Evaluating Dairy Manure as Initial Fertility Driver for Mudflat Soil ...

Evaluating Dairy Manure as Initial Fertility Driver for Mudflat Soil Amendment YANCHAO BAI1,2, CAIYUN ZANG1, CHUANHUI GU3, YONGXIANG GUAN4, XUKUI WANG4, MINJING GU1, LIJUAN MEI1, HAITAO ZHAO1, YUHUA SHAN1,* and KE FENG1,5 2State

1College

of Environmental Science and Engineering, Yangzhou University, Yangzhou 225009, China Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China 3Department of Geology, Appalachian State University, Boone 28608, North Carolina, USA 4Jiangsu Cultivated Land Quality and Agro-Environment Protection Station, Nanjing 210036, China 5Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, Yangzhou 225009, China ABSTRACT: The mudflats along the East Coast of China can be important alternative sources for arable lands if amended by large amount of organic fertilizers. Rich in organic matter and other nutrients, dairy manure has been considered as the economic choice for an initial fertility driver. Therefore, the goal of this study was to evaluate the impact of dairy manure amendment (DMA) as an initial fertility driver at application rates of 0, 30, 75, 150, and 300 t ha–1 on soil physicochemical properties, biomass and growth of ryegrass (Lolium perenne L.) grown in mudflat soil. The results showed that the DMA decreased soil bulk density in comparison to the unamended soil. The organic matter (OM) content in mudflat soil increased with increasing DMA rates. The salinity of mudflat soil decreased with increasing DMA rates, and the salinity at 30, 75, 150 and 300 t ha–1 DMA rates, corresponded to decreases of 26.1%, 35.8%, 37.8% and 45.4%, compared to 8.63 g kg–1 in the unamended soil. Electric conductivity (EC) of mudflat soil decreased with increasing DMA rate, while cation exchange capacity (CEC) increased duo to DMA. The contents of total N, total P, alkaline N, and available P in mudflat soil increased with increasing DMA rates. The increment of green herbage yield of ryegrass at 210 DAS at 30, 75, 150, and 300 t ha–1 DMA rates were 257.7%, 303.5%, 414.8%, and 516.6%, compared to the unamended soil (p < 0.05). Soil total Cu and Zn increased while total Mn, Ni, and Cr remained unchanged in response to DMA due to the high Cu and Zn content in the dairy manure. However, The DMA increased most of available metals except for Ni. In summary, land application of dairy manure as initial fertility driver could be an effective and safe way to amend mudflat soil, due to the rapid development of soil initial fertility, which enhanced green manure ryegrass (Lolium perenne L.) growth.

1. INTRODUCTION

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self-reliant in crop production of China has been faced with the challenge of rapid shrinkage of cropland [1]. In order to stop cropland loss, the China’s national strategy of arable land requisition-compensation balance was implemented in 1996. However, inland land resources for compensation are depleted. Mudflats (also known as tidal flats) as valuable land resources for compensation are located in the interaction zone between sea and land and are found in many parts of the world [2]. About 20 thousand-hectare (ha) mudflats have been formed in east coast of China evhe

*Author to whom correspondence should be addressed. E-mail: [email protected]; Tel: +86 0514 87979645

ery year. About 1.2 million-ha mudflats have been reclaimed to croplands in the past 50 years [3]. It is estimated that additional 180 thousand-ha mudflats will be reclaimed to cropland in 2020s, according to the policy of coastal development planning in Jiangsu province in China. The newly reclaimed mudflats are high in salinity and not suitable for cultivation as indicated by poor soil structure, extremely low organic matter (OM) content, low nutrient level, and lack of microbial diversity. The keys to mudflat reclamation to arable-lands are to reduce salinity, and to increase the soil OM content thus soil fertility [4]. Salinity reduction is often accomplished through freshwater irrigation. Fertility enhancement is usually achieved through instantaneous application of a great amount of OM because soil natural OM formation is extremely slow.

