Advances in agronomy volume 60

V O L U M6 0E .> Advisory Board Martin Alexander Eugene J Kamprath Cornell University North Carolina State University Kenneth J Frey Larry P.Wilding Iowa State University Texas A&M University Prepared in cooperation with the American Society of Agronomy Monographs Committee William T Frankenberger, Jr., Chaimnan P S Baenziger David H Kral Dennis E Rolston Jon Bartels Sarah E Lingle Diane E Storr Jerry M Bigham Kenneth J Moore Joseph W Stucki M B Kirkham Gary A Peterson DVANCES IN Edited by Donald L Sparks Department of Plant and Soil Sciences University of Delaware Newark, Delaware ACADEMIC PRESS San Diego London Boston New York Sydney Tokyo Toronto This book is printed on acid-free paper @ Copyright 1997 by ACADEMIC PRESS All Rights Reserved No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the Publisher The appearance of the code at the bottom of the first page of a chapter in this book indicates the Publisher’s consent that copies of the chapter may be made for personal or internal use of specific clients This consent is given on the condition, however, that the copier pay the stated per copy fee through the Copyright Clearance Center, Inc (222 Rosewood Drive, Danvers, Massachusetts 01923), for copying beyond that permitted by Sections 107 or 108 of the U.S Copyright Law This consent does not extend to other kinds of copying, such as copying for general distribution, for advertising or promotional purposes, for creating new collective works, or for resale Copy fees for pre-1997 chapters are as shown on the title pages, if no fee code appears on the title page, the copy fee is the same as for current chapters 0065-21 13/97 $25.00 Academic Press a division of Harcourr Brace & Company 525 B Street, Suite 1900, San Diego, California 92101-4495, USA http://www.apnet.com Academic Press Limited 24-28 Oval Road, London NWI 7DX UK http://www.hbuk.co.u Wapl International Standard Book Number: 0- 12-OOO760-6 PRINTEDIN THE UNITEDSTATESOF AMERICA 97 98 9 0 01 02BB Contents CONTRIBUTORS PREFACE vii u NUTRIENT C Y C L ~ TRANSFORMATIONS G AND FLOWS: IMPLICATIONS FOR A MORESUSTATNABLE AGRICULTURE I I1 111 Fred Magdoff Les Lanyon and Bill Liebhardt Introduction Framework for Evaluating Nutrient Dynamics Soil-Plant System Cycling and Flows a t the Field Level Farm-Scale Cycling and Flows Watershed, Regional, and Global Issues Iv v; VI VII Promoting a More Sustainable Agriculture through Changes Influencing Nutrient Cycles and Flows VIII Conclusions References 13 23 38 47 56 65 66 ADAPTATIONOF PLANTSTO SALINITY Michael C Shannon I Invoduction I1 Rationale for Breeding for Salt Tolerance III Selection for Salt Tolerance IV Salt Tolerance Mechanisms v Genetic Variability VI Breeding Methods VII Novel Concepts VIII Summary and Conclusions References V 76 77 78 84 88 101 105 107 108 vi CONTENTS INFLUENCEOF NO-TILL CROPPINGSYSTEMS ON MICROBIAL RELATIONSHIPS L F Elliot and D E Stott I Introduction I1 Decomposition of Surf-ace-Managed Crop Residues I11 Modeling Crop Residue Decomposition n? Root-Microbial Relationships v Deleterious Rhizobacteria for Weed Control VI Low-Input On-Farm Composting References 121 122 125 129 137 141 144 PRACTICAL ETHICSIN AGRONOMICRESEARCH Don Holt I Introduction I1 Basic Concepts I11 Ethics of Choosing Research Subject Matter rv Difficulties with the Utilitarian Approach v Agricultural Ethics and the World Food Situation VI Ethics in the Conduct of Research VII Ethics in Research Administration References 150 151 154 158 162 165 184 190 AREAGROECOSYSTEMS SUSTAINABLE IN SEMIARID REGIONS? B A Stewart and C A Robinson I Introduction I1 Agroecosystems ILL Semiarid Regions n? v VI VII The Issue of Sustainability Technologies for Increasing Plant-Available Water Soil Organic Matter Maintenance Summary References INDEX 191 193 194 198 205 223 224 225 229 Contributors Numbers in parentheses indicate the pages on which the authors’ conlribulions begin L F ELLIOT (12 l), National Forage Seed Production Research Center, Corvallis, Oregon 97331 DON HOLT (149), College of Agricultural, Consumer, and Environmental Sciences, Illinois Agricultural Experiment Station, University of Illinois, Urbana, Illinois 61801 LES LANYON (l), Department of Plant and Soil Science, University of Vermont, Burlington, Vermont 05405-0082 BILL LIEBHARDT (l), Department of Plant and Soil Science, Universityof Vermont, Burlington, Vermont OS405-0082 FRED MAGDOFF (l), Department of Plant and Soil Science, University of Vermont, Burlington, Vermont 05405-0082 C A ROBINSON (191), Dryland Agriculture Institute, West Texas A&M University, Canyon, Texas 79016 MICHAEL C SHANNON ( , United States Department of Agriculture, Agriculture Research Service, U