by
John Q. Rijks, Consultant, Statistics Division, FAO
RESUME
COMMUNICATION No. 2: Activités antérieures de la FAO dans le domaine des statistiques relatives aux plantes-racines: aperçu, résultats et recommandations
L'objectif de cette communication est de passer en revue quelques-unes des principales activités menées jusqu'ici par la FAO dans le domaine des statistiques relatives aux cultures sarclées afin de montrer certaines évolutions récentes et de fournir une sorte de base commune ou de point de départ pour les présentations et discussions qui se succéderont au cours de cette réunion.
On constate que l'importance des racines et tubercules comme éléments essentiels de la sécurité alimentaire des ménages est depuis longtemps reconnue mais qu'en termes de statistiques, l'accent a été mis sur les cultures céréalières. La méthodologie que l'on a pu observer au cours des années s'est attachée à traiter les problèmes spécifiques aux cultures sarclées comme des cas particuliers de méthodes utilisées pour les cultures vivrières, priorité étant donnée à d'autres domaines tels que la polyculture, la plantation et récolte en continu, etc.
A l'occasion de diverses réunions techniques, on a insisté sur le fait qu'il convenait de mieux prendre en compte les aspects agronomiques spécifiques des cultures sarclées ainsi que l'évolution des besoins en matière de données. Il a également été indiqué qu'il ne serait pas possible de concevoir une méthode simple capable de répondre aux besoins d'information particuliers que requièrent ces cultures.
En développant une méthodologie statistique pour la culture de racines et tubercules, on pourrait essayer d'adapter des stratégies existantes. Certains estiment toutefois qu'il vaudrait mieux lancer une nouvelle réflexion. En outre, vu l'importance accrue accordée à la surveillance de la sécurité alimentaire au niveau des ménages, il est probable que le meilleur moyen de répondre à l'évolution des besoins en matière de données soit de recourir à une combinaison de méthodes, tout en veillant à établir un équilibre entre précision et faisabilité au niveau de la mise en œuvre. De toute évidence, il sera nécessaire de tester la méthodologie dans le cadre d'études pilotes réalisées sur différents sites.
ABSTRACT
The purpose of this paper is to review some of the most important activities by FAO in the area of statistics on root and tuber crops, in order to illustrate some of the developments that have taken place over the years and to provide a kind of common base and starting point for the successive presentations and discussions in the meeting.
It was found that the importance of roots and tubers as a basis for household level food security was long recognized, but that the emphasis in agricultural statistics has been mainly on the cereal crops. Methodology documented over the years tried to deal with the specific problems of the root and tuber crops as particular cases of existing methods for food crops, concentrating mainly on aspects such as mixed cropping, continuous planting and harvesting, etc.
In successive technical fora, the attention was drawn to the fact that the specific agronomic aspects of the root and tuber crops need to be taken into account more prominently as well as changes in data requirements. It was also felt that it would not be possible to devise a simple method that could take care of the specific requirements for data and information of these crops.
Development of statistical methodology for the root and tuber crops might try to adapt existing approaches, but it was also argued that some new thinking would be required. Given also the increased emphasis on monitoring household level food security, a combination of methods might be the most appropriate way of responding to changes in users data needs, whereby a balance need to be found between accuracy and feasibility of implementation. Obviously, pilot studies for testing methodology in multiple locations will be required.
1. Introduction.
The contribution of roots and tubers to staple food requirements of rural and urban population is significant in many developing countries. In addition, these crops have since long been part of the regular food habits and frequently contribute to cross-substitution when cereals are short in supply. In consequence, these crops play thus an important role in the national and household level food security. Over the past 20 years, Governments in many developing countries have promoted the cultivation of roots and tubers in a specific effort to support household level food security, but sometimes this has been at the expense of cereal crops.
Unfortunately, national assessments of the forthcoming food supply-demand situation are hampered by a general lack of information on yield and production of the root and tuber crops. Time series of past production are hard to come by and, if at all existing, they often show considerable inconsistencies. Consequently, in many countries these crops have been left out of the food supply-demand balances and have in other countries seriously complicated the compilation of national food balances, whereby the contribution of roots and tubers have been included in a qualitative or very approximate manner. Similarly, it has been difficult to judge the impact of the promotional programmes for root crop cultivation.
