moderate wetting and drying increases rice yield …moderate wetting and drying increases rice yield...

T H E C R O P J O U R N A L X X ( 2 0 1 6 ) X X X – X X X

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Moderate wetting and drying increases rice yield and reduceswater use, grain arsenic level, and methane emission

Jianchang Yanga,⁎, Qun Zhoua, Jianhua Zhangb

aKey Laboratory of Crop Genetics and Physiology of Jiangsu Province/Co-Innovation Center for Modern Production Technology of Grain Crops,Yangzhou University, Yangzhou 225009, ChinabSchool of Life Sciences and State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Hong Kong, China

A R T I C L E I N F O

Abbreviations: AGP, ADP glucose pyrophosgases; GWP, global warming potential; HNI, nuse efficiency; ROA, root oxidation activity; Ssucrose synthase; SWP, soil water potential;⁎ Corresponding author.E-mail address: [email protected] (J. YanPeer review under responsibility of Crop

http://dx.doi.org/10.1016/j.cj.2016.06.0022214-5141/© 2016 Crop Science Society of Chopen access article under the CC BY-NC-ND

Please cite this article as: J. Yang, et al.,Moand methane emission, The Crop Journal

A B S T R A C T

Article history:Received 28 April 2016Received in revised form30 May 2016Accepted 1 June 2016Available online 5 July 2016

To meet the major challenge of increasing rice production to feed a growing populationunder increasing water scarcity, many water-saving regimes have been introduced inirrigated rice, such as an aerobic rice system, non-flooded mulching cultivation, andalternate wetting and drying (AWD). These regimes could substantially enhance wateruse efficiency (WUE) by reducing irrigation water. However, such enhancements greatlycompromise grain yield. Recent work has shown that moderate AWD, in whichphotosynthesis is not severely inhibited and plants can rehydrate overnight during thesoil drying period, or plants are rewatered at a soil water potential of −10 to −15 kPa, ormidday leaf potential is approximately −0.60 to −0.80 MPa, or the water table is maintainedat 10 to 15 cm below the soil surface, could increase not only WUE but also grain yield.Increases in grain yield WUE under moderate AWD are due mainly to reduced redundantvegetative growth; improved canopy structure and root growth; elevated hormonal levels,in particular increases in abscisic acid levels during soil drying and cytokinin levels duringrewatering; and enhanced carbon remobilization from vegetative tissues to grain. ModerateAWD could also improve rice quality, including reductions in grain arsenic accumulation,and reduce methane emissions from paddies. Adoption of moderate AWD with anappropriate nitrogen application rate may exert a synergistic effect on grain yield andresult in higher WUE and nitrogen use efficiency. Further research is needed to understandroot–soil interaction and evaluate the long-term effects of moderate AWD on sustainableagriculture.© 2016 Crop Science Society of China and Institute of Crop Science, CAAS. Production and

hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Keywords:Alternate wetting and drying (AWD)Grain yieldNitrogen use efficiencyRiceWater use efficiency

phorylase; AWD, alternate wetting and drying; CI, conventional irrigation; GHG, greenhouseitrogen harvest index; LWP, leaf water potential; IEN, internal N use efficiency; NUE, nitrogenBE, starch branching enzyme; SPS, sucrose-phosphate synthase; StS, starch synthase; SuS,WUE, water use efficiency; Z, zeatin; ZR, zeatin riboside.

g).Science Society of China and Institute of Crop Science, CAAS.

ina and Institute of Crop Science, CAAS. Production and hosting by Elsevier B.V. This is anlicense (http://creativecommons.org/licenses/by-nc-nd/4.0/).

deratewetting anddrying increases rice yield and reduceswater use, grain arsenic level,(2016), http://dx.doi.org/10.1016/j.cj.2016.06.002

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2 T H E C R O P J O U R N A L X X ( 2 0 1 6 ) X X X – X X X

