Characteristics and management options for rice–maize systems in thePhilippines

Field Crops Research 144(2013)52–61

Contents lists available at SciVerse ScienceDirect

Field Crops

Research

j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /f c

r

Characteristics and management options for rice–maize systems in the Philippines

S.M.Haefele ?,N.P.M.Banayo,S.T.Amarante,J.D.L.C.Siopongco,R.L.Mabesa

International Rice Research Institute,DAPO Box 7777,Metro Manila,Philippines

a r t i c l e

i n f o

Article history:

Received 2November 2012

Received in revised form 16January 2013Accepted 17January 2013

Keywords:

Cropping system Drought Maize

Nutrient balance Rice

Topography

a b s t r a c t

In the Philippines,maize (corn)is the second major cereal crop after rice.Around 0.12million ha of maize are grown in rice–maize (R–M)systems,mostly situated in the lowlands,and the area of this system is growing fast.The objectives of this study were to describe the targeted cropping system,to test several management options that could help to optimize it and reduce the production risk,and to develop a simple nutrient balance as a sustainability indicator.For this,we conducted participatory on-farm trials in Pangasinan province,where about 33,600ha of yellow maize are grown,mostly in R–M https://www.360docs.net/doc/b314203576.html,bined grain yields of the system reached 14t ha ?1in the ?rst year and 21t ha ?1in the second year,depending on the treatment.Yield differences were mostly due to climate-induced stresses in the ?rst year and very favorable conditions in the second year.Varietal choice in rice was an option to reduce production losses by selecting the variety according to average ?eld-speci?c characteristics (drought-prone,favorable,?ood-prone).Balanced fertilizer applications reduced stress-dependent rice yield losses considerably,and helped to maximize grain yield in the favorable season.The rice fertilizer treatment without any application caused lower yields in the subsequent maize crop but the effect was not signi?cant.No effects of ?eld topography on soil characteristics or on grain yields of rice or maize were detected.The nutrient balance indicated the considerable danger of soil nutrient mining in this cropping system,which could aggravate possible trends of declining soil organic matter concentrations in R–M systems that have been shown in previous studies.We concluded that a combination of adjusted management components can reduce production risk and optimize system productivity.To maintain system productivity,it seems most promising to combine different management elements,including balanced NPK fertilizer rates with limited PK mining,recycling of waste products from residue use on the farm as much as possible,and only limited removal of residues from the ?elds.

?2013Elsevier B.V.All rights reserved.

1.Introduction

Rice,maize,and wheat are the most important crops for food security in most of Asia.Depending on bio-physical conditions,they are either grown as monocultures or in rotations in speci?c crop-ping systems.In rice-based systems,rice–wheat and rice–maize (R–M)are the dominating mixed cropping systems;rice–wheat is common in South and East Asia whereas smaller areas of R–M sys-tems can be found all over Asia (Timsina et al.,2011).The total maize area in Asia was estimated by the same authors at about 43.8million ha,but only a fraction of this maize is grown in R–M sys-tems (about 3.34million ha).However,these systems are rapidly spreading in some areas because of rising demand,tightening world export–import markets,high market prices for cereals,and in some places because of increasing water shortages and/or costs (Gerpacio

?Corresponding author.

E-mail address:s.haefele@https://www.360docs.net/doc/b314203576.html, (S.M.Haefele).

et al.,2004;Buresh and Haefele,2010;Timsina et al.,2011).Espe-cially in the case of maize demand is changing quickly,globally because to its use for biofuel production and locally because of the rapidly increasing livestock/poultry production.

In the Philippines,maize is the second major cereal crop after rice.About 4.2million ha of rice and 2.6million ha of maize are grown,and the overlapping area of R–M systems is estimated at around 0.12million ha.In these systems,rice is either grown as the wet-season crop followed by maize in the dry season (common in lowlands where abundant water in the wet season favors rice cultivation)or maize is grown in the wet season followed by rice in the dry season (drier lowlands and uplands)(Gerpacio et al.,2004).A third crop might be grown if the conditions are suitable.Timsina et al.(2011)distinguished four main R–M agro-ecosystems,and R–M in the Philippines would mostly ?t into the ?rst agro-ecosystem identi?ed (tropical,warm,humid,and sub-humid,no winter).Long-term trends in the Philippines indicate a mostly decreasing total maize area in the last 40years but an increasing total maize production.These ?gures mask

0378-4290/$–see front matter ?2013Elsevier B.V.All rights reserved.https://www.360docs.net/doc/b314203576.html,/10.1016/j.fcr.2013.01.011

S.M.Haefele et al./Field Crops Research144(2013)52–6153

two different underlying trends:a strongly decreasing area of low-yielding white maize mostly produced for home consumption (human consumption and animal feed)and an increasing area of high-yielding yellow maize mostly sold as animal feed for poultry and livestock production.The national average yield for maize in the Philippines is around1.8t ha?1according to Gerpacio et al.(2004),but this is based on an average of low-yielding white maize(≈1.2t ha?1)and higher-yielding yellow maize(≈2.8t ha?1). Average yield ranges in the Philippines and for modern maize hybrid varieties are between1.6and6.0t ha?1,and the highest yields of5.5–9.0t ha?1were reported from the rainfed lowland environments of Mindoro Occidental.These low average yields and huge yield ranges,as well as the analysis of the climatic-genetic yield potential(Timsina et al.,2011),indicate considerable scope for improving maize production by narrowing the yield gap.

R–M systems offer several advantages for farmers in the Philippines.Even with water-saving technologies for rice cultiva-tion,the water requirements for rice remain higher than for other cereal crops,especially in the dry season when very little rain falls and evaporation losses can be very high.Thus,expensive and/or limited supplies of irrigation water together with opportunities for income from non-rice crops serve as drivers for diversi?cation from a rice monoculture with soil submergence to a rotation of rice with other crops such as maize grown on well-drained aerobic soils.Also, R–M systems can be very productive as the analysis of Timsina et al. (2011)for a site in Laguna,Philippines,showed.Their theoretical analysis showed even higher productivity for maize–rice systems (M–R,maize in the wet season and rice in the dry season)but such a system would probably risk crop loss due to?ooding in the wet season and have very high water requirements in the dry season.

Research efforts to understand and optimize R–M systems in Asia,including a focus on the Philippines,comprise an overview of maize and related cropping systems in the Philippines(Gerpacio et al.,2004),the analysis of optimized systems based on crop modeling conducted by Timsina et al.(2010,2011),and the devel-opment of site-speci?c nutrient recommendations for rice and maize(Witt et al.,2008).The effect of R–M systems on soil organic matter in comparison with rice–rice systems was analyzed by Pampolino et al.(2008).However,?eld data on the performance and management of existing R–M systems in the Philippines are still hard to?nd and are mostly gray literature(e.g.,Pasuquin et al., 2010).

Therefore,we conducted our study in an existing R–M system in Pangasinan,Central Luzon,Philippines.The experiments were conducted on-farm to ensure that the results were relevant for farmers in the region,and to learn from their experience.Our objec-tives were to describe the targeted cropping system,to test several management options that could help to optimize the system and to reduce the production risk,and to develop a simple nutrient balance as a sustainability indicator.

