Calibrating the Leaf Color Chart for Nitrogen Management in Different Genotypes of Rice and Wheat in...

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Calibrating the Leaf Color Chart for Nitrogen Management in Different Genotypesof Rice and Wheat in a Systems Perspective

Arvind K. Shukla, Jagdish K. Ladha,* V. K. Singh, B. S. Dwivedi, Vethaiya Balasubramanian, Raj K. Gupta,S. K. Sharma, Yogendra Singh, H. Pathak, P. S. Pandey, Agnes T. Padre, and R. L. Yadav

ABSTRACT tions at specified growth stages is the most commonpractice followed by the farmers (PhilRice, 1991; PillaiLow N use efficiency (NUE) continues to be a problem in the riceand Kundu, 1993).This does not consider the dynamic(Oryza sativa L.)–wheat (Triticum aestivum L.) cropping system.

The leaf color chart (LCC)–based real-time N management can be crop N requirement and soil N supply because N recom-used to optimize/synchronize N application with crop demand or to mendations were mainly derived from empirical testingimprove existing fixed split N recommendations. We conducted a field of N response to few fixed doses. In fixed-time recom-experiment during 2001–2003 at Modipuram, India, to determine the mended N split schedule, the N splitting is skewed, thethreshold LCC values for N application in rice and wheat, assess the first two splittings [one as basal at the time of planting/need for basal N application, calibrate the LCC with a chlorophyll sowing and another at 25 to 30 d after transplantingmeter (SPAD), and work out the economics of rice–wheat systems.

(DAT) in rice and 21 to 25 d after sowing (DAS) inTreatments consisted of LCC scores of 2 to 5 for different cultivarswheat] occur at 21 to 30 DAS/DAT, and third dose isof rice and wheat and were compared with the zero-N control and asplit at panicle initiation (PI) stage. In some rice-grow-recommended fixed-time N splitting. In rice, LCC � 3 for ‘Basmati-ing countries, present recommendations call for 50 to370’, 4 for ‘Saket-4’, and 5 for ‘Hybrid 6111/PHB-71’ produced higher

yield and NUE than recommended N splits. In wheat, maintenance 67% of total fertilizer N inputs to be broadcast-incorpo-of LCC � 4 required 120 kg N ha�1, which produced higher grain rated before transplanting and the remainder top dressedyield, N uptake, and NUE than that of recommended N splits. Chloro- at 5 to 7 d before PI (Cassman et al., 1998). Farmersphyll meter reading and crop growth rate (g m�2 day�1) at 15 d after do not appear to recognize differences in soil N supplytransplanting in rice and 21 d after seeding in wheat were not signifi- because no relationship exists between the amount ofcantly different with or without basal N application, indicating that N fertilizer they apply and crop N uptake in plots estab-basal N application in rice and wheat was not necessary in soils having

lished within their fields that did not receive applied Nrelatively high indigenous N supply. Both LCC and SPAD readings(Cassman et al., 1998).(r � 0.84 to 0.91) were highly correlated in rice and wheat. Net returns

The optimum use of N can be achieved by matchingwere 19 to 31% higher in LCC-based N management than in fixed-N supply with crop demand. A potential solution hastime N application for rice–wheat cropping.been tried to regulate the timing of N application in riceand wheat using a chlorophyll meter (or SPAD meter)or a LCC to determine the plant N needs (Balasubra-Rice and wheat, the staple food crops for Southmanian et al., 2003; Bijay-Singh et al., 2002). The conceptAsian people, are of great significance, as theseis based on results that show a close link between leafcrops contribute more than 80% of the total cereal pro-chlorophyll content and leaf N content. Moreover, leaf-duction in South Asia—Bangladesh, Pakistan, India, andarea–based N concentration (Na) varies within a narrowNepal (Timsina and Connor, 2001). Nitrogen is the nutri-range at different growth stages. The close relationshipent that most often limits crop production. Cereals in-between Na and SPAD or LCC readings facilitates thecluding rice and wheat accounted for approximatelyuse of a single critical value for SPAD or LCC to moni-56% of the worldwide N fertilizer utilized (IFA, 2002).tor leaf N status at all growth stages. Thus, the chloro-Nitrogen use efficiency in rice and wheat is low. Basedphyll meter or LCC can be used to quickly and reliablyon a recent worldwide evaluation, the fertilizer N recov-assess the leaf N status of crops at different growthery efficiency has been found to be around 30% in ricestages. The LCC, because of its low cost for farmers,and wheat with current practices (Krupnik et al., 2004).has shown much promise in real-time N managementThe main reason of low NUE is inefficient splitting ofstudies conducted in India and elsewhere. But, theseN applications, including the use of N in excess to thestudies were restricted to coarse rice cultivars havingrequirements. Fixed-time recommended N split applica-similar genetic potential and harvest index (Balasubra-manian et al., 1999, 2003; Bijay-Singh et al., 2002). In

A.K. Shukla, V.K. Singh, B.S. Dwivedi, S.K. Sharma, P.S. Pandey, LCC-based N management, chart readings start at 15and Y. Singh, Project Directorate for Cropping Syst. Res. (PDCSR),

DAT in rice and 21 DAS in wheat. An important issueModipuram, Meerut-250110, India; J.K. Ladha, V. Balasubramanian,is whether to use the basal N (at planting) when the LCCand A.T. Padre, Int. Rice Res. Inst., DAPO Box 7777, Metro Manila,

Philippines; R.K. Gupta, Rice–Wheat Consortium for IGP, CIMMYT-RWC, CG Block, NASC Complex, DPS Marg Pusa Campus, New

Abbreviations: AEN, agronomic efficiency of nitrogen; CRI, crownDelhi-110012, India; H. Pathak, Indian Agric. Res. Inst., New Delhi,root initiation; DAS, days after sowing; DAT, days after transplanting;India; and R.L. Yadav, Natl. Agric. Technol. Project, Krishi Anusan-INS, indigenous nitrogen supply; LCC, leaf color chart; Na, leaf nitro-dhan Bhawan-II, New Delhi 110012, India. Received 22 Oct. 2003.gen content on leaf area basis; Ndw, leaf nitrogen content on dry weight*Corresponding author ([email protected]).basis; NR, net return(s); NUE, nitrogen use efficiency; PI, panicleinitiation; REN, recovery efficiency of nitrogen; SLW, specific leafPublished in Agron. J. 96:1606–1621 (2004).

© American Society of Agronomy weight; SPAD, soil plant analysis development; TCC, total cost of cul-tivation.677 S. Segoe Rd., Madison, WI 53711 USA

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SHUKLA ET AL.: CALIBRATION OF LEAF COLOR CHART FOR N MANAGEMENT IN RICE–WHEAT 1607

(160 g clay kg�1, 190 g silt kg�1, and 630 g sand kg�1). Theis used as an approach for managing N. In the rice–wheatorganic C, Olsen P and available K, and diphenyl triaminecropping systems, genotypes of various background andpenta acetic acid (DTPA) extractable Zn were 5.4 g kg�1,growth duration are grown in a sequence (wheat after10.6 mg kg�1, 0.19 C mol kg�1, and 0.60 mg kg�1, respectively.the harvest of rice in the same plot) to fit in a system.

