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FAO/IAEA research and trainingin soil fertility at the IAEA'sSeibersdorf LaboratoriesNuclear technology in soil and plant sciences is beingdeveloped and transferred through various mechanisms

by F. Zapata and G. Hardarson

The present century is experiencing an explosiveincrease in the world's population. It is estimated that bythe year 2015 the population will be about 8 billion. Asa consequence, there is a continuously rising demand forcultivated food, feed, fibre, and biofuel from effectivelylimited land resources. Several solutions have been sug-gested. In the developing countries, the most promisingsolution for the near future has become the intensifica-tion of agricultural production on currently cultivatedland through either increased cropping intensity and/orhigher yields.

The intensification of agriculture through the "greenrevolution" involved the development of new technolo-gies and improved agronomic practices. These includethe use of high-yielding cultivars, mechanization, irriga-tion, and especially agrochemicals. In intensive agricul-tural systems, crops remove substantial amounts ofnutrients, which are replenished by the application offertilizers. There has been, however, an increasingawareness over the last 10 years that the "green revolu-tion" has made limited impact on the small-holderfarmers in developing countries. Because of the lack ofresources, and the increasing prices of commercialinputs, attention has been focusing on the analysis andsubsequent improvement of low input cropping systems,and on a more efficient use of limited resources. Due tothese factors, a systems approach concept to plant nutri-tion that integrates all sources of plant nutrients and cropproduction factors into a productive agriculture systemto enhance soil fertility, crop productivity, and profit-ability has been recommended. This integrated plantnutrition system includes both the highest possible effi-ciency in the use of available chemical fertilizers and themaximum use of alternative sources of nutrients such asorganic fertilizers, rock phosphates, and biologicalnitrogen fixation.

Mr Zapata is the Head, and Mr Hardarson is a staff member, of theSoil Science Unit at the Seibersdorf Laboratories.

IAEA BULLETIN, 4/1989

Nuclear techniques in soil science and plantproductivity: Historical overview

Since its foundation in 1964, the Joint FAO/IAEADivision of Nuclear Techniques in Food and Agriculturein collaboration with the IAEA Agricultural Laboratoryat Seibersdorf has promoted research, development, andtransfer of nuclear technology to help countries establishbetter conditions for crop and livestock production. Inthe field of soil science and plant productivity, suchresearch has been done through co-ordinated researchprogrammes and technical co-operation projects con-ducted by the Soil Fertility, Irrigation, and CropProduction Section of the Joint FAO/IAEA Division.Isotopes are used as tracers, for instance to determineamounts and movement of nutrients, especially thosederived from fertilizers in plants and soils. Radiationtechniques using equipment such as neutron moisturemeters and gamma density probes make it possible tofollow the moisture and to measure bulk density changesin soil profiles in a reliable non-destructive way whilesaving time, effort, and money.

Isotopes and fertilizer use efficiency

It has been well established that crops respond to fer-tilizer application on most soils. Regular applications areessential for maintaining and enhancing soil fertilityrequired for high productivity. About 50% increase ingrain yield of cereals can be attributable to fertilizers.From 130 million tons consumed in 1984-85, nitrogen(N) accounted for 54%, phosphorus (P) for 26%, andpotassium (K) for 20%. In 1985 the developing coun-tries used 48 million tons of fertilizer worth approxi-mately US $4950 million. This accounted for 38% ofthe total fertilizer consumption. The fertilizer consump-tion in developing countries had been increasing about6% annually during 1980-85, whereas in the sameperiod it only increased 1.8% in the developed coun-tries. To meet world food needs, the use of N-P-K

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Advanced instrumentation availableat the Soil Science Unit — such as anautomatic nitrogen analyser coupledto a stable isotope ratio analyser —permits an increased sample through-put for routine analytical services insupport of the field projects of theJoint FAO/IAEA programme.

fertilizers must increase four to five times in the next20 years. This projected increase in world fertilizer con-sumption is an indicator of the role fertilizers are likelyto play in feeding an increasing world population.

