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Growth of sugarcane under high input conditions in tropical Australia. II. Sucrose accumulation and commercial yield
ELSEVIER
Field Crops Research 48 (1996) 27-36
Field Crops Research
Growth of sugarcane under high input conditions in tropical Australia. II. Sucrose accumulation and commercial yield R.C. M u c h o w a,*, M.J. Robertson u, A.W. Wood c a CSIRO Division of Tropical Crops and Pastures, St. Lucia, Queensland, Australia b CSIRO Division of Tropical Crops and Pastures, Aitkenvale, Queensland, Australia c CSR, Technical Field Department, lngham, Queensland, Australia
Accepted 27 March 1996
Abstract Information on the processes controlling the accumulation of sucrose over time can be used to assess the physiological basis of yield variation and consequently the scope for yield improvement in sugarcane. As commercial yield is commonly expressed on a fresh weight basis, and dry weight measures of sucrose accumulation aid biological interpretation, there is a need to study yield accumulation on both a fresh and dry weight basis. This study analysed the pattern of sucrose accumulation in the stalk in relation to crop biomass, and the concentration of sucrose in the stalk on a fresh and dry weight basis of two contrasting cultivars (Q117 and Q138) of sugarcane during the same season in tropical Australia, with irrigation and under plant and ratoon crop conditions. Over the 15 month season, 11 crop samplings were conducted. The key findings were that (1) greater than 95% of the aboveground sucrose accumulation is in the stalk; (2) a logistic relationship described the time trend in stalk sucrose accumulation, with maximum sucrose yield occurring 100 days before final harvest; (3) stalk biomass rather than stalk sucrose concentration was the major determinant of stalk sucrose accumulation; (4) maximum stalk sucrose concentration was stable across cultivars and crop classes at a value of 0.48 g g - 1 stalk dry weight; (5) commercial yield expressed as the fresh millable stalk yield plateaued up to 230 days before final harvest and well before the attainment of maximum stalk biomass and sucrose yield due to increases in dry matter content during growth; (6) maximum stalk sucrose concentration on a fresh weight basis was obtained at a later crop age and was more variable across crops than maximum stalk sucrose concentration on a dry weight basis. The study highlighted the major influence that stalk dry matter content has on the relationship between sucrose yield and commercial yield, and that biological interpretation of crop response to climatic and management factors is difficult based on commonly available fresh weight measures of productivity. Optimising economic return from commercial sugarcane production requires further understanding on the factors controlling the dynamics of stalk dry matter content. Keywords. Sugarcane; Sucrose accumulation; Harvest index; Cane yield; CCS
* Corresponding author. Tel.: +61-7-33770253; fax: +61-7-33770206; e-mail: [email protected]. 0378-4290/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved. PH S 0 3 7 8 - 4 2 9 0 ( 9 6 ) 0 0 0 4 2 - 1
28
R.C. Muehow et al. / Field Crops Research 48 (1996) 27-36
1. Introduction
The previous paper in this series (Robertson et al., 1996) examined the utilisation of solar radiation in biomass production in two high-yielding cultivars Q117 and Q138 growing in tropical Australia. Since sugarcane is harvested at a range of crop ages, knowledge on the pattern of sucrose accumulation over time is vital to maximise economic return. Accordingly, the primary purpose of this paper is to examine the relationship between biomass and sucrose accumulation in two current and contrasting Australian sugarcane cultivars growing under highinput tropical conditions. A number of studies have reported time-trends in sucrose accumulation under irrigated conditions (e.g.; Borden, 1942; Borden, 1944; Borden, 1948; Glover, 1971; Rostron, 1972; Cox et al., 1994). However, little information is available for modern cultivars on the partitioning of crop biomass to stalk sucrose during growth. Similarly, in the international literature there are relatively few studies (e.g. Das (1936) in Hawaii, Thompson (1988) in South Africa, and Julien and Delaveau (1977) in Mauritius) where the processes of sucrose accumulation over time have been examined under field conditions. Crop sucrose accumulation (g m-Z), defined as the sum of that present in the components of stalk, leaf and cabbage (tops), can be expressed as the product of aboveground biomass production and the proportion of the biomass present as sucrose. Stalk sucrose (g m - 2 ) can then be calculated based on the proportion of total sucrose present in the stalk component. For commercial sugarcane production in Australia, the payment for sucrose is based on the fresh millable stalk (cane) yield and CCS (Commercial Cane Sugar), which is closely related to the sucrose concentration in fresh millable stalks. A premium is paid for CCS which is a measure of cane quality. The stalk concentration on a fresh weight basis (g sucrose g i FW) is dependent on the stalk sucrose (g m-2 ), the stalk sucrose concentration on a dry weight basis (g sucrose g - t D W), and the stalk dry matter content (g DW g ~ FW). Similarly, fresh millable stalk yield (g FW m -2) can be calculated from stalk biomass (g DW m - 2 ) and stalk dry matter content. This framework is used to analyse the pattern of sucrose accumulation in the four crops de-
Table 1 Days after planting/ratooning at 95% value of the fitted maxim u m value of attribute Attribute
Millable stalk sucrose (g m - 2 ) Millable stalk sucrose concentration (g g - l DW) Millable stalk biomass (g m -z ) Fresh millable stalk (g m - 2 ) Millable stalk sucrose concentration (g g - l FW)
Plant crop
Ratoon crop
QlI7
Q138
Ql17
Q138
341 305
337 308
318 248
280 288
318
288
301
283
247 386
226 319
226 336
215 295
scribed in the previous paper by Robertson et al. (1996).
2. Materials and methods 2.1. Location and cultural details
Details of the field study conducted at Macknade Research Station, Ingham Q. (lat. 18.7°S, long. 146.2°E) are given in the previous paper (Robertson et al., 1996). Briefly, cultivars Ql17 and Q138 were grown as plant crops (planted on 23 July 1992) and as 1st ratoon crops (ratooned after harvest on 26 August 1992) under trickle irrigation and high nutrient supply. 1.00
t~
•ll
0.99
ee
0,98
0
g
•
o 0,97 o
,o
[] 0.96
0 • [] •
O
R# 0.95
QII7 Q138 QlI7 Q138
!
I
1000
2000
Plant Plant Ratoon Ratoon 3000
Above-ground sucrose ($ m -2) Fig. 1. Fraction sucrose in millable stalk with aboveground sucrose.
R.C. Muchow et aL / Field Crops Research 48 (1996) 2 7-36
2.2. Measurements
The crop was sampled 11 times during growth (Table 1, Robertson et al., 1996) with final sampling at 455 DAP (days after planting) in the plant crops and 421 DAR (days after ratooning) in the ratoon crops. Due to lodging and stalk breakage, it was not
3000
,
,
(~ Plant
,
,
Q138
V'
|
2500
(b) R a t o o n [] Q l 1 7 • Q138
1500
1000
1000
500
500
100
0.55
200
i
.(c) Plant O QlI7
0.50
"ee 0.45
•
0.40
Q138
o
%7, 0.35 0.30 0.25
---~'~/
0
vw
0
300
400
i
I
i
1..IZ.- -[] [] •
~
2000
1500
0
-~
3000
V
2000
o
possible to recover a complete sample from the Q138 plant crop at the last two samplings (418 and 455 DAP). However, a stalk sample was taken at these two samplings for determination of stalk sucrose concentration and stalk dry matter content. In each plot at each sampling a 15 m -2 quadrat was cut and a 15 stalk subsample was taken and
~'~
Q117
~" 2500
29
100
500
I
I
I
200
300
400
500
0.55
~
0.50
V v V
0.45 0.40
.(d) R a t o o n [] Q l 1 7 • Q138
a •
0.35 0.30 0.25
0.20
0.20
~ o.t5
0.15
~
0.10
0.10
'~
0.05
0.05
0.00
0
100
I
I
I
200
300
400
Days after planting
--~-
0.00
500
0
100
I
I
I
200
300
400
500
Days after ratooning
Fig. 2. Millable stalk sucrose with time after (a) planting for the plant crop, and (b) after ratooning for the ratoon crop. The fitted logistic equations were: Plant Q117 Y = 2454 + 2 1 5 / ( 1 + e x p ( - 0.027 _+ 0.007 * ( X - 232 + 11.9))), R 2 = 0.93. Plant Q138 Y = 2560 + 125/(1 + exp( - 0 . 0 2 8 ± 0.004 * ( X - 232 ± 5.8))), R 2 = 0.98. Ratoon Q117 Y = 2495 ± 6 3 / ( 1 + exp( - 0.025 ± 0.003* ( X - 200 ± 4.6))), R 2 = 0.98. Ratoon Q138 Y = 2107 ± 5 5 / ( 1 + e x p ( - 0 . 0 3 4 ± 0 , 0 0 5 * ( X - 193 + 4.3))), R 2 = 0.99. Points shown as triangles were excluded from the fitted equations. Stalk sucrose concentration (g g - l DW) with time after (c) planting for the plant crop, and (d) after ratooning for the ratoon crop. The fitted logistic equations were: Plant Q117 Y = 0.483 ± 0 . 0 1 5 / ( 1 + e x p ( - 0 . 0 1 8 ± 0.005 * ( X - 141 ± 14.0))), R z = 0.87. Plant Q138 Y = 0.478 ± 0 . 0 1 2 / ( 1 + e x p ( - 0 . 0 2 4 ± 0.003 * ( X - 185 _+ 4.3))), R 2 = 0.96. Ratoon Q117 Y = 0.489 ± 0 . 0 0 7 / ( 1 + e x p ( - 0 . 0 2 1 _+ 0.004" ( X - 108 ± 10.5))), R 2 = 0.90, Ratoon Q138 Y = 0.485 ± 0 . 0 1 4 / ( 1 + e x p ( - 0.022 ± 0.005 * ( X - 154 ± 7.6))), R 2 = 0.95. Points shown as triangles were excluded from the fitted equations.
