The effect of climate on irrigated cotton yields under semi-arid conditions: Temperature-yield relationships

Agricultural Meteorology, 18(1977) 435--453 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

THE EFFECT OF CLIMATE ON IRRIGATED COTTON YIELDS UNDER SEMI-ARID CONDITIONS: TEMPERATURE--YIELD RELATIONSHIPS

J. LOMAS, M. MANDEL and Z. ZEMEL Division of Agricultural Meteorology, Central Meteorological Institute, Bet-Dagan (Israel) (Received March 14, 1977; accepted April 15, 1977)

ABSTRACT Lomas, J., Mandel, M. and Zemel, Z., 1977. The effect of climate on irrigated cotton yields under semi-arid conditions: Temperature--yield relationships. Agric. Meteorol., 18: 435--453. Multivariate temperature yield analysis of commercial cotton production in the central coastal plain of Israel using Fisher's (1924) method clearly shows a wave-like response. Weekly maximum temperatures accounted for 28% and weekly minimum temperatures for 14% of the variability of cotton yields. During the early stages of growth the positive response to lower minimum temperatures remains unexplained. During the main flowering period maximum temperatures above 29°C are required for higher cotton yields. While the flowering period indicates potential yield conditions, the boll formation period determines the extent to which this potential is realized. For optimum boll development mean maximum temperatures below 30°C are required. This period is, however, less significant under local climatic conditions, due to the relatively stable climate at the time (mean maximum 30.5 + 0.7°C and mean minimum 19.2 + 1.0°C). During the final ripening and harvesting period warm and rain-free weather will permit the cotton yield grown to be harvested under favourable climatic conditions. LITERATURE REVIEW Studies relating to the e f f e c t s o f t e m p e r a t u r e o n c o m m e r c i a l c o t t o n prod u c t i o n are o f a generally f r a g m e n t a r y a n d s o m e t i m e s c o n f l i c t i n g n a t u r e . Most investigations relate t e m p e r a t u r e e f f e c t s on c o t t o n g r o w t h and developm e n t at specifically d e f i n e d p h e n o l o g i c a l stages. V e r y little was f o u n d , h o w ever, in t h e l i t e r a t u r e relating t e m p e r a t u r e s t h r o u g h o u t t h e growing season to c o t t o n yields. In general t h e scientific l i t e r a t u r e o n t h e e f f e c t s o f t e m p e r a t u r e on c o t t o n yields can c o n v e n i e n t l y be r e v i e w e d u n d e r t h e f o l l o w i n g f o u r headings: (1) seed g e r m i n a t i o n a n d e m e r g e n c e ; (2) early g r o w t h ; (3) flowering; a n d (4) boll d e v e l o p m e n t a n d m a t u r a t i o n .

Seed germination and emergence It is generally c o n s i d e r e d t h a t soil t e m p e r a t u r e s b e l o w 15°C severely r e t a r d

436

cotton seed germination (Eaton, 1955; Basinski, 1963; and Cams and Mauney, 1968). Under field conditions Lomas and Shashoua (1969) showed that no practical seed germination of the Acala 4--42 variety takes place at soil temperatures of 17°C or below and that commercially unacceptable low germination rates are obtained between 18--20°C. At 21°C and above 60--70% germination is obtained within 4--10 days depending on soil temperatures. There seems to be no practical varietal difference in the effect of temperature on cotton seed emergence (Anderson, 1971). On the other hand, cotton seedlings were damaged when temperatures were outside the range of 14°--28°C (Balls, 1953).

Early growth Most authorities agree that the daily maximum temperature must exceed 20°C before initiation will occur and that 30°C is a desirable level (Eaton, 1955; Basinski, 1963; Carns and Mauney, 1966}. Mauney (1965) showed that early growth, up to the stage of 5 expanded leaves, is temperature-controlled The time required to reach this stage varied between 22 days at 32°C and 45 days at 22°C depending upon the mean daily temperature. Hesketh and Low (1969) showed that the greatest increases in plant height at squaring for a 30day period occurred at 30°/25°C day/night temperatures and 33°/28°C, for all strains tested. Optimum growth rate for leaf area was 33°/28°C and for dry weight accumulation was between 30°/25°C to 33°/28°C. Cotton plants exposed to moderately low temperatures of 24°/19°C after germination for a period of 2--3 weeks will have 30--50% less leaf area then plants growing at temperatures of 33°/28°C (Moraghan et al., 1968).

