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V. Current New Directions in Germplasm Management and Research
NEW DIRECTIONS IN PLANT GENETIC RESOURCES
storage-can be a useful tool so that a manageable set of accessions can be
worked on. The core should be a representative assembly based on ecogeographic origin and specific characteristics (Frankel and Brown, 1984;
The selection of core collections should not be seen simply as developing a workable subset out of large collections, thereby negating the
necessity of other aspects of management such as sorting out redundance
and excessive duplication within and between collections (Perret, 1989). It
can also be a useful management tool combined with better use of collections (Peeters and Williams, 1984; Williams, 1989).
Most crops can be conserved as seed in seed storage gene banks;
however, running such facilities can be costly. Hence, two areas of
strategic research need to be pursued. First, a more cost-effective storage
should be explored, for example, reducing seed moisture content and
relaxing the degree of refrigeration, and storage using natural phenomena
(e.g., permafrost). Second, the biggest use of seed of stored samples is in
routine viability testing, and alternative nondestructive methods are
For conservation of other crops, other methods are needed. The conceptual framework for in uitro genebanks is well established but a great
deal of research is needed before they can be implemented for more than a
few crops (such as cassava, potato, apple, and pears). The past decade has
seen the sorting out of principles (Withers and Williams, 1982, 1985) and
the establishment of linkages to other genetic resources activities (Withers, 1989).
Other sections of this article have pointed to the practical difficulties of
managing collections of wild species and linking seed and in uitro conservation to materials conserved in situ.
There has been much written about ex situ genetic resources work being
justified by its applications and the need for better use of the materials
conserved. In part this represents a misunderstanding of the methods
currently used by breeders, whereby they tend, in the first instance, to use
breeding materials with which they are familiar and which cause the fewest
problems. Additionally the existing coliections need a great deal of “sort-
J. T. WILLIAMS
ing out” and many more relevant characterizations and evaluation data
generated. This is a lengthy and costly exercise (Williams, 1989).
Germplasm collections are essential for much applied research at the
molecular level, including genome mapping and studies of biodiversity.
There are exciting challenges that will increase the utility of the collection
for highly bred crops and rapidly enhance others that have not received a
great deal of breeding attention. The dialogue between scientists involved
with applied research and those with genetic resources will be a continuing
VI. CONCLUDING REMARKS
The groundwork has been laid for a “system” to make genetic resources
available and to conserve them for the future. In any system, embracing so
many countries, institutions, and plant diversity, efficiency can certainly
be increased by upgrading scientific standards and skills of those scientists
involved. Many programs have started on the basis of good intentions but
there is a duty to see that today’s poorly prepared partners are not tomorrow’s marginal workers. The future of a global heritage depends on the
skills and productivity of the emerging work force to run an increasingly
sophisticated system. The needs for rapid transfer of new technology and
the forging of new partnerships is apparent from this article and this
requires a new vision involving agronomists as well as breeders and research scientists.
Against this vision stands a sobering reality: It is impossible to conserve
everything, and only a small part of the system can be user-driven by
breeders and others. The user-driven sector has been very successful in
relation to staple crop gene pools; however, the need to preserve minor
crops with a back-up in nature conservation is not user-driven. Additionally, the funding for crop genetic resources work has not grown to
match even the needs of the 1980s, and estimates of funding are largely
unchanged (Plucknett et al., 1987). One reason for this is that these funds
are largely for development assistance. Trends in funding of relevant
scientific research are worrisome since they have been transferred in many
cases to molecular work. However, the future for plant genetic resources
work is bright if the funding for scientific research can be targeted in a
strategic way so that the development assistance part has a solid back-up
of research and development. This, I believe, is the challenge for the 1990s
and requires vision and new noncompetitive partnerships between agriculture, science, and wider conservation interests.
NEW DIRECTIONS IN PLANT GENETIC RESOURCES
Balick, M. J. 1989. In “New Crops for Food and Industry”(G. E. Wickens, N. Haq, and P.
Day, eds.), pp. 323-332. Chapman & Hall, London.
Bramwell, D., Hamann, O., Heywood, V., and Synge, H., eds. 1987. “Botanic Gardens and
the World Conservation Strategy.”Academic Press, London.
Brewkaker, J. L., and Hutton, E . M. 1979. In ”New Agricultural Crops” ( G . A. Ritchie, ed.),
pp. 207-259. Westview Press, Boulder, Colorado.
Brown, A. H . D. 1989. In “The Use of Plant Genetic Resources” (A. H. D. Brown, 0. H .