S Salinity Laboratory, Riverside, California 92507 B A STEWART (191), Dryland Agriculture Institute, West Texas A&M University, Canyon, Texas 79016 D E STOTT (12 l), National Soil Erosion Research Laboratory, Purdue University, West Lajayette, Indiana 47906 vii This Page Intentionally Left Blank Preface Volume 60 contains five outstanding chapters that address cutting-edge research and timely issues in the plant and soil sciences Chapter discusses nutrient cycling transformations and flows and the implications for a sustainable agriculture Topics that are included are the soil-plant system; cycling and flows at the field level; farm scale cycling and flows; watershed; state, regional, and global issues; and promoting a more sustainable agriculture Chapter is a state-of-the-art review on adapting plants to salinity The most contemporary research on selection for salt tolerance, salt tolerance mechanisms, genetic variability, breeding methods, and novel biotechnological tools for improving plant adaptation to salinity, including tissue culture and molecular biology, is included Chapter discusses the effects of no-tillage cropping systems on soil microbiological relationships, including decomposition of surface-managed crop residues, modeling crop residue decomposition, root-microbial relationships, deleterious rhizobacteria for weed control, and low-input, on-farm composting Chapter discusses the very timely topic of ethics in agronomic research This treatise should be of great interest to students in the plant and soil sciences and to practicing professionals The author defines personal ethics and scientific conduct and then discusses the ethics of choosing research subject matter, agricultural ethics and the world food situation, and ethics in research and administration Chapter discusses the question of the sustainability of agroecosystems in semiarid regions Semiarid regions, the issue of sustainability,and technologies for increasing plant available water are covered The editor expresses sincere gratitude to the authors for their fine contributions ix 222 B A STEWART AND C A ROBINSON sons-a humid season when corn is grown and a semiarid season when the wheat is produced The wheat is harvested only a few days prior to the start of the dominant rainy season Corn is seeded directly in the standing wheat residue as soon as it is feasible after the wheat is harvested At this time, the stored soil water has been depleted by the wheat crop and germination and emergence of the corn does not occur until the dominant rainy season begins During the high rainfall period of July and early August, the emerging corn crop does not use large amounts of water so the soil profile is largely replenished with water There is also substantial rainfall during the remainder of the corn growing season so the soil water storage at the end of the corn growing season remains high (TableVII) Following the harvest of the corn in mid-September, the soil is tilled and manure and other fertilizers are applied to the land in preparation for seeding wheat The wheat is grown during the drier part of the year when the average precipitation is substantiallyless than one-half of the average potential evapotranspiration Therefore, the wheat crop depends on soil water accumulated during the corn growing season for about one-half of the total amount of water used for evapotranspiration,and water stress is common during the latter stages of the wheat growing season This example, however, shows that cropping systems can be designed in certain instances to utilize nearly all the precipitation during the growing season Table VII Relation between Yield and Growing Season Evapotranspirationfor Wheat and Corn in Northwest China” Dates Wheat 16/10/83-31/5/84 7/10/84-30/5/85 11/10/85-1/6/86 8/10/8&1/6/87 18/10/87-1/6/88 Average Corn 716-81984 6/6/4/9/85 2/6/-10/9/86 516- 15/9/87 1216- I 2/9/88 Average Available water at seeding (mm in 1.3 m) Available water at harvest Evapotranspiration Rainfall Yield (mm in 1.3m) (mm) (mm) (Mg ha-’) 253 262 260 86 222 217 18 67 86 11 13 39 369 399 38 I 285 329 353 134 204 207 210 120 175 6.27 5.28 5.01 4.25 4.69 5.21 18 64 86 95 40 61 229 I77 80 I78 244 182 27 290 175 305 275 263 482 403 169 389 479 384 5.13 6.36 0.64 7.09 6.30 5.10 “Adapted from Zhu Zixi et al (1994) AGROECOSYSTEMS SUSTAINABLE IN SEMIARID REGIONS? 