30
R. C, Muchow et al./ Field Crops Research 48 (1996) 27-36
partitioned into trash (defined as dead leaf and dead sheaths), millable stalks, cabbage (defined as the immature top o f the stalk plus green leaf sheaths), and green leaf blades. The fresh weight of each component was determined. Fresh millable stalk yield was calculated as the product of the field quadrat total fresh weight and the proportion of millable stalks on a fresh weight basis. Then the material from each component was fibrated using a Jeffco cutter/grinder. The fibrated material was mixed thoroughly, and two subsamples were placed into 850 ml aluminium foil trays for drying to constant weight at 80°C. After the dry matter content was determined, the trash, millable stalk, cabbage and green leaf biomass per unit land area were determined from the field quadrat fresh weight, the component proportion o f the total aboveground material on a fresh weight basis, and the component dry matter content. From the fresh fibrated material of each component, two further 500 g samples were taken for CCS and sucrose analysis, following the methods outlined by Muchow et al. (1993). High Performance Liquid Chromatography (HPLC) was carried out following the procedures set out by the International Committee for Uniform Methods of Sugar Analysis (1994).
6000
i
yV
|
(a) Plant 5000 t~
O Ql17 @ Q138
4000
The time-course of yield attributes was described by fitting a logistic relationship, to individual replicates, o f the form Y= Ymax/(1 + exp(a* ( X - b)), in order to estimate final m a x i m u m values of the yield attributes (]/max)" The plant crop lodged at 194 D A P and it was impossible to recover a representative weight from the 15 m -2 quadrat of Q138 due to stalk breakage at samplings at 418 and 455 DAP. Consequently, to allow comparison with the Q l 1 7 plant crop, the logistic relationship was only fitted up to sampling at 389 D A P (16 August 1993) in both the Q l 1 7 and Q138 plant crops. Whilst the ratoon crops lodged at 160 DAR, the logistic relationship was fitted to all data up to the final sampling at 421 D A R on 21 October 1993. The D A P and D A R at the 95% fitted Ymax value for each yield attribute was calculated to assess the crop age at attainment of the m a x i m u m value of the yield attribute.
3. Results 3.1. S t a l k s u c r o s e
The proportion of the aboveground sucrose present as stalk sucrose was more than 95% during
6000
!
5000
(b) Ratoon [] Ql17
!
|
i
I:I /
..--O'IIII
4000
16 0
3000
2.3. D a t a a n a l y s i s
~ ~
3000
,D
"~ 2000
2000
1ooo
1000
0
0
1O0
I
I
I
200
300
400
Days after planting
. . ~ mm - -m -
500
,
I
I
I
100
200
300
400
500
Days after ratooning
Fig. 3. Stalk biomass with time after (a) planting for the plant crop, and (b) after ratooning for the ratoon crop. The fitted logistic equations were: Plant QI17 Y=5019++_333/(l+exp(-O.O29+_O.OO6*(x-216++_9.3))), R2=0.94. Plant Q138 Y=5076+205/(1+ exp(- 0.033 + 0.005* (X - 199 + 5.4))), R2 = 0.98. Ratoon Ql17 Y= 5077 + 161/(1 + exp(-0.026 _ 0.003 *( X - 188 + 6.0))), R2 = 0.97. Ratoon Q138 Y= 4569 + 159/(1 + exp(-0.029 + 0.004"(X- 181 ___6.4))), R2 = 0.96. Points shown as triangles were excluded from the fitted equations.
R.C. Muchow et al./Field Crops Research 48 (1996) 27-36
early growth and over 98% during later growth (Fig. 1). Slightly more sucrose was present in the cabbage component than in the leaf component, but the differences and absolute proportions were small (data not shown). A logistic relationship fitted the accumulation of stalk sucrose in both the plant and ratoon crops (Fig. 2a and b). For the plant crops, there was little difference between cultivars in the pattern of sucrose accumulation up to sampling at 389 DAP, and fitted
maximum values of 2454 and 2560 g m -2 were not significantly different. In contrast, the maximum aboveground sucrose in the ratoon crops was lower in Q138 than in Ql17. Maximum stalk sucrose was achieved earlier in the ratoon crops than in the plant crops with sucrose accumulation tending to plateau earlier in Q138 than in Q l l 7 (Table 1). Sucrose accumulation plateaued well before the final harvest in the ratoon crops (Fig. 2b), and tended to decline after the sampling at 389 DAP in the Ql17 plant
20000
20000
(a) P l a n t
i
•
0 Ql17 • Q138
15000
~
31
(b)
i
l
i
Ratoon
[]
[] Q I 1 7
V 15000
'q'
I 10000
10000
II
5000
5000
l O0 0.4
!
I
!
200
3 O0
400
|
|
m
500
0 0.4
m
0 Qll7 • Q138
/
VV V
y
0.2
0.1
0.1
0
300
400
m
u
m
u
i
f
i
t
1O0
200
3 O0
400
Days after planting
[] Q I I 7 • Q 1
0.3
~ 0.2
0.0
200
500
(d) R a t o o n
(c) P l a n t 0.3
100
0.0
5 O0
0
3
8
f
t
I
I
a
1O0
200
3 O0
400
5 O0
Days after ratooning
Fig. 4. Fresh millable stalk with time after (a) planting for the plant crop, and (h) after ratooning for the ratoon crop. The fitted logistic equations were: Plant Q117 Y = 16740 ± 699/(1 + e x p ( - 0.047 _ 0.013 *(X - 184 ± 5.9))), R 2 ~ 0.96. Plant Q138 Y = 17766 + 519/(1 + exp(- 0.055 ± 0.015 * ( X - 172 ± 5.2))), R 2 = 0.98. Ratoon Q117 Y = 16374 ± 439/(1 + exp(-0.038 ± 0.007 * ( X - 149 _+5.3))), R 2 = 0.97. Ratoon Q138 Y = 16019 ± 374/(1 + exp(- 0.043 ± 0.008 *(X - 147 ± 4.6))), R 2 = 0.97. Stalk dry matter content with time after (c) planting for the plant crop, and (d) after ratooning for the ratoon crop. The standard error of the mean is shown where larger than symbol size. Points shown as triangles were excluded from the fitted equations.
R.C. Muchow et al. / Field Crops Research 48 (1996) 27-36
32
crop (Fig. 2a). The maximum aboveground sucrose concentration was similar for Q117 and Q138 in the plant and ratoon crop (Fig. 2c and d) at around 0.48 g g-1 DW. This maximum stalk sucrose concentration value is much higher than the average maximum aboveground sucrose concentration value of 0.41 g g - l DW), due to the much lower sucrose concentration in the cabbage and leaf components compared to the stalk (data not shown). The pattern of accumulation of stalk biomass (Fig. 3a and b) showed a similar pattern to the accumulation of stalk sucrose (Fig. 2a and b). This indicates the dominant effect of biomass accumulation rather than partitioning of biomass to sucrose (i.e. stalk sucrose concentration) in determining stalk sucrose accumulation. Stalk sucrose concentration (g g - i DW) plateaued earlier than stalk biomass and stalk sucrose in all crops except the Q138 ratoon crops where there was little difference (Table 1).
