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Africa is a very large continent with extremely wide range of soils (Bationo et al., 2006). The soils range from shallow with meager life-sustaining capacities to deeply weathered profiles that recycle and support large biomass. In many parts of Africa, inappropriate land use, poor management and lack of inputs have led to soil erosion, salinization and loss of vegetation resulting in a decline of agricultural productivity (Bationo et al., 2006). In Africa and particularly Southern Africa, the most limiting factor to agricultural productivity is soil fertility (Ramaru et al., 2000). Soil fertility is defined as a condition of the soil that enables it to provide nutrients in adequate amounts and in proper balance for the growth of specified plants when other growth factors, such as light, water, temperature, and physical, chemical and biological conditions of soil, are favorable (van der Watt and van Rooyen, 1995).
Large areas of sub-Saharan African (SSA) soils, in particular, are affected by various types of degradation, including fertility decline (FAO, 2001). Soil fertility decline is a deterioration of chemical, physical and biological soil properties. The main contributing processes, besides soil erosion, are: decline in organic matter and soil biological activity; degradation of soil structure and loss of other soil physical qualities; reduction in availability of major nutrients (N, P, K) and micro-nutrients; and increase in toxicity, due to acidification or pollution (FAO, 2001). Soils in most of SSA have inherently low fertility and do not receive adequate nutrient replenishment (FAO, 2001). The SSA has the lowest mineral fertilizer consumption, about 10 kg nutrients (N, P2O5, K2O)/ha per year, compared to the world average of 90 kg, 60 kg in the Near East and 130 kg/ha per year in Asia (Stoorvogel and Smaling, 1990). Agricultural growth in sub-Saharan African countries slightly increased over the past three decades, although not in line with the high population growth rate (FAO, 2001). Food production per capita in sub-Saharan Africa (SSA) has declined since the 1970s, in contrast with the increase in Asia and South America (Figure 1.1). Soil productivity in SSA is also constrained by aridity (low rainfall) and acidity (FAO, 2001) (Table 1.1). South Africa has to face high population growth, poverty, accelerated soil degradation and increasing pressure on land (FAO, 1999b) (Table 1.1).
Depletion of soil fertility, along with the related problems of weeds, pests, and diseases, is a major biophysical cause of low per capita food production in Africa. This is the result of the breakdown of traditional practices and the low priority given by governments to the rural sector (Sanchez, 1997). The 1996 World Food Summit highlighted sub-Saharan Africa as the remaining region in the world with decreasing food production per capita (Figure 1.1). The worst levels of poverty and malnutrition in the world exist in this region (Sanchez et al., 1997). A team of scientists has identified declining soil fertility as the fundamental agronomic cause for declining food productivity in Africa. A “Soil Fertility Initiative for Africa” has been created by a group of international organizations including the World Bank, Food and Agriculture Organization (FAO), International Center for Research on Agroforestry (ICRAF), International Fertilizer Development Center (IFDC), International Fertilizer Association (IFA), and International Food Policy Research Institute (IFPRI).
Table 1.1: Characteristics of major agro-ecological zones in Africa (FAO, 1986)
Figure 1.1: Regional trends in food production per capita (FAO, Statistical Analysis Service, 2000)
As the main source of economic activity in SSA is agricultural production, declining soil productivity means not only that less food can be grown but also that production of cash crops for export is endangered (FAO, 1999a). It is therefore essential that production and soils be managed in a sustainable way, so that the present generation is fed and soil conditions are improved to support future generations.