No information is available on critical LCC values forExperimental Design and Treatmentsrice genotypes having different genetic background, plant

type, and leaf color. It is also important to determine The experiment was laid out in a split-plot design withwhether the LCC could be useful for applying N in rice and wheat grown in sequence. In rice, three genotypes,

Basmati-370 [traditional, tall, long fine grain, scented, long-wheat, particularly before the maximum tillering stage.duration (155–160 d), high-value crop], Saket-4 [inbred, coarseTherefore, this study was designed to examine thesegrain, short duration (115–120 d)], and Hybrid 6111/PHB-71issues while considering a systems perspective. Our ob-[improved, high yield potential, coarse grain, medium durationjectives were to (i) assess the need for basal N applica-(135–140 d)], were grown in main plots with three replications.tion in LCC-based N management in rice and wheat,In wheat, cultivars PBW-343 (early sown), HD-2687 (timely(ii) establish the validity of LCC with chlorophyll meter sown), and PBW-226 (late sown) were grown in the same

readings and leaf N status of crop, (iii) determine thresh- layout in the plots vacated from Saket-4, the hybrid, and Bas-old LCC values for different rice and wheat genotypes mati-370, respectively. The five fertilizer N (as urea) manage-based on agronomic parameters [i.e., yield, agronomic ment treatments assigned to subplots are described in Tablesefficiency of N (AEN) and recovery efficiency of N 1 and 2. In rice, the LCC scores of � 2, 3, and 4 for Basmati-

370 and � 3, 4, and 5 for Saket-4 and Hybrid 6111/PHB-71(REN)], and (iv) determine economic return of differentwere compared with fixed-time recommended N rates (80,rice–wheat genotype combinations, using LCC and120, and 150 kg N ha�1 for Basmati-370, Saket-4, and Hybridfixed-N split methods for N management.6111/PHB-71, respectively). In wheat, LCC scores of � 3, 4,and 5 were evaluated as critical values for all three cultivars

MATERIALS AND METHODS and compared with locally recommended N splits (120 kg Nha�1). In the recommended N rate treatment, N was appliedExperimental Sitein three equal splits at transplanting (basal), midtillering, and

A field experiment during two consecutive years (2001– PI in rice and at sowing (basal), crown root initiation stage2002 and 2002–2003) was conducted on a typic Ustrochrept (CRI), and PI in wheat. Both rice and wheat received P and K(Sobhapur sandy loam) soil of the research farm of the Project at the uniform rate of 26 and 33 kg ha�1 through single super-Directorate for Cropping Systems Research, Modipuram, phosphate and muriate of potash, respectively. In addition,Meerut (29�4�N, 77�46�E; 237 m above mean sea level), in 5 kg Zn ha�1 was also applied uniformly as zinc sulfate to eachwestern Uttar Pradesh, representing Transect 3 (the Upper rice crop.Gangetic Plains) of the Indo-Gangetic Plains Region. This isan intensively cultivated transect with 150% cropping inten- Crop Managementsity. The climate of Meerut is semiarid subtropical, with dry,hot summers and cold winters. The average annual rainfall is The land was prepared by two crisscross plowings and two

harrowings. Land was leveled and puddled for rice trans-810 mm, 75% of which is received during July–September.Mean maximum and minimum temperatures were 34.0 and planting on 7 July 2001. Thereafter, 25-d-old seedlings were

transplanted at 20- by 15-cm spacing in 8- by 6-m subplots on 824.1�C during rice cropping (July to Oct.) and 26.9 and 10.1�Cduring the wheat (Nov. to Apr.) season. The soil of the experi- July 2001. After harvest on 14 Oct. (Saket-4), 30 Oct. (Hybrid-

6111), and 21 Nov. 2001 (Basmati-370), the individual plotsmental sites derived from Gangetic alluvium is well drained,slightly alkaline in reaction (pH 8.2), and sandy loam in texture were prepared after irrigation for wheat sowing. The wheat

Table 1. Treatments used in rice under rice–wheat system during 2001–2002 and 2002–2003 at Modipuram, Meerut, India.

Treatment details No. of splits Total N applied Time of N application

Genotype � N management 2001–2002 2002–2003 2001–2002 2002–2003 2001–2002 2002–2003

no. kg ha�1 DAT†Basmati-370 (traditional tall)

Zero N (control) – – 0 0 – –20 kg N ha�1 at LCC‡ � 2, no basal N 1 1 20 20 55 5520 kg N ha�1 at LCC � 3, no basal N 4 4 80 80 16, 35, 45, 65 15, 35, 47, 6520 kg N ha�1 at LCC � 4, no basal N 5 5 100 100 16, 35, 45, 55, 65 15, 35, 47, 55, 65Recommended splits (80 kg N ha�1 in three equal splits) 3 3 80 80 1, 25, 55 1, 25, 55

Saket-4 (inbred, short structure)Zero N (control) – – 0 030 kg N ha�1 at LCC � 3, no basal N§ 2 2 60 75 25, 45 25, 4530 kg N ha�1 at LCC � 4, no basal N§ 4 4 120 135 15, 25, 35,45 15, 25, 47, 5530 kg N ha�1 at LCC � 5, no basal N§ 4 4 120 150 15, 25, 35, 45 15, 25, 35, 47Recommended splits (120 kg N ha�1 in three equal splits) 3 3 120 120 1, 25, 50 1, 25, 50

Hybrid 6111/PHB-71 (improved short structure)Zero N (control) – – 0 0 – –30 kg N ha�1 at LCC � 3, no basal N§ 3 3 90 90 15, 35, 55 15, 35, 5530 kg N ha�1 at LCC � 4, no basal N§ 5 4 150 135 15, 25, 35, 45, 55 15, 25, 35, 5530 kg N ha�1 at LCC � 5, no basal N§ 5 5 150 165 15, 25, 35, 45, 55 15, 25, 35, 45, 55Recommended splits (150 kg N ha�1 in three equal splits) 3 3 150 150 1, 25, 55 1, 25, 55

† DAT, days after transplanting.‡ LCC, leaf color chart.§ In 2002–2003, 45 kg N ha�1 was applied during rapid growth stage (29–45 DAT).

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1608 AGRONOMY JOURNAL, VOL. 96, NOVEMBER–DECEMBER 2004

Table 2. Treatments used in wheat under rice–wheat system during 2001–2002 and 2002–2003 at Modipuram, Meerut, India.

Treatment details No. of splits Total N applied Time of N application

Genotype � N management 2001–2002 2002–2003 2001–2002 2002–2003 2001–2002 2002–2003

no. kg ha�1 DAS†PBW 343 (early sown,‡ 145- to 155-d duration)

Zero N (control) – – 0 0 – –30 kg N ha�1 at LCC§ � 3, no basal N 2 2 60 60 42, 66 42, 8730 kg N ha�1 at LCC � 4, no basal N 4 4 120 120 21, 42, 66, 84 21, 42, 64, 9140 kg N ha�1 at LCC � 5, no basal N 4 4 160 160 21, 42, 58, 84 21, 42, 64, 87Recommended splits (120 kg N ha�1 in three equal splits) 3 3 120 120 B¶, 21, 60 B¶, 21, 66

HD 2687 (timely sown,# 130- to 140-d duration)Zero N (control) – – 0 030 kg N ha�1 at LCC � 3, no basal N 2 2 60 60 43, 80 43, 8730 kg N ha�1 at LCC � 4, no basal N 4 4 120 120 21, 43, 65, 80 22, 43, 68, 8740 kg N ha�1 at LCC � 5, no basal N 4 4 160 160 21, 43, 65, 80 22, 43, 68, 101Recommended splits (120 kg N ha�1 in three equal splits) 3 3 120 120 B, 21, 55 B, 21, 60

PBW 226 (late sown,†† 115- to 120-d durationZero N (control) – – 0 0 – –30 kg N ha�1 at LCC � 3, no basal N 3 3 90 90 21, 42, 81 21, 43, 7630 kg N ha�1 at LCC � 4, no basal N 4 4 120 120 21, 42, 61, 81 21, 43, 54, 7640 kg N ha�1 at LCC � 5, no basal N 4 4 160 160 21, 34, 61, 81 21, 43, 54, 76Recommended splits (120 kg N ha�1 in three equal splits) 3 3 120 120 B, 21, 60 B, 21, 55

† DAS, days after sowing.‡ Early sown � sown in the first week of November.§ LCC, leaf color chart.¶ B, basal N application at sowing.# Timely sown � sown in the last week of November.†† Late sown � sown in the second week of December.

