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V. Modifications for Different Applications

V. Modifications for Different Applications

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FIG. 5 . Some modifications of net radiometers. Upper left: The basic Fritschen

net radiometer operated at optimum height (25 cm) above a surface of dry, bare

soil. Note the presence of the strip of white paint on the thermal transducer,

which recent research has proven to be unnecessary. Upper right: An underwater

solarimeter formed by replacing polyethylene domes with glass, painting the lower

dome black, and waterproofing the lead connecter. Lower right: A solarimeter

for terrestrial use made by applying white paint over the blackened lower glass

dome of the upper right instrument and attaching the double-layered shield to

reduce lower dome heating. Lower left: A hemispherical all-wave radiometer made

by applying black, and then white, paint to the outside of the lower dome of

a polyethylene-shielded net radiometer, taping a thermocouple to it, and attaching

the double-layered shield.

amount of either short- or long-wave radiation and thereby become warmer

than the clear dome, resulting in a net nonzero exchange of long-wave radiation between the two domes and the thermal transducer. White paint applied

upon the black that reflects considerable short-wave radiation and an

opaque circular shade that shields the painted dome from the direct rays

of the sun or the thermal emission and reflected short-wave radiation from

the ground can effectively eliminate this source of error (Idso, 1971b).

This technique thus eliminates the need for black and white-hot and cold

junctions of standard solarimeter thermopiles, such as the original KimbaII

and Hobbs (1923) instrument and later models of Blackwell-Anderson

(Anderson, 1967), Dirmhirn (Gates, 1962; Robinson, 1966), Ianishevsky

(Monteith, 1959), and Monteith (1959), which cannot be transformed


27 1

into total all-wave radiometers because of the differing spectral properties

of black paint and of white paint in the short- and long-wave regions.

It also allows for a more accurate measurement of solar radiation at low

intensities, where solarimeters based upon the black and block-hot and

cold junction design of the Moll thermopile (Moll, 1923; Gorczynski,

1924) often exhibit large zero offset errors (Maxwell, 1969).

One of the polyethylene domes of the original net radiometer can also

be similarly painted and shielded, resulting in either a total hemispherical

radiometer or a total albedo and long-wave emission radiometer. In this

case the temperature of the painted dome must also be known. Originally,

Idso (1971b, 1972a) obtained this temperature from three or four fine

thermocouples sandwiched between a double-layered polyethylene dome.

Later research, however, demonstrated that equally good results could be

obtained with a single thermocouple merely taped to a normal singlelayer

painted dome (Idso, 1 9 7 2 ~ ) .

The three underwater applications of the net radiometer derive from

merely waterproofing the lead connectors of some of the previously mentioned modifications. The short-wave balance meter thereby becomes an

underwater short-wave balance meter; and the solarimeter and albedometer

convert to their underwater counterparts. For shallow applications, even

polyethylene versions can be used in this way (Idso, 1972d), since no

long-wave radiation moves in water and it makes no difference whether

polyethylene or glass envelops the transducer. In this case, increased air

pressure must be supplied to keep the domes from collapsing; whereas for

the glass-domed instruments, air need not be supplied for most applications. Idso and Gilbert (1974) and Idso and Foster (1974) have kept

glass versions underwater for as long as 6 months without any leakage

or other deleterious effects.

In addition to these nine variations of the basic net radiometer, there

is also a tenth use to which it may be put, although this modification is

somewhat more difficult to make and use. It is the transformation of a

net all-wave radiometer into a net long-wave radiometer described by Paltridge ( 1969).

The procedure involves constructing two hemispheres of black polyethylene and joining them at their circumference so that they completeIy encase

a regular net radiometer. Both the domes of the net radiometer and the

outer black polyethylene sphere are then inflated by dry air; and the outer

shell is spun continuously about the stationary net radiometer. In this way

the asymmetric heating of the black polyethylene due to solar radiation

absorption is neutralized; and the output of the net radiometer becomes

proportional to the net long-wave radiation transmitted by the black polyethylene and absorbed at the radiometer’s transducer.





Knowledge of net radiation is essential to many agricultural research

endeavors and to most practical schemes of irrigation scheduling. For both

of these applications, estimation techniques are not suitable for all-weather

utilization; and direct measurement must be relied upon to obtain sufficiently accurate net radiation data.

The primary component of a net radiometer is a thermal transducer

or thermopile. Two different approaches are used to minimize or equalize

convection effects from its upper and lower surfaces; these are to ventilate

both surfaces equally or to shield them with transparent domes. The material most used for this latter purpose today is polyethylene.