Journal of Residuals Science & Technology, Vol. 14, No. 1—January 2017 1544-8053/17/01 027-08 © 2017 DEStech Publications, Inc. doi:10.12783/issn.1544-8053/14/1/4

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Y. BAI, C. ZANG, C. GU, Y. GUAN, X. WANG, M. GU, L. MEI, H. ZHAO, Y. SHAN and K. FENG

Dairy manure generated in dairy industry has caused serious environmental pollution and ecological safety concern. There were 105 centralized dairy farms (more than 500-head stock every year) in Jiangsu province in China in 2014 [5]. 130 million tons dry dairy manure was produced every year [5]. Land application of dairy manure has a great incentive in view of waste disposal, soil amendment, and nutrient recycling and reuse including OM, N, P and other plant nutrients. The past research mainly focused on the application of dairy manure in farmlands [6,7], which showed that land application of dairy manure increased soil OM [8], yield of plant [9–11], and heavy metals accumulation in plants [12,13]. Safe disposal of dairy manure is now becoming a challenge in Jiangsu province, due to livestock supporting capacity of cropland based on nitrogen and phosphorus was above the soil carrying capacities in many regions (e.g. Nantong and Xuzhou city) [14]. Therefore, mudflat soil that needs organic amendment may become a potential land source for safe disposal of massive dairy manure. However, the dairy manure amendment mudflat soil has received little attention. The effect and mechanism of dairy manure amendment (DMA) in mudflat is quite different because farmlands are different from mudflats in soil nutrient, soil structure, background level of heavy metals, and microbial flora [2,15]. In this study, we used dairy manure as an initial fertility driver to amend mudflat soils. Infertile mudflat soil could obtain the initial fertility through one-time DMA to support growth of green manure ryegrass (Lolium perenne L.). The goal of the present work was to assess the land application of dairy manure as an initial fertility driver for mudflat soil amendment. Specifically, the effects of DMA on soil physicochemical properties, biomass and growth of ryegrass (Lolium perenne L.) grown in mudflat soil were investigated. 2. MATERIALS AND METHODS 2.1. Study Area The experiment site was at the farm of Senmao Company Ltd located in Rudong county, Jiangsu Province, China (E 121°24′04″, N 32°20′00″). This site is a newly reclaimed (4-year old) mudflat located in the north shore of the Yangtze River estuary. The region is characterized by subtropical humid monsoon climate with distinct seasons. Precipitation is mainly concentrated from June to August.

2.2. Experimental Materials The experimental mudflat soil was typic halaquepts subgroups, which belonged to the halaquepts group of aquepts suborder in inceptisols order based on USDA soil taxonomy. The experimental dairy manure was collected from the Dairy Farm of Rudong County in September 2011. The chemical properties of mudflat soil and dairy manure were shown in Table 1. 2.3. Experimental Design A randomized complete block design (RCB), with each plot of 4.0 m length and 4.0 m width, was carried out in this experiment. There were five treatments, i.e. control, 30, 75, 150, and 300 t ha–1 DMA rates on a dried weight basis, and each treatment had triplicates. With the help of a rototiller, the dairy manure was mixed uniformly with soil down to the depth of 20 cm on October 20th, 2011. Ryegrass (Lolium perenne L.) as a popular high-quality green manure was chosen for the experimental work, and sowed at 35 g per plot on October 25th, 2011. Plant samples were collected for analysis at 60 days-after-sowing (DAS) (December 26th, 2011), 150 DAS (March 26th, 2012) and 210 DAS (May 26th, 2012). 2.4. Soil Analysis Soil samples for 0–20 cm depth were collected in quadruplicate from control, 30, 75, 150 and 300 t ha–1 DMA at 210 DAS. For soil OM content, 0.3 g air-dried sample through 0.150-mm mesh size was measured by the K2Cr2O7 method, and soil salinity was measured Table 1. Basic Chemical Properties of the Mudflat Soil and Dairy Manure Used in This Study. Parameters pH Salinity (‰) Organic Matter (g kg–1) Total N (N g kg–1) Total P (P g kg–1) Alkaline N (N mg kg–1) Available P (P mg kg–1) Total Cd (mg kg–1) Total Cr (mg kg–1) Total Cu (mg kg–1) Total Mn (mg kg–1) Total Ni (mg kg–1) Total Zn (mg kg–1)