1. Introduction

Global agriculture in the 21st century faces the tremendouschallenge of providing sufficient and healthy food for agrowing population under increasing water scarcity, whileminimizing environmental consequences [1–3]. Rice (Oryzasativa L.) is one of the most important food crops in the worldand is consumed by more than 3 billion people [4]. It isestimated that, by the year 2025, it will be necessary toproduce about 60%more rice than currently produced to meetfood needs [4,5]. About 75% of total rice production comesfrom irrigated lowlands [5,6]. Irrigated rice accounts for about80% of the total fresh water resources used for irrigation inAsia [7]. Fresh water for irrigation, however, is becomingincreasingly scarce because of population growth, increasingurban and industrial development, and decreasing availabilityresulting from pollution and resource depletion [1,8]. Ricefields have been identified as an important source ofatmospheric methane (CH4), one of the major potent green-house gases (GHG), and contribute approximately 15–20% ofglobal anthropogenic CH4 emissions [9,10]. Nitrous oxide(N2O), another potent GHG, may be emitted from rice fieldsas a combined effect of nitrogen (N) fertilization and watermanagement [11–13]. Furthermore, there have been recenthealth concerns associated with arsenic (As) concentrationsin rice grain [3,14–16]. In certain parts of the world, As con-centrations in rice grain are high and exert adverse healtheffects [3,14–17].

These concerns posed by rice may be addressed bychanges in water management, in particular from continu-ously flooded anaerobic systems to those in which aerobiccycles are introduced periodically during the growing season.This regime is often referred to as alternate wetting anddrying (AWD) [3,18,19]. It is proposed [20,21] that adoption ofmoderate AWD such that soil drying in the AWD regime iscontrolled properly, plant water status is not adverselyaffected during the drying period, and an appropriate nitrogenapplication rate is used can result in a synergistic effect onrice yield and in high WUE and nitrogen use efficiency (NUE).It would advance the development of sustainable agricultureto disseminate the effectiveness of moderate AWD, identifythe mechanism by whichmoderate AWD increases both grainyield and WUE, and elucidate the effects of interaction

Table 1 – Increase (+) or decrease (−) in grain yield, water use effemission of greenhouse gases (GHG) from paddy field under altunder conventional irrigation in rice (unit: %).

Item Moderate AWD

Grain yield 5.6 to 12.8Irrigation water −22.4 to −34.6WUE (grain yield/irrigation water) 27.3 to 55.7Head rice 5.6 to 12.8Chalkiness −1.2 to −3.4Amylose content −0.4 to 0.7As in grain −50.3 to −66.5CH4 −51.4 to −72.5N2O 15.5 to 98.6Global warming potential (GWP) −48.6 to −67.2GHG index (GWP/grain yield) −48.3 to −78.9

Please cite this article as: J. Yang, et al.,Moderatewetting anddryinand methane emission, The Crop Journal (2016), http://dx.doi.org/

between moderate AWD and N application rates on yield,WUE, and NUE. This review addresses these topics.

2. Effectiveness of water-saving techniques and theirrigation index for moderate AWD

To counter water shortage and increase WUE, many water-saving regimes have been introduced, including an aerobicrice system [22–24], a system of rice intensification [25–27],non-flooded mulching cultivation [28–30], and AWD irrigation[31–33]. These regimes could substantially enhance WUE byreducing irrigation water. However, such enhancement great-ly compromises grain yield [20,22,28,31]. Among these tech-nologies, AWD has been applied mostly in China in an areaof more than 12 million ha each year [18,32–37] and is beingadopted in Asian countries such as Bangladesh, India, ThePhilippines, and Vietnam [1,8,22,31]. It also remains debatablewhether the technology can achieve the dual goals ofincreasing grain yield and saving water [31–38]. The discrep-ancies between studies are attributed to variation in soilhydrological conditions and timing of the irrigation methodsapplied [31–33]. The work of Yang et al. [15,18], Chu et al. [19],and Zhang et al. [33–36] has shown that the drying conditionin AWD is the most important factor affecting yield. Ifmoderate AWD is adopted, such that soil drying in theAWD regime is controlled properly, photosynthesis is notseverely inhibited and plants can rehydrate overnight, such aregime could not only save water but also increase grain yield(Table 1). Furthermore, moderate AWD improves rice quality,including a reduction in As accumulation in grain. It reducesCH4 emissions from the paddy field, thereby decreasing globalwarming potential (GWP) and greenhouse gas intensity (GWP/grain yield) (Table 1). In contrast, a severe AWD regime inwhich photosynthesis is severely inhibited and plants cannotrehydrate overnight during the soil drying period couldmarkedly decrease grain yield and quality, although it alsoincreases WUE and reduces grain As and CH4 emissionfrom paddy fields compared to a continuous flooding regime(Table 1).

