Urea deep placement for minimizing NH3 loss in an intensive rice cropping system

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Urea deep placement for minimizing NH3 loss in an intensive rice cropping system Yuanlin Yaoa,b,1, Min Zhanga,b,1, Yuhua Tiana, Miao Zhaoc, Bowen Zhanga,b, Meng Zhaoa,b, ⁎ Ke Zenga, Bin Yina, a b c

State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China University of Chinese Academy of Sciences, Beijing 100049, China Chengdu University of Information Technology, Chengdu 610225, China

A R T I C L E I N F O

A B S T R A C T

Keywords: Ammonia volatilization N use efficiency N diffusion 15 N uptake

It is urgently necessary to reduce environmental harm while simultaneously ensuring food security from agriculture in China. Fertilizer deep placement, especially urea deep placement (UDP), has been widely recognized as an efficient way to increase rice yield with less N use in flooded rice fields; however, few studies have explored UDP as a way to abate N loss, particularly ammonia (NH3) volatilization, in intensive rice cropping systems. Therefore, a field experiment was performed in the Taihu Region with five treatments (two surface split broadcasting treatments: a current traditional practice with 300 kg N ha−1 (CT) and a reduced N practice with 225 kg N ha−1 (RN), two one-time UDP treatments: a current traditional practice under UDP (CTDP) and a reduced N practice under UDP (RNDP), and a CK treatment with no urea). The NH3 volatilization, grain yield and N use efficiency in terms of the N recovery efficiency (NRE) were investigated during the 2014–2016 rice growing seasons. Additionally, N diffusion and 15N-labeled urea experiments were conducted to explore the N release pattern and the fate of 15N under UDP. The results demonstrated that little NH4+-N could diffuse into surface water under UDP, thus, negligible floodwater NH4+-N was detected. The seasonally cumulative NH3 volatilization of the UDP accounted for only 1% of the total applied N, which decreased by 91% compared to surface broadcasting treatments. As a result, the NH3 intensity (NH3-N loss per crop yield) was reduced by 92% over surface broadcasting. Moreover, the deep placement of urea could supply a higher NH4+-N concentration in the soil during the early growth stage and prolong the duration of N availability for 2 months; as a result, UDP remarkably increased the N uptake by 28% compared with surface broadcasting treatments in the 3 years. The UDP treatments significantly increased the yield and NRE by 10% and 55% under favorable weather conditions (2015 and 2016 rice seasons), respectively. The RNDP treatment obtained the lowest N surplus (36 kg N ha−1), and the plant 15N uptake was 62% higher and the 15N loss was 38% lower with RNDP than surface broadcasting. Therefore, the deep placement of urea can be considered a slow release fertilizer, which better matches the N demand of rice plants and effectively minimizes N losses, especially NH3 volatilization. The RNDP treatment, with a 25% reduction in the N dose, can represent an effective and promising strategy to achieve environmental integrity and food security in intensive rice cropping systems.

1. Introduction As a source of food, agriculture has a major global environmental impact that affects human health and ecosystem function (Tilman et al., 2011; van Noordwijk and Brussaard, 2014). During the first 35 years of the Green Revolution, world food production doubled and was accompanied by a nearly sevenfold increase in N fertilizer use (Tilman et al., 2002), so the great increase in food production has come at the cost of

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high nutrient consumption and reactive N (Nr) losses to the atmosphere, soil, and water (Power, 2010; Foley et al., 2011). China is experiencing greater agricultural challenges than other major countries due to the high demand for food under a continuously increasing population and the accompanying environmental degradation (Liu and Diamond, 2005). The dramatic increase in N input without a correspondingly large increase in crop yield has resulted in a major decline in N use efficiency (NUE), and large Nr losses have occurred (Liu and

Corresponding author. E-mail address: [email protected] (B. Yin). The two authors contributed equally to this work.

http://dx.doi.org/10.1016/j.fcr.2017.03.013 Received 24 March 2017; Accepted 30 March 2017 0378-4290/ © 2017 Elsevier B.V. All rights reserved.

Please cite this article as: Yao, Y., Field Crops Research (2017), http://dx.doi.org/10.1016/j.fcr.2017.03.013

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1990) and promoting root growth and nutrient uptake (Kapoor et al., 2008; Nkebiwe et al., 2016). It has been widely recognized that UDP can substantially increase rice yields by 15–20% and improve NUE up to 50–70% compared with surface broadcasting (Alam et al., 2013; Mazid Miah et al., 2016), however, very few studies have assessed the N loss of UDP in paddy rice fields, especially through NH3 volatilization. The advantages of UDP in previous studies were mainly at low N application rates (< 120 kg N ha−1) and were especially apparent at even lower rates (Savant and Stangel, 1990; Mohanty et al., 1998; Kapoor et al., 2008; Huda et al., 2016). However, the Chinese rice cropping systems are highly fertilized, so it is unclear whether the further reduction of NH3 emissions and an improvement in rice yields in Chinese rice fields can be realized simultaneously. Currently, an increase in non-agricultural wages and the migration rate have made labor-intensive agricultural production expensive in Asia (Otsuka, 2013). This leads to a large amount of conversion from small laborintensive farms to large mechanized farms in Chinese agriculture, so mechanization is rapidly expanding (Wang et al., 2016b). Moreover, placement machinery has been successfully developed and improved recently (Luo et al., 2008; Hoque et al., 2013; Ahamed et al., 2014; Fujii et al., 2016). UDP should gain more consideration under the current Chinese rice cropping systems. Therefore, a field experiment was conducted during 3 consecutive rice cropping seasons in the Taihu Region of China. The goals of this paper were to (a) monitor the effect of UDP on NH3 volatilization in a highly fertilized rice cropping system, (b) elucidate the NH4+-N and NO3−-N diffusion dynamics under UDP, and (c) evaluate the fate of 15N under UDP.

Diamond, 2005; Fan et al., 2012; Hofmeier et al., 2015), of which ammonia (NH3) is a major component (Behera et al., 2013). China is the world’s largest NH3 emitter with annual emissions that are 2.7 and 3.0 times higher than those of the European Union and the United States, respectively (Paulot et al., 2014). Agriculture is the main source of NH3 emission (through livestock manure and synthetic fertilizers), contributing 80–90% of the total emission (Kang et al., 2016). The emitted NH3 can lead to soil acidification and surface water eutrophication through N deposition (Behera et al., 2013). In addition, NH3 can be considered a dominant air pollution source, and NH3 and its secondary components account for 25–60% of the total PM2.5 mass (Fang et al., 2009; Sutton et al., 2013). In China, air quality in large cities is evidently influenced by the aerial transformation of large amounts of agricultural NH3 volatilization (Gu et al., 2012); thus, it is urgent to take measures to minimize NH3 volatilization. Paddy rice fields occupy 33% of the total arable land in China and provide food for more than 65% of Chinese people (Peng et al., 2009; FAO, 2013; Zhao et al., 2015). NH3 volatilization from paddy fields is greater than from other crop systems (Huang et al., 2016), and it is generally considered to be the major N loss pathway from paddy fields (Zhu, 1997; Huang et al., 2016). The total annual NH3 emission has reached 0.3 Tg from Chinese rice fields, with an average NH3 volatilization rate of 17% of the applied N (Cui et al., 2014; Paulot et al., 2014). The current high input, high output and high surplus of Chinese agriculture has resulted in its low N use efficiency (NUE) and high Nr emissions (Chen et al., 2016). Unfortunately, rice yield have suffered from stagnation in 79% of Chinese national rice area, but rice grain demand is expected to increase about 20% by 2030 in response to continuing population growth (Peng et al., 2009; Ray et al., 2012). The Taihu Region, which covers 36,500 km2, is one of the five major rice growing regions in China. The average N application rate in this region has reached 300 kg ha−1, which is the highest among the rice growing regions (Hofmeier et al., 2015; Wu et al., 2015), but rice yield has already plateaued (7.5 t ha−1) and NUE has been low (< 30%) (Ju et al., 2009; Zhao et al., 2015). The NH3 loss can be as high as 40% of the total applied N due to the strong sunlight and high temperatures in the summer (Cai et al., 1988; Wang et al., 2016a). Fortunately, in 2015, the Chinese Ministry of Agriculture announced a ‘Zero Increase Action Plan’ for national fertilizer use by 2020, aiming to reduce the environmental damage costs while simultaneously increasing crop yields without further increase of fertilizer use (Liu et al., 2016a). Therefore, it is imperative to conquer the tradeoff between reducing NH3 loss while improving rice yields. Many efforts have been made, such as increasing the N split application numbers, adjusting the N rate and time, using enhanced N fertilizers (i.e., urease inhibitors, controlled release fertilizer or combining synthetic fertilizer with biochar or organic fertilizer) and applying site-specific N management (Xu et al., 2012; Sun et al., 2015; Zhao et al., 2015; Wang et al., 2016a). However, more labor or knowledge requirements in N management or higher prices in enhanced N fertilizers have limited the expansion of these alternative techniques, and their effects on increasing yield and NUE and mitigating NH3 loss have varied with climate conditions, soils, water regimes and agronomic practices (Mohanty et al., 1998; Linquist et al., 2013; Chen et al., 2016). The great challenge ahead is to further minimize the NH3 loss while simultaneously ensuring food security (Foley et al., 2011; Fan et al., 2012). The traditional surface broadcasting of N fertilizer suggested for rice production is often inefficient (Mohanty et al., 1998; Nkebiwe et al., 2016), whereas the simplified one-time urea deep placement (UDP) (at depths of 5–15 cm) may be a promising approach to resolve the tradeoff between reducing Nr losses while improving crop production (Savant and Stangel, 1990; Afroz et al., 2014; Huda et al., 2016; Nkebiwe et al., 2016). There are increasing interests in UDP compared with broadcasting due to benefits such as reducing the floodwater NH4+ concentration (Kapoor et al., 2008; Afroz et al., 2014; Huda et al., 2016), ensuring prolonged N availability up to flowering (Savant and Stangel,

