IRPS 59 Energy Requirements for Alternative Rice Production Systems in the Tropics

8/4/2019 IRPS 59 Energy Requirements for Alternative Rice Production Systems in the Tropics

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IRPS No. 59, April 1981

ENERGYREQUIREMENTSFOR ALTERNATIVE RICE PRODUCTIONSYSTEMS IN THE TROPICS~I

ABSTRACT

The energy requirements of three alternative riceproduction systems used by most small Asianfanners are identified by task and energy sourceand the energy levels and components of eachsystem compared. Human energy contributes a small

portion of total energy input into most trad-tional Asian rice fanning systems. As foodproduction systems modernize, they become lessenergy efficient and more dependent on commercialenergy.

1/By Donald O . Kuether and Bart Duff, associate agricultural engineer and associate agriculturaleconomist, International Rice Research Institute, Los Bafics , Laguna, Philippines. A paper preparedfor the Annual Meeting, Society of Automotive Engineers, September 1979. Revised and reprinted withpermission of the Society of Automotive Engineers, Inc.


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IRPS No. 59, April 1981

ENERGYREQUIREMENTSFORALTERNATIVERICE PRODUCTIONSYSTEMSIN THE TROPres

In the developing nations, the rising costs of en-ergy and the resulting increase in prices ofmarketed commodities and factors of productionhave serious implications for achieving and sus-taining economic growth. Because a greater portionof the population of many of these countries arein rural areas and derive a major share of theirnational income from agriculture, the adverse ef-fects of higher energy costs are particularly re-levant. During the past two decades, agriculturein many Asian countries has undergone dramaticchange, much of it centered in the smallholdersector. Most of these farms are on the averageless than 2 ha and in the past a substantial shareof the energy to operate them has come from on-farm sources such as human labor and animal power.Recent developments in agriculture have been sti-mulated by the introduction of a biological chemi-cal technology package consisting of improved cropvarieties and chemical fertilizers, herbicides,and insecticides. In many areas, these develop-ments were accompanied or brought about by theintroduction of mechanical technologies such aspower pumps, tractors, and mechanical threshers.Traditional agricultural systems, in which littleis bought or sold outside the home, have a low de-pendence on outside inputs and are largelyinsen-sitive to changing economic conditions. In con-trast, improved production systems, which resultin increased land and labor productivity, are

highly dependent on purchased inputs, many ofwhich embody substantial energy derived from fos-sil fuels. Because of this high level of depend-ence, those concerned with agricultural productionin these nations are particularly interested inthe level of energy input s req ui red to sus tainmodern systems and to evaluate their sensitivityto changing technologies and economic condi tions.This report focuses on two dimensions of the en-ergy issue in small-farm rice production systems.The firs t section part i tLons the energy req ui re-ments of alternative systems by task and source.The second examines the relative costs of thealternative systems, and their sensitivity tochanges in energy costs or to technology whichchanges the efficiency with which energy is used.

ALTERNATIVERICE PRODUCTIONSYSTEMSThe rice production systems analyzed here repre-sent those used by the majority of Asian farmers:traditional, mechanical, and transitional systemsas defined in Table 1. A small amount of Asianrice land is still tilled completely by human po-wer. Conversely, there are a few large, highlymechanized rice farms that use the same machineryand cultural techniques used in the developed na-tions. Figure 1 illustrates typical machines usedin the three production systems. Variations in the

Table 1. Components of alternative rice production systems.

Component Traditional Transitionalechanical

Land preparationPrimary tillageSecondary tillageLevee repair

Water buffalo and plow 5- 7-hp tiller and plowWater buffalo and harrow 5- 7-hp tiller and harrowManual Manual

50-hp tractor and rototillerWater buffalo and harrowingManual

PlantingSeedbedTransplanting

Wetbed systemManual

Crop care ManualHarvesting Hand sickleThreshing and drying Manual threshing

Sun drying

Hetbed systemManual

Hetbed systemManual

Manual ManualHand sickle Hand sickleIRRI-type power thresherMechanical batch dryer