3.2. Commercial yield (fresh millable stalk yield and CCS) For commercial sugarcane production in Aus-
0.20 u..,
0.15
ms
g
0.20
!
(a) Plant O Ql17 • Q138
A
tralia, the payment for sucrose is based on the flesh millable stalk yield and the CCS (a measure of stalk sucrose concentration on a fresh weight basis). The accumulation of fresh millable stalk yield (Fig. 4a and b) was more rapid than the accumulation of stalk biomass (Fig. 3a and b), and the maximum fresh millable stalk yield was achieved much earlier during growth than the maximum stalk biomass (Table 1). These effects were associated with the stalk dry matter content increasing during growth (Fig. 4c and d). In the plant crops, whilst there was no difference in the maximum stalk biomass between Ql17 and Q138 (Fig. 3a), the maximum fresh millable stalk yield was higher in Q138 than in Ql17 (Fig. 4a). Conversely, whilst the stalk biomass of Q138 was lower than in Q l I 7 in the ratoon crops (Fig. 3b), there was little difference between the two cultivars in fresh millable stalk yield (Fig. 4b). The stalk sucrose concentration on a fresh weight basis measured using HPLC was compared with CCS calculated based on measurements of pol, brix and fibre. The fitted equation was CCS = 1.22 ± 0.16" HPLC - 2.91 _+ 0.01, R 2 = 0.99, indicating that there was close agreement between the measures
0.15
0.10
0.10
0.05
0.05
i
i
I
(b)Ratoon I"1 QI17 •Q 1 3 8 ~
i
¢1
o o
,M
0.00 0
~ 100
i 200
t 300
Days after planting
I 400
0.00 500
___.
-]o 0
,
,
,
200
300
400
500
Days after ratooning
Fig. 5. Stalk sucrose concentration (g g - 1 FW) with time after (a) planting for the plant crop, and (b) after ratooning for the ratoon crop. The fitted logistic equations were: Plant Q117 Y = 0.150 5= 0 . 0 0 9 / ( 1 + e x p ( - 0 . 0 1 7 5: 0.004" ( X - 213 _ 9.3))), R 2 = 0.94. Plant Q138 Y=O.1325:O.OO4/(l+exp(-O.O28+_O,OO3*(X-2145:3.6))), R 2 = 0 . 9 8 . Ratoon Q l 1 7 Y = 0 . 1 5 1 _ 0 . 0 0 3 / ( l + e x p ( - 0 . 0 1 8 _ 0,002 * ( X - 172 + 3.6))), R 2 = 0.98. Ratoon Q138 Y = 0.143 + 0 . 0 0 3 / ( 1 + e x p ( - 0.027 + 0.003 * ( x - 186 _+ 3.7))), R 2 = 0.99. Points shown as triangles were excluded from the fitted equations.
R.C. Muchow et al. / Field Crops Research 48 (1996) 27-36
in the range of CCS values between 10 and 15%. At lower values, CCS underestimated sucrose concentration, and at higher values, CCS tended to slightly overestimate sucrose concentration. The time trends in stalk sucrose concentration on a fresh weight basis (Fig. 5a and b) differed from those on a dry weight basis (Fig. 2c and d). On a fresh weight basis, there was little difference between cultivars during early growth, but the fitted maximum value was higher for Q117 (0.15 g g-1 FW) than for Q138 (0.132-0.143 g g-~ FW). On a dry weight basis, there were marked cultivar differences during early growth, but the maximum value was similar for all crops (0.48 g g - l DW). Clearly, the dry matter content of the stalk material has a major impact on the measures of commercial yield.
4. Discussion June to November is the harvesting season for sugarcane in Australia. This corresponds to the last four samplings in the current analysis (ie 321-455 DAP and 287 and 421 DAR). During this period 98% of the crop sucrose was present in the stalk, even though stalks comprised only 80% of the crop biomass (Robertson et al., 1996). Based on the data presented in Table 1, maximum stalk sucrose accumulation occurred early in this harvesting period. Since maximum sucrose concentration on a dry weight basis occurred before (Q117 plant and ratoon crops and Q138 plant crop) or at the beginning (Q138 ratoon) of this harvesting period (Table 1), biomass accumulation was the dominant influence on stalk sucrose accumulation. The plateau in biomass accumulation associated with the loss of live millable stalks as discussed in the previous paper (Robertson et al., 1996), resulted in the plateau and in some cases the decrease in sucrose yield late in the harvesting period. These results suggest that maximising the accumulation of sucrose yield during the harvesting season should include practices that allow maximum biomass accumulation. During the commercial harvesting period, the stalk sucrose concentration on a dry weight basis was similar at 0.48 g g i DW for plant and ratoon crops of both cultivars Q117 and Q138. The data presented by Thompson (1988) for cultivar N14 growing in
33
South Africa showed stalk (including cabbage) sucrose concentration increased during growth to a maximum value of 0.49 g g-1 DW for both plant and ratoon crops. Similarly, Das (1936) showed for a plant crop of the early Hawaiian cultivar H109 that stalk sucrose concentration increased to 0.45 g g l DW at 12 months, then decreased due to the growth of suckers, and later increased to a value of 0.49 g g ~ DW at 24 months. Other similar values have been quoted by Julien and Delaveau (1977) and Rostron (1971). Nonetheless, data expressed on a dry weight basis are rare in the literature, and on the basis of these comparisons, it appears that the maximum sucrose concentration of sugarcane is stable across cultivars and locations, and has been so for several decades. The apparent stability of sucrose DW concentration allows the simple calculation of sucrose yield from stalk biomass. Our analysis has shown that stalk dry matter content has a major influence on the relationship between sucrose yield and commercial yield during the commercial harvesting period. Maximum stalk sucrose concentration on a fresh weight basis was much more variable than maximum stalk sucrose concentration on a dry weight basis. Similar findings exist in the literature. In the study of Thompson (1988), the maximum stalk sucrose concentration of 0.491 g g-1 DW corresponded to a fresh stalk sucrose concentration of 0.125 g g-1 FW and a dry matter content of 0.254 g DW g-1 FW. The maximum stalk sucrose concentration of 0.49 g g - l DW observed by Das (1936) occurred when the fresh stalk sucrose concentration was 0.130 g g-~ FW and the stalk dry matter content was 0.268 g DW g-1 FW. In our study, a stalk sucrose concentration for Q l l 7 at the final sampling of 0.485 g g-~ DW occurred when the fresh stalk sucrose concentration was 0.151 g g - 1 FW and the stalk dry matter content was 0.312 g DW g-1 FW. These comparisons show that CCS (a measure of stalk sucrose concentration on a fresh weight basis) can range from 12.5 to 15.1% when sucrose concentration in the dry stalk material is similar. This shows that stalk dry matter content has a dominant influence on commercial yield, and interpretation of crop dry matter response to climatic and management factors is difficult based on the commonly available fresh weight measures of productivity. Moreover, optimising economic return
R.C. Muchow et al. / Field Crops Research 48 (1996) 27-36
34
from commercial sugarcane production requires further understanding on the factors controlling the dynamics of stalk dry matter content. In the current study, early season differences between the cultivars for DW sucrose concentration were largely responsible for the higher FW sucrose concentration in Q117, suggesting that the cultivars differed in partitioning of dry matter to sucrose. However, during late growth, Ql17 had a higher maximum value than Q138 for FW sucrose concentration due to higher stalk dry matter content, as DW sucrose concentration was similar for all crops. This study highlights that the interpretation of the basis for cultivar differences in sucrose concentration on a FW basis is affected by crop age. It also demonstrated the importance of cultivar differences in stalk dry matter content in determining FW sucrose concentration at time of harvest. Lonsdale and Gosnell (1976) showed large cultivar differences in the seasonal pattern and final value at harvest of stalk dry matter content. Stalk dry matter content had a larger effect on fluctuations in FW sucrose concentration than did the DW sucrose concentration during the commercial harvesting period. CCS, the commercial measure of cane quality, was closely related to stalk sucrose concentration on
0.5
a fresh weight basis determined by HPLC during the commercial harvesting period. However, during early growth, CCS underestimated sucrose concentration, and this is likely to be associated with a higher proportion of the reducing sugar fructose relative to glucose present in the stalk material. Fructose has a negative polarising effect and glucose has a positive polarising effect, and a higher concentration of fructose biases the polarimeter reading downwards, hence underestimating the quantity of sucrose present in the juice sample (DeStefano, 1985). The harvest index concept is commonly used to measure the proportion of biological yield present as economic yield. In high yielding grain crops, harvest index commonly ranges from 0.50 to 0.55, with a theoretical maximum of 0.63 predicted for wheat (Austin et al., 1980). In sugar beet, harvest index ranges from 0.4 to 0.5 (Fick et al., 1975). A measure of harvest index in sugarcane would be the ratio of stalk sucrose yield to crop biomass, The time trend in harvest index for the sugarcane crops analysed in this study is shown in Fig. 6. Harvest index increases more or less linearly during early growth and plateaus at a maximum value. This is a similar time trend as observed for grain crops (eg. Muchow, 1990). However, the maximum value of 0.39 observed for sugar-
0.5
I
o.4
O Q117 • Q138
0.4
/,
o
0.3
,~ 02
0.2
0.I
0.1
0
I00
l
l
l
I 200
I 300
D a y s a f t e r planting
I 400
i 200
i 300
, 400
o Q117 •
V
0.3
o.o
i
(b) Ratoon
(a) Plant
0.0 500
Q138
---- I I00
500
Days after ratooning
Fig. 6. Harvest index defined as the ratio o f stalk sucrose to crop b i o m a s s with time after (a) planting for the plant crop and (b) after r a t o o n i n g for the ratoon crop. The fitted logistic equations were: Plant Q l 1 7 Y = 0.383 _+ 0 . 0 1 3 / ( l + e x p ( - 0 . 0 3 2 + 0.004* ( X - 194 _+ 4.9))), R 2 = 0.98. Plant Q 1 3 8 Y = 0.395 _+ 0 . 0 1 1 / ( 1 + e x p ( - 0 . 0 3 2 + 0.003 * ( X - 207 + 3.5))), R 2 = 0.99. R a t o o n Q 1 1 7 Y = 0.403 _+ 0 . 0 0 6 / ( 1 + e x p ( - 0 . 0 3 3 + 0.003 * ( X - 157 _+ 3.1))), R 2 = 0.99. R a t o o n Q 1 3 8 Y = 0.387 + 0 . 0 1 1 / ( 1 + e x p ( - 0 . 0 3 0 + 0.004 * ( X - 175 _+ 5.3))), R 2 = 0.98. Points s h o w n as triangles w e r e e x c l u d e d f r o m the fitted equations.