2.Materials and methods

2.1.Site description

Based on available statistics of areas with a signi?cant occur-rence of rainfed rice and R–M systems(PhilRice,2008),we selected the municipalities Sto Tomas,San Nicolas,and Alcala in Pangasinan province,Central Luzon,for our study.The whole region is located in the warm humid tropics with a long rainy season from June to December,a cool dry season from January to March,and a hot dry season from April to May.Mean annual rainfall in the region is about1500mm and the average annual temperature is around 27?C.At each location/town,two collaborating farmers were chosen based on their interest in participating in the experiments and the cultivation of suitable?elds.For the?eld experimentation, we chose together with each farmer two neighboring?elds, representing a lower(wetter)and upper(drier)toposequence position.However,at two sites,the trials succeeded in only one toposequence in2009.An overview of basic site and cropping information is presented in Table1.

Top-soil(0–0.2m)samples were collected from all selected ?elds(a composite sample from?ve sub-samples taken randomly in each?eld)before crop establishment in2009.Samples were analyzed for soil texture(Gee and Or,2002),pH(1:1soil–H2O mix-ture),total soil organic carbon(Nelson and Sommers,1996),total soil N(Bremner,1996),available P(Olsen et al.,1954),exchange-able K(NH4O-Ac extraction;Helmke and Sparks,1996),and cation exchange capacity(Sumner and Miller,1996).

2.2.Experimental layout

In the wet season,two experiments targeting rice were estab-lished on-farm in all?elds:a nutrient management trial and a germplasm evaluation trial.In each?eld(site×toposequence posi-tion),only one replication of treatments was tested,and the same treatments in the same position and season were planned as replications.In the following dry season,maize was grown in all experimental?elds and both experiments followed the cropping system practiced by the farmers in the region.Details for all three trials are given below.

2.2.1.Nutrient management experiment

Five different fertilizer treatments were tested.The treatments were as follows:T1=0-0-0,T2=90-0-0,T3=90-20-0,T4=90-20-20,and T5=90-30-20(all rates in kg N-P2O5-K2O per hectare). Treatment T1represents the control and served to determine yield without fertilizer,T2and T3represent common farmer practices to apply only N or only N and P.Treatment T4represented a best-bet fertilizer rate for the site,the wet season,and a target yield of 4.8t ha?1(determined using the nutrient manager for rice in the Philippines;https://www.360docs.net/doc/b314203576.html,/nm/ph).The higher P rate in T5was meant to test the hypothesis that higher P rates help to reduce drought damage because P is becoming limited?rst under drought (Marschner,1986;Sardans and Pe?nuelas,2004).

Nitrogen was applied basally and topdressed at early tillering and panicle initiation(i.e.,in three splits of20-35-35kg N ha?1). Only urea and ordinary superphosphate(OSP)were used for treat-ments T2and T3.Urea and a common complete fertilizer source (14-14-14)were used for treatments T4and T5,but additional OSP was used for T5.A blanket application of zinc(20kg ZnO ha?1)was used for the entire experimental area at all sites to exclude Zn lim-itation.Maize stubbles from the previous season were plowed in during?eld preparation.

For the nutrient experiment,variety‘Penaranda’(PSBRC82), commonly used by the participating farmers,was planted using transplanting(TPR)as the method of crop establishment.For each treatment,subplots of5m×10m were used,in both the upper and lower toposequence positions.Apart from the establishment and the nutrient management treatments that were controlled by researchers,farmers managed the crop according to their own practice.

In the wet season,farmers relied on the rains and no farmer irri-gated the rice crop.To characterize the seasonal?eld hydrology, observations of?eld hydrology were made at least once a week (1:ponded water,2:wet soil surface,3:dry soil surface)and used to calculate the mean seasonal?eld hydrology,a value between1 and3for each?eld.Climate data were collected from the nearest weather station(Agno River Integrated Irrigation Project[ARIIP]). At maturity,grain yields were determined from a5-m2area in the center of each subplot.Grain moisture content was determined

54

S.M.Haefele et al./Field Crops Research 144(2013)52–61

T a b l e 1B a s i c s i t e i n f o r m a t i o n f o r a l l e x p e r i m e n t s i n t h e p r o v i n c e o f P a n g a s i n a n ,P h i l i p p i n e s ,a n d t h e t r i a l p e r i o d f r o m 2009t o 2011.

L o c a t i o n

G e o r e f e r e n c e

T o p o -

V a r i e t y u s e d

P l a n t i n g t o h a r v e s t

(B a r r i o a n d t o w n )

S e q u e n c e p o s i t i o n

a

R i c e

M a i z e

R i c e 2009

M a i z e 2009/10

R i c e 2010

M a i z e 2010/11

S t o D o m i n g o (S t o T o m a s )

15?52 4.73 N 120?34 42.92 E L o w P S B R C 18

30T 80

12J u n e –25S e p t e m b e r S a n J o s e (S t o T o m a s )

15?51 35.29 N 120?34 32.06 E H i g h a n d l o w

P S B R C 18

30T 80

J u l y 3–16O c t o b e r

S a n A g u s t i n (S t o T o m a s )

15?52 43.89 N 120?35 25.61 E H i g h a n d L o w

P S B R C 18

30T 80

J u l y 16–29O c t o b e r

13J u n e –14O c t o b e r

27N o v e m b e r –24M a r c h

L u n g a o (S a n N i c o l a s )

16?4 56.22 N 120?45 1.88 E H i g h a n d L o w

P S B R C 82

30T 80

J u l y 23–23O c t o b e r

21N o v e m b e r –23M a r c h

13J u n e –1O c t o b e r

12N o v e m b e r –13M a r c h

C a m a n g g a a n (S a n N i c o l a s )

16?4 52.34 N 120?44 54.05 E H i g h a n d L o w P S B R C 8230T 80J u l y 23–23O c t o b e r

22N o v e m b e r –24M a r c h

18J u n e –6O c t o b e r

A n u l i d (A l c a l a )

15?48 59.46 N 120?29 13.35 E

L o w P S B R C 82

30T 80

J u l y 25–25O c t o b e r

a

U s e d i n b o t h s e a s o n s o f t h e n u t r i e n t m a n a g e m e n t e x p e r i m e n t a n d f a r m e r s ’p r e f e r r e d v a r i e t y .

Table 2

Rice varieties used in the two wet seasons of comparative variety evaluation in Pangasinan,Philippines,and their target environment.

