Paul L. G. Vlek

• Doctor of Philosophy
• University of Bonn

The organic matter status of soil is vital to maintenance of the productive capacity of land and has a modifying influence on the atmosphere, espeeiallv with respect to green house gases. Studies in the US, Canada and elsewhere have shown that as much as 40 to 60% of organic matter in many soils have been lost as a result of converting the land fro...

Climate change is projected to have a serious impact on all sectors of the world. The agriculture sector is one of the most vulnerable sectors with implications for smallholder farmers in semi-arid regions of Africa in terms of poverty and food security. Several researches have been carried out on perception and adaptation with a little investigati...

Regional climate change assessments show a likely temperature increase that is higher than the global average for all seasons in Africa, which would have extreme negative implications for ecosystem health and productivity. Most extreme climate change effects in West Africa are predicted to occur in desert and grassland areas. It is important for sm...

Syahrinudin, Denich M, Becker M, Hartati W, Vleg PLG. 2020. Biomass and carbon distribution on Imperata cylindrica grasslands. Biodiversitas 21: 74-79. Invasive plants can alter the diversity and composition of ecological communities leading to ecosystem change both function and biodiversity issues. Imperata cylindrica is an invasive grass thrives...

Land degradation is one of the threats to human and natural systems. Fortunately, over the past few decades awareness of this challenge has grown, and 122 countries have committed to setting land degradation neutrality (LDN) targets, of which 84 have officially validated their targets, and 51 have put their targets into legislation. In this concept...

Presents the benefits of utilizing long-term satellite data to analyze the potentials of targeted land management and restoration measures for improving land productivity in SSA.

Surface observations provide ground evidence of climate change to support the scientific guidance paving the way to better adaptation and mitigation actions. The West African Science Service Centre on Climate Change and Adapted Land Use (WASCAL) has designed a multi-stakeholder initiative to rescue the deteriorated near-surface weather, climate and...

Tackling land degradation and restoring degraded landscapes require information on areas of priority intervention, since it is not economically and technically possible to manage all areas affected. Recent developments in data availability and improved computational power have enhanced our understanding of the major regional drivers of land degrada...

Climate change and variability challenge crop productivity and resource use efficiency in West Africa. Despite abundant research on climate change impact on crop yields and food security, little is known about climate change effects on the resource use efficiencies of the main staple crops in the dry savanna agro-ecological zone of northern Benin,...

Poor soil fertility is a major challenge in food production in Ghana especially in the upper east region. Fertilizer which is known to increase soil fertility is not widely adopted especially by female headed households. This research is aimed at investigating the influence of gender on inorganic fertilizer adoption in the Upper East Region of Ghan...

Low soil fertility and limited ability of farmers to purchase fertilizers in the Sudan savannah zone of Ghana has resulted in the decline in the yield of cereals over the years. There is, therefore, the need to identify soil parameters that are critical to crop production, to manage them effectively and improve fertilizer use efficiency to increase...

Jatropha curcas has been introduced as a low-cost energy crop in Burkina Faso for the production of straight vegetable oil (SVO) and biodiesel. It is cultivated in different plantation systems including smallholder inter-plantings with annual crops, large-scale monoculture, afforestation on marginal land, in traditional hedge systems along contour...

Land provides a host of ecosystem services, of which the provisioning services are often considered paramount. As the demand for agricultural products multiplies, other ecosystem services are being degraded or lost entirely. Finding a sustainable trade-off between food production and one or more of other ecosystem services, given the variety of sta...

This study assesses the economic value of supplemental irrigation as a rainfall variability adaptation strategy in a small catchment in south-western Burkina Faso. The bio-economic model built for the catchment maximises net cash income by optimally allocating land, labour, water and capital. Yields vary according to soil type, agricultural practic...

Soil degradation is a serious environmental problem in Ethiopia. However, little information is documented on indicators such as variations in soil properties across different landforms in a catchment. This study was aimed to assess soil properties and their changes across sites with different erosion statuses, and identify landscape positions that...

