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Zambia country paper
Wetland classification for agricultural
development in Eastern and Southern Africa:
the Zambian case

Introduction

Zambia is a landlocked country in Southern Africa, and covers about 752 600 km2 located between latitudes 8 and 18 South and longitudes 22 and 33 East. A large part of Zambia is on the Central African plateau between 1 000 and 1 600 metres above sea level. The plateau is incised by large rivers and the alluvial plains of the Kafue, Zambezi and Chambeshi form expansive wetlands.

Although Zambia is tropical, temperatures are moderated by altitude. There are three seasons: the cool dry (April-August), the hot dry (August-November) and the hot wet season(November-April). The average temperatures range from a mean monthly minimum of about 10C in June and July to a mean monthly maximum of 30C in October and November. Rainfall varies from 700 mm in the south to 1 500 mm in the north, with most of it concentrated over the period November to March.

The natural vegetation is savanna woodland dominated by Miombo woodlands which cover about 50% of the country.Mopane and Munga woodlands cover much of the hot and dry southern valleys of the Zambezi, Luangwa and Lunsenfwa. Wetlands are generally dominated by grasslands.

Agro-ecological regions

Zambia is subdivided into 36 agro-ecological zones, each with its own characteristics. These characteristics include: rainfall, length of growing period, occurrence of drought, minimum night and maximum day temperatures during December to February, occurrence of frost in the dry season (June to August), amount of sunshine during the dry season. The 36 zones have been grouped up into 3 Agro-ecological regions mainly on the basis of rainfall:

Agro-ecological region I

This region covers the semi-arid, rift trough areas of Zambia, largely the Luangwa, Lunsenfwa and Zambezi valleys,the Sesheke low altitude plateau areas in the south and south-west and Senanga in the

Nawa Mukanda 
Soil Correlator/Principal Research Officer 
Soil and Water Management Division, Mount Makulu Research Centre 

west. The region is characterized by high temperatures, high evaporative losses and a short growing season due to low and poorly distributed rainfall of less than 800mm.

The main soil limitations in this region include severe wetness problems, salinity/sodicity and heavy textured nature making workability ( in wet and dry states) difficult. Drought and short growing period reduces the choice of crops to be viably grown, especially by small scale farmers, and leaves the environment delicate.

Agro-ecological region II

This region includes the entire plateau stretching from Eastern through Central and Lusaka Provinces to the Western Province and also covering Southern Province. The annual rainfall ranges from 800 to 1 000 mm. Region IIb consists of the Kalahari sands area.

The soils of Region II are characterized by strong acidity, low nutrient retention and low water holding capacity, dominance of coarse textured topsoils (abrupt textural change) and severe topsoil capping which results in seedling emergence problems.

Agro-ecological region III

This region is popularly known as the high rainfall area. It covers the Northern, Luapula, Copperbelt, North-Western and part of Central Provinces. Annual rainfall ranges from 1 000 to 1 500 mm.

The high rainfall areas of Zambia generally have highly leached soils and are characterized by very strong acidity, severe aluminium toxicity, low nutrient reserves and low nutrient retention capacity. Leaching thus leaves the soil lacking in most major and some minor nutrients.

Human population

Zambia is characterized by a high demographic growth rate and high urbanization. The 1969, 1980 and 1990 national census reported total populations of 4.0 million, 5.7 million, and 7.8 million, respectively (Central Statistical Office, 1990). This implies population growth rates of 3.1% per year between 1969 and 1980 and 3.2% per year between 1980 and 1990, amongst the highest in Africa.

Urbanization has been very rapid since independence in 1964, when about 20% of the people lived in urban areas. The proportion of the population living in urban areas increased steadily from 29% in 1969 to 42% in 1990, making Zambia the most urbanized African country South of the Sahara.

The economy

Copper mining has been the backbone of Zambia's economy since independence, and to date the industry still provides about half of Government revenue and 85% of the country's export earning.

Although agriculture accounts for only 13% of Gross Domestic Product, it provides livelihood for about half of Zambia's population. Small-scale farm families, cultivating land with oxen or hand hoes, make up over 90% of the farming population. A further 7-9% are classified as medium scale farmers and only 1-3% are in the large-scale farming sector. The main crops are maize, sorghum and cassava. Other cash crops which control land allocation are cotton, tobacco, sunflower and soyabean. Generally, once an individual has been allocated a piece of land, ownership is inherited upon the death of the owner. Land, forests and wildlife resources in uncultivated areas are continually utilized between periods of cultivation, especially through grazing. These tenurial arrangements have been an obstacle to investment in fixed land resources, including land conservation structures or tree planting activities. However, it is now becoming possible to obtain leasehold titles to land in traditional areas.