Wet season 2009

Wet season 2010

Target environment

V1PSBRC 14

V1PSBRC 14

Rainfed lowland,transplanted (TPR)

V2PSBRC 18V2PSBRC 18Irrigated lowland,TPR V3PSBRC 82V3PSBRC 82

Irrigated lowland,TPR

V4PSBRC 68

Rainfed lowland,direct-seeded,submergence-tolerant

V5PSBRC 158

Irrigated lowland,TPR,high yield potential

V4NSIC 192

New,rainfed lowland,TPR,drought-tolerant

V5NSIC 222

New,irrigated lowland,TPR,high yield potential

immediately after threshing (Riceter grain moisture meter,Kett Electric Laboratory,Tokyo,Japan)and grain yields were reported at the standard moisture content of 14%.Additional site-speci?c observations (e.g.,diseases,lodging,etc.)were collected by the farmer-cooperators.

https://www.360docs.net/doc/b314203576.html,parative variety evaluation

A selection of farmers’preferred and promising new rice varieties was grown at all the sites and in both toposequence positions (Table 2).At all sites and for all varieties,the same fer-tilizer treatment (90-20-20N-P 2O 5-K 2O per hectare;treatment T4)and application scheme (as described for the nutrient man-agement experiment)were used.The establishment method was transplanting,only establishment and fertilizer management were researcher-controlled,and all other management practices were according to farmer’s own practice.Subplot size for each vari-ety was 5m ×10m in both toposequence positions.Based on the ?rst-year results,two varieties were changed in the second season (Table 2).The varieties PSBRC 14,PSBRC 18,and PSBRC 82were widespread varieties preferred by many farmers,PSBRC 68and PSBRC 158were varieties with speci?c qualities (submergence tol-erance and high yield potential),and NSIC 192and NSIC 222were promising (drought-tolerant and high yield potential,respectively)and very recently released varieties in the Philippines.The dates of crop development stages recorded in the ?eld were establishment,panicle initiation (PI;visual veri?cation of panicle primordia devel-opment),50%?owering,and physiological maturity.Average plant height (central tiller from ground level to the tip of ?ag leaf)and tiller number were determined for four hills in each replication at mid-tillering,PI,and maturity.Grain and straw yield at har-vest were measured from a central area of 5m 2in each subplot.Grain moisture content was determined immediately after thresh-ing (Riceter grain moisture meter,Kett Electric Laboratory,Tokyo,Japan)and grain yields (paddy,with husks)were reported at the standard moisture content of 14%.

As described above,farmers relied on the rains in the wet season and no farmer irrigated the rice.The seasonal ?eld hydrology was observed as described for the previous experiment above.Addi-tional site-speci?c observations (e.g.,diseases,lodging,etc.)were collected by the farmer-cooperators.

2.2.

3.The effect of experimental treatments in the rice season on maize yields after rice

To evaluate the effect of rice management treatments on the dry-season crop,in both the varietal screening and the nutrient management set up in the described trials,we planted maize in all plots at Camanggaan and Lungao sites in the 2009/2010dry season (San Augustin and Lungao in the 2010/2011dry season),using a no-tillage establishment method and leaving the rice stubbles in

S.M.Haefele et al./Field Crops Research144(2013)52–6155 Table3

Selected soil characteristics from all experimental sites in Pangasinan,Philippines.

Low High Low High Low High Low High Low High

Sto Domingo San Jose San Agustin Lungao Camanggaan Anulid

pH(1:1) 6.77.17.1 6.8 6.8 6.8 6.8 6.8 6.67.0

Org C(%) 1.04 1.10 1.290.83 1.010.870.86 1.36 1.240.74 Total N(%)0.110.110.130.090.110.090.090.140.130.08 Olsen P(mg kg?1)11353791115148109

Avail K(cmol kg?1)0.200.340.310.150.170.430.160.220.250.31 Avail Zn(ppm)0.500.310.260.660.730.260.110.130.150.68 Exch K(cmol kg?1)0.240.400.370.200.200.530.210.240.330.41 Exch Na(cmol kg?1)0.390.520.660.310.330.180.350.230.330.29 Exch Ca(cmol kg?1)17212313162024232313

Exch Mg(cmol kg?1)8.28.18.8 3.4 4.87.17.27.17.5 4.4

CEC(cmol kg?1)22.725.928.715.318.225.727.92828.515.2 Clay(%)19222611151719262610

Sand(%)21181649362620101238

Silt(%)60605940495861636252 Texture SiL SiL SiL L L SiL SiL SiL SiL SiL

the?eld.Directly before planting maize,the herbicide“Round-up”was applied.Maize seed of the hybrid variety30T80(Bt-Round-up ready maize,Pioneer HiBred Philippines)was manually planted by dibbling with one seed per hill at about5.0cm depth,and the seed was covered with carbonized rice husk.Planting density was 0.60m between rows and0.20m between hills.In almost all plots, we used a best-bet fertilizer rate(200-40-40kg N-P2O5-K2O ha?1), which had a much higher N rate than the national fertilizer rec-ommendation for hybrid maize(110-42-42kg N-P2O5-K2O ha?1; AFMIS,2011)but used almost the same P and K rate.The high N rate was chosen to achieve a high target yield of10–11t ha?1,and to optimize the use ef?ciency of the more expensive P and K fer-tilizers(Janssen et al.,1990),accepting possible P and K mining for the short duration of the experiment.Only in two plots was an even higher rate of250-80-80kg N-P2O5-K2O tested in2009(at Lungao High T4and V4treatments for rice).The?rst fertilizer split(50%of the N,all P2O5and K2O)was applied at10days after emergence (DAE)by manual point-placement into a hole about5cm deep in between the maize hills.The second split(50%of N)was applied at30DAE,and the fertilizer was locally placed on top of the soil in between maize hills.The crop was irrigated after each fertilizer application,and thereafter with a frequency of two times a month depending on water availability to about2weeks before harvest (Table1).

2.2.4.Nutrient(NPK)balance

To evaluate the system sustainability,we estimated a simple nutrient balance for the“standard”R–M system.We assumed that this system was represented by the rice and maize crop grow-ing in the subplot of treatment T4in the nutrient management experiment.Based on the respective grain and straw yield data observed for rice and maize in these plots and in both seasons (2009and2010),total aboveground NPK uptake was calculated using standard NPK concentration in rice(rice grains:1.10%N, 0.20%P,0.29%K;rice straw:0.65%N,0.10%P,1.40%K;Fairhurst et al.,2007)and maize(maize grains:1.300%N,0.263%P,0.363%K; maize stover:0.811%N,0.052%P,2.182%K;Setiyono et al.,2010).As nutrient inputs,only inputs from applied fertilizer were considered, that is,90-20-20kg N-P2O5-K2O ha?1for rice plus200-40-40kg N-P2O5-K2O ha?1for maize.

3.Data analysis

Data gathered in the experiment were statistically analyzed using procedures described by Gomez and Gomez(1984).Grain yield data were analyzed using IRRISTAT and SAS software.For the analysis of variance,?elds in the same position and season were treated as replications,and treatment effects were analyzed only for individual seasons.Analysis of variance was conducted using the Mixed Procedure in SAS9.1for Windows(SAS Institute,Cary, NC).Tukey’s test was used for mean comparison and differences were considered signi?cant at p≤0.05.

4.Results

4.1.Soil characteristics

Soil characteristics from the experimental sites are given in Table3.Across sites,the soil reaction was near neutral or slightly acid,the soil organic carbon content was above1%at almost all sites, and the C/N ratio was usually around10.According to Fairhurst et al. (2007),availability tests indicated probable P limitations at some sites(Olsen P values between5and10mg P kg?1),probable K lim-itations at almost all sites(exchangeable K values between0.15 and0.45cmol kg?1),and possible Zn de?ciency at several sites(at <0.6ppm Zn).Cation exchange capacity was high at all sites and the exchange complex was dominated by Ca and Mg cations.Low clay content but equal amounts of silt and sand were observed at San Agustin and Anulid(soil texture“Loam”),whereas higher clay and sand contents occurred at the other sites(soil texture“silty Loam”). At all sites,the height difference between upper and lower?elds was small(less than1m)and had no signi?cant effect on texture and related soil characteristics although there was a slight trend for ?ner texture in lower?elds at most sites.