cultivars PBW-343 (early sown), HD-2687 (timely sown), and Leaf Color Chart and ChlorophyllPBW-226 (late sown) were sown in rows 20 cm apart in the Meter Measurementsame layout using 100 kg seed ha�1 on 8 Nov., 26 Nov., and

The LCC jointly developed by the International Rice Re-13 December 2001 in plots vacated from Saket-4, Hybrid-6111,search Institute (IRRI) and Philippine Rice Research Instituteand Basmati-370, respectively. These wheat cultivars were(PhilRice), consisting of six green shades from yellowish greenharvested on 10, 16, and 20 Apr. 2002, respectively. Similarly,to dark green, was used in this study. In rice, 15 hills wereduring the second year (2002–2003), rice genotypes Saket-4,selected at random in each plot. From each hill, three readingsHybrid-PHB-71, and Basmati-370 were transplanted on 10were taken from the uppermost fully expanded leaf. In wheat,July and harvested on 15 Oct., 2 Nov., and 24 Nov. 2002,10 disease-free plants were chosen in each plot, and the colorrespectively. Wheat cultivars PBW-343, HD-2687, and PBW-of the youngest fully expanded leaf was measured. The SPAD226 were sown on 2 Nov., 22 Nov., and 16 Dec. 2002 andreading of the same leaf used for LCC measurement was alsoharvested on 8, 11, and 15 Apr. 2003, respectively.taken simultaneously for calibration of the LCC. In rice, bothBoth crops were grown under assured irrigation. For riceLCC and SPAD readings were taken at 10-d intervals, startingcultivation, plots were kept continuously flooded 2 wk afterfrom 15 DAT till 50% flowering. In wheat, the LCC andtransplanting. In addition to rainfall, a total of 9, 9, and 11SPAD meter readings started at the CRI stage (21 DAS)irrigations during 2001 and 14, 15, and 16 irrigations duringand ended at 50% flowering. In addition, the LCC score and2002 were given to rice genotypes Saket-4, Hybrid-6111/PHB-chlorophyll meter reading were also taken at PI. Whenever71, and Basmati-370, respectively. At each irrigation, 3 to 5 cmthe LCC reading was equal to or below the set critical value,of water was applied, and the interval between two irrigationsfertilizer N was applied at 20 kg N ha�1 for Basmati-370 anddepended on the disappearance of water. In wheat, the number30 kg N ha�1 each for Saket-4 and Hybrid-6111/PHB-71 inof irrigations depended on time of sowing (cultivar duration)2001–2002. Since LCC � 5 could not be attained in Year 1,and rainfall events during the growing season. In 2001–2002,45 kg N ha�1 was applied to Saket-4 and Hybrid-PHB-71early sown wheat cultivar PBW-343 received four irrigationsduring the rapid growth period (29 to 49 DAT) in Year 2. Inat 21, 42, 66, and 112 DAS; timely sown HD-2687 receivedwheat, 30 kg N ha�1 was applied in LCC � 3 and 4 and 40irrigations at 21, 42, 66, and 101 DAS; and late-sown PBW-kg N ha�1 in LCC � 5 treatments. No basal N was applied226 received only three irrigations at 21, 42, and 81 DAS. Inin the LCC-based treatments on rice or wheat.2002–2003, the early sown wheat (PBW-343) received five

irrigations at 21, 42, 64, 85, and 111 DAS, and four irrigationswere applied to both timely sown HD-2687 at 21, 43, 64, and Potential Yield Simulation101 DAS and late-sown PBW-226 at 21, 40, 76, and 92 DAS.

Potential yields, i.e., maximum yield of a variety restrictedStandard practices were followed for insect pest and diseaseonly by the season-specific climatic conditions, of rice andcontrol. At maturity, rice and wheat were harvested manuallywheat grown during the experiment were estimated usingat ground level, and grain and straw yields of both rice andCERES-RICE 3.5 (98.0) (Singh et al., 1998) and CERES-wheat were determined from an area of 27 m2 located in theWHEAT 3.5 (98.0) (Ritchie et al., 1998) models, respectively.center of each plot. The grains were threshed using a plotThe genetic coefficients for the cultivars in this study werethresher, dried in a batch grain dryer, and weighed. Grainestimated from the first year of the field observations by re-moisture was determined immediately after weighing, and sub-peated iterations until close matches were observed betweensamples were dried at 70�C for 48 h. Grain yield of rice andsimulated and observed phenology and yield. The perfor-wheat were reported at 140 and 120 g kg�1 moisture content,mance of the models has been well validated in the rice–wheatrespectively. Straw weights were expressed on an oven dry

weight basis. growing environments of India (Timsina et al., 1998; Pathak

https://www.researchgate.net/publication/250103935_Cultivar_Nitrogen_and_Moisture_Effects_on_a_Rice-Wheat_Sequence_Experimentation_and_Simulation?el=1_x_8&enrichId=rgreq-0523d15352223b192662b046a9a828b0-XXX&enrichSource=Y292ZXJQYWdlOzI0MjI0NDI1MztBUzoyMTI5Mzc5MTU1Mzk0NTZAMTQyNzc3OTc2MzgyNQ==


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et al., 2003). The daily weather data (solar radiation, maximum their interactions using IRRISTAT Version 1992 (IRRI, 1992).Duncan’s multiple range test (DMRT) was used at the �0.05temperature, and minimum temperature) required for simula-

tion were collected from the meteorological observatory lo- level of probability to test differences between treatment means.The relationship of LCC score to SPAD readings was deter-cated at Modipuram.mined for different rice and wheat genotypes by regressionanalysis using the data at different growth stages and dataPlant Sampling Measurements and Analysispooled across growth stages, N management options, and

Leaf samples of 1-m row length were collected for the years. To test the significance of LCC and SPAD regressionmeasurement of leaf area, dry weight, and N content at PI equation, the confidence limit (95%) was calculated as givenand flowering stages. Leaf area was measured by leaf area by Draper and Smith (1986). Correlations between LCC scoresmeter (LI-3100, LI-COR, Lincoln, NE). The crop growth rate and SPAD readings were determined by correlation analysis.was determined by harvesting the plant aboveground biomassfrom 1-m row length area at 7, 11, 15, and 20 DAT of rice

Calculationsand 8, 11, 15, 21, and 31 DAS of wheat following the method ofLeopold and Kriedemann (1975). Dry weight was determined Nitrogen Use Efficiencyafter oven drying at 70�C to constant weight. Grain and straw

Agronomic efficiency of added N (AEN) was calculatedsamples of rice and wheat collected from each plot were dried(Cassman et al., 1998):at 70�C in a hot-air oven. The dried samples were ground in

a stainless steel Wiley Mill, and N content in leaf, grain, and AEN (� kg grain/kg N applied) �straw was determined by digesting the samples in sulfuric acid

Grain yield in N-fertilized plots �(H2SO4) followed by analysis of total N by the Kjeldahl method(Bremner and Mulvaney, 1982) using a Kjeltec autoanalyzer. grain yield in zero–N plot

Quantity of N fertilizer applied in N–fertilized plot [3]Economic Analysis

Recovery efficiency of added N (REN) was calculated (Cass-The total cost of cultivation (TCC) of rice and wheat was man et al., 1998):

calculated on the basis of different operations performed andmaterials used for raising the crops, including the cost of fertil- REN (%) �izer N. The cost of labor for recording LCC readings was Total N uptake (kg N ha�1) in N-fertilized plot �calculated on actual basis. For each recording date, 2 persondays ha�1 were required, and depending on crop duration, total uptake (kg N ha�1) in zero–N plot � 100