Background

Wetlands are areas that are either periodically wet and periodically dry or permanently flooded with a water layer not exceeding several metres. This definition of wetland clearly excludes open waters that are several metres deep, but includes permanent swamps, floodplains, and dambos. Wetlands in Zambia, based on this definition, occupy slightly more than 20% (150 520 km2)of the country's total area of 752 600 km2.

This paper will attempt to review the characterization and classification of wetlands for agricultural production with special reference to dambos in Zambia.

Occurrence and distribution of wetlands

The wetlands of Zambia can be identified through a combination of three factors:

  1. mode of formation
  2. physiographic position
  3. moisture regime

The following are the broad divisions of wetlands whose modes of formation, physiographic position and moisture regime are apparent in the definitions.

Swamps

A swamp is a vast, usually inundated, depression that consists essentially of floating vegetation and wet peaty land. Ferreira (1981) identified two basic morphological units of a swamp area: (a) an outer belt, which is flooded annually, and (b) the main swamp, which is permanently flooded and covered with floating vegetation. Small swamps in the northern provinces of Zambia support a lush vegetation. The major swampy areas of Zambia are Busanga, Lukanga, Bangweulu swamps, and Lake Mweru - Wantipa and Lake Mweru marshes.

Floodplains

Floodplains are zones along major river systems that are low-lying and seasonally flooded. Major floodplains with several kilometres wide occur along stretches of the Kafue, Zambezi, and Chambeshi rivers. Floodplains are usually made up of a complex pattern of lagoons, oxbow lakes, backswamps, levees, cut-off river channels and terraces, offering a highly variable relief. They are usually flooded towards the end of the rainy season.

Dambos

Dambos are seasonally or permanently wet grassy valleys, depressions, or seepage zones on slopes. The first two often show a catenary sequence of soils, being well drained on the upper slopes and poorly to very poorly drained in low-lying areas. Dambos have a polygenetic origin, but they are often essentially alluvial deposits and nearly always underlain by laterite at some depth (in some cases at considerable depth).

Characterization and classification of dambos

Broadly, a dambo can be defined as a wide and low lying gently sloping treeless grass covered depression, which is seasonally waterlogged by seepage from surrounding high ground assisted by rainfall and has water tables for most part of the year in the upper 50-100 cm of the soil profile from which they drain into streams. The area covered by dambos in Zambia amounts to 35 000 km2 (Ferreira, 1981) or 4.6% of the national area.

Ferreira (1981) tried to rationalize the definition of a dambo to emphasize its land-use potential and redefined it as "an area of land where the water table, either seasonally or permanently, is located in the upper 20 cm of the soil, often reaching the ground surface itself and occasionally rising to 0.5m above the surface during the rainy season."

Characterization of dambo soils

There is a fair amount of literature on the wetlands of Zambia, especially dambos, but in most instances soil data are lacking. The omission of soil information stems from the traditional desire to retain dambos for water conservation and micro-climate control alone, except those for rough grazing in tsetse fly-free areas. Essentially, the studies have been confined to ecological features (species composition). It was formerly felt that cultivation of dambos would grossly damage the headwaters. More recently, however, the policy has slightly changed to allow utilization of the dambos for agriculture under strictly controlled conditions.

Brammer (1973) conducted a fairly comprehensive study on wetland soils in Zambia.

All the wetland soils examined across the country had a black, mucky or highly humic topsoil, consisting of largely decomposing organic matter. The 15-30 cm thick surface horizon overlies mineral soil layers that range from loamy sand to clayey texture, which get heavier with increasing depth. The subsoil colour is usually dark-greyish brown to grey and is strongly mottled with yellow or brown mottles. The organic topsoil is medium acid and the acidity increases with depth. Correspondingly, their base saturation is lower in Ca, Mg, and K than that of most adjoining plateau soils. The wide C-N ratios in the topsoils suggest that N might be relatively deficient.

Swamp soils are the least investigated among the wetland soils. Brammer's study on swamp soils was confined mainly to the Bangweulu swamps in Northern and Luapula provinces, and the soils studied were located on the relatively higher parts (fringes) surrounding the swamps. No information is available for soils of the lower lying areas that are permanently wet.

