Paper 4: Quantification of Root Crops in National Food Balance Sheets and Problems encountered

By
Mr. Bentry P. Chaura
Senior Statistician,
SADC Regional Early Warning Unit (Food Security)
E-mail: [email protected]

Résumé

L'objectif de la communication est de présenter certaines procédures appliquées pour la quantification des plantes-racines dans les bilans alimentaires nationaux et les problèmes majeurs que rencontrent les pays, en particulier ceux de la SADC.^[3]

Quantifier les plantes-racines dans le bilan alimentaire national implique essentiellement deux procédures. Il faut, en premier lieu, normaliser les différentes formes sous lesquelles sont recueillies les données relatives à la plante concernée. Cette procédure permet d'agréger les différentes formes de la denrée alimentaire pour lesquelles les données sont rassemblées en un seul chiffre. Par exemple, les données concernant les stocks de manioc peuvent être collectées sous la forme de manioc humide, manioc séché, farine de manioc ou produits transformés. Ces formes de la plante-racine ne peuvent pas être simplement additionnées sur la base de tonnage car elles contiennent des valeurs alimentaires différentes.

Deuxièmement, il est nécessaire de convertir la plante-racine en un type prédéterminé de denrée de base en utilisant les valeurs énergétiques. Cette conversion permet de procéder à des comparaisons et agrégations entre différentes denrées dans le bilan alimentaire national. Dans les pays de la SADC où s'effectue cette conversion (par exemple, au Malawi), le maïs est la denrée de base et toutes les autres denrées alimentaires, y compris les plantes-racines, sont converties en équivalent maïs.

Les deux principales étapes de la quantification des plantes-racines dans le bilan alimentaire national sont relativement faciles à accomplir une fois que les données sur les plantes-racines sont disponibles et que les taux de conversion sont connus. Comme il est indiqué plus loin, c'est la non disponibilité de données fiables concernant ces produits qui constitue le principal problème dans tous les pays de la SADC. Les méthodes de collecte des données utilisées actuellement ne sont pas assez sûres pour pouvoir interpréter convenablement les données figurant dans les bilans. De plus, les taux de conversion spécifiques à chaque pays ne sont pas disponibles à l'heure actuelle.

Par conséquent, il est recommandé, d'une façon générale, à la FAO d'aider les pays à élaborer des méthodes fiables de collecte des données sur les plantes-racines. Les experts de la FAO peuvent également initier des études/expériences au niveau national afin de produire les divers taux de conversion spécifiques aux pays.

Summary

The paper outlines some procedures that are followed in quantifying rootcrops in the national food balance sheets and the main problems that countries, especially in the SADC^[4] region, are encountering.

Quantifying root crop in the National Food Balance Sheet basically involves two main procedures. These include, firstly, standardisation of the various forms in which data is collected on the concerned root commodity into one form. This procedure allows aggregation of the various forms of the commodity in which data is collected into a single figure. For example, cassava stock data may be collected in the form of wet cassava, dried cassava, cassava flour, or in the form of processed products. These forms of the root crop cannot just be added on a tonnage basis as they contain different food values.

Secondly, it is necessary to convert the root crop into some predetermined base commodity by the use of food energy values (fev). This conversion makes it possible to compare and aggregate across commodities in the National Food Balance Sheet. In the countries where this conversion is done in the SADC region (for example, Malawi), maize is the base commodity and all other food commodities, including root crops are converted into maize equivalent.

The two main steps in quantifying root crops in the National Food Balance Sheet are relatively easy to follow once the data on the root crops are available and the conversion rates are known. As indicated later, it is the unavailability of reliable data on root crops, which is the main problem in all SADC countries. Methods of data collection currently in use are not reliable enough for a proper interpretation of the data in the balance sheets. In addition, country specific conversion rates are currently not available.

The general recommendation in this paper, therefore, is that FAO should help countries develop reliable methods of data collection on root crops. FAO experts may also initiate in-country studies/experiments to generate the various country specific conversion rates.