2. Materials and methods 2.1. Experimental site The field experiment was conducted at the Changshu Agroecosystem Experimental Station (31°15′15″N, 120°57′43″E) located in the Taihu Lake region, China. Approximately 75% of its total land area is under rice cultivation (Xu et al., 1980; Zhao et al., 2015). The dominant cropping pattern is summer rice and winter wheat rotation. The area is 1.3 m above sea level, and the climate is classified as humid subtropical monsoon with an average air temperature of 15.5 °C, a mean annual precipitation of 1038 mm, and a frost-free period of 224 days. The soil is classified as a Gleyi-stagnic Anthrosol, which is a waterlogged soil developed from a lacustrine deposit. The physicochemical properties of the topsoil (0–20 cm) are pH of 7.36 (H2O), 35 g kg−1 organic carbon, 2.09 g kg−1 total N, 0.93 g kg−1 total P, and 20.20 cmol kg−1 CEC, 1.20 g cm−3 soil bulk density. The soil porosity of 0–15 cm and 15–28 cm soil depth are 60.8% and 51.7%, and the clay, silt and sand content are 32.6%, 44.7% and 22.7% in the 0–15 cm soil depth, and are 36.2%, 45.3% and 18.7% in the 15–28 cm soil depth, respectively (Chen et al., 2007). The mean daily air temperature and precipitation during the experimental period from 2014 to 2016 are shown in Fig. 1. 2.2. Experimental design and agricultural management practices The field plot experiment was conducted for the 3 consecutive rice cropping seasons of 2014 and 2016. Five treatments were assigned to the field plots: (i) CK (a control following the local practice with no Nfertilizer); (ii) CT (the current traditional practice with 3-split surface broadcasting); (iii) RN (a reduced N dose of 25%, as recommended by Hofmeier et al. (2015) and Zhao et al. (2015), with 3-split surface broadcasting); (iv) CTDP (the current traditional practice with one-time point urea deep placement); (v) RNDP (the reduced N dose of 25% with one-time point urea deep placement). The rates and timing of fertilizer application for the five treatments are shown in Table 1. The CK, CT and RN plots have been in place since 2009. Each treatment had four replicates. 2

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Fig. 1. Mean daily air temperature and precipitation during 2014–2016 rice seasons.

For the surface broadcasting treatments (CT and RN), urea was applied as a basal application (40%), first topdressing (20%) and second topdressing (40%) in the plots (Table 1), and urea was homogeneously broadcasted manually onto the surface water. For the urea deep placement treatments, the urea was point deep-placed at one time as a basal fertilizer (2.61 g urea hill−1 for CTDP, 1.96 g urea hill−1 for RNDP), and urea was manually placed at 10 cm soil depth, 5 cm away from the seedlings using a steel-pipe tool (the pipe structure is similar to the injection syringe). To facilitate urea deep placement, the water was first drained in the CTDP and RNDP plots, and after the deep placement was completed, the plots were re-flooded. P2O5-fertilizer (90 kg ha−1) and K2O-fertilizer (120 kg ha−1) were broadcast as basal fertilizers in all treatments. Pre-flooding irrigation was performed in each plot approximately one week prior to rice transplanting, and floodwater was continuously maintained at a depth of 3–5 cm in all plots, except during the mid-season aeration (from about July 20 to August 1) and the final drainage (after October 20) before crop harvest (Table 1). All irrigation events were coordinated with precipitation events, and the same irrigation practices were followed in the 2015 and 2016 rice seasons. Pesticide and herbicide applications were the same for all treatments. Rice was harvested by manual labor on November 5, 2014, November 5, 2015 and November 3, 2016. Experiment I, the measurement of NH3 volatilization, NUE and crop yield for different urea application methods The NH3 volatilization was monitored using a dynamic chamber method, which composed of a dynamic chamber, a vacuum pump, and an acid solution to capture gaseous NH3 (Cao et al., 2013; Zhao et al., 2015). The cylindrical dynamic chamber was made from poly-methyl methacrylate, with a height of 15 cm and an inner diameter of 20 cm. Ambient air located at 2.5 m above the surface water was pumped to complement the inner air in the chamber. When collecting NH3 volatilization, the chamber was inserted into the surface water and soil to a depth of approximately 10 cm, and the NH3 in the chamber was then captured using an acid solution containing 60 mL of a sulfuric acid solution (0.05 mol L−1). The air flow rate through the chamber was set to 15–20 min−1. NH3 volatilization was measured twice per day, in the morning (7:00–9:00) and afternoon (15:00–17:00). Following each fertilizer application, the volatilization of NH3 was continually measured until NH3 was no longer detected. The concentration of NH4+-N in the acid trap was measured by the indophenol blue method (Novozamsky et al., 1974). The cumulative NH3 volatilization flux was the sum of the NH3 volatilization fluxes on sampling days. The paddy field surface floodwater was collected when the NH3 volatilization was sampled and filtered, and the NH4+-N and NO3−-N concen-

Table 1 Date and rate of urea applications and water management regimes. Application method

N rate (kg N ha−1)

Basal fertilization (kg N ha−1)

First topdressing (kg N ha−1)

Second topdressing (kg N ha−1)

Broadcasting Broadcasting Placement Placement

0 300 225 300 225

0 120 90 300 225

0 60 45 0 0

0 120 90 0 0

Basal fertilization Jun 26 Jun 24 Jun 24

First topdressing Jul 5 Jul 7 Jul 7

Second topdressing Aug 15 Aug 14 Aug 8

2014

Pre-flooding irrigation Jun 19

Final drainage Oct 21

2015

Jun 17

2016

Jun 17

Mid-season aeration Jul 23–Aug 2 Jul 20–Aug 3 Jul 21–Aug 4

Code

CK CT RN CTDP RNDP

Application date 2014 2015 2016 Water management

Oct 20 Oct 20

CK, control with no N-fertilizer; CT, 3-split surface broadcasting with 300 kg N ha−1; RN, 3-split surface broadcasting with 225 kg N ha−1; CTDP, one-time UDP with 300 kg N ha−1; RNDP, one-time UDP with 225 kg N ha−1.

The five treatments were arranged in a randomized complete block with four replicates. The plot dimensions were 6 m × 7 m for CK, CT and RN, and each plot was separated by 30 cm-wide earthen banks covered with plastic film to prevent lateral water movement. Three CTDP plots (2 m × 2 m) were designed as subplots distributed in each CT plot, the same as RNDP plots, one subplot was used for calculation of yield at harvest without any disturbance, the rest two subplots were used for destructive sampling of N diffusion and 15N fate experiments, respectively. The CTDP and RNDP plots were bounded by polyvinyl chloride plastic frames. The frames were inserted into the soil to a depth of 23 cm, and they protruded 10 cm above the soil to prevent any runoff or run-on water from removing or adding N fertilizer. Water pipes were installed in the frames for irrigation. The synthetic fertilizers used were prilled urea (N, 46%), superphosphate (P2O5, 12%), and potassium chloride (K2O, 60%). The rice cultivar was Oryza sativa L., cv. Nanjing 46 (http://www.ricedata.cn/ variety/), a local prevailing cultivar, and the rice seedlings (30 days of age) were transplanted at a spacing of 20 cm × 20 cm in all treatments. 3

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tration in floodwater was measured by the indophenol blue method and the ultraviolet spectrophotometer method (HJ/T 346-2007). At the same time, the temperature and pH of the surface water were measured; the pH was measured with a portable pH meter (Germany Sartorius PB10). After crop maturation, the aboveground parts of the plants in each plot were harvested to determine the actual yield. For each plot, a 3 m2 sample area was reserved and divided into straw and grain and then airdried and weighed to calculate the dry matter yield. Grain and straw were oven-dried for 24 h at 80 °C, and then powdered and passed through a 150-μm screen to determine the N concentration. The N content of the grain and straw were measured using the Kjeldahl method, and the N uptake was calculated based on the N concentration and the oven dry weight. The NUE was calculated in the terms of N recovery efficiency (NRE), and the N surplus was the difference between the total fertilizer N input and the aboveground plant N uptake.

NRE =

(Flash EA Delta V Advantage, Thermo Fisher Scientific Inc., Waltham, MA, USA), with an analytical error of ± 0.02%. All 15N was expressed as the atom percent excess corrected for the background abundance (i.e., 0.366%). The percentage and the amount of N derived from fertilizer (Ndff) were calculated according to Hauck and Bremner (1976).

Ndff(%) =

B−A C− A

Plant Ndff (kg N ha−1) = Ndff (%) × Plant total N content × Plant dry matter biomass Soil Ndff (kg N ha−1) = Ndff (%) × Soil total N content × Soil bulk density × Soil volume where A is the natural abundance of 15N; B is the 15N atom percent excess in the plant or soil; and C is the 15N atom percent excess in the fertilizer N.

Nyieldin treatment − Nyield in CK Ninput

2.3. Data analyses The statistical data analyses and graphs were prepared with both SPSS 19.0 analytical software (SPSS China, Beijing, China) and Origin 8.5 software (Origin Lab Ltd., Guangzhou, China). All data were tested for normality and homogeneity of variances, and an ANOVA or t-test was applied to test for significant differences among the different treatments at the 0.05 probability level. The correlation between NH3 flux and floodwater pH and NH4+-N concentration was analyzed by Pearson correlation. The NH4+-N and NO3−-N diffusion dynamics were performed by Surfer 8.0 (Surface mapping system, Golden software. Inc. USA).