Mudflat Soil

Dairy Manure

8.92 8.82 3.16 0.209 0.565 17.48 17.86 0.451 13.08 15.89 152.8 30.4 49.9

7.74 11.61 415.7 32.3 5.31 358.1 111.9 2.15 41.7 769.4 133.9 18.0 146.7

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Evaluating Dairy Manure as Initial Fertility Driver for Mudflat Soil Amendment

by the gravimetric method [16]. The pH and electric conductivity (EC) of soil were measured in suspension of 1:5 (weight/volume) by pH meter (Model IQ150, Spectrum, USA) and conductivity meter (Item 2265FS, Patent, USA). The cation exchange capacity (CEC) of samples was measured using the ammonium acetate (NH4OAc) method [16]. Total N and total P contents in soil samples were determined by Semi-micro Kjeldahl method and Digestion Mo-Sb Anti spectrophotometric method, respectively. Alkaline hydrolysis diffusion method and NaHCO3 extraction method was used for the quantification of soil alkaline N and available P. For analysis of total metals (Cd, Cr, Cu, Mn, Ni and Zn) in soil samples, 0.5 g air-dried sample through 0.150-mm mesh size was digested in 20 ml tri acid mixture (HNO3:H2SO4:HClO4 5:1:1). After complete digestion solution was analyzed for Cu, Mn, Ni and Zn using Flame Atomic Absorption Spectrometer (FAAS) (Model SOLAAR M6, Thermo Elemental, Thermo Fisher Scientific Inc., USA), and the filtrate of ten folds dilution rate for Cd and Cr using Graphite Furnace Atomic Absorption Spectrometer (GFAAS). Available metals were analyzed by Diethylenetriaminepentaacetic acid (DTPA) extraction method. 25.0 g air-dried sample through 1 mm mesh size was extracted in 50 ml DTPA solution. After complete extraction solution was analyzed for Cu, Mn, Ni and Zn using FAAS, while the filtrate of ten folds dilution rate was analyzed for Cd and Cr using GFAAS. Soil bulk density was measured by cutting ring method at 210 DAS.

mass determination, plants were washed with deionized water to remove soil particles adhering on them, separated the fresh plants into roots and aboveground parts, deactivated at 105°C for 15 minutes, and ovendried at 80°C until constant weight was achieved. The plant parts were then weighed separately and biomass accumulation was expressed as g plant–1. The ryegrass roots were separated from the shoots, spread on a glass tray (A4-size) and scanned using a root scanner system (Epson Transparency Unit, Model EU-35, Seiko Epson Corp., Japan). Root measurements for length, surface area, average diameter and volume were conducted using WinRHIZO image analysis software version Pro 2005b (Regent Instruments Inc., Canada). 2.6. Statistical Analysis The data mining were conducted using SPSS software (version 13). The significant difference between the treatments was detected with Duncan’s multiple range test at the 0.05 level of significance assess. 3. RESULTS 3.1. Physicochemical Properties of Mudflat Soil The effect of DMA on physicochemical of mudflat soil was shown in Table 2. DMA decreased soil bulk density in comparison to the unamended soil. Soil bulk density of mudflat soil decreased with increasing DMA rates. The decrease in soil bulk density was 8.58%, 9.57%, 18.17% and 21.76% at 30, 75, 150 and 300 t ha–1 DMA rates, respectively, as compared to the unamended soil (Table 2).

2.5. Plant Analysis Forty plants were sampled randomly from each plot to determine biomass and plant growth. For bio-

Table 2. Selected Physicochemical Properties of Mudflat Soil at Different Dairy Manure Amendment Rates. Dairy Manure Amendment (t ha–1) Parameters Bulk density (g cm–3) Organic Matter (g kg–1) Salinity (‰) pH (5:1) EC (ms cm–1) CEC (cmol kg–1) Total N (N g kg–1) Total P (P g kg–1) Alkaline N (N mg kg–1) Available P (P mg kg–1)

0

30

75

150

300

1.411 ± 0.022a 2.94 ± 0.36c 8.63 ± 0.46a 8.37 ± 0.13a 2.44 ± 0.69a 5.39 ± 0.30b 0.189 ± 0.021c 0.572 ± 0.007c 18.9 ± 0.4c 18.7 ± 1.5c