4.2.Rice response to fertilizer treatments

In2009,the rice crop was transplanted between12June and 25July.The trial at“Alcala Low”failed due to long submergence of the newly planted crop.The trial at“Sto Domingo High”failed due to a typhoon that severely damaged the crop at a later stage. In2010,only six sites could be established,transplanting took place between13June and18June,and no weather-related com-plete crop loss occurred.In both wet seasons,farmers did not use irrigation in their own or the experimental?elds.

Grain yields in the nutrient management trial ranged between 1.0and5.0t ha?1in the2009wet season,and between2.3and 5.6t ha?1in the2010wet season(Table4).The main reason for this difference was that in our target region the2009wet season had several longer dry spells,whereas rains were well distributed in the2010wet season.In both seasons,nitrogen was clearly the most limiting nutrient element,but,especially at low-yielding sites, further yield increases were observed for additional P and K appli-cations(comparison of T2versus T3and T3versus T4at the sites

56S.M.Haefele et al./Field Crops Research144(2013)52–61 Table4

Rice grain yield(t ha?1)as affected by different fertilizer treatments under rain-

fed conditions at various sites in Pangasinan,Philippines(for the variety used,see

Table1).

Site code a Fertilizer treatment(N-P2O5-K2O kg ha?1)b Mean

T1T2T3T4T5

0-0-090-0-090-20-090-20-2090-30-20

2009wet season

SD-L 2.42 4.94 4.31 4.76 4.09 4.11a

SA-H 3.47 4.18 3.97 4.44 4.23 4.06ab

SA-L 3.08 3.71 3.93 3.32 3.33 3.47bc

SJ-H 1.76 3.44 3.54 4.40 4.96 3.62bc

SJ-L 2.36 3.45 3.58 4.07 4.21 3.53bc

LU-H 1.95 2.31 3.35 4.28 4.11 3.20cd

LU-L 1.01 2.51 2.80 3.28 3.20 2.56e

CA-H 1.09 1.91 2.16 2.65 3.38 2.24e

CA-L 1.30 1.91 2.16 2.19 2.53 2.02e

AL-H 2.06 2.27 3.13 2.87 2.71 2.61de

Mean b 2.05c 3.06b 3.29ab 3.63a 3.67a LSD c

2010wet season

SA-H 4.41 4.91 4.96 4.97 5.26 4.90a

SA-L 4.04 4.92 5.33 5.64 5.39 5.06a

LU-H 2.95 5.09 5.27 5.58 5.45 4.87a

LU-L 3.91 4.90 5.31 5.17 5.52 4.96a CA-H 2.69 3.66 4.02 4.33 4.17 3.77b CA-L 2.25 4.12 3.78 5.08 4.74 3.99b Mean b 3.37c 4.60b 4.78ab 5.13a 5.09a LSD d

a SD-L:Sto Domingo Low;SA-H&L:San Agustin High and Low;SJ-H&L:San Jose High and Low;LU-H&L:Lungao High and Low;CA-H&L:Camanggaan High and Low;AL-H:Alcala High.

b A blanket application of20kg ZnO ha?1was applied in all treatments.

c LSD5%2009wet season=426kg ha?1among fertilizer treatments per site;LSD 5%=602kg ha?1among sites per fertilizer treatment.

d LSD5%2010wet season=427kg ha?1among fertilizer treatments per site;LSD 5%=468kg ha?1among sites per fertilizer treatment.

in Lungao,Camanggaan,and Alcala;comparison of T4versus T5at Camanggaan).But across sites and in both seasons,only the com-bined P and K application(T4)increased yields signi?cantly above the application of only N(T2).Also,the higher P rate(T5)did not signi?cantly increase grain yield above treatment T4.The average yield response to fertilizer use was similar in both years.Across sites,the average grain yield increased by1.0t ha?1from T1to T2 and by1.6t ha?1from T1to T4in the2009wet season.In the2010 wet season,the average grain yield increased by1.2t ha?1from T1 to T2and by1.7t ha?1from T1to T4.

There was a clear trend of decreasing yields with increas-ing average?eld water stress(Fig.1).The?gure also shows that yield losses due to drought were highest for T1and T2 (0-0-0and90-0-0kg N-P2O5-K2O ha?1),medium for T3(90-20-0kg N-P2O5-K2O ha?1),and lowest for T4and T5(90-20-20and 90-30-20kg N-P2O5-K2O ha?1).Average T1yields of lower and upper?elds were not signi?cantly different.However,across treat-ments,the yield data showed a trend of lower yields on lower?elds in the dryer2009wet season,whereas grain yields on upper and lower?elds were very similar in the wetter2010wet season.

4.3.Varietal performance in rice

Table5shows the grain yield performance of the different rice varieties tested in both seasons.As in the nutrient management tri-als,substantially higher average yields were achieved in the2010 wet season.In the2009wet season and across sites,only vari-ety PSBRC68had a statistically lower average yield,whereas the yield of the other four varieties was not signi?cantly different.The two best performing varieties in2009were PSBRC14and PSBRC 82,both characterized by high yields under good conditions and the highest yields under water stress(especially at Camanggaan;

Mea n sea sonal field water stress

1.0

1.2 1.4 1.6 1.8

2.0 2.2 2.4

G

r

a

i

n

y

i

e

l

d

(

k

g

h

a

-

1

)

1000

2000

3000

4000

5000

6000

Fig.1.Grain yield of rice across all sites and fertilizer treatments but dependent on the mean seasonal?eld water stress.Field water stress levels were scored according to1=permanently?ooded,2=permanently wet soil surface,and3=permanently dry soil surface.The envelope lines were?tted manually.

CA).Variety PSBRC68had the lowest average yield,partly due to a taller plant type and the resulting occurrence of lodging damage at some sites.Across varieties,the data on varietal performance also showed a trend of higher yields on upper?elds,as already observed in the nutrient management trial,but again this difference was not statistically signi?cant.

In the second trial season,we removed PSBRC68and PSBRC 158because of their limited performance and replaced them with the new and highly promising varieties NSIC192and NSIC222. The by far best performing variety in the2010wet season was the newly released NSIC222,which outyielded all other varieties at5 of6sites,and achieved maximum yield of up to7.1t ha?1.The new drought-tolerant and short-duration variety NSIC192achieved the second-highest average yield across sites and yielded consistently above5t ha?1at all sites.The signi?cantly lowest average yield was observed for rainfed-lowland variety PSBRC14.

4.4.Maize performance in the dry season

Rainfall in the dry season was very low in both experimental sea-sons(but higher in the2009/10dry season)and maize was always irrigated.The irrigation frequency varied between farmers and sites but usually between6and10furrow irrigations were applied.In both experimental seasons,maize was grown with the same man-agement in all plots,the only differences were the treatments of the previous rice crop.Grain yield results from both seasons are shown in Table6.