Quantity of fertilizer N applied in N-fertilized plot [4]LCC readings were recorded 5 to 7 times in rice and 7 to 10times in wheat. One person day ha�1 was required for supply-ing the extra N split. Thus, on average, 26 to 32 person dayswere engaged in various LCC treatments. The cost of addi- RESULTS AND DISCUSSIONtional fertilizer, if any, was also added to the TCC. The pricesof important materials used and operations performed were Assessing Need for Basal Nitrogenrice seed, US$0.76, US$0.23, and US$3.26 kg�1 for Basmati- Application in Rice and Wheat370, Saket-4, and Hybrid-6111/PHB-71, respectively; wheat

In 2001, total N applied with LCC � 3 in Basmati-seed, US$0.45 kg�1; N, US$0.23 kg�1; irrigation, US$4.13 irri-gation�1 ha�1; labor, US$1.57 person days�1 d�1; plowing/har- 370 and � 4 for Saket-4 and Hybrid 6111 was the same asrowing, US$2.61 ha�1 operation�1; puddling, US$9.35 ha�1 in fixed-schedule recommended N treatment (Table 1).operation�1. The current exchange rate is US$1 � Rs46. But grain yield, AEN, and REN were higher for LCC-

Gross returns (GR) were calculated by multiplying grain based N treatments than for fixed-schedule N applica-yield by grain price: US$0.24 kg�1 for Basmati-370, US$0.12 tion (Table 3). The threshold LCC values that optimizedkg�1 for both Saket-4 and Hybrid-6111/PHB-71, and US$0.14 the yield, AEN, and REN were LCC � 3 for Basmati-370kg�1 for wheat. Net returns (NR) were calculated as

and LCC � 4 for Saket-4 and Hybrid 6111 during 2001.NR � GR � TCC [1] In 2002, the threshold value of LCC � 3 with an

application 80 kg N ha�1 optimized the yield, AEN, andThe NR of rice genotypes Basmati-370, Saket-4, and Hybrid-REN for Basmati-370; the threshold value of LCC � 46111/PHB-71 were added to the NR of wheat cultivars PBW-for Saket-4 required 135 kg N ha�1 to optimize yield,226, PBW-343, and HD-2687, respectively, to calculate theAEN, and REN; similarly, the threshold value of LCC �system net return (SNR) as5 required 165 kg N ha�1 for Hybrid PHB71 to optimize

SNR � NRr NRw [2] yield, AEN, and REN (Table 4). This means that Saket-4and hybrid PHB71 required 15 kg ha�1 more N forwhere NRr is the net return from rice and NRw is the net

return from wheat. LCC-based N management than for fixed-schedule NThe NR of the rice–wheat system was calculated for the application during 2002. In wheat also, the LCC � 4

LCC-based N management at agronomically determined opti- treatment (120 kg N ha�1without basal) produced amum threshold values and compared with the fixed split rec- higher grain yield and greater AEN and REN than recom-ommended N application. mended N splits (Tables 5 and 6). These results indicate

that N applied starting at 14 DAT in rice and at 21 DASData Analysis in wheat based on crop need as determined by the LCC

was used more efficiently to optimize both grain yieldThe statistical analysis of data consisted of analysis of vari-and NUE. Results of this study and published elsewhereance for yield parameters of rice and wheat to determine the

effects of rice genotypes/wheat cultivars, N treatments, and (Ladha et al., 2000) showed that the current recommen-

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Table 3. Grain yield, total N uptake, and N use efficiencies [agronomic efficiency of nitrogen (AEN) and recovery efficiency of nitrogen(REN)] of three rice genotypes grown during 2001 with different N management treatments at Modipuram, India.

N management treatments Total N applied Grain yield Total N uptake AEN REN

kg ha�1 Mg ha�1 kg ha�1 kg grain kg�1 N %Genotype: Basmati-370

No N control 0 2.8 d† 63 d – –LCC‡ � 2, no basal N 20 3.4 c 77 c 27.0 a 70 aLCC � 3, no basal N 80 4.3 a 110 a 17.9 b 58 bLCC � 4, no basal N 100 3.9 b 112 a 12.5 c 49 cRecommended N 80 3.8 b 100 b 12.9 c 46 c

Genotype: Saket 4No N control 0 3.6 d 54 d – –LCC � 3, no basal 60 4.9 c 88 c 22.3 a 59 aLCC � 4, no basal 120 6.1 a 114 a 21.2 a 50 bLCC � 5, no basal 120 6.2 a 116 a 21.6 a 52 bRecommended N 120 5.5 b 105 b 15.8 b 43 c

Genotype: Hybrid 6111No N control 0 3.8 d 62 d – –LCC � 3, no basal N 90 6.0 c 115 c 24.8 a 58 aLCC � 4, no basal N 150 7.4 a 136 a 23.8 a 50 bLCC � 5, no basal N 150 7.3 a 137 a 23.5 a 50 bRecommended N 150 6.8 b 124 b 19.8 b 41 c

Source of variation Analysis of variance for yield and uptake Analysis of variance for AEN and REN

df F value (grain yield) F value (N uptake) df F value (AEN) F value (REN)Genotype (G) 2 254.3** 28.1* 2 29.6* 5.1*N management (N) 5 86.4** 311.2** 4 141.3** 64.0**G � N 10 5.6** 9.26** 8 28.4** 5.9**Residual 30 24

* Significant at P � 0.05.** Significant at P � 0.01.† Within a column, means followed by the same letter are not significantly different at the 0.05 level of probability by Duncan’s multiple range test.‡ LCC, leaf color chart.

dation of fixed-time split N applications at specified nous N supply (INS). Although basal N application (ap-plied just before or at planting) is recommended, itsgrowth stages is not adequate to synchronize N supply

with actual crop N demand because of poorly designed need has not been based on the early-season INS. TheINS is defined as plant N accumulation in grain andN splitting and variations in crop N demand and indige-

Table 4. Grain yield, total N uptake, and N use efficiencies [agronomic efficiency of nitrogen (AEN) and recovery efficiency of nitrogen(REN)] of three rice genotypes grown during 2002 with different N management treatments at Modipuram, India.


kg ha�1 Mg ha�1 kg ha�1 kg grain kg�1 N %Genotype: Basmati-370

No N control 0 2.7 d† 58 d – –LCC‡ � 2, no basal N 20 3.2 c 72 c 26.7 a 69 aLCC � 3, no basal N 80 4.3 a 106 ab 20.7 b 58 bLCC � 4, no basal N 100 4.1 a 112 a 15.2 c 52 cRecommended N 80 3.7 b 103 b 14.5 c 49 d

Genotype: Saket 4No N control 0 3.5 c 54 d – –LCC � 3, no basal 75 5.2 b 98 c 23.2 a 59 aLCC � 4, no basal 135 6.5 a 122 a 21.5 a 50 bLCC � 5, no basal 150 6.7 a 126 a 20.6 a 48 bRecommended N 120 5.4 b 101 b 16.1 b 39 c

Genotype: Hybrid PHB-71No N control 0 3.8 e 61 e – –LCC � 3, no basal N 90 6.6 cd 114 d 30.9 a 59 aLCC � 4, no basal N 135 7.6 b 137 b 28.1 b 57 abLCC � 5, no basal N 165 8.1 a 149 a 25.9 c 54 bRecommended N 150 6.9 c 127 c 20.7 d 44 c


df F value (grain yield) F value (N uptake) df F value (AEN) F value (REN)Genotype (G) 2 212.0** 14.8* 2 18.1* 34.9**N management (N) 5 76.8** 219.4** 4 140.4** 84.3**G � N 10 4.8** 7.4** 8 8.1** 3.9*Residual 30 24


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Table 5. Wheat grain yields, total N uptake, and N use efficiencies [agronomic efficiency of nitrogen (AEN) and recovery efficiency ofnitrogen (REN)] of three wheat cultivars grown during 2001–2002 using different fertilizer N management criteria at Modipuram, India.


kg ha�1 Mg ha�1 kg ha�1 kg grain kg�1 N %Cultivar: PBW-343 (early sown)

