Ludger Herrmann

Identification and Quantification of Dust Additions in Perisaharan Soils

The Saharan desert is a vast source of soil derived dust, which is transported into the surrounding regions. In the areas of deposition the dust influences the sediment, element and nutrient balances of marine and terrestrial ecosystems. This paper deals with the identification and quantification of dust additions in soils and the influence on the development and properties of soils. Three case studies are presented. The research sites are situated in SW-Niger, Lanzarote (Canary Islands, Spain) and S-Portugal. They differ concerning climate, parent material and knowledge about the local dust characteristics. Therefore different approaches have been used in order to quantify the dust additions in soils. The approaches comprise physical, mineralogical, geochemical and morphological investigations. The determined amounts represent between 4 and 66% of the recent soil material. The accretion depends mainly on the distance from the sources, climate and stability of the land surface (age of the soils). In some soils local and far transported material as well as fluvial additions are found. The impact on soil development depends on the amount and characteristics of the deposited dust in comparison to the autochthonous soil material and the stage of soil development. In general the effects decrease with distance from the dust source areas.

Testing a new method for sequential silicon extraction on soils of a temperate–humid climate

The importance of silicon (Si) compounds in agriculture and geochemical cycles has received increasing attention over the last decade; however, quantitative data on non-crystalline pedogenic Si phases in soils are still rare. Recently, the authors developed a method for sequential Si extraction from soils, in order to improve the quantification of different Si compounds in soils. The method has been tested on samples of known composition. Here, the method is applied for the first time to complete soil profiles. Six different soil types from south-west Germany that have developed since the end of the last glacial period were selected. Most of the Si in these soils was bound in primary and secondary silicates. In mineral soil horizons, the second-highest proportion of Si was in precipitates of amorphous silica (minerogenic amorphous silica), whereas in some O horizons, the second-most important Si fraction was in biogenic amorphous silica. Topsoil horizons and clayey subsoil horizons of a Luvisol and a Stagnosol especially accumulate amorphous silica. Silicon from bio-opal contributed up to 14% to the total Si in Oa horizons of the studied soils. The smallest amounts of Si were found in the mobile and adsorbed Si fractions. Some methodological limitations are identified and discussed; however, the new sequential method of Si extraction enabled separation of different Si fractions in typical soils of a temperate–humid climate.

Overcoming Phosphorus Deficiency in West African Pearl Millet and Sorghum Production Systems: Promising Options for Crop Improvement.

West Africa (WA) is among the most food insecure regions. Rapid human population growth and stagnating crop yields greatly contribute to this fact. Poor soil fertility, especially low plant available phosphorus (P) is constraining food production in the region. P-fertilizer use in WA is among the lowest in the world due to inaccessibility and high prices, often unaffordable to resource-poor subsistence farmers. This article provides an overview of soil P-deficiency in WA and opportunities to overcome it by exploiting sorghum and pearl millet genetic diversity. The topic is examined from the perspectives of plant breeding, soil science, plant physiology, plant nutrition, and agronomy, thereby referring to recent results obtained in a joint interdisciplinary research project, and reported literature. Specific objectives are to summarize: (1) The global problem of P scarcity and how it will affect WA farmers; (2) Soil P dynamics in WA soils; (3) Plant responses to P deficiency; (4) Opportunities to breed for improved crop adaptation to P-limited conditions; (5) Challenges and trade-offs for improving sorghum and pearl millet adaptation to low-P conditions in WA; and (6) Systems approaches to address soil P-deficiency in WA. Sorghum and pearl millet in WA exhibit highly significant genetic variation for P-uptake efficiency, P-utilization efficiency, and grain yield under P-limited conditions indicating the possibility of breeding P-efficient varieties. Direct selection under P-limited conditions was more efficient than indirect selection under high-P conditions. Combining P-uptake and P-utilization efficiency is recommendable for WA to avoid further soil mining. Genomic regions responsible for P-uptake, P-utilization efficiency, and grain yield under low-P have been identified in WA sorghum and pearl millet, and marker-assisted selection could be possible once these genomic regions are validated. Developing P-efficient genotypes may not, however, be a sustainable solution in itself in the long-term without replenishing the P removed from the system in harvested produce. We therefore propose the use of integrated soil fertility management and systems-oriented management such as enhanced crop-tree-livestock integration in combination with P-use-efficiency-improved varieties. Recycling P from animal bones, human excreta and urine are also possible approaches toward a partially closed and efficient P cycle in WA.