Manual threshingSun drying


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4 IRPS No. 59, April Inl

systems, such as mechanical threshing combinedwith animal tillage or mechanical threshing andsolar drying, occur. The manpower and ene rg y in-puts of each system ar e presented in sufficientdetail to permit the reader to calculate the man-power and energy requirements reflecting a combi-nation of tasks or operations for a specific farm-ing situation.Table 2 and F'tgur e 2 present the labor require-ments for each system. The values were obtained byaveraging the labor hours r epor ted in indicatedreferences. Most of the data result from researchconducted in the Philippines but compare favorablywi th information on labor requirements from otherparts of Asia (Chancellor 1977). The use of mecha-nical tillage and improved postharvest processingr educ ed labor hours per hectare from 735 to 545,or 26%. The introduction of the 4-wheel tractor inthe tLansitional system had a less pronouncedeffect -- it reduced total labor hours by only 8%compared with the traditional system. Peak . labordemands in most nonmechanized production systems

occur during land preparation, transplanting, har-vesting, and threshing. Crop care requires a largelabor input but is generally allocated more uni-formly over the entire growing season. Land prepa-ration, planting, and harvesting-threshing, on theother hand, should ideally be completed in theshortest possible time fOL timely planting of thecrop to maximize use of available moisture andsunlight and to harvest at optimum maturity toreduce losses.The energy inputs for each production system aregiven in Tables 3, 4, and 5. This information ispresented as percentages of total energy by inputand operation in Figures 3 and 4. Appendix A pre-sents the energy constants and consumption ratesused in the calculations. The energy available infue I, oil, and seed is used as a di rect inputwhereas the energy value of fertilizer, herbi-cides, insecticides, and farm machinery considersall energy used to produce the material, includingthe .direct energy used in production and the ener-gy to build and maintain the production facilities

Fig. 1. Machines used in the traditional, mechanical, and transitional rlce productionsystems.


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IRPS No. 59, April1981 5

Table 2. Labor inputs (labor hours/ha) by system and task for alternative rice production systems.a

Traditional Mechanical Transitional

Land preparation 138 68 76,3Primary tillage } 105h 35c 4.lSecondary tilla.;c 39fLevee repair 33c 33 33

Planting 142a 142 142Seedbed preparation and care }eedling pulling 142 142 142Transplanting

Crop care 163 163 163Fertilizer application 8~ 8 8Insecticide application 10~ 10 10Herbicide application 8J 8 8Heeding 137k 137 137

Harvesting 121Z 121 121Cutting and stacking 121 121 121

Threshing and drying 171 51 171Threshing } 14L.m 37nCleaning and bagging 144Hauling

27nDrying 14n 27Total 735 545 673.3

aLabnr inputs are averages of those reported in indicated sources. bSources: Barker et al 1969, Barkerand Cordova 1978, Duff 1978, Johnson 1969a, Kiamco and McMennamy 1978, Singh and Yadao 1979. cSou&ces:Duff 1978, Johnson 1969a, Kiamco and McMennamy 1978, Orcino and Duff 1974, Singh and Yadao 1979. &curce:Orcino and Duff 1973. cSources: Barker and Cordova 1978; Johnson 1969a,b; Singh and Yadao 1979. JSources:Duff 1978, Orcino and Duff 1974, Singh and Yadao 1979. gsgurces: Barker et al 1969, Barker and Cordova1978, Johnson 1969b, Ledesma 1978, Singh and Yadao 1979. Sourcesk Johnson 1969a, Singh and Yadao 1979.1'Source: Johnson 1969a. Zf!p:ssumesame as fertilizer application. Sources: Barker and Cordova 1978, DeDatta and Barker 1975. Sources: IRRI 1978c, Johnson 1969a, Ledesma 1978, Singh and Yadao 1979, Tgqueroet al 1977. mSources: Barker and Cordova 1978, IRRI 1978c, Johnson 1969a, Singh and Yadao 1979. Sources:IRRI 1978c, Toquero et al 1977.

and provide for worker's food and transportation,packaging, and distribution. The human energyexpenditures used in this paper for the rice grow-ing tasks were obtained experimentally with porta-ble cardiac monitoring instruments (Duff 1978). Asexpected, the energy consumption values varied bytask but an average of expenditures for all tasksapproximate those generally cited in the litera-ture (Chancellor 1977). Human energy in thosetasks not measured directly in the study wereestimated using values from similar tasks.