The cultivation of the biofuel crop Jatropha curcas L. in Burkina Faso may contribute to ameliorating the soil fertility of severely declining cropland through increased organic matter input and erosion control. This study addresses the potential for the soil organic carbon (SOC) sequestration in traditional and newly introduced J . curcas producti...

Nitrogen fertilizer recovery by lowland rice can be as low as 10% and rarely exceeds 60%. Azolla contributes to the nitrogen (N) nutrition of rice plant through biological N fixation (BNF). This study aimed at assessing the influence of Azolla pinatta on floodwater chemistry, rice yield, total dry matter and N uptake of rice. The study was carried...

Reservoir siltation is one of the most important off-site effects of soil erosion. In Burkina Faso a large number of small dams have been built to store rainfall and runoff water in the rainy season, which is much needed for domestic use, irrigation and stock watering in the dry season. This study quantifies the siltation rates of two small reservo...

Apart from the earmarked Ramsar sites along the coastal zones of Ghana, no inventory has been conducted to determine the location, distribution, and status of wetlands within any of its river basins. In this study, a logistic regression model was used within the GIS platform to predict, at pixel level, the presence of a wetland in the basin of the...

Mismanagement of irrigation water and the ensuing secondary salinization are threatening the sustainability of irrigated agriculture especially in many dryland regions. The permanent raised-bed/furrow system, a water-wise conservation agriculture-based practice, is gaining importance for row- and high-volume-crops in irrigated agriculture. However,...

http://www.v-r.de/_files_media/mediathek/downloads/893/inhalt_978-3-8471-0297-7.pdf Central Asia underwent an agricultural transformation in the 20th century that was neither efficient nor sustainable. There is a need for innovations that will remedy these deficits by reversing environmental degradation and ensuring poverty alleviation. This book...

In the irrigated cropping areas in Central Asia, tree hedgerow systems were established during the Soviet era for protecting the bordering croplands from wind erosion and for improving their microclimate, thus increasing yields. Due to a lack of a suitable, cost-effective methodology in the current transition period of the Central Asian countries (...

Environmental damage in the irrigated areas of Central Asia calls for the adoption of land-use alternatives. The findings from a field experiment conducted on highly salinized cropland in the Amu Darya lowlands between 2006 and 2008 illustrate numerous benefits of afforesting marginal cropland. In particular, nitrogen (N2)-fixing species such as ac...

Rubber agroforests in the mostly deforested lowlands of Sumatra, Indonesia are threatened by conversion into monoculture rubber or oil palm plantations. We applied an agent-based model to explore the potential effectiveness of a payment for ecosystem services (PES) design through a biodiversity rich rubber eco-certification scheme. We integrated co...

Identification and social-ecological characterization of areas that experience high levels of persistent productivity decline are essential for planning appropriate management measures. Although land degradation is mainly induced by human actions, the phenomenon is concurrently influenced by global climate changes that need to be taken into account...

In the subsistence-based, nutrient-poor soils, and fertilizer-limited agriculture of northern Ghana, 45-65 % of land cover is annually burned for purposes of hunting and agricultural land preparation. The effects of burn-season, fractional nutrient losses, combusted plant parts and vegetation type on the fire-mediated nutrient cycling are unclear....

Even though scientific information on spatial distribution of hydrophysical parameters is critical for understanding erosion processes and designing suitable technologies, little is known in Geographical Information System (GIS) application in developing spatial hydrophysical data inputs and their application in Morgan-Morgan-Finney (MMF) erosion m...

Soil degradation is a threat to sustainable development in Ethiopia. However, degradation indicators, such as sediment enrichment ratio (SER), are not adequately documented in literature. This study aims to investigate the SER of different erosion-status sites (aggrading, stable, eroded) in various landforms in Mai-Negus catchment, northern Ethiopi...

Soil quality (SQ) assessment from farmers' point of view can be used as a primary indicator for planning sustainable agriculture. Despite this fact, limited information is documented with regard to SQ indicators, for example weed species, crop types and management practices from farmers' knowledge perspectives. The aims of this study are to analyse...

Land and water degradation due to on-site soil/nutrient loss and off-site pollution/ sedimentation are serious environmental problems. Landscape planning and management tools are essential to implement best management practices targeted at locations where they are needed most. Although many soil/water-landscape studies have been published in the la...