Only a fraction of the fertilizer applied to the soil istaken up by the crop. The rest either remains in the soilor is lost through leaching, physical wash-off, fixationby the soil, and/or release to the atmosphere throughchemical and microbiological processes. It is thus neces-sary to obtain information on the relative merits ofdifferent fertilization practices such as methods of fertil-izer placement, times of application, and sources offertilizers. This information would help to achieve maxi-mum efficiency of fertilizer utilization in the most eco-nomical way and hence reduce costs of production.

The best combination of fertilizer practices (rate,placement, timing, and source) can be established forselected cropping systems by carrying out field experi-ments under different environmental (soil and climate)conditions. The classical methods used for this purposeare indirect because they are based on the measure ofyield differences due to fertilization treatments.Experimentation using fertilizers labelled with stableand radioactive isotopes provides a direct and quickmeans of obtaining conclusive answers to the questionswhere, when, and in what forms fertilizers should beapplied. 32P- and 15N- labelled fertilizers have beenextensively used for such studies in several FAO/IAEAco-ordinated research programmes on rice, maize, andwheat during 20 years. The isotope technique involvesapplying labelled fertilizer to the crop and determiningthe percentage of nutrient element in the crop that wasderived from the fertilizer. Fortunately, many isotopesare available and can be used as tracers in soil/plant rela-tionships and related studies. The Soil Science Unit atthe IAEA Seibersdorf Laboratories has played a key role

in the implementation of these programmes by develop-ing isotope techniques, providing analytical services,and transferring this technology to Member Statesthrough training. The adoption of these improved fertil-izer practices in many countries around the world hasresulted in savings of fertilizers worth many millions ofdollars each year.

Isotope techniques also offer a quick and reliablemeans of obtaining information on the distribution ofactive roots, the location of zones where the density ofabsorbing roots is highest, and how these vary with sea-sons. Placement of fertilizer close to the zone of highestroot activity and at a time when the roots are most activewould therefore be of direct value for the formulation ofrational fertilizer practices in tree crop plantations. Asoil injection technique using 32P-labelled phosphatesolution was developed and used to determine the rootdistribution of various tree crops of economic impor-tance to developing countries. The experimental detailsof injection and sampling techniques were worked out atthe Seibersdorf Laboratories with the objective of reduc-ing the experimental error. The Laboratories furthersupported the implementation of this programme bypreparing and shipping thousands of ampoules filledwith 32P-labelled solution.

Radiation and management of water resources

In addition to mineral nutrient supply, water is one ofthe main limiting factors of agricultural production inmany areas of the world. Therefore it is essential todevelop adequate water management methods for betteruse of rainfall under dry farming conditions, or toimprove the efficiency of water use on irrigated land. Inthis context, research with radiation techniques usingequipment such as neutron moisture meters and gamma

56 IAEA BULLETIN, 4/1989

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Supportive research and fellowshiptraining is carried out at the SoilScience Unit for a co-ordinatedresearch programme on the manage-ment of nitrogen-fixing trees inrestoring and maintaining soilfertility.

7 *%.«*«- "•- 1 M'^-T "

density probes has also been applied to developimproved water management practices in arid and semi-arid environments.

Water and fertilizer use efficiency studies underirrigated and rainfed agriculture in semi-arid regionswere conducted to determine the management conditionsunder which crops best utilize costly inputs likemanufactured fertilizers and irrigation water.

Techniques to study alternative nutrient sources

Inorganic fertilizers can be replaced to some extentwith other sources of nutrients which are locally avail-able or less expensive. Only certain plants, such aslegumes and a few other families in symbiosis withappropriate microorganisms, are able to directly utilizeatmospheric N2. This process is called biological nitro-gen fixation (BNF). The contribution of N to the nitro-gen economy of both soils and plants through properlymanaged N2 fixing systems appears to be the mostpromising alternative to supplement chemical fertilizerN in agro-ecosystems.

During the last decade, several FAO/IAEA researchprogrammes have focused on measuring and enhancingthe natural process of biological nitrogen fixation, espe-cially symbiotic legume N2 fixation in various systems.Furthermore, current programmes emphasize theimprovement of both yield and nitrogen fixation in grainlegumes through an integrated approach.