N surplus = Ninput − Nyield where Ninput is total fertilizer N input; and Nyield is aboveground plant N uptake. Experiment II, monitoring of NH4+-N and NO3−-N diffusion dynamics under UDP Destructive soil samples were collected from another set of CTDP and RNDP plots at 8, 15, 30, 63, 101 and 125 days after one-time deep fertilization during the 2015 rice season. The water was drained before the soil sampling, and a 20 cm depth section, 3 cm away from the rice plant and the urea placement site, was carefully dug out using a sharp shovel. Then four soil samples (3 cm in diameter) were collected in each direction (up, down, left and right) of the urea placement site at an interval of 3 cm using a steel auger (3 cm in diameter). In total, twelve soil samples were collected from the horizontal (left and right) and vertical directions (up and down). Another 20 cm depth section in the UDP plot was used to determine the NH4+-N and NO3−-N of the 0–20 cm soil depth. Four soil cores from the 0–20 cm soil depth were collected and mixed as one soil sample for surface broadcasting and CK plots. Fresh soil samples were immediately transported to the laboratory and mineral N was extracted with 1 M KCl (10 g of field moist soil in 50 mL of KCl solution). The soil slurries were shaken for 1 h on a reciprocal shaker (120 strokes per min.) and filtered through Whatman no. 42 filter papers. The extracts were stored (−4 °C) until analysis, and the soil NH4+-N and NO3−-N concentrations were measured using the indophenol blue method and the ultraviolet spectrophotometer method, respectively. Experiment III, the monitoring of the 15N fates under different fertilizer application methods Microplots were established in the RN and in another set of RNDP plots in the 2015 rice season. The polyvinyl chloride plastic columns were inserted to a soil depth of 23 cm and protruded 10 cm above the soil; the inner diameter of the columns was 40 cm. The 15N-labeled urea (15N abundance was 5%) was provided by the Shanghai Research Institute of Chemical Industry. The plant and soil samples were collected after crop maturation. Four soil cores from 0–20 cm soil depth were collected from each microplot using a steel auger and mixed well into a single soil sample. The plant samples were divided into straw, root and grain, and all roots from the 0–20 cm soil layer of each microplot were collected and washed. Straw, roots, grain and soil were oven-dried for 24 h at 80 °C and then powdered and passed through a 150-μm screen to determine the N concentration. The N contents of the grain, straw and roots were measured using the Kjeldahl method. The 15 N abundance was analyzed using an isotope ratio mass spectrometer

3. Results 3.1. NH3 volatilization, NH4+-N and NO3−-N concentration and pH in floodwater As clearly shown in Fig. 2, the UDP treatments (CTDP and RNDP) effectively reduced the daily NH3 volatilization fluxes in the 2014 and 2015 rice seasons. The daily NH3 volatilization fluxes in the UDP treatments were negligible and similar to those in the CK treatment. There were no peaks in the daily NH3 volatilization fluxes for UDP treatments during the entire rice season. In contrast, strong daily fluxes in NH3 volatilization occurred under the surface broadcasting treatments (CT and RN) in the 2 rice seasons, and NH3 volatilization was particularly remarkable in the first three days following fertilizer broadcasting and then sharply dropped to relatively low levels. The daily NH3 volatilization fluxes under UDP were significantly lower than those of surface broadcasting (p < 0.05) within 4–9 days after fertilizer application in the 2 rice seasons. The UDP treatments produced very weak cumulative NH3 losses during the entire rice season (Table 2), and the total NH3 losses from the UDP treatments were dramatically lower than those from the CT treatment (p < 0.05); there were no significant differences between the UDP treatments and CK (p > 0.05). The average total NH3 loss from the UDP treatments was 2.94 kg N ha−1 (2.04–3.58 kg N ha−1) in the 2 rice seasons, which accounted for 1% (1–2%) of the total N applied and were 91% (89–93%) lower than those of the surface broadcasting treatments. However, the highest total NH3 losses were recorded in the CT treatment for the 2 rice seasons, which were 30.09 kg N ha−1 (28.74–49.44 kg N ha−1) and accounted for 13% (10–17%) of the total N inputs, respectively. Meanwhile, the total NH3 losses from the RN treatment were 26.69 kg N ha−1 (30.94 and 22.44 kg N ha−1), which accounted for 11% (10–14%) of the total N inputs in the 2 rice seasons, respectively. The cumulative NH3 losses during the basal and first additional fertilization periods constituted 4

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Fig. 2. Seasonal changes in NH3 volatilization flux (a and b), floodwater NH4+-N concentration (c and d), floodwater NO3−-N concentration (e and f) floodwater pH (g and h) from different treatments in rice seasons of 2014 (left) and 2015 (right).Asterisk (*) at bottom axis means that UDP treatments differ significantly with surface broadcasting treatments at the given date (p < 0.05). The arrows denote fertilizer application. CK, control with no N-fertilizer; CT, 3-split surface broadcasting with 300 kg N ha−1; RN, 3-split surface broadcasting with 225 kg N ha−1; CTDP, one-time UDP with 300 kg N ha−1; RNDP, one-time UDP with 225 kg N ha−1.

Table 2 Seasonally cumulative NH3 volatilization and NH3 intensity in 2014 and 2015 rice seasons. Code

Application method

N rate (kg N ha−1)

Cumulative NH3 loss (kg N ha−1) BF

T1

T2

Total

Percentage of total N inputs (%)

Decrease in NH3 loss relative to CT (%)

NH3 intensitya (kg N t−1 grain)

2014 CK CT RN CTDP RNDP

Broadcasting Broadcasting Placement Placement

0 300 225 300 225

0.71a 18.36b 10.68c 1.19a 1.11a

1.72a 20.14b 12.88c 1.38a 1.60a

0.68a 10.94b 7.38c 1.01a 0.84a

3.11a 49.44b 30.94c 3.58a 3.55a

17 14 1 2

– 37 93 93

0.64a 6.44b 3.97c 0.44a 0.37a

2015 CK CT RN CTDP RNDP

Broadcasting Broadcasting Placement Placement

0 300 225 300 225

0.86a 11.40b 8.18b 0.90a 1.03a

0.58a 9.36b 8.00b 0.60a 0.37a

0.45a 7.97b 6.26b 1.09a 0.64a

1.90a 28.74b 22.44c 2.59a 2.04a

10 10 1 1

– 22 91 93

0.41a 3.21b 2.50c 0.26a 0.20a

BF, basal fertilization period; T1, first topdressing period; T2, second topdressing period. CK, control with no N-fertilizer; CT, 3-split surface broadcasting with 300 kg N ha−1; RN, 3-split surface broadcasting with 225 kg N ha−1; CTDP, one-time UDP with 300 kg N ha−1; RNDP, one-time UDP with 225 kg N ha−1. The different letters within the same column indicate significant differences among the different treatments, at p < 0.05. a NH3 intensity is the total NH3-N loss divided by rice yield.

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most of the total NH3 losses throughout the rice growing season for CT and RN. In contrast, the cumulative NH3 losses under the UDP treatments exhibited no peaks and remained similar to that under CK (p > 0.05). Similarly, the NH3 intensity values (NH3-N loss per unit crop yield) of the UDP treatments were 0.32 kg N t−1 grain (0.20–0.44 kg N t−1 grain), which were significantly lower by 92% (88–94%) than those under the surface broadcasting treatments for the 2 years (p < 0.05). Similar to daily NH3 fluxes, the daily floodwater NH4+-N contents exhibited the same pattern (Fig. 2c–d). The floodwater NH4+-N concentrations in UDP were significantly lower than those in surface broadcasting within 3–8 days after fertilizer application for the 2 years (p < 0.05). The daily floodwater NH4+-N concentrations remained low in the UDP treatments; the maximum NH4+-N concentration in CTDP was only 1.42 mg N L−1, and it was only 1.47 mg N L−1 under RNDP in the 2 rice seasons. There were no significant differences of the floodwater NH4+-N concentrations between the UDP treatments and the CK treatment (p > 0.05). In contrast, for the surface broadcasting treatments, the maximum NH4+-N concentrations in CT and RN were 42.63 mg N L−1 and 22.07 mg N L−1 in the 2 rice seasons, respectively, and the daily floodwater NH4+-N concentrations increased sharply after fertilization and reached peak values within 1–3 days, then declined rapidly to near the CK levels after 4–9 days. The NO3−-N concentrations in floodwater remained at a low level (< 3 mg N L−1) during the 2 rice seasons for all treatments (Fig. 2e–f), and they were not significantly different between surface broadcasting and UDP (p > 0.05) for almost all days of the 2 rice seasons (except 5 days in 2014). Furthermore, UDP could significantly lower the floodwater pH compared to surface broadcasting within 1–3 days after fertilizer application for the 2 years (p < 0.05) (Fig. 2g–h). The pH in RNDP averaged 7.95 and 7.9, and the pH of CTDP averaged 7.89 and 7.87 for the 2 years, respectively. For CT, the pH averaged 8.13 and 8.07, whereas the pH of RN averaged 8.1 and 8.05 in the 2 years, respectively. The daily NH3 volatilization fluxes were positively correlated with NH4+-N contents in floodwater, not only for surface broadcasting treatments, but also for UDP treatments in the 2014 (p < 0.05, n = 23) and 2015 (p < 0.05, n = 16) rice seasons (Table 3). The daily NH3 volatilization fluxes were positively correlated with floodwater pH for surface broadcasting (p < 0.05, n = 20 for 2014, n = 13 for 2015), but there were no correlations between daily NH3 volatilization fluxes and floodwater pH for UDP treatments.

Table 4 Analysis of variance results for yield, straw biomass, NRE, N uptake and N surplus (p value).

CK CT RN CTDP RNDP

Broadcasting Broadcasting Placement Placement

0 300 225 300 225

NRE

N uptake

N surplus

Application method N rate Year N rate * Year Method * Year N rate * Application method N rate * Application method * Year

< 0.01

< 0.01

< 0.01

< 0.01

< 0.01

0.77 < 0.01 0.59 < 0.01 0.57

0.12 < 0.01 0.86 0.60 0.79

0.23 < 0.01 0.47 0.22 0.26

< 0.01 < 0.01 0.34 < 0.05 0.61

< 0.01 < 0.01 0.41 0.08 0.64

0.42

0.60

0.70

0.38

0.44

The NH4+-N movement under UDP was slow and could prolong the duration of N availability for 2 months, and it mainly occurred at 4–13 cm under the soil surface. Its movement from the placement site was preferentially upward compared with left, right and downward (Fig. 3). The highest NH4+-N contents occurred at 0–3 cm around the placement site, with 2096 and 2596 mg kg−1 for 8 DAF, and with 19 and 84 mg kg−1 for 63 DAF in RNDP and CTDP, respectively. As for the 0–4 cm soil depth (soil surface layer), the maximum NH4+-N concentrations were 129 and 114 mg kg−1 at 8 DAF, and then were nearly halved at 15 DAF for RNDP and CTDP, respectively. The NH4+-N contents of the 3–10 cm away from placement site in downward, left and right directions remained low level, i.e., no more than 107 mg kg−1 for RNDP and CTDP during the rice season. The average NH4+-N contents of 0–20 cm soil depth in UDP treatments were significantly higher than that of surface broadcasting treatments (p < 0.05) (Fig. 4), the contents were 147, 134, 69, 17, 10 and 9 mg kg−1 for RNDP and 159, 102, 19, 11, 16 and 6 mg kg−1 for CTDP at 8, 15, 30, 63, 101 and 135 DAF, respectively. In contrast, the average NH4+-N content of the 0–20 cm soil depth in surface broadcasting treatments was kept low level (< 31 mg kg−1) during the rice season.