An agent-based modelling approach (LB-LUDAS model) was applied to simulate and visualize the temporal and spatial scale effects of the Payments for Ecosystem Services (PES) scheme on the trade-offs between goods and services in the rubber agroforest landscapes in Jambi Province, (Sumatra) Indonesia. The PES scheme under investigation is a form of e...

Management practices may influence yield and nitrogen (N) use efficiency of irrigated cotton (Gossypium hirsutum L.) in irrigated arid lands such as those of the Aral Sea basin. A field experiment was conducted to compare the effects of conservation tillage (permanent raised beds; PB) with conventional plow tillage (CT) under three different N appl...

Rice is the second major food crop in central Asia. Climate change may greatly affect the rice production in the region. This study quantifies the effects of projected increases in temperature and atmospheric CO2 concentration on the phenological development and grain yield of rice using the "ORYZA2000" simulation model. The model was parameterized...

Intensive soil tillage and mismanagement of irrigation water and fertilizers are increasing production costs, reducing soil fertility and crop water productivity and threatening the sustainability of crop production systems in the irrigated arid lands of Uzbekistan, Central Asia. Conservation agriculture (CA) practices combined with optimum nitroge...

Increasing water shortage and low water productivity in the irrigated drylands of Central Asia are compelling farmers to develop and adopt resource conservation technologies. Nitrogen (N) is the key nutrient for crop production in rice–wheat cropping systems in this region. Nitrogen dynamics of dry seeded rice-(aerobic, anaerobic) planted in rotati...

Producing 70% more food for an additional 2.3 billion people by 2050 is one of the main challenges world agriculture will face in the coming decades (FAO 2009). Considering the escalating scarcity of natural resources, increasing water and nutrient use efficiency in crop plants is a key component of the strategy to sustainably enhance agricultural...

Like many irrigation schemes in Central Asia, the one in Khorezm faces a two-fold challenge: on the one side, the severe problems inherited from the past need to be remedied and on the other side, the rising supply-demand gap driven by sharpening competition for water and climate change must be dealt with. Located in the lower part of the Amu Darya...

Understanding the patterns of land degradation indicators can help to identify areas under threat as basis for designing and implementing site-specific management options. This study sort to identify and assess the patterns of land degradation indicators in selected districts of western Kenya. The study employed the use of Land Degradation Sampling...

Inappropriate agricultural practices and conversion of marginal land to cultivation and grazing have led to severe land degradation in the Ethiopian highlands. Consequently, the government has invested substantial resources in soil and water conservation (SWC). One of such interventions was exclosure, which was aimed restoring biodiversity, biomass...

Like many irrigation schemes in Central Asia, the one in Khorezm faces a twofold challenge: on the one side, the severe problems inherited from the past need to be remedied and on the other side, the rising supply–demand gap driven by sharpening competition for water and climate change must be dealt with. Located in the lower part of the Amu Darya...

Recognizing the socio-economic and biophysical causes of land degradation at the national level is important for cause-targeted strategies when designingin the designing of policies for combating land degradation. This study aims to identify the biophysical and socio-economic factors that exert significantly effects onaffect land degradation across...

Even though soil degradation challenges sustainable development, the use of degradation indicators such as nutrient export (NE) and nutrient replacement cost is not well documented at landform level. This study is aimed to investigate the extent of soil degradation, NE rates, and their replacement cost across landforms in the Mai-Negus catchment, n...

Spatial variations for selected soil chemical and physical properties were examined for a landscape at Navrongo, Ghana. This was done in order to identify their spatial distribution to assist in designing land management that seeks to reduce the extremes of land productivity and support more uniform agricultural production. A landscape of 1.5 km 2...

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In this study we use agent-based simulations to explore the impact of social-mix policies on the segregation dynamics of São José dos Campos, a medium-sized Brazilian city. We use the model MASUS, Multi-Agent Simulator for Urban Segregation, to test two policy strategies: one based on the spatial dispersal of poverty, and the other on the spatial d...

