Protecting Our Drylands: Land and Water Management Technologies for Semi-Arid Environments of Kenya

By Prof. Elijah K. Biamah

Kenya covers a total land area of 582,646 km2. This land area is classified in terms of agricultural potential as: 12.7% of medium to high potential for agricultural production; 11.5% of arable land, subject to periodic droughts; 70.7% of drylands; and 5.6% of non-agricultural land. High population densities are more prevalent in areas of high agricultural potential than those of low potential (drylands). Most of Kenya's population (approx. 80%) lives in rural areas and therefore depends on agriculture and livestock for food and income.
This book reviews sustainable technological options for land and water management and that are appropriate to soil and moisture conservation in drylands areas of Kenya. Of significant importance are: Environment and Resource Conservation in Semi-Arid Kenya; Dryland agriculture and conservation technologies in Kenya; Sustainable Soil Management Technologies for Effective Erosion Control in Semi-Arid Kenya; Development of Sustainable Conservation Techniques for Dryland Agriculture in Semi-arid Kenya; Agroforestry for Environmental Conservation in Dryland Environments of Kenya; Carbon Sequestration in Dryland Soils; Integrated Watershed Resource Management in Semi-arid Kenya; Runoff Water Management Systems for Dryland Agriculture in Semi-Arid Kenya; Land and Water Management for Poverty Alleviation: Experiences from Iiuni Watershed, Machakos County, Kenya; and Participatory Role of Communities in Sustainable Development and Management of Resources in semi - arid environments of Kenya 

• Language: English
• Publisher: Dolman Scott Publishing
• Release date: Feb 14, 2018
• ISBN: 9781911412595

Book preview

Kenya

Preface

Kenya covers a total land area of 582,646 km². This land area is classified in terms of agricultural potential as: 12.7% of medium to high potential for agricultural production; 11.5% of arable land, subject to periodic droughts; 70.7% of drylands; and 5.6% of non-agricultural land. The country’s population growth rate of 3.9% per annum is the highest in Sub-Saharan Africa. High population densities are more prevalent in areas of high agricultural potential than those of low potential (drylands). Most of Kenya’s population (approx. 80%) lives in rural areas and therefore depends on agriculture and livestock for food and income.

Based on the above statistics, more than four fifths of Kenya’s total land area is classified as dryland areas (otherwise referred to as ASAL areas) and has a fragile ecology that is experiencing widespread degradation due to demographic pressure. Drylands areas represent a potentially important natural resource base which requires sustainable land and water management to generate more income, employment, food and fodder requirements for the rapidly increasing human and livestock population in Kenya. The drylands (ASALs) development strategy emphasizes the need for careful and efficient utilization of the limited land and water resources through a functionally integrated and well coordinated land use and conservation approach; and that conservation technologies should conform to the prevailing environmental and socio economic conditions. The technologies must be compatible with existing traditional farming practices and are expected to provide feasible and sustainable conservation packages adapted to suit area specific conditions. The sustainability of land and water management in dryland areas would depend on some pertinent issues(e.g. demographic pressure, incentives, security of tenure, beneficiary participation, management of communal resources, selection of appropriate technologies ) relating to increased and sustainable agricultural production.

In the drylands, the intended beneficiaries (farmers and pastoralists) have been sensitized on the immediate economic returns of a production oriented land and water management strategy where moisture conservation, agroforestry, livestock and crop development interventions are integrated within existing farming/grazing systems. The interventions that have been introduced to the beneficiaries are done as per their inclinations or priorities and with their maximum contribution.

This book reviews sustainable technological options for land and water management and that are appropriate to soil and moisture conservation in drylands areas of Kenya. Of significant importance are: Environment and Resource Conservation in Semi-Arid Kenya; Dryland agriculture and conservation technologies in Kenya; Sustainable Soil Management Technologies for Effective Erosion Control in Semi-Arid Kenya; Development of Sustainable Conservation Techniques for Dryland Agriculture in Semi-arid Kenya; Agroforestry for Environmental Conservation in Dryland Environments of Kenya; Carbon Sequestration in Dryland Soils; Integrated Watershed Resource Management in Semi-arid Kenya; Runoff Water Management Systems for Dryland Agriculture in Semi-Arid Kenya; Land and Water Management for Poverty Alleviation: Experiences from Iiuni Watershed, Machakos County, Kenya; and Participatory Role of Communities in Sustainable Development and Management of Resources in semi- arid environments of Kenya

Prof. Elijah K. Biamah

Professor of Environmental and Water Systems Engineering,

School of Engineering, University of Nairobi, Kenya.