Table 3 The relationship between daily NH3 volatilization fluxes and daily floodwater NH4+-N contents and pH. N rate (kg N ha−1)

Aboveground biomass

3.3. NH4+-N and NO3−-N diffusion dynamics under UDP

The fertilizer application method and year significantly affected the

Application method

Yield

rice yield, aboveground plant biomass, NRE, N uptake and N surplus (the difference between the total fertilizer N input and aboveground plant N uptake) in this study (p < 0.01) (Table 4). The N rate had no effect on the rice yield, aboveground plant biomass and NRE among the 3 years (p > 0.05), but remarkably influenced the N uptake and N surplus (p < 0.01). The UDP treatments achieved 10% (4–15%) higher yields and 55% (32–73%) higher NRE than surface broadcasting treatments in the 2015 and 2016 rice seasons (p < 0.05) (Table 5), but the yields were not differed significantly between UDP treatments and surface broadcasting treatments in 2014 (p > 0.05), due to crop lodging caused by a typhoon at 86 days after basal fertilization (DAF). The RNDP treatment also significantly increased the NRE by 64% (45–83%) in 2014 over surface broadcasting treatments (p < 0.05), while the NRE for CTDP was not significantly different than that of RN in 2014 (p > 0.05). The aboveground plant biomass of UDP treatments was remarkably higher by 17% (12–23%) than that of the surface broadcasting treatments in the 3 years (p < 0.05). The UDP treatments resulted in significantly higher N uptake by 28% (14–49%) than that of surface broadcasting treatments in the 3 years (p < 0.05) (Table 5). Moreover, the RNDP produced the lowest N surplus level with an average of 36 kg N ha−1 (15–53 kg N ha−1) for the 3 years (p < 0.05), which decreased the N surplus by 65% over surface broadcasting treatments.

3.2. Yield, NRE, N uptake and surplus

Code

Source of variance

Correlation between NH3 volatilization and floodwater NH4+-N contents

Correlation between NH3 volatilization and floodwater pH

2014

2015

2014

0.16 0.49* 0.59** 0.63** 0.64*

−0.06 0.70** 0.71** 0.52* 0.69**

*

0.47 0.47* 0.58** 0.23 0.42

2015 0.13 0.54* 0.61* −0.10 −0.45

CK, control with no N-fertilizer; CT, 3-split surface broadcasting with 300 kg N ha−1; RN, 3-split surface broadcasting with 225 kg N ha−1; CTDP, one-time UDP with 300 kg N ha−1; RNDP, one-time UDP with 225 kg N ha−1. * Significant correlation at the 0.05 level (two-tailed). ** Significant correlation at the 0.01 level (two-tailed).

6

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Table 5 Yield, aboveground biomass, NRE, N uptake and N surplus for different treatments at harvest in 2014–2016 rice seasons. Code

Application method

N rate (kg N ha−1)

Yield (t ha−1)

Aboveground biomass (t ha−1)

NRE (%)b

N uptake (kg N ha−1)

N surplus (kg N ha−1)c

2014 CK CTa RN CTDPa RNDPa

Broadcasting Broadcasting Placement Placement

0 300 225 300 225

4.88a 7.68b 7.80b 8.19b 8.02b

9.66a 14.64b 14.83b 17.30c 16.63c

23a 29ab 35bc 42c

78a 149b 143b 185c 172c

151a 82b 115c 53d

2015 CK CT RN CTDP RNDP

Broadcasting Broadcasting Placement Placement

0 300 225 300 225

4.58a 8.99b 8.99b 10.16c 10.38c

8.98a 17.18b 16.68b 20.12c 20.26c

30a 31a 45b 52b

67a 156b 136c 203d 185d

144a 89b 97b 40c

2016 CK CT RN CTDP RNDP

Broadcasting Broadcasting Placement Placement

0 300 225 300 225

4.91a 8.75b 8.32c 9.08d 9.13d

11.04a 17.59b 16.39b 20.09c 19.87c

35a 41a 54b 60c

79a 184b 172b 242c 210d

116a 53b 58b 15c

The arrows denote fertilizer application. CK, control with no N-fertilizer; CT, 3-split surface broadcasting with 300 kg N ha−1; RN, 3-split surface broadcasting with 225 kg N ha−1; CTDP, one-time UDP with 300 kg N ha−1; RNDP, one-time UDP with 225 kg N ha−1. The different letters within the same column indicate significant differences among the different treatments, at p < 0.05. a The rice crop lodging occurred on September 22, 2014 (12 days after flowering) caused by typhoon. b The NRE is apparent N recovery efficiency, the difference in the total N uptake between the N treatment and the control treatment as a percentage of the total N input. c The N surplus was the difference between the total fertilizer N input and aboveground plant N uptake.

The NO3−-N diffusion obtained a great temporal and spatial variability (Fig. 3). The highest NO3−-N contents reached 21 and 31 mg kg−1 at 8 DAF, and they decreased at 15 DAF and achieved 55 and 51 mg kg−1 at 30 DAF (mid-season aeration) in RNDP and CTDP, respectively. After 30 DAF, the NO3−-N diffusion became dispersed and its downward movement was apparent. At 125 DAF, the NO3−-N content increased for CTDP, especially at 0–4 cm soil depth. The average NO3−-N content of the 0–20 cm soil depth ranged from 5 to 16 mg kg−1 for all treatments during the rice season (Fig. 4), and peak values were appeared at 8 DAF and 30 DAF in the rice season, with a tail at 125 DAF (the final drainage period). There were no significant differences between UDP treatments and surface broadcasting treatments in the NO3−-N contents of the 0–20 cm soil depth (p > 0.05). 3.4.

et al., 2009), 17% in Changshu (Lin et al., 2007), 17% in Changshu (Zhao et al., 2015), and 18% in Yangzhou (Lin et al., 2012). In contrast, based on the results of this study, it can be concluded that UDP has the ability to reduce NH3 volatilization to 1–2% of the applied N, with a reduction of 91% over surface broadcasting (Table 2). Similarly, Liu et al. (2015) reported that the NH3 volatilization of the basal period was only occupied 1% of the applied N when half of urea was deep-placed (20 cm soil depth) during the basal period in Hubei Province of central China. There have been limited studies that have documented that the deep placement of N fertilizer could minimize NH3 volatilization (Table 7), and they were focused on low N rates. This study confirmed that UDP also had a large NH3 elimination effect at high N rates. As a result, UDP significantly reduced the NH3 intensity compared to surface broadcasting. Meanwhile, a number of studies have recently reported that the deep placement of N fertilizer was effective in reducing NH3 loss in upland crop systems (Cai et al., 2002; Khalil et al., 2009; Rochette et al., 2013). We also found that UDP could substantially depressed NH3 volatilization in the wheat season at the same experiment site (unpublished data), with a total seasonal NH3 volatilization of 1.0–1.7 kg N ha−1, which was a decrease of 77–88% compared to CT. The Taihu Region is the largest watershed in East China, and this region is the most economically developed, with intensified agriculture. A considerable proportion of NH3 volatilization, resulting from surface broadcasting of fertilizer N into rice fields, contributes to air pollution and surface water eutrophication in this Region (Fang et al., 2009). Although many strategies have been implemented to reduce the NH3 volatilization in this region, they are unlikely to further reduce NH3 volatilization. UDP is a promising strategy to further abate NH3 loss in paddy fields. The total health damage related to atmospheric Nr emissions accounted for US$19-62 billion in 2008 in China, of which 52–60% were derived from NH3 emissions (Gu et al., 2012). The total annual NH3 emitted from Chinese rice fields was 0.3 Tg during the 2005–2008 period, with an average NH3 volatilization rate of 17% of the applied N (Cui et al., 2014; Paulot et al., 2014). If the average NH3 volatilization rate can be reduced from 17% to 1–2% of the applied N in Chinese rice fields through the deep placement of N fertilizer, we roughly estimate that the total NH3 volatilized from the Chinese rice system can be reduced from 0.3 to 0.02–0.04 Tg. As a result, the cost of environmental damage caused by NH3 emissions can be reduced by US$

15

N fate and recovery

The 15N fate and recovery at harvest were shown in Table 6. A significantly higher aboveground plant 15N uptake was observed in RNDP than in RN (p < 0.05). For RNDP, 117.4 kg N ha−1 (52%) of the 15 N was found in the aboveground plant (45.2 kg N ha−1 (20%) in the straw, 72.2 kg N ha−1 (32%) in the grain) at harvest, which was 62% higher (p < 0.05) than that in RN. The soil residual 15N in 0–20 cm under RNDP was 29.4 kg N ha−1 (13%), which was 20% higher than that of the RN treatment (p < 0.05). The 15N loss for RNDP was 38% lower than under RN (p < 0.05). The 15N recovery by plant for RNDP (52%) was 62% higher than that of RN (32%) (p < 0.05). 4. Discussion 4.1. NH3 loss from UDP versus surface broadcasting NH3 volatilization from N fertilizer application in agricultural systems is a global concern that needs to be addressed, especially in China, the largest NH3 emitter. The average NH3 volatilization reached 17% of applied N in Chinese rice systems (Cui et al., 2014; Wu et al., 2015). In this study, the seasonal NH3 loss from surface broadcasting treatments (CT and RN) accounted for 10–17% of the total N inputs (Table 2), which was comparable with the results of other studies using similar N inputs in the same region, including 12% in Yixing (Zhao 7

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Fig. 3. The NH4+-N (a-l) and NO3−-N (m-x) diffusion dynamics of after urea deep fertilization in 2015 rice season.CTDP, one-time UDP with 300 kg N ha−1; RNDP, one-time UDP with 225 kg N ha−1. DAF, days after basal fertilization. Urea was point deep-placed at 10 cm soil depth. The urea placement site is the starting point of coordinate axis, the positive coordinate denotes upward or right direction of placement site, and the negative coordinate refers to downward or left direction of placement site.

4.2. Mitigation effect of UDP on NH3 volatilization

0.1-0.9 billion (the damage costs per kg NH3-N in China was estimated at US$ 0.4-3.3 (World Bank, 2007; Gu et al., 2012)). We admit that this estimate is not accurate, so more studies across different fertilizer types, soils, climate conditions and management practices are needed to further explore and accurately evaluate the NH3 elimination effect of UDP in China.