1.0 Introduction

In the SADC region and indeed worldwide, a food balance sheet is normally used to quantify a country/region's food supply and demand during a specified reference period. In this case, the country's overall food security situation is analysed by comparing food requirements with availability, thereby obtaining an estimate of the food deficit or surplus. The main strength of analysing overall food security in this way is that it offers an objective methodology based on quantifiable facts rather than qualitative judgements. As a result, it is possible to make comparisons and aggregations of food security assessments across countries or regions. Table 1 shows a typical SADC National Food Balance Sheet.

However, food balance analysis only provides an assessment of the adequacy of overall food supplies by indicating the extent of any food shortfall/surplus, thus quantifying the amount of food that needs to be imported or is available for export. It does not quantify the number of people affected or identify locations where the food shortages are most severe. In short, the food balance sheet is only concerned with overall food availability, normally at the national level, leaving out the question of access to food, which is another important aspect of food security assessment.

Ideally, to obtain a full picture of the overall food security situation in a country using the National Food Balance Sheet, all food commodities, from whatever source, should be quantified and included in the balance sheet. The food balance sheet for SADC should therefore include cereals (maize, rice, wheat, sorghum and millet), root crops (cassava, potatoes), plantains, livestock products, fruits and many other foods.

However, in practice, this is not a minor task due to diversity of diets and problems associated with collecting data, especially on minor food commodities. Within the SADC region, the rule of thumb is currently to try to include at least 75% of the caloric food intake into the Food Balance Sheet.

Table 1: ‘Standard' National Food Balance Sheet^[5] as currently used within the SADC Early Warning System.

This rule can be largely fulfilled at the aggregated SADC level by including only cereal commodities into the Regional Food Balance Sheet. However, National Balance Sheets of some countries within the region, namely Angola, Mozambique, Tanzania, Malawi, Zambia and DRC need the inclusion of root crops, especially cassava. In all these countries, cassava is becoming more and more important, especially given the frequent poor harvests of cereal crops in recent years.

This paper outlines steps one can take in order to quantify and include root crops in the National Food Balance Sheet, using cassava as an example. Similar quantifications could be done for other root crops.

2.0 Quantification of Root Crops in National Food Balance Sheet

To meaningfully include root crops into the National Food Balance Sheet, it must be possible to compare and aggregate rootcrop commodities with other commodities in the balance sheet. In general, this requires quantification at two levels. The first is the conversion of the difference forms of the same crop into one form so that aggregation can be done. The second quantification allows comparison and aggregation across all commodities in the balance sheet, accomplished by converting all commodities into a single base commodity using food energy values.

2.1 Standardisation of Different Forms of the Same Commodity

This is achieved through several procedures depending on the form of the commodity when the data is collected.

2.1.1 Wet Vs Dry Weight: Data on cassava production and stocks are usually collected when the crop has high moisture content, as the crop is normally stored underground and only harvested when the need arises. When estimating production, for example through a sample subplot, it is normal to convert the wet weight to dry weight. This may be achieved by, first determining the moisture content (using a moisture meter) of the fresh cassava and then using the following relationship to obtain the dry weight:

Dry weight = (wet weight × 100 - T)/(100 - D)

Alternatively, dry weight can be determined by allowing the harvested tuber from the subplot to dry in the sun. The dry weight is then realised once the weight becomes constant and no longer changes after further drying.

In most cases, however, the wet weight tonnage is typically deflated in a straight-forward manner using a predetermined rate to come up with dry weight tonnage. For example, in Malawi the dry weight cassava is assumed to be 30% of wet weight. Hence once the wet weight tonnage is known, say 20,000 tonnes, the dry weight is found as follows:

Dry weight = 20000 × (30%) = 20000 × 0.3 = 6000 tonnes.

2.1.2 Whole dry cassava Vs Flour: The National Food Balance Sheet typically includes only one aggregate figure for ‘production', ‘stock', ‘import', ‘export' and so on under each food item. However, data, for example on stocks, may be collected in the form of whole cassava, cassava flour or other processed products. One cannot just add the weight of these different forms of cassava to come up with ‘total stock' of cassava. The different forms of cassava have to be converted into one form before adding them up to determine the total stock, as the same weight of the different forms of cassava have different food values. For example, one kilogramme of cassava flour has more calories than the same weight of whole cassava, and therefore aggregating the two forms without due consideration would not be correct.