Chapter One

1.Introduction

1.1Country Background

1.1.1Resource Exploitation

The scope of expanding cultivated land in high/medium rainfall areas (about 20% of total land area), is rapidly diminishing due to population pressure and ongoing fragmentation of land. Besides land fragmentation, population pressure has led to soil exhaustion, widespread encroachment into steep (>55% slope) water catchment areas and riverbanks. The intensification of farming practices in these high/medium rainfall areas and consequent soil degradation have limited the scope for increased agricultural productivity. Thus as arable land becomes limited and scarce in these areas, the tendency now is for landless people to move, settle and eventually develop new cultivable lands in marginal rainfall areas. This movement of people into the marginal land (approximately 72% of total land area) has brought into production these arid and semi-arid lands so as to meet the food and fibre requirements of the ever increasing human and livestock population.

More of the landless people settling in the drylands have contributed significantly to the destabilization of dryland’s fragile ecology through wrong technological transfer(e.g continuous cultivation of rangelands) and overstocking (higher than recommended land carrying capacities). These bad land management practices have accelerated the processes of soil erosion/degradation through overgrazing, faster rates of soil fertility depletion (by erosion and continuous cultivation), destruction of soil structure (of sodic/saline soils), increase in pests and diseases and other forms of degradation.

1.1.2Climate and Agro-climatic Zones

The seasonal rainfall patterns in Kenya are governed by the seasonal shifts and intensity of the low pressure Inter Tropical Convergence Zone (ITCZ). The mean annual rainfall ranges from about 250 mm in the northern areas to more than 2500 mm in the highlands. The areas of Kenya that receive 1000 mm or more of rain per year are restricted to the coastal belt, the highlands east and west of the Rift Valley and isolated hills (e.g Taita Hills). Rainfall occurrence is primarily bimodal with two distinct rainy seasons, long and short rains from March to May and October to December respectively. Arid and semi arid areas receive average annual rainfall of 200 to 900 mm. The short rains account for about 65% of the total annual rainfall. Potential evaporation ranges from 1450 to 2200 mm. The rainfall though low and erratic, occurs in high intensities of short duration and is highly erosive. High amounts of runoff are often generated from these storms due to inherent low infiltration rates of the soils. Concentrated runoff flows are responsible for the severe erosion that occurs in these marginal rainfall areas.

Figure 1.1. Agro-climatic Zones of Kenya.

All climatic elements, whether singly or in combination, affect crop and livestock production. The climatic elements of greatest significance to agricultural production in Kenya are rainfall, temperature and evaporation. On the basis of a relationship between rainfall and evaporation, Kenya is divided into seven Agro-climatic Zones(ACZs) based on the r/Eo ratio, where r is average annual rainfall and Eo is average annual potential evaporation in mm(see Figure 1.1). Nearly half of Kenya consists of zone VII(very arid) and nearly 2/3 of the country consists of zones VI and VII(arid to very arid). The agriculturally potential areas (zones I,II,III and some parts of IV) make up about 20% of the total land area.