The question raised is how to control soil drying properlyand to develop moderate AWD. There are several ways tocontrol soil drying in AWD, such as by fixing the number of

iciency (WUE), grain quality, grain arsenic (As) content, andernate wetting and drying (AWD) irrigation relative to those

Severe AWD Data adapted from references

−18.5 to −35.3 [3], [18–21], [33–36]−38.4 to −49.521.6 to 36.7−18.5 to −35.3 [34]3.2 to 5.3−0.9 to 1.2−54.5 to −70.6 [3,63]−90.7 to −112.8 [3,19]125 to 167−73.1 to −99.5−67.5 to −92.7

g increases rice yield and reduceswater use, grain arsenic level,10.1016/j.cj.2016.06.002


Fig. 1 – Using a polymerized vinyl chloride (PVC) tube to monitor water depth in soil. The inner diameter, outer diameter andlength of a PVC tube are 19, 20, and 40 cm, respectively. Holes 0.5 cm in diameter are drilled in the lower 25 cm at 1 cm verticaland 3 cm lateral intervals. The bottom part of the drilled tube is inserted into the soil to 25 cm depth before rice transplanting,and the soil in the tube is removed. The depth of water in the tube is observed daily. When the water depth in the tube reaches10–15 cm below the soil surface in most growth stages (see Table 2), a thin (2–3 cm) water layer is applied to the field.

3T H E C R O P J O U R N A L X X ( 2 0 1 6 ) X X X – X X X

non-flooding days, setting certain thresholds of leaf waterpotential (LWP), soil moisture content, or soil water potential(SWP), or water table below the soil surface, and observingvisual symptoms in plant leaves and/or soil [31–38]. Theoret-ically, using LWP as an irrigation index is the most accurate ofthese measures because LWP directly reflects plant waterstatus. However, LWP is difficult to determine. Yang et al.[18,39] suggest using SWP as the index for rice irrigation.Although there are several advantages in the use of SWP forwater-saving irrigation, it is difficult for some farmers to usetension meters to monitor SWP. To solve this problem, wehave recently used the water table below the soil surface as anirrigation index by installing a polymerized vinyl chloride(PVC) tube in the soil (Fig. 1). The method using a PVC tube tomonitor water depth in soil is briefly described in the legendto Fig. 1. The depth of water in the PVC tube is observed daily.When the water depth in the PVC tube reaches 10–15 cmbelow the soil surface in most growth stages (Table 2), a thin

Table 2 – Thresholds for alternate wetting and moderate drying

Growth stage

Effective tillering (from recovery to the critical leaf age of productive tilleJointing (from the critical leaf age of productive tillers to panicle initiatioPanicle differentiating (from panicle initiation to the beginning of headinHeading and flowering (from heading to the end of flowering)Early and mid grain filling (7–20 days after headingLate grain filling (21 days after heading to final harvest)

a Irrigation is recommended as soon as the threshold is reached. The upplower threshold is used for hybrid rice or for clay soil. The intermediate vb Data are adapted from references [18,19,21,33,38,39].c Unpublished data.


(2–3 cm) layer of water is applied to the field. Such a methodcan be easily used by farmers.

Owing to the variable sensitivity of rice to soil drying indifferent growth stages [18,40], the thresholds for irrigationshould be adapted to a special growth stage. Table 2 presentsthe thresholds of LWP, SWP, and the water table at eachgrowth stage for moderate AWD. In most growth stages ofrice, the threshold of SWP at −10 to −15 kPa, or midday LWP atapproximately −0.60 to −0.80 MPa, or a water table at 10 to15 cm below the soil surface, could be used as indices formoderate AWD (Table 2). Moderate AWD using the values inTable 2 as irrigation indices has been demonstrated andapplied in the rice-growing areas of the provinces of Jiangsu,Anhui, Jiangxi, Zhenjiang, Shandong, and Henan in China.Compared with conventional irrigation (CI) employing drain-age in midseason and flooding at other times, the moderateAWD technique increased grain yield by 6.1% to 15.2%,reduced irrigation water by 23.4% to 42.6%, and increased

(moderate AWD) irrigation in rice a.

Leaf waterpotential(MPa) b

Soil waterpotential(kPa) b

Water level belowthe soil surface

(cm)c

rs) −0.60 to −0.65 −5 to −10 8 to 12n) −0.85 to −0.90 −15 to −20 15 to 25g) −0.75 to −0.80 −8 to −12 10 to 15

−0.75 to −0.80 −8 to −12 10 to 15−0.95 to −1.00 −10 to −15 12 to 18−1.05 to −1.10 −15 to −20 20 to 25

er threshold applies to japonica inbred cultivars or to sandy soil. Thealue relates to indica inbred cultivars or to loam soil.




water productivity (grain yield per cubic meter of irrigationwater) by 27% to 51% [18,33,41,42].