Across sites,maize yields were considerably higher in the 2010/2011dry season,and especially at San Agustin very high grain yields of12.4–13.9t ha?1were achieved.Maize grain yields across treatments in the previous rice crop did not show any effect of the toposequence position,but in the2010/2011dry season the site had a clear effect on maize yields and much higher yields were observed at San Agustin.

Maize yields in both experimental seasons did not seem to be affected by the fertilizer treatment in the previous rice crop,with the exception of slightly lower maize yields in the T1treatment (this was the unfertilized treatment in the previous rice crop)but the difference was non-signi?cant.Similarly,varietal treatments

S.M.Haefele et al./Field Crops Research144(2013)52–6157 Table5

Rice grain yield(t ha?1)of different rice varieties fertilized with a standard NPK+Zn rate under rainfed conditions at various sites in Pangasinan.

Site code a Variety Mean PSBRC14PSBRC18PSBRC82PSBRC68b PSBRC158

2009wet season

SD-L 4.64 4.93 4.15 2.90 4.18 4.16a

SA-H 3.67 4.27 4.78 2.74 3.98 3.89ab SA-L 3.80 3.91 3.38 2.95 3.27 3.46abc SJ-H 4.38 4.03 3.15 2.78 3.03 3.47abc SJ-L 3.14 3.93 3.06 2.84 3.11 3.22abc LU-H 3.92 2.90 4.03 3.02 3.60 3.49abc LU-L 2.80 2.34 2.42 3.05 2.76 2.73cd CA-H 2.29 1.43 2.71 1.85 2.07 2.07d

CA-L 2.24 1.07 2.36 1.25 2.08 1.80d

AL-H 3.09 3.29 2.88 3.10 3.15 3.10bc Mean 3.40a 3.21a 3.32a 2.65b 3.13a LSD c

Site code a Variety Mean PSBRC14PSBRC18PSBRC82NSIC192NSIC222

2010wet season

SA-H 5.42 5.85 6.69 5.307.09 6.07a SA-L 5.47 5.33 5.41 5.417.05 5.73ab LU-H 3.87 5.57 5.08 5.18 5.58 5.06bc LU-L 3.26 4.84 5.47 5.42 5.94 4.99bc CA-H 4.10 4.29 4.90 5.45 4.45 4.64c CA-L 3.54 4.92 4.24 5.74 6.22 4.93c Mean 4.28c 5.13b 5.30b 5.42ab 6.05a LSD d

a SD-L:Sto Domingo Low;SA-H&L:San Agustin High and Low;SJ-H&L:San Jose High and Low;LU-H&L:Lungao High and Low;CA-H&L:Camanggaan High and Low; AL-H:Alcala High.

b Affected by?ood(and drought)across all sites because this was a tall,easily lodging variety.

c LSD5%2009wet season=438kg ha?1among variety treatments per site;LSD5%=620kg ha?1among sites per variety treatment.

d LSD5%2010wet season=715kg ha?1among variety treatments per site;LSD5%=783kg ha?1among sites per variety treatment.

Table6

Grain yield(t ha?1)of maize grown after rice in the fertilizer and variety trial.

Treatment of the previous rice crop Camanggaan Camanggaan Lungao Lungao Mean b

High Low High Low

Maize yield in t ha?1

2009/10dry season

T10-0-08.48.67.8 6.97.9ab

T290-0-08.59.4 6.78.58.3ab

T390-20-08.59.97.18.18.4ab

T490-20-208.58.59.9a 6.48.3ab

T590-30-208.27.28.59.38.3ab

V1PSBRC147.17.37.07.17.1b

V2PSBRC18 6.98.97.07.87.7ab

V3PSBRC827.8 5.9 6.88.87.3b

V4PSBRC688.59.29.6a8.28.9a

V5PSBRC158 6.27.47.78.97.5ab Mean7.9a8.2a7.8a8.0a

San Agustin San Agustin Lungao Lungao Mean b

High Low High Low

Maize yield in t ha?1

2010/11dry season

T10-0-012.513.210.910.311.7a

T290-0-012.913.512.110.412.2a

T390-20-012.713.911.111.312.3a

T490-20-2012.613.810.810.912.0a

T590-30-2012.413.211.211.012.0a

V1PSBRC1413.313.210.810.712.0a

V2PSBRC1813.213.410.611.112.1a

V3PSBRC8213.413.110.212.012.2a

V4NSIC19213.413.210.812.012.4a

V5NSIC22213.113.211.810.912.3a Mean13.0a13.4a11.0b11.1b

a A higher fertilizer rate(250-35-66kg N-P-K)was applied at Lungao High T4and V4in2009,in all other plots,the standard experimental rate was used(200-17-33kg N-P-K ha?1).

b For each trial,means in a column followed by the same letter are not signi?cantly different at5%level of signi?cance by LSD.

58S.M.Haefele et al./Field Crops Research144(2013)52–61

Table7

Estimated above-ground N,P,and K uptake for the yearly rice–maize sequence at two sites,in two toposequence positions,and in two years at Pangasinan,Philippines. 2009WS–2010DS High toposequence Low toposequence

Plant material Elements(kg ha?1)Elements(kg ha?1)

N P K N P K

Lungao

Rice Grain4791236710 Straw56912043792 Maize Grain1292636831723 Stover805216523140

Total3124938421434265

Grain only17635481192433

Camanggaan

Rice Grain29582446 Straw3457428461 Maize Grain11122311112231 Stover694185694185

Total2433729823235284

Grain only13227391342637 2010WS–2011DS High toposequence Low toposequence

Plant material Elements(kg ha?1)Elements(kg ha?1)

N P K N P K

San Agustin

Rice Grain551014621116 Straw65101397311158 Maize Grain16433461803650 Stover7351981127301

Total3565839742765525

Grain only21943602424766

Lungao

Rice Grain611116571015 Straw73111566710145 Maize Grain14129391422940 Stover715191855228

Total3465540335155428

Grain only20240551993955 Fertilizer applied:rice90-9-17N-P-K kg ha?1,maize200-17-33N-P-K kg ha?1,and annual total290-26-50N-P-K kg ha?1.

in the rice season did not signi?cantly affect maize yields in the following dry season;only the low-yielding varietal treatment V4 in2009seemed to cause higher yields in the following maize crop. In the2009/2010dry season,the higher fertilizer rates in two sub-plots at Lungao High increased maize yields considerably,but this effect could not be statistically tested.

4.5.Estimated nutrient balances of the cropping system

Aboveground NPK uptake of straw and grain for rice and maize is given in Table7.Total uptake for each crop obviously mirrors the grain yields,and is thus generally higher in the second year of the cropping systems than in the?rst.And,resulting from the higher maize yields and NPK concentrations in grain and straw,the total aboveground uptake of all elements is considerably higher for maize at all sites and in both https://www.360docs.net/doc/b314203576.html,paring the total NPK uptake of the system with the total NPK applied(290-26-50N-P-K kg ha?1)shows that,at both sites and even in the low-yielding year,2009/2010,the P and K applied was less than what was taken up by the two crops,and that,in the high-yielding year,2010/2011, NPK inputs were far below aboveground uptake of the cropping system.But,even if only the grains were removed,the PK balance would be equalized only at low-yielding site/season combinations such as Camanggaan2009/2010,and would still be highly negative for all sites in the high-yielding season(2010/2011).

