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Ecological Impact of Tropical Pastures and the Potential of Forage Plants for Sustainable Land Use Systems in the Tropics An Annotated Bibliography A Christinck K Probst R Schultze Kraft Contents 1 Abstract 2 2 Introduction 3 3 Forage plants and pastures within tropical farm ecosystems 4 3 1 Soil properties 4 3 1 1 Soil chemical properties 4 3 1 2 Soil physical properties 8 3 1 3 Soil biological properties 9 3 2 Nutrient cycling 10 3 3 Erosion control 13 3 4 Microclimate 16 3 5 Diseases pests and weeds 17 4 Tropical pastures within regional and global ecosystems 20 4 1 Hydrology 20 4 2 Regeneration of degraded land 22 4 3 Biodiversity 24 4 4 Atmosphere and global warming 27 5 Conclusions 31 6 References 33 7 List of keywords 144 2 Chapter 1 Abstract 1 Abstract This annotated bibliography lists and summarizes the most relevant references on the ecological impact of pastures and forage plants in tropical land use systems It attempts to provide knowledge from ecosystem and ecology relevant disciplines to researchers and development workers The bibliography is structured into different sections considering on the one hand research results at farm ecosystem level and on the other hand studies at the regional and global level Numerous reports are presented on the cultivation of multipurpose herbaceous and woody forage plants and their effects on soil properties nutrient cycling erosion microclimate and phytosanitary aspects On a regional and global level focus is given to hydrological aspects the regeneration of degraded land biodiversity and climate The review indicates that basic data on ecological effects of pasture establishment and livestock production are still scarce This is the case in particular for long term effects at the regional and global levels Areas of future research are suggested For a successful development of sustainable land use systems interdisciplinary and interinstitutional collaboration is indispensable Chapter 2 Introduction 3 2 Introduction In view of the growing human population and progressive degradation and destruction of the natural resources the search for sustainable land use systems is one of the most important challenges of our decade Farming practices and livestock production are generally known to contribute on a large scale to environmental degradation if they focus on short term productivity only The aim of this study is to summarize current tropical pasture related knowledge from different ecosystem and ecology relevant research fields A second aim is to encourage interdisciplinary research for developing sustainable farming systems that make use of the potential that tropical pasture plants are suggested to offer for a wide range of ecological and socio economic conditions The bibliography is structured into different sections considering research at farm ecosystem level on the one hand soil properties nutrient cycling erosion control microclimate diseases pests and weeds and studies at the regional and global ecosystem level on the other hand hydrology regeneration of degraded lands biodiversity atmosphere and global warming Each section consists of a summarizing review giving insight into the subject the main approaches of current research and the lack of knowledge References are numbered and are presented in Chapter 6 in numerical order including keywords and abstracts The list of keywords Chapter 7 was especially prepared for this bibliography and does not necessarily represent the keywords given in common databases e g CAB Abstracts TROPAG Agricola If a reference lacked an abstract or summary an own abstract was added and is identified as such Abstract by bibliography authors The study is based on an effort to gather relevant literature that was readily accessible in 1995 but by no means do the authors claim the bibliography to be complete The intention is rather to provide a starting point for subsequent exhaustive literature searches within the nine individual research areas that are outlined in this study 4 Chapter 3 Forage plants and pastures within tropical farm ecosystems 3 Forage plants and pastures within tropical farm ecosystems 3 1 Soil properties Although a wide range of soil types are found in tropical regions highly weathered and lowactivity clay soils Ultisols Oxisols and Alfisols in tropical forest and savanna regions are the most important groups used for farming generally because of the favorable topographic and climatic conditions in the respective regions 1 2 Ultisols and Oxisols are strongly acid and leached soils with low cation exchange capacity CEC very low inherent fertility multiple nutrient N P K Ca Mg Zn deficiencies and nutrient imbalances e g toxic levels of Al or Mn Alfisols which are less acid and have high base saturation are characterized by inherently low nutrient N P K S and Zn status and low structural stability 1 3 Maintaining soil fertility and productivity are the major management problems when these soils are used for crop and pasture production 1 In traditional cropping systems based on shifting cultivation or bush fallow rotation soil fertility was regenerated during fallow periods through the activity of trees and other natural vegetation 4 5 6 7 8 With the rapidly raising human population and increasing pressure on cropping land fallow periods are becoming shorter so that fertility regeneration is less effective and productivity declines 1 4 5 7 8 9 10 In recent years the cultivation of multipurpose herbaceous and woody forage plants became more and more relevant to maintain soil productivity in low input productions systems under shortening fallows 1 4 5 7 8 10 11 12 13 14 15 16 17 18 Numerous studies have been conducted to assess changes in soil chemical physical and biological properties associated with the growth of pasture plants in different integrated farming systems 3 1 1 Soil chemical properties Nitrogen deficiency is a major cause of declining soil fertility 13 19 20 21 As N is a very expensive nutrient to manufacture necessitating high energy inputs 13 22 section 4 4 the use of leguminous plants as a source of N is particularly interesting in low input farming systems of the tropics 14 23 24 25 26 Leguminous plants used as mulches green manures cover crops or as components of pastures or fallow vegetation are generally known to improve soil organic matter OM and enhance total N through symbiotic nitrogen fixation 4 5 6 10 11 12 13 14 16 17 21 22 24 25 27 28 29 30 31 32 33 34 35 36 37
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