Within the SADC Early Warning System, the established convention is to measure cassava in terms of unmilled dry amounts of cassava, just as cereals are measured in terms of whole grain (except for rice, which is expressed in milled amounts rather than paddy). This, therefore, means that data collected in the form of flour is converted into whole grain for cereals and unmilled dry amounts for cassava. The conversion is done using milling extraction rates, defined as the percentage of the whole grain/unmilled dry amount remaining after the milling process. The following are some standard extraction rates in use in the SADC region:

Table 2: Milling Extraction Rates^[6]

Source: FAO and SADC

The extraction rates for dry cassava of between 75% to 80% means that a 100 kilogrammes of whole dry cassava would, after milling, be converted to between 75 to 80 kilogrammes of cassava flour (or an average of 77.5 kilogrammes).

Example: 50,000 tonnes of cassava flour would be converted to the whole dry cassava equivalency as follows (using an average extraction rate of 77.5%):

Whole dry cassava = 50000 × (100/77.5) = 64,516 tonnes.

Similar standardisation should be carried out on processed products of root crops as well as cereals. Currently, however, SADC countries only make use of grain equivalents of processed cereal products, as insignificant processed products of root crops are available.

2.2 Conversion to a Base Commodity^[7]

Converting the root crop into one form (flour to whole cassava) is a start, but may not be enough if the commodity is to be included in a balance sheet with other food commodities, where aggregation and comparison is done across commodities. This is because an equivalent weight of different food commodities (say, cassava and maize) does not necessarily contain the same amount of energy and, therefore, it is not strictly correct to add them up on a simple tonnage basis.

Accordingly, it is more accurate to convert all commodities in the balance sheet into equivalent amounts of a predetermined base commodity using food energy values (fev). The base commodity is normally the dominant food commodity in the balance sheet. In the case of the SADC region, the dominant food crop is maize and, therefore, all other food items in the balance sheet are converted into maize equivalents. Table 3 shows food energy values of the most important food staples in the SADC region.

Table 3: Food Energy Values (fev)

Source: FAO and SADC

The conversion from one commodity to the equivalent amount of the base commodity using the food energy values is fairly easy and is done by multiplying the number of tonnes of the commodity to be converted by its own food energy value, and then dividing by the food energy value of the base commodity.

Example: Suppose the base commodity is maize (fev = 3570) and the dry cassava (fev = 3180) amount of 7000 tonnes is to be converted into maize equivalent. The calculation would be as follows:

Cassava maize equivalent = [7000 × 3180] ÷ 3570 = 6235 tonnes.

The 6235 tonnes would then be the amount going into the cassava column under the relevant row item; be it production, stock or any row item for which the calculation was done. Once the conversion is done for all commodities included in the balance sheet, it is possible to do cross commodity assessment, and cross substitutions of one deficit food item by the surplus commodity.

3.0 PROBLEMS

While the quantification of given root crop data into a balance sheet may be fairly easy, there are however, some problems in the overall procedure that must be considered for a meaningful interpretation of the balance sheet.

3.1 Reliability of the Data

As mentioned in the introduction, the balance sheet is a tool used to analyse the overall food supply and demand for a given period within a given country or region. The balance sheet relies on collected basic data on population, supply and demand of different foods and their nutritive values. As is always the case when analysing data, the analysis can only be as good as the data itself. The method of data collection, therefore, becomes very important as it usually has a direct impact on the quality of the data.

Unfortunately, current methods of data collection on root crops within the SADC region are quite questionable. None of the SADC countries currently employ statistical methods of collecting production, stock or other necessary data on cassava or other root crops such as sweet potatoes. Wholly subjective or partly objective methods, such as crop reports from extension services, with questionable reliabilities, are currently employed to collect production data.

Mostly due to this problem, SADC regional food balances do not give due emphasis to the production and utilization of root crops, although it is generally acknowledged that root crops and other food commodities are very important in the region.

