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VIII. Maintenance of Genetic Stability during Seed Multiplication

VIII. Maintenance of Genetic Stability during Seed Multiplication

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RED CLOVER BREEDING AND GENETICS



149



Causal factors involved in genetic shifts are not completely understood. Apparently, a shift toward earliness and winter susceptibility occurs with increases

at southern locations (Bula et al., 1965, 1969). According to Taylor et al.

(1966), early-flowering genotypes, particularly at southern locations, produce

the most seed, shifting the cultivar toward an earlier type. Earliness and lack of

persistence have been shown to be related (Taylor et al., 1966). Other factors,

such as lack of attention to land history, volunteer seedlings, lack of isolation,

and seed mixtures in harvesting and seed-cleaning equipment, cannot be ruled

out. Differential survival of genotypes due to diseases in diverse environments

also is a factor, particularly in old stands.

Prevention of genetic shifts is important because of the necessity of continuing

seed production in high producing areas. Steps that have been taken to prevent or

minimize shifts include:

(1) Limiting the number of generations of seed increase (example,

KENSTAR).

(2) Restricting the area of seed increase to more northern locations (example,

KENSTAR).

(3) Clipping the first growth to allow more equal flowering of genotypes. This

practice reduces seed yield in the western United States (Dade, 1966; Rincker et

al., 1977) but is a prevalent practice in the forage-producing area of the eastern

United States (Taylor et al., 1966).

(4) Preventing seed production on first-year stands (Example, KENSTAR).

Some evidence indicates that differences in seed production exist between stands

that have or have not been subjected to freezing (Bula et al., 1965, 1969).

(5) Restriction to less heterogeneous cultivars (Example, TEPA vs. ALASKALAND, Dovrat and Waldman, 1966). Apparently, the less diverse cultivars

are less subject to changes in population structure.

(6) Strict adherence to AOSCA certification requirements, consisting in land

history, isolation, control of volunteering, and seed mixtures.



In summary, most investigations, while indicating the possibility of genetic

shifts in red clover cultivars, also suggest means of limiting shifts. It appears

likely that seed increases can be continued outside the area of forage adaptation

without serious loss of desirable agronomic characteristics.

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ADVANCES IN AGRONOMY, VOL. 31



THE AVAILABILITY OF NUTRIENTS IN THE SOIL AS

DETERMINED BY ELECTRO-ULTRAFILTRATION (EUF)

K. Nbmeth

Bhntehof Agricultural Research Station, Hannover, Federal Republic of Germany



1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

II. Problems of Conventional Soil Testing Practice ...............................

III. Electro-ultrafiltration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A. Component Processes of Electro-ultrafiltration .

....

B. Electro-ultrafiltration with Varying Voltage and Temperature during the Extraction

process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .



C. Interpretation of EUF Results for Plant Nutrition

IV. The EUF Values Required for Optimal Plant Nutritio

.............

A. The EUF-K and EUF-P Values

B . Calculation of Physiological Lime Requirement ............................

V. Conclusions for Practical Soil Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References . . . . . .

........................................



I55

156

158

158

160



183

185



1. Introduction



In a fertile soil, it is understood that the most important plant nutrients (including water and air) are effectively available in the course of the vegetation period.

The practical farmer needs to know the amount of effective available nutrients in

his soil before the crop is grown so that he can adapt his fertilizer measures

accordingly.

Methods of soil analysis should be simple to apply, rapid, and cheap. For this

reason, attempts have been made to determine the soil nutrients chemically by

single extractions (for example, NH, acetate for potassium) affording speed and

simple operation. With these rapid methods (Bray, 1937; Egner et al., 1%0; Olsen

et al., 1954, etc.) it was possible even a few decades ago to single out nutrientdeficient soils for corrective application of fertilizer to obtain higher yields. The

nutrient contents of most agricultural soils are higher today than they were a

decade ago. Also, high yields are necessary for farming to be economic and to

raise world food production. These yields are possible because of the genetic

potential of modem cultivated plants. A more detailed evaluation of the status of

nutrients in the soil by a more precise method is required, therefore, to ascertain

the reliability of fertilizer recommendations. After numerous tests, the electroultrafiltration (EUF) method with varying voltage and temperature presented here

appears especially suitable to characterize the nutrient status of a soil comprehensively.

155

Copyright @ 1979 by AEadcrnic Rcss. Inc.

All rights of npmductim in MY form rrsemd.

ISBN 0.12-000731-2



156



K . NEMETH



11. Problems of Conventional Soil Testing Practice



In soil analysis, only methods that can well define the amount of effectively

available nutrients are suitable for the determination of the fertilizer requirements

of a plant. Which nutrients are efectively available? Certainly those nutrients are

effectively available that are present in the soil solution in a dissolved ionic form,

as illustrated in Fig. 1. This figure shows a root hair, the soil solution with

dissolved ions, and a clay mineral with adsorbed ions. The ions of the soil

solution are moving permanently (in a thermal motion). The principle is, therefore, easy to understand: The more ions that are present in the soil solution-that

is, the higher the concentration-the more ions can reach the plant roots per unit

of time by diffusion and mass flow, and consequently the more ions can be taken

up by the plant (Barber, 1962; Barber et al., 1963; Rowel1 et a / . , 1967; Mengel

et a f . , 1969; Fox and Kamprath, 1970; Grimme et al., 1971; Nemeth, 1975).

The mineral lattice ions are also available, but somewhat less readily. They

must first go into the soil solution by diffusion from the interlattice sites of the

clay minerals. The mobility of ions in soil-for instance, of K-may be meacm2/sec

sured by their diffusion coefficient, which ranges from less than

for interlayer K in unexpanded illite, to approximately

cm*/sec for K in a

dry soil and lop6cm2/sec in a moist one (Nye, 1972). The mobility of nutrients

as mineral lattice ions is thus so low that the life span of the root hairs is often not

long enough for these ions to arrive in time. Nutrients that cannot go into the soil

solution in the course of the vegetation period by desor$ion or solution processes

are, therefore, only potentially available. This is what makes soil analysis so



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Soil solutiorr

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FIG. 1.



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Schematic representation of root hair, soil solution, and soluble and sorbed ions



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