Under low input subsistence farming systems, increased pressure on land use and decreased fallow periods have led to a decline in soil productivity. The soils in sub-humid region of Ghana are generally poor and require mineral fertilizer to increase crop productivity. This paper presents the use of Agricultural Production Systems sIMulator (APSIM)...

Soil-erosion-induced land degradation is a great challenge in the Ethiopian highlands. Consequently, the government has invested in soil and water conservation measures to tackle the problem where farmland terracing is one of the commonly implemented measures in the country. The purpose of this study was to analyze the role of farmland terracing in...

Afforestation of degraded croplands by planting N2-fixing trees in arid regions is highly recognized. However, fixation of atmospheric nitrogen gas (N2) by woody perennials is often limited on phosphorus (P) poor soils, while any factor limiting N nutrition inhibits tree growth. In a two-factorial field experiment, the effect of three P amendments...

Leaf chlorophyll meters can be used to support easy and efficient crop nitrogen (N) management. They can be used on tree species native to Central Asia that have been suggested for afforesting salt-affected croplands, but its use demands a priori calibration as the relationship between chlorophyll meter measurements and leaf N contents is crop/spec...

Soil degradation is a serious problem in the central and northern Highlands of Ethiopia. It has been so for several decades as a result of over exploitation and mismanagement. Relocation of a portion of the population from these regions to the relatively less populated Southwestern Highlands has taken place for decades to try to address the problem...

This section summarizes the findings of a multidisciplinary, long-term research program that assessed the potential of plantation forestry to rehabilitate a degraded, irrigated-agriculture ecosystem. Bio-physical and socio-economic studies conducted during 2002–2009 in Khorezm assessed the suitability of afforestation with multipurpose species as a...

In the irrigated areas of Uzbekistan the nitrogen (N) fertilizer efficiency in crop production is low, as N is partially leached to the groundwater. The N-fertilizer use is still based on recommendations from Soviet times when fertilizer supply was subsidized to maximize production at all costs. Also irrigation water is applied sub-optimally, and g...

Climate change is projected to have serious environmental, economic, and social impacts on Ghana, particularly on rural farmers whose livelihoods depend largely on rainfall. The extent of these impacts depends largely on awareness and the level of adaptation in response to climate change. This study examines the perception of farmers in Sekyedumase...

This study aims to identify and classify the geographic hotspots of human-induced land degradation in Vietnam. We used the long-term (1982–2006) trend of inter-annual NDVI, derived from AVHRR/NOAA imageries, as a proxy for the decline or improvement in biomass productivity on a national scale. By analyzing the temporal correlation between rainfall...

A multi-agent simulation modelling approach (LB-LUDAS model) was applied to simulate and visualize the temporal and spatial scale effects of the Payments for Ecosystem services (PES) scheme on the tradeoffs between goods and services. The PES scheme under investigation is a form of eco-certification of biodiversity-friendly rubber agroforests, with...

Stable soil aggregates and high microbial diversity are essential for efficient nutrient recycling in soil. This study evaluated effects of different arable land-use systems on soil aggregation and associated composition and total diversity of bacteria and fungi. For this purpose, 5- and 3-year-old field trials were selected, two in sub-humid (orth...

This study has assessed the seasonal occurrence of annual vegetation fires and defined inter-seasonally burned area for the different vegetation cover types across Ghana and the northern region of Ghana using 10-year (2001–2010) remote sensing data. These values were used with fire induced elemental losses to estimate greenhouse gas emissions and n...

This paper describes three fundamental pitfalls or caveats of empirical modeling of land-use decision making in agent-based models for land-use/cover change. A case study in the villages of Jambi Province (Sumatra), Indonesia, is presented to demonstrate the construction of empirical decision-making models using utility functions while taking into...

Separating human-induced land degradation from that caused by natural processes in the world of global cli-mate and atmospheric change is a challenging task, but important for developing mitigation strategies. Cur-rent remote-sensing data and spatio-temporal analyses allow the distinction of climate and human-induced land degradation on a sub-conti...