R.C. Muchow et al. / Field Crops Research 48 (1996) 27-36
cane (Fig. 6) is much lower than the harvest index values recorded for high-input grain crops or for sugar beet (Fick et al., 1975). Irvine (1983) discusses the concept of harvest index in sugarcane and quotes a world average of 0.19. He also points out that harvest index would be higher if reducing sugars are included in the economic yield, as would the inclusion of sucrose that is not extracted from the stalks. The challenge remains as to whether the harvest index of sugarcane can be raised. The fact that the proportion of stalk biomass present as sucrose has remained relatively constant at a maximum value of 0.5 g g-1 DW for decades suggests that harvest index of sugarcane may be a conservative character. The main avenue for further yield improvement is more likely to be associated with improvement in crop biomass.
35
a major influence on the relationship between sucrose yield and commercial yield.
Acknowledgements The authors thank M.F. Spillman and M. Clowes of CSIRO Division of Tropical Crops and Pastures, and L. Baker, B. Mostachetti, W. Gilbey, P. Camp, M. Pryor, R. Rutherford, S. Pennisi of the CSR Technical Field Department for crop management and assistance with the field and laboratory sampling. H.L. Vogelsang assisted with data presentation. This study was funded in part by the Sugar Research and Development Corporation.
References 5. Conclusions The key findings from this analysis are (i) most ( > 95%) of the aboveground sucrose accumulation is present in the stalks; (ii) a logistic relationship described the time trend in stalk sucrose accumulation, with maximum sucrose yield occurring well before final harvest; (iii) stalk biomass accumulation rather than the partitioning of biomass to sucrose (stalk sucrose concentration) was the major determinant of stalk sucrose accumulation; (iv) maximum stalk sucrose concentration on a dry weight basis was stable across cultivars and crop classes at a value of 0.48 g g l; (v) commercial yield expressed as the fresh millable stalk yield plateaued up to 230 days before final harvest and well before the attainment of maximum stalk biomass and sucrose yield due to increases in dry matter content during growth; (vi) Commercial cane sugar (CCS) was closely related to stalk sucrose concentration on a fresh weight basis in the range of CCS values from 10 to 15% and was unaffected by crop and cultivar, but CCS underestimated sucrose concentration at lower values; (vii) maximum values of CCS were obtained at a later crop age and were more variable across crops than were maximum values of stalk sucrose concentration on a dry weight basis due to changes in stalk dry matter content; and (viii) stalk dry matter content has
Austin, R.B, Bingham, J., Blackwell, R.D., Evans, L.T., Ford, M.A., Morgan, C.L. and Taylor, M., 1980. Genetic improvements in winter wheat yields since 1990 and associated physiological changes. J. Agric. Sci. Camb., 94: 675-689. Borden, R.J., 1942. A search for guidance in the nitrogen fertilization of the sugar cane crop. Part 1 - The plant crop. Hawaii. Plant. Rec., 46: 191-238. Borden, R.J., 1944. A search for guidance in the nitrogen fertilization of the sugar cane crop. Part 2 - The first ratoon crop. Hawaii. Plant, Rec., 48: 271-306. Borden, R.J., 1948. Nitrogen effects upon the yield and composition of sugarcane. Hawaii. Plant. Rec., 52: 1-51. Cox, M.C., Hansen, P.B. and Halili, E.R., 1994. Growth and sugar accumulation in one- and two-year crop cycles in New South Wales. Proc. Aust. Soc. Sugar Cane Technol. 1994 Conf., 38-54. Das, U.K., 1936. Nitrogen nutrition of sugar cane. PI. Physiol., 11: 251-317. DeStefano, R.P., 1985. False pol in sugarcane juice - causes and detection. J. Am. Soc. Sugar Cane Technol., 4: 80-85. Fick, G.W., Loomis, R.S, and Williams, W.A., 1975. Sugar beet. In: ed. L.T. Evans, Crop Physiology: Some Case Histories. Cambridge University Press, Cambridge, 374 pp. Glover, J., 1971. Changes in sucrose % cane and yield of sucrose per unit area associated with cold, drought and ripening. Prnc. S. Afr. Sugar Technol. Assoc., 45: 82-86. International Committee for Uniform Methods of Sugar Analysis, 1994. Methods Handbook. ICUMSA, p. GS7.23 Irvine, J.E., 1983. Sugarcane. In: Syrup. on Pot. Prod. of Field Crops under Diff. Environ.. IRRI, Los Banos, pp 361-381. Julien, M.H.R. and Delaveau, P., 1977. The effects of time of harvest on the partitioning of dry matter in three sugarcane varieties grown in contrasting environments. Proc. XVI Congr. 1SSCT, 1755-1769.
36
R.C. Muchow et al. / Field Crops Research 48 (1996) 27-36
Lonsdale, J.E. and Gosnell, J.M, 1976. Growth and quality of four sugarcane varieties as influenced by age and season. Proc. S. Afr. Sugar Technol. Assoc., 50: 82-86. Muchow, R.C., 1990. Effect of high temperature on grain-growth in field-grown maize. Field Crops Res., 23: 145-158. Muchow, R.C., Wood, A.W., Spillman, M,F., Robertson, M.J. and Thomas, M.R., 1993. Field techniques to quantify the yielddetermining processes in sugarcane. I. Methodology. Proc. Aust. Soc. Sugar Cane Technol. 1993 Conf., 336-343. Robertson, M.J., Wood, A.W. and Muchow, R.C., 1996. Growth of sugarcane under high-input conditions in tropical Australia.
I. Radiation use, biomass accumulation and partitioning. Field Crops Res. (in press). Rostron, H., 1971. The growth and productivity of sugarcane. Proc. S. Afr. Sugar Technol. Assoc., 45: 152-156. Rostron, H., 1972. The effects of age and time of harvest on the productivity of irrigated sugarcane. Proc. S. Afr. Sugar Technol. Assoc., 46: 142-150. Thompson, G.D., 1988. The composition of plant and ratoon crops of variety NI4 at Pongola. Proc. S. Afr. Sugar Technol. Assoc., 62: 185-189.