5.Discussion

One hypothesis determining the layout of the trials was that even small height differences between?elds could affect crop management and performance because of their effect on available nutrient and water resources.High variability of soil characteris-tics in rice environments with undulating topography and some relation to?eld position in the topography as well as crop perfor-mance has been reported in several studies(e.g.,Oberthuer and Kam,2000;Boling et al.,2008;Haefele and Konboon,2009).But,in the case of the soil characteristics in the target area in Pangasinan, no general trend in any of the observed soil characteristics could be detected,probably because the height differences between“high”and“low”?elds were too small,and perhaps also because the soils at the sites were relatively“young”soils with some recent volcanic ash input from the nearby Pinatubo eruption in1991.In agreement with these results,no signi?cant yield difference between topo-graphic positions could be detected,and the trend of lower yields on lower?elds across sites in the dryer2009wet season could not be explained and was probably an artifact in the data.Widespread

S.M.Haefele et al./Field Crops Research144(2013)52–6159

limitation of high-yielding rice crops by limited soil N,P,and K sup-plies,as indicated by the soil tests,has been reported frequently for the region(Dobermann and Oberthuer,1997;Wade et al.,1999). However,the soil test result of possible Zn de?ciencies has rarely been con?rmed by fertilizer experiments in the area.

The existing R–M system as practiced by many farmers in the region is the combination of mostly rainfed wet-season rice with irrigated dry-season maize.According to of?cial statistics,Pangasi-nan province has about146,400ha of irrigated rice,92,200ha of rainfed lowland rice(PhilRice,2008),and about33,600ha of yellow maize(AFMIS,2011).The analysis of potential cropping systems by Timsina et al.(2011)at a site with conditions similar to those in our target region indicated two options:rice in the wet sea-son followed by maize in the dry season(R–M)or the other way around(M–R),and the latter even had a slightly higher total yield potential(21.7t ha?1versus20.5t ha?1).But,the R–M system has several important advantages:the high water requirements of rice are dif?cult to ful?ll in the dry season when water is scarce;heavy wet-season rains regularly cause complete soil saturation in low-lands,which can be impossible to drain and may severely damage a maize crop;typhoons usually occur during the wet season and do less damage to rice than to maize;and maize suffers from a whole range of diseases in the wet season whereas rice has few disease problems even in humid conditions.Thus,the R–M sys-tem clearly seems the better choice.And,combined maximum yields achieved in the second season of our trials at San Agustin (7.1t ha?1of rice for variety NSIC222[Table5]and an average of 13.4t ha?1of maize[Table6])were close to the average potential yields simulated by Timsina et al.(2011)for the site Pila in Laguna. But,it must be noted that the2010/2011wet and dry season were very favorable due to suf?cient and well-distributed rains in the wet season and high solar radiation in the dry season(a La Ni?na phase).

The climatic characteristics of our two experimental seasons indicated some of the variability farmers have to deal with.Drought stress affected rice yields in the2009wet season(Table5and Fig.1)but none of the collaborating farmers irrigated during the wet season(for various reasons,including the damaged irrigation infrastructure).These typical rainfed conditions favored the old “rainfed”variety PSBRC14and it had the highest average yields although no signi?cant differences were detected.Then,shortly before harvest,the devastating typhoon Ondoy hit the region(26 September2009),causing some lodging in our trials,and espe-cially damaging the tall variety PSBRC68(Table5).The following dry season was relatively cloudy and low yielding,followed by a favorable wet season.The“rainfed”variety PSBRC14yielded low-est,surpassed by the“irrigated”varieties PSBRC18and PSBRC82. However,the new drought-tolerant rainfed lowland variety NSIC 192(breeding line IR74371-54-1-1,released in2011)kept up with the irrigated varieties and had particularly stable yields across sites, which was an important selection criterion for this variety(Kumar et al.,2012).The signi?cantly highest yields were achieved by NSIC 222,a very recently released high-yielding variety.The following dry season was also favorable due to the“La Nina”conditions with a mostly clear sky and almost no rainfall at all.These results show that even in this relatively favorable system weather-induced stress is common,which can be partially addressed by an adjusted vari-etal choice,and that conventional inbred varieties can still help to signi?cantly reduce production risk and improve system produc-tivity.

The fertilizer response in rice con?rmed the dominant N limi-tation,followed by a less strong P and K limitation,as described by other authors(e.g.,Dobermann and Oberthuer,1997;Wade et al., 1999).But,the fertilizer trial data also show the potential of nutri-ent management to mitigate drought-stress-induced yield losses (Fig.1).That nutrient×water interactions could be an important component for improving crop management for rice-based rainfed systems has been repeatedly hypothesized(Wade et al.,1998; La?tte,1998;Haefele and Bouman,2009).This hypothesis was based on?eld observations where improved nutrition alleviated the effects of drought stress(e.g.,Biswas et al.,1982;Tanguilig and De Datta,1988;Otoo et al.,1989;Jabbar et al.,2008).Accordingly, the results presented in Fig.1and Table4clearly show that improved plant nutrition reduces yield losses due to drought stress.However,the experiments could not statistically con?rm a special role of P supply in drought stress mitigation;the higher P rate in treatment T5seems to provide an advantage over T4only at the highest stress level(Fig.1).But,given the very low solubility of P in the soil solution and the importance of diffusion for P uptake, which are both directly affected by soil moisture,a positive effect of increased P availability on crop performance under drought is very likely,and has been described in other studies(e.g.,Khuntasuvon et al.,1998;Chin et al.,2010;Rodriguez et al.,1996).

The maize crop performance in our trials was strongly affected by the climatic conditions of the two experimental seasons;yields were low in the cloudy dry-season2009/2010,and very high in the sunny dry season2010/11.The trials also indicated the consid-erable scope for improvement of the current maize management practice by farmers and of existing recommendations,as was also shown by Pasuquin et al.(2010).The best-bet fertilizer rate we used for maize at our site had a considerably higher N rate(200-17-33kg N-P-K ha?1,estimated for a target yield of10–11t ha?1) than the existing general recommendation for hybrid maize in the Philippines(110-18-35kg N-P-K ha?1)or the average rate of farmers in the Philippines(129-12-20kg N-P-K ha?1)as reported by Pasuquin et al.(2010).The same authors developed a tool for site-speci?c nutrient and crop management for maize,which recommended an average rate of156-32-64kg N-P-K ha?1in the Philippines,indicating intermediate N rates and much higher and expensive P and K rates.The rates used in our experiments probably maximized internal P and K ef?ciency by allowing maximal dilution in the plan tissue(Janssen et al.,1990)but increased P and K mining at the same time.The?nal nutrient management tool as developed by Pasuquin et al.(2010)needs to?nd a compromise between agro-nomic,economic and sustainability targets,but should then allow optimizing maize production and adjusting fertilizer recommenda-tions to local conditions and target yields.Our results also suggest that the tool needs to take the performance and management of the previous crops into consideration,because grain yields achieved as well as straw and stover management have a signi?cant effect on adequate P and K rates(see discussion below).And although the fertilizer management in the rice crop seemed to have a limited effect in the following maize crop(Table6),this might not be true the other way round.