Consumption rates for fuel and oil were obtainedfrom test reports of similar machines being de-veloped by the International Rice Research Insti-tute Department of Agricultural Engineering, farm-er surveys, and engine manufacturer's speciftca-

tions. Energy equivalents for machinery use anddepreciation were obtained by multiplying theestimated energy requirement to produce a kilogramof machine by 1.33 times the weight of the ma-chine, prorated over machine life by hours usedper hectare. The one-third weight increase is anadjustment for repairs based on the assumptionthat total repair cost approaches machine firstcost over total life. Repairs cost 3 to 4 timesthe original part it replaces, so we assume thatabout one-third the weight of the machine in ener-gy equivalents is replaced over its useful life.

Overall energy consumption increased 26% when me-chanical land preparation and mechanical threshingand drying replaced human and animal power (Tables3 and 4). Fuel, especially that used for drying,


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6 lRPS No. 59, April 1981

Table 3. Energy inputs (J x 106/ha) for the traditional rice production system.

Operation Human Animal Machine Fuel Seedand oil

Fertil- Insecti- Herbi-izer cide cide

Total

L an d p re pa ra ti onP ri ma ry t il la geS ec on da ry t il la geLe vee repair

} 1l0.526.2

PlantingS ee db ed p re pa ra ti onS ee dl in g p ul li ngTransplanting } ll2.7

Crop careF er ti li ze r a pp li ca ti onI ns ec ti ci de a pp li ca ti onH er bi ci de a pp li ca ti onWeeding

13.817.213.8

213.9Harvesting

Cutting and stacking 150.0Threshing and drying

Threshing }Cleaning and baggingHaulingDrying

174.021.4

Total 853.5E ne rg y e qu iv al en t

(liters of diesel fuel) 22.3

1099.0 331. 3

617.1

53.7

1099.0 331. 3 53.7 617.1

28.7 8.6 1.4

aSee Appendix A for constants and calculations.

T ra d it io n al S y st em Me ch an ic al S ys te m

Fig. 2. Labor (labor hours) distribution by major task.

1567.0

729.8

3880.93243.3

304.174.8

150.0

249.1

3243.3 6576.804.1 74.8

16.1 1.9 1 71 . 44.5 7.9

T rans it iona l Sy s tem


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IRPS No. 59. April 1981 7

6Table 4. Energy inputs (J x 10 /ha) for the mechanical rice production system.

Operation Totaluman Animal Machine Fueland oil

Seed Fertil- Insecti- Herbi-

Land preparationPrimary tillageSecondary til1agpLevee repair

} 42.226.2

PlantingSeedbed preparationSeedling pullingTransplanting } 112.7

Crop careFertilizer applicationInsecticide applicationHerbicide applicationHeeding

13.817.213.8

213.9Harvesting

Cutting and stacking 150.0Threshing and drying

Threshing }Cleaning and baggingHaulingDrying

41.114.2

Total 645.1Energy equivalent

(liters of diesel fuel) 16.8 1. 9 227.1

420.5 981. 8

157.1 300.653.7

1722.495.3o 3058.572.9

o 20.2 79.7


T r ad it io n a l S y s temHarvesting(23%)

Harvesting(1.7%)

Me c h an ic a l S y s temHarvesting(22%)

Fig. 3. Energy inputs (Joules) by major task.

lzer cide cide

617.1

3243.3304.1

74.8

617.1 74.8243.3

16.1 84.5 7. 9

T ra ns it iona l Sy s t emThreshing anddrying(3.6%)

1470.7

729.8

3880.9

150.0

2484.4

8715.8


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8 IRPS No. 59, April 1981

Table 5. Energy inputs (J x 106/ha) for the transitional r~ce production system.Tnpu ts'?