Flowering Mean daily temperatures higher than 20°/12°C are necessary for proper squaring and flowering (Nosov, 1959). When the daily maximum exceeds 40°C and the minimum exceeds 27°C flowering tends to be inhibited (Eaton, 1955; Basinski, 1963; Carns and Mauney, 1968). Temperatures below 20°C (Sowell and Rouse, 1956) or above 45°C (Fisher, personal communication to Mauney) have been associated with pollen sterility and incomplete fertilization. Flowering can be delayed by high day and high night temperatures. This delay expressed itself in the time required from planting to initiation and by flowering at a higher node (Mauney, 1966). High day temperatures can cause earlier floral initiation if coupled with low night temperatures. Low day temperature did not prevent the expression of the high night temperature delay, but its magnitude was diminished. Thus Mauney (1966) concluded that the day and night temperatures during early growth are of major importance in conditioning the flowering response of Upland cotton. In general it can be stated that relatively cool night temperatures and short days promote flowering.

437 Boll development and maturation Temperatures of 27°-32°C are desirable during the period of boll development and maturation (Mauney, 1974). The most rapidly maturing bolls are formed in early and mid-season when temperatures are optimum (Gipson and Joham, 1968; Mauney et al., 1972). Maturation of bolls range from 40 to 90 days. Maximum temperatures in excess of 38°C may reduce yields considerably (Eaton and Belden, 1929) especially if soil moisture is not adequate. The rate of boll development is inversely related to temperature. A decrease of either day or night temperature results in slower boll development, thus increasing the boll period (Gipson and Joham, 1968). Hesketh and Low (1969) showed that optimum air temperatures for boll production are affected by light intensity. At 370 langleys per day optimum air temperatures for three cotton varieties were 33°/28°C, while at 510 langleys per day the optimum temperatures were 3°C lower. The temperature for optimum boll weight was 27°/22°C. Optimum temperatures for boll production seem lower than that for vegetative growth. This temperature effect was also noted by Okagaki (1963) who suggested that higher early temperatures promote boll numbers and lower temperatures at boll maturation reduces shedding. Hesketh and Low (1969) found that plant growth rates close to maximum occurred at 36/31°C but few bolls were formed because of shedding. Summary Fig.1 summarizes the effect of temperature on the rate (in days) of cotton germination, growth and development, as obtained from the literature, which has been reviewed above.

METHOD OF ANALYSIS Data base The basic data analysed consisted of fiber yields from communal settlements in the central coastal plain of Israel, covering an l l - y e a r period from 1961--71. During this period the daily maximum and minimum temperatures were recorded at three agrometeorological stations in the region, i.e., Geva Karmel (34°57'E 32°59'N), Gan Shomeron (35°00'E 32°27'N)and Ein Hahoresh (34 ° 56'E 32°23'N). In addition information on various agricultural practices were obtained such as sowing and harvesting dates, the timing and amounts of irrigation and fertilization. Soil characteristics were obtained from the Ministry of Agriculture, Soil Conservation Service (Dan and Raz, 1970). Maximum and minimum temperatures were averaged over 24 weekly intervals beginning at sowing. The data consisted of 464 plots (ACALA 442)

438

being a sufficiently large sample to permit sub-division into smaller homogeneous groups obtained by cross-frequency analysis of the yield with planting dates. Table I gives a summary of the three subsets which form the basis 140

~4

I

t

[

]

I

l

I

I

120

100 U3

o

80

0 ne

N

60

z 40

20 ]

"'i'"i .... ;"7

16

20

24

.... , ....,-

28

32

I

36

Fig.1. T e m p e r a t u r e e f f e c t s on the d u r a t i o n of: 1 = g e r m i n a t i o n ( L o m a s and S h a s h o u a , 1969 - - soil t e m p e r a t u r e s ) ; 2 = g r o w t h (Mauney, 1966 - - i n t e g r a t e d t e m p e r a t u r e s ) ; 3 = flowering ( H e s k e t h a n d Low, 1969 - - day t e m p e r a t u r e ) ; and 4 = f r o m flower t o o p e n boll ( H e s k e t h and Low, 1969 - - day t e m p e r a t u r e ) .

of the study. The division of the data into three sowing periods is useful as a means of assessing the effect of a shift in the temperature throughout the growing season. In view of the 3 main planting dates the r h y t h m of the development of the cotton crop varies. This should be borne in mind when relating the crop coefficients to the various weekly temperatures. It is obviously also for this reason that the three response curves, for each planting date, are not complementary in time. TABLE I Basic c r o p data used in the t e m p e r a t u r e yield s t u d y Sowing date