223 Tow and Schultz (1991) present a comparative analysis of dryland farming rotations occumng throughout the Australian cereal belt, from the southwest of Western Australia to north Queensland The influences of rainfall amount and annual distribution and of soil type are explained The analysis is an excellent example of how crop calendars can be designed as strategies for developing sustainable agroecosystems One strategy that perhaps should be utilized more in water-deficient regions is the production of forages rather than grain crops Forage production is not dependent on water being available late in the season as is the case for grain crops In water-deficientregions such as Bushland, Texas, illustrated in Fig 1, a forage crop can be grown each year, whereas it is necessary to use a fallow system to ensure successful grain production This strategy can utilize a higher percentage of the precipitation for transpiration rather than water being lost as evaporation from the soil surface VI SOIL ORGANIC MATTER MAINTENANCE Soil organic matter has over the centuries been considered by many as an elixir of life-in this case, plant life Since the dawn of history, man has appreciated the fact that dark soils, found chiefly in river valleys and on broad level plains, are usually (but not always) productive soils Man also realized at a very early date that soil color and productivity are commonly associated with organic matter derived mainly from decaying plant materials A sustainable agroecosystem requires the conservation or enhancement of the soil resource base over the long term, and it is imperative that the organic matter content of soils be sustained A decrease in soil organic matter content is an indicator of lower soil quality in most soils This is because soil organic matter is extremely important in all soil processes-biological, physical, and chemical Soil organic matter acts to store nutrients, improves nutrient cycling, increases the cation-exchange capacity, and reduces the effects of compaction It builds soil structure and increases the infiltration of water It serves as a buffer against rapid changes in pH and serves as an energy source for soil microorganisms Organic matter tends to make very fine-textured soils behave like coarser-textured ones; the reverse is true for sandy soils An annual loss of or 2% of the organic matter in the surface 15 cm of topsoil by decomposition is not uncommon In some climates, the loss rate can be considerably higher Pieri (1995) summarized data from semiarid regions of Africa and reported that on very sandy soils, annual plowing with fertilizers led to an annual loss of 5% or more Without exception, only the methods with manure application prevented a decline in soil organic matter The effect of plowing was less 224 B A STEWART AND C A ROBINSON clear but several of the reported studies did indicate that plowing increased the decline rate Pieri (1995) proposed that there is a critical level for soil organic matter that is dependent on the soil organic matter%age and the sum of clay plus silt He states that if the soil organic matter percentage falls below the critical level, the maintenance of soil structure is difficult to achieve However, he disagrees with agronomists that argue that if soil organic matter is important in soil quality, then the higher soil organic matter content is, the better the soil is Pieri states that in semiarid Africa, where there are so many technical and economic constraints to crop performance, it is fruitless to aim for a soil organic matter percentage above the critical value Johnson er al (1974) reported on a 29-year study at Bushland, Texas, where various cropping systems were compared for their effects on wheat production and soil organic matter maintenance (Table 111) They clearly showed that organic matter decline was increased when the length of the fallow period was increased or when tillage was intensified, and the greatest loss occurred when both circumstances were present There was also a large accumulation of nitrate nitrogen in the soil profile for all treatments but it was particularly large for the intensively tilled fallow areas The delayed subtilled plots, although not socially acceptable because of the uncontrolled weed production, had the smallest decline in soil organic matter and yielded about the same amount of wheat as the systems that controlled weed growth Organic matter maintenance in semiarid regions is clearly one of the greatest constraints in the development of sustainable agroecosystems This challenge is particularly great in many developing countries where the crop residues are so important as a source of animal feed and fuel for cooking Whenever feasible, it is best to let animals graze the crop residues so the manure will be distributed over the area When it is necessary to utilize the crop residues as animal feed away from the land, every attempt should be made to return manure to the land whenever feasible Otherwise, the soil organic matter level will continue to decline to the point that