Nitrogen Cycling in Ecosystems of Latin America and the Caribbean PDF
Preview Nitrogen Cycling in Ecosystems of Latin America and the Caribbean
Developments in Plant and Soil Sciences Volume 6 Also in this series 1. J. Monteith and C. Webb, eds., Soil Water and Nitrogen in Mediterranean type Environments. 1981. ISBN 90·247·2406·6 2. J.C. Brogan, ed., Nitrogen Losses and Surface Run·off from Landspreading of Manures. 1981. ISBN 90·247·2471·6 3. J.D. Bewley, ed., Nitrogen and Carbon Metabolism. 1981. ISBN 90·247·24724 4. R. Brouwer, I. Ga~parfkova, J. Kolek and B.C. Loughman, Structure and Function of Plant Roots. 1981. ISBN 90·247·2405·8 5. Y.R. Dommergues and H.G. Diem, eds., Microbiology of Tropical Soils and Plant Productivity. 1982. ISBN 90·247·2624·7 In preparation J.R. Freney and J.R. Simpson, eds., Gaseous Losses of Nitrogen from Plant·Soil Systems. Series ISBN 90·247·2405·8 NITROGEN CYCLING IN ECOSYSTEMS OF LATIN AMERICA AND THE CARIBBEAN United Nations Environment Program (UNEP) Nitrogen Cycling in Ecosystems of Latin America and the Caribbean edited by G.P. ROBERTSON R.HERRERA T. ROSSWALL Reprinted from Plant and Soil Vol. 67 (1982) 1982 MARTINUS NIJHOFF / DR W. JUNK PUBLISHERS THE HAGUE / BOSTON / LONDON Proceedings of a regional workshop arranged by the SCOPE / UNEP International Nitrogen Unit of the Royal Swedish Academy of Sciences under UNEP contract FP /1303·78·01 (1330) at the Centro Internacional de Agricultura Tropical (CIAT), Cali, Colombia, 16·21 March, 1981; a meeting sponsored by SCOPE, UNEP, MAB and COSTED. Distributors for the United States and Canada Kluwer Boston, Inc. 190 Old Derby Street Hingham, MA 02043 USA for all other countries Kluwer Academic Publishers Group Distribution Center P.O.Box 322 3300 AH Dordrecht The Netherlands l.ibrary of Congress Cataloging in Publication Data Main entry under title: Nitrogen cycling in Latin American and Caribbean escosystems. (Developments in plant and soil sciences ; v. 6) "Reprinted from Plant and soil, vol. 67." Papers from a workshop held at Ciat, Cali, Colombia in March 1981, which was arranged by the SCOPE/UNEP , International Nitrogen Unit. Includes bibliographies and index. 1. Nitrogen cycle--Latin America--Congresses. 2. Nitrogen cycle--Caribbean area--Congresses. 3. Agricultural ecology--Latin America--Congresses. 4. Agricultural ecology--Caribbean area--Congresses. I. Robertson, G. P. II. Herrera, R. III. Rosswall, T. (Thomas) IV. SCOPE/UNEP International Nitrogen Unit. V. Series. QJU06.5.N57 1982 631.4'17 82-12631 ISBN 90-247-2719-7 ISBN-13: 978-94-009-7641-2 e-ISBN-13: 978-94-009-7639-9 DOl: 10.1007/978-94-009-7639-9 Copyright © 1982 by Martinus Nijhoff / Dr W. Junk Publishers, The Hague. Softcover reprint of the hardcover 1st edition 1982 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publishers, Martinus Nijhoff / Dr W. Junk Publishers, P.O.Box 566, 2501 CN The Hague, The Netherlands. Preface The large and rapidly expanding body ofliterature related to nitrogen cycling in both managed and native terrestrial ecosystems reflects the importance accorded to the behaviour of this vital and often limiting nutrient. Research at the organism, ecosystem and landscape levels commonly addresses questions concerning nitrogen acquisition, internal cycling and retention. Goals for this research include increased agricultural productivity and a better understanding of human impact on local, regional and global nitrogen cycles. Nitrogen cycle research in tropical regions has a long and distinguished history. Research on different aspects of nitrogen cycling in ecosystems of the tropics has been carried out in many regions. In relatively few instances has there, however, been a focus on the biogeochemical cycles at the ecosystem level. The meeting resulting in this volume was an attempt to bring together existing information on nitrogen cycling in ecosystems of Latin America and the Caribbean and discuss this in an ecosystem context. The papers represent the proceedings of a workshop on Nitrogen Cycling in Ecosystems of Latin America and the