 in Supporting Information). At the
same time, the Ash, CF, ADF and NDF yields in the north-
west and northeast regions were also higher than those in
other regions (Table S2 in Supporting Information).
DISCUSSION
Trade-off between the yield and nutritive value
Our study found that positive quality parameters (CP, EE and
RFV) showed a negative relationship with yield (Figure 2),
which indicated that silage maize with high dry matter pro-
duction would be accompanied by a relatively low nutritive
value in general. This apparent trade-off between forage
yield and nutritive value has been found in natural grassland
(Shi et al., 2012) and forage crop (Guyader et al., 2018;
Hargreaves et al., 2009;Salama, 2019). The negative re-
lationship between yield and quality might be due to the
dilution effect of dry matter accumulation on the CP and EE
contents (Guyader et al., 2018). The proportion of mechan-
ical tissue with higher cellulose and lignin contents would
increase as yield increased, consequently resulting in a de-
crease in nutritive value (Grant et al., 2014;Kerkhoff et al.,
2006;Niklas et al., 2005). Trade-off between yield and
quality implies that it is unnecessary to pursue yield max-
imization but instead emphasizes a balance between yield
and quality in practice to improve the economic efficiency.
Effects of planting density and fertilization application
on yield and quality
Planting density and fertilization application exerted pro-
found impact on the silage maize yield and quality (Figure
3). Consistent with previous studies (Cox et al., 1998;Cu-
sicanqui and Lauer, 1999;Subedi et al., 2006;Widdicombe
and Thelen, 2002), our results found that increasing planting
density increased the silage maize yield but not nutritive
value (Figure 3). This was mainly attributed to the increased
intraspecific competition for available soil nutrient, water
and light (Ferreira et al., 2014;Mandic et al., 2015). Com-
petition between plant individuals caused a decrease in plant
N uptake, which decreased forage quality, especially CP
contents (Zhang et al., 2006). In addition, cell volumes were
unable to expand sufficiently under high planting density
Figure 6 Bivariate relationships of silage maize yield and quality with growth duration. (a) Yield, dry matter yield; (b) CP; (c) EE; (d) Ash; (e) CF; (f)
ADF; (g) NDF; (h) NFE; (i) RFV. The red and blue lines represent significant positive and negative relationship, and nis the number of observations.
7
Zhao, M., et al. Sci China Life Sci

leading to increase in the cell wall thickness (Lukuyu et al.,
2013), resulting in a decrease in nutritive value (Zhang et al.,
2006). Appropriate planting density is necessary for silage
maize yield and quality balance (Morris et al., 2018).
N, P and K are essential nutrients that play critical roles in
protein and enzyme synthesis and participate in entire me-
tabolic processes (Kaplan et al., 2016;Kerkhoff et al., 2006).
Many studies have shown that fertilizer application can in-
crease silage maize yield (Kaplan et al., 2016;Masoero et al.,
2011), but we only found a positive effect of P fertilizer
amount on silage maize yield (Figure 3). A possible ex-
planation for this positive effect may be the large shortage of
soil available P across the country (Han et al., 2005;Shen
and Chen, 1998). Nonetheless, nutritive value of silage
maize increased with increasing fertilizer application (Figure
3), which was in line with previous studies (Lawrence et al.,
2008). For example, increasing the N fertilizer amount could
dramatically increase the CP content and reduce ADF and
NDF contents (Kaplan et al., 2016;Liu et al., 2018;Yolcu
and Cetin, 2015). Notably, we should always follow the
Figure 7 The dry matter (DM) yield and CP yield (Mg ha−1) of silage maize among six regions in China. Different letters indicate significant differences at
P<0.05 among six regions. The figures in parentheses show the number of observations. This map was reviewed by Ministry of Natural Resources of the
People’s Republic of China (GS (2021) 8687).