long-term sustainability of the soil resource base will be threatened Robinson er al (1996) reported that the maintenance or enhancement of soil organic matter is proportional to the amounts of residues returned Maintenance of soil organic matter is important to maintain yield potential (Bauer and Black, 1994) MI SUMMARY Achieving sustainable agroecosystems is the challenge of the coming century With increasing population and improved living standards, the demand for food and fiber will force the development of agroecosystems into less favorable regions There is often an imbalance between natural resources, population, and basic human needs in many regions and this is often particularly true for semiarid regions AGROECOSYSTEMS SUSTAINABLE IN SEMIARID REGIONS? 225 Agroecosystems in these areas can be developed and sustained, but careful management is required The prevention of soil degradation is the first and most important issue that must be addressed in such areas Soil degradation is a complex phenomenon It is driven by strong interaction among socioeconomic and biophysical factors It is fueled by increasing population, fragile economies, and poorly designed farm policies, and propelled by the fragility of the soil and harshness of the climate Soil degradation can be subtle and slow until a certain threshold is reached, and then deterioration can occur quickly and, sometimes, irreversibly Soil organic matter is significantly correlated with soil productivity Maintaining soil organic matter, therefore, is of critical importance This is a tremendous challenge in semiarid regions because insufficient precipitation seriously limits carbon inputs and the often warm conditions accelerate the decomposition of native soil organic matter during periods of favorable soil water conditions Extensive tillage generally increases the rate of decomposition There exists a considerable body of research knowledge and producer experiences This information is sufficient in most cases to develop sustainable agroecosystems.The biggest challenge, however, is the implementation and execution of sound management plans Sustainable systems must focus on long-term goals, but the reality is that short-term benefits and solutions almost always take precedence over long-term issues Historically, agroecosystems have been developed for short-term benefits without a thorough analysis of what long-term consequences would result Scientists, producers, policymakers, and governments must work together very closely in the future to meet the challenge of sustaining the natural resource base while producing adequate amounts of food and fiber REFERENCES Allison, F E (1973) “Soil Organic Matter and Its Role in Crop Production.” Developments Soil Science Elsevier Amsterdam, The Netherlands Bauer, A,, and Black, A L (1994) Quantification of the effect of soil organic matter content on soil productivity Soil Sci Soc Am J 58, 185-193 Brown, L R (1995).Nature’s limits In “State of the World,” pp 3-20 Norton, New York Brown, L R., and Postel, S (1987).Thresholds of change In “State of the World,” pp 1-19 Norton, New York Cook, R L (1962) “Soil Management for Conservation and Production.” Wiley, New York Cornish, P S., and Pratley, J E (1991) Tillage practices in sustainable farming systems In “Dryland Farming-A Systems 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(1981) “Soil and Water Resources: Research Priorities for the Nation,” pp 229 Soil Science Society of America, Madison, WI Lun, S., Zhongmin, L., Xiping, D., and Yequan, X (1992) Field water balance under the different crop rotations patterns in the Loess Plateau, China In “Conservation Tillage Practices for Grain Farming in Semiarid Regions,” Proceedings International Symposium, July 7-9, (1992) Shortandy, Kazakhstan CIS Mageed, Y.A ( 1986) “Anti-Desertification Technology and Management.” United Nations Environment Programme, Nairobi, Kenya Musick, J T., and Dusek, D A (1971) Grain sorghum response to number, timing, and size of irrigations in the Southern High Plains Trans Am SOC.Agric Eng 14,401404 Musick, J T., and Porter, K B (1990) Wheat In “Irrigation of Agricultural Crops” (B A Stewart and D R Nielsen Eds.), pp 598-888 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Madison, WI Musick, T., Jones, R., Stewart, B A,, and Dusek D A (1994) Water-yield relationships for irrigated and dryland wheat in the U.S Southern Plains Agron J 86,980-986 National Research Council (1993) “Soil and Water Quality: An Agenda for Agriculture.” National Academy Press Washington, DC Newcombe, K (1984) An economic justification for rural afforestation: The case for Ethiopia Energy Depr Paper No 16 World Bank, Washington, DC AGROECOSYSTEMS SUSTAINABLE IN SEMIARID REGIONS? 