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V. Current New Directions in Germplasm Management and Research

V. Current New Directions in Germplasm Management and Research

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NEW DIRECTIONS IN PLANT GENETIC RESOURCES



87



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;

Brown, 1989).

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).



C. SAFETY

OF COLLECTIONS

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

needed.

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.



D. LINKS

TO APPLIED

RESEARCH

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-



88



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

process.



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



89



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Tejwani, K. 1988. I n “Multipurpose Tree Species for Small-farm Use” (D. Wilmington,

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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



I.



11.



111.



IV.



V.

VI .

VII.

VIII.



IX.

X.



Introduction

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

A. Nitrogen

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

Summary

A. Progress

B. Future Needs

References

93

Copyright 0 1991 by Academic Press. Inc.

All rights of reproduction in any form reserved.



94



PAUL E. RASMUSSEN AND HAROLD P. COLLINS



I. INTRODUCTION

A. BENEFICIAL

EFFECTSOF ORGANIC

MATTERIN



SOIL



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

soil.

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.



B. DETERMINATION

OF ORGANIC

MATTER

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).



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