Observations (n)

Mean yield (kg/ha)

S.D. (kg/ha)

E a r l y - b e f o r e 1 2 t h April N o r m a l - 1 2 t h t o 26th April L a t e - after 26th April

172 132 160

117 120 118

31 30 29

439

Statistical analysis The method used was first developed by Fisher (1924) in a rainfall--wheat yield analysis. Essentially, the method is one of multiple linear regression of yield with temperature throughout the growing season. Since the independent variables, in this case maximum and minimum temperatures, are continuous in time, the regression or response coefficients, may be interpreted as discrete values obtained from a continuous response function r(t), such that: T

Yi = Yo + f Ti r dt

(1)

o

where Yi is the yield for a given plot, i, Yo is the mean yield, Ti is the departure of the temperature from the normal, and T is the length of the growing season. If now, both r and Ti are expressed as a linear combination of functions orthogonal over the period r, i.e. : K=p

r= ~

c~KXK(t)

(2a)

bKiXK(t)

(2b)

K=O

K=p

Ti = ~ K~O

where ~K and bKi

are

the expansion coefficients for r and Ti respectively, and:

T

fo XmXn dt

(3)

= 5ran

where 5mn is the Kronecker delta: 0 m4:n ~mn =

1 rn = n

Thus we obtain: K=p

Yi = Yo + ~

aKbui

(i = 1, 2 . . . . m)

(4)

K=O

where m is the number of observations and p is the highest order orthogonal function. The (~K may be interpreted as unknowns which are obtained by conventional stepwise multiple linear regression of yield on the components of the orthogonal representation of the temperature variation from sowing to harvest. As in conventional statistical analysis requiring a digital computer, discretization is necessary to achieve results. In most practical analyses, therefore, the bKi defined by integration are approximated by numerical

440

quadrature. A more appealing approach is to resolve the discrete data into a linear combination of functions which are orthogonal over a discrete set of equally-spaced (weekly) periods, t: /=24

~ Xm Xn = ~mn

(5)

t=l

The orthogonal functions we use are those of Legendre. Each of the 24 weekly temperature values from sowing were decomposed using 7 orthogonal functions. The appropriate weights which are required to orthogonalize the data may be obtained in Milne (1949). Finally, after the regression coefficients a~ (~: = 0, 1 . . . 6) are obtained, the response function is recovered at each of the weekly periods, t:

K=p r(t) = ~ = 1 c~KX~(t)

(6)

Discussion o f the method The numerous pathways by which the influence of temperature affects the c o t t o n crop makes multivariate analysis of the kind described here a desirable adjunct to controlled experiments. While a carefully controlled experiment, such as that in a p h y t o t r o n , is an important research tool, the results are rarely applicable in the field were several environmental factors influence crop production. In discussing the extrapolation from controlled environments Evans (1963) stated: "When we c o m p o u n d the temporal changes and special diversity of natural microclimates with the complexity of interactions between environmental factors and between plants growing together, the prediction of performance in the field from that under controlled conditions may seem an impossible task." Consequently this type of statistical research can be looked upon as complementary to that carried out under controlled environments. The method described here in which the final yield is related to the temperature pattern throughout the season affords a means of evaluating the effect of temperature fluctuations on commercial cotton yields. The limitations of the m e t h o d should not be minimized: (a) the assumption of linearity between temperature and cotton yield throughout the growing season; (b) serial interaction is not accounted for; and finally, (c) the irreproducibility of the results. These drawbacks are to some extent alleviated by averaging the temperature over a week and by the fact that 11 years are sufficient to establish a representative temperature climate. Such relationships, once established, are an extremely useful tool in assessing the effect of climate on production, and can also be used in evaluating agrotechnical practices. It is obvious that such

441

response curves are " t r u e " only for those areas for which they were developed.

RESULTS

The general temperature~yield response curve

In order to establish the general effect of temperature on cotton yields, 300 plots with a high and relatively even standard of agro-technology (mean yield of 1360 kg/ha) were selected during 1961--71. The response curves which indicate the effect on yield (kg/ha) for a change in maximum and minimum temperatures of I°C are shown in Fig.2. GENERAL RESPONSE CURVE MAIN BIOLOGICAL STAGES +

Y --+

O .,C

~

l.IJ ff'l Z 0

20

i_

m__L2

'J_

,

10 0

-

~

MIN.TEMP. MAX.TEMP

~ -10 W

I

II 01

I

I

I

I

I

!

