Springer Japan KK N. Ae, J. Arihara, K. Okada, A. Srinivasan (Eds.) Plant Nutrient Acquisition New Perspectives With 230 Figures, Including 6 in Color , Springer NORIHARU AE, Ph.D. Laboratory of Soi! Biochemistry National Institute for Agro-Environmental Sciences 3-1-3 Kannondai, Tsukuba, Ibaraki 305-8604, Japan JOJI ARIHARA, Ph.D. Legume Physiology Laboratory National Institute of Crop Science 2-1-18 Kannondai, Tsukuba, Ibaraki 305-8518, Japan KENSUKE OKADA, Ph.D. Crop Production and Environment Division Japan International Research Center for Agricultural Sciences 1-1 Owashi, Tsukuba, Ibaraki 305-8686, Japan ANCHA SRINIVASAN, Ph.D. Regional Science Institute 4-13, Kita-24 Nishi-2, Kita-ku, Sapporo 001-0024, Japan ISBN 978-4-431-66904-3 ISBN 978-4-431-66902-9 (eBook) DOI 10.1007/978-4-431-66902-9 Library of Congress Cataloging-in-Publication Data Plant nutrient acquisition: new perspectives I N.Ae, .... [et al.], (eds.) p.cm. Paper presented at the International Workshop held in Tsukuba, Japan, March 24-27, 1998. Includes bibliographical references (p. ). ISBN 978+431-66904-3 1. Plants--Nutrition--Congresses. 2. Plant-soil relationships--Congresses. 3. Roots (Botany)--Congresses. 4. Plant nutrients--Congresses. 1. Ae, N. (Noriharu), 1946- QK867 .P53 2001 575.7'6--dc21 Printed on acid-free paper 2001020401 © Springer Japan 2001 Originally published by Springer Verlag Tokyo Berlin Heidelberg New York in 2001 Softcover reprint of the hardcover Ist edition 2001 This work is subject to copyright. AII rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcast ing, reproduction on microfilms or in other ways, and storage in data banks. The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. SPIN: 10691853 Foreword KATSUYUKI MINAMI Director General, National Institute for Agro-Environmental Sciences (NIAES) Plant Nutrient Acquisition: New Perspectives is a compilation of research papers presented at the International Workshop held in Tsukuba, Japan, March 24-27, 1998. The Workshop was organized by the National Institute of Agro-Environ mental Sciences (NIAES) and was sponsored by the Secretariat of the Research Council of the Ministry of Agriculture, Forestry and Fisheries, Japan. The objectives of the Workshop were to discuss newly emerging concepts of the mechanisms that plants use to acquire soil nutrients, and to relate those con cepts in the context of applied agriculture. Some 40 papers and posters highlight ing recent advances in this exciting field were presented. I greatly appreciate the efforts of the authors in critically evaluating the past work and presenting new experimental findings and concepts of both theoretical and applied significance. The scope of the Workshop was defined by the Organizing Committee-the members of which are the editors of this book-by holding regular discussions for one year prior to the Workshop. The Committee also received excellent pro fessional support from several staff members and researchers of NIAES in orga nizing the Workshop. I express my sincere thanks to all of them. I am confident that this book will serve as a valuable reference for researchers, students, and extension staff in their efforts to develop more effective approaches to sustainable nutrient management. May 2001 v Welcoming Address MICHINORI NISHIO Professor, University of Tsukuba Former Director General, National Institute for Agro-Environmental Sciences (NIAES) On behalf of the Organizing Committee and the National Institute of Agro-Envi ronmental Sciences, I extend a warm welcome to all of you. The concept of sus tainable agriculture has become the most important concern in the global farm ing sector since the Earth Summit in Rio de Janeiro in 1992. The concept itself is beautiful, and no one denies that. However, there are many interpretations of this concept. It is quite natural to have such diverse interpretations, as types of agri culture vary widely across countries, regions, and areas, depending on different natural and social conditions. Broadly speaking, there are two types of agriculture: extensive and intensive. Different factors are threatening sustainability of both types. For example, the deficiency of nutrients is threatening extensive agriculture while the surplus of nutrients is damaging intensive agriculture. One of the most important concerns for sustainable agriculture, therefore, is the management of plant nutrients. In intensive agriculture, overuse of chemical fertilizers is a matter of concern, while in extensive agriculture, acquisition of nutrients from alternatives to chemical fertilizers is of main interest. There are many ways to approach