Reducing the floodwater NH4+-N content is effective in mitigating NH3 volatilization in paddy fields. A positive linear relationship existed between the daily NH3 fluxes and the floodwater NH4+-N contents in the N fertilized treatments (Table 3), similar to previous studies (Cao 8

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previous studies (Chauhan and Mishra, 1989; Mohanty et al., 1998; Kapoor et al., 2008; Afroz et al., 2014; Huda et al., 2016). Deep-placed urea is quickly hydrolyzed at 8 DAF, but the first hydrolyzed NH4+-N is absorbed by soil particles around the fertilizer placement site, and further hydrolysis of urea and NH4+ movement away from the placement site was slow and restricted to a limited soil volume (4–13 cm soil depth) (Fig. 3), due to the negative charge of soil colloids and relatively high clay content (33–36%); and the diffusion was influenced by the ion-exchange process (Mohanty et al., 1998; Liu et al., 2016b). However, when urea was broadcast onto surface water, it was easily hydrolyzed to NH4+, and the high NH4+-N content in the floodwater was easily lost through NH3 volatilization due to the flooded condition, strong sunlight, high temperatures and high pH in the field during the rice growing stage (Cai et al., 1988; Cao et al., 2013). Most of the NH3 loss occurred during the basal period and the first top dressing period from June to July for surface broadcasting, which was attributed to the inefficient root systems of rice plants for absorbing the applied N and inadequate rice canopy for intercepting solar radiation accompanied by the relatively higher air temperature at this stage (Fig. 1). The cumulative highest NH3 loss period for the surface broadcasting treatments took place in the first additional fertilization period in 2014 and in the basal fertilization period in 2015, respectively, which might be a result of the difference in the rainfall pattern during the time of fertilizer application between the two rice seasons (Fig. 1). Surface broadcasting supplied abundant nutrients to floodwater and thus favored vigorous algae growth and algal photosynthetic activity, which resulted in the depletion of dissolved CO2 and elevated surface water pH (Buresh et al., 2008; Huda et al., 2016). The floodwater pH determined the NH3/NH4+ ratio; thus, the high floodwater pH could stimulate high NH3 volatilization (Fillery et al., 1984). In contrast, the negligible floodwater NH4+-N concentration under UDP made it difficult for algae to survive. UDP significantly lowered the floodwater pH compared to surface broadcasting within 1–3 days after fertilizer application (Fig. 2 g-h). In addition, UDP also could lower soil urease activity than surface broadcasting (Liu et al., 2015), resulting in reduced NH4+ hydrolyzation from N fertilizer in the soil and floodwater. Meanwhile, UDP generated greater straw biomass over surface broadcasting (Table 5), which could increase the leaf area and reduce sunlight intensity and air movement and mixing with ambient air flow, resulting in less NH3 volatilization in paddy fields. Rice cultivars may have an important influence on NH3 volatilization. The rice cultivars with high-NUE can enhance N uptake and offer significant potential for mitigating N loss (Hakeem et al., 2011; Chen et al., 2015). It was indicated that high-NUE rice cultivars possessed greater surface area, roots length and N metabolic enzymes compared with low-NUE rice cultivars (Shi et al., 2009; Hakeem et al., 2011; Chen et al., 2015). The development of high-NUE rice cultivars with the ability of uptake more N during the early growth stage was effective in decreasing N loss (Chen et al., 2015). Currently, too much N fertilizer is applied as basal fertilization in paddy fields, especially in the Taihu Lake region, with excessive N application at the early stage in combination with inefficient N absorption by root systems, increasing the risk of NH3 loss. Chen et al. (2015) found that there was a trend toward smaller NH3 loss with the high-NUE cultivars (Wuyunjing 23, Zhendao 11 and Aoyusi 386) over a conventional cultivar (Wuyunjing 3) in the Taihu Region. The NH3 mitigation effect of UDP may have different responses among rice cultivars with different NUE cultivars, thus it is necessary to understand the agronomic and physiological performance of rice cultivars used to pursue environmental integrity and ensure food security. However, we only examined a local prevailing rice cultivar (Nanjing 46) with a medium NUE in this study, thus we suggest that further studies on the NH3 mitigation effect among different rice cultivars under UDP are needed. It was considered that the reduction of NH3 loss depended on the placement depth, and the cumulative NH3 loss decreased with increasing placement depth (Rochette et al., 2013; Liu et al., 2015). Thus

Fig. 4. The NH4+-N (a) and NO3−-N (b) content of 0–20 cm soil depth under different urea application method in 2015 rice season.Asterisk (*) at bottom axis means that UDP treatments differ significantly with surface broadcasting treatments at the given days after fertilization (p < 0.05). The arrows denote fertilizer application. CK, control with no Nfertilizer; CT, 3-split surface broadcasting with 300 kg N ha−1; RN, 3-split surface broadcasting with 225 kg N ha−1; CTDP, one-time UDP with 300 kg N ha−1; RNDP, one-time UDP with 225 kg N ha−1. Table 6 Fertilizer Code

RN RNDP

15

N fate and recovery in 2015 rice season.

Ndff (kg N ha−1)

15

N recovery by plant (%)a

15 N loss (%)

Straw

Grain

Root

Soil

Total in aboveground plant

22.2 (10)a 45.2 (20)b

50.5 (23)a 72.2 (32)b

7.8 (3)a

24.5 (11)a 29.4 (13)b

72.7a

32a

53.3a

117.4b

52b

33.1b

3.7 (2)b

RN, 3-split surface broadcasting with 225 kg N ha−1; RNDP, one-time UDP with 225 kg N ha−1. Values in parentheses indicate the percentage of N derived from fertilizer. The different letters within the same column indicate significant differences among the different treatments, at p < 0.05. a 15 : N recovery by plant is the ratio of aboveground plant 15N uptake by rice and total 15 N inputs.

et al., 2013; Zhao et al., 2015). Although the upward movement of NH4+-N was easier than downward, left and right movement in this study (Fig. 3), which was mainly due to the soil being muddier and more puddled closer to the surface and a plow pan at the 15–20 cm soil depth with a low permeability rate (Zhu, 1997; Zhao et al., 2012a), the daily floodwater NH4+-N contents under UDP were similar to CK (p > 0.05) during the entire rice season (Fig. 2), indicating that few NH4+-N could diffuse upward into surface water. The negligible floodwater NH4+-N content under UDP agrees with the findings from 9

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Table 7 Summary of the proportion of N loss as NH3 after placement (only studies reporting losses for surface broadcasting or incorporation were included, upland or aerobic conditions were excluded, only urea was included). N rate

NH3 volatilization losses, % of applied N Surface broadcast

Incorporation

Deep placed prilled urea

Deep placed urea supergranule

Deep placed NPK briquette

Mudballs

depth (cm)

Reference

Chauhan and Mishra (1989)

40

22.1

0.8

10

80 120 90 90 60 78 156 78 78 90a 90a 90a 90 90 95 184 53 80 80 80

21.4 19.3 3.2 2.3 0.8 18.3 23.1 15.4 9.5 26.6

1.1 0.8 0.2 0.8 0.5 1.0 1.0 0.4 0.0

10 10 5 5 5 7–10 7–10 7–10 7–10 5 10 20 10–12 10–12 8 10

a

1.4 0.6 −0.1

15.8 8.6 1.4

5.9 18.0

<1 <1 50

24 48 56 47 27

<5 2

11 7 13 13

Patel et al. (1989)

Huda et al. (2016)

Liu et al. (2015)

Mikkelsen et al. (1978) Vlek and Craswell (1979) Eriksen et al. (1985) De Datta et al. (1989) Fillery et al. (1984)

Only 90 kg N ha−1 was deep placed.

UDP in paddy fields (Zhu, 1997; Zhao et al., 2012b). Zhao et al. (2012b) found that the denitrification could reach 27% of total fertilizer N input in paddy fields of the Taihu Region. The N diffusion experiment revealed that there was a great temporal and spatial variability of the soil NO3−-N content (Fig. 3), which was mainly affected by the water regime and plant growth stage. Due to the residual soil NO3−-N of the former wheat season and the bypass flow caused by deep fertilization and rice cultivation (Cao et al., 2014), high NO3−-N content occurred during the initial stage of the rice season (8 DAF). The mid-season aeration and final drainage could promote soil cracking within the dried layers, and the rice rhizosphere created an oxidized microenvironment; thus, they favored the nitrification-denitrification cycle of N in soil, which were responsible for the peak value at 30 DAF and the tail at 125 DAF. However, the magnitude of nitrification-denitrification under UDP is not clear so far; only several studies have reported the effects of N fertilizer placement on N2O and NOx emissions (Gaihre et al., 2015; Adviento-Borbe and Linquist, 2016), but the mitigation effects varied among regions. Thus further studies are needed to clarify the influence of UDP on nitrification-denitrification processes and green house gas emissions.

placement depth should be chosen cautiously because the upward movement of NH4+-N could lead to its entry into floodwater. It was suggested that the proper placement depth of N fertilizer is at 10 cm when site-specific information is unavailable, but it is needed to place deeper in sandy loam soil (Mohanty et al., 1998; Liu et al., 2015). Many recommended farming practices in reducing NH3 loss by previous studies, such as N fertilizer broadcasting followed by irrigation, fertilizer incorporation and side-dress or furrow (Fillery et al., 1984; Mohanty et al., 1998; Cai et al., 2002), could result in the movement of most of the N fertilizer into the subsurface soil layer; thus, in fact, these practices are similar to deep placement. Compared to these practices, the point deep placement may be the most effective practice in reducing NH3 loss, due to its better preservation and concentration of N fertilizer beneath rice roots and the reduction of weeds and soil microbes competing with plants for the point deep placed N. Other N loss pathways, such as runoff, N leaching and nitrificationdenitrification processes, may be influenced by UDP. Tian et al. (2007) once reported that the N loss through runoff could reach 0.3–5.8% of the applied N at the same experiment site. UDP may be a promising approach to eliminate N runoff due to the negligible floodwater NH4+N concentration (Fig. 2). Leaching from paddy soil is considered to be minimal in the Taihu Region (Zhu, 1997). An unpublished N leaching experiment conducted at the same experiment site showed that there were no significant differences in the amounts of total N (TN) and NO3−-N leaching between UDP and surface broadcasting treatments; TN leaching only accounted for 2–3% of applied N (4–9 kg N ha−1) under UDP during the rice season, of which NO3−-N and NH3+-N leaching composed 35–76% and 10–24% of TN, respectively. This low percolation rate was consistent with previous studies in the Taihu Region (Tian et al., 2007; Zhao et al., 2012a; Cao et al., 2014), which might be attributed to the formation of a plow pan with low permeability, the relative high clay content in soil, and the low level of floodwater NO3−-N content (< 3 mg N L−1) during the rice season for all treatments (Fig. 2e–f). The 15N fate experiment verified that the 15N loss under RNDP was apparently lowered by 38% over surface broadcasting, but 33.1% of the 15N was still unaccounted for the RNDP, therefore, the denitrification may be the major N loss pathway under