No N control 0 2.2 d† 44 eLCC‡ � 3, no basal N 60 4.2 c 83 d 32.1 a 65.4

a‡LCC � 4, no basal N 120 5.6 a 119 b 27.5 b 63.2 aLCC � 5, no basal N 160 6.0 a 131 a 24.1 c 54.8 bRecommended N 120 4.9 b 103 c 22.4 c 49.3 c

Cultivar: HD 2087 (timely sown)No N control 0 2.3 d 45 fLCC � 3, no basal 60 4.1 c 84 e 31.1 a 63.9 aLCC � 4, no basal 120 5.7 a 121 b 27.8 a 62.4 aLCC � 5, no basal 160 6.1 a 139 a 22.6 b 56.1 bRecommended N 120 4.9 b 104 d 19.3 b 48.9 c

Cultivar: PBW 226 (late sown)No N control 0 1.8 c 35 eLCC � 3, no basal N 90 4.0 b 84 d 23.6 a 54.9 aLCC � 4, no basal N 120 4.4 ab 97 b 21.7 a 51.4 bLCC � 5, no basal N 160 4.6 a 107 a 17.4 b 45.0 cRecommended N 120 3.9 b 88 cd 18.3 a 44.4 c


df F value (grain yield) F value (N uptake) df F value (AEN) F value (REN)Genotype (G) 2 18.3 31.2* 2 18.4* 308.4**N management (N) 5 115.8** 121.4** 4 144.4** 170.3*G � N 10 1.8 NS 5.4* 8 2.6 NS 3.2*Residual 30 – – 24 – –


straw at physiological maturity in zero-N plots, which (Dobermann et al., 2003). The INS capacity varies withcropping season, soil, and crop (Dobermann et al., 2002;represents all sources of N (soil, organic materials, crop

residues, rhizosphere N fixation, irrigation water, rain- Adhikari et al., 1999; Stalin et al., 1996). The INS capac-ity in the present study (calculated from N omissionfall, etc.) available to crops during the growing season

Table 6. Wheat grain yields, total N uptake, and N use efficiencies [agronomic efficiency of nitrogen (AEN) and recovery efficiency ofnitrogen (REN)] of three wheat cultivars grown during 2002–2003 using different fertilizer N management criteria at Modipuram, India.


kg ha�1 Mg ha�1 kg ha�1 kg grain kg�1 N %Cultivar: PBW-343 (early sown)

No N control 0 2.1 d† 45 eLCC‡ � 3, no basal N 60 4.2 c 88 d 34.3 a 71.6 aLCC � 4, no basal N 120 5.7 a 121 b 29.7 b 63.3 bLCC � 5, no basal N 160 6.1 a 134 a 24.0 c 55.6 cRecommended N 120 5.2 b 108 c 25.0 c 52.5 c

Cultivar: HD 2087 (timely sown)No N control 0 2.2 d 46 eLCC � 3, no basal N 60 4.1 c 85 d 31.6 a 65.0 aLCC � 4, no basal N 120 5.6 a 120 b 29.0 b 61.6 aLCC � 5, no basal N 160 5.9 a 136 a 23.1 c 56.2 bRecommended N 120 5.0 b 109 c 23.3 c 52.5 c

Cultivar: PBW 226 (late sown)No N control 0 1.8 d 36 dLCC � 3, no basal N 90 4.1 c 85 c 25.5 a 54.4 aLCC � 4, no basal N 120 4.5 b 99 b 22.7 b 52.5 aLCC � 5, no basal N 160 4.8 a 109 a 18.8 c 45.6 bRecommended N 120 4.1 c 89 c 19.1 c 44.2 b

Source of variation Analysis of variance for grain yield uptake Analysis of variance for AEN and REN

df F value (grain yield) F value (N uptake) df F value (AEN) F value (REN)Genotype (G) 2 14.2* 18.6* 2 37.4* 69.2*N management (N) 5 148.4** 151.1** 4 154.1** 123.6**G � N 10 3.2** 3.8* 8 4.1* 2.1 NSResidual 30 – – 24


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Fig. 1. Chlorophyll meter reading as influenced by N management—zero-N control, leaf color chart (LCC)-based (no basal N), and fixed-timerecommended N split (28, 40, and 50 kg N ha�1 in Basmati-370, Saket, and hybrid rice, respectively, and 40 kg N ha�1 in each cultivar ofwheat) in rice and wheat. Vertical bar indicates the mean standard error (in rice, n � 15; in wheat, n � 30).

plots) was 60 3.2, 54 2.2, and 61 2.6 kg N ha�1 phyll meter readings taken at 15 DAT in rice and at 21DAS in wheat in the LCC � 4 treatment (no basal Nfor Basmati-370, Saket-4, and Hybrid 6111/PHB-71 and

44.3 1.8, 45 2.5, and 35 1.5 kg ha�1 for wheat application), fixed-time recommended N split (40 kg Nha�1 basal), and zero-N control plot did not show acultivars PBW-343, HD-2687, and PBW-226, respec-

tively. The low INS in wheat could be due to less residual significant difference (Fig. 1). The crop growth rate upto 15 DAT in rice and up to 21 DAS in wheat also didN left after rice harvest and low biological activity in

the winter season when wheat is grown. Since the leaf not exhibit a difference between treatments, i.e., withand without basal N application (Fig. 2). This indicatedchlorophyll content is closely related to leaf N concen-

tration, SPAD meter readings during the early stage of that basal N application had no effect on early cropgrowth and N absorption by plants and that INS levelscrop growth should reflect the INS status. The chloro-

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Fig. 2. Initial crop growth rate (CGR, g m�2 day�1) of rice and wheat as influenced by N management—zero-N control, leaf color chart (LCC)-based (no basal N), and fixed-time recommended N split (28, 40, and 50 kg N ha�1 in Basmati-370, Saket, and hybrid rice, respectively, and40 kg N ha�1 in each cultivar of wheat). Vertical bar indicates the mean standard error (n � 6).

of 50 to 60 kg ha�1 for rice and 35 to 45 kg ha�1 for growth begins (Cassman et al., 1996; Peng et al., 1995a).Further, the LCC- and SPAD-based N managementwheat were adequate to meet the plant’s need of N at

early stages in these soils. The contribution of N ac- experiments conducted by Bijay-Singh et al. (2002) with20 kg N ha�1 as basal and without basal N applicationquired during early vegetative growth to grain and total

biomass production at maturity is considerably less im- showed no difference in grain yield. Rice seedlings needabout 7 to 8 d to recover from transplanting shockportant than the contribution of N uptake after midtill-

ering when crop demand is greatest and reproductive (Meelu and Gupta, 1980), and thus, N uptake within 2

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wk of transplanting is very small (Peng and Cassman, of determination were comparable in Basmati-370 andHybrid 6111/PHB 71 (Fig. 5). In wheat, slope intercept1998). Likewise, in wheat, N uptake at 21 DAS remained

very small (3 to 5 kg ha�1). We also found that wheat and coefficients in PBW-343 were as good as in HD-2687.However, cultivar PBW-226 had different slope and in-N uptake at 21 DAS in treatments with and without

basal N did not differ (data not shown), suggesting that tercept and coefficient than PBW-343 and HD-2687.The regression equations between LCC scores and SPADN uptake up to 21 DAS was very low and N demand

could be met from the seed (100 kg ha�1 wheat seed readings for rice and wheat genotypes, combining dataacross growth stages, N management options, and year,supply 1.6 kg N ha�1) and INS. In both 2001 and 2002,

the rice grain yields in zero-N control plots were �3 are found in Table 7.In rice, Basmati-370 and hybrid genotypes had similarMg ha�1 in Saket-4 and Hybrid 6111/PHB-71 and �2.5