Among the floodplains, the Kafue Flats soils of Mazabuka and Chanyanya areas have very dark topsoils with varying muckiness. The topsoil texture ranges from silty or sandy clay loam to clay. The subsoils of most profiles are dark grey, cracking clay with hard lime nodules present at variable depth and with varying degrees of mottling. Ferrolysis has been observed, leading to the development of light coloured and very acid topsoils in some places.

Dambo soils can be divided into two broad categories:

Since Brammer in the seventies and Ferreira in the early eighties, there have been a number of studies undertaken in dambos pertaining to their characterization for agricultural development.

Central Province

Mukanda (1983), during routine soil mapping of parts of central province of Zambia, characterized the soil distribution and showed the relationship of soil mapping units to dambo morphology. Three distinct units are common in the dambos of Central Zambia. These are:

  1. dambo fringes surrounding broad-head dambos. The soils are dominantly colluvial sands occasionally with faint yellowish mottles in the subsoil;
  2. the broad-head dambo proper with colluvial dambo sands and a relatively high water table but with no stream channel, characterized by brown mottles throughout the horizon with low base status; and
  3. valley dambos and/or slopes down to rivers and streams with dambo alluvium or colluvial or river alluvium with undifferentiated hydromorphic soils. Where clayey soils are found Fe and Mn concretions will occur in the matrix.

In central Zambia, generally dambos are widest near their heads becoming narrower down stream as flow becomes strong enough to form incised courses. Dambos in this region vary from 50 m to 1 km (rarely more) in width and they dry up during the hot dry season.

Western Province

In Western Province, Brammer (1973) identified extensive hydromorphic soils and soils in colluvial and terrace deposits. Soils in the Zambezi alluvium being fine-textured or medium and coarse-textured are also widespread. Dambos on the other hand occur in varying proportions within the Barotse sands area. Linear dambos are frequent in the loamy yellow soil areas east of Kaoma and there are many large circular dambos and lagoons in the podzol areas east of Mongu. Elsewhere in the province, dambos are generally far apart.

The dambos of Western Province can be divided into three categories: (i) grey dambo soils with mottled loams to sands with dark grey to black topsoils. Such soils generally occupy dambo centres. These soils are strongly acid and where they are used, it is for grazing or, locally, for cultivation of early maize; (ii) black clays, generally known as dark-coloured cracking clays occuring extensively on the mopane covered flats in the south of the province; (iii) organic soils, or dambo peats occupying most valleys in the podzol area east of Mongu and west of Kalabo in the Nyengo plains. The soils generally comprise a metre or more of black to dark brown organic material, mainly mucky, but with interstratified layers or more peaty material. They overlie white sand and, except where artificially drained, the soils remain wet throughout the year. Where drained, the surface layer becomes firm and has subangular blocky structure. Typically, the soils are very poorly drained 20-60cm, black (N2/-) mucky loams and mucky silt loams overlying black to brownish black liquid mucks and peaty mucks. Sandy subsoil occurs generally below 120 cm. Drained soils are intensively farmed as in the case of rice, in some localities, but the majority of the soils are undrained and carry sour dambo grassland.

Eastern Province

In Eastern province, Clayton (1985) and Raussen et al (1995) carried out comprehensive dambo characterisation for agricultural development.

An ultra-detailed soil study of a dambo through a trench in Katete district by Clayton (1985) made three separate dambo segments: dambo margin, dambo flank and dambo centre. The dambo margin was characterized as deep imperfect to poorly drained loamy sand soil with open syzgium woodland. The dambo flank had characteristics similar to those of the dambo fringe, but with a poorer drainage characterized by dambo grassland and scattered trees. The dambo centre was characterized by loamy sands over sandy clay loams grading into clay soils in the subsoil, with very poor drainage. The vegetation is typically dambo grassland.

Raussen et al (1995) carried out an informal survey on dambos in plateau areas of Eastern province, concentrating on their agro-ecology and use. This study covered three districts, Petauke, Chipata and Lundazi, and purposely selected extensively used dambos. The focus was on establishing the nature and utility of dambos within each community and six dambos were characterized in total. Generally, the pattern of soil distribution in the topo-sequence in all the six dambos showed that sandy clay loam/clay loams covered the upper-dambo zones and cracking clays covered the central and lower dambo zones. Soil fertility in all cases was moderate except in Lundazi where levels of elements were generally low.