3. Mechanism by which moderate AWD increasesgrain yield and WUE

The mechanism by which moderate AWD increases grainyield and WUE is not fully understood. Many agronomic andphysiological processes are likely to be involved, such asaltered hormonal levels in rice plants, increase in proportionof productive tillers and decrease in the leaf angle of the topthree leaves at heading time, greater root biomass in deepersoil and higher root oxidation activity (ROA), and an enhance-ment in carbon remobilization from vegetative tissues tokernels [18–21,33,41,42], as summarized in Fig. 2.

Three pointsmerit attention. The first is thatmoderate AWDelevates abscisic acid (ABA) levels in plants during the soildrying period [43–47]. ABA is generally regarded as a verysensitive signal and has been observed to increase duringthe soil drying period [43–48]. It has been proposed that ABAhas a major role in relation to sugar-signaling pathways andenhances the ability of plant tissues to respond to subsequentsugar signals [49]. There are many reports that ABA canenhance the movement of photosynthetic assimilates towardsdeveloping seeds by enhancing activities of sucrose phosphatesynthase (SPS) in stems and sucrose synthase (SuS), ADPglucose pyrophosphorylase (AGP), starch synthase (StS), andstarch branching enzyme (SBE) in kernels [46,47,50,51]. SPS isbelieved to play a major role in the resynthesis of sucrose[52,53]. The significance of enhanced SPS activity by elevatedABA during the soil drying period in moderate AWD is that itcan not only accumulate the disaccharide as a response to thesoil drying, but also sustain the assimilatory carbon fluxes fromsource to sink [52–54]. SuS, AGP, StS, and SBE are generallyconsidered to be key enzymes involved in the sucrose-to-starch

Fig. 2 – The mechanism involved in increases in grain yield, watrice. AWD: alternate wetting and drying; SPS: sucrose phosphate[33–36] and [41–47].


pathway in kernels [55,56], and the activities of these enzymesare significantly correlated with grain filling or starch accumu-lation rates in rice and wheat kernels [36,57–59]. It would beunderstandable that elevated ABA levels in rice plants undermoderate AWDpromote carbon remobilization from vegetativetissues to sink organs and grain filling by enhancing sinkactivity via regulation of the key enzymes involved.

The second point is that a “rewatering” effect has beenobserved in AWD [21,33,35]. In comparison with a CI regime orwith during the soil drying period, moderate AWD markedlyincreases cytokinin levels (zeatin + zeatin riboside) (Z + ZR) inroots and leaves, ROA, and leaf photosynthetic rate during therewatering period (Table 3). Both Z and ZR are believed to bevery active cytokinins in plants and play a major role inpromoting cell division and delaying senescence [60,61]. Highcytokinin concentrations under moderate AWD during grainsetting and filling periodsmay contribute to better grain fillingby promoting endosperm cell division, delaying senescence,and/or regulating key enzymes involved in the sucrose-to-starch pathway in rice kernels [18,35].

The third point is that there is a compensatory effect inAWD. Compared with a CI regime, a moderate AWD regimecan reduce the maximum number of tillers by 21–23% andtotal leaf area by 14%, but the number of productive tillers andeffective leaf area (leaf area of main stems and productivetillers) show no significant difference between the tworegimes [20]. As a result, moderate AWD markedly increasesthe percentage of productive tillers and the proportion ofeffective leaf area. The improved canopy quality would beexpected to reduce the water used in production of un-productive tillers and transpiration from redundant leafarea. Furthermore, reduced redundant vegetative growthand increased carbon remobilization from vegetative tissuesto kernels during grain filling can contribute to a higherharvest index, leading to increases in grain yield and WUE[20,21,33,36].

er and N use efficiencies under moderate AWD irrigation insynthase. The figure is drawn based on references [20,21],



Table 3 – Re-watering effects of alternate wetting and drying (AWD) irrigation on root oxidation activity (ROA),zeatin + zeatin riboside (Z + ZR) content in leaves, and leaf photosynthetic rate (Pr) of rice 1.