Field Crops Research 48 (1996) 27-36
Field Crops Research
Growth of sugarcane under high input conditions in tropical Australia. II. Sucrose accumulation and commercial yield R.C. M u c h o w a,*, M.J. Robertson u, A.W. Wood c a CSIRO Division of Tropical Crops and Pastures, St. Lucia, Queensland, Australia b CSIRO Division of Tropical Crops and Pastures, Aitkenvale, Queensland, Australia c CSR, Technical Field Department, lngham, Queensland, Australia
Accepted 27 March 1996
Abstract Information on the processes controlling the accumulation of sucrose over time can be used to assess the physiological basis of yield variation and consequently the scope for yield improvement in sugarcane. As commercial yield is commonly expressed on a fresh weight basis, and dry weight measures of sucrose accumulation aid biological interpretation, there is a need to study yield accumulation on both a fresh and dry weight basis. This study analysed the pattern of sucrose accumulation in the stalk in relation to crop biomass, and the concentration of sucrose in the stalk on a fresh and dry weight basis of two contrasting cultivars (Q117 and Q138) of sugarcane during the same season in tropical Australia, with irrigation and under plant and ratoon crop conditions. Over the 15 month season, 11 crop samplings were conducted. The key findings were that (1) greater than 95% of the aboveground sucrose accumulation is in the stalk; (2) a logistic relationship described the time trend in stalk sucrose accumulation, with maximum sucrose yield occurring 100 days before final harvest; (3) stalk biomass rather than stalk sucrose concentration was the major determinant of stalk sucrose accumulation; (4) maximum stalk sucrose concentration was stable across cultivars and crop classes at a value of 0.48 g g - 1 stalk dry weight; (5) commercial yield expressed as the fresh millable stalk yield plateaued up to 230 days before final harvest and well before the attainment of maximum stalk biomass and sucrose yield due to increases in dry matter content during growth; (6) maximum stalk sucrose concentration on a fresh weight basis was obtained at a later crop age and was more variable across crops than maximum stalk sucrose concentration on a dry weight basis. The study highlighted the major influence that stalk dry matter content has on the relationship between sucrose yield and commercial yield, and that biological interpretation of crop response to climatic and management factors is difficult based on commonly available fresh weight measures of productivity. Optimising economic return from commercial sugarcane production requires further understanding on the factors controlling the dynamics of stalk dry matter content. Keywords. Sugarcane; Sucrose accumulation; Harvest index; Cane yield; CCS
* Corresponding author. Tel.: +61-7-33770253; fax: +61-7-33770206; e-mail: [email protected]. 0378-4290/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved. PH S 0 3 7 8 - 4 2 9 0 ( 9 6 ) 0 0 0 4 2 - 1
28
R.C. Muehow et al. / Field Crops Research 48 (1996) 27-36
1. Introduction
The previous paper in this series (Robertson et al., 1996) examined the utilisation of solar radiation in biomass production in two high-yielding cultivars Q117 and Q138 growing in tropical Australia. Since sugarcane is harvested at a range of crop ages, knowledge on the pattern of sucrose accumulation over time is vital to maximise economic return. Accordingly, the primary purpose of this paper is to examine the relationship between biomass and sucrose accumulation in two current and contrasting Australian sugarcane cultivars growing under highinput tropical conditions. A number of studies have reported time-trends in sucrose accumulation under irrigated conditions (e.g.; Borden, 1942; Borden, 1944; Borden, 1948; Glover, 1971; Rostron, 1972; Cox et al., 1994). However, little information is available for modern cultivars on the partitioning of crop biomass to stalk sucrose during growth. Similarly, in the international literature there are relatively few studies (e.g. Das (1936) in Hawaii, Thompson (1988) in South Africa, and Julien and Delaveau (1977) in Mauritius) where the processes of sucrose accumulation over time have been examined under field conditions. Crop sucrose accumulation (g m-Z), defined as the sum of that present in the components of stalk, leaf and cabbage (tops), can be expressed as the product of aboveground biomass production and the proportion of the biomass present as sucrose. Stalk sucrose (g m - 2 ) can then be calculated based on the proportion of total sucrose present in the stalk component. For commercial sugarcane production in Australia, the payment for sucrose is based on the fresh millable stalk (cane) yield and CCS (Commercial Cane Sugar), which is closely related to the sucrose concentration in fresh millable stalks. A premium is paid for CCS which is a measure of cane quality. The stalk concentration on a fresh weight basis (g sucrose g i FW) is dependent on the stalk sucrose (g m-2 ), the stalk sucrose concentration on a dry weight basis (g sucrose g - t D W), and the stalk dry matter content (g DW g ~ FW). Similarly, fresh millable stalk yield (g FW m -2) can be calculated from stalk biomass (g DW m - 2 ) and stalk dry matter content. This framework is used to analyse the pattern of sucrose accumulation in the four crops de-
Table 1 Days after planting/ratooning at 95% value of the fitted maxim u m value of attribute Attribute
Millable stalk sucrose (g m - 2 ) Millable stalk sucrose concentration (g g - l DW) Millable stalk biomass (g m -z ) Fresh millable stalk (g m - 2 ) Millable stalk sucrose concentration (g g - l FW)
Plant crop
Ratoon crop
QlI7
Q138
Ql17
Q138
341 305
337 308
318 248
280 288
318
288
301
283
247 386
226 319
226 336
215 295
scribed in the previous paper by Robertson et al. (1996).
2. Materials and methods 2.1. Location and cultural details
Details of the field study conducted at Macknade Research Station, Ingham Q. (lat. 18.7°S, long. 146.2°E) are given in the previous paper (Robertson et al., 1996). Briefly, cultivars Ql17 and Q138 were grown as plant crops (planted on 23 July 1992) and as 1st ratoon crops (ratooned after harvest on 26 August 1992) under trickle irrigation and high nutrient supply. 1.00
t~
•ll
0.99
ee
0,98
0
g
•
o 0,97 o
,o
[] 0.96
0 • [] •
O
R# 0.95
QII7 Q138 QlI7 Q138
!
I
1000
2000
Plant Plant Ratoon Ratoon 3000
Above-ground sucrose ($ m -2) Fig. 1. Fraction sucrose in millable stalk with aboveground sucrose.
R.C. Muchow et aL / Field Crops Research 48 (1996) 2 7-36
2.2. Measurements
The crop was sampled 11 times during growth (Table 1, Robertson et al., 1996) with final sampling at 455 DAP (days after planting) in the plant crops and 421 DAR (days after ratooning) in the ratoon crops. Due to lodging and stalk breakage, it was not
3000
,
,
(~ Plant
,
,
Q138
V'
|
2500
(b) R a t o o n [] Q l 1 7 • Q138
1500
1000
1000
500
500
100
0.55
200
i
.(c) Plant O QlI7
0.50
"ee 0.45
•
0.40
Q138
o
%7, 0.35 0.30 0.25
---~'~/
0
vw
0
300
400
i
I
i
1..IZ.- -[] [] •
~
2000
1500
0
-~
3000
V
2000
o
possible to recover a complete sample from the Q138 plant crop at the last two samplings (418 and 455 DAP). However, a stalk sample was taken at these two samplings for determination of stalk sucrose concentration and stalk dry matter content. In each plot at each sampling a 15 m -2 quadrat was cut and a 15 stalk subsample was taken and
~'~
Q117
~" 2500
29
100
500
I
I
I
200
300
400
500
0.55
~
0.50
V v V
0.45 0.40
.(d) R a t o o n [] Q l 1 7 • Q138
a •
0.35 0.30 0.25
0.20
0.20
~ o.t5
0.15
~
0.10
0.10
'~
0.05
0.05
0.00
0
100
I
I
I
200
300
400
Days after planting
--~-
0.00
500
0
100
I
I
I
200
300
400
500
Days after ratooning
Fig. 2. Millable stalk sucrose with time after (a) planting for the plant crop, and (b) after ratooning for the ratoon crop. The fitted logistic equations were: Plant Q117 Y = 2454 + 2 1 5 / ( 1 + e x p ( - 0.027 _+ 0.007 * ( X - 232 + 11.9))), R 2 = 0.93. Plant Q138 Y = 2560 + 125/(1 + exp( - 0 . 0 2 8 ± 0.004 * ( X - 232 ± 5.8))), R 2 = 0.98. Ratoon Q117 Y = 2495 ± 6 3 / ( 1 + exp( - 0.025 ± 0.003* ( X - 200 ± 4.6))), R 2 = 0.98. Ratoon Q138 Y = 2107 ± 5 5 / ( 1 + e x p ( - 0 . 0 3 4 ± 0 , 0 0 5 * ( X - 193 + 4.3))), R 2 = 0.99. Points shown as triangles were excluded from the fitted equations. Stalk sucrose concentration (g g - l DW) with time after (c) planting for the plant crop, and (d) after ratooning for the ratoon crop. The fitted logistic equations were: Plant Q117 Y = 0.483 ± 0 . 0 1 5 / ( 1 + e x p ( - 0 . 0 1 8 ± 0.005 * ( X - 141 ± 14.0))), R z = 0.87. Plant Q138 Y = 0.478 ± 0 . 0 1 2 / ( 1 + e x p ( - 0 . 0 2 4 ± 0.003 * ( X - 185 _+ 4.3))), R 2 = 0.96. Ratoon Q117 Y = 0.489 ± 0 . 0 0 7 / ( 1 + e x p ( - 0 . 0 2 1 _+ 0.004" ( X - 108 ± 10.5))), R 2 = 0.90, Ratoon Q138 Y = 0.485 ± 0 . 0 1 4 / ( 1 + e x p ( - 0.022 ± 0.005 * ( X - 154 ± 7.6))), R 2 = 0.95. Points shown as triangles were excluded from the fitted equations.