8Zhao, M., et al. Sci China Life Sci

principle of “selecting reasonable amounts of N, P and K
fertilizer for maximum economic compensation and mini-
mum environmental costs” (Chen et al., 2014). Moreover,
optimal fertilization and other reasonable management
practices such as precision irrigation or cropping insect-re-
sistant varieties, could minimize the potential environmental
drawbacks from farming activities and achieve the goal of
environmental-friendly and resource-saving silage maize
production (Cong, 2020;Irmak et al., 2016;Wang, 2020).
Effects of growth duration on yield and quality
Silage maize yield increased and the nutritive value de-
creased from south to north (Figure 4), which was in
agreement with simulation model conducted on wheat yield
(Anderson et al., 2015). Consistent with the negative corre-
lation between crop yield and temperature (Liu et al., 2010;
Tao et al., 2006;Welch et al., 2010), silage maize yield de-
creased and nutritive value increased with increasing MAT
and MAP (Figure 5). Furthermore, we found that growth
duration increased from warm (south) to cold (north) regions
(Figure S2 in Supporting Information). Silage maize yield
increased and the nutritive value decreased with increasing
growth duration (Figure 6), which is consistent with previous
studies based on a single species (Karn et al., 2006;Salama,
2019) or conducted at a community level (Michaud et al.,
2012;Zhang et al., 2018). Such a pattern indicated that the
growth duration was a major controlling factor of geographic
pattern of silage maize yield and quality. Climatic factors,
such as temperature, precipitation and sunshine hour, influ-
ence significantly growth and development of silage maize
(Liu et al., 2013b;Yang et al., 2004). Relatively high tem-
peratures and water availability can promote silage maize
growth and meet the accumulated temperature required for
silage maize ripening, consequently resulting in a shorter
growth duration than that grown in the region with low
temperature and precipitation (Liu, 2013;Liu et al., 2013b).
On the other hand, silage maize as a typical short-day plant,
would postpone the tasseling stage with prolonged sunshine
hours (Liu, 2013), resulting in delayed maturity and ex-
tended growth duration (Figure S3 in Supporting Informa-
tion). As growth durations prolonged, the forage quality
always gradually declined because the stem-to-leaf ratio and
cell wall composition (e.g., cellulose and lignin contents)
increased and dry matter digestibility decreased (Bumb et al.,
2016;Guyader et al., 2018;Hargreaves et al., 2009;Salama
and Nawar, 2016). Low temperature also resulted in a con-
striction in leaves, thickening cell walls and increasing ADF
and NDF contents (Kaplan et al., 2016). These findings in-
dicate that silage maize varieties with short growth duration
and cold tolerance should to be planted at high latitude areas.
The silage maize yields in the northwest and northeast
regions were higher and the nutritive values were lower than
in southwest and south-central China (Figure 7). The CP and
EE yield are critical for economic evaluation because they
are usually used as economic indicators of energy yield,
production costs, and gross margin (Solati et al., 2018). We
found that CP and EE yields were higher in the northeast and
northwest regions than in other regions (Figure 7; Table S2 in
Supporting Information). That is, the northwest and north-
east regions with higher output values per unit area are
considered prolific zones. The relationship among yield,
MAT and MAP also showed that under low precipitation, the
yield is relatively high (Figure S4 in Supporting Informa-
tion), which suggests that the yields in the northern regions
are significantly higher than those in the southern regions.
These results provide a base for guiding the regional plan-
ning of silage maize cultivation in China.
Limitations and future research needs
Previous studies revealed that in addition to the amount of
fertilizer, fertilizer type (e.g., N, P2O5or organic fertilizer)
(Baghdadi et al., 2018), the time of fertilization (e.g., basal
fertilizer and seed fertilizer) (Messiga et al., 2020) and fer-
tilizer application frequency (Yolcu and Cetin, 2015) can
affect silage maize yield and quality. Furthermore, the po-
tential cofounding effects of a variety of management prac-
tices (e.g., irrigation and insecticide application) cannot be
separated since a uniform management protocol is un-
realistic. Except for climate factors and management prac-
tices, the soil nutrient content (D’Hose et al., 2014), the
interaction effect between soil nutrients and fertilizer appli-
cation amount (Feng et al., 2019), and varieties and geno-
types (Liu et al., 2013b) may also affect the yield and quality
of silage maize. These limitations merit further investigation
and indicate that developing a multi-site unified experiment
to explore the relative importance of management practices
and environmental factors on silage maize yield and quality
is imperative.