Soil degradation by erosion is the most serious threat to food security in Ethiopia. Thus, effective management strategies (scenarios) that reduce soil degradation are crucial. However, the application of models such as Soil and Water Assessment Tool (SWAT) that simulate the impact of different scenarios on soil degradation by erosion in Ethiopia c...

Modelling soil erosion requires a holistic understanding of the sediment dynamics in a complex environment. As most erosion models are scale-dependent and their parameterization is spatially limited, their application often requires special care, particularly in data-scarce environments. This study presents a hierarchical approach to overcome the l...

Crop simulation models afford the opportunity to study and understand underlying processes that impact on crop yield, hence, helps in designing appropriate strategies to improve crop production. The response of maize to N fertilization in a sub-humid environment was evaluated using DSSAT (crop simulation model). Two field experiments were conducted...

Through a forest inventory in parts of the Amudarya river delta, Central Asia, we assessed the impact of ongoing forest degradation on the emissions of greenhouse gases (GHG) from soils. Interpretation of aerial photographs from 2001, combined with data on forest inventory in 1990 and field survey in 2003 provided comprehensive information about th...

Khorezm, a district of Uzbekistan, is a textbook example of irrigated agriculture in the Aral Sea Basin causing the Aral Sea Syndrome. It offers an opportunity to study the complex human-environment relations in the context of strong government control in transformation economies. Agricultural production and rural livelihood in Khorezm rely entirel...

This book summarizes results from a long-term research project addressing land and water use in irrigated areas of the Aral Sea basin. In an interdisciplinary approach, natural and human sciences are combined to elucidate challenges of economic transition that affect the use of land, water and biological resources, ecological sustainability, econom...

This study evaluates the potential impact of climate change on sorghum (Sorghum bicolor (L.) Moench) grain yield under different crop residue and nutrient management systems in a smallholder farming system. The Agricultural Production Systems Simulator (APSIM) was used in this scenario analysis. Two crop residue management types (crop residue reten...

O objetivo do presente trabalho foi avaliar a sobrevivência de árvores leguminosas plantadas para recuperar áreas degradadas e as produtividades de milho e mandioca num sistema tradicional de agricultura de derruba-e-queima. Foram utilizados os espaçamentos 1 m x 1 m, 2 m x 1 m e 2 m x 2 m para plantio de Acacia angustissima, Clitoria racemosa, Ing...

Crop cover and crop rotation mapping is an important and still evolving field in remote sensing science for which robust and highly automated processing chains are required. This study presents an improved mapping procedure for crop rotations of irrigated areas in Central Asia by using classification and regression trees (CARTs) applied to transfor...

This study was aimed at quantifying soybean (Glycine max) nitrogen fixation under reduced tillage (RT) and conventional tillage (CT) in a tropical Ferralsol of the sub-humid zone of western Kenya, using the isotope ¹⁵N dilution method. Crop residue (CR) management was a superimposed treatment in soybean-maize rotation and intercropping systems. Thi...

Scientific information on the spatial variability and distribution of soil properties is critical for understanding ecosystem processes and designing sustainable soil–crop and environmental management decisions. However, little is known on spatial distribution and variability of soil properties at catchment-scale in many tropical developing regions...

p>O objetivo do presente trabalho foi avaliar a sobrevivência de árvores leguminosas plantadas para recuperar áreas degradadas e as produtividades de milho e mandioca num sistema tradicional de agricultura de derruba-e-queima. Foram utilizados os espaçamentos 1 m x 1 m, 2 m x 1 m e 2 m x 2 m para plantio de Acacia angustissima, Clitoria racemosa, I...

There is a growing interest in the understanding of the dynamics of sap flow and the transpiration process in plants. In this study, Xylem sap flux was monitored in a 4-year-old cashew (Anacardium occidentale) orchard for eight months (2–4 weeks per month), covering both wet and dry seasons of 2002 at Ejura in Ghana. Sap flux (Fd) was related diurn...

While Jambi Province is pioneering reduce emission from deforestation and degradation (REDD) program through Hutan desa (or village forest), eco-certification of jungle rubber is currently negotiated to couple with REDD for saving the remaining rich biodiversity in the area. The conservation agreements (CAs) with smallholder-rubber farmers in the v...