The measurement of the amount of N2 fixed underfield conditions is an essential requirement in anyprogramme aimed at maximizing BNF. Of the manymethods available, the 15N isotopic techniques are themost reliable for providing quantitative and integratedvalues of nitrogen fixed in both natural and agriculturalsystems. It is the only method which permits one to dis-

tinguish the relative contribution of soil, fertilizer, andatmospheric nitrogen to the total plant nitrogen in thelegume. This method has now become accepted world-wide as the most practical and useful tool for obtainingmaximum benefits of BNF to crop growth.

The 15N methodology for quantifying the amount ofbiologically fixed nitrogen by field-grown legumes waslargely developed at the Agricultural Laboratory atSeibersdorf and has since been adapted to otherN2-fixing systems such as pastures and tree legumes,actinorhizal trees, and Azolla.

Similarly, rock phosphates are important potentialsources of phosphorus in many countries. Direct appli-cation of finely ground rock phosphate, using localphosphate deposits, may be the cheapest source ofphosphorus to crop growth on acid soils of the tropics.The Laboratory has also developed 32P-radioisotopetechniques for evaluating the phosphorous availability oflocal rock phosphates to plants. These techniques areroutinely used by the FAO/IAEA programme for theagronomic evaluation of natural rock phosphatematerials in connection with projects of the FAO Fertil-izer Programme. Current research is focusing on meas-uring genotypic differences of nitrogen-fixing trees inphosphorus uptake from rock phosphates with the aim ofmaximizing nitrogen fixation and increasing soilfertility.

Support of IAEA's Seibersdorf Laboratory

The Soil Science Unit of the Agency's SeibersdorfLaboratories provides invaluable research and develop-ment support for the co-ordinated research programmes(CRP) and field technical co-operation projects co-ordinated by the soil fertility, irrigation, and cropproduction section of the Joint Division of the IAEA and

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FAO/IAEA symposium in 1990on the use of stable isotopes

In October 1990, the IAEA and FAO are jointly spon-soring a major scientific gathering — the internationalsymposium on the use of stable isotopes in plant nutri-tion, soil fertility, and environmental studies. Early appli-cations of stable isotopes were made in the geologicalsciences. Over the past few years, recent instrumentaldevelopments and innovative studies using variousstable isotopes have led to widespread application in lifesciences, agriculture, and environmental research.

This symposium is being organized to fosterexchange of scientific information and main achieve-ments in these important fields. It is anticipated that theparticipants will help to identify new research areas,potential applications, and means for developing andtransferring such technologies with the ultimate goal ofdeveloping a sustainable and environmentally soundagriculture.

The symposium will be held in Vienna, Austria, from1 to 5 October 1990. Further information may beobtained by writing to the Soil Fertility, Irrigation, andCrop Production Section of the Joint FAO/IAEA Division.

Food and Agriculture Organization (FAO). The Unit hasplayed a key role in the development and transfer ofnuclear technology in soil science and plant productivitysince the inception of the Joint Division's programme in1964.

Current back-up research. Ongoing research in theunit covers a wide range of topics, which generally canbe grouped in two main areas:• The first main research area is related to the restora-tion of soil fertility through biological nitrogen fixationas a means of improving plant productivity. Researchactivities in support of the CRP on the management ofnitrogen fixing trees in restoring and maintaining soilfertility include genetic variation in nodulation and nitro-gen fixation in tree species; selection of effectivemicroorganisms (Rhizobium/Frankia) for tree speciesand inoculum technology; isotope methodologicalstudies for measuring nitrogen fixation in trees; effectsof environmental factors (soil and climatic) on nodula-tion and nitrogen fixation in tree species; effect ofmanagement practices on nitrogen fixation in tree spe-cies; selection of strains of Rhizobium for effective nitro-gen fixation in tropical legume trees; and movement ofstrains of Rhizobium in the rhizosphere of legume trees.