227 O’Connell P F (1991) Sustainable agriculture In “Agriculture and the Environment The (1991 Yearbook of Agriculture,” pp 175-185 USDA, Washington, DC Pierce, J J., Larson, W E., Dowdy, R H., Graham, W A P (1983) Productivity of soils: Assessing long-term changes due to erosion J Soil Water Consen! , Pieri, C (1995) Long-term soil management experiments in semiarid Francophone Africa In “Soil Management: Experimental Basis for Sustainability and Environmental Quality” (R La1 and B A Stewart, Eds.), pp 225-266 CRC Press, Boca Raton, FL Quimby, J R., Kramer, N W., Stephens, J C., Lahr, K A., and Karper, R E (1958) Grain sorghum production in Texas Texas Agric Exp Stn Bull 912 Texas Agric Exp Stn., College Station Rangely, W R ( I 985) Irrigation and drainage in the world In “Proceedings, Water and Water Policy in World Food Supplies” (W R Jordan, Ed.), pp 29-35 Texas A&M Univ., College Station Robinson, C A., Cruse, R M., and Kohler, K A (1994) Soil management In “Sustainable Agriculture Systems” (1 L Hatfield and D L Karlen, Eds.), pp 109-134 Lewis, Boca Raton, FL Robinson, C A,, Cruse, R M., and Ghaffarzadeh, M (1996) Cropping system and nitrogen effects on mollisol organic carbon Soil Sci Soc Am J 60, 264-269 Rodale, R (1988) Agricultural systems: The importance of sustainability Phi Kappa Phi J 2.6 Ruttan, V W (1989 Spring) Sustainability is not enough Better Crops Plant Food, 6-9 Sharma, M L., and Williamson, D R (1984) Secondary salinization of water resources in Southern Australia In “Salinity in Watercourses and Reservoirs” (R H French, Ed.), pp 571-582 Butterworth, Boston Shengxiu, L., and Ling, X.(1992) Distribution and management of drylands in the People’s Republic of China Adv Soil Sci.%RR 18, 148-302 Siming, H., Chungfeng, Y., Juntong, S., and Huancheng, P (1988) Stubble mulching in dryland on the Loess Plateau in China Agric Res Arid Areas 3, 1-12 Souleimenov, M K (1992) Development of soil conservation farming practices for steppe areas of northern Kazakhstan In “Conservation Tillage Practices for Grain Fanning in Semiarid Regions,” Proceeding International Symposium, July 7-9, (1992) Shortandy, Kazakhstan, CIS Squires, V R ( 199I ) A systems approach to agriculture In “Dryland Fanning-A Systems Approach” (V Squires and P Tow, Eds.), pp 3-15 Sydney Univ Press, South Melbourne, Australia Stewart, B A (1989) Dryland fanning: The North American experience p 54-59 In “Challenges in Dryland Agriculture: AGlobal Perspective” (P W Unger, T V Sneed, W R Jordan, and R Jensen, Eds.), pp 54-59 Proceeding International Conference Dryland Fanning, AmarillolBushland, Texas, August 15-19, (1988) Texas Agric Exper Stn., College Station Stewart, B A,, and Burnett, E (1987) Water conservation technology in rainfed and dryland agriculture In “Water and Water Policy in World Food Supplies” (W R Jordan, Ed.), pp 355-359 Proceedings of the Conference, May , (1985) Texas A&M Univ., College Station Stewart, B A,, and Steiner, J L (1990) Water-use efficiency Adv SoilSci 13, 151-173 Stewart, B A,, Musick, J T., and Dusek, D A (1983) Yield and water-use efficiency of grain sorghum in a limited irrigation-dryland system Agron J 75,629-634 Stewart, B A,, Lal, R., and El-Swaify, S A (1991) Sustaining the resource base of an expanding world agriculture In “Soil Management for Sustainability” (R La1 and F J Pierce Eds.), pp 125-144 Soil and Water Conservation Society, Ankeny, IA Stewart, B A,, Jones, R., and Unger, P W (1993) Moisture management in semiarid temperate regions p 67-80 In “Agriculture and Environmental Challenges” (J P Srivastava and H Alderman, Eds.), Proceedings of the 13th Agricultural Sector Symposium The World Bank, Washington, DC Stewart, B A,, Zixi, Z., and Jones, R (1994) Optimizing rainwater use In “Stressed Ecosystems and Sustainable Agriculture” (S M Virmani, J C Katyal, H Eswaran, and I P Abrol, Eds.), pp 253-265 Oxford & IBH, New Delhi, India Technical Advisory Committee (1990) “Towards a Review of CGIAR Priorities and Strategies.” Technical Advisory Committee Secretariat, Rome 228 B A STEWART AND C A ROBINSON Tow, P G and Schultz, J E (1991) Crop and croppasture sequences In “Dryland Fanning-A Systems Approach” (V Squires and P Tow, Eds.), pp 55-75 Sydney Univ Press, South Melbourne, Australia United Nations Educational, Scientific and Cultural Organization (UNESCO) (1977) “World Map of Desertification,” NConf 74/2 Food and Agricultural Organization, United Nations, Rome United States Department of Agriculture, Agricultural Research Service (USDA-ARS) ( 1990) EPIC-Erosioflroductivity Impact Calculator Tech Bull 1768 USDA-ARS, Washington, DC Unger, P.W (1978) Straw-mulch rate effect on soil water storage and