30
R. C, Muchow et al./ Field Crops Research 48 (1996) 27-36
partitioned into trash (defined as dead leaf and dead sheaths), millable stalks, cabbage (defined as the immature top o f the stalk plus green leaf sheaths), and green leaf blades. The fresh weight of each component was determined. Fresh millable stalk yield was calculated as the product of the field quadrat total fresh weight and the proportion of millable stalks on a fresh weight basis. Then the material from each component was fibrated using a Jeffco cutter/grinder. The fibrated material was mixed thoroughly, and two subsamples were placed into 850 ml aluminium foil trays for drying to constant weight at 80°C. After the dry matter content was determined, the trash, millable stalk, cabbage and green leaf biomass per unit land area were determined from the field quadrat fresh weight, the component proportion o f the total aboveground material on a fresh weight basis, and the component dry matter content. From the fresh fibrated material of each component, two further 500 g samples were taken for CCS and sucrose analysis, following the methods outlined by Muchow et al. (1993). High Performance Liquid Chromatography (HPLC) was carried out following the procedures set out by the International Committee for Uniform Methods of Sugar Analysis (1994).
6000
i
yV
|
(a) Plant 5000 t~
O Ql17 @ Q138
4000
The time-course of yield attributes was described by fitting a logistic relationship, to individual replicates, o f the form Y= Ymax/(1 + exp(a* ( X - b)), in order to estimate final m a x i m u m values of the yield attributes (]/max)" The plant crop lodged at 194 D A P and it was impossible to recover a representative weight from the 15 m -2 quadrat of Q138 due to stalk breakage at samplings at 418 and 455 DAP. Consequently, to allow comparison with the Q l 1 7 plant crop, the logistic relationship was only fitted up to sampling at 389 D A P (16 August 1993) in both the Q l 1 7 and Q138 plant crops. Whilst the ratoon crops lodged at 160 DAR, the logistic relationship was fitted to all data up to the final sampling at 421 D A R on 21 October 1993. The D A P and D A R at the 95% fitted Ymax value for each yield attribute was calculated to assess the crop age at attainment of the m a x i m u m value of the yield attribute.
3. Results 3.1. S t a l k s u c r o s e
The proportion of the aboveground sucrose present as stalk sucrose was more than 95% during
6000
!
5000
(b) Ratoon [] Ql17
!
|
i
I:I /
..--O'IIII
4000
16 0
3000
2.3. D a t a a n a l y s i s
~ ~
3000
,D
"~ 2000
2000
1ooo
1000
0
0
1O0
I
I
I
200
300
400
Days after planting
. . ~ mm - -m -
500
,
I
I
I
100
200
300
400
500
Days after ratooning
Fig. 3. Stalk biomass with time after (a) planting for the plant crop, and (b) after ratooning for the ratoon crop. The fitted logistic equations were: Plant QI17 Y=5019++_333/(l+exp(-O.O29+_O.OO6*(x-216++_9.3))), R2=0.94. Plant Q138 Y=5076+205/(1+ exp(- 0.033 + 0.005* (X - 199 + 5.4))), R2 = 0.98. Ratoon Ql17 Y= 5077 + 161/(1 + exp(-0.026 _ 0.003 *( X - 188 + 6.0))), R2 = 0.97. Ratoon Q138 Y= 4569 + 159/(1 + exp(-0.029 + 0.004"(X- 181 ___6.4))), R2 = 0.96. Points shown as triangles were excluded from the fitted equations.
R.C. Muchow et al./Field Crops Research 48 (1996) 27-36
early growth and over 98% during later growth (Fig. 1). Slightly more sucrose was present in the cabbage component than in the leaf component, but the differences and absolute proportions were small (data not shown). A logistic relationship fitted the accumulation of stalk sucrose in both the plant and ratoon crops (Fig. 2a and b). For the plant crops, there was little difference between cultivars in the pattern of sucrose accumulation up to sampling at 389 DAP, and fitted
maximum values of 2454 and 2560 g m -2 were not significantly different. In contrast, the maximum aboveground sucrose in the ratoon crops was lower in Q138 than in Ql17. Maximum stalk sucrose was achieved earlier in the ratoon crops than in the plant crops with sucrose accumulation tending to plateau earlier in Q138 than in Q l l 7 (Table 1). Sucrose accumulation plateaued well before the final harvest in the ratoon crops (Fig. 2b), and tended to decline after the sampling at 389 DAP in the Ql17 plant
20000
20000
(a) P l a n t
i
•
0 Ql17 • Q138
15000
~
31
(b)
i
l
i
Ratoon
[]
[] Q I 1 7
V 15000
'q'
I 10000
10000
II
5000
5000
l O0 0.4
!
I
!
200
3 O0
400
|
|
m
500
0 0.4
m
0 Qll7 • Q138
/
VV V
y
0.2
0.1
0.1
0
300
400
m
u
m
u
i
f
i
t
1O0
200
3 O0
400
Days after planting
[] Q I I 7 • Q 1
0.3
~ 0.2
0.0
200
500
(d) R a t o o n
(c) P l a n t 0.3
100
0.0
5 O0
0
3
8
f
t
I
I
a
1O0
200
3 O0
400
5 O0
Days after ratooning
Fig. 4. Fresh millable stalk with time after (a) planting for the plant crop, and (h) after ratooning for the ratoon crop. The fitted logistic equations were: Plant Q117 Y = 16740 ± 699/(1 + e x p ( - 0.047 _ 0.013 *(X - 184 ± 5.9))), R 2 ~ 0.96. Plant Q138 Y = 17766 + 519/(1 + exp(- 0.055 ± 0.015 * ( X - 172 ± 5.2))), R 2 = 0.98. Ratoon Q117 Y = 16374 ± 439/(1 + exp(-0.038 ± 0.007 * ( X - 149 _+5.3))), R 2 = 0.97. Ratoon Q138 Y = 16019 ± 374/(1 + exp(- 0.043 ± 0.008 *(X - 147 ± 4.6))), R 2 = 0.97. Stalk dry matter content with time after (c) planting for the plant crop, and (d) after ratooning for the ratoon crop. The standard error of the mean is shown where larger than symbol size. Points shown as triangles were excluded from the fitted equations.
R.C. Muchow et al. / Field Crops Research 48 (1996) 27-36
32
crop (Fig. 2a). The maximum aboveground sucrose concentration was similar for Q117 and Q138 in the plant and ratoon crop (Fig. 2c and d) at around 0.48 g g-1 DW. This maximum stalk sucrose concentration value is much higher than the average maximum aboveground sucrose concentration value of 0.41 g g - l DW), due to the much lower sucrose concentration in the cabbage and leaf components compared to the stalk (data not shown). The pattern of accumulation of stalk biomass (Fig. 3a and b) showed a similar pattern to the accumulation of stalk sucrose (Fig. 2a and b). This indicates the dominant effect of biomass accumulation rather than partitioning of biomass to sucrose (i.e. stalk sucrose concentration) in determining stalk sucrose accumulation. Stalk sucrose concentration (g g - i DW) plateaued earlier than stalk biomass and stalk sucrose in all crops except the Q138 ratoon crops where there was little difference (Table 1).