Research in support of CRPs and technical co-operation programmes on biological nitrogen fixation bygrain legumes is continuing. This research has mainlyinvolved further development of the 15N methodologyto quantify biological nitrogen fixation under field andgreenhouse conditions as well as ecological studies ofrhizobia, the root-nodule producing bacteria, in therhizosphere of grain legumes. The following list illus-trates the type of work being conducted at the labora-

tory: quantification of N2 fixation by various I5Nisotope approaches; effect of inoculation treatments onthe movement of rhizobia in the rhizosphere, nodule for-mation and N2 fixation of soybean, common bean, andtree legumes; time course of N2 fixation of grainlegumes; and effect of environmental stresses such asdrought, salinity, and acidity on nitrogen fixation ingrain legumes.• The second main area of research is devoted to theimprovement of the productivity of saline, acidic, andother deleterious soils. Research activities are carriedout in support of two CRPs in this field: (1) use ofnuclear techniques to improve crop production in salt-affected soils; and (2) increasing and stabilizing plantproductivity in low phosphate and semi-arid and sub-humid soils of the tropics and sub-tropics.

Back-up research focuses on the identification ofplant genotypes highly efficient in the utilization ofresources under low input technology, as follows: initialscreening and field testing of plant genotypes adaptableto certain deleterious soil conditions (saline or acidic,for example) or with high efficiency of water andnutrient uptake and use; and root biology and efficientuse of soil resources (water and nutrients). Isotopicmethods are being used to study the uptake (rootparameters) and use of the resource in the plant (physio-logical parameters).

All these research projects are of great significancenot only to sustainable agriculture but also in restoringand maintaining soil fertility for increased plantproductivity.

Future research directions

Future programmes will continue to emphasize theuse of nuclear techniques for developing a sustainableagriculture. In December 1988, a consultants' meetingdiscussed the application of techniques in molecularbiology/modern biotechnology to the immediate andfuture programmes of the Agency's Soils Section. Theconsultants recommended work to be initiated in thisfield and indicated that the Section could make unique,highly important contributions in developing DNAprobe work mainly in microbial ecology, as an effectiveextension of the existing vigorous programmes onmanagement of nitrogen fixation by trees and grainlegumes in the developing countries.

Similarly, the members of a review team of the JointFAO/IAEA programme (28 November to 2 December1988) recommended that increased emphasis should begiven to the efficient use of water resources and methodsof safeguarding and improving the quality of waterresources. In many developing countries, food produc-tion is greatly limited by the inefficient use and/orimproper management of water and by failure to ade-quately safeguard water quality. The off-the-farmimpacts on fisheries and wildlife of water polluted byagriculture and by soil sediments are of grave concern.

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Estuaries, lakes, and continental shelves are being ren-dered non-productive. This situation has serious eco-nomic and public health implications.

Training activities

Together with the back-up research, training is con-tinuously provided by the Soil Science Unit at Seibers-dorf in the form of training courses and fellowships inthe applications of nuclear technology in soil science andplant productivity. This predominant role of training insoil science has a historical and scientific research anddevelopment basis in the laboratory.

• Training courses. Interregional training courses onthe use of isotopes and radiation techniques on soil/plantrelationship studies have been held yearly since 1978 atthe Seibersdorf Laboratories. In addition, two special-ized training courses on biological nitrogen fixationwere conducted in 1985 and 1986. Each training courseusually lasts 4 to 8 weeks and can be attended by about20 participants. Advanced training on the use of stableand radioactive isotopes and radiation techniques isprovided to scientists from developing countries activelyengaged in several areas of soil science research, i.e soilfertility, plant nutrition, biological nitrogen fixation, andwater use efficiency and irrigation management prac-tices. A major new development was the 1988 Seibers-dorf's training course focusing on root studies and howto study them using nuclear and related techniques.

The Soil Science Unit at Seibersdorf, with their avail-able expertise and resources, is supporting regional andnational training courses as well as other training events.It trains personnel of the other host centres, defines thesyllabus of such training courses, provides lectures, andsupplies training materials such as manuals, brochures,and video films.