Frankel, D. R. Marshall, and J. T. Williams, eds.), pp., 136-156. Cambridge Univ.
Press, Cambridge, England.
Burley, J., and von Carlowitz, P., eds. 1984. “Multipurpose Tree Germplasm.” ICRAF,
Chang, T. T., Dietz, S. M. N., and Westwood, M. N. 1989. In “Biotic Diversity and
Germplasm Preservation” (L. Knutson and A. K. Stoner, eds.), pp. 127-159. Kluwer
Academic Publishers, Dortrecht, The Netherlands.
Chapman, C. G. D. 1985. “Genetic Resources of Wheat: A Survey and Strategy for Collecting.” IBPGR, Rome.
Chapman, C. G. D. 1989. In “The Use of Plant Genetic Resources” (A. H. D. Brown, 0. H.
Frankel, D. R. Marshall, and J. T. Williams, eds.), pp. 263-279. Cambridge Univ. Press,
Clement, C. R., and Arkcoll, D. B. 1989. In “New Crops for Food and Industry’YG. E.
Wickens, N. Haq, and P. Day, eds.), pp. 306-332. Chapman & Hall, London.
Duvick, D. N., and Brown, W. L. 1989. In “Biotic Diversity and Germplasm Preservation”
(L. Knutson, and A.K. Stoner, eds.), pp. 499-513. Kluwer Academic Publishers, Dordrecht, The Netherlands.
Felker, P. 1979. In “New Agricultural Crops” (G. A. Ritchie, ed.), pp. 89-132. Westview
Press, Boulder, Colorado.
Frankel, 0. H. 1983. In “Conservation of Tropical Plant Resources” (S. K. Jain, and K. L .
Mehra, eds.), pp. 55-65. Botanical Survey of India, Howrah.
Frankel, 0. H. 1985. In “Proceedings of the International Symposium on South East Asian
Plant Genetic Resources” (K. L. Mehra, and S., Sastrapradja, eds.), pp. 26-31. LIPI,
Frankel, 0. H., and Brown, A. H. D. 1984. In “Crop Genetic Resources: Conservation and
Evaluation” ( J . H. W. Holden and J. T. Williams, eds.), pp. 249-257. Allen & Unwin,
Frankel, 0. H., and Soule, M. E . 1981. “Conservation and Evolution.” Cambridge Univ.
Press, Cambridge, England.
Harlan, J. R. 1975. J . Hered. 66, 184-191.
Hazell, P. B. R., ed. 1986. “Summary Proceedings of a Workshop on Cereal Yield Variability.” IFPRI, Washington, D. C.
Holden, J. H. 1986. In “Summary Proceedings of a Workshop on Cereal Yield Variability”
(P. B. R. Hazell, ed.), pp. 71-76. IFPRI, Washington, D. C.
Ingrarn, G. B., and Williams, J. T. 1984. In “Crop Genetic Resources: Conservation and
Evaluation” (J. H . W. Holden and J. T. Williams, eds.), pp. 163-179. Allen & Unwin,
International Board for Plant Genetic Resources (IBPGR). 1986. “Genetic Resources of
Tropical and Sub-tropical Fruits and Nuts (Excluding Musa).” IBPGR, Rome.
International Board for Plant Genetic Resources (IBPGR). 1988. “Annual Report for 1987.”
J. T. WILLIAMS
International Institute of Tropical Agriculture (IITA). 1988. “The Use of Biotechnology for
the Improvement of Cassava, Yams and Plantain in Africa,” IITA Meet. Rep., Ser.
1988/2, IITA, Ibadan, Nigeria.
Jensen, C. J. 1981. I n “Genetic Engineeringfor Crop Improvement” (K. 0. Rachie and J. M.
Lyman, eds.), pp. 87-104. Rockefeller Foundation, New York.
Konopka, J., and Hanson, J., eds. 1985. “Information Handling Systems for Genebank
Management.” IBPGR, Rome.
Larkin, P. J., and Scowcroft, W. R. 1981. Theor. Appl. Genet. 60, 197-214.
Lugo, A. E., Clark, J. R., and Child, R. D. 1987. “Ecological Development in the Humid
Tropics. Guidelines for Planners.” Winrock International Morilton, Arkansas.
Markert, C. L., and Moller, F. 1959. Proc. Natl. Acad. Sci. U.S.A. 45,753-763.
Marshall, D. R. 1989. I n “Plant Population Genetics, Breeding, and Genetic Resources”
(A. H. D. Brown, M. T. Clegg, A. L. Kahler, and B. S. Weir, eds.), pp. 362-388. Sinauer
Assoc., Sunderland, Massachusetts.