1.290 ± 0.042b 3.19 ± 0.19c 6.38 ± 0.74b 8.60 ± 0.13a 1.50 ± 0.66ab 6.01 ± 0.38b 0.195 ± 0.016c 0.580 ± 0.040c 25.1 ± 6.3c 39.7 ± 8.3c

1.276 ± 0.034b 3.60 ± 0.05c 5.54 ± 0.84bc 8.57 ± 0.06a 1.72 ± 0.50ab 6.51 ± 0.19ab 0.217 ± 0.019bc 0.607 ± 0.021bc 30.2 ± 7.5c 68.2 ± 25.2b

1.194 ± 0.045c 5.65 ± 1.09b 5.37 ± 0.77bc 8.52 ± 0.16a 0.97 ± 0.16b 6.61 ± 0.51ab 0.275 ± 0.068b 0.681 ± 0.060ab 68.8 ± 13.5b 150.9 ± 4.1a

1.104 ± 0.060d 7.38 ± 0.42a 4.71 ± 0.63c 8.38 ± 0.26a 0.94 ± 0.21b 7.85 ± 1.68a 0.376 ± 0.025a 0.728 ± 0.098a 100.0 ± 23.2a 181.9 ± 2.4a

EC, electric conductivity; CEC, cation exchange capacity; N, nitrogen; P, phosphorus. Values are mean ± SD of three replicates. Different letters in each row meant significant difference at p < 0.05 by Duncan’s multiple range test.

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The OM content in mudflat soil increased with increasing DMA rates. Compared to the OM content of 2.94 g kg–1 in the unamended soil, there were increases in OM content by 8.5%, 22.4%, 92.2% and 151.0% at 30, 75, 150 and 300 t ha–1 DMA rates, respectively. However, the increase in OM of mudflats soil was small relative to the increase in DMA rates. The salinity of mudflat soil decreased with increasing DMA rates. The salinity decreased by 26.1%, 35.8%, 37.8% and 45.4% at 30, 75, 150 and 300 t ha–1 DMA rates, respectively, compared to 8.63‰ in the unamended soil. The DMA soils had lower EC, higher CEC, N, and P than the unamended soil. EC of mudflat soil decreased with increasing DMA rate, while CEC increased with DMA. The increases in CEC were 11.5%, 20.8%, 22.6% and 45.6% at 30, 75, 150 and 300 t ha–1 DMA rates, respectively, as compared to the unamended soil. The soil contents of total N, total P, alkaline N, and available P increased with increasing DMA rates. Maximum increases of 98.9%, 27.3%, 429.1%, and 872.7% in total N, total P, alkaline N, and available P in mudflat soil were observed at 300 t ha–1 DMA rate. The pH of mudflat soil did not show any significant change in response to DMA (p > 0.05). The DMA increased total Cu and Zn concentrations at 75, 150, and 300 t ha–1 rates (p < 0.05), whereas there were either no changes (p > 0.05) for total Mn, Cr, and Ni concentrations, or decreases (p < 0.05) for total Cd concentrations in the DMA soils compared to the unamended soil (Table 3). The increments in total Cu and Zn concentrations were 31.5%, 80.0%, 184.2%, 277.5% and 10.0%, 18.1%, 29.8%, 52.0% at 30, 75,