Mg ha�1 in Basmati–370 (Tables 3 and 4), indicating coefficients of determination, but the intercepts andslopes were different. However, Saket-4 and the hybridadequate native N supply from soil. This supports the

suggestion of Balasubramanian et al. (1999) that for rice were comparable in slope, with different interceptand coefficients, and Saket-4 and Basmati-370 were alikehigh-yielding rice varieties, soils producing a grain yield

of �3 Mg ha�1 without any fertilizer application may in intercept with different slopes and coefficients. Forwheat, coefficients, intercepts, and slopes were similarnot need basal N application. Dobermann et al. (2003)

found that about 50% of rice soils in their studies had for all cultivar–planting date combinations. On the basisof grain yield, N uptake, and NUE, LCC � 3 was appro-INS � 53 kg ha�1 and required no basal N application

while only 25% of the soils had INS � 41 and responded priate for Basmati-370, LCC � 4 for Saket-4, LCC � 5for Hybrid 6111/PHB-71, and LCC � 4 for all threeto basal N application. These results strongly indicate

that fertilizer NUE could be increased by using the LCC- cultivars of wheat. The corresponding SPAD values fordifferent varieties/LCC were Basmati-370 (LCC � 3),or SPAD-based N management strategy without any33; Saket-4 (LCC � 4), 44; and Hybrid 6111/PHB-71basal N application at planting for both rice and wheat(LCC � 5), 47. The relationship between SPAD valuecrops provided that INS is sufficiently high (50–60 kgand LCC score for rice cultivar IR72 reported by YangN ha�1 for rice and 35–45 kg N ha�1 for wheat).et al. (2003) was SPAD � 11.67 7.25LCC, where LCCSince the issue of basal N application has an important3, 4, and 5 corresponded to SPAD values of 33, 41, andbearing on overall N management in the rice–wheat48, respectively, which are nearly similar to those of oursystem, further on-farm studies need to be conductedstudy except for Saket-4, which exhibited higher valuefor a long enough period to determine the minimumof SPAD at a specified LCC score. We speculate theyield level in zero-N plots above which no basal N is re-greater leaf thickness/specific leaf weight (SLW) of Sa-quired.ket-4 could be the reason for getting higher SPAD valuein Saket-4. In wheat, LCC 4 corresponded to a SPADCalibration of Leaf Color Chart with SPADvalue of 41.3, 41.7, and 40 for PBW-343, HD-2687, PBW-Value and Leaf Nitrogen Content226, respectively. A study conducted by Follett et al.

The LCC and SPAD readings of all the genotypes (1992) to estimate leaf N content and determine thehad a strong positive correlation (r � 0.84 to 0.91) in need for additional fertilizer N in dryland winter wheatboth rice and wheat. The regression analysis showed a revealed that grain yield responded with a meter readingsignificant linear relationship between LCC and SPAD of less than about 42. Another study conducted by Bijay-value at all growth stages for all cultivars of rice and Singh et al. (2002) at Ludhiana, India, indicated thatwheat (Fig. 3 and 4). But the coefficients of determi- wheat responded to N application at maximum tilleringnation, slopes, and intercepts varied among the growth when SPAD values were �42. Thus, these results in-stages within the genotype and between the genotypes. In ferred that the LCC could replace the SPAD meter forrice, the coefficients of determination at different growth real-time N management in rice and wheat.stages varied from 0.68 to 0.87, 0.65 to 0.85, and 0.71 to To establish the validity of LCC for assessing leaf N0.82 for Basmati-370, Saket-4, and Hybrid 6111, respec- content, the SPAD value, leaf N content on dry weighttively (Fig. 3). Similarly in wheat, the coefficients of de- (Ndw), SLW, and Na recorded at PI and flowering stagestermination varied from 0.61 to 0.89 at different growth had significant responses to N management options andstages among the three cultivars (Fig. 4). In general, the rice genotypes/wheat cultivars in both 2001 and 2002 (Ta-LCC score and SPAD values increased with increasing bles 8 to 11). In rice, LCC score, SPAD, Ndw, and Na

increased with increasing the N application rates as perthe crop age and LCC threshold value from 3 to 5, butno definite trend was noticed in coefficients of determina- LCC threshold value from 3 to 5, but SLW decreased

as the N application increased at both PI and floweringtion among the growth stages and N management options.When data were pooled across the cultivars and growth stages (Table 8). Similar findings were reported by Yang

et al. (2003) while estimating leaf N content using LCCstages, treatments had no significant effect on the rela-tionship between SPAD and LCC score. When data in the Philippines. However, the values reported for Na

were greater in this study for Saket-4 and hybrid ricewere pooled across N management options, the differ-ence in slopes and intercept disappeared. When data than those reported by Yang et al. (2003). This could

be attributed to higher values of SLW and Ndw recordedwere pooled across growth stages and N managementoptions, rice cultivars Saket-4 and Hybrid 6111/PHB 71 for these genotypes in the present study than that of

‘IR72’, ‘PSBRc52’, and ‘IR65620’ used by Yang et al.exhibited similar slopes and intercepts while coefficients

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Fig. 3. Relationship between leaf color chart (LCC) score and chlorophyll meter reading starting from 15 d after transplanting till 50% flowering(45–65 d after transplanting) at 10-d interval in rice cultivars across N management options in 2001 and 2002.

(2003). Within a growth stage, the SPAD reading, SLW, was measured on leaf area basis (Na), there was a similarlinear correlation between SPAD values and Na for allNdw, and Na were comparable for Saket-4 and hybrid

rice. However, these parameters were significantly dif- stages of development and lines tested (Peng et al.,1995b, 1996). Moreover, the direct relationship of LCCferent than those of Basmati-370 rice (Table 9). Growth

stages had no significant effect on the relationship be- score with Na and SPAD across growth stages providesconfidence that one value can be used as the criticaltween Na and LCC score. When leaf N concentration

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Fig. 4. Relationship between leaf color chart (LCC) score and chlorophyll meter reading from 21 (crown root initiation) to 81 to 91 (50%flowering) d after sowing at 10-d interval in wheat cultivars across N management options in 2001–2002 and 2002–2003.

LCC color for the timing of N topdressing with a given Peng et al. (1996). The differences in leaf thickness arelargely responsible for variations in the relationship be-cultivar (Yang et al., 2003). The estimated Na across

growth stages and cropping years at LCC scores 3, 4, tween Ndw and SPAD values in rice (Peng et al., 1993).Since Na is equal to the product of Ndw and SLW, theand 5 in Basmati-370, Saket-4, and Hybrid 6111/PHB-

71 rice were 1.26, 1.89, and 2.36 g m,�2 respectively. greater leaf thickness in Saket-4 and hybrid rice as evi-denced by higher SLW resulted in greater value of NaExcept for Basmati-370, these values are higher than

the 1.4 g m�2 at SPAD � 35 for IR72 as reported by compared with Basmati-370.

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Fig. 5. Relationship between leaf color chart (LCC) score and chlorophyll meter reading (SPAD) for rice and wheat cultivars across N managementoptions and growth stages in 2001–2002 and 2002–2003.