Caribbean, the third workshop on nitrogen cycling within particular regions organized by the SCOPEjUNEP International Nitrogen Unit of the Royal Swedish Academy of Sciences, Stockholm. The purpose of the workshop was fivefold: 1) to emphasize the importance of the nitrogen cycle in the different ecosystems of the region, 2) to provide a forum for scientists from the region to present papers describing ongoing nitrogen-cycle research, 3) to compile available data into coherent nitrogen budgets for the region's main ecosystems, and 5) to define nitrogen-cycle research priorities for the region. Previous workshops have been held in West Africa 1 and in Southeast Asia 2. The three workshops have been supported by UNEP under contract FPj1303-78.01(1330). The present workshop was held 16-21 March, 1981, at CIAT (Centro Internacional de Agricultura Tropical) in Cali, Colombia. Three days of symposia and contributed paper sessions were followed by two days of workgroup discussions organized around major ecosystems of the region. These included shifting cultivation and traditional agroecosystems, sugarcane, cereal and grain crops, coffee and cacao plantations, savannas and shrublands, forests, and wetlands and aquatic systems. Workgroups were charged with building informal nitrogen budgets of the respective systems and thereby summarizing the current state of knowledge regarding nitrogen cycles in each system. They were also asked to discuss research priorities, which were later reviewed by the plenary session. These priority rankings will, we hope, be useful for efficiently focusing increasingly scarce research resources on important but little-understood nitrogen-cycle processes. v The volume contains most ofthe papers presented at the meeting and the work group reports. Three additional papers by scientists from the region unable to participate in the meeting are also included. A number of papers were originally presented in Spanish or Portuguese. In order to ensure as large an audience as possible for these reports we decided to publish all papers in English with a Spanish summary. Co-sponsors of the meeting apart from SCOPE and UNEP included the Man and the Biosphere (MAB) programme of Unesco, and the Committee on Science and Technology in Developing Countries (COSTED). We are greatly indebted to all the sponsoring organizations for their interest and support. The organizers also extend particular thanks to CIA T Director General J. L. Nickel and his hospitable staff, and also to the simultaneous translators. We are also indebted to Britta Myrvik, Gudrun Sunnerstrand and Peter Wigren for artwork revisions and to Dina Soderstrom and Gun Martinsson for typing the final manuscript. Despite minor difficulties with communicating in three languages, we think most participants will agree that the workshop was a success and that its major objectives were well-met. East Lansing and Uppsala, April, 1982 G. P. Robertson, R. Herrera and T. Rosswall References Rosswall T (Ed.) 1980 Nitrogen Cycling in West African Ecosystems. Stockholm: Royal Swedish Academy of Sciences, 450 p. 2 Wetselaar R, Simpson J Rand Rosswall T (Eds.) 1981 Nitrogen Cycling in South-East Asian Wet Monsoonal Ecosystems. Canberra: Australian Academy of Sciences. 216 p. VI Contents Preface V A. A. Franco, and D. N. Munns, Plant assimilation and nitrogen cycling I T. Rosswall, Microbiological regulation of the biogeochemical nitrogen cycle 15 P. S. C. Rao, R. E. Jessup and A. G. Hornsby, Simulation of nitrogen in agro-ecosystems: Criteria for model selection and use 35 D. J. Greenwood, Nitrogen supply and crop yield: The global scene 45 E. Sanhueza, The role of the atmosphere in nitrogen cycling 61 G. P. Robertson, Regional nitrogen budgets: Approaches and problems 73 A. J. Holding, Some priority research areas in nitrogen studies 81 P. A. Simchez, Nitrogen in shifting cultivation systems of Latin America 91 S. R. Gliessman, Nitrogen distribution in several traditional agro-ecosystems in the humid tropical lowlands of south-eastern Mexico 105 J. D. H. Lambert and