• Fellowship training. The Soils Science Unit is alsoactively involved in fellowship training as an effective

Training manual onthe use of nuclear techniques in studies

of soil/plant relationships

The IAEA is currently preparing a training manualcovering all aspects of relevant nuclear techniques insoil fertility and plant nutrition research. This comprehen-sive coverage replaces and updates earlier manuals(1964, 1976) and incorporates the available expertise onthe topics in the Joint FAO/IAEA Programme. Majorheadings and sections include:• Stable and radioactive isotopes• Methods for 15N determination• Isotope techniques in soil fertility and plant nutrition

studies• Use of 15N methodology to assess biological nitrogen

fixation• Photosynthesis and crop productivity• Use of neutron water and gamma density gauges in

soil water studies.The manual is intended to help young scientists from

developing countries in the use of nuclear techniques inimproving plant nutrition and therefore increasing foodproduction in their countries. Further information may beobtained from the Soil Fertility, Irrigation, and CropProduction Section, Joint FAO/IAEA Division, or the SoilScience Unit at the IAEA's Laboratories, A-2444 Seibers-dorf, Austria.

way of transferring its research and development todeveloping countries. Every year approximately10 IAEA fellows involving approximately 55 man/months are trained for periods varying from 3 to12 months.

There are two categories of fellows: Analyticalfellows are accepted for short-term periods of 2 to4 months to learn isotope analytical techniques used insoil/plant research studies. This form of training

13%

Training activities at the Seibersdorf Laboratories' Soil Science Unit

TRAINEES

3 2 %

FELLOWS

19%

26%

27%

29%

18%

36% m

Africa

Middle East & Europe

Latin America

Asia & Pacific

The Soil Science Unit at Seibersdorf has trained a total of 243 participants from 72 Member Statesin courses during 1978—88 and 90 scientific fellows during 1962—88 involving 635 man-months.

IAEA BULLETIN, 4/1989 59

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includes technical tutoring and hands-on practical ses-sions. Particular emphasis is given to specific techniquesrelevant to research conducted under technical co-operation projects, i.e. N-15 assay techniques by emis-sion spectrometry. Whenever possible, group training oftwo to four such fellowship holders is arranged once ortwice a year. Research fellows are accepted for periodsbetween 6 and 12 months to work on a question withinthe unit's research programme. The fellows receiveguidance on experimental strategies and use of isotopeand related techniques relevant to a particular area ofresearch which he or she will pursue upon return to hisor her home country. The fellow is expected to completeand write up a piece of research work. This type offellowship gives an opportunity for the fellow to workon the application of nuclear techniques to solving aparticular research problem.

In addition, the Soil Science Unit receives IAEAsponsored scientific visitors, each spending 1 to 2 weeksin the IAEA Laboratory to get acquainted with recentdevelopments on a particular topic of soil scienceresearch. There is also opportunity for fellow scientiststo get on-the-job training as cost-free interns.

Supportive services

In support of the international/regional networkscreated by the co-ordinated research programmes of theJoint FAO/IAEA Division, the unit provides the neededanalytical services of plant, soil, and water fertilizersamples for over 100 research contract holders par-ticipating in the various programmes. In this contextapproximately 15 000 isotopic and related analyses were

performed last year. In addition 15N-labelled fertilizerrequired for carrying out the experimental plans isweighed out and dispatched to participants in these CRPprogrammes.

The Unit also provides necessary analytical supportto laboratories in developing Member States receivingIAEA technical assistance and lacking appropriateanalytical facilities.

The Unit plays a leading role in the development ofnew isotopic measurement techniques/equipment andthe refinement of those already in use for routine pur-poses. These developments are currently being used inIAEA technical assistance projects. For instance, theUnit has designed and assembled metallic vacuum linesfor sample preparation for 15N analysis by emissionspectrometry. It supplies these to relevant technical co-operation projects in Member States.

Dissemination of scientific/technical information

The Soil Fertility, Irrigation, and Crop ProductionSection, with the support of the Soil Science Unit, hasbeen very active in publishing the major scientificachievements from co-ordinated research programmesand results of practical importance from technicalassistance projects.

The main findings of the Unit's back-up research car-ried out by the unit are also published in scientific jour-nals. Some 10-15 scientific papers are published eachyear in reviewed journals.

The Unit also has a particular involvement in thepreparation of training materials, such as trainingmanuals and specialized video films.

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