In wheat, the LCC score, SPAD, Ndw, SLW, and Na to improve NUE. Crop N requirements are closely re-increased with increasing LCC threshold values for N lated to yield levels, which in turn are sensitive to cli-application (Table 10). However, at the same LCC score, mate, particularly solar radiation and the supply of nu-the SPAD, Ndw, and Na values were higher than those trients and crop management practices. A fertilizer Nof rice. Within a growth stage, the LCC score, SPAD, management strategy must therefore be responsive toNdw, SLW, and Na were similar for cultivars PBW-343 variations in crop N requirements and soil N supply. The(early sown) and HD-2687 (timely sown); however, these LCC strategy, which has been calibrated with SPAD, isvalues were significantly higher than those of late-sown a simple and efficient way of managing N in real time.wheat cultivar PBW-226 (Table 11). It appears that the However, this requires the determination of criticalvegetative phase in late-sown wheat was abridged as LCC values for a group of varieties exhibiting similarthe increase in minimum and maximum temperature plant type and growth duration (e.g., traditional longhastened the early flowering. The relationship between duration, semidwarf short duration, hybrid, etc.). OnceLCC score and Na was similar for PBW-343 (early sown) the critical values for different varietal groups are deter-and HD-2687 (timely sown) cultivars. However, late- mined, they are valid for similar groups of varietiessown wheat (PBW-226) had different slope, intercept, grown elsewhere in the tropics. Areas with distinct dif-and regression coefficient during both years. The values ferences in radiation between dry and wet seasons (e.g.,of Na at LCC 4 were 2.08, 2.21, and 1.86 g m�2 for Central Luzon, Philippines) may require different LCCcultivars PBW-343, HD-2687, and PBW-226, respec- critical values for dry and wet seasons to optimize Ntively. Since the LCC values are closely related to SPAD use in rice.and Na, LCC can be used directly for diagnosing leaf Critical or threshold LCC values are defined as thoseN status and determining the timing of N topdressing that optimize simultaneously the grain yield and NUEfor real-time N management in rice and wheat. (AEN and REN). Based on published data (Dobermann

et al., 2004) and experience, AEN and REN exceedingDetermination of Threshold Leaf Color Chart 20 and 50, respectively, with consistent high grain yieldValue for Rice and Wheat Genotypes Based are regarded as efficient for rice germplasm. Likewise,

on Agronomic Parameters AEN of 20 and REN of 50 for late-sown wheat and AEN

of 25 and REN of 60 for early and timely sown wheatImproving the synchronization between crop N de-mand and the available N supply is an important key with high grain yields are regarded as efficient. Using

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Table 7. Regression equations between leaf color chart (LCC) scores and SPAD readings for rice and wheat genotypes.

Genotypes/cultivar Equations R2 95% confidence interval

RiceBasmati-370 SPAD � 9.9 7.60 LCC 0.78 7.03 to 8.17Saket-4 SPAD � 13.9 7.57 LCC 0.82 6.90 to 8.24Hybrid 6111/PHB-71 SPAD � 14.8 6.33 LCC 0.75 5.79 to 6.87

WheatPBW-343 SPAD � 10.7 7.65 LCC 0.79 7.18 to 8.12HD-2687 SPAD � 11.4 7.58 LCC 0.78 7.06 to 8.08PB-226 SPAD � 10.2 7.46 LCC 0.81 6.98 to 7.94

Table 8. Mean values of leaf color chart (LCC) score, chlorophyll meter (SPAD) reading, leaf N concentration per unit dry weight(Ndw), specific leaf weight (SLW), and leaf N content per unit leaf area (Na) of rice at panicle initiation (PI) and flowering (FL) indifferent N management across three genotypes during 2001 and 2002.

2001 2002

Growth stage N management LCC score SPAD Ndw SLW Na LCC score SPAD Ndw SLW Na

g kg�1 g m�2 g kg�1 g m�2

PI No N control 2.9 28.3 21.2 57.3 1.22 2.9 30.2 19.0 62.3 1.18LCC � 3, no basal N 3.2 34.8 27.0 52.3 1.42 3.4 33.5 26.2 58.4 1.52LCC � 4, no basal N 3.7 38.0 34.3 49.0 1.69 3.6 38.2 31.1 55.8 1.72LCC � 5, no basal N 3.8 39.9 37.3 47.8 1.74 3.9 40.3 34.1 53.9 1.81Recommended N 3.3 35.7 29.3 47.7 1.40 3.5 36.9 29.5 55.4 1.56

LSD (P � 0.05) 0.2 1.8 1.3 4.1 0.08 0.2 2.1 2.4 3.9 0.09FL No N control 3.0 31.6 20.8 65.2 1.36 3.1 32.4 21.6 70.2 1.45

LCC � 3, no basal N 3.6 35.4 29.1 57.6 1.61 3.6 37.1 25.3 66.9 1.67LCC � 4, no basal N 4.0 39.9 36.9 56.3 2.07 4.1 39.8 35.6 61.3 2.04LCC � 5, no basal N 4.1 40.4 40.5 55.4 2.14 4.4 42.6 39.9 56.7 2.10Recommended N 3.6 37.7 31.4 55.8 1.72 3.9 39.6 32.0 57.8 1.81

LSD (P � 0.05) 0.2 1.4 1.5 3.6 0.14 0.3 1.6 3.0 4.3 0.08

Table 9. Mean values of leaf color chart (LCC) score, chlorophyll meter (SPAD) reading, leaf N concentration per unit dry weight(Ndw), specific leaf weight (SLW), and leaf N content per unit leaf area (Na) of rice genotypes Basmati-370, Saket 4, and Hybrid 6111/PHB-71 at panicle initiation (PI) and flowering (FL) across N management options during 2001 and 2002.

2001 2002

Growth stage Cultivar LCC score SPAD Ndw SLW Na LCC score SPAD Ndw SLW Na


PI Basmati-370 2.9 30.9 25.1 47.1 1.18 3.1 32.1 23.8 45.2 1.09Saket 4 3.7 39.8 29.7 60.4 1.76 3.8 40.2 31.6 62.0 1.90Hybrid 6111/PHB-71 3.5 35.7 30.5 50.8 1.69 3.7 38.1 32.8 56.8 1.76

LSD (P � 0.05) 0.3 2.2 2.1 3.3 0.14 0.2 1.8 2.6 3.4 0.08FL Basmati-370 3.3 32.0 27.6 45.3 1.24 3.5 32.0 27.3 48.1 1.35

Saket 4 3.9 40.4 32.0 61.2 1.90 4.1 40.8 33.8 63.8 2.01Hybrid 6111/PHB-71 3.8 38.6 33.3 58.6 1.87 4.0 38.9 30.7 58.2 1.84

LSD (P � 0.05) 0.2 2.6 2.4 3.8 0.13 0.3 2.3 3.0 2.1 0.16

these agronomic parameters, the following LCC values compensating for the differences. Rainfall had a largevariation in different growth stages, but this is of nowere judged to be critical values: LCC � 3 for Basmati-

370, LCC � 4 for Saket-4, and LCC � 5 for Hybrid significance because the experiments were conductedunder fully irrigated condition. Relatively smaller differ-PHB-71 for rice (Table 3 and 4) and LCC � 4 for all

wheat cultivars (Tables 5 and 6). ences in weather parameters were further reflected inmodel-simulated climatic potential yields of rice andwheat. The potential yields of rice and wheat varietiesPotential Yieldwere 6.4, 10.2, and 11.6 Mg ha�1 in Basmati-370, Saket-4,The actual yields of both rice and wheat were remark-and Hybrid 6111 during 2001 and 6.5, 9.9, and 11.7 Mgably similar between 2 yr (Tables 3 to 6). Excellentha�1 in 2002, respectively. In wheat, the potential yieldssoil, crop, and water management followed during thefor PBW-343, HD-2687, and PBW-226 were 6.4, 7.5,experiment must have contributed to this consistency ofand 4.9 Mg ha�1 and 6.2, 8.3, and 5.2 Mg ha�1 duringthe data. In addition, the analysis of weather parameters2001–2002 and 2002–2003, respectively.showed that the differences between 2 yr were not large

(except rainfall). On an average, differences at critical Economic Analysisgrowth stages (tillering, PI, and flowering) between 2 yrin average minimum temperatures were 0.7�C in rice The economics of rice–wheat system depends on two

parameters, namely the relative yield of rice and wheatand 0.3�C in wheat, and in solar radiation, differenceswere 33.3 MJ m�2 in rice and 37.8 MJ m�2 in wheat as determined by N treatments and wheat yield as deter-

mined by the time of planting of wheat. The rice–wheat(Table 12). Maximum temperature during maximumtillering in rice was lower in 2001 than that of 2002, combinations that provide optimum planting dates for

wheat will maximize yield and profit. The TCC for rice–but at PI and flowering stages, it was reversed, thereby

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Table 10. Mean values of leaf color chart (LCC) score, chlorophyll meter (SPAD) reading, leaf N concentration per unit dry weight(Ndw), specific leaf weight (SLW), and leaf N content per unit leaf area (Na) of wheat at panicle initiation (PI) and flowering (FL) indifferent N management options across three cultivars during 2001–2002 and 2002–2003.