Northern and Luapula Provinces

Slordal (1978) carried out detailed soil survey of eight proposed rice schemes in Northern and Luapula Provinces. The survey areas involved three plateau dambos and two floodplain/swamp/flat zones in Luwingu, Kasama and Chinsali districts of Northern Province. In Luapula Province three dambos were covered: two in Samfya and one in Mansa districts.

Soil profile studies from the Northern Province wetlands show that the dambo zones are generally sandy with low fertility status (BSP<30, CEC m.e.:<3.0, O.C.<1.0 and pH 4.2), while the floodplain soils were generally clayey with low to moderate fertility status (BSP>15, CEC m.e. % 10, pH 4.1, Organic Carbon <2% and Available P 3-5ppm). The soil profiles unfortunately do not indicate where they occur in the plain's micro-relief. It is expected that lower levels/depressions, for example backswamps will have finer textured soils than higher levels, such as levees.

Seven out of the ten profiles studied by Slordal (1978) in Luapula were clayey, two were loamy and one was sandy. While the BSP, CEC and pH are within the same ranges as those recorded in the Northern Province profiles, the organic carbon percent and P are generally higher (averaging >5 and >7 respectively).

Mukanda et al (1995) carried out a rapid/exploratory soil characterization of some dambos in Luapula Province. This study was undertaken under a multi-disciplinary socio-economic survey on dambo utilization in the province.

The soils in all the dambos sampled were characterized by a dark colour in the top 0 - 30 cm of the soil profile. In the majority of cases the soil profile was characterized by silt loams underlain by silt clay loams or clay soils in the deeper horizons. Generally, the exchangeable bases were found to be low with CEC m.e. % in the range of 5 - 15 and pH averaging 4.5. Organic carbon of the topsoil was in the range of 0.5 to 2.0 and phosphorus ranging from 3 - 15 ppm. In a few cases Aluminium saturation percentage (>50%), Fe (>100), Cu (>4) Mn (14-56) and Zn (>3) were found to be in toxic levels. Detailed soil investigations and analytical procedures will be required in major dambos which are already in use and also those with high potential.

During this study, it was clear from the farmers' point of view that dambos mainly recharge from rainfall. It was common that most dambos quickly got flooded soon after the onset of the rains and began to dry out in some parts three months after the end of the rains. Although some dry dambos were noted, most dambos in the province are wet for most parts of the year (with a good number also being perennial).

The various data presented above were collected during various levels of survey including exploratory, reconnaissance, semi-detailed, detailed and ultra-detailed levels. The tools and techniques employed in soil data collection involved site observations, soil augering, sampling and testing, transect diagrams of dambos and gardens, and hydrological assessments.

Dambo classification

Numerous attempts have been made in Zambia to classify dambos. From these attempts, however, only four criteria can be recognized in this report and these are soils, hydrology, morphology and climate.

Soil classification

Verboom (1981) proposed the classification of dambos based upon their acidity. Three classes have been proposed: sweet, intermediate and sour dambos.

Sweet dambos are dambos formed mainly on basic parent material and recent alluvium and have a pH slightly higher than 7.0. These dambos are confined mostly to the wetter parts of the country in Northern, North-Western, parts of Western and Copperbelt provinces and coincide with basic parent materials. They are, however, also widespread in the southern half of the country. The main plant species found in sweet dambos are Acroceras macrum, Paspalum commersonii, Echinochloa pyramidalis, Setaria spp., Sporobolus spicatus and Hemarthria altissima (Verboom, 1981). A feature of such dambos is an abundance of herbaceous legumes. The herbaceous legumes associated with sweet dambos are Teramnus gillettii, Alysicarpus rugosus and Aeschynomene indicus. Acacia trees are normally found on sweet dambo margins. Only a few sedges are found in these wetlands.

Intermediate dambos have soils developed from mixed sediments with a pH between 5.5 and 6.5. The species composition of the vegetation of these wetlands is a mixture between sweet and sour dambo species.

Sour dambos are dambos developed on sandy and peaty soils derived from more acidic parent material and old alluvium. Soil pH in these dambos is below 5.5 and they are common in the northern half of the country. In the southern part of the country they occur also over the granites and basement complex rocks. The vegetation found in sour dambos is characterized by many sedges. The main grass species are Andropogon eucomus, Monocymvium cereciiforme, Elyoneurus argentens, Hyparrhenia bracteata, Aristida atroviolacea and Trachypogon spicatus. Desmodium salicifolium is the associated legume.

