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VI. O2 Flux and Plant Response

VI. O2 Flux and Plant Response

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SOIL AERATION BY PLATINUM MICROELECTRODE



279



of their experiments use has been made of the same soil with the same

technique. Where measurements were made using another soil, with

various amendments, for growth of turfgrass, their threshold values

g cm-2 min-I

for root extension broadened to a range of 12 to 33 x

(Letey et af., 1966).

Waddington and Baker ( 1 965) found that root growth of Merion Kentucky bluegrass was not stopped till 0 2 flux was between 5 and 9 X 1Ow8g

cmP2min-l [against 20 X

g cm-2 min-I found by Letey et al. (1964)

for Newport bluegrass] and Penncross creeping bentgrass roots grew well

at an 0 2 flux of 5 X lo-" g cm-2 min-I. Gradwell (1967, 1969) found that

ryegrass roots grew freely in soil for which O2flux was 7.5 x

g cm-*

min-' and that for white clover root growth was not impaired but shoot

g cm-2 min-I; West and

growth was depressed at an O2 flux of 10 X

Black (1969) found that pasture grasses grew at near-zero fluxes and

apparently grew well at a mean O2 flux of 1 1 X lop8g cm-2 min-'. Although they did not examine root growth, they concluded from their

measurements of dry matter from a mixture of ryegrass, bluegrass, and

fescue grown on very wet soils, that "flux minima previously suggested

as limiting for root growth have been overestimated." However, their

relatively uncontrolled (field) experimental conditions, and comparatively

few measurements, do not really justify such a conclusion.

In other work Williamson (1964) found that although corn, sorghum,

and cabbage yields were reduced by a decrease in O2flux from 15 X

to 5 x

g cm-2 min-I, somegrowth took place and yields were obtained

at the lower value. On the other hand, Campbell et al. (1969) found that

seed set and wheat yield were increased when the range of O2flux altered

with altered water regime from that of 20 to 100 X IO-' g cm-' min-' to

that of 28 to 200 X

g cm-' min-'. Even a t the low O2flux end of the

range, calculation from their results indicates that air-filled porosity was

in excess of 20%. Letey et al. (1965), once more using Krilium-treated

Yo10 silt loam, found that corn roots would grow a t an O2 flux greater

than 10 X lo-' g cm-' min-', and Valoras and Letey (l966), again with

the same soil, showed that rice roots extended at 0 2 fluxes down to 7 X

g ern+ min-I. In both cases it could be shown that O2was supplied

by internal diffusion, thus accounting, in their opinion, for a threshold

value less than 20 X 1 0-8 g cm-' min-'.

Wengel ( 1966) obtained a highly significant relation between emergence

of corn and O2 flux; emergence reached a maximum (near 100%)at a flux

of 20 to 25 X 10-8g cm-' min-'. Kaack and Kristensen ( 1967)using a very

similar technique found a similar correlation between wheat emergence



280



D. S. MCINTYRE



and Or flux, but the actual values of O2flux at which emergence began and

reached a maximum were more than 5 times as great as those of Wengel

at comparable soil moisture suctions. It is significant that while Wengel

used an applied voltage of -0.7 volts with respect to SCE, Kaack and

Kristensen corrected for ohmic losses by the method of Kristensen (1966)

and measured current at an effective voltage of -0.65 volts with respect

to SCE. As in most measurements Wengel's true (effective) voltage is

unknown. Kaack and Kristensen (1967) also correlated root length and

top growth with O2 flux and found that, using a constant effective voltage of -0.65 volts, root extension was zero at Or flux values less than

about 50 X lo-* g cm-2 min-' and reached a maximum at values which

are in excess of 150 X lo-* g ern+ min-'. Top growth appeared to reach

a maximum at about the same value. The technique of these workers is

much more likely to give a reliable value than those in which current is

measured at constant applied voltage.

Plant growth and Oe flux studies prior to 1964 have been previously

reviewed by Stolzy and Letey (1 964a,b) who then and in later publications explain different results obtained by other workers as due to either

a larger diameter electrode or a higher applied voltage. The latter undoubtedly has some effect; however they correct these values in terms

of diameter on the basis of diffusion theory and in terms of voltage on

the basis of their previously measured current-voltage curves. Diffusion

theory shows that 0 2 flux is inversely proportional to electrode diameter

for saturated media, although for unsaturated media it should, as a first

approximation, on the model normally used be independent of electrode

diameter. Experimentally (McIntyre, 1966a) these have been shown to

be so, and Fig. 9d from Birkle et al. (1964) shows a case in which Os flux

is greater for the larger diameter under very wet conditions. Hence,

correction on this basis is not legitimate, and low threshold values cannot

be accounted for in terms of larger diameter electrodes.