The Republic of South Africa covers an area of 121, 9 million ha and has a total population of about 46,6 million people (NDA, 2007). Approximately 83 % of agricultural land in South Africa is used for grazing, while 17 % is cultivated for cash crops. Forestry comprises less than 2 % of the land and approximately 12 % is reserved for conservation purposes (NDA, 2007, Land Type Survey Staff, 1972-2002 & Land Type Survey Staff, 1972-2006). Land used for agriculture comprises 81% of the country’s total area, while natural areas account for about 9% (Abstract, 2005). High-potential arable land comprises only 22 % of the total arable land and only about 13 % of South Africa’s surface area can be used for crop production (NDA, 2007). Slightly more than 1,3 million ha of land is under irrigation. Rainfall is distributed unevenly across the country, with humid, subtropical conditions occurring in the east and dry, desert conditions in the west (NDA, 2007). The most important factor that limits agricultural production is the non-availability of water. Almost 50 % of South Africa’s water is used for agricultural purposes.
Areas of moderate to high arable potential occur mainly in the eastern part of the country, in Mpumalanga and Gauteng provinces (Figure 1.2). Scattered patches also occur in KwaZulu-Natal, Eastern Cape and Limpopo provinces. Low to marginal potential areas occur in the eastern half of the country and in parts of the Western Cape. Map in Figure 1 shows large areas in the drier parts of South Africa (e.g. south-western Free State; western parts of the Eastern Cape and the North West Province) that are being cultivated, but which are not classified as having any potential for arable agriculture. Repeated crop failure and subsequent abandonment of these less than marginal lands can have important consequences for soil erosion and land degradation in general (Hoffman, M.T. & A. Ashwell, 2001).
Figure 1.2: The distribution of arable potential land in South Africa (ARC – ISCW, 2002).
Soil fertility challenges coupled with shortages of rainfall could result in a compounded problem of food shortage and famine. For soil fertility to be sustained, extracted soil nutrients must equal replenished soil nutrients, but in large areas of Africa and other parts of the world, more soil nutrients are extracted than replenished (Ndala and Mabuza, 2006). There is therefore global concern of fertility management especially with the recent increases in food prices. Soil fertility and its management thus have continued to play an important role in farm productivity. Farmers, their advisors, and any growers need to be knowledgeable of the soil properties which have an influence on soil fertility, some of which include soil texture, structure, organic matter, cation exchange capacity, base saturation, bulk density and pH. These properties also have an influence in determining land capability for agriculture as they are also key indicators for soil quality.
Although significant progress has been made in research in developing methodologies and technologies for combating soil fertility depletion, the low adoption rate is a reason for the large difference between farmers’ yields and potential yields (Bationo et al., 2006). This study thus aims to determine the influence of soil physico-chemistry and clay fraction mineralogy on the fertility status of selected potential uncultivated arable soils of University of Limpopo Experimental farm (Syferkuil) in Limpopo Province. This will encourage expansion of arable agriculture in the area to improve the livelihoods in terms of alleviating food insecurity and poverty.
When assessing land for agricultural capabilities, attributes such as slope, stoniness and thickness of the soil stratum are taken into consideration. Soil physico-chemical and soil clay mineralogical properties are often overlooked. Ekosse et al. (2011) showed that these soil physico-chemical and clay mineralogical properties and their compositions play a significant role in suitability of land for arable agriculture. Information on the mineralogy and nutrient status of uncultivated soils in Limpopo Province is lacking, especially of soils found in the communal areas where smallholder agriculture is practiced. Such information is crucial for any strategy that seeks to increase and improve the productivity of cropped or potential arable agricultural land.
One important prerequisite of food security is access to land, as more people need to produce their food supplies and make a living from the land. Traditional land management systems are dependent on the availability of sufficient land to allow long fallow periods to maintain soil fertility. When there is no more access to new land, the fallow land has to be used and soil fertility falls. More intensive use of the land also implies that it becomes more prone to soil erosion. To maintain and raise its productivity, new sustainable management measures have to be introduced.
As the main source of economic activity in Limpopo Province besides mining is the agricultural production, declining soil productivity not only means less crops is grown but also that, production of cash crops and income are endangered. Vast majority of South Africans, particularly Limpopo residents, buy their staple food from commercial suppliers, rather than growing them themselves (Statistics South Africa, 2009). Rising food prices, particularly of maize and wheat which are the staple diet of the poor in South Africa, pose serious problems for the urban and rural poor as most are net buyers rather than growers of their staple food. Recent information from the Food and Agricultural Organisation (2009) and Heady & Fan (2008) suggest that food prices will increase steadily over the next decade even if there are some fluctuations and the occasional drop in prices (Evans, 2009). This therefore poses the need for more expansion of arable land for agriculture so as to improve livelihoods of the poor households.