1.1.3Soil Types

Most of the soil types occurrying in Kenya are well drained and deep and these include the nitisols, acrisols, luvisols, ferralsols, andosols and phaeozems(see Figure 1.2). The other soil types are shallow to deep, well drained to poorly drained soils and these include solonetz, solonchaks, regosols, luvisols and cambisols. The most dominant soils in marginal rainfall areas are Luvisols, Acrisols and Vertisols. Except for the Vertisols, the other two soils are characterized as shallow soils with inherent low organic matter, water retention capacity, salt and sodium content and strong surface sealing and crusting properties. The dominant clays of Luvisols/Acrisols are usually of the 1:1 ratio (Kaolinite). Water infiltration in the soils is rather low especially in the B horizons where the textures are heavy. The management of these soils requires deep ploughing (to break the crust and subsoil hardpans) and addition of organic matter content from residue mulch or organic manure. Luvisols/Acrisols are often cropped during the rainy season. Vertisols are characterized as deep soils having moderate to high salt and sodium content, montmorillonitic (2:1) clay mineralogy, and low infiltration rates (due to swelling when wet). Structural tillage practices are not feasible on Vertisols due to their unstable structure (2:1 clays). Vertisols, due to their swelling and shrinking properties, affect crop root development when dry and infiltration when wet. These soils are workable immediately after the rainy season (under optimum soil moisture conditions) when the soils are loose and crumbly and hence requiring low draught per unit area. Vertisols are usually cropped after the rainy season.

Figure 1.2: Generalized Soil Types in Kenya (after Sombroek 1980, Muchena, Mbuvi and Wokabi, 1988).

Overall, tillage management requirements of these three soils would depend on clay mineralogy, workability, moisture holding capacity and other soil characteristics. Luvisols/Acrisols have a compact subsoil layer (argillic horizon) due to an increase in clay content from A to B. These soil problems (especially the sealing and crusting) are known to affect seedling emergence, decrease rain infiltration and consequently result in high surface runoff rates (with minimal soil loss unless the soils are disturbed and have a cloddy top soil structure).

1.1.4Resource Degradation

Soil erosion and degradation in Kenya is a widespread problem threatening the sustainability of agricultural productivity and causing the deterioration of both land and water resources. The severity of this problem is more pronounced in arid lands (especially on grazing lands) where high rainfall intensities of short duration, susceptibility of the soils to erosion (due to a low organic matter content) and human mismanagement of land (through overgrazing, bush clearing and charcoal burning) have accelerated and magnified soil losses by erosion and consequently reduced crop yield potential.

The onset of degradation in arid lands areas is attributed to various factors such as long and severe droughts, heavy rains and floods, locust infestations, overgrazing, deforestation and over-cultivation.

The assessment of soil erosion (due to uncontrolled grazing and overgrazing) in arid lands and subsequent classification of its severity, manifests itself in erosion features such as severe sheet erosion, scattered dendritic rills, gullies, riverbank erosion and wind erosion. Due to the exposure of poor subsoils, the degraded areas have a low capacity of regeneration of herbaceous vegetative cover. With the resultant erosion of nutrient rich topsoil, the remaining subsoil cannot support the establishment of any grass or vegetal cover. Worse still some of the shrubs like Acacia reficiens are known to inhibit any other vegetative growth underneath. The lack of ground cover coupled with the high rainfall intensities and high susceptibility of the soils to erosion, have accelerated the processes of soil detachment and sediment transportation. The transported nutrient rich soil is deposited along the floodplains.

Besides reducing the crop yield potential of the arid lands soils, soil erosion also results in high sediment yields from watersheds and could result in siltation of water retention reservoirs such as dams and lakes.

1.1.5Resource Conservation

The primary objective of resource conservation efforts in arid lands of Kenya is to conserve soil, water, forest and rage resources. These efforts while addressing themselves to soil and water conservation, fuelwood and fodder production, water resources and livestock development, and range management, require integrated land use approaches that are acceptable to the local people. Fodder production and water conservation are priorities that require immediate consideration due to the prevailing aid lands conditions and pastoral background of the people.

Current attempts to reduce soil erosion and degradation include the catchment(watershed) approach to soil conservation, gully stabilization, terracing, tree planting(for fuelwood and fodder), range reseeding and rainwater harvesting in dams and waterpans. These efforts have helped to minmize in situ detachment of soil particles and hence the loss in soil productivity. Production of grasses like Makarikari, Eragrostis superba and Cenchrus ciliaris and trees like Leucaena leucocephala and Prosopis spp have proven successful in providing fodder and fuelwood and minimizing soil erosion and degradation.

