Thomas Gaiser

Water retention characteristics of soils with contrasting clay mineral composition in semi-arid tropical regions

In semi-arid tropical regions, the availability of reliable data for water retention in relation to soil type, texture, and organic matter content is low. It would be therefore desirable to develop pedotransfer functions (PTF) in order to estimate water retention characteristics from easily available soil parameters. In the present study, a soil database containing water retention characteristics, particle size distribution, and total organic carbon content of 663 horizons from semi-arid regions in NE Brazil and SE Niger was used to investigate the effect of contrasting clay mineral composition on water retention and PTF characteristics for soils from semi-arid tropical regions. For soil water content at field capacity (–33 kPa) and wilting point (–1500 kPa), PTFs were established and validated with disturbed samples from LAC soils (soils containing predominantly low activity clay; CEC < 24 cmol/kg clay) and non-LAC soils. The PTFs for the LAC soil group differed considerably from the PTFs for non-LAC soils with respect to the contribution of total organic carbon and silt content to the prediction of soil water content at field capacity and wilting point. For the particle size classes sand, loamy sand, sandy loam, and sandy clay loam, the mean measured soil water contents in LAC soils were significantly smaller than in non-LAC soils at a matric potential of –33 kPa. The results demonstrate the influence of clay mineral composition on soil water retention and its importance for the development of pedotransfer functions.

A soil and terrain digital database (SOTER) for improved land use planning in Central Benin

Abstract The soil is a natural resource, non-renewable in the short term and expensive either to reclaim or to improve following erosion or degradation. In the Republic of Benin (West Africa) the increasing pressure on land caused by steady population growth induces soil degradation. The reduced site productivity calls for an information system on soil resources, which allows the analysis of land suitability, potential food production, environmental impact of land use and the identification of conservation measures. On the basis of such a system, sound policy formulation and development planning at all levels can be carried out, utilizing both internal and external resources efficiently. For the central part of Benin, the development of a soil information system has been initiated. The data structure for the description of the land resources was established according to the Soil and Terrain Digital Database (SOTER) manual (Global and National Soils and Terrain Digital Databases (SOTER). Procedures Manual. International Soil Reference and Information Centre, Wageningen, The Netherlands, 1993) with slight modifications (Mitteilg. Dtsch. Bodenkdl. Ges. 76 (1995) 1221). Based on field observations and data analysis, land areas have been delineated showing similar response to management practices. On the uppermost level, seven so called ‘terrain units’ could be distinguished. The main differentiating criteria were landscape morphology, geology and hydromorphy. The terrain units are subdivided at a second level into 25 terrain components according to the soil parent material and landform. The FAO/ITC land suitability procedure was used to identify crop specific constraints to the production of sorghum, cowpea, maize, cotton, groundnuts and cassava. With regard to the soil induced limitations to crop production, unfavorable textural properties prevail, except for terrain components on gabbro or basaltic parent material. Unfavorable climatic conditions determine the suitability of this region for cotton, maize and cassava production. The ranking of the physical suitability of the six crops for Central Benin was in the order sorghum>groundnut>cowpea, cassava>maize>cotton. The problem of interannual variability of precipitation and its effects on the climatic suitability is discussed.

An Information System for Land Resources in Piauí and Ceará

The Brazilian federal states of Piaui and Ceara are characterized by a semiarid environment that is highly variable in terms of soil resources and climatic conditions. The assessment of areas with high potential far agricultural production as weil as the identification and quantification of constraints to crop production are high priorities for the planning authorities of both states. Attempts towards land suitability classification have been made with different approaches at the regional scale for Ceara (SEARA 1988) and Piaui (Cordeiro 1985) and at the national scale for Brazil (SUPLAN 1979; EMBRAPA 2000). However, national classification approaches are not detailed enough for regional planning and, in some cases, lack climatic evaluations. The need for land resource information has been confirmed by a series of joint workshops with the participation of scientists of the research program WAVES and representatives of several ministries of the state of Ceara. Far this purpose, the Soil and Land Resources Information System for the states of Plaui and CEara (SPICE) has been established. The present paper focuses on applications of SPICE with special emphasis on the assessment of the spatial and temporal crop production risk. Further examples of applications are available on the SPICE homepage (http://www.uni-hohenheim.de/spice).

General View of the WAVES Program

The globalization of the world’s economy at the dawn of the new millennium is most likely to continue and will be accompanied by social and environmental changes that will affect the entire earth system. The causes of global environmental problems are not fully understood: emission of greenhouse gases and pollutants by the industrialized world, overuse of soil and biotic resources, destruction of forests and natural vegetation, and the extinction of ecosystems with their genetic resources (WBGU 1993; IPCC 1997). In addition, the consumption of natural resources and environmental pollution are even more pronounced through the world’s rapidly growing population. The totality of these processes, their interactions and consequences is called global change. The observed symptoms are interdependent and interrelated in various ways. Global change is therefore a complex phenomenon, which cannot be completely understood through the analysis and evaluation of single phenomena. The understanding of global change and its impacts necessitates the analysis of the relevant system components and their interactions. When using scenario assumptions, the global effects can be described with simulation runs of complex models and can be visualized as global average values of the principal components. However, the results are very general and mask the strong regional differences (Walker and Steffens 1999). At the regional level, the effects of global change may vary considerably due to geographical location, climatic variability, natural resources as well as socio-economic conditions.

Validation of the EPIC model for nitrogen and phosphorus uptake by intercropped maize and cowpea on Alumi Haplic Acrisol

Simulation models can be used for predicting several aspects of agricultural activities such as irrigation, conservation practices and crop management and their impact on yield, nutrient availability and environment. Most part of the research on crop models has been carried out for temperate or subtropical conditions. In order to evaluate the accuracy of the EPIC 8120 model to tropical semi-arid conditions on a highly acid soil, the results of a three year field experiment measuring biomass production and nutrient uptake of 3 years field experiment for intercropping maize and cowpea were compared with the results of simulations. EPIC overemphasised the effects of water shortage and aluminium stress on the production and nutrient uptake by the crops. This indicates the need to calibrate and adjust the model for those conditions in order to be able to consider the interaction of nutrient and water stress and the dynamics of pH as changed by tillage and lime.

Seepage and Groundwater Recharge in Sandy/Loamy Chapada Soils of the Picos Region, Piauí

Water scarcity poses a serious problem in the semiarid northeast of Brazil since the region is affected by an irregular rainfall distribution within rainy seasons of 3–5 months duration (November–April) and also by regularly recurring El Nino events, causing strong decreases in rainfall (up to annual zero-rainfall at some locations) every 8–10 years (Halm et al. 1999). In addition, nearly 50% of the state of Piaui (mainly chapadas and serras) is covered by sandy soils, which generally show low water storage and plant-available water capacities but medium to high infiltration and percolation rates (EMBRAPA/SNLCS 1983, 1986).