Operation Human Animal Machine Fuel Seed Fertil- Insecti- Herbi Totaland oil izer cide cide

Land preparation 1887.2Primary tillage 3.4 151. 9 1148.7Secondary tillage 38.4 408.2 1l0.4Levee repair 26.2

Planting 729.8Seedbed preparation }eedling pulling ll2.7 617.1Transplanting

Crop care 3880.9Fertilizer application 13.8 3243.3Insecticide application 17.2 304.1Herbicide application 13.8 74.8Weeding 213.9

Harvesting 150.0Cutting and stacking 150.0

Threshing and drying 249.1Threshing }leaning and bagging 174.0Hauling 53.7Drying 21.4

Total 784.8 408.2 262.3 1202.4 617.1 3243.3 304.1 74.8 6897.0

Energy equivalent 7.9 1.9 179.6(liters of diesel fuel) 20.5 10.6 6.8 31. 3 16.1 84.5


contributed significantly to the increase, al-though decreases in human and animal energy of f-set some of the increase. Use of a 4-wheel tractorfor primary tillage in the transitional system in-creased total energy requirements by only 5% andtillage energy by 20%, yet shortened the time re-quired for land tillage from 105 to 43 hours. Manyfarmers pay for the added energy input to obtainthe benefits of timely land preparation and reducelabor requirements.Crop care and the related inputs make up more than44% of the total energy inputs in all systems,primarily because fertilizer and agricultural che-micals require high amounts of energy in theirproduction (Fig. 3, 4). Application rates used tocalculate these energy costs approximate thoseused by Filipino farmers although they are lessrecommended by extension services for maximumyield. The high cost of these inputs, a reflectionof high energy inputs in their production, is aprimary reason for low application rates. Thispoints to the need for more efficient applicationmethods to increase the effectiveness of the che-micals and increase refinement of alternative fer-tilizer sources such as nitrogen-producing Azolla

and composting. Root-zone placement of fertilizercan Lncr eas e efficiency by up to 50% compared totraditional broadcast methods (IRRI 1978a), but amachine to apply the chemical efficiently and eco-nomically in the environment of the small Asianfarmer has yet to be developed.Reduced tillage or adoption of minimum-tillagepractices could also contribute to energy reduc-tion but weed control problems increase, so im-proved herbicides and more efficient applicationmethods are r eq uir ed before net e na rg y savings canbe realized.Human effort contributes a relatively small por-tion of the total energy consumed in each produc-tion system (Fig. 4, 5), never exceeding 13% ofthe total although 735 labor hours/ha is requiredto produce that share of the energy. This empha-sizes the very low power production potential ofhumans and indicates that their abilities are mostvaluable in tasks that require decision-makingcapabilities as opposed to those requiring onlyroutine energy inputs. Weeding, although still alaborious task, requires human decision capabili-ties (selecting the weeds from the rice plants)


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and uses human energy more efficiently than suchtasks as tilling with a hoe.The input-output energy ratio or efficiency ofeach system is based on a 3.5 tlha yield which isthe average for the inputs used in this analysis.The input-output ratio is 6.57 for the traditionalsystem, 4.95 for the mechanical system, and 6.26for the transitional system. These efficiencyratios are in part an artifact of the assumptionwe have made relating to yield for the three sys-tems included in the analysis. A higher yieldwithout an increase in the energy inputs for anyof the systems would clearly modify the rankingspresented here. Alternatively, a decrease in theinput of energy without a commensurate decrease inyield would also alter the ratios. Judged purelyon the energy obtained in rice (output) to the en-ergy required to produce the rice, the traditionalsystem is superior. Empirical evidence substan-tiates the finding that efficiency in energy usedeclines as the total energy used in the systemincreases (Heichel 1973). Frequently this rela-t ionship comes about because systems wi th lowenergy inputs tend to involve high levels of landper unit energy input and high levels of humandecision making per unit of energy input, with theresult that output is more a product of these orother non-energy inputs. With the prevailing ener-gy prices in the recent past and using availabletechnology, lower efficiency ratios were accepta-ble in achieving higher absolute levels of yieldand production. The evidence bearing on this issueclearly demonstrates that increased output andproductivity have been the result of larger inputsof energy per unit of output.To feed an increasing world population a higherproduction per unit of land is required. Hence,the use of greater cropping intensity, throughsubstitution of mechanical for human and animalpower, higher chemical application rates, andincreased irrigation is necessary to supplementhigh-yielding varieties and improved management.These inputs are high energy consumers and willprobably reduce the energy efficiency of the riceproduction system.The rice production systems analyzed here are de-fined as rainf ed , These are flooded wetland sys-tems that receive all moisture from accumulatedrainfall. More than 50% of South and SoutheastAsia's rice land is classified as rainfed. Another25-35% is irrigated for at least one crop with theremainder categorized as dryland in which water isnot impounded (IRRI 1978b). Irrigation can in-crease crop yields even during the dry season whendrought often occurs. Controlled water suppliescan also mean the difference between a good cropand no crop during the dry season. The majority ofthe irrigation systems in Asia draw water, by gra-vi ty, from reservoirs or diversion structures. Anincreasing number of farmers are, however, turningto powered pump sets to draw water from shallowwells or low-lying water sources. Table, 6 presentsthe energy requirements for a small, low-lift pumpirrigation system. To maintain the energy effi-ciency of the traditional system, the yield would