Raussen et al (1995), in a socio-economic survey of dambos in Eastern Province, reported that most dambo users perceive the quality of dambos in terms of soil type and its attributes of fertility, wetness and depth to the plough layer. This perception comes from the classification that dambos are depositional areas where organic matter and soil nutrients accumulate, making the soil richer than the surrounding upland.

Texture is one good parameter for use in dambo classification as it can be related directly to the suitability of specific uses, especially for rice production. A loam or sandy loam topsoil over a clayey subsoil at shallow depth is the most ideal for rice production. Such a topsoil leaves the soil workable and still firm enough to make stable ridges, mounds or bands. The heavy textured subsoil is desired for creation of a water table on top of the subsurface or upper subsoil layer. Lighter topsoils are less fertile and there is a risk of drought during prolonged periods without rain. Lighter subsoils tend to leak. Heavier topsoils require mechanized traction to work the land.

Other physical properties of the soil such as structure, variability in texture profile, the presence of gravel or stones at the surface strongly influence the type of water management especially in relation to the decrease in the loss of water through the soil profile. The presence of gravel or stones at the surface seriously limits land preparation.

Chemical properties necessary in classifying dambo soils include organic matter and peat, acidity, alkalinity, salinity, zinc deficiency, iron and manganese toxicities. For example, phosphate deficiency is related to low pH, but under flooded conditions Al-toxicity is seldom a constraint. The higher the organic matter the better the soil, but Zn deficiency is accelerated by high organic matter contents. Iron and manganese toxicity occur in poorly drained soils with low ECEC or in soils derived from soils with a high iron content. Detailed studies are needed in the chemistry of dambo soils for classification purposes.

Hydrology

The classification of dambos based on their moisture regimes is very important. The potential of a wetland for agriculture depends in the first place on hydrological factors. The supply of water, the drainage of water and the excess or shortage of water are of utmost importance.

The supply of water is among other factors determined by the geological structure of the watershed in which a particular wetland is situated. Other factors are the rainfall within the watershed area and the amount of evapotranspiration. In general, two main types of wetlands are distinguished on the basis of the hydrological conditions (Veldkamp, 1986):

The availability of water during the dry season is an important factor in dambo classification as this will determine its agricultural potential. Many dambos, especially in the Central, Southern and Western Provinces and even in the high rainfall areas, may be wet during some dry seasons, but become completely dry and without groundwater within several metres depth in other dry seasons.

The drainage of water in a dambo is also of great significance to dambo classification. Most dambos have an outlet, but a few isolated dambos or pans especially in the Kalahari sands of Western Province have no proper outlet. In the case of pan dambos, drainage is seepage through the subsoil to lower lying areas or can only escape the system by evaporation as no natural form of drainage is available.

Flooding can also be an important characteristic in classifying dambos. The details needed are on the depth, speed, rate of rise, duration and period of flooding. Where there is no flooding, the groundwater level is important, especially its fluctuating range. The more stable a groundwater level is, the easier it is to make a wetland productive. The classification can be based on the average highest and lowest groundwater levels (Veldkamp, 1986).

Special studies are required to understand interflows in dambo systems. On side slopes, groundwater appears at the soil surface as a kind of spring. This is common in Luapula, Northern and North/Western Provinces. Such interflows are considered not very important as a source of water supply, but significant in relation with iron toxicity occurrence (Veldkamp, 1985).

Daka (1993), in a hydrological study of a dambo in a semi-arid region of southern Zambia, found that in general the water table receded from cessation of the rain-season to another rain season, with the level of recession differing with respect to the dambo zone. Further, he found that the water tables in dambos remain reasonably high within 0.8 to 1 m below the soil surface at least during the driest part of the year and that a departure of 1-2 m of the water table from the soil surface safely induces a capillary rise which ensures a wetness attribute in dambos during the peak dry periods. The water table sharply responds by rising immediately following appreciable infiltration of heavy rains. However, some low land dambos remain permanently inundated and thus unsuitable for the production of most crops except rice.

This study shows that soil physical characteristics such as hydraulic conductivity and infiltration rate as well as piezometric readings can be used in the study of water dynamics in dambos and indeed in their classification.

Dambo morphology

Physiographically, wetlands have characteristics that relate to their extent and their form and are also determined by the adjacent slopes and the surrounding uplands. The extent of a wetland usually is a matter of amount of water, for example the width of a floodplain is determined by the highest floods and the stability of the sides of the floodplain.