Irrigationregime

ROA(μg α-naphthylamine

g−1 DW h−1)

Z + ZR content(pmol g−1 DW)

Pr(μmol m−2 s−1)

D W D W D W

CI 549 a2 545 b 138 a 141 b 21.5 a 21.4 bModerate AWD 536 a 612 a 132 a 169 a 20.9 a 26.8 aSevere AWD 382 b 526 b 101 b 137 b 17.2 b 22.7 b

1 CI, D, and W represent conventional irrigation, soil drying period, and rewatering period, respectively. Data are adapted from references[20,21,35].2 Different letters within the same column indicate significance at the 0.05 probability level.


The mechanism by which an AWD regime decreases grainAs concentrations remains unclear. A likely explanation isthat As can be reduced from As (V) to As (III) under floodedanaerobic soil conditions or in a CI regime, increasing thephytoavailability and uptake of As by rice [62–64]. In contrast,an AWD regime increases soil oxidation potential and therebyinhibits the reduction of As (V) to As (III), consequentlydecreasing As uptake by rice [2,19,63].

4. Effect of interaction betweenmoderate AWD andN application rate on rice yield, WUE, and NUE

Besides water, N is another key factor determining crop yield,and also represents the main input in rice production [65–67].However, the use of N fertilizer is generally inefficient, and theapparent recovery efficiency of N fertilizer (the percentage offertilizer N recovered in aboveground plant biomass at theend of the cropping season) is only 33% on average [68–70].The adoption of AWD-based technologies could reduce totalcumulative plant N and NUE by stimulating N losses throughincreases in ammonia volatilization, nitrification and denitri-fication [8,11,31]. But some researchers [19,21,33,38,42,71]

Table 4 – Grain yield, nitrogen use efficiency, and water usetreatments1.

Irrigationregime

N rate(kg ha−1)

Grain yield(t ha−1)

N uptake(kg ha−1)

CI 100 7.79 f6 109.6 f200 9.26 b 142.7 c300 8.69 d 149.9 b

Moderate AWD 100 8.31 e 112.9 e200 9.81 a 142.0 c300 9.89 a 154.9 a

Severe AWD 100 6.65 h 88.2 g200 8.02 f 114.0 e300 8.72 c 135.5 d

1 CI, moderate AWD, and severe AWD represent conventional irrigation,wetting and severe drying irrigation, respectively. Data are adapted from2 IEN, Internal N use efficiency: grain yield (kg)/N uptake of plants (kg).3 PFPN, Partial factor productivity of applied N: grain yield in N applicatio4 NHI, N Harvest index (%): N in grain (kg)/N uptake of plants (kg) × 100.5 WUE, water use efficiency: grain yield (kg)/(amount of irrigation water6 Different letters indicate statistical significance at the 0.05 probability l


propose that whether AWD irrigation stimulates N lossesdepends on soil drying conditions. Severe AWD could,whereas moderate AWD could not, increase N loss due tothe reduction in vertical NH4

+-N and total N leaching, andaccordingly, could not decrease NUE [19,21,33,71]. It ishypothesized that there would be a synergistic interactionbetween soil moisture and N fertilizer on crop growth if bothwater and N were managed properly, and that such asynergistic interaction would increase crop yield, WUE andNUE [38,72,73].

Recent work of Wang et al. [21] has demonstrated thatgrain yield, WUE, and NUE in rice are determined not only byirrigation regimes but also by their interaction with N rates(Table 4). They conclude that a synergistic water–N inter-action can be achieved by adoption of a moderate AWDregime with a normal amount of N application, consistingof rewatering at SWP of −15 kPa and N rate at 200 kg ha−1

or midday LWP at approximately −0.69 and −0.86 MPa andspecific leaf N content at 2.2–2.3 and 2.0–2.1 g m−2 at earlyand late growth stages, respectively. Such a synergisticinteraction could achieve the goal of increasing grainyield, WUE, and NUE. Reduced redundant vegetative growth,enhanced root and shoot growth, and increased pre-stored

efficiency of rice under various irrigation and nitrogen

IEN 2

(kg kg−1)PFPN3

(kg kg−1)NHI 4

(%)WUE5

(kg m−3)

71.0 b 77.9 b 65.2 a 0.72 e64.9 c 46.3 e 61.7 b 0.85 c57.9 d 29.0 h 56.3 c 0.79 d73.6 a 83.1 a 66.9 a 0.87 c69.1 b 49.1 d 65.1 a 1.01 a63.9 c 33.0 g 61.6 b 1.02 a75.4 a 66.5 c 67.8 a 0.76 d70.3 b 40.1 f 65.7 a 0.91 b64.5 c 29.2 h 61.4 b 0.99 a

alternate wetting and moderate drying irrigation, and alternatereference [21].

n plots (kg)/N rate (kg).