The causes for this lack of information lie in the very characteristics of these crops: the edible parts are under ground and are not easy to assess in terms of growth and condition. In addition and contrary to cereal crops, the production of the edible parts of root and tuber crops is mainly a vegetative process, i.e. their development is not dependent on specific cycles including flowering, fruit setting, ripening, etc. Also, planting of several of these crops can take place over a much more extended period as compared to cereals. The development of the root or tuber begins after a number of months and generally continues for a considerable length of time. Harvesting can take place from as early as six months after planting up to 18 months or more for crops like cassava. It is in particular this latter characteristic that makes these crops so important for household level food security, as it permits the family to bridge over periods when other foodstuffs are short in supply. (It may also be noted that, for example, leaves of the cassava plant are nutritious and in several countries are used as vegetable.)
The above described difficulties in obtaining reasonable data on root and tuber production are since long recognized in various quarters. However, the international attention has often been forced to focus on cereals, as this commodity can be shipped, stored and distributed in an efficient manner, which are important requisites when it comes to deal with large-scale food shortages. In other words, even when data on the magnitude of possible shortfall in root and tuber production would be available, decision takers would not be able to effectively deal with such shortfall other than responding in terms of assistance in the form of cereals. Hence, the priorities in agricultural data collection were also more focussed on the cereal crops.
The shortcomings in data described above was well known to many agricultural statisticians and in several cases small-scale experiments were initiated to test various options of making qualitative or quantitative assessments of production of roots and tubers. Some of these experiments or tests were conducted in the framework of on-going projects for which FAO provided the technical assistance, whilst others took place in the ambit of agricultural research. Because of the characteristics of these crops, there was never a real breakthrough in terms of development of a simple and practical methodology for production estimation in small-scale cultivation, which could be applied at the national level. In response to this situation, a number of activities were developed over the past years and the most significant of these in which FAO was involved, are reviewed below.
2. Overview of selected activities.
2.1 Introduction.
In this section, a small selection of activities will be reviewed on their relevance and/or applicability towards the question of production estimation for roots and tubers. In the context of the present Expert Consultation, it is not the intention to try and review in this paper all that has been undertaken or published on the subject, nor to summarize all methodologies tried in various parts. In fact, some of the papers to be presented later in this meeting will be dealing with these aspects. However, it was felt useful to provide an overview and summary of the most important past activities by FAO in order to constitute a kind of common base and starting point for the successive reviews, presentations and discussions.
2.2 FAO Publication.
An important series of discussions took place in FAO in the late seventies and early eighties on the subject of estimation of area and yield of crops, leading to the publication of “Estimation of area and yield in agricultural statistics” (FAO Economic and Social Development Paper no 22, reprinted various times). The questions and problems surrounding assessment of roots and tuber crops was recognized, but no separate methodology was defined for the specific purpose. At the time, it was preferred to obtain the solution(s) in the context of what was considered to be appropriate methods for dealing with “continuous planting and harvesting” as well as “incomplete harvesting”.
It was also recognized that a further complication was caused by the fact that often cultivation took place as mixed cropping. A distinction was made between continuous harvesting as the result of continuous planting, or being the consequence of the crop characteristics which permit successive harvests from the same crop (particularly from temporary crops), but not to be confused with successive cropping.
An important conclusion reached at the time was that in such cases an estimation of crop area cannot be achieved in a single operation. Multi-round surveys would be necessary with the number of rounds being dependent on the various combinations of crops being grown. Another element that was recognized was that the planted area of a crop would not be relatively constant as in the case of a single-harvest crop, but could significantly increase or decrease over the crop season. To this end, a mathematical formula was developed, leading to a theoretical estimation of the area under crop in the form of average soil occupation.
Furthermore, it was recognized that continuous harvesting could be the result of crops being planted within the field at different times, in which case the yield estimation cannot be carried out by the objective techniques of crop-cutting in random plots. The same situation would arise when plants mature at different times. The latter is a characteristic for the root and tuber crops, i.e. there is no specific maturity date within a large interval and differences in harvesting date will mainly be reflected in different quantities collected per plant. From another standpoint, it was argued that the long range, during which a root or tuber crop could be harvested, could be interpreted as a form of incomplete harvesting. This is particularly the case when the crop is considered as a reserve crop whereby only that quantity is harvested that is required to make up for shortfall in other crops, and the rest may be left in the ground and eventually get wasted. This is not dissimilar to the situation with cash crops when a drop in market prices may not justify to continue harvesting the entire crop.