sorghum yield Soil Sci Soc Am J , I World Bank (1986) “The World Bank Atlas.” World Bank, Washington, DC World Bank (1992) “World Bank Development Report.” World Bank, Washington, DC Zixi, Z., Stewart, B A., and Xiandun, F (1994) Double cropping wheat and corn in a sub-humid region of China Field Crops Res 36,175-183 Index A Activity reports, 186 Administrators, evaluating, 188 Agricultural research, see Ethics Agricultural themes, ethical dimensions, 155 Agriculture, sustainable, see Sustainability Agroecosystems, 191-225 climatic effect, 201-202 increasing plant-available water, 205-223 crop calendars, 19-223 lengthening fallow period, 206-213 mulches, 13-2 I7 tillage, 217-219 productivity, 193 socioeconomic effect 203-205 soil degradative processes, 200-201 soil effect, 202-204 soil organic matter maintenance, 223-224 stability, 194 sustainability 194 Alfalfa salt tolerance, 95 Animakrop mix, changing, 62 Animal feeds, promoting more efficient use of nutrients, 62 Animal products, reducing consumption, 62-63 Animals ethical treatment in research, 177-179 integrating into cropping system, 64 waste management, 53 Aridity index, 195 Authorship, ethics, I73 Avocado, salt tolerance, 100- I0 I B Bacteria, nutrient uptake stimulation, 19 Bermuda grasses, salt tolerance, 95 Berries, genetic variability and salt tolerance, 98-101 Boundaries, nutrient flows and cycles, 8-9 C Canola, salt tolerance, 92 Carbon, decomposition dynamics, 123, 127 Chinampas, 61 Chloride, toxicity in woody species, 98-101 Citrus, salt tolerance, 100 Clover introduction in Europe, 49 salt tolerance, 95 Commerce, ethics codes, 161 Communication, honest, with constituents, 189-190 Competition, ethics and, 179-180 Composting, low-input, on-farm, 141-144 Conflicts of interest, research ethics, 174-175 Consulting, ethics, 184 Copyright, infringement, 176 Corn relation of yield and growing season evapotranspiration, 222 salt tolerance, 90 Costs, indirect, recovery, ethics, 171-173 Cotton, salt tolerance, 91 Cover crops, 35-36 minimizing leaching losses, 59 Credibility, establishing and maintaining, researchers, 168-169 Cropping double, 221-222 pattern, matching with climate, 22G221 Crop residue burning, 141 chemical composition, 122 decomposition, modeling, 125-129 expert systems and erosion models 126 RESMAN, theory in, 126-129 as nutrient cycling, 32-33 soil protection by, 122 surface managed, decomposition, 122-125 Crops calendars, plant-available water and, 219-223 229 230 INDEX Crops (conrinued) management, practices and soil ecology, 20-2 mix, changing, 62 rotation, 34-35 substitution as method of dealing with salinity, 76 D Data analysis, ethics, 167-168 collecting and reporting, ethics, 167 Decomposition crop residue, modeling, 125-129 surface-managed crop residues, 122-125 Desertification, 204 Dust mulch 212 E Ecosystem relations, 9-12 Energy, use and nutrient flows, 50-52 Environmental factor, residue decomposition, 127 Environmental stresses, interactions with salinity, 84 Ethical behavior, practical principles, 152-1 54 Ethical codes, as rules, 160 Ethical disputes, resolving, 156-157 Ethics, 149-1 90 choosing research subject matter, 154157 dimensions of agricultural themes, 155 resolving ethical disputes, 156-157 science paradigm criticism, 156 sustainable agriculture, 154-155 in conduct of research, 165- I84 authorship and shared recognition, 173 collecting and reporting data, 167 competition, 179-180 conflicts of interest, 174-175 consulting, 184 data analysis, 167-168 designing experiments, 166-167 drawing and reporting inferences, 168 establishing and maintaining credibility, 168- 169 ethical treatment of animals, 177-179 indirect cost recovery, 171-173 intellectual property rights, 175-177 peer review, 173 performing to specifications, 180 proposal budgets, 17I proposal preparation, 169-170 technology transfer, 180-183 topic selection, 166 whistle-blowing, 173-174 definitions, 151 difficultieswith utilitarian approach, 158-162 abiding by rules, 162 difficulty in evaluating outcomes, 158 ethics codes as rules, 160-162 evaluation of principles, 159-160 sea of uncertainty, 158-159 personal and group, 151-152 research administration, 184-190 activity reports, 186 equity and merit, 189 evaluating administratorsand managers, 188 hiring and termination, 184-185 honest communication with constituents, 189-1 90 job applications, 188 letters of recommendation,support, and evaluation, 186- I87 nurturing scientists, 185-186 promotion documents and decisions, 187 scientific misconduct, 152 world food situation and, 162-165 driving forces, 162-164 message for agronomists, 165 moot questions, 164-165 sources of research support, 165 Experiments designing, ethics, 166167 drawing and