I

I

I

13 10 9 5 2 30 MAY JUNE JULY AUG. SEPT. MEANCALENDARDATE I

4

I

8 12 16 20 WEEK AFTERSOWING

I

24

Fig.2. The average weekly effect of a c h a n g e of 1°C d u r i n g t h e c o t t o n growing season o n yield (kg/ha/°C), for 300 c o t t o n plots w i t h a high s t a n d a r d o f a g r o t e c h n o l o g y . Main biological stages: 1 = early g r o w t h ; 2 = flowering; 3 = boll d e v e l o p m e n t ; 4 = ripening.

The abscissa is the time after sowing rather than some fixed date so the response is standardized with respect to the biologic development of the cotton crop. The mean growth and development stages of the c o t t o n crop are as follows: Planting Flowering period Boll development period Ripening period Harvest date

April 15th + 12 days June 10th to July 10th July 20th to August 10th August 15th to September 5th From October 1st.

442 The w e e k l y response values t o t e m p e r a t u r e changes o f I ° C t o g e t h e r with the m e a n e x t r e m e t e m p e r a t u r e s are given in Table II. The response exhibits a wave-like p a t t e r n , and f o u r distinct periods m a y be observed t h r o u g h o u t the life c y c l e o f the c r o p (a) A p e r i o d o f negative t e m p e r a t u r e response during the first 5--6 weeks after sowing, c o r r e s p o n d i n g a p p r o x i m a t e l y t o the period o f early g r o w t h until the active d e v e l o p m e n t o f squares. The peak response to the variations TABLE II Mean weekly maximum and minimum temperatures and their standard deviation and their corresponding response values (coefficients) to changes of 1°C for 300 cotton plots with a high standard in agro-technology Week

Maximum temperature (°C)

S.D. (°C)

Response (kg/ha/°C)

Minimum temperature (°C)

S.D. (°C)

Response (kg/ha/°C)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

24.4 24.9 25.3 26.4 27.2 28.2 28.4 28.7 29.3 29.2 29.2 29.3 29.5 29.8 30.0 30.2 30.4 30.5 30.6 30.5 30.2 30.0 29.8 29.6

2.9 3.1 2.8 3.2 2.8 2.8 2.6 2.3 1.7 1.1 0.7 0.7 0.8 0.8 0.8 0.7 0.7 0.6 0.6 0.6 0.8 0.9 1.0 1.3

-4 -3 -3 -2 1 4 7 10 12 12 10 7 2 -3 -8 -11 -13 -11 -7 0 8 14 13 -2

10.7 11.1 11.3 12.4 13.1 14.2 14.9 15.6 16.4 16.9 17.5 18.0 18.4 18.7 19.0 19.2 19.4 19.2 19.2 18.9 18.1 18.0 17.1 16.6

1.7 1.8 2.0 2.0 2.3 2.4 2.0 2.0 1.7 1.4 1.3 1.1 1.0 1.0 1.0 1.0 1.0 1.1 1.3 1.3 1.4 1.5 1.6 1.9

-3 -7 -7 -5 -1 2 5 6 7 6 4 1 -1 -4 -6 -7 -6 -5 -2 1 5 7 7 3

in m i n i m u m t e m p e r a t u r e is --7 k g / h a / ° C c o m p a r e d with --3 kg/ha/~C for m a x i m u m t e m p e r a t u r e . The negative response indicates t h a t within the f r a m e w o r k o f the variation in t e m p e r a t u r e t h r o u g h o u t the g r o w t h and d e v e l o p m e n t cycle o f the crop, c o o l t e m p e r a t u r e s d u r i n g the early g r o w t h stage have a beneficial e f f e c t o n t h e yield. (b) A p e r i o d o f positive response e x t e n d i n g f r o m the 5 t h - - 6 t h w e e k until a b o u t t h e 1 3 t h - - 1 4 t h week after sowing. This p e r i o d covers the greater