+ precipitation) (m3).evel within the same column.




carbon remobilization from stems during the maturity periodand harvest index contribute to higher grain yield and higherresource use efficiency in a moderate AWD regime with anormal amount of N application. The authors also observedthat a severe AWD regime may save irrigation water, butreduces grain yield, and that increase in N application underthis regime could increase grain yield and WUE.

Interestingly, either a moderate or a severe AWD regimeshows a higher internal NUE (IEN, grain yield/N uptake ofplants) than a CI regime at the same N rate (Table 4). Similarobservations have also been reported by Liu et al. [38], Xueet al. [41], and Chu et al. [42]. The mechanism underlying ahigher IEN in both AWD regimes is not understood. A probableexplanation is that a moderate or severe AWD regime leads toa higher harvest index [18–21]. A higher harvest index meansless N to produce the biomass of vegetative tissues and moreN to produce grain yield [20,21], resulting in a higher IEN.

It is noteworthy that the IEN observed by Wang et al. [21] ishigher than that reported elsewhere under similar experi-mental conditions [68,70]. This higher IEN may be explainedby the separation of the plots in their experiments by analley 1 m wide with plastic film inserted into the soil to adepth of 0.50 m to form a barrier, which could reduce N losscaused by runoff. The higher IEN may also be attributed to areduction in N application at the basal and early vegetativestages and a delayed in-season N application. Such N manage-ment can increase N uptake and accumulation in plants byreducing unproductive tillers and increasing dry matter accu-mulation during the grain filling period, leading to a higher IEN[21,38,41,68].

5. Concluding remarks

The soil drying condition in AWD is the most important factoraffecting rice yield. Adoption of moderate AWD, such thatphotosynthesis is not severely inhibited and plants canrehydrate overnight during the soil drying period, or plants arerewatered at an SWP of −10 to −15 kPa or a midday LWPat approximately −0.60 to −0.80 MPa, or the water table ismaintained at 10 to 15 cm below the soil surface, can notonly save water, but also increase grain yield. Furthermore,moderate AWD can improve rice quality, reduce arsenicaccumulation in grain, and reduce CH4 emission from thepaddy field, thereby decreasing GWP and greenhouse gasintensity. However, a severe AWD regime, in which photosyn-thesis is severely inhibited and plants cannot rehydrateovernight during the soil drying period, maymarkedly decreasegrain yield and quality, although it may also increase WUE andreduce As in grain and CH4 emission from the paddy fieldcompared to a CI regime. Reduced redundant vegetative growthand improved canopy structure, enhanced root growth, namelya greater root biomass in deeper soil and ROA, elevated ABAlevels during the soil drying period, and increased cytokininlevels during the rewatering period, which promote carbonremobilization from vegetative tissues to grain and grain fillingby enhancing the activities of key enzymes involved inresynthesis of sucrose in stems and in the sucrose-to-starchpathway in kernels, contribute to the increases in both grainyield and WUE under moderate AWD. A synergistic water–N


interaction can be achieved by adoption of a moderate AWDregime with an appropriate N application rate. Such a syner-gistic interaction could achieve the goal of increasing grainyield, WUE, and NUE. Several questions including root–shootand root–soil interactions and N losses via ammonia volatiliza-tion, nitrification, and denitrification under water-saving irri-gation; the mechanism involved in rewatering effects andcompensatory effects under AWD; and the long-term effectsof moderate AWD on sustainable agriculture, such as on soilquality, merit further investigation.

Acknowledgments

We are grateful for grants from the National Basic ResearchProgram (973 Program, No. 2012CB114306), the National NaturalScience Foundation of China (Nos. 31461143015; 31271641,31471438), the National Key Technology Support Program ofChina (Nos. 2014AA10A605; 2012BAD04B08), the Priority Aca-demic Program Development of Jiangsu Higher EducationInstitutions (PAPD), the Top Talent Supporting Program ofYangzhou University (No. 2015-01), and Jiangsu CreationProgram for Postgraduate Students (No. KYZZ15_0364).

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moderate wetting and drying increases rice yield …moderate wetting and drying increases rice yield...

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