150, 300 t ha–1 DMA rates, respectively, as compared to the unamended soil. The available metal concentrations increased with DMA in most cases except for Ni, which did not show any change in response to DMA (p > 0.05). There were sharp increases in soil available Cu, Cr and Zn with increasing DMA rates, whereas the available Cd and Mn showed only minor increases with increasing DMA rates. The DMA increased available Cd and Mn concentrations significantly at the 300 t ha–1 rates (p < 0.05). The increments in available Cu and Zn concentrations were 97.6%, 256.1%, 335.8%, 465.0% and 61.1%, 194.4%, 205.6%, 448.2% at 30, 75, 150, 300 t ha–1 DMA rates, respectively, as compared to the unamended soil. The available Cr concentrations at 75, 150 and 300 t ha–1 DMA rates were 0.168, 0.214 and 0.257 mg kg–1, respectively, which corresponded to increases of 58.5%, 101.9% and 142.5%, compared to 0.106 mg kg–1 in the unamended soil. 3.2. Ryegrass Biomass and Growth Ryegrass biomass at 60 and 150 DAS were significantly higher at DMA soils than the unamended soil [Figure 1(a) and 1(b)]. The increment of ryegrass biomass at 60 DAS at 30, 75, 150, and 300 t ha–1 DMA rates were 40.1%, 79.3%, 84.4%, and 373.8%, compared to the unamended soil. The ryegrass biomass of aboveground and root parts at 60 and 150 DAS increased monotonically with increasing DMA rates. Green herbage yield of ryegrass at 210 DAS was significantly higher in the DMA soils than the unamended soil (p < 0.05) (Figure 2). The increment of green

Table 3. Total and Available Metal Concentrations (mg kg–1) in Mudflat Soil at Different Dairy Manure Amendment Rates. DDairy manure amendment (t ha–1) Parameters

0

30

75

150

300

Total Cd Total Cr Total Cu Total Mn Total Ni Total Zn Available Cd Available Cr Available Cu Available Mn Available Ni Available Zn

0.485 ± 0.055a 12.83 ± 0.44a 15.45 ± 1.08d 152.2 ± 3.2a 28.16 ± 1.61a 51.52 ± 6.15c 0.057 ± 0.001b 0.106 ± 0.025c 1.23 ± 0.13d 9.09 ± 0.28b 0.523 ± 0.034a 0.54 ± 0.24c

0.393 ± 0.023b 12.92 ± 0.07a 20.32 ± 2.42cd 158.5 ± 3.8a 29.58 ± 0.35a 56.65 ± 6.95bc 0.059 ± 0.009ab 0.156 ± 0.020bc 2.43 ± 0.32c 9.85 ± 0.28ab 0.516 ± 0.058a 0.87 ± 0.65bc

0.368 ± 0.030bc 12.29 ± 0.77a 27.81 ± 2.79c 154.6 ± 8.9a 27.57 ± 2.90a 60.49 ± 9.97b 0.062 ± 0.007ab 0.168 ± 0.039b 4.38 ± 0.09b 9.42 ± 0.55b 0.524 ± 0.031a 1.59 ± 0.58b

0.300 ± 0.053cd 12.67 ± 0.22a 43.91 ± 10.06b 158.4 ± 3.5a 28.70 ± 1.61a 66.46 ± 2.10b 0.065 ± 0.011ab 0.214 ± 0.026ab 5.36 ± 0.29b 9.98 ± 0.35ab 0.482 ± 0.063a 1.65 ± 0.34b

0.273 ± 0.010d 12.44 ± 0.69a 58.32 ± 8.92a 154.6 ± 6.2a 27.62 ± 0.55a 77.80 ± 8.64a 0.074 ± 0.003a 0.257 ± 0.028a 6.95 ± 0.24a 10.36 ± 0.86a 0.520 ± 0.065a 2.96±0.61a

Values are mean ± SD of three replicates. Different letters in each row meant significant difference at p < 0.05 by Duncan’s multiple range test.


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Figure 1. Effect of dairy manure amendment (DMA) on ryegrass biomass at (a) 60 days-after-sowing (DAS) and (b) 150 DAS. Vertical bars indicate standard deviations of the means. Columns with different letters show significant difference between DMA rates at p < 0.05 by Duncan’s multiple range test. Non-italic and italic letters correspond to aboveground and root, respectively.