443 portion of the flowering process, with the peak flowering corresponding very nearly to the maximum positive response some 4 weeks following the major portion of square development. The remaining 3--4 weeks cover the later flowering and early boll growth. The peak response in this period is 12 kg/ha/ °C for changes in maximum temperature compared with 7 kg/ha/°C for minimum temperature. The range of temperatures encountered are indicated in Table II. Thus, unlike in the period of 5 to 6 weeks up to squaring, the maximum temperature is a more effective index of response of yield to thermal effects compared with minimum temperature. (c) This period covers the major portion of boll growth of about 3--4 weeks and an additional period of 3--4 weeks up to the opening of the bolls. The peak value of response coincides with the period of boll development and is - 1 3 kg/ha/°C for changes in maximum temperature and - 7 kg/ha/°C for changes in minimum temperature. (d) The final period covers the ripening phase as well as the growth of late flowering and fruiting cotton. This is a period of positive response with peak values of 14 kg/ha/°C for changes in maximum temperature and 7 kg/ha/°C for changes in minimum temperature. A comparison of the response of cotton yields to changes in maximum and minimum temperatures indicates that the response of the two curves are basically in phase. It is interesting to note that only during the first phase (up to squaring) the response to changes in minimum temperature is greater than that compared with maximum temperature, whilst during the rest of the cotton season maximum temperatures affect the yield more significantly.

The effect o f temperature on cotton yields for three planting periods The emergence and early growth period Cotton is generally planted when the mean air temperatures are about 15°C. Optimum sowing dates are generally obtained by planting sufficiently early to assure a long growing season and yet sufficiently late to assure a favorable soil thermal regime for quick and uniform germination. The general effect of maximum and minimum temperature on t h e early growth period of cotton has been shown in Fig.3 and described on pp. 441--443. The effects of maximum and minimum temperature for the emergence and early growth period to squaring at three planting periods are now discussed. The response of cotton yields to maximum temperatures during this early period is generally negative (Fig.3) although the actual response is small (Table III). For the early planted cotton a distinctly wave-like response is to be noted with both a positive and a negative response during the first six weeks after planting. The late planted cotton shows a negative response for only the first three weeks, while the normally planted cotton shows the most consistent negative response. The response of cotton yields to minimum temperature is negative for all three planting periods. Indeed our results indicate that the earlier the planting date the greater is the response of cotton

445

temperature "per se" was the causative factor. For it seems reasonable to assume that would the cotton plant have responded favourably to lower temperatures during the early growth period, the greatest response to lower minimum temperatures could have been expected at 13°C + 1.9 (late planting) and not at 11.6°C -+ 1.5 (early planting). It may therefore be concluded TABLE III Greatest weekly response values (coefficients) to changes of I°C in the maximum and minimum temperatures, during the early growth stage of cotton, for three planting periods Planting period

Response (kg/ha/°C)

Weeks after planting

Mean temperature (°C)

S.D. (°C)

Maximum temperature

early normal late

--6 --15 --11

5 4 3

26.2 25.1 26.3

2.8 1.8 2.4

Minimum temperature

early normal late

--48 --24 --18

5 5 3

11.6 12.9 13.0

1.5 2.2 1.9

that the results obtained for this early growth period need further investigation. Possible explanations may be looked for in the correlation of temperature with other meteorological parameters such as rainfall or evaporation or in the indirect effect of temperature on plant pest and disease development. Flo wet development period The influence of temperature during the flowering period on the final yield is particularly complex. There is general agreement that the effect of temperature is already influenced significantly by cumulative thermal TABLE IV Greatest weekly response values (coefficients) to changes of 1°C of maximum and minimum temperatures during the flower development stage, for three planting periods Planting period

Response (kg/ha/°C)

Weeks after planting

Mean temperature (°C)

S,D°

Maximum temperature

early normal late

33 38 25

11 10 6

29.1 29.0 28.5

1.0 0.9 2.5

Minimum temperature

early normal late

51 26 15

12 11 7

17.2 17.3 16.2

1.0 1.0 1.3

(°C)

446

factors prior to floral initiation. The general effect of maximum and minimum temperatures on the flower development has been shown in Fig.2, and described on pp. 441--443. The effects of temperature on the flower development stage at three planting periods are now discussed (see Fig.4). 32 ~'~ .~, F(OWE|NG L RI PERIOD N

u.i

__

._=__.

-

=---~-

u

24 ~

'

4°I ~

I

5

I

I

I

7

_ I

I

1

I

9 11 AFTER SOWING

WEEK

1/

I

13

@ FLOWERING PERIOD 20 od uJ~ Z ~

12

~+ Z

~

40

. ]..___N. --

-4o.I

5

~

"1 ~

I

7

I

I

I

I

9 11 WEEK AFTER SOWING

I

I

13

I

1

15

I

Fig.4. T h e average weekly e f f e c t of a change o f l ° C o f (a) m a x i m u m t e m p e r a t u r e s and ( b ) m i n i m u m t e m p e r a t u r e s d u r i n g t h e flowering period for t h r e e m e a n p l a n t i n g periods: E = early; N = n o r m a l ; a n d L = late.