4.3. Improving the NRE and rice yield under UDP The UDP treatments significantly increased the rice yield and NRE by 10% and 55% under favorable weather conditions (2015 and 2016 rice seasons) compared with surface broadcasting treatments (Table 5). Similarly, previous studies also noted that the deep placement of N fertilizer could increase the NRE up to 50–70% and improve rice yields by 15–20% over surface broadcasting (Savant and Stangel, 1990; Kapoor et al., 2008; Alam et al., 2013; Huda et al., 2016; Mazid Miah et al., 2016). Rice yields varied yearly among the 3 rice seasons in this study, which might be driven by environmental conditions (e.g., extreme weather, rainfall pattern, solar radiation). In the 2014 rice season, almost all the rice in the UDP and CT plots were lodging at 86 DAF (12 days after flowering), which was caused by a typhoon; thus, grain filling process was failed for lodging plants. As a result, the yields in UDP were not significantly different than that of surface broadcasting 10

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inhibitors could increase plant 15N recovery from 33 to 65%, and reduce N loss from 43 to 18% compared with urea deep placement alone. Thus innovative fertilizers under deep placement may be an alternative approach to further shrink N loss through leaching and denitrification in paddy fields, especially with high percolation rates and course-textured or sandy soils. Therefore, the agronomic, economic, and environmental advantages of deep placement of different types of fertilizers across different rice growing regions with different soil properties are required to obtain more definitive conclusions. In recent decades, demands for food quantity and quality have increased sharply in China due to improved living standards (Peng et al., 2009). However, the potential increase in crop production is constrained by resource scarcity (i.e., land, water, energy, nutrients), increases in wages and migration rates and environmental degradation (Fan et al., 2012). The Chinese government has hope for lowering the N rate while ensuring food security and decreasing environmental harm, and farmers are willing to accept the simplified fertilization method. The UDP may be the fastest and the most practical near-term strategy to break through these constraints in rice fields in China, with less fertilizer, a one-time application and the same conventional water, pesticide and herbicide management as local practices. UDP technology has been widely adopted in lowland paddy rice systems in South Asia, especially in Bangladesh (Mazid Miah et al., 2016). The results of this study also suggest that lodging-resistant rice cultivars should be considered under UDP because lodging risk increases as grain yield improves. The self-cultivated land size in China is small and laborintensive, and scaling UDP technology was inhibited by the laborintensiveness of hand application and once there was no satisfactory applicator in standing water and muddy soil (Mohanty et al., 1998; Wang et al., 2016b). However, placement machinery was successfully developed and improved recently, such as the deep placement applicator, the push type prilled urea applicator, the urea supergranule applicator and the precision hill-drilling machine (Luo et al., 2008; Hoque et al., 2013; Ahamed et al., 2014; Islam et al., 2015; Khatun et al., 2015; Fujii et al., 2016). Notably, in recent applications deeply placed fertilizer with a precision hill-drilling machine has worked well in the paddy fields in 10 provinces in China (Luo et al., 2008; Kargbo et al., 2016). These advancements can enable UDP to become an easily applied and cost-effective technology at the farm level in China. Meanwhile, the medium- and large-sized fertilizer deep placement machines combined with a rice transplanter should be developed and provided by government subsidies to facilitate the operation of large farms and improve production efficiency. On the other hand, the land institutions in China should be more flexible to allow farms to be enlarged through active land rental markets, which will facilitate the expansion of mechanization.

in 2014, and the yields in 2014 were significant lower than those in 2015 and 2016. Obviously, only reducing the N dose under surface broadcasting (RN) could not attain a higher yield and NUE (Table 5). Equally as important, the RNDP treatment achieved these benefits with a 25% reduction in the N dose. It has been widely recognized that increasing pre-heading N accumulation, post-heading dry matter accumulation and post-heading N redistribution is essential to improve the NUE and rice yield (Ntanos and Koutroubas, 2002; Jiang et al., 2004; Kamiji et al., 2011). Changing the N application method from surface broadcasting to deep placement increased the nutrient content in the root zone (Figs. 3, 4). UDP significantly increased plant N uptake by 28% compared with surface broadcasting treatments in the 3 years (Table 5), and the 15N uptake by the plant under RNDP was significantly higher by 62% than surface broadcasting (Table 6), indicating that deep placement of urea could greatly enhance fertilizer N uptake. UDP could maintain a high NH4+-N content in the root zone during the early growth stage (Fig. 3). When roots encounter a nutrient-rich zone, they can enhance its proliferation and nutrient capture capabilities (Hodge, 2004), and a continuous higher N supply during the early growth stage can result in higher tiller numbers, panicle and spikelet numbers and aboveground biomass (Sheehy et al., 1998; Liu et al., 2016b). In contrast, when urea was broadcast onto surface water, it was easily hydrolyzed to NH4+ and lost through NH3 volatilization and runoff, especially at early rice growing stage, because rice plants are too small and require about 1–2 weeks for the establishment and development of sufficient root systems and a substantial demand for N (Savant and Stangel, 1990; Linquist et al., 2013). It was found that the highest NH4+-N concentration under surface broadcasting only occurred at the soil surface layer, and the soil NH4+-N lasted a shorter time in surface soil than UDP (Liu et al., 2016b), thus traditional surface broadcasting is not effective for improving plant N uptake and N utilization efficiency. Moreover, NH4+-N could prolong the duration of N availability for 2 months (Fig. 3). It was considered that the maximum N uptake appears between mid-tillering and 10 days after panicle initiation; after this stage, plant N uptake becomes much smaller (Ntanos and Koutroubas, 2002). The panicle initiation occurred at 55 DAF in this study, thus the high N uptake at this stage explained why the NH4+-N content sharply decreased between 15 DAF and 63 DAF. The enhanced N uptake before the panicle initiation stage could have a positive effect on N translocation and dry matter accumulation at the ripening stage, thus higher yields under UDP were produced over surface broadcasting under favorable weather conditions. Furthermore, the high N utilization efficiency and grain yield under point UDP may contribute to the reduction of the use of point deep placed N by weeds and microbes, and the point UDP can reduce the NH4+ fixation and immobilization in soil (Mohanty et al., 1998). Meanwhile, UDP can stimulate biological N fixation (BNF) in rice fields because the floodwater NH4+-N concentration remained low during the rice season (Roger et al., 1980). Therefore, N fertilizer deep placement should be given more attention and be recommended as an optimal fertilization pattern for paddy fields. The placement of innovative fertilizers (urea supergranule, NPK briquette, controlled-release fertilizer, urease inhibitor and nitrification inhibitor) can provide an innovative way to improve the NUE and rice yields, which can induce greater N uptake, increased fertilizer recovery and improved fertilizer use efficiency (Soliman and Monem, 1996; Mohanty et al., 1998; Afroz et al., 2014; Das et al., 2016). The innovative fertilizers under surface broadcasting can significantly increase N uptake and rice yield and reduce N loss (Rahman et al., 2016; Xia et al., 2016); thus, it is considered that the deep placement of innovative fertilizers may perform better than deep placement of urea alone (Kapoor et al., 2008; Afroz et al., 2014; Bandaogo et al., 2014; Das et al., 2016), due to its further slow release or the inhibition of urea hydrolysis or nitrification. Soliman and Monem (1996) found that urea deep placement combined with urease inhibitors and nitrification

5. Conclusions UDP had a great potential for eliminating NH3 volatilization and was compatible with improving the NUE and rice yield in a highly fertilized Chinese paddy rice system. The UDP treatments produced negligible floodwater NH4+-N; thus, the seasonally cumulative NH3 volatilization was negligible. Deep-placed urea could supply a high soil NH4+-N level during early rice growth stage and prolong the duration of N availability for 2 months, which remarkably enhanced plant 15N uptake and reduced 15N loss. Therefore, UDP had an advantage in preventing N loss, especially NH3 volatilization in intensive paddy rice systems. While the RNDP treatment (225 kg N ha−1) with a 25% reduction in the N dose could achieve these advantages simultaneously and result in the lowest N surplus. The government should support the development of medium- and large-sized, low-cost deep fertilizer placement applicators and encourage farmers to adopt new technologies to expand the use of UDP technology nationwide.