Verboom (1969), in his morphological classification of dambos in Luapula Province, identified five types. These are:

  1. Upland dambos, found on the main plateaux;
  2. Valley dambos, being dambos occurring in major valleys;
  3. Hanging dambos, found only in Luapula province and confined to the high plateau of Kawambwa District;
  4. Flush dambos, mainly confined to relatively hilly areas;
  5. Sand dune dambos which are also only unique to Luapula province and confined to the shores of Lake Bangweulu and its associated lagoons.

In the Kalahari sands area, pan dambos are also unique to the Western Province. They are usually circular in nature.

Wet dambos are characterized by concave linear depressions and their width vary from 500 m - 5 000 m especially in Luapula Province. In most cases, the upper catchment areas of most dambos are well vegetated with trees, mainly miombo woodlands. Coupled with good rainfall, this factor has been responsible for the wetness of the dambos, especially in the high rainfall areas of Zambia. Water from surrounding catchment areas runs off slowly to the dambos due to vegetation and the rest infiltrates into the ground and recharges the water tables in the dambos through both vertical and radial subsurface flow. Some water, which flows (run-off) directly on the surface, accumulates at the central zone of the dambos. The seepage zone is usually associated with an underground drainage line which usually culminates into a stream through which a dambo may drain any excess water. Except for flush dambos, water tables occur within 0-100cm of the soil surface in the seepage and central zones.

Flush or dry dambos are very common especially in the low and medium rainfall areas of Zambia. This type of dambo is generally flat (or `shallow') and can be sub-divided into the sandy type and the heavy clay soil type. The sandy type dries out quickly as its water is lost through seepage and/or stream flow. The clayey type does not gain its water from surrounding high ground but floods because of poor drainage of the heavy soils. This type floods immediately after the first few rains but also quickly dries out after the rains because of runoff to the stream and excessive evaporation of shallow water spread on flat ground.

Climate

Solar radiation is one of the climatic factors influencing the extent of dambo utilization, especially for rice growing. Both high and low radiation at the wrong stages of specific crop physiological stages is undesirable.

Temperature is another critical climatic factor, though in most instances it is related to altitude and aspects of the dambo. Frost as an extreme condition is just as undesirable as temperatures over 35C during certain crop growth stages. The temperature of a dambo is therefore critical to classifying dambos for agricultural use.

Dambo utilization and research needs

Land use

The utilization of wetlands in Zambia is wide spread. Nature, type and location of the wetland determine the intensity and kind of use. In the last 10 to 15 years, growing human population, increased need for food production, income generation and the occurrence of drought have been major factors leading to intensified and diversified utilization of wetlands.

Wetlands in Zambia present the opportunity to support a wide range of livelihood activities. These include crop production, livestock rearing, fishing, gathering of wild products, brick making, craft and building materials and above all water for domestic use, especially in the dry season when wells in the upland become dry.

The utilization of dambos during both the dry and rain seasons adds diversity and increase the possibility of different livelihoods and combinations of livelihoods. This diversity is expressed spatially through activities taking place in different parts of the landscape, temporally (both seasonally and inter-annually) and socially with different user groups (Kokwe, 1995).

Crop production in dambos and other wetlands in most cases occupies the entire calendar year. Depending on the socio-economic set up of the ethnic group, rice and/or early maize are the major crops produced in dambos during the rain season. Other starch crops such as cassava and sweet potatoes as well as sugar cane and bananas are also found in the drier parts of dambos during the rainy season. Early maize from dambos helps to alleviate the "hunger period" in the mid rainy season (January to March). Vegetable production is, with some exceptions, restricted to the dry season. The most common vegetable crops grown are rape, cabbage, tomato, and onion. This is mainly due to the high incidence of vegetable pests and diseases as well as high water tables during the rainy season. There is a definite competition for dambo uses by cattle keeping ethnic groups and garden owners, who fence their fields and/or guard their gardens from livestock during the gardening period.

The major crop production constraints in dambos generally include weed infestations, flooding, acidity and pest and disease attacks. Weed infestation, especially in rice production, is severe where the water level is irregular and comes sometimes too late in the season. Flooding on the other hand is a big threat where flood levels can rise quickly and too early in rice fields. Acidity and other chemical toxicity cause sterility in rice production. Blast in rice production is a major threat especially where water control is bad and also where water saturation of the soil is not permanent.

Legislation, regulations and biodiversity

The land, water, flora and fauna are the property of the dead, now living, and yet-to-be-born people inhabiting that area. As the resources were plentiful in the past, access to land was freely granted both to kin and to newcomers (Mickels, 1994).