J. T. Amason, Nitrogen distribution in hybrid and local corn varieties and its possible relationship to a declining soil nitrogen pool under shifting agriculture at Indian Church, Belize 119 R. L. Victoria, P. L. Libardi, K. Reichardt and E. Matsui, 15N-urea transport and transformation in two deforested Amazonian soils under laboraiory conditions 129 A. P. Ruschel and P. B. Vose, Nitrogen cycling in sugarcane 139 S. Valdivia Vega, Nitrogen gains and losses in sugarcane (Saccharum sp.) agro-ecosystems on the coast of Peru 147 M. N. Versteeg, I. Zipori, J. Medina and H. Valdivia, Potential growth of alfalfa (Medicago sativa L.) in the desert of Southern Peru and its response to high NPK fertilization 157 N. Ahmad, E. D. Reid, M. Nkrumah, S. M. Griffith and L. Gabriel, Crop utilization and fixation of added ammonium in soils of the West Indies 167 M. A. Lazzari, Distribution of l'N fertilizer in field-Iysimeters sown with garlic (Allium sativum) and foxtail millet (Setaria italica) 187 P. L. Libardi, R. L. Victoria, K. Reichardt and A. Cervellini, Nitrogen cycling in a l'N-fertilized bean (Phaseolus vulgaris L.) crop 193 K. R. Reddy, Nitrogen cycling in a flooded-soil ecosystem planted to rice (Oryza sativa L.) 209 E. Schalscha B. and I. Vergara F., The nitrogen balance of vegetable crops irrigated with untreated effluent 221 J. R. Jardim Freire, Research into the Rhizobium/Leguminosae symbiosis in Latin America 227 E. Bomemisza, Nitrogen cycling in coffee plantations 241 J. Aranguren, G. Escalante and R. Herrera, Nitrogen cycle of tropical perennial crops under shade trees: I. Coffee 247 J. Aranguren, G. Escalante and R. Herrera, Nitrogen cycle of tropical perennial crops under shane trees: II. Cacao 259 M. B. M. Santana and P. Cabala-Rosand, Dynamics of nitrogen in a shaded cacao plantation 271 J. P. Roskoski, Nitrogen fixation in a Mexican coffee plantation 283 J. Pereira, Nitrogen cycling in South American savannas 293 E. Medina, Nitrogen balance in the Trachypogon grasslands of Central Venezuela 305 R. H. Braun Wilke, Net primary productivity and nitrogen and carbon distribution in two xerophytic communities of central- west Argentina 315 C. Jordan, W. Caskey, G. Escalante, R. Herrera, F. Montagnini, R. Todd and C. Uhl, The nitrogen cycle in a 'Terra Firme' rainforest on oxisol in the Amazon territory of Venezuela 325 J. T. Amason and J. D. H. Lambert, Nitrogen cycling in the seasonally dry forest zone of Belize. Central America 333 P. W. Runde!, E. T. Nilsen, M. R. Shariji, R. A. Virginia, W. M. Jarrell, D. H. Kohl and G. B. Shearer, Seasonal dynamics of nitrogen cycling for a Prosopis woodland in the Sonoran Desert 343 U. Irmler, Litterfall and nitrogen turnover in an Amazonian blackwater inundation forest 355 R. E. Cisternas and L. R. Yates, Nitrogen in litterfall and precipitation and its release during litter decomposition in the Chilean piedmont matorral 359 E. Salali, R. Sylvester-Bradley and R. L. Victoria, Regional gains and losses of nitrogen in the Amazon basin 367 S. Cabrera S. and V. Montrcino B .. Eutrophy in Lake Aculeo. Chile 377 Work group reports Shifting cultivation and traditional agriculture 389 Sugarcane 395 Cereal and grain crops 399 Coffee and cacao plantations 403 Savannas and shrublands 409 Latin American forests 415 Wetlands (including rice) and aquatic systems 421 List of participants 425 Index 429 VII Plant and Soil 67, 1-13 (1982). 0032-079X/82/0671-0001$01.95. SU-01 © 1982 Martinus Nijhoff/Dr W Junk Publishers, The Hague. Plant assimilation and nitrogen cycling Asimilacion de nitrogeno por las plantas y el cicio de este elemento A.A.FRANCO Empresa Brasileira de Pesquisa Agropecuaria (EM BRAP A), SN LCS-P F BN -km 47, Seropedica, Rio de Janeiro 23460, Brazil and D. N. MUNNS Department of Land, Air and Water Resources, University of California, Davis, California 95616, USA Key· words N-assimilation N-cycling N-fertilization N 2-fixation Nitrogenase N- mineralization N-reductase pH changes Abstract Nitrogen, an abundant and yet limiting nutrient for crop and food production, enters the plant as nitrate