Population pressure and urban expansion seem to be causing the loss of high potential agricultural lands. Hence food demand is rising which leads to food insecurity, thus extension of arable agricultural lands would highly be required. In a recent study, Van Averbeke and Khosa (2007) reported that while income is the most important determinant of household food security in some areas around Limpopo Province, food obtained from various types of dry-land agriculture contributed significantly to household nutrition. They argue that without farming the food security of these households would be reduced, especially for the ultra-poor.
The land is used beyond its capability, the type of usage would not be sustainable and the land degradation would result. Equally important is the fact that if land is used below its true capability then the full economic potential of the use of the land would not be realized. Although little production increase has taken place at the Experimental farm (Syferkuil farm), which has been obtained by cultivation of poor and marginal lands, the productivity of most existing lands has been ignored. With population continuing to increase in the area and the country as a whole, the need to take note of the fallow or abundant lands on the farm has become more important. Improving soil fertility could trigger rural and national economic development, achieve long-term food security and improve farmers’ standards of living, while mitigating environmental and rural migration. Thus, rectifying land degradation and enhancing productivity through appropriate soil management and conservation can play a major role in achieving farm household food security and agricultural development in the area.
This research will therefore contribute to the existing database on the physico-chemistry and mineralogy of agricultural soils of Limpopo Province, particularly those at Syferkuil farm. It will also assist farmers and individuals around the area with information and awareness on the fertility status and capability of the soils in their community, so they can initiate agricultural activities on those lands which are left fallow or abundant.
1.3. AIM OF THE STUDY
The aim of this study is to determine the soil physico-chemistry, clay mineralogy and fertility status of selected uncultivated arable soils within the University Of Limpopo Experimental Farm Of Capricorn District in Limpopo Province, with the view of identifying additional potential arable lands for agriculture in the region.
1.4. OBJECTIVES OF THE STUDY
To determine physico-chemical properties of selected uncultivated and cultivated soils on the farm and their influence on soil fertility.
To determine the clay mineralogical composition of the selected uncultivated and cultivated soils on the farm and their influence on soil fertility.
To determine the chemistry of the selected uncultivated and cultivated soils on the farm and their influence on soil fertility.
To determine the fertility index of the selected uncultivated and cultivated soils on farm and their influence on soil fertility.
To uncover and understand the role of soil physico-chemical and clay mineralogical properties influencing the fertility of the selected soils on the farm.
These questions will assist in attaining the objectives of the study:
What are the physico-chemical properties of the selected soils?
What is the clay mineralogical composition of the selected soils?
What is the chemical composition of the selected soils?
What is the fertility index of the selected soils?
Do the soil physico-chemical and clay mineralogical properties affect the fertility status of the selected soils on the farm for sustainable agriculture?
This research will be guided by the following hypotheses:
Most potential uncultivated arable lands on the farm could be used to expand and improve agricultural yields.
Soil physico-chemical and clay mineralogical properties with their influence on soil fertility are key indicators for sustainable agriculture.
1.7. RATIONALE OF THE STUDY
South Africa has a wide range of soils of different physico-chemical and clay mineralogical composition. Limpopo Province alone has a diversity of soils and climatic conditions permitting a variety of different forms of agriculture, (White Paper on Agriculture, 1995). In support of food security and self preservation, it is now strategically important for any area to have available information on the relative suitabilities of their soils for agriculture, so that preference may be given for the land more suitable for agriculture. In this process, it is important to know the relative quality of the land so that its use can be regulated in accordance with the suitability of the particular soils.
