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III. Botanical and Physiological Considerations
FIG.2. Longitudinal section of a plant crop pineapple developed from a slip planted
22 months earlier. (Photo by courtesy of Pineapple Growers Association of Hawaii.)
D. L. PLUCKNETT, J. P. EVENSON, A N D W. G. SANFORD
stem may also develop into shoots, but these usually do not produce
satisfactory yields. A very unusual selective harvest system in horseradish (Armoracia rusticana) has been employed in Czechoslovakia
(Courter and Rhodes, 1969). In this system the original or mother plant
is left in place and only the young side roots are harvested annually.
In dicotyledons new growth may occur from new shoots on the lower
branches or stems following harvest. Total harvest ratooning may be
necessary to produce satisfactory regrowth, but not always. Cotton, for
example, can produce ratoon crops either by taking a second harvest
from old plants, or by cutting to near ground level and harvesting from
new growth (Fig. 3) (Thomson, 1964).
Because more is known of tillering in sugarcane than for most other
crops, a detailed discussion of this subject may be of value in pointing
out the important botanical and physiological factors of ratooning.
Upon removal of the apical bud at harvest, lateral buds develop into
tillers. Tillering is governed by such factors as inherent varietal qualities,
soil moisture and irrigation, time of planting, spacing, soil nutrient supply,
soil tilth and aeration, temperature, and other factors (Subba Rao and
In sugarcane, underground buds that develop into ratoon tillers are
borne on joints of the tapered base of the primary stalks (Martin et al.,
196 1). The old “stubble piece” or stool left after harvest usually consists
of 3 to 10 short joints, each having a bud (Edgerton, 1938). Upper buds
germinate first, and are most susceptible to cold or mechanical injury
(Edgerton, 1938). N. J. King et al. (1965) recommended discing or other
tillage to damage these surface buds, thus allowing germination of deeper
buds to ensure a deeper root system in the ratoon crop.
The sequence of tiller origin in sugarcane is as follows: lateral buds of
the primary stalk develop into secondary shoots, buds on secondary
shoots develop into tertiary shoots, etc. (Martin et al., 1961).
Loh and Tseng (1956) distinguished four types of tillers in sugarcane,
based on the angle formed by the tiller stalk and the ground. More or less
erect tillers displayed most active growth, semidecumbent or sprawling
tillers were least active. Tiller mortality was determined by the time of
emergence of indi-idual tillers and by tiller growth type. As in many crops
only a portion of total tillers produced may survive, perhaps as few as
one-third (Sastry and Venkatachari, 1962). In subtropical areas where
frost injury may occur it has been observed that early tillers have greater
FIG.3. Ratoon crops in cotton may result in two ways, differing in method of management following harvest. (A) Ratoon cotton not slashed to ground level following harvest.
(B) Left: ratoon cotton, not slashed; center: ratoon cotton slashed to ground level following
harvest: right: sown cotton o f same age as ratoon cotton in center (small plants almost indiscernible).
D. L. PLUCKNETT, J. P.
A N D w.
chance of survival than later shoots (Raheja, 1956). Stokes (1956) found
that carbohydrate reserves in stubble were influenced by date of harvest,
and highest brix and sucrose were found in stubble of the late-harvested
crop: further, h.e attributed poor ratoon growth to low food reserves of the
early harvested crop. Edgerton ( 1938) found poor ratooning varieties
had a lower number of viable healthy buds in late winter.
Raheja ( 1 956) examined physiological factors relating to tiller growth
of sugarcane. Heavy tillering was found to be desirable. Early-formed
tillers had greater chance of survival and contributed more to yield, mainly because crop quality was higher with early tillers. Nitrogen applications and irrigation greatly influenced tillering, while ambient temperatures below 70°F retarded tiller formation. Tillering of ratoon crops was
earlier and more profuse than in the plant crop.
Tang and Ho (1962) studied six successive sugarcane ratoons in a
sandy loam soil in Taiwan. Total tillers per acre ranged from 77,000 to
125,000 while millable stalks ranged from 36,000 to 40,000. Yields were
highest in the fourth ratoon, lowest in the fifth ratoon. The authors concluded climatic effects had more influence on yield than the number of
ratoon crops harvested.
The question of whether roots of the old sugarcane stool continue to
function after harvest has been a matter of controversy. Baver et al.
( 1962) presented rather convincing evidence that the old root system
ceases to function soon after harvest. Ratoon shoots contained 32Pwhen
labeled fertilizer was applied 4 inches deep within a split stool, but not
when the phosphorus was applied 4 inches deep and either 6 or 12 inches
on either side of the stool. The authors concluded the old roots did not
absorb 32Pfrom the root zone, but rather that only the new roots were
active. Water extraction curves following harvest were identical with
those of the preceding plant crop, indicating little function of the old root
system in water uptake for the new shoots. Additional evidence was
supplied by time-lapse cinegraphy of ratooned plants using a window
box technique. Rapid deterioration of the old root system and rapid
growth of the new root system resulted following harvest.