3.2 Unavailability of Country Specific Conversion Rates

Countries within the region do not have country specific milling rates to convert flour of the various commodities to grain equivalent or dry whole cassava. Using FAO extraction rates may not be suitable for a given country. Even within each country, extraction rates are likely to be different among different milling practices, say among commercial, small scale or household practices.

3.3 Substitutability of Root crops for other foods in the National Food Balance Sheet

Root crops are generally very bulky and are therefore mostly eaten locally where they are grown. Although part of the problem may have something to do with taste, especially among households in the SADC region whose main staple is maize, the main problem why root crops and in particular cassava are not easily moved from surplus areas to deficit areas is the bulkiness of the crop and the fact that the crop is best stored underground and not in any other storage facilities. Within the SADC region, this is also complicated by the fact that most cassava growing areas, for one reason or another, have very poor roads. Hence, when quantifying and aggregating cassava and other root crops in the National Balance Sheet, one has to bear in mind that surpluses in one area may not substitute deficits of other food commodities in another area of the country.

4. Conclusion and Recommendations

The importance of root crops and, in particular, cassava cannot be overemphasised in the SADC region. Both recent meetings of SADC Food, Agriculture and Natural Resources Ministers in Mozambique^[8], as well as the SADC Heads of States meeting in Luanda^[9], Angola, instructed the SADC Regional Early Warning Unit to broaden its current, mostly cereal balance analysis to include other food commodities. This is in recognition of the increasing importance of other foods, especially root crops, in the fight against hunger in the SADC region.

However, as indicated above, the main problem is basically the reliability of the data on other food commodities other than cereals. This problem is not new in the region, as several meetings and workshops have been held in the past among experts within SADC as well as with FAO, aimed at finding reliable, innovative and cost-effective methods of estimating production of root crops, and in particular, cassava. The various meetings and workshops held in the past came up with several recommendations that are still valid today. These are included below together with specific recommendations to help in quantifying root crops in the National Food balance Sheet. They include;

• Asking FAO to provide technical help to countries in the region to develop and adopt improved method of root crop production forecasting/estimation. It is realised within the region that the difficulty of developing an appropriate methodology of estimating cassava production is partly to do with the way the crop is harvested. The crop is normally harvested on a piecemeal basis over a period of time, not necessarily within the same year or season when the crop becomes mature. It is normal to keep mature cassava in the field and only harvest enough amounts for immediate needs. As such sorting out the question of what constitutes cassava production between ‘in the ground availability' and ‘harvested cassava' is also essential in developing a methodology of estimating cassava.

• Studies need to be initiated in root crop producing countries, probably with FAO help, in order to obtain county specific harvesting coefficients. Within the SADC region, it has been agreed that since the crop is kept underground, the amount harvested and consumed should be estimated from the mature ‘in the ground availability' to cover the time period of the food balance sheet (Monthly harvest consumption coefficients for Monthly Food Balances or yearly consumption coefficients for Yearly Food Balances). These studies could be conducted within each of producing countries during the course of a year or better still, for some two to three years which would possibly help to take into account variations in amounts harvested and consumed due to various reasons such as the availability of other foods etc.

• Initiate research on country specific conversion rates - FAO should help provide technical for this. As indicated earlier, country specific conversion rates, such as those of converting wet weight tonnage to dry weight tonnage as well as extraction rates, are needed for a proper and meaningful quantification and inclusion of the various data sets on root crops in the National Food Balance Sheets.

References

SADC Regional Early Warning Unit, Proceedings of a Workshop on Cassava Production Forecasting and Estimation, September 1996, Kadoma, Zimbabwe.

SADC/FAO Early Warning System, J.M. Rook: Technical Handbook on Food Balance Sheets, Vol. 1: General Guidelines, June, 1994, Harare, Zimbabwe.

M.O. Akoroda, USAID Sponsored Study: Study of the Contribution of Cassava and Sweet potatoes to Total Food Availability in Malawi, May 1999, Lilongwe, Malawi.