Net radiometers are calibrated for sensitivity to short-wave radiation

(0 5 A 5 3pm) by simple shading techniques employing standard solarimeters for comparison. Long-wave calibrations ( A > 3pm) may be obtained from either special calibration chambers or from a simple flat-plate

technique, neither of which approaches requires any other radiometer. The

most recent intensive work in this area has indicated that popular polyethylene-shielded net radiometers have comparable sensitivities for both

short- and long-wave radiation and that they therefore do not need the

small strip of white paint that has routinely been applied to their black

transducers by most manufacturers in an attempt to correct for an erroneously assumed inequality in these two calibration factors.

Height placement of net radiometers is dependent upon the homogeneity

of the underlying surface and its temperature relative to that of ambient

air. When these two temperatures differ, common polyethylene-shielded

net radiometers ( 6 cm diameter) are preferably located at a height of

20-25 cm.

Polythylene-shielded net radiometers are extremely versatile instruments,

being easily transformed for utilization in nine additional applications. As

such, they enjoy a wide range of use in many fields of environmental



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R. H. Moll* and C. W.



of Genetics, North Carolina Stote University, and t U . 5 Department of

Agriculture, Agricultural Research Service, Raleigh, North Carolina

I. Introduction



11. Genetic Variability





A. Basic Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

B. Experimental Estimates in Crop Species ..........................

Inbreeding Depression and Heterosis ...............................

A. Inbreeding Depression . .


B. Heterosis ....................................................

Genotype-Environmental Interactions ...............................

A. Measurement of Genotype-Environmental Interactions . . . . . . . . . . . . . .

B. Evaluation of Stability .........................................

Response to Selection .............................................

A. Genetic Variances and Expected Response ........................

B. Experimental Evaluation of Selection Procedures . . . . . . . . . . . . . . . . . .

C. Correlated Responses and Selection Indexes ......................

Implications of Quantitative Genetics to Breeding Methodology . . . . . . . .

A. Breeding Objectives ...........................................

B. Development of Genetic Material with Breeding Potential . . . . . . . . . .

C. Testing and Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References ......................................................






















Quantitative genetics deals with the inheritance of those differences

among individuals that are expressed in terms of degree rather than kind.

In contrast with qualitative traits, in which variation is characterized by

discrete classes, variation in quantitative traits forms a continuous array

of values from one extreme to the other. Nearly every organ or function,

including most economically important traits of crop species, show differences of a quantitative nature.

The relevance of quantitative genetics to plant breeding lies in the fact

that manipulation of genetic variability of quantitative traits through in-

' Paper No. 4236 of the Journal Series of the North Carolina State University

Agricultural Experiment Station, Raleigh, North Carolina.




breeding, crossbreeding, and selection are essential features of any plant

breeding program. A primary objective of quantitative genetic research is

an understanding of the genetic consequences of such manipulations.

A basic premise of quantitative genetics is that the genes that affect quantitative traits follow the same laws of transmission as genes that affect qualitative traits. Usually many loci with small individual effects are involved;

therefore, it is necessary to study these traits through statistics appropriate

for continuous variables, such as means, variances, and covariances. Fisher

( I 918) provided the initial framework for the study of quantitative inheritance. Since that time, his developments have been clarified, elaborated,

and extended by numerous geneticists and statisticians. Unfortunately, the

experimental aspects of quantitative genetics have lagged behind theory.

Because it is difficult to design quantitative genetic experiments with definitive alternative hypotheses, many of the experimental conclusions have

been reached from the experience of numerous individual empirical investigations that have shown similar results.

Most of our emphasis will be concentrated on reviewing and interrelating

recent research results in areas of most significance to plant breeders, such

as ( 1 ) kinds of genetic variability found, (2) effects of inbreeding and

crossbreeding, ( 3 ) genotype-environmental interaction, and (4) selection

methodology and response. It is not our purpose to present a detailed description of quantitative genetic theory. Cursory summaries (using nomenclature from Falconer, 1960) are included to provide background

for readers untrained in quantitative genetics and to aid in understanding

results from experimental research.


Genetic Variability


Evaluations of inheritance mechanisms in quantitative genetics research

depend on valid assessments of genotypic values. However, the genotypic

value of an individual must be ascertained from measurements made on

its phenotype. Phenotypic value then, is defined as the performance of

a particular genotype in the environment in which it is grown. The two

components of the phenotypic value (P)-genotypic value ( G ) and environmental deviation (E)-are

usually represented in the equation for

phenotypic value as: P = G E.

A genotype is considered as the particular assemblage of genes possessed

by an individual, and genotypic value for a given genotype is defined as

the average of all possible phenotypic values, expressed as a deviation from

the population mean. In other words, it is the average phenotypic value


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