McNeeley, J., Miller, K. R., Reid W. V., Mittermeier, R. A., and Werner, T. B. 1990.
“Conserving the World’s Biological Diversity.” IUCN, WRI, CI, WWF-US, World
Bank, Gland, Switzerland.
Nair, P. K. R. 1980. “Agroforestry Species. A Crop Sheets Manual.” ICRAF, Nairobi,
Orton, T. J., and Steidl, R. P. 1980. Theor. Appl. Genet. 57,89-95.
Pateek, 0 . P. 1988. I n “Plant Genetic Resources Indian Perspective” (R. S. Paroda, R. K.
Arora, and K. P. S. Chandel, eds.), pp. 320-334. NBPGR, New Delhi, India.
Peeters, J. P., and Williams, J. T. 1984. Plant Genet. Resour. Newsl. 60,22-32.
Perret, P. M. 1989. I n “The Use of Plant Genetic Resources” (A. H. D. Brown, 0. H.
Frankel, D. R. Marshall, and J. T. Williams, eds.), pp. 157-170. Cambridge Univ. Press,
Pickett, S. T. A., and White, P. S., eds. 1985. “The Ecology of Natural Disturbance and
Patch Dynamics.” Academic Press, San Diego, California.
Plucknett, D. L., Smith, N. J., Williams, J. T., and Anishetty, N. M. 1987. “Gene Banks and
the World’s Food.” Princeton Univ. Press, Princeton, New Jersey.
Prentice, W. E. 1979. Zn “Proceedings of a Workshop on Agro-forestry Systems in Latin
America,” pp. 153-157. UNUKATIE, CATIE, Turrialba, Costa Rica.
Rachie, K. 0. 1983. I n “Plant Research and Agroforestry” (P. A. Huxley, ed.), pp. 103-1 16.
ICRAF, Nairobi, Kenya.
Sastrapradja, S. 1989. In “Biotic Diversity and Germplasm Preservation, Global Imperatives” (L. Knutson and A. K. Stoner, eds.), pp. 63-77. Kluwer Academic Publishers,
Dordrecht, The Netherlands.
Saunders, R. M., and Becker, R. 1989. I n “New Crops; for Food and Industry” (G. E.
Wickens, N. Haq, and P. Day, eds.), pp. 288-302. Chapman & Hall, London.
Scowcroft, W. R. 1985. In “Genetic Flux in Plants” (B. Hohn, and E. S. Dennis, eds.), pp.
217-245. Springer-Verlag, Vienna and New York.
Shankarnarayan, K. A. 1988. I n “Plant Genetic Resources Indian Perspective” (R. S.
Paroda, R. K. Arora, and K. P. Chandel, eds.), pp. 443-456. NBPGR, New Delhi, India.
Shonewald-Cox, C. M., Chambers, S.M., MacBryde, B., and Thomas, W. L. 1983. “Genetics and Conservation: A Reference for Managing Wild Animal and Plant Populations.”
Benjamin Cummings, Menlo Park, California.
Simmonds, N. W. 1979. “Principles of Crop Improvement.” Longman Group, New York.
SoulC, M. E., ed. 1987. “Viable Populations for Conservation.” Cambridge Univ. Press,
SoulC, M. E., and Kohn, K. A., eds. 1989. “Research Priorities for Conservation Biology.”
University of Michigan, Ann Arbor.
NEW DIRECTIONS IN PLANT GENETIC RESOURCES
Tejwani, K. 1988. I n “Multipurpose Tree Species for Small-farm Use” (D. Wilmington,
K. G. MacDicken, C. B. Sastry, and N. R. Adams, eds.), pp. 13-25. Winrock International, USA/IDRC, Canada.
von Carlowitz, P. G . 1989. I n “Multipurpose Trees Selection and Testing for Agroforestry”
(P. A. Huxley, and S. B. Westley, eds.), pp. 31-33. ICRAF, Nairobi, Kenya.
Williams, J. T . 1982. Nature and Resources, UNESCO 18, 14-15.
Williams, J. T . 1985. I n “Genetic Resources: Conservation and Evaluation” (J. H. W.
Holden, and J. T. Williams eds.), pp. 1-17. Allen & Unwin, London.
Williams, J. T. 1985. I n “15 Years Collection and Utilisation of Plant Genetic Resources by
the Institute of Crop Science and Plant Breeding FAL Braunschweig,” pp. 41-48.