3.2. Commercial yield (fresh millable stalk yield and CCS) For commercial sugarcane production in Aus-
0.20 u..,
0.15
ms
g
0.20
!
(a) Plant O Ql17 • Q138
A
tralia, the payment for sucrose is based on the flesh millable stalk yield and the CCS (a measure of stalk sucrose concentration on a fresh weight basis). The accumulation of fresh millable stalk yield (Fig. 4a and b) was more rapid than the accumulation of stalk biomass (Fig. 3a and b), and the maximum fresh millable stalk yield was achieved much earlier during growth than the maximum stalk biomass (Table 1). These effects were associated with the stalk dry matter content increasing during growth (Fig. 4c and d). In the plant crops, whilst there was no difference in the maximum stalk biomass between Ql17 and Q138 (Fig. 3a), the maximum fresh millable stalk yield was higher in Q138 than in Ql17 (Fig. 4a). Conversely, whilst the stalk biomass of Q138 was lower than in Q l I 7 in the ratoon crops (Fig. 3b), there was little difference between the two cultivars in fresh millable stalk yield (Fig. 4b). The stalk sucrose concentration on a fresh weight basis measured using HPLC was compared with CCS calculated based on measurements of pol, brix and fibre. The fitted equation was CCS = 1.22 ± 0.16" HPLC - 2.91 _+ 0.01, R 2 = 0.99, indicating that there was close agreement between the measures
0.15
0.10
0.10
0.05
0.05
i
i
I
(b)Ratoon I"1 QI17 •Q 1 3 8 ~
i
¢1
o o
,M
0.00 0
~ 100
i 200
t 300
Days after planting
I 400
0.00 500
___.
-]o 0
,
,
,
200
300
400
500
Days after ratooning
Fig. 5. Stalk sucrose concentration (g g - 1 FW) with time after (a) planting for the plant crop, and (b) after ratooning for the ratoon crop. The fitted logistic equations were: Plant Q117 Y = 0.150 5= 0 . 0 0 9 / ( 1 + e x p ( - 0 . 0 1 7 5: 0.004" ( X - 213 _ 9.3))), R 2 = 0.94. Plant Q138 Y=O.1325:O.OO4/(l+exp(-O.O28+_O,OO3*(X-2145:3.6))), R 2 = 0 . 9 8 . Ratoon Q l 1 7 Y = 0 . 1 5 1 _ 0 . 0 0 3 / ( l + e x p ( - 0 . 0 1 8 _ 0,002 * ( X - 172 + 3.6))), R 2 = 0.98. Ratoon Q138 Y = 0.143 + 0 . 0 0 3 / ( 1 + e x p ( - 0.027 + 0.003 * ( x - 186 _+ 3.7))), R 2 = 0.99. Points shown as triangles were excluded from the fitted equations.
R.C. Muchow et al. / Field Crops Research 48 (1996) 27-36
in the range of CCS values between 10 and 15%. At lower values, CCS underestimated sucrose concentration, and at higher values, CCS tended to slightly overestimate sucrose concentration. The time trends in stalk sucrose concentration on a fresh weight basis (Fig. 5a and b) differed from those on a dry weight basis (Fig. 2c and d). On a fresh weight basis, there was little difference between cultivars during early growth, but the fitted maximum value was higher for Q117 (0.15 g g-1 FW) than for Q138 (0.132-0.143 g g-~ FW). On a dry weight basis, there were marked cultivar differences during early growth, but the maximum value was similar for all crops (0.48 g g - l DW). Clearly, the dry matter content of the stalk material has a major impact on the measures of commercial yield.
4. Discussion June to November is the harvesting season for sugarcane in Australia. This corresponds to the last four samplings in the current analysis (ie 321-455 DAP and 287 and 421 DAR). During this period 98% of the crop sucrose was present in the stalk, even though stalks comprised only 80% of the crop biomass (Robertson et al., 1996). Based on the data presented in Table 1, maximum stalk sucrose accumulation occurred early in this harvesting period. Since maximum sucrose concentration on a dry weight basis occurred before (Q117 plant and ratoon crops and Q138 plant crop) or at the beginning (Q138 ratoon) of this harvesting period (Table 1), biomass accumulation was the dominant influence on stalk sucrose accumulation. The plateau in biomass accumulation associated with the loss of live millable stalks as discussed in the previous paper (Robertson et al., 1996), resulted in the plateau and in some cases the decrease in sucrose yield late in the harvesting period. These results suggest that maximising the accumulation of sucrose yield during the harvesting season should include practices that allow maximum biomass accumulation. During the commercial harvesting period, the stalk sucrose concentration on a dry weight basis was similar at 0.48 g g i DW for plant and ratoon crops of both cultivars Q117 and Q138. The data presented by Thompson (1988) for cultivar N14 growing in
33
South Africa showed stalk (including cabbage) sucrose concentration increased during growth to a maximum value of 0.49 g g-1 DW for both plant and ratoon crops. Similarly, Das (1936) showed for a plant crop of the early Hawaiian cultivar H109 that stalk sucrose concentration increased to 0.45 g g l DW at 12 months, then decreased due to the growth of suckers, and later increased to a value of 0.49 g g ~ DW at 24 months. Other similar values have been quoted by Julien and Delaveau (1977) and Rostron (1971). Nonetheless, data expressed on a dry weight basis are rare in the literature, and on the basis of these comparisons, it appears that the maximum sucrose concentration of sugarcane is stable across cultivars and locations, and has been so for several decades. The apparent stability of sucrose DW concentration allows the simple calculation of sucrose yield from stalk biomass. Our analysis has shown that stalk dry matter content has a major influence on the relationship between sucrose yield and commercial yield during the commercial harvesting period. Maximum stalk sucrose concentration on a fresh weight basis was much more variable than maximum stalk sucrose concentration on a dry weight basis. Similar findings exist in the literature. In the study of Thompson (1988), the maximum stalk sucrose concentration of 0.491 g g-1 DW corresponded to a fresh stalk sucrose concentration of 0.125 g g-1 FW and a dry matter content of 0.254 g DW g-1 FW. The maximum stalk sucrose concentration of 0.49 g g - l DW observed by Das (1936) occurred when the fresh stalk sucrose concentration was 0.130 g g-~ FW and the stalk dry matter content was 0.268 g DW g-1 FW. In our study, a stalk sucrose concentration for Q l l 7 at the final sampling of 0.485 g g-~ DW occurred when the fresh stalk sucrose concentration was 0.151 g g - 1 FW and the stalk dry matter content was 0.312 g DW g-1 FW. These comparisons show that CCS (a measure of stalk sucrose concentration on a fresh weight basis) can range from 12.5 to 15.1% when sucrose concentration in the dry stalk material is similar. This shows that stalk dry matter content has a dominant influence on commercial yield, and interpretation of crop dry matter response to climatic and management factors is difficult based on the commonly available fresh weight measures of productivity. Moreover, optimising economic return
R.C. Muchow et al. / Field Crops Research 48 (1996) 27-36
34
from commercial sugarcane production requires further understanding on the factors controlling the dynamics of stalk dry matter content. In the current study, early season differences between the cultivars for DW sucrose concentration were largely responsible for the higher FW sucrose concentration in Q117, suggesting that the cultivars differed in partitioning of dry matter to sucrose. However, during late growth, Ql17 had a higher maximum value than Q138 for FW sucrose concentration due to higher stalk dry matter content, as DW sucrose concentration was similar for all crops. This study highlights that the interpretation of the basis for cultivar differences in sucrose concentration on a FW basis is affected by crop age. It also demonstrated the importance of cultivar differences in stalk dry matter content in determining FW sucrose concentration at time of harvest. Lonsdale and Gosnell (1976) showed large cultivar differences in the seasonal pattern and final value at harvest of stalk dry matter content. Stalk dry matter content had a larger effect on fluctuations in FW sucrose concentration than did the DW sucrose concentration during the commercial harvesting period. CCS, the commercial measure of cane quality, was closely related to stalk sucrose concentration on
0.5
a fresh weight basis determined by HPLC during the commercial harvesting period. However, during early growth, CCS underestimated sucrose concentration, and this is likely to be associated with a higher proportion of the reducing sugar fructose relative to glucose present in the stalk material. Fructose has a negative polarising effect and glucose has a positive polarising effect, and a higher concentration of fructose biases the polarimeter reading downwards, hence underestimating the quantity of sucrose present in the juice sample (DeStefano, 1985). The harvest index concept is commonly used to measure the proportion of biological yield present as economic yield. In high yielding grain crops, harvest index commonly ranges from 0.50 to 0.55, with a theoretical maximum of 0.63 predicted for wheat (Austin et al., 1980). In sugar beet, harvest index ranges from 0.4 to 0.5 (Fick et al., 1975). A measure of harvest index in sugarcane would be the ratio of stalk sucrose yield to crop biomass, The time trend in harvest index for the sugarcane crops analysed in this study is shown in Fig. 6. Harvest index increases more or less linearly during early growth and plateaus at a maximum value. This is a similar time trend as observed for grain crops (eg. Muchow, 1990). However, the maximum value of 0.39 observed for sugar-
0.5
I
o.4
O Q117 • Q138
0.4
/,
o
0.3
,~ 02
0.2
0.I
0.1
0
I00
l
l
l
I 200
I 300
D a y s a f t e r planting
I 400
i 200
i 300
, 400
o Q117 •
V
0.3
o.o
i
(b) Ratoon
(a) Plant
0.0 500
Q138
---- I I00
500
Days after ratooning
Fig. 6. Harvest index defined as the ratio o f stalk sucrose to crop b i o m a s s with time after (a) planting for the plant crop and (b) after r a t o o n i n g for the ratoon crop. The fitted logistic equations were: Plant Q l 1 7 Y = 0.383 _+ 0 . 0 1 3 / ( l + e x p ( - 0 . 0 3 2 + 0.004* ( X - 194 _+ 4.9))), R 2 = 0.98. Plant Q 1 3 8 Y = 0.395 _+ 0 . 0 1 1 / ( 1 + e x p ( - 0 . 0 3 2 + 0.003 * ( X - 207 + 3.5))), R 2 = 0.99. R a t o o n Q 1 1 7 Y = 0.403 _+ 0 . 0 0 6 / ( 1 + e x p ( - 0 . 0 3 3 + 0.003 * ( X - 157 _+ 3.1))), R 2 = 0.99. R a t o o n Q 1 3 8 Y = 0.387 + 0 . 0 1 1 / ( 1 + e x p ( - 0 . 0 3 0 + 0.004 * ( X - 175 _+ 5.3))), R 2 = 0.98. Points s h o w n as triangles w e r e e x c l u d e d f r o m the fitted equations.