herbage yield of ryegrass at 30, 75, 150, and 300 t ha–1 DMA rates were 257.7%, 303.46%, 414.8%, and 516.6%, compared to the unamended soil. Plant heights of ryegrass at 60 and 150 DAS were significantly higher at all DMA rates than the unamended soil (p < 0.05) [Figure 3(a)]. Ryegrass tiller number per plant increased with increasing DMA rates. The tiller number at 60 DAS was significantly higher than the unamended soil at 300 t ha–1 DMA rate. The tiller numbers at 150 DAS were significantly higher than the unamended soil at 150 and 300 t ha–1 DMA rates [Figure 3(b)]. The DMA increased length, surface area, average diameter and volume of ryegrass roots, except for the root length of ryegrass at 60 DAS (Figure 4). The responses of ryegrass root growth, with respect to length, surface area, and volume, to DMA at 60 DAS differed from 150 DAS. At 60 DAS, surface area and volume of ryegrass roots was significantly higher than the unamended soil only at 300 t ha–1 DMA rate. While at 150 DAS, length, surface area and volume of ryegrass roots were significantly higher than them in the unamended soil at all DMA rates. The root average diameter of ryegrass were significantly higher than that in the unamended soil (p < 0.05) when DMA rate was equal or greater than 150 and 75 t ha–1 at 60 and 150 DAS, respectively.

physicochemical fertilization by increasing OM contents and decreasing bulk density. As a result, salinity of mudflat soil dropped. Previous studies have shown that cropland application of dairy manure increased OM contents, improved soils aggregation status [5], enhanced infiltration rate [21], and reduced the bulk density, dispersion ratio and soil strength correspondingly [22–24]. The high salinity in mudflat soils is caused by capillary rise that brings salts to soil surface [25]. Therefore, salinity reduction by DMA might be attributed to the fact that OM enrichment by DMA reduced soil bulk density and broke capillary rise. Correlation analysis showed that salinity of mudflat soil correlated negatively with OM content and bulk density. The nonlinear fit equation between salinity and OM content

4. DISCUSSION Many studies have reported that the land application of dairy manure has a major effect on the chemical fertility of cropland soil [17–20]. Dairy manure as an initial fertility driver to the mudflat soil improved its

Figure 2. Effect of dairy manure amendment (DMA) on green herbage yield of ryegrass at 210 days-after-sowing (DAS). Vertical bars indicate standard deviations of the means. Columns with different letters show significant difference between DMA rates at p < 0.05 by Duncan’s multiple range test.

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Figure 3. Effect of dairy manure amendment (DMA) on (a) shoot height and (b) tiller numbers of ryegrass at 60 days-after-sowing (DAS) and 150 DAS. Vertical bars indicate standard deviations of the means. Columns with different letters show significant difference between DMA rates at p < 0.05 by Duncan’s multiple range test. Non-italic and italic letters correspond to 60 and 150 DAS, respectively.

Figure 4. Effect of dairy manure amendment (DMA) on (a) length, (b) surface area, (c) average diameter and (d) volume of ryegrass roots at 60 days-after-sowing (DAS) and 150 DAS. Vertical bars indicate standard deviations of the means. Columns with different letters show significant difference between DMA rates at p < 0.05 by Duncan’s multiple range test. Non-italic and italic letters correspond to 60 and 150 DAS, respectively.


Y = 12.479e–0.1156X (R2 = 0.7291) existed, which was consistent with the results of previous studies [26]. The best-fit linear equation for salinity and bulk density of mudflat soil was y = 12.321x – 9.3367 (R2 = 0.8616, p < 0.05). The results are in agreement with those of Edmeades [27] who reported that soils amended with manures showed lower bulk density and higher hydraulic conductivity. Soil N and P contents increased in the mudflat soil due to higher N and P concentrations in the dairy manure. In addition, poultry manure may promote P availability by decreasing sorption of Al- and Fe-associated phosphates [11]. The DMA increased CEC of mudflat soil, probably due to increasing soil OM content [28,29]. In this study, the pH of mudflat soil did not show significant variation between treatments, which is in agreement with findings by Leytem et al. [30]. Previous studies found soil pH increased with dairy manure application in alum shale soil [12] and Rosholt soil [31], and did not change in Plano soil [31]. The various effects of DMA on soil pH might be due to original soil pH, OM content and soil buffering capacity. The dairy manure as an initial fertility driver enhanced the growth of green manure ryegrass in mudflat soil by improving initial fertility formation of mudflat soil. Miron et al. [32] also confirmed that the DMA increased yield of forage. The DMA also enhanced shoot and root biomass of pasture grass [33]. Others found that DMA increased the yields of rice [20], wheat and maize [23], Italian ryegrass and prairie grass [33]. The present study showed that DMA increased the biomass of ryegrass grown in the mudflat soil by increasing soil fertility while decreasing soil salinity. The DMA increased total Cu and Zn and available Cd, Cr, Cu, Mn and Zn in mudflat soil. In our study, total Cu and Zn concentrations in dairy manure used in this study were 48.4 and 2.6-times higher than those in mudflat soil, and Cd, Cr, Mn and Ni concentrations in the dairy manure were similar to the mudflat soil. The increase of total Cu and Zn in the DMA mudflat soil can be attributed to much higher Cu and Zn concentrations in the dairy manure. Both Cu and Zn are usually added to most dairy rations as part of a mineral mix [13]. Previous studies also reported evidential accumulation of Cu and Zn in the surficial soil, without translocation through soil [13]. As a result, the available Cu and Zn concentrations in mudflat soil increased sharply with increasing DMA rates. However, available Cd, Cr and Mn concentrations also increased with increasing DMA rates, probably due to low molecular weight organic molecules of dairy manure [34]. Low molecular