2.3 Cassava Production Estimation Workshop.
In the SADC[1] countries, cassava and other root crops are an important component of the daily food consumption. The problem of estimation of production of root and tuber crops was recognized already in the late eighties and has been on and off included in agendas of various meetings in the Region. Some member countries tried to include actual (qualitative) information on cassava production in their monthly food balances, whilst others were facing considerable difficulties in doing so. In the SADC Region there is a Regional Early Warning System for Food Security in operation, based on national systems in the member countries (details in one of the next papers). In 1995 the question of estimation production of cassava was discussed at length between SADC and FAO and it was decided to devote a specific meeting of national statisticians to the subject. In cooperation with FAO, SADC organized a Workshop on Cassava Production Forecasting and Estimation in 1996. The stated purpose was to try to come up with better methodologies for estimating cassava availability among the cassava producing countries in the region. Prior to the workshop, five member countries producing cassava were asked to complete a questionnaire in order to find out the importance of cassava as a food crop, to evaluate cassava forecasting/estimation methods currently in use and to assist in deciding whether or not it was necessary to devise new statistical methods for the purpose.
Methodology used in the SADC countries concerned was illustrated and discussed on merits and shortcomings. It was found that none of the countries was actually using an objective method for forecasting or estimating cassava production or consumption, due to a combination of technical reasons and resource constraints (human and financial). The meeting noted that in Tanzania, Malawi and Mozambique methods were used whereby area under cassava was estimated using sample surveys, but yields were either assumed to be constant or were subjectively obtained from extension service reports or extrapolated from agricultural research. None of these were considered satisfactory. Because of the crop characteristics, it was found necessary that major statistical work had to be carried out in order that both underground availability of cassava and amount actually harvested per month could be derived. One way of obtaining this information was to establish ”monthly cassava harvesting coefficients” through special studies over a couple of years.
The question was kept on the agenda of annual meetings of the statisticians of SADC countries in order to provide information on action taken in individual countries and exchange experience with implementing alternative solutions for obtaining any information on cassava production. Due to financial constraints, it was deemed necessary that external technical and financial assistance would be needed for the further development of methodology. Several proposals were prepared in consultation between SADC and FAO but despite various efforts it appeared difficult to initiate such special studies.
2.4 Regional Technical Meetings.
During 1999 and 2000, FAO organized a series of “Technical Meetings on Methodology for Crop Forecasting” in Bangkok for the Asia and Pacific Region, in Bamako for the West Africa Region and in Harare for the Eastern and Southern African Region. This was in response to calls for improving national capacity on crop forecasting systems in order to extend forecasts up to at least the district level and to improve authenticity of forecast figures. The Technical Meeting in Harare was a joint FAO/SADC effort and its purpose was to address various recommendations through the preparation of a series of technical documents on methodology, supported by case studies on selected country practices. This was done through contracting a number of specialists, serving in their personal capacities, to document the different methodological aspects and their experience with developing and implementing food crop production forecasts in the Region. Given the importance of root and tuber crops in this Region, a special session was devoted to the forecasting and estimation of their production.
The participants in the meeting found that current methodologies were limited in their applicability to the specific problems of root and tuber crops. The main reasons identified were: determination of area planted was done in a subjective way, yields were usually also determined subjectively, sometimes estimates were used by extrapolating results from research stations and finally, crop cutting measurements were giving at best the “in the ground availability”. The statisticians further observed that the resource cost (human and funds) was high in relation to the results obtained.
Some suggestions were tabled as to simplifying area estimation and crop cutting and deriving a proportion between “in the ground available” and “actually harvested” within a season. Specifically regarding root and tuber crops, the meeting urged FAO to help regional governments develop methodologies that can be used to forecast (minor) crops and FAO and SADC were also requested to facilitate the introduction of suitable methodology for estimating production of cassava and other root crops. Importantly, the meeting suggested the formation of a small group of national and international experts to develop a suitable method of cassava production forecasting.
Statisticians at the Bamako meeting also devoted a session to discussing the difficulties in making assessments of root and tuber crops and reviewed some examples of methods used. In their conclusions, the participants underlined the need for methodological development with emphasis on ease and simplicity of implementation.