1.1.6Cropping Systems

Agricultural cropping systems in Kenya vary widely, reflecting both the range of agroclimatic zones and the variety of land ownership patterns. The major cash crops are coffee and tea. Other cash crops are pyrethrum, cotton, wheat, barley, sunflower, sugar, sisal, groundnuts and fruits. The staple food crops are maize, beans, sorghum, millet, cassava, pigeon peas, sweet potatoes, and cowpeas. Crop performance and yield are significantly influenced by the amount of rainfall and distribution throughout the rainy season and soil conditions. Where soil conditions and rainfall are limiting (e.g. drylands) there are inherent soil moisture deficits which confine the period of cropping to the rainy season. The potential length of growing season as determined by the long and short rains influences the choice of crops in these areas. Most crops are grown during the short rains since more rainfall occurs within this period. Intercropping is a very common farming practice as it minimizes the risks of crop failure due to unexpected soil moisture deficits. Usually combinations of two or three crops are evident in most of these areas.

1.1.7Land Productivity

During the past two to three decades, human and livestock population in Kenya has significantly increased and consequently led to an over exploitation of the limited land and water resources especially in drylands. In marginal rainfall areas, soil and vegetative degradation have become widespread due to overgrazing, deforestation, burning and over cultivation. Accompanying this unprecedented population increase, is the fragmentation of landholdings and sedentarization of pastoralists which has destabilized the very fragile ecology of the areas. This has adversely affected food and fodder production and left the entire population vulnerable to food and fibre shortages. Unpredictable weather conditions have exacerbated the problems and further eroded the production potential of the shrinking resource base.

Chapter Two

2.Environment and Resource Conservation in Semi-Arid Kenya

2.1Background of Semi-Arid Kenya

2.1.1Area and Agroclimatic Zones

Arid and Semi Arid Lands of Kenya occupy more than four fifths of the country’s land area, holds about one fifth of the human population and just over half of the livestock population. Drylands environment areas (otherwise referred to as ASALs) are classified according to climatic zones [based on the ratio of rainfall to potential evaporation (r/Eo)] into four agroclimatic zones (IV to VII). On this basis, agroclimatic zones in semi-arid areas have a ratio of rainfall to evaporation of less than 50%. Annual rainfall in these areas ranges from 900 mm in ACZ IV (transitional zone) to 200 mm in ACZ VII (very arid zone). Periods of drought are usually very long and often range between 7 and 8 months per year. Prolonged droughts often lead to food, forage and water shortages. The very high soil moisture deficits experienced in semi-arid areas often result in significant decreases in agricultural production.

2.1.2Rainfall

Rainfall, particularly total amount, distribution and duration significantly limit agricultural production in the drylands. The rainfall regime is generally bimodal, with two peaks in November and April separated by a very long dry period of about 7 to 8 months. For cereal crops, rainfall totals are on average very low for optimal crop yields and season to season rainfall variability is unpredictable. In many areas, 65% of the total annual rainfall occurs during the short rains period.

2.1.3Water Resources

Water is perhaps the most valuable and yet the most scarce resource of semi-arid areas. Both ground and surface water sources vary spatially and temporally. Where available, water source points have become the focal points of environmental degradation. Surface water sources can persist in natural or artificial river pans but are unpredictable, even where seasonal rivers flow from highland rains. Rivers are increasingly being regulated as more dams are constructed. The amount of water flowing in the dry season in some rivers has been reduced by dam construction and water abstraction upstream. The dams also create problems of water borne diseases and could potentially lead to disasters in earthquake prone areas.

Most rivers in drylands environment are ephemeral and are subject to high and low seasonal flows with varying sediment loads depending on the degree of degradation and deforestation in water catchment areas. Flush floods in the rivers are also increasingly being regulated as dams are constructed (e.g. along the Tana, Omo and Turkwel Rivers). This impoundment of seasonal floods besides minimizing the destructive effects of the floods on flora and fauna, have negative impacts especially in limiting flood agriculture along the floodplains(e.g. in Tana River) and also result in limited availability of water (e.g. sand/subsurface dams). Groundwater potential is very variable in both quantity and quality. Much of its use is based on shallow water sources which are affected by variation in rainfall and river flooding.