sustainable nutri ent management, including the utilization of slow-release fertilizers, improvement of fertilization methods, utilization of renewable resources, recycling of farm wastes, and so on. But I am convinced that the essential approach to sustainable nutrient management is the utilization of biological functions of plants and soil organisms. While studies on the role of microorganisms in relation to nutrient supply are relatively many, there are few studies on plant nutrient acquisition. I believe that effective utilization 'of nutrient acquisition mechanisms by plants themselves and by plant-soil organism combinations is a fundamental and reli able approach to sustainable nutrient management in both intensive and exten sive agriculture. With these considerations, the Organizing Committee planned this Workshop. The Committee made special efforts to identify and send invitations to distin guished international experts in various fields. I am happy to learn that almost all invited researchers kindly agreed to participate and share their views with us. I am especially glad to see Dr. Swindale and Dr. Johansen, who extended valuable help to the Committee members in their research at International Crops Research Institute for the Semi-Arid Tropics (ICRISAT). VI Welcoming Address VII Let me once again welcome all of you to Tsukuba and wish you success in your research endeavors. I am confident that discussions held here will lead to new collaborations that will guide plant nutrition research in the years ahead. March 1998 Preface LESLIE D. SWINDALE Director General (Emeritus), International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) Plants, like people, need food. The scientific study of plant nutrients commenced in the mid-nineteenth century with the work of Justus von Liebig and his application of scientific principles to "the means of nutrition of vegetables and with the influence of soils and action of manures upon them:' Liebig proposed the Law of the Minimum, that is, that plant growth was dependent upon the least available nutrient. Soon after the turn of the century it was accepted that the primary means of nutrient uptake was by ion exchange at root surfaces with H+ ions being released from the roots in cation uptake and OH- and HC0 being released in the uptake of anions. By the early 3- 1920s it was recognized that nutrient supply to any plant was dependent upon both the amount of nutrient available in the surrounding soil and the rate at which the nutrient was supplied to the plant, the so-called capacity and intensity factors. After it was realized that nutrients would first need to pass into the soil solution that existed between the soil and the plant roots-although some adhered to the idea of nutrient supply through direct contact between the solid phases of soil and plant- a physico-chemical model of nutrient uptake was developed and held sway for several decades. In this model there were basically three rate-determin ing steps: the rate at which a nutrient was removed from the soil particle into the soil solution, the rate at which the nutrient diffused through the solution, and the rate at which it was subsequently taken up by the plant. The model, to this stage, was essentially a physical one. Jacobsen and Overstreet in the 1960s were among the first to introduce a biological dimension by propos ing that organic chelating compounds occurred in the soil solution and affected both the removal of ions from the soil and the activities of ions in solution. The metabolic products of the microbial breakdown of carbohydrates in soils include citrate, malate, and malonate, all of which have chelating abilities. In more recent years the possible role of enzymes in nutrient release and particularly in nutrient uptake has received attention. Chelating compounds would have particular importance on the availability of phosphate (P), which is one of the three most important nutrients that plants derive from soils. It is often one of the least available because it can be fixed in unavailable forms and because it is not very mobile in soil solutions. Plants for age for P. Several authors have shown how P uptake is related to the total mass VIII Preface IX and volume of roots. Nitrogen can influence P uptake not only by increasing the root mass but also by altering the nature of root systems. The Workshop on New Concepts of Plant Nutrient Acquisition, held at Tsukuba, Japan, March 24-27, 1998, the proceedings of which are reported in this publica tion, brought together people from allover the world to exchange views on old and new perspectives of plant nutrient