IRPS No, 59. April 1981


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10 IRPS No. 59, April1981

Traditional System Mechanical System

Machine use(50%)Fig. 4. Energy inputs (Joules) by source.

Table 7. Estimate energy equivalents for alterna-tive Eroduction systems, in kg/ha of unmilledrlce.

Item Traditional Transitional MechanicalUnmil.l.ed nee equivalent (kg l ha)

SeedFertilizerInsecticideHerbicideFuel and oilMachineryAnimal powerHuman labor

50.0262.024.55.94.3

26.789.069.2

50.0262.024.55.9

247.162.6o52.1

50.0262.024.55.9

97.021.132.963.6

Total 531. 6 704.257.0

aBased on 2,952 Kcal per kg unmilled rice.

Table 7 contains a comparative energy budget inwhich all energy requirements have been convertedto unmilled rice equivalents. To the farmer, thefigures shown represent the amount of rice thatmust be produced to generate the energy needed byeach system. PriCing the unmilled rice at US$0.l6/kg gives the relative energy costs in monetaryterms (Table 8).In Table 9, inputs are valued at market prices. Wecan now compare the energy costs in Tables 7 and 8with the monetary costs in Table 9. In energyterms, the use of chemicals and mechanical landpreparation, threshing, and drying increase energyrequirements significantly. In monetary terms,however, substitution of mechanical for animal andhuman energy decreases the average per-hectarecosts. The use of machines substitutes low-costfossil fuel energy for higher-cost man and animalenergy. The use of market prices also allows us toexamine the possible impact of changes in energy

Transitional System

Table 8. Relative costs (US$) of commercial and nocommercial energy in alternative rice production sytems.a

Source Traditional Transitional Mechanical

CommercialOn farm

51. 7533.38

96.3416.32

65.6823.52

Total 85.13 ll2.669.20

aBased on the data In Table 7 and all energy chargedat the cost of energy in unmilled rice priced at$0.16/kg.

cos ts on choice of technique. An example is theprice of fuel. Doubling the price of fuel reducesbut does not change the comparative advantage ofthe mechanical system over others. Incorporatingindirect effects of a fuel price change, such in-creases in the costs of machinery would, however,partially reduce the advantage of the transition-al and mechanical systems.

Reviewing particular operations wi thin each sys-tem, we find that crop care, particularly the useof fertilizer, uses the most commercial energy forall systems. In the mechanical system, fertilizeris closely followed by fuel and oil. These itemsare used at a much lower level in both the tran-sitional and traditional systems. These findingsreinforce our hypothesis that the development oftechnologies that use high-energy inputs such asfertilizer more efficiently is beneficial. Furtherexploration of alternative forms of energy such asbiogas or use of crop residues for such operationsas mechanical drying, which consumes almost 60% ofthe overall fuel requirements in the mechanicalsystem, should also be highly beneficial.


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E nergy ( J oules x 106 )

IRPS No. 59, April 1981 II

Fig. 5. Total energy inputs (Joules per hectare) by source.

Mechanicalsystem

Trans i t iona lsystem

Tradi t iona lsystem

Tradilional MechanicalRice p r od u ct io n s y s tem

Transitional

a 100Energy requi rement ( diesel fuel liter! ha)

200

Fig. 6. Comparative level of commercial energy utilizationfor three alternative rice production systems.