Another important crop management factor that needs to be addressed is maize establishment.Currently,farmers practice standard soil tillage with2–3passes and drill seeding,whereas we successfully used zero-till technology for maize establishment. This could reduce establishment costs substantially but adequate machinery for zero-till establishment is rarely available in the Philippines.Given the widespread availability of two-wheel trac-tors,zero-till drill-seeding equipment for such tractors might be the best option.

System sustainability is another important aspect to consider. Intensive R–M systems in lowlands are a relatively recent devel-opment in the Philippines and not much long-term experience is available.In a long-term trial at the International Rice Research Institute,a rapidly decreasing soil organic matter(SOM)content has been observed,whereas the parallel rice–rice cropping system had no such trend(Pampolino et al.,2008).This mineralization of SOM could of course contribute considerable amounts of nutrients to the crop,but probably not for very long.And,the estimation

60S.M.Haefele et al./Field Crops Research144(2013)52–61

of total NPK uptake in the analyzed R–M system made clear that, even if only the rice and maize grains were removed,the PK balance would be equalized only in“low”-yielding years(which is never-theless remarkable given the relatively low P and K rates we used in both seasons).Higher fertilizer rates as proposed by Pasuquin et al.(2010)could cover the nutrient removals with the grain,but it was argued before that partial mining might be the best strategy, especially for the abundant element K(Buresh et al.,2010;Pasuquin et al.,2010).But,even such approaches quickly become very expen-sive if substantial amounts of straw and stover are removed from the?eld too,as the total NPK uptake of the cropping system in Table7illustrates.Farmers participating in our experiments did not remove much rice straw and most of it remained in the?eld. However,at least part of the maize stover was used or sold as fodder and,in the latter case,these resources were lost from the system. Thus,to maintain system productivity,it seems most promising to combine different management elements,including balanced NPK fertilizer rates allowing some mining,recycling of waste products from residue use on the farm as much as possible,and only par-tial removal of residues from the?elds.Even then,we assume that the SOM concentration will be declining from the level of a rice–rice system but it can be expected to stabilize at a lower level(Jenkinson, 1988).

6.Conclusions

The R–M system we analyzed was highly productive in the two experimental years,and con?rmed earlier theoretical analy-ses of potential grain yields above20t ha?1(rice and maize)in a favorable year.However,sub-optimal climate conditions affected grain production in the other year considerably,highlighting the need for resilient crop management options.Varietal choice con-stitutes such an option and can help to reduce production losses,for example,by selecting the variety according to average?eld-speci?c characteristics(drought-prone,favorable,?ood-prone).Balanced fertilizer applications also reduced stress-dependent yield losses, and helped to maximize grain yield in a favorable year.Across all sites,we could not con?rm any signi?cant effect of the topose-quence on soil characteristics or grain yields,probably because the height differences in this environment were too small and because the soils were relatively young.And although the fertilizer manage-ment in the previous rice crop did not signi?cantly affect maize crop performance,fertilizer management in the maize crop might have a stronger effect on the rice crop,and nutrient recommendations should take such effects into consideration.Establishing the tech-nology of minimum tillage and drill seeding is promising and could help to reduce production costs;however,suitable machinery is not yet available to farmers in the Philippines.A simple nutrient balance indicated the considerable danger of soil nutrient mining in the cropping system,which could aggravate possible trends of declining soil organic matter concentrations in R–M systems.We concluded that a combination of speci?c management components can reduce production risk and optimize system productivity.And, it seems most promising to combine different management ele-ments to maintain system productivity,including balanced NPK fertilizer rates with limited P and K mining,recycling of waste prod-ucts from residue use on the farm as much as possible,and only partial removal of residues from the?elds.The study shows,that the tropical R–M system has large potential and some important elements for better management are already available.However, some more adaptive on-farm research will be needed to further optimize system management.

Acknowledgments

This study was partly funded through the Bureau of Agricultural Research by the Department of Agriculture of the Republic of the Philippines as part of the project“Improved Nutrient Management Options for Unfavorable Rainfed Lowlands in the Philippines(IRRI Project reference number:DPPC2008-69)”.

References

AFMIS,https://www.360docs.net/doc/b314203576.html,modity pro?le of corn region I.Agriculture and?sheries market information system,online available at https://www.360docs.net/doc/b314203576.html,.ph/

Biswas Jr.,A.K.,Nayek,B.,Choudhuri,M.A.,1982.Effect of calcium on the response of a?eld-grown rice plant to water stress.Proc.Indian Natl.Sci.Acad.B48,669–705. Boling,A.A.,Tuong,T.P.,Suganda,H.,Konboon,Y.,Harnpichitvitaya,D.,Bouman,

B.A.M.,Franco,D.T.,2008.The effect of toposequence position on soil properties.

hydrology,and yield of rainfed lowland rice in Southeast Asia.Field Crops Res.

106,22–33.

Bremner,J.M.,1996.Nitrogen–total.In:Sparks,D.L.(Ed.),Methods of Soil Analy-sis.Part3.Chemical Methods.Soil Science Society of America,Inc.&American Society of Agronomy,Inc.,Madison,WI,USA,pp.1085–1121.

Buresh,R.J.,Haefele,S.M.,2010.Changes in paddy soils under transition to water-saving and diversi?ed cropping systems.In:CD,19th World Congress of Soil Science,Brisbane,Australia,1–6August2010.

Buresh,R.J.,Pampolino,M.F.,Witt,C.,2010.Field-speci?c potassium and phosphorus balances and fertilizer requirements for irrigated rice-based cropping systems.

Plant Soil335,35–64.

Chin,H.J.,Lu,X.,Lu,X.,Haefele,S.M.,Gamuyao,R.L.,Ismail,A.M.,Wissuwa,M.,Heuer, S.,2010.Development and application of gene-based markers for the major rice QTL Phosphate uptake1.Theor.Appl.Genet.120,1073–1086.

Dobermann.,A.,Oberthuer,T.,1997.Fuzzy mapping of soil fertility—a case study of irrigated Riceland in the Philippines.Geoderma77,317–339.

Fairhurst,T.H.,Witt,C.,Buresh,R.J.,Dobermann,A.,2007.A Practical Guide to Nutri-ent Management,2nd ed.International Rice Research Institute/International Plant Nutrition Institute/International Potash Institute,Singapore,p.89. Gee,G.W.,Or,D.,2002.Particle-size analysis.In:Dane,J.H.,Topp,G.C.(Eds.),Methods of Soil Analysis.Part4.Physical Methods.Soil Science Society of America,Inc., Madison,WI,USA,pp.255–293.

Gerpacio,R.V.,Labios,J.D.,Labios,R.V.,Diangkinay, E.I.,2004.Maize in the Philippines:Production Systems,Constraints and Research Priorities.CIMMYT, Mexico,DF,p.38.

Gomez,K.A.,Gomez,A.A.,1984.Statistical Procedures for Agricultural Research,2nd ed.John Wiley&Sons,New York,USA,p.680.