or ammonium, or as dinitrogen through biological fixation by procaryotes associated with the plant. Nitrogen incorporation into the soil-plant-animal system is ultimately restricted by rates of biological and industrial fixation. Biological fixation conserves fossil fuel, but fertilization is preferred in most present agriculture. Nitrogen-metabolism research has the practical objectives of allowing more efficient N-fertilizer utilization by plants, including those that fix N 2 but benefit from fertilizer-N supplements. Nitrogen accumulation by harvested crops results in changes in soil acidity, with the direction of change depending on the N-source. There is little information on long-term effects of crop N- nutrition on acidity, and acidity is a critical factor that affects agricultural productivity in many tropical soils. Thus, plant control of pH and the acid/base balance in the soil as a consequence of nitrogen uptake and assimilation are important areas of future research. Resumen EI nitr6geno, abundante pero sin embargo limit ante para los cultivos, entra en las plantas en forma de nitrato 0 amonio 0 es incorporado al sistema a traves de fijaci6n biol6gica. La incorporaci6n del nitr6geno al sistema suelo-planta-animal est a limitado por las tasas de fijaci6n biol6gica e industrial. La primera ahorra energia fosil pero la segunda fuente es la predominante en la agricultura moderna. La investigaci6n del metabolismo de nitr6geno tiene objetivos practicos tales como el permitir un uso mas eficiente de los fertilizantes nitrogenados por los cultivos, incluyendo aquellos que puedan fijar N 2 pero se benefician de suplementos de fertilizantes nitrogenados. La acumulaci6n de nitrogeno en los cultivos trae como consecuencia cam bios de acidez en el suelo cuya direccion depende de la forma de nitrogeno utilizada. Aun existe poca informacion sobre los efectos a largo plazo de la fertilizacion nitrogenada sobre la acidez del suelo, factor que es determinante de la productividad de muchos suelos en los tropicos. Asi pues, el control de pH por las plantas y el balance de acidez en el suelo son areas de interes para futuras investigaciones. Introduction Nitrogen is abundant but is the nutrient that most often limits crop and food production. A crop can accumulate up to 800 kg N ha - 1 yr - \ most non- fertilized tropical soils under agriculture deliver less than 50 kg N ha - 1 yr - 1 (Sanchez 53 ). 2 FRANCO AND MUNNS The availability of nitrogen in soil is limited by rates of organic matter decomposition unless availability is enhanced by biological N rfixation or additions of fertilizer-N. Optimizing these three sources for crop production is desirable for economic and ecological reasons. In this paper we discuss the turnover and availability of nitrogen in the soil and plant uptake and nitrogen assimilation, including the special case oflegumes and the balance of pH as a consequence of N uptake. pH balance is of special importance because of its impact on the already acid soils found in most of the tropics. Nitrogen in the soil Forms of nitrogen Inorganic nitrogen in soil has three main sources: soil organic matter, atmospheric N z, and N-fertilizer. During decomposition of organic matter in most agricultural soils, excess NH4 + not utilized by microbes is released, and subsequently usually oxidized mostly by autotrophic bacteria to NOz - and then N03 -. Nitrite does not usually accumulate except temporarily in the special situation where pH is above 7 and excess NH40H (or urea hydrolysing to NH40H) together inhibit the NO z - oxidizers. When atmospheric N z is fixed, the first form of combined nitrogen to appear is NH4 + , and most of it is immediately assimilated into organic forms so that very little is exuded to soil. Both organic and exuded NH4 + and fertilizer-N follow the same path as N derived from organic matter. Total nitrogen in soil varies with soil organic matter content; soil organic matter usually contains ca. 5% N. In surface mineral soils, values of 0.03% N (Vertisol from Sudan) to 0.69% N (Oxisol from