Williams, J. T. 1989. In “The Use of Plant Genetic Resources” (A. H. D. Brown, 0. H .
Frankel, D. R. Marshall, and J. T. Williams, eds.), pp. 235-244. Cambridge Univ. Press,
Williams, J. T., and Creech, J. L. 1987. I n “Botanic Gardens and the World Conservation
Strategy” (D. Bramwell, 0. Hamann, V. Heywood, and H. Synge, eds.), pp. 161-173.
Academic Press, London.
Withers, L. A. 1989. In “The Use of Plant Genetic Resources” (A. H. D. Brown, 0. H.
Frankel, D. R. Marshall, and J . T . Williams, eds.), pp. 309-336. Cambridge Univ. Press,
Withers, L. A , , and Williams, J. T., eds. 1982. “Crop Genetic Resources-The Conservation
of Difficult Material.” IUBS/IGF/IBPGR, IUBS, B42, Paris.
Withers, L. A , , and Williams, J. T. 1985. I n “Biotechnology in International Agricultural
Research,” pp. 11-26. Int. Rice Res. Inst., Los Batios, Laguna, Philippines.
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ADVANCES IN AGRONOMY, VOL. 45
LONG-TERM IMPACTS OF TILLAGE,
FERTILIZER, AND CROP RESIDUE
ON SOIL ORGANIC MATTER IN
TEMPERATE SEMIARID REGIONS
Paul E. Rasmussen and Harold P. Collins
U. S. Department of Agriculture
Agricultural Research Service
Columbia Plateau Conservation Research Center
Pendleton, Oregon 97801
A. Beneficial Effects of Organic Matter in Soil
B. Determination of Organic Matter
C. Factors Influencing Soil Organic Matter Content
D. Temperate Semiarid Regions
E. Effects of Cultivation of Grasslands
F. Evaluating Changes in Organic Matter Content and Quality
Tillage Effects on Soil Organic Matter
A. Frequency of Fallow
B. Intensity of Tillage
C. Conservation Tillage
Fertilizer Effects on Soil Organic Matter
B. Phosphorus, Potassium, Sulfur, and Other Nutrients
Organic Residue Effects on Soil Organic Matter
A. Crop Residues
B. Animal Manure
C. Green Manure
Organic Matter and Microbial Biomass
Management Effects on Physical Properties
Cultivation and Future Change in Soil Organic Matter
Impact of Soil Erosion
Predicting Soil Organic Matter Turnover
A. Carbon Pools and Carbon Cycling
B. Models of Soil Organic Matter Turnover
B. Future Needs
Copyright 0 1991 by Academic Press. Inc.
All rights of reproduction in any form reserved.
PAUL E. RASMUSSEN AND HAROLD P. COLLINS
Organic matter in soil has been of concern for decades because it has a
pronounced beneficial effect on soil management and crop productivity
(Allison, 1973). In recent years, soil organic matter has received additional
attention because of its potential to sequester carbon emanating from
atmospheric Cot increases. Organic matter also has a strong influence on
the persistence and degradation of pesticides and organic wastes in soil,
yet full appreciation of this effect remains largely ignored in today’s agricultural sector. Presently, increasing awareness and concern that environmental quality is deteriorating has fostered renewed interest in improving
soil and water management. It is therefore appropriate that we review past
progress towards enhancing the level and quality of organic matter in
Allison (1973) listed the important contributions of organic matter to
soil: (1) it is the major natural source of inorganic nutrients and microbial
energy, (2) it serves as an ion exchange material and a chelating agent to
hold water and nutrients in available form, (3) it promotes soil aggregation
and root development, and (4) it improves water infiltration and water-use
efficiency. A productive soil that is easy to till is identified as having “good
tilth.” An appreciable amount of organic matter is usually a prime prerequisite for good tilth, especially in soils with high sand or clay content. Good
tilth has no defined limits (Karlen et al., 1990), but is readily recognized by
everyone from weekend gardeners to biological scientists.
Most organic matter values are derived from organic carbon (organic C )
values because the quantitative determination of organic matter has high
variability and questionable accuracy (Nelson and Sommers, 1982). A
conversion factor of 1.724 is used to convert organic C to organic matter,
even though it is generally recognized that the value can range from 1.6 to
3.3 (Jackson, 1958; Nelson and Sommers, 1982). Organic C analysis is
reasonably accurate. Values from wet digestion with acid-dichromate and
heat (modified Walkley-Black) correlate fairly well with results from dry
combustion (Tabatabai and Bremner, 1970; Kalembasa and Jenkinson,
1973; Sheldrick, 1986).