3. Commentary and Outcome of the review.
From the time of the FAO publication onwards and as emerging from the above review, it was found that the problems of estimating root and tuber crops have attracted a good deal of discussion and divergent views, but also that the only agreement was that the problems have not been solved. As an outcome of the above review, the statistical aspects of assessment of production of roots and tubers may be summarized as follows, recognizing that various other formulations might be possible:
a) Statement of the problems:
How is area planted estimated during a growing season? In a way, it could be visualized as a continuous process visualized as a pool whereby the area is gradually being reduced (withdrawn from the pool) because of some harvesting is taking place and simultaneously (or gradually during the season/year) is increased because some planting is taking place. It is further understood that this process often takes place in the same field or plot.
What constitutes production? This could be the potential, in-the-ground-availability or the actual quantity(s) harvested. Much depends on the purpose for which the data are being collected. For example, national food security balances for Early Warning purposes might prefer to use potential production since it is assumed that flexibility exists with the consumers (i.e. the possibility of cross-substitution), whilst household level food balances would require data on actual quantities collected from the field preferably on a weekly or monthly basis.
Continuous harvesting (as well as successive and incomplete harvesting), as particular cases of the above, poses the problems of estimating (cumulative) area harvested in a given season and estimating quantity harvested in that season.
b) Statement of some of the conclusions drawn by the reviewed activities:
Potential production estimation does not seem to present a major problem other than selecting the most suitable period for the field work to be carried out in relation to the optimum quality being pursued. Prior knowledge on the cumulative growth of roots and tubers would facilitate the process.
Actual production estimation of root crops when specifically produced for the market (i.e. a single harvest of all produce) can be dealt with very much the same as most other crops.
Actual production estimation in small-scale cultivation or as a subsistence crop poses significant problems, as it is not possible to estimate the area harvested or yield or production through direct data collection. It was concluded that field experiments were necessary for estimating total (underground) availability and that only food consumption surveys with repeated visits could offer a solution for obtaining information on amounts actually harvested.
Development of improved methodology is seen as complex and requiring an approach with multiple components such as: area estimation, crop cutting, reporting and household food consumption surveys. In many countries, developing or adapting these components to root and tuber crops is not seen as feasible at the national level, but requires international cooperation.
The present meeting may consider discussing these statements and deciding whether they are still adequate to meet the present-day requirements.
4. Some conclusions and recommendations resulting from the review.
4.1 Despite their importance as food crops, many countries, if not most, are facing problems with the estimation procedures for obtaining reasonable data on area and production of roots and tubers under small-scale farming. Some experimentation was done in many countries, but often the necessary guidance was lacking.
4.2 Existing definitions used in agricultural statistics are not entirely adequate for dealing with the problems of root and tuber crops without appropriate modifications. Some of the concepts used with mixed cropping and continuous cultivation and harvesting might be useful, be it with some adaptation.
4.3 From the review it appeared that the direct application of yield rates obtained from agricultural research to production estimation is not sufficient to reflect actual farmers' growing conditions.
4.4 Any improved methodology will need to be applicable under actual field conditions and should thus be adequately tested in pilot studies in multiple locations. Both the concepts used and the operational aspects should be sufficiently simple to allow implementation under the usual human and financial resource constraints in developing countries, whilst meeting the various data requirements.
4.5 Improved methodology should aim at producing “reasonable” data on production and consumption of root and tuber crops. Given the usual margins of uncertainty in the conversion factors of wet weight to dry weight, there is no need to strive for unwarranted accuracy at high resource inputs.
References.
Estimation of crop areas and yields in agricultural statistics.
FAO Economic and Social Development Paper no. 22.
FAO, Rome, 1982, with various reprints.
Proceedings of a Workshop on Cassava Production Forecasting and Estimation.
SADC Regional Early Warning Unit, Harare, Zimbabwe, 1996.
Report on Joint FAO/SADC Technical Meeting on Methodology for Food Crop Forecasting, 10-11 April 2000.
Prepared by SADC regional Early Warning Unit, Harare, Zimbabwe, 2000.
Réunion technique sous-régionale sur les méthodes de prévisions de récoltes des cultures vivrières. Bamako 15-16 mai 2000.
Rapport de Synthese. FAO/AFRISTAT, 2000.
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[1] Southern African
Development Community. |