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weight organic matter may increase metal mobility, as it can complex metals previously bound to soil particles [35]. Previous studies have showed increasing available metals concentrations with DMA [12,36]. In addition, release of dissolved organic carbon (DOC) from biodegradation of OM-rich dairy manure may contribute to higher soil available metals concentrations at DMA [37]. For example, organic acids for DOC such as citric, malic, oxalic, aspartic and glutamic acids, are potential metal chelators [35,38]. In summary, total metals contents of the dairy manure amended-soils were lower than the environmental quality standard for soils in China (GB 15618-1995). Dairy manure as an initial fertility driver to amend mudflat soil was feasible and 300 t ha–1 is the optimum amendment rate with maximum green manure yield yet permissible soil metal accumulation. 5. ACKNOWLEDGEMENTS This work was supported by the National Natural Science Foundation of China (31101604), Jiangsu Agricultural Science and Technology Innovation Fund (CX(15)1005), Ministry of Science and Technology Research Fund of China (2015BAD01B03), Jiangsu Agricultural Three New Project Fund (SXGC[2016]277), Jiangsu Agricultural Important Development Research Fund (BE2015337), Ministry of Housing and UrbanRural Research Fund of China (2014-K6-009), Foundation of State Key Laboratory of Soil and Sustainable Agriculture of China (Y412201402), and Shuangchuang Talent Plan of Jiangsu Province. 6. REFERENCES 1. Yu, B., Lu, C., Change of cultivated land and its implications on food security in China, Chinese Geogr. Sci., Vol. 16, No. 4, 2006, pp. 299– 305. http://dx.doi .org/10.1007/s11769-006-0299-4 2. Wang, F., Wall, G., Mudflat development in Jiangsu Province, China: Practices and experiences, Ocean Coast. Manag., Vol. 53, No. 11, 2010, pp. 691–699. http://dx.doi.org/10.1016/j.ocecoaman.2010.10.004 3. Cao, W., Wong, M.H., Current status of coastal zone issues and management in China: A review, Environ. Int., Vol. 33, No. 7, 2007, pp. 985–992. http://dx.doi.org/10.1016/j.envint.2007.04.009 4. Bai, Y., Gu, C., Tao, T., Wang, L., Feng, K., Shan, Y., Growth characteristics, nutrient uptake, and metal accumulation of ryegrass (Lolium perenne L.) in sludge-amended mudflats, Acta Agric. Scand. Sect. B Soil Plant Sci., Vol. 63, No. 4, 2013, pp. 352–359. http://dx.doi.org/10 .1080/09064710.2013.782424 5. Sun, H., Chen, Z., Fang, Y., Hua, D., Report of Dairy development of Jiangsu in 2014, China Dairy, Vol. 167, No. 11, 2015, pp. 44–47. (In Chinese) http://dx.doi.org/10.16172/j.cnki.114768.2015.11.011 6. Domingo-Olive, F., Bosch-Serra, A.D., Yague, M.R., Poch, R.M., Boixadera, J., Long term application of dairy cattle manure and pig slurry to winter cereals improves soil quality, Nutr. Cycl. Agroecosys.,

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