Local farmers have always relied on the agricultural research output and extension from Syferkuil experimental farm since their climate, and the soils they farm on developed from the same parent material as the ones at Syferkuil. The surrounding farm community and authorities of the area, will therefore benefit from this study by obtaining information on the physico-chemistry and clay mineralogy of their soils as well as the soils’ relative suitability for agriculture. Economically, capability classification of the soils in Mankweng area can assist in encouraging the authorities toward initiation of the various farming systems on the identified potential arable lands. In this way individual soils could be best utilized for the types of agricultural production for which they are best and most economically suited.
1.8. STUDY AREA
The location, topography, climate, vegetation, soils, geology and hydrology of the area are briefly described below in the subsequent subsections.
1.8.1. Location of the study area
Limpopo is South Africa’s northernmost province, lying within the great curve of the Limpopo River. The province borders the countries of Botswana to the west, Zimbabwe to the north and Mozambique and Swaziland to the east as shown in Figure 1.3 (DBSA, 1998). Limpopo Province is divided into five Municipal districts (Figure 1.3): Capricorn, Mopani, Sekhukhune, Vhembe and Waterberg , which are further divided into 24 local Municipalities (Limpopo Province Natural Resource Maps, 2003). The Province occupies a total surface area of 125 755 km2, about 10.3% of South Africa’s land area (Limpopo Province Natural Resource Map, 2003).The population is about 5 355 172 which is 11.3% of South African population (Statistics SA, 2003).
Syferkuil is the experimental farm of the University of Limpopo (23o49′ S; 29o41′ E) situated in the Mankweng area, in Capricorn district municipality, South Africa. The farm is 1 650 ha in size (Moshia et al., 2008). Syferkuil experimental farm, for almost 39 years now (Moshia et al., 2008) has served as the main centre of University of Limpopo’s horticultural, agronomic, and animal production researches, on which both undergraduate and graduate student researches along with hands-on trainings are conducted. The farm is bordered by five populated rural farming communities which are Mamotintane, Ga-Makanye, Ga-Thoka, Solomondale and Mankweng. On this farm, about 25 ha are currently allocated for rain fed crops, 80 ha for irrigated crops, and 40 ha are used for rotation of winter and summer crops. The 80 ha irrigated crops are served by an automated linear move irrigation system (Moshia, 2008).
Figure 1.3: Locality Map of the study area
Figure 1.4: A scale aerial photograph map (scaled 1: 10 000) of University of Limpopo (Syferkuil)’s experimental farm (Moshia et al., 2008)
1.8.2. Land-Use of the study area
Limpopo Province constitute a total of 12.3 million hectares land, out of which about 9.24 million ha. is utilized as farmland (LDA, 2002). This 9.24 million hectares of farmland nearly 0.93 million ha. of it is utilized as arable land, 6.68 million ha. as natural grazing, 1.7 million ha. For nature conservation, 0.1 million ha for forestry and for other purposes. Seventy six percent of the arable Land is allocated to dry land (0.7 million ha) cultivation and only 0.223 million ha for irrigation systems.
1.8.3. Geology of the study area
The geology of Limpopo is complex and diverse; it varies from Palaeo-Archaean mafic, ultramafic and felsic extrusives to Mesozoic sedimentary rocks and flood basalts (RSA Geological Map series, 1984). The rock formations in the Province can be considered in four main divisions based on time and general homogeneity namely: the Archaean, generally known as the ‘Basal’ or ‘Fundamental’ Complex; the Pre-Cambrian, or Algonkian Systems; the Palaeozoic, pre-Karoo Formations; the Mesozoic and the Karoo System. The topography of the region varies from relatively flat areas to mountainous terrain (Barker et al., 2006).
Limpopo is rich in minerals with economic value (White Paper on Agriculture, 1995). Predominant minerals in the eastern part of Limpopo include platinum and its group metals, chrome, copper, phosphate and andalusite. The Western side is characterised by platinum, granite, and coal minerals, while diamonds, coal, magnesite, and traces of granite dominate the Northern part of the Province. Mineral resources that are currently being mined in the province are Andalusite, Antinomy, calcite, chrome, clay, coal, copper, diamonds, emeralds, feldspar, fluorspar, gold, granite, limestone, magnesite, manganese, ornamental stone-Slate, phosphate, platinum, salt, sand & stone, silica and zinc (Dramstad et al., 1996).