uptake and to show how the newer per spectives might be applied to practical agriculture. It was to a large extent an outgrowth of a 15-year-Iong project between International Crops Research Insti tute for the Semi-Arid Tropics (ICRISAT) and the Japan International Research Center for Agricultural Sciences (JIRCAS), with core support from the Consulta tive Group on International Agricultural Research (CGIAR) and special project support from the Government of Japan. The project, entitled "Development of Sustainable Cultivation of Upland Crops in the Semi-Arid Tropics:' was conducted in three phases (I: 1984-1989,11: 1989- 1994, III: 1995-1999). During that time Japanese scientists worked at ICRISAT with ICRISAT scientists and fellows. The project addressed the issues of food se curity and poverty alleviation by looking for ways to increase the availability of nutrients without additions of fertilizers in food crops commonly used by poor people in the semi-arid tropics. The project first tried to elucidate the mecha nisms by which some of these crops were more efficient than others in extracting nutrients from soils, then studied the role of roots and root development, and, in the final phase, moved on to learning how plant breeding could be combined with management options to improve nutrient availability in soils with low nutrient supplying powers. We have known for a long time that pigeonpea seemed to be able to extract P from soils in ways that other crops could not. Project scientists obtained evidence that suggested that root exudates of pigeonpea might be the cause, or at least a cause, of the plant's ability to extract P from soil. Piscidic acid was identified as one of the constituents of the exudates. Mechanisms involving root exudates may make limited contributions to the P nutrition of most plants in most soils, but they seemed to be important in the case of pigeonpea growing in soils with low nutrient-supplying power. This finding was the first report indicating that crop plants are also able to modify rhizosphere conditions, thereby solubilizing P from Fe compounds, which are regarded as the most insoluble form of P. Several papers at the Workshop in Tsukuba further explored the role of plant exudates in P uptake. Otani and Ae found that pigeonpea, groundnut, and rice had greater abilities to release P from Fe- and AI-fixed forms in Andosols than did sorghum if root volume was constrained. Pigeonpea exudates were shown to be able to dissolve FeP0 and AIP0 in artificial conditions. In addition to piscidic 4 4 acid, malonates and citrates were also found as the components of the exudates. P uptake by maize and soybean from soils with low available P was enhanced when artificial pigeonpea exudates were added to the rhizosphere soil. Their effect, in fact, was to create conditions through which P can be solubilized from the soil so that absorption by the plant becomes possible. Papers presented at this workshop highlight various new aspects of plant nu trient acquisition. One set of papers discusses recent models regarding nutrient X Preface uptake that place greater emphasis on the active role of plants in that process. This is followed by several papers describing management options designed to reduce the reliance on chemical fertilizer inputs. The important role of soil mi croorganisms for nutrient acquisition is stressed and evidence presented that shows that organic fertilizers can be used directly by plants as a result of their ability to take up organic nitrogen forms. Finally, the potential for improving the nutrient acquisition ability of crops by plant breeding methods is explored. Re sults presented indicate that breeding effective crops is possible even for tropical soils, which have long been considered to be problem soils due to low P-fertility. It was also shown that another important problem of tropical soils-soil acidity can be overcome by exploring the genetic diversity present in crop plants. Ge netic improvements in combination with adjustments in cropping systems will have a significant impact not only in developing countries characterized by low fertilizer use but also in developed countries, where they will contribute to mak ing agricultural systems more environmentally sound. The organizers of the workshop in an epilogue made a plea for reducing de pendence upon mineral fertilizers to increase food crop production in and for the developing world through greater use of natural soil components and pro cesses. I believe that the publication of these proceedings will stimulate research into these more sustainable forms of plant nutrient acquisition.