The response of the cotton crop to maximum temperature during the flower development stage is generally positive, and this response can be seen for both the maximum and minimum temperature curves. It is worthwhile noting that the response of the cotton crop (yield) to changes in I°C is greater for the early or normal planting periods compared with late planted cotton. This is especially so as far as the response to minimum temperature is

447

concerned. Table IV presents the relevant data at the period of greatest response. From this table, it can be seen that the greatest response to changes of 1°C is 33 and 51 kg/ha for maximum and minimum temperature respectively, for early planted cotton, whilst for late planted cotton, it is only 25 and 15 kg/ha respectively. Our data seem to indicate that, in spite of the fact that maximum and minimum temperatures are within the optimum range as indicated in the scientific literature in the central coastal plain of Israel during the flower development stage, the cotton crop (yield) responds favourably to slightly higher temperatures. Generally speaking, the greatest response may be obtained for an increase in the maximum temperature, except for cotton planted relatively early, where a change of minimum temperature has a more substantial effect on yield.

Boll development and maturation It is generally agreed that mean maximum temperatures of 27°--32°C are favourable for the boll development period especially if accompanied by relatively cool night temperatures. The general effect of maximum and minimum temperatures for the period of boll development and maturation has been shown in Fig.2 and described on pp. 441--443. TABLE V Greatest weekly response values (coefficients) to changes of 1°C of maximum and minimum temperatures during the boll development and maturation stage, for three planting periods Planting period

Response (kg/ha/°C)

Weeks after sowing

Mean temperature (°C)

S°D.

Maximum temperature

early normal late

--65 --65 --32

19 19 13

29.2 30.2 29.2

1.0 0.9 1.3

Minimum temperature

early normal late

--20 --28 --19

18 17 13

19.0 19.2 18.2

1.2 1.2 1.4

(°C)

The effect of temperature on the boll development and maturation period of three planting dates is now discussed. The response on the c o t t o n crop for both changes in minimum and maximum temperature is negative, irrespective of the date of planting. Furthermore, the results indicate that the greatest response is to be found in relation to maximum temperatures for c o t t o n planted in the early and normal periods. The response of the c o t t o n crop (yield) to changes in I°C is presented in Fig.5. Table V presents the relevant data at the period of greatest response. From the table it can be seen that the peak response to a change of I°C in the

448

maximum temperature is --32 kg/ha for cotton planted late compared with nearly --65 kg/ha for the other two planting periods. On the other hand, the effect of changes of I°C in the minimum temperature is smaller and ranges from --20 to --30 kg/ha for the three planting dates. (~BOLL

GROWTH AND DEVELOPMENT PERIOD

-

30

IRL

w~

~ I o. ~'.-4Ol--

-

"-

/

-6011

O_"

11

I

1

13

I

1

1

I

I

15 17 WEEK AFTER SOWING

1

I

19

, ~ B O L L GROWTH AND DEVELOPMENT PERIOD 22j I 1 l l l l I i I

I

I

21

I

1|

K +4O .

E ~

10

12

I_

I

X

.

1

I"-"~"

14 16 WEEK AFTER SOWING

1

18

I

I

2O

I

Fig.5. The average weekly effect of a change of 1°C of (a) m a x i m u m temperatures and (b) m i n i m u m temperatures during the boll growth and d e v e l o p m e n t period for three mean planting periods: E = early; N = normal; and L = late.

The ripening stage The ripening stage is a period of some 4--5 weeks when most o f the crop is ready for commercial harvesting. The general effect o f m a x i m u m and minimum temperatures on the final stage o f c o t t o n development has been shown in Fig.2, and described on pp. 0 0 - 0 0 . The effect of temperature on the ripening stage at three planting dates is n o w discussed.