Table 9. Costs of inputs (US$/ha) at market prices for alternative rlce production systems.a

Item Unit cost Traditional Transitional

Seed 0.16/kg 8.00 8.00Fertilizer 0.58/kg N 23.20 23.20Insecticide 36/kg a.l. 27.00 27.00Herb~cide 38/kg a.i. 26.60 26.60Fuel 0.193/liter 0.38 6.04Machinery c 10.00 24.00Animal power d 0.65/h 68.25 25.35Human labor 0.17/h 125.00 114.46

Total 288.43 254.65

Mechanical

8.0023.2027.0026.6015.4229.34o

92.68222.24

aInput prices are averages prevailing in rural areas of the Philipgines. US$ ~ 7.35. bFuel costs are~alued in terms of diesel fuel equivalents (Tables 3, 4, and 5). Includes only fixed cost component.Based on daily rental rate without operator.


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Orcino, N., and B. Duff. 1973. Technical and eco-nomic characteristics of tractor contractoperations in Central Luzon. Paper presentedat a Saturday seminar, June, InternationalRice Research Institute, Los Banos, Lagu-na, Philippines.

Orcino, N., and B. Duff. 1974. Experimental re-sults from alternative systems of land prepa-ration. Paper presented at a Saturday semi-nar, 27 July, International Rice ResearchInstitute, Los Banos, Laguna, Philippines.

IRPS No. 59, April 1981 13

Singh G., and G. S. Yadao, 1979. Field study ofagricultural mechanization in Central Minda-nao, Philippines. Agric. Mech. Asia 10(1):13-15.

Toquero, Z., C. Maranan, L. Ebron, and B. Duff.1977. Assessing quantitative and qualitativelosses in rice post-production systems.Agric. Mech. Asia 8(3):31-40.


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Appendix A. Constants and calculations.

1. Energy values (J x 106)Gasoline: .74 kg/liter at 48.16 - 43.45/kg = 33.89/1iterDiesel fuel: .87 kg/liter at 45.08 - 42.36/kg = 38.36/literKerosene: .83 kg/liter at 45.84 - 42.97/kg = 36.68/1iterLub oil: .93 kg/liter at 44.15 - 4l.62/kg = 40.10/1iterNitrogen: 80 - 82.2/kg = 8l.l/kg N2,4-D, 2,4,5-T: 85 - 135/kg a.i. = 110.0/kg a.i.Carbofuran: 357 - 454 kg a.i. 405.5/kg a.l.Seed 12.36/kgMachinery: 86.7-90/kg 88.4/kg

2. Human energy expenditures (J x 106/h) by taskTillage with animal (plowing and harrowing)Tillage with tiller (plowing and harrowing)Tillage with 4-wheel tractor (estimate)Harrow with animalLevee repair (assumed same as transplanting)TransplantingFertilizer application (used herbicide application value)Insecticide application (used herbicide application value)Herbicide applicationWeeding (average of hand and manual rotary)Harvesting (average of cutting and stacking)Threshing (manual)Threshing (mechanical) (prorated stacking and table thresher)Drying (sun) (author estimate)Drying (mechanical) (author estimate)

3. Animal energy expenditure (J x 106/h)Tillage with water buffalo

4. Input usage ratesOperation Input

Power tiller tillage Diesel fuelOil

4-wheel tractor tillage Diesel fueloi l

Threshing GasolineOil

Drying KeroseneGasolineOilSeedFertilizerInsectici~e (carbofuran)Herbicide (2,4-D, 2,4,5-T)

aAverage rates used by Philippine farmers (IRRI 1978 a,b,c).

1.051.210.790.980.790.791.721.721.721.561.241.211.670.791.02

10.47

References

Baumeister 1958Baumeister 1958Baumeister 1958Baumeister 1958Faidley 1977, Green 1978Faidley 1977, Green 1978Green 1978, Rutger and Grant 19Faidley 1977, Leach l197~7Duff 1978

Kiamco and McMennamy 1978

Rate.71iter/h3.0 liters/lOa h6.86 liters/h10 liters/lOa h1.22 liters/h1 liter/25 h2.7 liters/h1.5 liters/h1.0 liters/25 h50 kg/haa40 kg N/haa.75 kg a.i. /haa.7 kg a.i./haa


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The International Rice Research InstitutePO. Box 933, Manila, PhilippinesStamp