reporting inferences, 168 Expert system, residue decomposition models, 126 F Fairness, 153, 189 Fallow period efficiency and tillage, 218 lengthening, 206-2 13 mulch and plant-availablewater, 214-217 Fertilizers overuse, 2-3 utilizing more efficiently, 60 23 INDEX Field crops, genetic variability and salt tolerance, 1-92 Field screening techniques, salt tolerance, 103 Flow nutrients, nearby, agricultural use, 61 Food, consuming local produce, 64 Forages, genetic variability and salt tolerance, 94-95 Fruits, genetic variability and salt tolerance, 98-101 Fungi, nutrient uptake stimulation, 19 G Genes, salt tolerance, 101-102 Geologic deposits, nutrient dynamics, 50 Grains, genetic variability and salt tolerance, 88-91 Grasses, genetic variability and salt tolerance, 94-95 H Harvest, nutrient loss, 24-26 Heritability, salt tolerance, 103 Hiring, ethical, 184-185 Honesty, 152-153 Human waste, land application, 53 I Immobilization, inorganic nutrients, 18-19 Inorganic nutrients, immobilization, 18-19 Integrity, 153 Intellectual property rights, ethics and, 175-177 Ion accumulation, salt tolerance and, 86 selectivity, salt tolerance and, 85-86 Irrigation, increasing salinity of lands and, 76 J Job applications I88 K Kentucky bluegrasses, salt tolerance, 95 L Land, increased yield, 192 Letters of recommendation, support, and evaluation, 186-187 Lettuce, salt tolerance, 98 Linseed, salt tolerance, 93 M Managers, evaluating, 188 Manure nutrient flow, 40 utilizing more efficiently, 60 Melon, salt tolerance, 97-98 Merit, rewarding, equity and, 189 Military, ethics codes, 161-162 Mineralization, 14-15 soil organic matter, 18 Modeling, salt tolerance, 107 Molecular biology, salt tolerance, 106-107 Mulches, increasing plant-available water, 21 3-2 I7 N Nitrate leaching, 26.42 Nitrogen decomposition dynamics, 123, 127 fixation, 19 by symbiotic and nonsymbiotic organisms, 6M1 recommendations, 30-3 Nondisclosure agreements, 177 No-till cropping systems, 121-144 deleterious rhizobacteria for weed control, 137-141 domination by fungi and earthworms, 136 low-input, on-farm composting, 141-144 root-microbial relationships, 129-1 37 Nutrient cycle, crop residues, 32-33 ecology, 17-2 efficiency, 9-10 plant strategies, 10 simplified managed system, 10-1 simplified natural system, 9-10 Nutrient dynamics, 1-66: see also Soil-plant system definitions, 7-9 232 INDEX Nutrient dynamics (continued) energy use and nutrient flows, 50-52 farm-level changes, 60-62 farm-scale cycling and Rows, to and from farms, 4 between farms, 43-44 nutrient exports > imports, 44-46 nutrient exports < imports, 46 nutrient exports = imports, 46-47 within-farm, at field level, 23-38 changes in nutrient, 36-37 changing to biologically based nutrient sources, 37-38 cover crops, 35-36 crop residues, 32-33 crop rotation, 34-35 inadvertent nutrient losses, 26-27 nutrient additions, 27-3 nutrient losses, 24-27 pastures, 35 tillage systems, 33-34 field-level changes, 58-60 finite geologic deposits, 50 harvest removal, 24-26 historical overview, 5-7 increasing soil nutrient availability, influences on flow patterns, 54-56 intercontinental flows, 49-50 landscape position, 12-13 possible changes in large-scale flows, 52-54 seasonal patterns, 12-1 societal-level changes, spatial cycle and ecosystem relations, 9-12 spatial scale of changes and time needed to complete, 57-58 utilizing fertilizers and manures more efficiently, 60 utilizing more efficiently taken up nutrient sources, 60-6 I watersheds, Nutrient flow, ecology, 17-2 field, changes in, patterns, potential implications, 44-45 Nutrient leaks, 62-63 Nutrients added, quantity, 29-3 I application timing and methods, 28-29 balances, mixed crop and livestock farm, MI degree of synchronization between availability and uptake needs, 58-59 enhancing uptake efficiency, 58-59 management issues, 2-4 sources biologically based, 37-38 soluble, sparing use, 61 transformations, ecology, 17-2 I transporting back to farmland, 64-65 Nuts, genetic variability and salt tolerance, 98-101 Oil seed crops, genetic variability and salt tolerance, 92-93 Organic matter maintenance, semiarid regions, 223-224 semiarid regions, 21 Ornamentals, genetic variability and salt tolerance, 101 Osmotic adjustment, salt tolerance and, 87 P Pastures, 35 Patent, infringement, 176 Peer review, ethics, 173 Performing to specifications, I80 Phosphorus, solubility, 19 Plant-animal-human trophic pyramid, segment separation, Plant nutrition, 13-17 Potato, salt tolerance, 92 Practices advocating, 182-183 testing and comparing, 181-182 Products advocating, 182-1 83 testing and comparing, 18 1-1 82 Promotion, documents and decisions, 187 Proposals budgets, ethics and, 17 preparing, ethics and, 169-1 70 R