2001–2002 2002–2003

Growth stage N management LCC score SPAD Ndw SLW Na LCC score SPAD Ndw SLW Na


PI No N control 3.2 35.4 24.4 66.4 1.58 3.0 34.2 22.8 68.2 1.43LCC � 3, no basal N 3.5 38.2 29.2 58.6 1.70 3.5 38.8 29.6 61.5 1.79LCC � 4, no basal N 3.8 41.0 36.4 52.7 1.91 4.1 42.0 35.3 57.4 1.98LCC � 5, no basal N 4.0 42.6 39.7 51.3 2.05 4.3 44.2 40.3 54.6 2.16Recommended N 3.6 38.3 31.4 55.3 1.74 3.7 40.7 32.7 56.4 1.84

LSD (P � 0.05) 0.1 1.2 1.8 3.8 0.11 0.2 1.8 3.6 3.4 0.13FL No N control 3.2 34.5 24.8 69.5 1.63 3.2 36.6 23.1 70.8 1.53

LCC � 3, no basal N 3.6 39.4 32.6 61.7 1.95 3.8 40.3 29.9 63.2 1.89LCC � 4, no basal N 4.3 44.7 39.6 57.1 2.29 4.2 43.2 37.8 61.7 2.33LCC � 5, no basal N 4.6 47.8 43.6 55.8 2.48 4.5 46.7 44.8 58.3 2.53Recommended N 3.9 42.1 33.4 56.8 1.92 3.9 40.1 33.4 58.7 1.93

LSD (P � 0.05) 0.2 1.7 2.3 4.1 0.18 0.2 1.7 2.8 3.2 0.21

Table 11. Mean values of leaf color chart (LCC) score, chlorophyll meter (SPAD) reading, leaf N concentration per unit dry weight(Ndw), specific leaf weight (SLW), and leaf N content per unit leaf area (Na) of wheat cultivars PBW 343, HD 2687, and PBW 226at panicle initiation (PI) and flowering (FL) across N management options during 2001–2002 and 2002–2003.

2001–2002 2002–2003

Growth stage Cultivar LCC score SPAD Ndw SLW Na LCC score SPAD Ndw SLW Na


PI PBW-343 3.7 39.4 33.2 57.2 1.90 3.8 41.2 31.9 59.4 1.89HD-2687 3.6 38.2 33.4 55.6 1.86 3.9 40.5 34.7 57.6 2.05PBW-226 3.5 36.6 29.1 55.8 1.60 3.5 38.6 27.4 55.4 1.51

LSD (P � 0.05) NS 1.6 2.3 NS 0.12 0.2 1.1 3.0 3.4 0.21FL PBW-343 4.0 43.0 35.8 61.3 2.19 4.1 42.2 33.1 61.3 2.07

HD-2687 4.1 41.5 37.3 60.3 2.25 4.0 40.4 35.3 60.8 2.12PBW- 226 3.6 37.8 30.9 56.4 1.71 3.7 38.6 28.6 56.3 1.65

LSD (P � 0.05) 0.2 1.9 3.1 3.8 0.16 0.2 2.0 2.5 2.1 0.13

Table 12. Weather parameters in various critical growth stages of rice and wheat.†

Rice Wheat

Max. Panicle Physio. Panicle Physio.Weather parameters tillering initiation Flowering maturity Total Tillering initiation Flowering maturity Total

2001–2002 2001–2002

Avg. max. temperature, �C 35.6 35.8 37.4 35.9 36.2 24.4 22.7 24.5 30.4 25.5Avg. min. temperature, �C 26.8 26.0 25.6 21.2 24.9 11.5 7.0 7.8 13.2 9.9Cumulative solar radiation 477.2 286.7 391.4 740.7 1896.0 507.7 183.3 153.1 977.1 1821.1Cumulative rainfall, mm 184.6 97.6 61.2 76.1 419.5 13.8 16.6 26.8 27.7 84.9

2002–2003 2002–2003

Avg. max. temperature, �C 38.8 33.1 32.5 32.9 34.3 24.2 20.1 21.5 27.3 23.3Avg. min. temperature, �C 28.5 24.9 23.7 19.6 24.2 8.0 6.4 9.5 14.4 9.6Cumulative solar radiation 518.5 280.0 308.2 756.0 1862.7 514.2 201.6 176.2 891.3 1783.3Cumulative rainfall, mm 68.5 307.2 461.3 202.0 1039.0 18.0 17.7 10.1 11.0 56.7

† Note: For average maximum and minimum temperature, the period averaged for the maximum tillering, panicle initiation, flowering, and physiologicalmaturity ranged from 1 to 35, 36 to 60, 61 to 85, and 86 to 135 d after transplanting in rice and 1 to 60, 61 to 75, 76 to 90, and 91 to 142 d after sowingin wheat, respectively. The same period was summed up for cumulative solar radiation and rainfall also.

wheat system varied from US$569.3 to US$678.7 and Among the three-genotype combinations of rice andwheat evaluated in the rice–wheat cropping system, theUS$576.8 to US$692.0 during 2001–2002 and 2002–2003,

respectively. Of the total system cost, rice and wheat crop NR from Basmati-370–late-sown wheat (PBW-226) andhybrid 6111/PHB-71–timely sown wheat (HD-2687)shared 48 and 52%, respectively. Among the rice culti-

var, Hybrid 6111 has highest cost of cultivation (US$306) combinations were comparable in both 2001–2002 and2002–2003. Saket-4–early sown (PBW-343) combinationfollowed by Saket-4 (US$292) and then Basmati-370

(US$285). The input costs for growing wheat varied from gave the lowest NR (i.e., US$702 and US$735, respec-tively) in both years.US$274 to US$342, depending on cultivar and planting

dates. Compared with fixed-time split N application, LCC- It is important to note that in both economically supe-rior rice–wheat combinations, the profit was dictated bybased N management required US$25.3 to US$58.4 ex-

tra investments in different LCC treatments. rice. In the Basmati-370–late-sown wheat combination,higher returns were due to the premium value of Bas-System’s net return varied from US$702 to US$851 in

first year and US$735 to US$886 in second year (Fig. 6). mati-370 rice, whereas in hybrid rice–timely sown wheat,

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and LCC � 5 and 4 for Hybrid 6111/PHB-71 rice-timelysown wheat (HD-2687) combinations. However, in Bas-mati-370–late-sown wheat (PBW-226) combination, thethreshold value, i.e., LCC � 3 in Basmati-370 and LCC �4 in wheat, proved superior over any other LCC combi-nation.

CONCLUSIONSThe simultaneous optimization of grain yield and N

use in rice and wheat crops is possible by matching Nsupply with crop N demand. In many field situations,more than 60% of applied N is lost due in part to thelack of synchrony of plant N demand with N supply.Results presented in a 2-yr rice–wheat system studyprovide evidence that current fertilizer N recommenda-tions (fixed-time split N) are not adequate for main-taining the high yields and efficient use of N in riceand wheat. The LCC-based N management assures highyields consistent with efficient N use in both rice andwheat and enhances rice–wheat systems’ total produc-tivity and farmer’s profit. The LCC is a simple and easy-to-use tool that can help farmers manage N judiciously.

Future studies can compare the efficiency, labor use,cost, and profit of improved fixed-time spilt N strategiesderived from this and other studies and the LCC-basedreal-time N management in rice and wheat. Improvedfixed-time split N recommendations will work well forhomogenous domains, but real-time N management willstill be needed to tackle high spatial and temporal vari-ability in INS and to refine fixed-time split N recommen-dations periodically (once every 4–5 yr).

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