Correction to a standard voltage is carried out by Stolzy and Letey

(1 964a,b) using a family of straight line current-voltage curves (Birkle

et al., 1964) determined in a lawn (presumably over a range of moisture

contents), at constant applied voltage. As previously discussed this set

of relationships will be peculiar to the set of soil and electrode conditions

occurring and will not necessarily apply to any other measurements made

(cf curves of McIntyre, 1966b and Kristensen, 1966). Hence any correction on this basis in untenable. That some approximate agreement

between results can be found by correction is probably due to the fact

that in poorly aerated soils moisture content will be relatively high and

measured O2flux relatively low.



SOIL AERATION BY PLATINUM MICROELECTRODE



28 1



It is, therefore, not known what if any are the critical values of oxygen

flux for root or plant growth. The “established correlations bktween

root and O.D.R.” (Valoras and Letey, 1966) are possibly established for

their soil and experimental conditions but for no other, and one cannot

use any O2flux figure with assurance as critical to plant growth.

VII. Summary



Soil physical and electrochemical processes fundamental to the operation of the platinum microelectrode are considered, and the experimental

results are related to them. It appears likely that the electrode response

will be different under different conditions of pH, salt content, and ion

species, as well as soil structure, O2concentration, and moisture content.

It is a mistake to assume that the strong dependence of current on the O2

diffusion rate, shown by saturated porous media, occurs in unsaturated

media. The continuous dependence of current on the voltage of the electrode found for unsaturated media means that processes that can be rleglected for saturated media assume great importance in unsaturated media.

In the latter, current is controlled by the rate of the reaction and hehce

by the voltage, over a significant part of the electrode area. The e f i c t

of penetration of the electrode on soil properties may be such that the

diffusion rate of O2 is the current-limiting process only in soils with water

at positive or zero pressure. A new model representing conditions at the

electrode is presented, and it is shown that if such a model applies, use

of the diffusion model to determine soil parameters is incorrect. The investigations that are necessary to determine usefulness of the method are

discussed.

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Greacen, E. L., Farrell, D. A., and Cockroft, B. 1968. Trans. 9th 1nt. Congr. SoilSci., 1968

VOI. I , pp. 769-779.

Harter, R. D., and Ahlrichs, J. L. 1967a. SoilSci. SOC.Amer., Proc. 31,30-37.

Harter, R. D., and Ahlrichs, J. L. 1967b. SoilSci. Soc. Amer., Proc. 31,578-579.

Hoare, J . P. 1968. “The Electrochemistry of Oxygen,” Chapter IV. Interscience, New

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RATOON CROPPING'

D. 1. Plucknett, J. P. Evenson,



a n d W. G. Sanford



College of Tropical Agriculture, university of Hawaii, Honolulu, Hawaii,

and



University of Queendand, Brisbane, Australia



Page



I . Introduction ......... .

B.



Importance of Ratooning



......



D. Advantages of Ratooning .....

E. Disadvantages of Ratooning

11. Genetic Aspects



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



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

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

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

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

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



111. Botanical and Physiological Considerations ..........................................

A. Tillering of Sugarcane ..................................................................



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

IV.



mental Factors ............................



*



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



A. General ....................................................................................

B. Effect of Environment on Regrowth or Tillering ..............................

V. Soil Relationships .............................................................................

A. Fertility ..............................................................................

B. Moisture .........................................

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

C. Compaction .............................

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

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

VI. Pests and Disease .........................

A. Weed Control ...........................................................................

B. Insects and P

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

C. Disease .......

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

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

VII. Management .... ....

A. General .

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



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

C . Postharvest Field Operations .... ....................................................

D. Cropping Systems ........................................

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

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

VIII. Future Outlook ...........................

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

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



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'Approved by the Director of the Hawaii Agricultural Experiment Station as Journal

Series No. 1168.



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D.



L.



PLUCKNETT, J.



P. EVENSON,

AND

I.



w.