CONCLUSION
This study underscores the trade-off between silage maize
yield and quality, and the key role of climatic factors and
management practices in controlling yield and quality. We
found that silage maize nutritive value decreased with in-
creasing yield. Planting density was positively correlated
with yield but negatively with nutritive value, while fertilizer
application was positively correlated with nutritive value.
Geographically, the silage maize yield increased and the
nutritive value decreased from warm (south) to cold (north)
regions, which were mainly controlled by growth duration.
Our findings help to understand the relationship between
yield and quality of silage maize and provide a basis for
9
Zhao, M., et al. Sci China Life Sci

cost-effective forage utilization and sustainable animal hus-
bandry in China.
MATERIALS AND METHODS
Data collection
Peer-reviewed journal articles were acquired using China
National Knowledge Infrastructure (http://www.cnki.net/),
covering articles published between 2000 and 2018 with the
following keywords: “silage maize” or “forage maize”. In
total, 196 publications reporting field experiments of silage
maize in China were collected. We compiled a dataset on
silage maize yield and quality derived from 177 different
sites widely distributed over China. A total of 1,955 sets of
data and 5,663 observations were contained in this dataset,
including 1,612, 1,125, 607, 435, 364, 604, 612, and 304
observations on yield, CP, EE, Ash, CF, ADF, NDF, and
NFE, respectively.
We also collected management practices (planting density
and fertilizer application) and planting cycle (sowing and
harvest dates) to assess their impact on silage maize yield
and quality. Fertilizer amount at a site was converted into N,
P2O5and K2O in kg ha−1 and planting cycle was converted
into growth duration (days). Furthermore, we extracted the
geographical variables (longitude, latitude and elevation)
and climate variables (MAT, MAP, and sunshine hours) of
each site. If the original publications lacked meteorological
information, the MAT and MAP data will be obtained from
the Chinese Academy of Sciences Resource and Environ-
mental Science Data Center (http://www.resdc.cn/).
Statistical analysis
The RFV parameter proposed by the American Hay Mar-
keting Task Force was used as an integrative parameter to
evaluate forage nutritive value. The RFV for a certain forage
is defined as the feed intake of digestible dry matter relative
to that of full bloom alfalfa (setting the RFV of full bloom
alfalfa to 100) (Rohweder et al., 1978). The RFV was cal-
culated as follows:
RFV = DDM × DMI ÷ 1.29,
where DDM and DMI represent digestible dry matter (% of
dry matter) and dry matter intake (% of body weight), re-
spectively (Grant et al., 2014). DDM and DMI can be esti-
mated with
DDM = 88.9 (0.779 × ADF),
DMI = 120 ÷ NDF,
where ADF and NDF are expressed as a percentage of dry
matter.
Pearson correlation analysis was used to investigate the
relationship between yield and quality, and their correlation
with management practices (planting density and fertilizer
application). Then, a linear mixed-effect model was em-
ployed to explore the relationships between yield (or quality)
and latitude, climate factors (MAT and MAP), and growth
duration. The model was specified as:
Y X= + × + + ,
0 1 publication
where β0,β1, and εare the intercept, slope, and sampling
error, respectively; πpublication is the random effect that ac-
counted for the variations among observations within each
publication. One-way ANOVA with Tukey’s post hoc test
was applied to examine the differences in yield and quality of
silage maize grown in the six major regions of China. All
statistical analyses were performed in R 3.6.1 (R Develop-
ment Core Team).
Compliance and ethics The author(s) declare that they have no conflict
of interest.
Acknowledgements This work was supported by the Strategic Priority
Research Program of the Chinese Academy of Sciences (XDA26010303)
and Science and Technology Services (STS) Network Program of Chinese
Academy of Sciences (KFJ-STS-ZDTP-056).
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12 Zhao, M., et al. Sci China Life Sci