11

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Gaihre, Y.K., Singh, U., Islam, S.M.M., Huda, A., Islam, M.R., Satter, M.A., Sanabria, J., Islam, M.R., Shah, A.L., 2015. Impacts of urea deep placement on nitrous oxide and nitric oxide emissions from rice fields in Bangladesh. Geoderma 259–260, 370–379. Gu, B., Ge, Y., Ren, Y., Xu, B., Luo, W., Jiang, H., Gu, B., Chang, J., 2012. Atmospheric reactive nitrogen in China: sources, recent trends, and damage costs. Environ. Sci. Technol. 46, 9420–9427. Hakeem, K.R., Ahmad, A., Iqbal, M., Gucel, S., Ozturk, M., 2011. Nitrogen-efficient rice cultivars can reduce nitrate pollution. Environ. Sci. Pollut. Res. 18, 1184–1193. Hauck, R.D., Bremner, J.M., 1976. Use of Tracers for Soil and Fertilizer Nitrogen Research. In: Brady, N.C. (Ed.), Adv. Agron. Academic Press, pp. 219–266. Hodge, A., 2004. The plastic plant: root responses to heterogeneous supplies of nutrients. New Phytol. 162, 9–24. Hofmeier, M., Roelcke, M., Han, Y., Lan, T., Bergmann, H., Böhm, D., Cai, Z., Nieder, R., 2015. Nitrogen management in a rice–wheat system in the Taihu Region: recommendations based on field experiments and surveys. Agric. Ecosyst. Environ. 209, 60–73. Hoque, M.A., Wohab, M.A., Hossain, M.A., Saha, K.K., Hassan, M.S., 2013. Improvement and evaluation of BARI USG applicator. Agric. Eng. Int.: CIGR J. 15. Huang, S., Lv, W., Bloszies, S., Shi, Q., Pan, X., Zeng, Y., 2016. Effects of fertilizer management practices on yield-scaled ammonia emissions from croplands in China: a meta-analysis. Field Crops Res. 192, 118–125. Huda, A., Gaihre, Y.K., Islam, M.R., Singh, U., Islam, M.R., Sanabria, J., Satter, M.A., Afroz, H., Halder, A., Jahiruddin, M., 2016. Floodwater ammonium, nitrogen use efficiency and rice yields with fertilizer deep placement and alternate wetting and drying under triple rice cropping systems. Nutr. Cycling Agroecosyst. 104, 53–66. Islam, A.S., Rahman, M.A., Rahman, A.L., Islam, M.T., Rahman, M.I., 2015. Field performance evaluation of push type prilled urea applicator in rice cultivation. Bangladesh Rice J. 19, 71–81. Jiang, L., Dai, T., Jiang, D., Cao, W., Gan, X., Wei, S., 2004. Characterizing physiological N-use efficiency as influenced by nitrogen management in three rice cultivars. Field Crops Res. 88, 239–250. Ju, X.T., Xing, G.X., Chen, X.P., Zhang, S.L., Zhang, L.J., Liu, X.J., Cui, Z.L., Yin, B., Christie, P., Zhu, Z.L., Zhang, F.S., 2009. Reducing environmental risk by improving N management in intensive Chinese agricultural systems. Proc. Natl. Acad. Sci. 106, 3041–3046. Kamiji, Y., Yoshida, H., Palta, J.A., Sakuratani, T., Shiraiwa, T., 2011. N applications that increase plant N during panicle development are highly effective in increasing spikelet number in rice. Field Crops Res. 122, 242–247. Kang, Y., Liu, M., Song, Y., Huang, X., Yao, H., Cai, X., Zhang, H., Kang, L., Liu, X., Yan, X., He, H., Zhang, Q., Shao, M., Zhu, T., 2016. High-resolution ammonia emissions inventories in China from 1980 to 2012. Atmos. Chem. Phys. 16, 2043–2058. Kapoor, V., Singh, U., Patil, S.K., Magre, H., Shrivastava, L.K., Mishra, V.N., Das, R.O., Samadhiya, V.K., Sanabria, J., Diamond, R., 2008. Rice growth, grain yield, and floodwater nutrient dynamics as affected by nutrient placement method and rate. Agron. J. 100, 526. Kargbo, M.B., Pan, S., Mo, Z., Wang, Z., Luo, X., Tian, H., Hossain, M.F., Ashraf, U., Tang, X., 2016. Physiological basis of improved performance of super rice (Oryza sativa) to deep placed fertilizer with precision hill-drilling machine. Int. J. Agric. Biol. 18, 797–804. Khalil, M.I., Buegger, F., Schraml, M., Gutser, R., Richards, K.G., Schmidhalter, U., 2009. Gaseous nitrogen losses from a cambisol cropped to spring wheat with urea sizes and placement depths. Soil Sci. Soc. Am. J. 73, 1335–1344. Khatun, A., Sultana, H., Zaman, M.A.U., Pramanik, S., Rahman, M.A., 2015. Urea deep placement in rice as an option for increasing nitrogen use efficiency. OALib 02, 1–11. Lin, D.X., Fan, X.H., Hu, F., Zhao, H.T., Luo, J.F., 2007. Ammonia volatilization and nitrogen utilization efficiency in response to urea application in rice fields of the Taihu Lake Region, China. Pedosphere 17, 639–645. Lin, Z.C., Dai, Q.G., Ye, S.C., Wu, F.G., Jia, Y.S., Chen, J.D., Xu, L.S., Zhang, H.C., Huo, Z.Y., Xu, K., Wei, H.Y., 2012. Effects of nitrogen application levels on ammonia volatilization and nitrogen utilization during rice growing season. Rice Sci. 19, 125–134. Linquist, B.A., Liu, L., van Kessel, C., van Groenigen, K.J., 2013. Enhanced efficiency nitrogen fertilizers for rice systems: meta-analysis of yield and nitrogen uptake. Field Crops Res. 154, 246–254. Liu, J.G., Diamond, J., 2005. China's environment in a globalizing world. Nature 435, 1179–1186. Liu, T.Q., Fan, D.J., Zhang, X.X., Chen, J., Li, C.F., Cao, C.G., 2015. Deep placement of nitrogen fertilizers reduces ammonia volatilization and increases nitrogen utilization efficiency in no-tillage paddy fields in central China. Field Crops Res. 184, 80–90. Liu, X., Vitousek, P., Chang, Y., Zhang, W., Matson, P., Zhang, F., 2016a. Evidence for a historic change occurring in China. Environ. Sci. Technol. 50, 505–506. Liu, X.W., Wang, H.Y., Zhou, J.M., Hu, F.Q., Zhu, D.J., Chen, Z.M., Liu, Y.Z., 2016b. Effect of N fertilization pattern on rice yield, N use efficiency and fertilizer-N fate in the Yangtze River basin, China. PLoS One 11, e0166002. Luo, X.W., Jiang, E.C., Wang, Z.M., Tang, X.R., Li, J.H., Chen, W.T., 2008. Precision rice hill-drop drilling machine. Trans. Chin. Soc. Agric. Eng. 24, 52–56 (in Chinese). Mazid Miah, M.A., Gaihre, Y.K., Hunter, G., Singh, U., Hossain, S.A., 2016. Fertilizer deep placement increases rice production: evidence from farmers’ fields in southern Bangladesh. Agron. J. 108, 805. Mikkelsen, D.S., De Datta, S.K., Obcemea, W.N., 1978. Ammonia volatilization losses from flooded rice soils. Soil Sci. Soc. Am. J. 42, 725–730. Mohanty, S.K., Singh, U., Balasubramanian, V., Jha, K.P., 1998. Nitrogen deep-placement technologies for productivity, profitability, and environmental quality of rainfed lowland rice systems. Nutr. Cycling Agroecosyst. 53, 43–57. Nkebiwe, P.M., Weinmann, M., Bar-Tal, A., Müller, T., 2016. Fertilizer placement to improve crop nutrient acquisition and yield: a review and meta-analysis. Field Crops

Acknowledgments This research was financially supported by the National Key Research and Development Project of China (2016YFC0207906) and the National Basic Research Program (973) of China (Grant No. 2013CB127400). We wish to thank our cooperators from the Changshu Agroecosystem Experimental Station for the help of conducting and managing the field experiments. References Adviento-Borbe, M.A.A., Linquist, B., 2016. Assessing fertilizer N placement on CH4 and N2O emissions in irrigated rice systems. Geoderma 266, 40–45. Afroz, H., Islam, M.R., Islam, M.R., 2014. Floodwater nitrogen, rice yield and N use efficiency as influenced by deep placement of nitrogenous fertilizers. J. Environ. Sci. Nat. Resour. 7, 207–213. Ahamed, M.S., Ziauddin, A.T.M., Sarker, R.I., 2014. Design of improved urea super granule applicator. Int. J. Appl. Sci. Eng. Res. 3, 98–100. Alam, M.M., Karim, M.R., Ladha, J.K., 2013. Integrating best management practices for rice with farmers’ crop management techniques: a potential option for minimizing rice yield gap. Field Crops Res. 144, 62–68. Bandaogo, A., Bidjokazo, F., Youl, S., Safo, E., Abaidoo, R., Andrews, O., 2014. Effect of fertilizer deep placement with urea supergranule on nitrogen use efficiency of irrigated rice in Sourou Valley (Burkina Faso). Nutr. Cycling Agroecosyst. 102, 79–89. Behera, S.N., Sharma, M., Aneja, V.P., Balasubramanian, R., 2013. Ammonia in the atmosphere: a review on emission sources, atmospheric chemistry and deposition on terrestrial bodies. Environ. Sci. Pollut. Res. 20, 8092–8131. Buresh, R.J., Reddy, K.R., van Kessel, C., 2008. Nitrogen transformations in submerged soils. In: Schepers, J.S., Raun, W.R. (Eds.), Nitrogen in Agricultural Systems. ASA, CSSA, and SSSA, Madison, WI, pp. 401–436. Cai, G.X., Freney, J.R., Humphreys, E., Denmead, O.T., Samson, M., Simpson, J.R., 1988. Use of surface films to reduce ammonia volatilization from flooded rice fields. Aust. J. Agr. Res. 39, 177–186. Cai, G.X., Chen, D.L., Ding, H., Pacholski, A., Fan, X.H., Zhu, Z.L., 2002. Nitrogen losses from fertilizers applied to maize, wheat and rice in the North China Plain. Nutr. Cycling Agroecosyst. 63, 187–195. Cao, Y.S., Tian, Y.H., Yin, B., Zhu, Z.L., 2013. Assessment of ammonia volatilization from paddy fields under crop management practices aimed to increase grain yield and N efficiency. Field Crops Res. 147, 23–31. Cao, Y., Tian, Y., Yin, B., Zhu, Z., 2014. Improving agronomic practices to reduce nitrate leaching from the rice–wheat rotation system. Agric. Ecosyst. Environ. 195, 61–67. Chauhan, H.S., Mishra, B., 1989. Ammonia volatilization from a flooded rice field fertilized with amended urea materials. Fert. Res. 19, 57–63. Chen, X., Wu, H., Wo, F., 2007. Nitrate vertical transport in the main paddy soils of Tai Lake region, China. Geoderma 142, 136–141. Chen, G., Chen, Y., Zhao, G., Cheng, W., Guo, S., Zhang, H., Shi, W., 2015. Do high nitrogen use efficiency rice cultivars reduce nitrogen losses from paddy fields? Agric. Ecosyst. Environ. 209, 26–33. Chen, M., Sun, F., Shindo, J., 2016. China’s agricultural nitrogen flows in 2011: environmental assessment and management scenarios. Resour. Conserv. Recyl. 111, 10–27. Cui, Z.L., Wang, G.L., Yue, S.C., Wu, L., Zhang, W.F., Zhang, F.S., Chen, X.P., 2014. Closing the N-use efficiency gap to achieve food and environmental security. Environ. Sci. Technol. 48, 5780–5787. Das, S., Islam, M.R., Sultana, M., Afroz, H., Hashem, M.A., 2016. Effect of deep placement of nitrogen fertilizers on rice yield and N use efficiency under water regimes. SAARC J. Agric. 13, 161–172. De Datta, S.K., Obcemea, W.N., Real, J.G., Trevitt, A.C.F., Freney, J.R., Simpson, J.R., 1989. Measuring nitrogen losses from lowland rice using bulk aerodynamic and nitrogen-15 balance methods. Soil Sci. Soc. Am. J. 53, 1275–1281. Eriksen, A.B., Kjeldby, M., Nilsen, S., 1985. The effect of intermittent flooding on the growth and yield of wetland rice and nitrogen-loss mechanism with surface applied and deep placed urea. Plant Soil 84, 387–401. FAO, 2013. Database-Agriculture Production. Food and Agriculture Organization of the United Nation, Rome. Fan, M., Shen, J., Yuan, L., Jiang, R., Chen, X., Davies, W.J., Zhang, F., 2012. Improving crop productivity and resource use efficiency to ensure food security and environmental quality in China. J. Exp. Bot. 63, 13–24. Fang, M., Chan, C.K., Yao, X.H., 2009. Managing air quality in a rapidly developing nation. China. Atmos. Environ. 43, 79–86. Fillery, I.R.P., Simpson, J.R., De Datta, S.K., 1984. Influence of field environment and fertilizer management on ammonia loss from flooded rice. Soil Sci. Soc. Am. J. 48, 914–920. Foley, J.A., Ramankutty, N., Brauman, K.A., Cassidy, E.S., Gerber, J.S., Johnston, M., Mueller, N.D., O’Connell, C., Ray, D.K., West, P.C., Balzer, C., Bennett, E.M., Carpenter, S.R., Hill, J., Monfreda, C., Polasky, S., Rockström, J., Sheehan, J., Siebert, S., Tilman, D., Zaks, D.P.M., 2011. Solutions for a cultivated planet. Nature 478, 337–342. Fujii, T., Hasegawa, H., Ohyama, T., Sinegovskaya, V.T., 2016. Evaluation of tillage efficiency and power requirements for a deep-placement fertilizer applicator with reverse rotational rotary. Russ. Agr. Sci. 41, 498–503.