450

30--35 kg/ha for early and late plantings compared with as much as 65 kg/ha for normal plantings. TABLE VI Greatest weekly response values (coefficients) to changes of I°C of maximum and minimum temperatures during the ripening stage, for three planting periods Planting period

Response (kg/ha/°C)

Weeks after sowing

Mean temperature (°C)

S.D. (°C)

Maximum temperature

early normal late

21 19 25

23 23 19

30.2 30.1 30.3

0.5 0.8 0.8

Minimum temperature

early normal late

30 65 35

22 22 24

18.7 27.7 14.9

1.2 1.0 2.0

DISCUSSION OF RESULTS

The contribution of this paper is to be found in the multivariate analysis of 464 commercial cotton fields over an 11 year period, that experienced the natural temperature variation of the central coastal plain of Israel (Table II). During this time, agrotechnical practices were relatively uniform and of a high standard, and there was no time trend. Table VII compares the basic temperature factors and cotton yields for some selected cotton growing regions throughout the world. From this table it may be seen that the central TABLE VII Annual temperature factors and yields for selected regions and corresponding values for the central coastal plain Place

Number of frost free days

Growing deg-days (10°C base)

Avr. temp. (6 -warmest months)

Yield (kg/ha)

Tashkent, U.S.S.R. Leeton, Aus. Lubbock, U.S.A. Phoenix, U.S.A. Skopje, Yug.

200 299 215 270 180

2,327 2,320 2,496 4,000 2,000

21 21 22 28 20

875 870 675 1,100 340

Mean values

232

2,629

22

770

Israel coastal plain

240

2,307

23

1,170

451

coastal plain of Israel has fairly similar climatic conditions to the mean climate of the 5 selected cotton growing regions of the world. Under eastern Mediterranean climatic conditions mean maximum temperatures increase from 24.4°C to 28.2°C and mean minimum temperatures from 10.7°C to 14.2°C during the first 5--6 weeks. The positive yield response to lower temperatures (especially minimum temperatures) found in our analysis for this early growth period seems to be unclear in view of the available scientific literature. It may well be that, under field conditions, this "temperature response" is correlated with other climatic variables or it effects cotton yields indirectly. Throughout the rest of the cotton crop's growth and development season the crop seems to be more sensitive to changes in maximum temperatures, except for the final ripening stage. From squaring and throughout the flowering period the cotton crop responds most favourably to increases in temperature, especially around the 9th week after planting. Thus it seems that a positive response is obtained during the flowering period for temperatures above 28°--29°C. There is no recent research dealing with optimum climatic conditions for cotton during its flowering period. Early work by Ewing (1918) indicates that low temperatures below 18.3°C caused a reduction in the opening of flowers, and modified the flowering process. On the other hand maximum temperatures in excess of 40°C tend to inhibit flowering (Mauney, 1974). Our results indicate that in the maximum and minimum temperature range of 29.3 + 1.7°C and 16.4 + 1.7°C, respectively, a favourable response of cotton yields can be obtained by higher temperature values. Cotton requires mean maximum temperatures of between 27°--32°C during the boll development and maturation period (Gipson and Joham, 1968). The authors indicate that within limits, cooler temperatures, especially at night, are generally favourable for boll development. Under such temperature conditions, a high proportion of flowers set bolls and boll weight tends to be relatively high compared with the weight of tops or stems and leaves. Our own results, on the other hand, indicate that the lower maximum temperature range seems to give the better response (yield). During the boll development and maturation period our mean maximum temperature is 30.0 + 0.6°C and the mean minimum is 19.0 -+ 1.0°C, yet the response curve clearly indicates negative values. Hesketh and Low (1969} showed that optimum temperatures for Acala 15--17 during the boll development period are in the 24°--27°C maximum and 19°--22°C minimum range. Finally, during the ripening stage of the cotton crop, the positive response to temperatures, especially minimum temperature, may be associated with both ripening and harvesting temperatures per se, as well as with the absence of rain, indicated by higher minimum temperature "requirements". This "requirement" may be due to the intercorrelation between mean minimum temperature and rainfall during the month of October. The commercial cotton yield will, from a temperature point of view, be

452

determined by two basic factors: (a) the magnitude of the coefficients of the response curve; and (b) the climatic variability of temperatures. Therefore, under our local climatic conditions the most critical period is during the flowering period (especially at peak flowering) when the standard deviation of the mean maximum temperature is 2.8°C and the yield response coefficient is 12 kg/ha/°C. Years with above normal temperatures during June and the first half of July and below normal temperatures during August and the beginning of September may increase cotton yields by as much as 20--30%. ACKNOWLEDGEMENTS

This research project was supported by the Cotton Marketing Board of Israel, the assistance of which is greatly acknowledged. The authors are specifically grateful to Prof. Marani of the Hebrew University, Jerusalem, Faculty of Agriculture, H. Pachter and Y. Ayalon of the Ministry of Agriculture, National Advisory Service, E. Kalter, regional agricultural advisory officer and to D. Becher of the Cotton Marketing Board -- for useful discussions. Furthermore, we are indebted to Mr. Kalter and Miss A. Nachmanovich for considerable assistance in the collection of the basic data on c o t t o n yields. Finally, we are much indebted to the 42 agricultural settlements for providing the cotton data.