This statement is still true today in as far as traditional land is concerned. Results from a socio-economic dambo survey in Luapula in 1995 showed that anybody who wanted to work in the dambo could do so as long as they belonged to the village and provided they informed the headman. This breakdown of traditional distributive mechanisms of land will have negative impact on the dambo environment. In addition, there is absence of local level institutions that could effectively control misuse of fragile environments like dambos. Mwiinga (1993), quoted in Kokwe (1995), pointed out the absence of reference to dambos (or wetlands in general) in the various pieces of legislation on environment in Zambia. Kokwe (1995) suggested that the implementation and control over dambo use must remain with the people and their traditional authorities, while external agents (including Government) could only play facilitatory and advisory roles.

Mismanagement of dambos, such as overcultivation, discriminate digging of drains and overgrazing, will lead to permanent drying up of dambos. The destruction of a dambo will lead to the loss of the ecological niches of the dambo and also loss of the biological diversity, the very basis for crop and animal improvement. New crop varieties can only be developed if there is sufficient biological (genetic) diversity and dambos are a great soure of plant breeding germplasm.

Research needs for improved characterization and classification.

To study the importance of various characteristics of wetlands for agricultural use, Veldkamp (1986) proposed to select 10 to 15 dambo benchmark sites. Each benchmark is to consist of a typical dambo or wetland, which is representative for a large number of wetlands. By assigning a particular dambo or wetland as benchmark, research can concentrate its efforts to these sites only. The advantage is that research can continue over a long time once a wetland is designated and preserved as a benchmark site. Secondly, agro-technology transfer would be easy and faster to apply (with slight modifications.)

A number of representative sites, cutting across the three agro-ecological regions of the country and representing agriculturally potential floodplains, swamps, lake shore terraces, upland dambos of sandy and clayey nature and river bank valleys, were proposed as benchmarks. The following list may help in the selection of dambo benchmarks in Zambia.

Inventory and mapping

Routine and specialized soil mapping involve the use of more or less the same techniques, methodologies and tools. What will differ is the intensity and frequency of sampling and/or the parameters to be sampled and mapped.

Dambo characterization can be subjected to similar levels of mapping and scales like any other land facet. For research purposes ultra-detailed or detailed levels are the most appropriate. For general information needs, semi-detailed or reconnaissance levels can suffice. The choice being determined, again, by the amounts of detail required.

Methodological requirements for various levels of mapping

Detailed surveys

The major stages of survey involve:

In a dambo survey, one expects to find muck, peat, sandy and clayey soils. Suitable augers in this case are required, such as barrels, Dutch and sand augers. With well funded mapping teams, a piece of GPS equipment is necessary. In a detailed survey, suitable map scales are 1 : 20 000 and greater. In soil studies, this level is needed for irrigation planning, farm planning where the soil pattern is complex, for characterizing of research sites, etc.

Anyone with the technical know-how and equipment can carry out such a survey. In Zambia, the Department of Research and Specialist Services as well as the Soil Science Department of the University of Zambia are the responsible institutions for soil mapping. However, a number of consulting companies now undertake such activities.

Semi-detailed surveys

The recommended and suitable map scales are between 1 : 20 000 to 1 : 50 000. The uses of this type of survey include feasibility studies, regional land use planning, farm boundary decisions, farm planning for rainfed agriculture, location of potential sites for irrigation, etc. The potential sites will then be surveyed at a detailed level.

The major stages of survey involve:

Reconnaissance surveys

These surveys are useful for offering an overview of soil and land resources in a region and for the selection of potential areas for development, which will then be surveyed at a more detailed level.

The major stages of survey will normally involve:

The typical map scales range from 1 : 100 000 to 1 : 250 000 and this level of mapping is the responsibility of the government.

At ultra-detailed, detailed, semi-detailed and even reconnaissance survey level the following data will usually be collected at each auger site, depending on the required degree of expression and the scale of examination:

Sustainable development

Systematic and long duration studies of dambos in Zambia have not taken place. However, there have been bits and pieces of research work carried out here and there, occasionally interrupted by a high staff turn-over and/or lack of funds.

Kokwe (1995) reports exploratory research in dambo utilization in Luapula Province, which ran from 1984 to 1986. This work looked at various agronomic aspects of dambo utilization. It was followed by an experimental phase (1987-88) which narrowed down to specific issues which resulted in the formulation of preliminary agronomic recommendations for dambo cultivation. Unfortunately, since 1988 there hasn't been any meaningful research work in dambos in Luapula province due to a very high staff turn-over and serious lack of funds to the Adaptive Research Planning Team (ARPT).