Haefele,S.M.,Bouman,B.A.M.,2009.Drought-prone rainfed lowland rice in Asia: limitations and management options.In:Serraj,J.,Bennett,J.,Hardy,B.(Eds.), Drought Frontiers in Rice:Crop Improvement for Increased Rainfed Produc-tion.World Scienti?c Publishing/International Rice Research Institute,Los Ba?nos (Philippines)/Singapore,pp.211–232.

Haefele,S.M.,Konboon,Y.,2009.Nutrient management for rainfed lowland rice in northeast Thailand.Field Crops Res.114,374–385.

Helmke,P.A.,Sparks,D.L.,1996.Lithium,sodium,potassium,rubidium,and cesium.

In:Bigham,J.M.(Ed.),Methods of Soil Analysis.Part3.Chemical Methods.Soil Science Society of America/American Society of Agronomy,Madison,WI,USA, pp.551–574.

Jabbar,S.M.A.,Haefele,S.M.,Sta Cruz,P.C.,2008.Grain yield and nitrogen utilization in rice(Oryza sativa L.)genotypes grown under irrigated and rainfed lowland conditions.Philipp.J.Crop Sci.34,22–37.

Janssen,B.H.,Guiking,F.C.T.,van der Eijk,D.,Smaling,E.M.A.,Wolf,J.,van Reuler,

H.,1990.A system for quantitative evaluation of the fertility of tropical soils

(QUEFTS).Geoderma46,299–318.

Jenkinson,D.S.,1988.Soil organic matter and its dynamics.In:Wild,A.(Ed.),Russell’s Soil Conditions and Plant Growth.Longman,London,pp.564–607. Khuntasuvon,S.,Rajatasereekul,S.,Romyen,P.,Fukai,S.,Basnayake,J.,Skulkhu,E., 1998.Lowland rice improvement in northern and northeast Thailand.1.Effects of fertilizer application and irrigation.Field Crops Res.59,99–108.

Kumar,A.,Verulkar,S.B.,Mandal,N.P.,Variar,M.,Shukla,V.D.,Dwivedi,J.L.,Singh,

B.N.,Singh,O.N.,Swain,P.,Mall,A.K.,Robin,S.,Chandrababu,R.,Jain,A.,Hae-

fele,S.M.,Piepho,H.P.,Raman,A.,2012.High-yielding,drought-tolerant,stable rice genotypes for the shallow rainfed lowland drought-prone ecosystem.Field Crops Res.133,37–47.

Marschner,H.,1986.Mineral Nutrition of Higher Plants.Academic Press Limited, London,p.674.

La?tte,H.R.,1998.Research opportunities to improve nutrient-use ef?ciency in rice cropping systems.Field Crops Res.56,223–236.

Nelson,D.W.,Sommers,L.E.,1996.Total carbon,organic carbon,and organic mat-ter.In:Sparks,D.L.(Ed.),Methods of Soil Analysis.Part3.Chemical Methods.

SSSA Book Series no.5.Soil Science Society of America&American Society of Agronomy,Madison,WI,USA,pp.961–1010.

Oberthuer,T.,Kam,S.P.,2000.Perception,understanding,and mapping of soil vari-ability in the rainfed lowlands of northeast Thailand.In:Tuong,T.P.,Kam,S.P., Wade,L.,Pandey,S.,Bouman,B.A.M.,Hardy,B.(Eds.),Characterizing and Under-standing Rainfed Environments.Proceedings of the International Workshop on Characterizing and Understanding Rainfed Environments,5–9December1999, Bali,Indonesia.International Rice Research Institute,Los Ba?nos,Philippines,pp.

75–96.

Olsen,S.R.,Cole,C.V.,Watanabe,F.S.,Dean,L.A.,1954.Estimation of available phos-phorus in soil by extraction with sodium bicarbonate.U.S.D.A.Circ.939.

S.M.Haefele et al./Field Crops Research144(2013)52–6161

Otoo,E.,Ishii,R.,Kumura,A.,1989.Interaction of nitrogen supply and soil water stress on photosynthesis and transpiration in rice.Jpn.J.Crop Sci.58,424–429. Pampolino,M.F.,Laureles,E.V.,Gines,H.C.,Buresh,R.J.,2008.Soil carbon and nitro-gen changes in long-term continuous lowland rice cropping.Soil Sci.Soc.Am.J.

72,798–807.

Pasuquin,J.M.,Witt,C.,Pampolino,M.,2010.New site-speci?c nutrient management approach for maize in the favourable tropical environments of Southeast Asia.

In:CD,19th World Congress of Soil Science,Brisbane,Australia,1–6August 2010.

PhilRice,2008.The Philippine Rice Master Plan2009–2013.Enhancing Provincial Rice Self-Suf?ciency.The Philippine Rice Research Institute,Mu?noz,Philippines, p.117.

Rodriguez,D.,Goudriaan,J.,Oyarzabal,M.,Pomar,M.C.,1996.Phosphorus nutrition and water stress tolerance in wheat plants.J.Plant Nutr.19,29–39. Sardans,J.,Pe?nuelas,J.,2004.Increasing drought decreases phosphorus availability in an evergreen Mediterranean forest.Plant Soil174,305–317.

Setiyono,T.D.,Walters,D.T.,Cassman,K.G.,Witt,C.,Dobermann,A.,2010.Estimating maize nutrient uptake requirements.Field Crops Res.118,158–168. Sumner,M.E.,Miller,W.P.,1996.Cation exchange capacity and exchange coef?cients.In:Sparks,D.L.(Ed.),Methods of Soil Analysis.Part3.Chemical

Methods.Soil Science Society of America,Inc.&American Society of Agronomy, Inc.,Madison,WI,USA,pp.1201–1229.

Tanguilig,U.C.,De Datta,S.K.,1988.Potassium effects on root growth and yield of upland rice(Oryza sativa L.)under drought and compacted soil conditions.

Phillip.J.Crop Sci.13,33.

Timsina,J.,Buresh,R.J.,Dobermann,A.,Dixon,J.,2011.Rice–maize systems in Asia: current situation and potential.International Rice Research Institute and Inter-national Maize and Wheat Improvement Centre,Los Ba?nos,Philippines,p.232. Timsina,J.,Jat,M.L.,Majumdar,K.,2010.Rice–maize systems of South Asia:current status,future prospects and research priorities for nutrient management.Plant Soil335,65–82.

Wade,L.J.,Amarante,S.T.,Olea,A.,Harnpichitvitaya,D.,Naklang,K.,Wihardjaka,A., Sengar,S.S.,Mazid,M.A.,Singh,G.,McLaren,C.G.,1999.Nutrient requirements in rainfed lowland rice.Field Crops Res.64,91–107.

Wade,L.J.,George,T.,Ladha,J.K.,Singh,U.,Bhuiyan,S.I.,Pandey,S.,1998.Oppor-tunities to manipulate nutrient-by-water interactions in rainfed lowland rice systems.Field Crops Res.56,93–112.

Witt,C.,Pasuquin,J.,Dobermann,A.,2008.Site-speci?c nutrient management for maize in favorable tropical environments of Asia.In:CD,5th International Crop Science Congress,Jeju,Korea,13–18April2008.