REFERENCES Anderson, W. K., 1971. Responses of five cotton varieties to two field soil temperature regimes at emergence. Cotton Grow. Rev., 48: 42--50. Balls, W. L., 1953. The yields of a crop. Spon, London. Basinski, J. J., 1963. Cotton growing in Australia, an agronomic survey. CSIRO. Camp, A. F. and Walker, M. N., 1927. Soil temperature studies with cotton. Florida Agric. Dep. Stn. Bull., 189. Dan, J. and Raz, Z., 1970. The soil association map of Israel. Ministry of Agr., Dep. of Scientific Publications (in Hebrew, with English summary). Cams, H. R. and Mauney, J. R., 1968. Physiology of the cotton plant; in cotton, principles and practices. Iowa State Univ. Press, Amer., pp. 41--74. Eaton, F. M., 1955. Physiology of the cotton plant. Ann. Rev. Plant Physiol., 6: 299--328. Eaton, F. M. and Belden, G. O., 1929. Leaf temperatures of cotton and their relation to transpiration, varietal differences and yields. U.S.D.A.Tech. Bull., 91. Evans, L. T., 1963. Environmental control of plant growth. Proceedings of a symposium held at Canberra, Australia, August 1962. Academic Press, New York, N.Y., p, 432. Ewing, E. C., 1918. A study of certain environmental factors and varietal differences in influencing the fruiting of cotton. Miss. Agric. Exp. Sta. Tech. Bull., 8. Fisher, R. A., 1924. The influence of rainfall on the yield of wheat at Rothamsted, 3. The analysis of the season. Trans. R. Soc., Ser. B, 213: 95--99. Gipson, J. R. and Joham, H. E., 1968. Influence of night temperature on growth and development of cotton (Gossypium hirsutum L.), I. Fruiting and boll development. Agron. J., 60: 292--295. Hesketh, J. P. and Low, A., 1969. The effect of temperature on components of yield and

453 fiber quality of cotton varieties of diverse origin. Cotton Gr. Rev., 45: 243--257. Lomas, J. and Shashoua, Y., 1969. Influence of soil temperature on emergence of cotton seedlings under field conditions. Cotton Grow. Rev., 46: 174--180. Low, A., Hesketh, J. and Muramoto, H., 1969. Some environmental effects on the variable node number of the first fruiting branch. Cotton Grow. Rev., 46(3): 181--188. Mauney, J. R., 1966. Floral initiation of Upland cotton (Gossypium hirsutum L.) in response to temperatures. J. Exp. Bot., 17(52). Mauney, J. R., 1974. Meteorological factors affecting the commercial production of cotton. Unpublished report. Mauney, J. R. and Phillips, L. J., 1963. Influence of dry bright and night temperature on flowering of Gossypium. Bot. Gaz., 124: 278--283. Mauney, J. R., Kittock, D. L. and Baniola, L. A., 1972. Limitation of late season green bolls in cotton: a possible new control of pink bollworm. Proc. Beltwide Cotton Prod. Conf., pp. 103--105. Milne, E. M., 1949. Numerical Calculus. Princeton Univ. Press, Princeton, N.J. Moraghan, J., Hesketh, J. and Low, A., 1968. Effects of temperature and photoperiod on floral initiation among strains of cotton. Cotton Grow, Rev., 45: 91--100. Nosov, A., 1959. Physiology of the development of fine fibred cotton. Khlopkovodstvo, 8 (in Russian). Okagaki, O., 1963. Effect of temperature on the growth and development in the upland cotton plant. Proc. Crop. Sci. Soc. Japan (in Japanese). Pinks, L. L. H., 1972. Influence of light and temperature environments preceding and during the dark period in floral initiation in Pima cotton (Gossypium barbadense L. ) Crop Sci., 12: 612--615. Sowell, W. F. and Rouse, R. D., 1956. Growth and fruiting of the cotton plant under controlled environmental conditions. Agron. J., 48: 581--582. Thompson, N. J. and Basinski, J. J., 1962. Ripening characteristics of irrigated cotton at the Kimberley Research Station; Northern Australia. Emp. Cott. Grow. Rev., 39: 27--34.