R.C. Muchow et al. / Field Crops Research 48 (1996) 27-36
cane (Fig. 6) is much lower than the harvest index values recorded for high-input grain crops or for sugar beet (Fick et al., 1975). Irvine (1983) discusses the concept of harvest index in sugarcane and quotes a world average of 0.19. He also points out that harvest index would be higher if reducing sugars are included in the economic yield, as would the inclusion of sucrose that is not extracted from the stalks. The challenge remains as to whether the harvest index of sugarcane can be raised. The fact that the proportion of stalk biomass present as sucrose has remained relatively constant at a maximum value of 0.5 g g-1 DW for decades suggests that harvest index of sugarcane may be a conservative character. The main avenue for further yield improvement is more likely to be associated with improvement in crop biomass.
35
a major influence on the relationship between sucrose yield and commercial yield.
Acknowledgements The authors thank M.F. Spillman and M. Clowes of CSIRO Division of Tropical Crops and Pastures, and L. Baker, B. Mostachetti, W. Gilbey, P. Camp, M. Pryor, R. Rutherford, S. Pennisi of the CSR Technical Field Department for crop management and assistance with the field and laboratory sampling. H.L. Vogelsang assisted with data presentation. This study was funded in part by the Sugar Research and Development Corporation.
References 5. Conclusions The key findings from this analysis are (i) most ( > 95%) of the aboveground sucrose accumulation is present in the stalks; (ii) a logistic relationship described the time trend in stalk sucrose accumulation, with maximum sucrose yield occurring well before final harvest; (iii) stalk biomass accumulation rather than the partitioning of biomass to sucrose (stalk sucrose concentration) was the major determinant of stalk sucrose accumulation; (iv) maximum stalk sucrose concentration on a dry weight basis was stable across cultivars and crop classes at a value of 0.48 g g l; (v) commercial yield expressed as the fresh millable stalk yield plateaued up to 230 days before final harvest and well before the attainment of maximum stalk biomass and sucrose yield due to increases in dry matter content during growth; (vi) Commercial cane sugar (CCS) was closely related to stalk sucrose concentration on a fresh weight basis in the range of CCS values from 10 to 15% and was unaffected by crop and cultivar, but CCS underestimated sucrose concentration at lower values; (vii) maximum values of CCS were obtained at a later crop age and were more variable across crops than were maximum values of stalk sucrose concentration on a dry weight basis due to changes in stalk dry matter content; and (viii) stalk dry matter content has
Austin, R.B, Bingham, J., Blackwell, R.D., Evans, L.T., Ford, M.A., Morgan, C.L. and Taylor, M., 1980. Genetic improvements in winter wheat yields since 1990 and associated physiological changes. J. Agric. Sci. Camb., 94: 675-689. Borden, R.J., 1942. A search for guidance in the nitrogen fertilization of the sugar cane crop. Part 1 - The plant crop. Hawaii. Plant. Rec., 46: 191-238. Borden, R.J., 1944. A search for guidance in the nitrogen fertilization of the sugar cane crop. Part 2 - The first ratoon crop. Hawaii. Plant, Rec., 48: 271-306. Borden, R.J., 1948. Nitrogen effects upon the yield and composition of sugarcane. Hawaii. Plant. Rec., 52: 1-51. Cox, M.C., Hansen, P.B. and Halili, E.R., 1994. Growth and sugar accumulation in one- and two-year crop cycles in New South Wales. Proc. Aust. Soc. Sugar Cane Technol. 1994 Conf., 38-54. Das, U.K., 1936. Nitrogen nutrition of sugar cane. PI. Physiol., 11: 251-317. DeStefano, R.P., 1985. False pol in sugarcane juice - causes and detection. J. Am. Soc. Sugar Cane Technol., 4: 80-85. Fick, G.W., Loomis, R.S, and Williams, W.A., 1975. Sugar beet. In: ed. L.T. Evans, Crop Physiology: Some Case Histories. Cambridge University Press, Cambridge, 374 pp. Glover, J., 1971. Changes in sucrose % cane and yield of sucrose per unit area associated with cold, drought and ripening. Prnc. S. Afr. Sugar Technol. Assoc., 45: 82-86. International Committee for Uniform Methods of Sugar Analysis, 1994. Methods Handbook. ICUMSA, p. GS7.23 Irvine, J.E., 1983. Sugarcane. In: Syrup. on Pot. Prod. of Field Crops under Diff. Environ.. IRRI, Los Banos, pp 361-381. Julien, M.H.R. and Delaveau, P., 1977. The effects of time of harvest on the partitioning of dry matter in three sugarcane varieties grown in contrasting environments. Proc. XVI Congr. 1SSCT, 1755-1769.
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Lonsdale, J.E. and Gosnell, J.M, 1976. Growth and quality of four sugarcane varieties as influenced by age and season. Proc. S. Afr. Sugar Technol. Assoc., 50: 82-86. Muchow, R.C., 1990. Effect of high temperature on grain-growth in field-grown maize. Field Crops Res., 23: 145-158. Muchow, R.C., Wood, A.W., Spillman, M,F., Robertson, M.J. and Thomas, M.R., 1993. Field techniques to quantify the yielddetermining processes in sugarcane. I. Methodology. Proc. Aust. Soc. Sugar Cane Technol. 1993 Conf., 336-343. Robertson, M.J., Wood, A.W. and Muchow, R.C., 1996. Growth of sugarcane under high-input conditions in tropical Australia.
I. Radiation use, biomass accumulation and partitioning. Field Crops Res. (in press). Rostron, H., 1971. The growth and productivity of sugarcane. Proc. S. Afr. Sugar Technol. Assoc., 45: 152-156. Rostron, H., 1972. The effects of age and time of harvest on the productivity of irrigated sugarcane. Proc. S. Afr. Sugar Technol. Assoc., 46: 142-150. Thompson, G.D., 1988. The composition of plant and ratoon crops of variety NI4 at Pongola. Proc. S. Afr. Sugar Technol. Assoc., 62: 185-189.