Penninkhoff (1986) gave an overview of wetland utilization in Western Province and estimated that 10-15% of the seepage soils in the province were under cultivation while another 20-30% was thought to be made productive when appropriate land, water and crop management methods were practiced. The present agricultural activities in wetlands of the province are not backed up by any research data. Studies of a hydrological and ecological nature as well as soil chemistry and physics are essential to provide an appropriate base for development of water, crop and livestock management methods.

In the other provinces, the same picture stands, that the increased usage of dambos is not supported by any research information. Raussen et al (1995) reported that only two studies, by Makungu and Waterworth (1985) and by Mwanza (1993), specifically analyzed aspects of gardening in dambos of Eastern Province. Raussen et al (1995) further reports that socio-economic surveys of dambo use had been carried out in Lusaka Province by Chileya et al in 1988 and in Central and Copperbelt Provinces by ARPT.

In conclusion, the literature review shows that not much work in terms of characterization, classification and research has been done in Zambia. Meanwhile pressure on dambos is increasing and government policy on wetlands is still unclear.

Bibliography

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Daka, A.E. 1993. An overview of a hydrological study of a dambo in a semi-arid region of southern Zambia: In: Kokwe (Editor). Sustainable use of dambos in Southern Africa. IIED, London.

Dalal-Clayton, D.B. 1980. Investigations into the nature and distribution of sandveldt soils of the Central Province of Zambia with observations on their land use potential. Department of Agriculture, Lusaka, Zambia.

Dalal-Clayton, D.B. 1985. The construction and critical appraisal of reconnaissance soil mapping. A geomorphic and soil taxonomy-based approach in Eastern Province of Zambia. Ph.D. Thesis (unpublished). University of Sussex, U.K.

Dougnac, M. 1992. The dimensions of seasonal production in Northern Zambia. Crop Production Science 13, Uppsala, Sweden.

Ferreira, R.E.C. 1981. Ecological aspects of rice production in dambos of Luapula Province. Research Memorandum No. 29, Research Branch, Ministry of Agriculture, Zambia.

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Mukanda, N. 1985. Land evaluation for multi-purpose land development in Masansa Area, Mkushi District, Zambia. Msc. Thesis. (unpublished). University of East Anglia, Norwich, U.K.

Mukanda, N. 1983. Soil studies of Matila Farm, Mkushi District, Central Province. Department of Agriculture, Chilanga, Zambia.

Mukanda, N. 1994. Environmental Impact Assessment and Sustainable agricultural development in Zambia: A framework for understanding land degradation using the holistic approach. In: Proceedings of the fifth annual scientific conference of SADC - Land and Water Management Research Programme. Gaborone, Botswana.

Mukanda, N. and Daka, A.E. 1995. Social-economic survey of Luapula dambos: trends and constraints on soil and water management. Chilanga, Zambia.

Mulenga, C.N. and Stoop, W.A. 1991. Soil fertility constraints in fields of small farmers in Western Province. ARPT, Mongu, Zambia.

Overseas Development Administration. 1987. The use of dambos in rural development, with reference to Zimbabwe. Final report of ODA Project R 3869. Loughburough University, U.K.

Owen, R. et al (Editors) (1992). Dambo farming in Zimbabwe: water management, cropping and soil potentials for smallholder farming in the wetlands. Proceeding of a national workshop. University of Zimbabwe, Harare.

Penninkhoff, P. 1986. Farming Systems of Wetlands in Western Province. In: Proceedings of the National Workshop on Dambos. MAWD/FAO, Lusaka, Zambia.

2Raussen, T. et al (1995). Dambos in Eastern Province: report of an informal survey. Department of Agriculture, Chipata, Zambia.

Slordal, J.A. 1978. Detailed soil survey of eight proposed rice schemes in Northern and Luapula Provinces. Soil Survey Report No. 59., Department of Agriculture, Chilanga, Zambia.

Veldkamp, W.J. 1986. Suitability of wetland for agricultural development. In: Proceedings of the National Workshop on Dambos. MAWD/FAO, Lusaka, Zambia.

Verboom, W.C. 1969. Range types and estimated carrying capacity of the grassland of Zambia. File report S. 560/69 Agriculture, Lusaka, Zambia.

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