Brazil) have been reported 53. Levels of nitrate to 0.006% N03-N (60mg N03-Nkg dry soil- 1) have been noted by Chapman 15 , while ammonium is usually much less except in waterlogged soils after the addition ofNH4 + -N, urea, or nitrification inhibitors. Factors affecting nitrogen release In the absence offertilizer N, the major source of fixed nitrogen the soil supplies to the plant is from soil organic matter undergoing decomposition. As illustrated in Fig. 1, the availability of nitrogen to plants depends on the amount and type of organic matter present, and on the presence of microbial populations and conditions favoring their activity. In general, microbial activity is favored under those conditions that are optimal for plant growth, though microbes generally have a wider tolerance range than plants. The direction ofN- transformation processes is dictated by the C: N ratio in the soil. A carbon limitation results in net N-mineralization; a nitrogen limitation (for example after the addition of excess carbon in the form of organic material with less than 1.3- PLANT ASSIMILA nON AND N-CYCLING 3 NZ Fixation Nz + NzO MineraLization \ Nitri fication loenitrification .. + III / I Organic matter N H4 • NO~3up take Immobilization Nitrate reduction "PLants Leachi ng Ground water Fig. I. Principle forms and pathways for soil nitrogen (from Broadbent 7). 1.5% N) results in the net immobilization of nitrogen until the C: N ratio is lowered to 20-30, when net N-mineralization is reinitiated 8. During periods of excess carbon, the free-living N 2-fixers are also favored, and fixation of considerable amounts of nitrogen may occur. However, the availability of nitrogen to plants during this period is restricted by competition with the large population of heterotrophs in the soil. Under aerobic conditions in most agricultural soils, nitrification is faster than nitrate reduction, mineralization faster than immobilization, and nitrification NH4 -limited 7. As a consequence, there is often a continual conversion of organic nitrogen to nitrate, with little or no accumulation of ammonium. Excess water in the soil will inhibit part of the soil aerobic microbial population, particularly fungi and actinomycetes. Also, aerobic metabolism is more efficient for cell synthesis than is anaerobic metabolism. Thus, as saturation is approached, immobilization decreases faster than mineralization, and mineral-N accumulates 7. In rice fields fertilized with high rates of ammonium, nitrification and denitrification proceed simultaneously: nitrification in the oxidized layer at the soil surface and above, and denitrification below, where anaerobiosis is dominant 48. This is reflected in the better response of rice to deeper application of ammonium or urea than to broadcast application 10. Nitrogen mineralization proceeds slowly in soils too dry for crops to grow 61 . There is also an increase in N-mineralization in re-wetted soil relative to soil kept moist 4 , and this may account for the initial flush of available nitrogen in pot experiments or when rain or irrigation follows dry weather when plant growth has been restricted. The effects of soil water on microbial activity depend to some extent on temperature. In one set of incubation studies 13, for example, rates of mineralization dropped by a factor of 3 as soil moisture potential dropped from the optimum 0.5 bar (25% H 20) to 2 bar (18% H 20), but the effect of water was most marked at the highest and most favorable temperature, 30°C. In general, low temperature slows down microbial activity, and maximum activity usually occurs at ca. 40°C. The period of N-immobilization is subsequently shorter at higher temperatures, although the total amount of nitrogen immobilized is not greatly affected 7. The surface horizon normally contains nearly all of the mineralizable-N in a soil profile. However, there are exceptions, for example deep undifferentiated alluvial soils in which more than half of the nitrogen released may come from depths below 20cm 13.
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