G. SANFORD



Introduction



Ratoon cropping is an old system which has been practiced for many

years, especially in the Tropics. Although the origin of ratooning is

probably not known for any particular crop, it may have begun when man

first noticed regrowth of new shoots following cutting of certain crops at

harvest, thus producing a new crop without replanting. Also, early man’s

observations of grassland regrowth following burning might have created

an interest in utilizing regrowth of plants as a basis for multiple harvesting from an original root system.

Because ratooning is practiced widely and is important in many crops,

a review of the practice may be valuable, especially since increased food

and fiber production is imperative in tropical areas. In preparing this

paper, we have found that review journals very often do not index for

ratooning, nor do authors make an effort to use the term as a key word for

indexing. We hope this review will stimulate interest in ratoon research,

and in determining situations in which the practice should be or should

not be employed.

A.



OF RATOONING

DEFINITION



The word ratoon seems to have originated either from the Latin words

retonsus-cut down or mown (Lewis and Short, 1958); or retono-to

thunder back, resound (Anonymous, 1950); the Spanish retono -fresh

shoot or sprout (Anonymous, 1960): or even the French rejeton-sucker

or shoot, scion, descendant, offspring, or sprout (Anonymous, 1962a).

The Shorter Oxford Dictionary (Anonymous, 1950) defines ratoon as,

“a new shoot or sprout springing up from the root of sugarcane after it

has been cropped.” This definition is much too narrow in its scopereferring only to sugarcane - and is also incorrect in that regrowth usually

does not occur from the roots of the plant, but rather from the stem,

crown, or stem modification. Winburne (1962) defined the term as, “a

basal sucker for propagation as in sugarcane, pineapple, and banana.”

This definition is probably more suitable because it recognizes that

ratooning is employed in crops other than sugarcane and that regrowth

occurs from basal suckers, but of unidentified origin.

Basically ratoon cropping implies:

1. more than one harvest from a single planting

2. regrowth from basal buds on the stem or crown (that part of the

stem which is situated at the surface of the ground: Lawrence,

1958)



RATOON CROPPING



287



and: 3. harvesting of most or all of the aerial portion of the plant

(called total harvest ratooning in this paper)

or:

4. harvesting of selected portions of the plant, e.g., fruit, leaves,

portions of the stem or combinations of these (called selective

harvest ratooning in this paper)

The first harvest of a crop is usually called the “plant crop” and each

succeeding harvest is designated “first ratoon,” “second ratoon,” etc.

The question of what crops to include in ratoon cropping must be

raised. The term has been applied traditionally to sugarcane, pineapple,

and banana (Simmonds, 1960) and more recently to grain and forage

sorghum, cotton, rice, ramie (Boehmeriu nivea) (Subra and Guillemot,

196 I), and even patchouli (Pogostemon cublin) (Werkhoven, 1968).

Crops destined for processing for fiber, essential oils, drugs, or other

natural plant products are often ratooned. Also, the grasses are sometimes ratooned for processing or for grain use. It is difficult to determine

just what crops to include or exclude in ratooning, for even forage crops

and pasture plants ( 1 ) produce more than one harvest from a single planting, (2) provide regrowth from basal buds on the stem or crown, and (3)

may have all or part of the top growth harvested. For purposes of this

paper we will confine our discussion to field crops but will draw on tillering research in pasture plants to discuss regrowth potential, since most

research has been done in this field.

B. IMPORTANCEOF RATOONING

Most sugarcane in the tropics or subtropics is ratooned at least once.

In Mauritius, where as many as 5 ratoon crops may be taken (Antoine

and Ricaud, 1963) 85% of the cane milled each year is produced by

ratoon cane (de Sornay, 1957). With hand-harvesting it is usually possible

to obtain several ratoon crops, and growing and maintaining good ratoons

is very important. In Hawaii, where mechanical harvesting is employed,

sugarcane is usually ratooned only once because of soil problems and

mechanical damage to the stools.

Most banana and abaca (Musa textilis) fields are harvested for many

years, and therefore ratooning is very important to these industries.

Ratoon cropping is also employed extensively in pineapple, although the

number of ratoon crops varies (Collins, 1960; Johnson, 1935).

Ratoon systems have been used in rice in Texas (Gay, 196 1 ; Evatt and

Beachell, 1960, 1962; Evatt 1958a,b, 1962), Colombia (Garcia Duran,

1962, 1963), Ecuador (Efferson, 1952), Swaziland (Evans, 1956, 1957;



288



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PLUCKNETT,

J. P. EVENSON,

AND w.