Optimising the extraction of amorphous silica by NaOH from soils of temperate-humid climate

This study focuses on optimising amorphous silica extraction from soils by using NaOH. Based on the results of this test series, a method for quantifying amorphous silica in soils from temperate-humid climate is proposed. All tests were carried out on materials of known composition (well-defined samples of feldspar, clay minerals, bio-opal, silica gel, and mixtures of these components) and on soil samples, to determine the optimum set of conditions, in terms of solid : solution ratio, temperature and extraction time, for dissolving amorphous silica without considerably attacking other solid silicon compounds. A solution of 0.2 m NaOH almost completely extracted amorphous silica, and when applied at room temperature and a solid : solution ratio of 1 : 400, only slightly broke down crystalline Si compounds. The predictable and reproducible underestimation was considered more acceptable than the variable partial dissolution of silicates that occurs during extraction at higher temperatures. We therefore recommend using this method on soils from temperate-humid climate to estimate the amorphous Si fraction.

Beyond the Horizons: Challenges and Prospects for Soil Science and Soil Care in Southeast Asia

The information available in relation to soils in Southeast Asia’s (SEA) mountainous regions is still limited, and so our research tried to rectify this situation in two key ways. The first approach was to gather soil information in order to help develop a soil database for parts of mountainous SEA. This approach also included two further issues important to soil knowledge in SEA, as reported in this study: Savanna regions with underlying limestone are unique to SEA, resulting in specific soil landscapes with soils of various degrees of weathering. Non-sustainable agriculture affects soil fertility in the uplands of SEA, in particular the frequent problem of soil erosion at hill slopes adversely affects both soil physical and chemical properties. The second approach was to develop and progress methods so as to improve soil research and soil analysis. These approaches included (1) gamma ray spectrometry to retrieve airborne and ground-based data on natural radioactive isotopes of potassium, thorium and uranium in soils, as proxies for rock and soil formation, (2) an inter-comparison of state of the art soil mapping approaches in an development oriented context, and (3) the evaluation of ethnic soil knowledge systems, those considered useful in the identification of local soil distribution patterns, though not suitable for transfer to a larger scale.

Variability of Soil Resources in Northern Thailand

There is still much of great value to discover about soil variability in the highlands of northern Thailand. Part of this chapter tries to review the state of knowledge of the highland soils and part presents results which have been produced within subproject B1 of SFB 564. This project follows a long-term strategy in which the variability of soil and water balance is researched beginning at a field scale and ending at a regional level. The same approach is also followed here.

ScalA-FS: expert-based ex-ante assessments of local requirements and success potential of upgrading strategies for improving food security in rural Tanzania

Enhancing food security is the main goal of subsistence farmers, who are vulnerable to food insecurity in sub-Saharan Africa. Participatory research across food value chains (FVC) can help stabilize and enhance food security by developing upgrading strategies (UPS). However, prior to successful widespread adoption and geographical upscaling, such practices need in-depth understanding of their suitability in target areas and their particular local requirements. Ex-ante assessments of selected UPS were carried out by German and Tanzanian agricultural scientists using the “ScalA-FS” tool. The participating experts included those responsible for implementation. The tool aims to systematically evaluate, at the community level, UPS that have been successfully implemented elsewhere, evaluate their potential for dissemination, and identify entry points for adjustments during implementation. Assessment indicators were developed through a participatory process. UPS relate to a) natural resource management and crop production; b) food processing and bioenergy; c) income generation and market participation; and d) food consumption. Here we present the ScalA-FS assessment results on UPS suitability as well as on its implementation requirements. We focused on the local context needed to enable a productive collaboration between smallholder farmers and implementing research and/or development organizations. Implementation requirements for the selected UPS were assessed as generally low to medium, and projected suitability in most cases was high. Local knowledge and education (human capital) along with visible success after a short time were important criteria of success of UPS. Here, careful consideration of the challenges before and after implementation of UPS is suggested. ScalA-FS should be applied early in the implementation process of UPS in order to support adaptations and successful upscaling at other locations.