Research, see Ethics RESMAN, theory used in, 126-129 Rhizobacteria, deleterious, 129-1 32 weed control, 137-141 INDEX Rice, salt tolerance, 90-91 Root environment, optimizing, 59 Root-microbial relationships, 128-1 37 deleterious rhizobacteria, 129-132 root zone temperature and, 133 Ruminant livestock, biological nitrogen fixation, 4041 S Safflower, salt tolerance, 92-93 Salinity problems, semiarid regions, 212 Salt, accumulation, 86 Salt stress, short- and long-term effects, 85 Salt tolerance, 75-108 breeding methods, 101-105 field screening techniques, 103 genes for tolerance, 101- 102 heritability, 103 selection methods 104-105 crop species, 77 genetic variability, 88-101 field crops, 91-92 fruit, nuts, and berries, 98-101 grains, 88-9 I grasses and forages, 94-95 oil seed crops 92-93 ornamentals, 101 vegetable crops, 95-98 in low-yielding varieties, 81 measurement, 79-80 mechanisms, 84-88 ion accumulation, 86 ion selectivity,85-86 organic solutes, 87 osmotic adjustment, 87 water use efficiency 87-88 modeling, 107 molecular biology, 106-107 rationale for breeding for, 77-78 selection for 78-84 environmentalinteractions, 84 growth stage, 82-83 specific ion tolerance, 83-84 yield and productivity, 80-82 tissue cultures, 105-106 Science, pure, ethics codes, 161 Science paradigm criticism, 156 Scientific misconduct, 152 Scientists, nurturing 185-1 86 233 Seasonal patterns, nutrient dynamics, 12-13 Selection methods, salt tolerance, 104-105 Semiarid regions, 194-198 aridity index, 195 characterization, 192 example locations, 196-198 length of growing period, 195-196 soil organic matter maintenance, 223-224 Soil chemical properties, 21 degradation, interdependenceon biological and socioeconomicfactors, 203, 205 effect on sustainability,202-204 erosion, 26 fertility, maintaining long-term, 15-17 management, practices and soil ecology, 20-2 nutrients, increasing availability,5 nutrient stocks, 13-17 organic matter depletion, dynamics, 17 maintaining high levels, 15-16 mineralization, 18 physical properties, 1-22 Soil-plant system, 13-23 biological, chemical, and physical interactions, 22-23 ecology of nutrient flows, transformations, and cycles, 17-21 maintaining long-term soil fertility, 15-1 satisfying short-term fertility needs, 14-15 simplified nutrient cycle, flows, and transformations, 14 Soil resources, wasteful use, 62 Solutes, organic, salt tolerance and, 87 Sorghum relation of yield and seasonal evapotranspiration, 208 salt tolerance, 90 Soybean, salt tolerance, 92 Spacial scale, 9-12 Stocks, 7-8 Straw mulch, 215-216 Stubble mulching, 213-215 Sugar beet, salt tolerance, 91-92 Summer fallow, 206.21 1-213 Sunflower, salt tolerance, 93 Sustainability,4, 56-57, 194, 198-205 climatic effect, 201-202 34 INDEX Sustainability (conrinued) definition, 198 ethics and, 154-155 reasons for importance in policy agenda, 199 socioeconomic effect, 203-205 soil effect, 202-203 T Technology transfer, ethical issues, 180-1 83 Technology transfer agents, responsibility, 181 , Temperature function, residue decomposition, 128 Termination, of employees, 185 Tillage, plant-available water and, 217-219 Tillage systems, 33-34 Tissue cultures, salt tolerance, 105-106 Tomato, salt tolerance, 97 Trade secrets, ethics and, 176177 Transformations, Trophic pyramid, V Vegetable crops, genetic variability and salt tolerance, 95-98 W Water, plant-available, technologies for increasing, 205-225 crop calendars, 19-223 lengthening fallow period, 206-213 mulches, 13-2 17 tillage, 217-219 Water function, 127 Watersheds, nutrient dynamics, 47-48 Water use, efficiency and salt tolerance, 87-88 Weed control, deleterious rhizobacteria, 137-14 Wheat relation of yield and growing season evapotranspiration, 222 relation of yield to seasonal evapotranspiration, 208-210 salt tolerance, 89-90, 102 Wheatgrass, salt tolerance, 94 Whistle-blowing, ethics, 173-174 Winter wheat deleterious rhizobacteria effect, 129-132 high crown set, 141-142 rhizoplane populations of inhibitory pseudomonads, 134-1 35 yield from fields inoculated with rhizobacteria, 138 World food, ethics and, 162-165 This Page Intentionally Left Blank ... stock of individual nutrients cannot go on indefinitely because the supply of potentially available nutrients is finite Maintaining Long-Term Soil Fertility at the Soil-Plant Level Maintaining soil... losses There are three stocks of nutrients (boxed in Fig 2): in the soil (including all living organisms), in living plants above ground; and in aboveground animals Nutrients are taken up from... soils coincide with the warming in the spring and are probably significantly enhanced by freezing and thawing over the winter (Magdoff, 1991a; DeLuca et al., 1992) When soils dry down during the