1.8.4. Climate of the study area
Limpopo falls in the summer rainfall region with the western part of the Province being semi-arid, and the eastern part largely sub-tropical, (Limpopo Province Natural Resource Maps, 2003). The western and far northern parts of the Province experience frequent droughts. Winter throughout Limpopo is mild and mostly frost-free. The average annual temperatures for the southern to central plateau areas of the province is generally below 20oC; in the Lowveld and northern parts average annual temperatures are above 20oC. The province receives summer rainfall between October and March peaking in January. The mean annual precipitation ranges between 380mm in the North and just over 700mm in parts of the Waterberg (Koch, 2005).
The climate of the study site is classified as semi-arid with the annual precipitation of roughly ±495 mm per annum. The mean annual temperature of 25±1oC (max) and 10±1oC (min) was common during the years of study. Annually, the farm averages 170 frost-free days extending from late October to mid April.
Figure 1.5: Monthly average rainfall as recorded in the Limpopo Province (LDA, 2002)
Rainfall data (figure 1.5) indicating that most rainfall occurs between November and March, ranging between 80 mm and 130mm. It should, however, be noted that these figures indicate an average rainfall and lower rainfall can be expected in most districts.
1.8.5. Soils of the study area
There are wide varieties of soils that occur in the Province, tending to be sandy in the west, but with more clay content toward the east, (Limpopo Province Natural Resource Maps, 2003). The soils are differentiated based on depth, the nature of diagnostic horizons and parent materials, (FAO, 1999). Those soils are mainly developed on basalt, sandstone and biotite gneiss and are generally of low inherent soil fertility (FAO, 1999).
Limpopo Province has diverse soils, however, five major soil associations have been identified, (FAO, 1999): of which Dystrophic, red and yellow, well drained clayed soils are highly leached, clay-like, acidic soils found in the high rainfall areas of Drakensberg and Soutpansberg range. They are rocky, found on steep slopes and are of low fertility. As such, they generally have limited value as arable land but are suitable for afforestation. Red, yellow and grey soils in caternary association are sandy and loamy soils in the 300-600 mm rainfall belt in the western and northwestern part of the Province. They are suitable for arable farming, but generally occur in the low rainfall areas west and north of Thabazimbi, Vaalwater, Lephalale and Polokwane. Black and red clay soils have with varying amounts of rock and lithosol, found in a narrow strip parallel to the eastern border, the Springbok Flats (Settlers and Roedtan) and the southwestern boundary near Dwaalpooort and Derdepoort. Although highly erodible, they are utilized extensively for dryland crops such as cotton and winter cereals.
Duplex and paraduplex soils are characterized by topsoil that is distinct from sub-soil with regard to texture, structure and consistency. Major occurrences are in Sekhukhune, south to southwest of Lephalale in Waterberg district, between Louis Trichardt and Tshipise, and sections of Vhembe District near the eastern border. They are generally not utilized as arable land due to high erodibility. Poorly developed soils on rock consist of topsoil overlying rock or weathered rock. They are found to the east of the Drakensberg, including a large section of Mopani District, and east and west of Musina. They tend to be rocky, with shallow soils and therefore generally unsuitable for arable farming.
Black and red, fertile clay soils occur on the Springbok Flats, with reddish brown sandy loam to the Northern and Western part of the province, (FAO, 1999). The mountains have deeper, highly leached red soils in wetter areas, with more exposed rock where it is also drier. Reddish brown, gravelly soils, which have a low fertility, predominate on the Lowveld, the best agricultural soils being alluvial soils adjacent to the rivers. The Province has a few high potential areas for dryland crop production and many opportunities for extensive ranching and irrigated fruit and crop production, (Limpopo Province Natural Resource Maps, 2003).