Fusion of indigenous knowledge and gamma spectrometry for soil mapping to support knowledge-based extension in Tanzania

Food shortages often threaten central Tanzania. Sustainable action adapted to local environmental conditions is desperately needed. In the framework of the TransSEC project, two food value chains in the Dodoma region of Tanzania were inspected in order to make propositions for improvement , spanning from soil preparation to product consumption. Therefore, soil mapping approaches were required to obtain rapid and reliable information. This would enable local farmers to participate in the development of upgrading strategies and extensionists to develop recommendations that take local soil conditions into account. In this study, a combination of participatory soil mapping and gamma ray spectrometry-assisted transect mapping was applied to establish local soil maps of two villages in the Dodoma region. Participatory mapping included key informant interviews, group discussions and transect walks. Local farmers indicated reference profiles for local soil types. Their gamma radiation signatures delivered base information for further soil exploration and soil unit delineation in the field. Finally, high resolution satellite images were used to establish the village soil maps. This approach allows capture of the major soil differences within a village territory and reduction of the costs of chemical analyses. Challenges were soil unit separation with gamma ray spectrometry due to erosional redistribution processes at the surface, correct translation of specific terms from local tongues as well as variable individual soil knowledge of local participants. Ultimately, the combination of local soil knowledge with innovative scientific mapping yielded quick results with sufficient spatial resolution for extension work.

Synthesis: Constraints to Sustainable Use of Soil and Water in the Northern Thailand Highlands and Consequences for Future Research

Research discussed in Chapter 2 leads to the following conclusions for sustainable resource use, land use planning and scenario development: i. There is a lack of information on the available resources at an acceptable resolution (i.e. 1:200.000 and finer). Neither for soil nor for water are sufficient data available (subchapter 2.2). This calls for action by the authorities at both the national and regional level. In future it needs to be recognized that the highlands cannot remain a forest reserve but are — respecting certain constraints and rules - a valuable resource for the growing population. ii. Thai soil taxonomy classifies highland soils as “Slope Complex Soil Series” which is meaningless and not helpful for any kind of land use planning. Modern approaches already call for three dimensional soil and terrain information, eg. including relief, geo-morphology etc. Therefore, the so called “slope complex” needs a detailed inventory with respect to soil and water resources and use. iii. Resource management has so far not been sustainable. Many cropping patterns, including cash crops, off season production, irrigation, hydroponics, have been proposed and tested by national and international institutions (subchapters 2.1 and 3.3). In particular, practicable anti-erosive cultural practices have been identified. However, such systems have not been successfully adopted or widely used by the highland stakeholders. Insecure land tenure, lack of access to markets and credit, and availability of extension services are some of the reasons. Consequently, the highland population needs help with a variety of infrastructure measures including transport and communication, education and institutional support. iv. For several decades, overuse of highland resources has caused severe on- and off-site effects (i.e. depletion of soil nutrients, overconsumption and pollution of water, and loss of water storage capacity). Poor education and a lack of consistent environmental laws prevent reasonable coordination and efficient resource allocation. v. Finally, the local communities have developed rules for the use of their limited resources (i.e. water allocation in their territory). Future progress should be built upon existing local knowledge and structures. Increasing shortages call for an overall coordination by state authorities to balance the interests of different stakeholders (i.e. up- vs. downstream users of water).

Stabilisation of Fruit Production by Optimised Plant Nutrition

In the orchards of small-scale farmers in northern Thailand, low input of fertiliser often results in insufficient, low quality fruit yields particularly from older trees. This generally low input of fertilisers and other agrochemicals has been well documented. Deficiencies of micronutrients such as boron (B) and zinc (Zn) have also been frequently reported for Southeast Asia (Dong et al., 1997; Bahadur et al., 1998) and might affect flower induction, fruit set and fruit growth.