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Field Crops Research xxx (xxxx) xxx–xxx

Y. Yao et al.

Blackall, T.D., Milford, C., Flechard, C.R., Loubet, B., Massad, R., Cellier, P., Personne, E., Coheur, P.F., Clarisse, L., Van Damme, M., Ngadi, Y., Clerbaux, C., Skjoth, C.A., Geels, C., Hertel, O., Wichink Kruit, R.J., Pinder, R.W., Bash, J.O., Walker, J.T., Simpson, D., Horvath, L., Misselbrook, T.H., Bleeker, A., Dentener, F., de Vries, W., 2013. Towards a climate-dependent paradigm of ammonia emission and deposition. Philos. T. R. Soc. B 368, 20130166. Tian, Y.-H., Yin, B., Yang, L.-Z., Yin, S.-X., Zhu, Z.-L., 2007. Nitrogen runoff and leaching losses during rice-wheat rotations in Taihu Lake Region, China. Pedosphere 17, 445–456. Tilman, D., Cassman, K.G., Matson, P.A., Naylor, R.S.P., 2002. Nature-agricultural sustainability and intensive production practices. Nature 418, 671–677. Tilman, D., Balzer, C., Hill, J., B.B, L., 2011. Global food demand and the sustainable intensification of agriculture. Proc. Natl. Acad. Sci. 108, 20260–20264. van Noordwijk, M., Brussaard, L., 2014. Minimizing the ecological footprint of food: closing yield and efficiency gaps simultaneously? Curr. Opion. Env. Sust. 8, 62–70. Vlek, P.L.G., Craswell, E.T., 1979. Effect of nitrogen source and management on ammonia volatilization losses from flooded rice-soil systems. Soil Sci. Soc. Am. J. 43, 352–358. Wang, H.H., Hegazy, A.M., Jiang, X., Hu, Z.Y., Lu, J., Mu, J., Zhang, X.R., Zhu, X.Q., 2016a. Suppression of ammonia volatilization from rice-wheat rotation fields amended with controlled-release urea and urea. Agron. J. 108, 1214. Wang, X.B., Yamauchi, F., Otsuka, K., Huang, J.K., 2016b. Wage growth, landholding, and mechanization in Chinese agriculture. World Dev. 86, 30–45. World Bank, 2007. Monitory of Environmental Protection of China (MEPC). Cost of Pollution in China: Economic Estimates of Physical Damages. World Bank, Washington, DC. Wu, L., Chen, X.P., Cui, Z.L., Wang, G.L., Zhang, W.F., 2015. Improving nitrogen management via a regional management plan for Chinese rice production. Environ. Res. Lett. 10, 095011. Xia, L., Lam, S.K., Chen, D., Wang, J., Tang, Q., Yan, X., 2016. Can knowledge-based N management produce more staple grain with lower greenhouse gas emission and reactive nitrogen pollution? A meta-analysis. Global Change Biol. 23, 1917–1925. Xu, Q., Lu, Y.C., Liu, Y.C., Zhu, H.G., 1980. Paddy soil of Tai-Lake Region in China. China Science Press, Shanghai (in Chinese). Xu, J.Z., Peng, S.Z., Yang, S.H., Wang, W.G., 2012. Ammonia volatilization losses from a rice paddy with different irrigation and nitrogen managements. Agr. Water Manage. 104, 184–192. Zhao, X., Xie, Y.X., Xiong, Z.Q., Yan, X.Y., Xing, G.X., Zhu, Z.L., 2009. Nitrogen fate and environmental consequence in paddy soil under rice-wheat rotation in the Taihu lake region, China. Plant Soil 319, 225–234. Zhao, X., Zhou, Y., Min, J., Wang, S.Q., Shi, W.M., Xing, G.X., 2012a. Nitrogen runoff dominates water nitrogen pollution from rice-wheat rotation in the Taihu Lake region of China. Agric. Ecosyst. Environ. 156, 1–11. Zhao, X., Zhou, Y., Wang, S.Q., Xing, G.X., Shi, W.M., Xu, R.K., Zhu, Z.L., 2012b. Nitrogen balance in a highly fertilized rice-wheat double-cropping system in southern China. Soil Sci. Soc. Am. J. 76, 1068–1078. Zhao, M., Tian, Y.H., Ma, Y.C., Zhang, M., Yao, Y.L., Xiong, Z.Q., Yin, B., Zhu, Z.L., 2015. Mitigating gaseous nitrogen emissions intensity from a Chinese rice cropping system through an improved management practice aimed to close the yield gap. Agric. Ecosyst. Environ. 203, 36–45. Zhu, Z.L., 1997. Nitrogen Balance and Cycling in Agroecosystems of China. Nitrogen in Soils of China, Netherlands, pp. 323–338.

Res. 196, 389–401. Novozamsky, I., Eck, R., van Schouwenburg, J.C., van Walinga, I., 1974. Total nitrogen determination in plant material by means of the indophenol-blue method. Neth. J. Ag. Sci. 22, 3–5. Ntanos, D.A., Koutroubas, S.D., 2002. Dry matter and N accumulation and translocation for Indica and Japonica rice under Mediterranean conditions. Field Crops Res. 74, 93–101. Otsuka, K., 2013. Food insecurity, income inequality, and the changing comparative advantage in world agriculture. Agric. Econ. 44, 7–18. Patel, S.K., Panda, D., Mohanty, S.K., 1989. Relative ammonia loss from urea-based fertilizers applied to rice under different hydrological situations. Fert. Res. 19, 113–119. Paulot, F., Jacob, D.J., Pinder, R.W., Bash, J.O., Travis, K., Henze, D.K., 2014. Ammonia emissions in the United States, European Union, and China derived by highresolution inversion of ammonium wet deposition data: interpretation with a new agricultural emissions inventory (MASAGE_NH3). J. Geophys. Res. –Atmos. 119, 4343–4364. Peng, S., Tang, Q., Zou, Y., 2009. Current status and challenges of rice production in China. Plant Prod. Sci. 12, 3–8. Power, A.G., 2010. Ecosystem services and agriculture: tradeoffs and synergies. Philos. T. R. Soc. B 365, 2959–2971. Rahman, M.M., Samanta, S.C., Rashid, M.H., Abuyusuf, M., Hassan, M.Z., Sukhi, K.F.N., 2016. Urea super granule and NPK briquette on growth and yield of different varieties of Aus rice in tidal ecosystem. Asian J. Crop Sci. 8, 1–12. Ray, D.K., Ramankutty, N., Mueller, N.D., West, P.C., Foley, J.A., 2012. Recent patterns of crop yield growth and stagnation. Nat.Commun 3, 1293. Rochette, P., Angers, D.A., Chantigny, M.H., Gasser, M.-O., MacDonald, J.D., Pelster, D.E., Bertrand, N., 2013. Ammonia volatilization and nitrogen retention: how deep to incorporate urea? J. Environ. Qual. 42, 1635–1642. Roger, P.A., Kulasooriya, S.A., Tirol, A.C., Craswell, E.T., 1980. Deep placement: a method of nitrogen fertilizer application compatible with algal nitrogen fixation in wetland rice soils. Plant Soil 57, 137–142. Savant, N.K., Stangel, P.J., 1990. Deep placement of urea supergranules in transplanted rice: principles and practices. Fert. Res. 25, 1–83. Sheehy, J.E., Dionora, M.J.A., Mitchell, P.L., Peng, S., Cassman, K.G., Lemaire, G., Williams, R.L., 1998. Critical nitrogen concentrations: implications for high-yielding rice (Oryza sativa L.) cultivars in the tropics. Field Crops Res. 59, 31–41. Shi, W.M., Xu, W.F., Li, S.M., Zhao, X.Q., Dong, G.Q., 2009. Responses of two rice cultivars differing in seedling-stage nitrogen use efficiency to growth under lownitrogen conditions. Plant Soil 326, 291. Soliman, S.M., Monem, M.A.S.A., 1996. Effect of method of N-application and modified urea on N-15 recovery by rice. In: Rodriguez-Barrueco, C. (Ed.), Fertilizers and Environment: Proceedings of the International Symposium Fertilizers and Environment, Held in Salamanca, Spain, 26–29, September, 1994. Springer Netherlands, Dordrecht, pp. 211–216. Sun, H.J., Zhang, H.L., Min, J., Feng, Y.F., Shi, W.M., 2015. Controlled-release fertilizer, floating duckweed, and biochar affect ammonia volatilization and nitrous oxide emission from rice paddy fields irrigated with nitrogen-rich wastewater. Paddy Water Environ. 14, 105–111. Sutton, M.A., Reis, S., Riddick, S.N., Dragosits, U., Nemitz, E., Theobald, M.R., Tang, Y.S., Braban, C.F., Vieno, M., Dore, A.J., Mitchell, R.F., Wanless, S., Daunt, F., Fowler, D.,

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