As in sugarcane, sorghum seems to produce a new root system very
quickly after harvest. Plucknett et al. (1970) observed a direct relationship between ratoon performance of both grain and forage sorghum lines
and the extent and vitality of root development (Fig. 4).
In banana the parent corm gives rise to buds usually on its middle
or upper section: these buds develop into sucker corms which pro-
t i c , . 4. Root system5 of sorghum, lifth ratoon, in Hawaii: ( A ) Roots of Haygrazer, a
ready-ratooning forage hybrid. The grid over the roots is spaced on a 6-inch scale: thus
Haygrazer roots extend over 12 inches deep and spread over 12 inches laterally from the
crown. ( B ) Shallow, poor root system of RS-610, a temperate grain sorghum. RS-610 ratoon performance is relatively poor.
D. L. PLUCKNETT, J. P.
A N D W. G. SANFORD
duce the ratoon crop (Simmonds, 1960). Because more sucker corms
develop than are necessary or desirable for high fruit yield and quality,
sucker corms and shoots which are located too close to the surface are
pruned, otherwise the entire plant “mat” complex will be shallow-rooted
and ratoon crops may not succeed. Other reasons for pruning include
undesirable orientation of the sucker corms in the row and selection of
suckers according to age in order to schedule fruit production during the
most favorable season.
IV. Ratooning a n d Environmental Factors
The fundamental basis for ratooning is the ability of the plant concerned
to behave as a perennial and to continue growth beyond one fruiting or
harvest cycle, environment permitting.
Ratooning may be used in any of the following situations:
1 . To carry a crop over from one season to the next for a period of
years without replanting, as in sugarcane (Antoine and Ricaud, 1963;
N. J. King et al., 1965), cotton (Harland, 1949; Ellern, 1966; Evenson,
1969, 1970), and rice (Garcia Duran, 1962, 1963; Evans, 1956, 1957;
2. To allow multiple harvesting from a single sowing to be carried out
throughout one year or more as in sorghum (Parbery, 1966; Plucknett
and Younge, 1963; Mackenzie and Parbery, 1966; Plucknett et al.,
1970) and rice (Garcia Duran, 1962, 1963).
3. To ensure maximum use of a growing season that may be too short
for two sown crops in succession, as in rice (Evatt, 1966).
4. To develop the subsequent crop in situ from basal suckers as in
bananas (Simmonds, 1960) and pineapples (Collins, 1960;Johnson, 1935).
5. In slow-growing species to develop a crop on the already established root system of the previous cycle. In particular the coppicing system of producing timber is an extreme example (Edlin, 1944; Wilson,
6. To reschedule crops that have gone out of phase with agronomic
schedules as is the case with early-sown cotton in northern Western
Australia that may ripen while the monsoon is still on, with disastrous
boll rot (Shedley, 1969).
The influence of environmental conditions on survival of ratoon crops
depends largely on the adverse effects of low temperatures and drought.
Cotton (Ellern, 1966; Evenson, 1969), sorghum (MacKenzie and Par-
bery, 1966), and rice (Evans, 1957) can withstand long periods of water
stress under tropical conditions when ratooned, and before regrowth
When crops which ratoon well in tropical areas are moved farther out
of the Tropics or into areas of increasing altitude within the Tropics, low
temperatures can become critical for ratoon survival. In northern parts
of the United States cotton belt, ratoon crops cannot survive the winter,
therefore cotton in these areas is essentially an annual (Templeton, 1925).
In the western United States ratooned cotton can survive in California
and Arizona (Wene, 1965; Van Schaik et al., 1962: Peebles and Fulton,
1944). In southern Australia low winter temperatures cause up to 95%
mortality of ratoons in the Murrimbidgee Irrigation Area unless the
“stubs” are adequately covered with soil, and even then 50% mortality
is recorded (Low, 1968). Rice cannot be grown all year round on the Gulf
Coast of Texas because low temperatures in winter will kill the ratoons
(Evatt, 1958a,b). Declining yields and crop failure have been reported in
sorghum grown at higher elevations in Hawaii, and this has been ascribed
to low-temperature effects (Plucknett et al., 1970).
B. EFFECTO F ENVIRONMENT
O N REGROWTH
As the regrowth system differs among crops, the effect of environmental factors will be considered in two categories depending upon whether
the plant tillers or suckers as in monocotyledons, or reproduces from
basal suckers or shoots formed on the stems or branches of the plant as in
the majority of dicotyledons considered.
I . Tillering in Grasses
Little published work exists on the effect of environment on tillering in
grasses other than in those used for pasture. However, by analogy the
work on tillering in pastures is of considerable interest. In pasture, tillers
are considered to be the primary growth unit (Mitchell, 1954; Langer,
1963) and the sward to be a community of tillers, each contributing to
total yield. This analogy is not true for crops like bananas, where control
of sucker density is maintained (Simmonds, 1960) and where satisfactory
yields depend upon adequate pruning.
The effect of increasing tiller density with successive ratoons is likely
to be a critical factor in crops such as grain, sorghum, and rice. When
these crops are ratooned the yield is likely to show an inverse relationship with density, as has been shown for several crops (Bleasdale, 1967).
In sugarcane, where there is a close relationship between total cane yield