1.8.6. Vegetation of the study area
The geographical location, rainfall patterns and varied physical and climatic conditions have given rise to diverse vegetation across the province. The vegetation found in the province have been classified into inland tropical forest; tropical bush and savannah; pure grassveld; and false grassveld types (Development Bank of South Africa, 1998). The inland tropical forests include the northeastern mountain sourveld and Lowveld sour Bushveld types. Tropical bush and savannah comprise the Lowveld, arid Lowveld, Springbok flats turf thornveld, other turf thornveld, arid sweet bushveld, mopani veld, mixed bushveld, sourish mixed bushveld and sour Bushveld types (Limpopo Province Natural Resource Maps, 2003). Pure grassveld types include the northeastern sandy Highveld types. The false grassveld types include the Polokwane plateau false grassveld.
1.8.7. Topography of the study area
Limpopo Province has diverse topographic features. In the east is the flat to gently undulating Lowveld plain, at an altitude of 300 to 600 m, bounded in the west by the Northern Drakensberg escarpment and Soutpansberg, with steep slopes and peaks up to the 2000m (LDA, 2002). The almost level Springbok flats in the South lie at an altitude of 900 m, while the Waterberg and Blouberg to the North, with undulating to very steep terrain, reach 2 000 m. The North- Western zone is a flat to undulating plain, which slopes down to the north and west at 800 to 1 000 m.
1.8.8. Hydrology/Water Resources of the study area
The Department of Water Affairs and Forestry (DWAF) classifies South Africa as a water-stressed country, prone to erratic and unpredictable extremes such as floods and droughts that reduce land to a dry and arid wasteland (Water Research Commission, 2002). Water resources in South Africa are limited making them critically important for the sustainable economic and social development of the country (Dennis and Nell, 2002). This is one of the reasons why it is important to protect the scarce water resources of the country. Rivers are the main source of water for the country. In the Limpopo Province, there are Four Management Areas namely: Limpopo; Luvubu & Letaba; Krokodil Wee & Merico and Olifants (NDA, 2000).
Applied research on irrigation and fertilizer methods are practiced on the research plots on the farm. There are two 10-ha plots fitted with separate irrigation systems used by researchers and students for research on field crops.
1.8.9. Agricultural activities of the study area
The agricultural sector in the province is divided into three broad sub-sectors namely commercial farms, emerging commercial farms and subsistence farms, (Development Bank of South Africa, 1998). The commercial farms fall in the larger farm size category, emerging commercial farms in the medium size and subsistence farms in the smallest size (LDA, 2002). The emerging and subsistence farms are collectively called small-scale farms which are mostly located in the former homelands. The varied climates of Limpopo Province allows it to produce a wide variety of agricultural produce ranging from tropical fruits such as banana, mangoes to cereals such as maize, wheat and vegetables such as tomatoes, onion and potatoes (NDA, 2001).
Limpopo Province has large area of land suitable for dry-land production (LDA, 2002). Maize is the staple food of majority of people in Limpopo Province and is largely grown by the different categories of farmers both for household, industrial and animal consumption. On the basis of area and volume of production, it remains the most important cereal grain produced in the Province despite the dry and drought prone agro-ecology of much of the region (LDA, 2002). Climatic variation could lead to variations in maize yields. As a staple food in the Province, maize has a large and stable market and is the most important agricultural product in South Africa (NDA, 2001).
1.9. Summary of chapter
The chapter has clearly provided the background of the study outlining the general concept of clay mineral and their influence on soil fertility for crop production. It has also outlined the aims, objectives, research questions, problem statement, rationale and hypothesis of the research project. The map of the study site illustrating the location of the site in Capricorn district municipality and the suitability map of the study site has been provided. The geology, mineralogy, climate, soils and agricultural activities of the study site have also been outlined. The soil physico-chemical and clay mineralogical properties are reviewed in the subsequent chapter.
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