G. SANFORD



Szokolay, 1956),India (Gupta and Mitra, 1948;Ganguly and Ralwani,

1954;Nezamuddin and Sinha, 1962;Saran and Prasad, 1952),Thailand

(Hashioka, 1963), Taiwan (Iso, 1954; S. C. Hsieh and Young, 1959;

C. F. Hsieh et al., 1964;Chang, 1964),the Philippines (Parago, 1963a,b),

and China (S.J. Yang, 1940; K. C. Yang et al., 1958;Pan, 1952;KaiChu, 1958). Ratooning of rice has not proved successful in all areas and

recommendations have been given against its use in Colombia (Garcia

Duran, 1962, 1963)and in areas where red rice (Oryza rufipogon) can

become a weed threat (Grist, 1965).

Ratooning of forage sorghum has been successful in India (Ambastha and Jha, 1955; Mandal et al.. 1965; D. Singh, 1957), Hawaii

(Plucknett and Younge, 1963; Plucknett et al., 1970; Sherrod et al.,

1968), and Australia (Parbery, 1966; Mackenzie and Parbery, 1966).

Grain sorghum has been grown as a ratoon crop in India (Mandal er al.,

1965; Shanmugasundram et al., 1967),Australia (Parbery, 1966;Mackenzie and Parbery, 1966),Hawaii (Plucknett and Younge, 1963;Plucknett et al., 1970),Arizona (Stith, 1964),California (Worker, 1961),and

the Philippines (Bradfield, 1969).

Ratoon cropping is also practiced to some degree in the following commercial crops: kodra millet (Paspalurn scrobiculaturn) in India (Divakaran et al., 1966);ramie (Boehrneria nivea) (Lagan and Rapista, 1957),

and the various grasses used for essential oils, especially the genus

Cy mbopogon.

Ratoon or “stub” cotton is or has been grown in the Western United

States, Peru, and Israel (Evenson, 1969, 1970)and in northern Western

Australia. In Israel and Australia ratooning is still undergoing development as a practice under modern intensive farming methods.

Coppicing (ratooning) of timber is a common practice and although

forestry is not being considered here in detail, some forest trees that have

been grown under coppice system (Steinlen, 1963)are listed below. The

range is quite wide and includes hornbean, red maple, turkey oak,

Eucalyptus spp., cork oak (Correia, 1969,monterey pine, hazel, willow,

chestnut, ash, alder, and oak (Zachev, 1965). Bamboo has also been

coppiced (Ladna, 1962).



c.



CROPS



IN



WHICH RATOONING

IS PRACTICED



A list of some crops is given in Table I. Justifiably, it may be said that

many of these crops are not usually considered as ratoon crops, but in

some ways the types of culture which are used or are possible do resemble

ratoon systems.



289



RATOON CROPPING



D. ADVANTAGES

OF RATOONING

Several advantages are often given for ratoon cropping:

1. Reduced cost of production through saving in land preparation and

care of the plant during early growth of the seedling or clone; such early

TABLE I

Some Crops in Which Ratoon or Ratoonlike Systems of Management are Employed,

and the Type of Ratooning System Employed

A. Total harvest (in which all crop above the ground is harvested)

Vernacular names used

Crop



Plant crop



Ratoon crop



Asparagus (Asparagus

oficinalis)

Bamboo (Bambusa spp.)

Buchu (Barosma betulina)

(Gentry, I96 I )

Chestnut

Coppice (Edlin, 1944)

Citronella (Cymbopogon nardus) and other cymbopogons

First ratoon, etc., second

Forage sorghum and sudan- Plant crop, first

cutting, etc.

grass (Sorghum vulgare; S.

cutting

vulgare var. sudanense)

Grain sorghum (Grain;

Plant crop

leaves and stems for

forage)

Geranium (Pelargonium

capitatum, P. odoratissima,

P. roseum) (Weiss, 1967)

Lemon grass (Cymbopogon

citratus)

Mint (Mentha. spp.)

Cutting

Napiergrass (Penniserum

purpureum)

Second, third harvest, etc.,

First harvest, first crop

Ramie (Boehmeria nivea)

second crop or cutting

or cutting

Red maple (Acer rubrum)

Red respberry (Rubus idaeus)

First, second ratoon, etc.,

Sugarcane (Saccharum spp.) Plant crop, virgin cane

(Antoine and Ricaud, 1963) stubble crop

Watercress (Nasturtium

oficinale)

Willow

Coppice

Coppice (Edlin, 1944).



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