Oth er pape rs in th is s e r ie sFOR NUMBERS 1-6. TITLES ARE LISTED ON THE LAST PAGE OF NO 46 AND PREVIOUS ISSUES ISSN 0115-3862No. 34 Evapot ranspiration from rice fieldsNo. 35 Genetic analysis of traits related to grain characteristics and quality

in two crosses of riceNo. 36 Aliwalas to rice garden: a case study of the intensification of rice

farming in Camarines Sur, PhilippinesNo. 37 Denitri fication loss of fertil izer nit rogen in paddy soi ls - it s recog-

nition and impactNo. 38 Farm mechanization, employment, and income in Nepal: tradi-

t ional and mechanized farming in Bara DistrictNo. 39 Study on kresek (wil t) of the rice bacter ial blight syndromeNo. 40 Implication ofthe international rice blast nursery data to the genet-

ics of resistance - an approach to a complicated host-parasiterelationshipNo. 41 Weather and cl imate data for Phi lippine rice researchNo. 42 The effect of the new rice technology in family labor utilization in

LagunaNo. 43 The contribution of varietal tolerance for problem soils to yield

stabili ty in riceNo. 44 IR42: a rice type for small farmers of South and Southeast AsiaNo. 45 Germplasm bank information retrieval systemNo. 46 A methodology for determining insect control recommendationsNo. 47 Biological nit rogen fixat ion by epiphytic microorganisms in rice

fieldsNo. 48 Quality characteristics of milled rice grown in different countriesNo. 49 Recent developments in research on ni trogen fert ilizers for riceNo. 50 Changes in community institutions and income distribution in aWest JavavillageNo.51 The IRRI computerized mailing list systemNo. 52 Different ial response of rice variet ies to the brown planthopper in

international screening testsNo. 53 Resistance ofJapanese and IRRI differential r ice varieties to patho-

types of Xanthomonas orvzae in the Phi lippines and in JapanNo. 54 Rice production in the Tarai of Kosi zone. NepalNo. 55 Technological progress and income distribut ion in a rice village in

West JavaNo. 56 Rice grain properties and resis tance to storage insects: a reviewNo. 57 Improvement of native r ices through induced mutationNo. 58 Impact of a special high yielding rice program in Burma

Mult i-si te tests environments and breeding s trategies for new r icetechnologyBehavior of minor elements in paddy soi lsZinc deficiency in rice: a review of research at the International RiceResearch InstituteGenet ic and sociologic aspects of rice breeding in IndiaUtilization of the Azolla-Anabaena complex asa nitrogen ferti lizerfor riceScientific communication among rice breeders in 10Asian nationsRice breeders in Asia: a lO-country survey of their back-grounds, att itudes, and use of genetic materialsDrought and rice improvement in perspectiveRisk and uncertainty as factors in crop improvement researchRice ragged stunt disease in the Philippines

No. 17 Residues ofcarbofuran applied as a systemic insecticide in irr igatedwetland rice: implications for insect controlDif fusion and adopt ion of genetic mater ials among rice breedingprograms in AsiaMethods of screening rices for varietal resistance to Cercospora leafspotTropical climate and its inf luence on riceSulfur nutri tion of wetland riceLand preparation and crop establishment for rainfed and lowlandnee

No. 7No. 8No. 9No. 10No. IINo. 12No. 13

No. 14No. 15No. 16

No. 18No. 19No. 20No. 21No. 22No. 23No. 24No. 25No. 26No. 27No. 28

Genetic interrelationships of improved rice varieties in AsiaBarriers to efficient capital investment in Asian agricultureBarr iers to increased rice production in eastern IndiaRainfed lowland rice as a research priori ty -- an economist' s viewRice leaffolder: mass rearing and a proposal for screening forvarietal resistance in the greenhouseMeasuring the economic benefit s of new technologies to smal l r icefarmers

No. 29 An analysis of the labor-intensive continuous rice production sys-tem at IRRI

No. 30 Biological constraints to farmers' rice yields in three Philippineprovinces

No. 31 Changes in rice harvesting systems in Central Luzon and LagunaNo. 32 Variat ion invar ietal react ion to r ice tungro disease: possible causes

Documents

IRPS 59 Energy Requirements for Alternative Rice Production Systems in the Tropics