In semi-arid Kenya, surface water sources are often exploited for livestock, domestic water supplies and irrigation, whilst subsurface water is only used for livestock and domestic purposes. Other sources of water include water pans, road catchments, tank dams, subsurface and sand dams, open hand dug wells, rock catchments, and deep and shallow boreholes. Development and rehabilitation efforts have been ongoing since 1954, but maintenance has proved to be a major problem. Another problem has been the concentration of people and livestock around the watering points which has led to extensive degradation around these sites. The development and rehabilitation of water sources should be limited to areas where user participation in construction and subsequent maintenance is possible. Use of surface water for irrigation is traditional in some semi-arid areas especially along the riverine floodplains.

2.1.4Soils

The dominant soils in semi-arid Kenya are luvisols, lixisols and ferralsols and vertisols (FAO/UNESCO Classification, 1974 and 1990) and have sandy loam, sandy clay loam, loamy sand and clay textures. They are brown to reddish, well drained and friable except for the vertisols. These soils are characterized as of low inherent fertility (due to a low organic matter content and CEC), they form subsurface hardpans (due to movement of clay from A to B horizons), moderate to low waterholding capacity, strong surface sealing and crusting properties, high silt and sodium content (especially in subsoils) and are highly susceptible to erosion.

The luvisols and lixisols are characterized by poor structural stability of the surface soils which have surface sealing and crusting properties and often result in low infiltration and high susceptability to erosion. The hardpans associated with subsoils lead to low porosity and water holding capacity. The ferralsols are light textured, strongly leached soils which are permeable and relatively resistant to erosion. They also occur as integrates with luvisols and arenosols and therefore tend to surface seal and become susceptible to erosion. The vertisols have a low profile permeability when saturated. However, they are fertile, have a high water holding capacity and require special tillage practices to drain and improve productivity.

Exceptions to the compaction and capping properties of drylands soils, are limited areas of soils of volcanic origin, alluvial and colluvial soils (which occur in floodplains and depressions) and heavy clays. Clays are avoided because they are hard to plough using traditional tillage practices (conventional Ox/donkey ploughing). Another constraint to the utilization of heavy soils is the salinity/sodicity of the soils. Phosphate is the main limiting mineral and phosphate fixation is associated with the ferralsols. Most of these deficiencies have in the past been overcome through the traditional shifting cultivation. However, this farming practice is increasingly becoming inneffective as the length of bush fallow decreases and tree cover is reduced by overgrazing. Farmyard manure application is becoming popular particularly in the less arid zones.

2.1.5Land Use

Semi-Arid Kenya could be divided into two main land use categories: ACZs IV and V where there is a potential for agricultural development, farmers are settled, and land is generally being demarcated, and ACZs VI and VII where the major activity is livestock production associated with range development and pastoralism; farming is possible only in depressions (e.g riverine floodplains).

In the past, semi arid areas were exclusively reserved for extensive grazing through the traditional group ranching or other grazing management techniques. An influx of people migrating from densely populated high and medium rainfall areas coupled with the rapid drylands population increase have significantly contributed to the current change in lifestyles of drylands people from nomadic pastoralism to sedentary agro-pastoralism. The extent of cropped land is increasing particularly in zones IV and V because of the increase in population.

With increasing population pressure and subsequent fragmentation of land and soil degradation, the scope of expanding cultivated land in dryland zones is decreasing. Alongside the increasing human population is an increasing livestock pressure on the fragile dryland environment and ecology. The carrying capacity of the land ranges from 3 ha per livestock unit (LU) of 300 kilogrammes in ACZ IV to about 7 ha per LU in ACZ VII. Dry season grazing areas are either overgrazed or kept under crop production. The wet season grazing areas can no longer provide sufficient forage for livestock. This trend of rapid environmental degradation destabilizes the fragile drylands ecology leaving it highly vulnerable to desertification.

2.1.6Resource Base

Dryland areas are characterized by a declining ability to ensure basic subsistence to an increasing population through pastoralism at existing levels of technology. In fact herd numbers have increased with population increase to the point where the rangeland’s carrying