THE EFFECT OF YEAR, CULTIVAR, AND TIME OF HARVEST ON SUGARCANE YIELDS IN FLORIDA. Belle Glade, FL 33430

Transcription

1 THE EFFECT OF YEAR, CULTIVAR, AND TIME OF HARVEST ON SUGARCANE YIELDS IN FLORIDA Robert A. Gilbert 1, James M. Shine Jr. 2, Jimmy D. Miller 3, Ronald W. Rice 2, and Curtis R. Rainbolt 4 1 University of Florida, Everglades Research and Education Center, 3200 E. Palm Beach Rd., Belle Glade, FL Sugar Cane Growers Cooperative of Florida, P.O. Box 666, Belle Glade, FL United States Department of Agriculture-Agricultural Research Service, Sugarcane Field Station, US Hwy. 441, Canal Point, FL Palm Beach County Extension Service, 2976 State Road 15, Belle Glade, FL ABSTRACT Sugarcane is harvested during a five-month period (October to March) in the Everglades Agricultural Area (EAA) of south Florida. Sugarcane biomass and sucrose accumulation will vary with annual climate (year of harvest), cultivar, and plant maturity (time of harvest). The objectives of this experiment were to determine the effect of year, cultivar, and time of harvest and their interactions on sugarcane yields in the EAA. Six non-confounded data sets from 1998 to 2001 (termed case studies ) were used to examine temporal trends in kilograms of sucrose per ton of cane (KST), tons of cane per hectare (TCH) and tons of sugar per hectare (TSH). Year had a significant effect on KST, TCH, and TSH in two of the six case studies, but was a less significant determinant of yield than either cultivar or time of harvest. TCH and TSH were significantly lower in 1999 than 2001, possibly due to low solar irradiance early in KST and TSH were significantly lower prior to mid-december and mid-november, respectively, than subsequent harvest dates. CP exhibited significantly greater KST than other cultivars in 23 of 25 pairwise comparisons. The year x time of harvest interaction was significant for KST in five of six case studies, with the largest between-year KST differences occurring early in the harvest season. Year x cultivar means were not significantly different between years for the vast majority of cultivars tested, indicating that the performance of most cultivars was stable across years. These results indicate that, unlike the effect of cultivar or time of harvest, the year effect on sugarcane yields in the EAA is sporadic, and likely to manifest itself primarily in early-season KST differences between years. Keywords: sugarcane, year, cultivar, time of harvest INTRODUCTION Sugarcane (Saccharum species hybrids) in south Florida is harvested during a five-month period (October March). Additionally, since sugarcane is ratooned, plantings are harvested across different years. Within any given year, sucrose accumulation will vary due to both annual meteorological conditions (year) and time of harvest. Information is limited regarding year effects on sugarcane yield in the Everglades Agricultural Area (EAA) of Florida. In Louisiana, Arceneaux and Hebert (1943) found cultivar x location, cultivar x year, and cultivar x location x year all highly significant for sugarcane tonnage (they did not measure sucrose content), and emphasized the need for multi-year testing of sugarcane germplasm. However, Legendre (1985) stated that relative sucrose contents of six cultivars in Louisiana did not change significantly over five seasons. 165

2 Gilbert: The Effect of Yield, Cultivar, and Time of Harvest on Sugarcane Yields in Florida Milligan et al. (1990) found that genotype by location variances were greater than genotype by year, implying locations could be substituted for years in the Louisiana breeding program. Jackson and Hogarth (1992) also found that genotype sugar yield rank in Australia across crop-years was similar, suggesting little gain in germplasm testing across multiple years. In Australia, Jones et al. (1993) presented a technique for minimizing confounding of genotype x year and genotype x crop effects by using mean yields recorded from neighboring farms to indicate the year effect. They concluded that the confounding effect of years on the interpretation of genotype x crop effects was small. Since 1962, average sugarcane tonnage in the EAA has fluctuated between 68 (1982) and 97 tons ha -1 (1998), displaying a difference of up to 30 % between years (Florida Sugar Cane League, Inc.). Changes in cultivar yield potential, management practices and climatic variability contribute to yearly fluctuations in sugarcane tonnage (TCH) yields. In the Dominican Republic, Ellis and Arceneaux (1963) reported a high correlation between yearly TCH with growth days (where soil moisture was deemed sufficient for crop growth), while Lumsden et al. (2000) used seasonal rainfall forecasts to predict sugarcane yield in S. Africa. Approximately % of EAA sugarcane is produced on Histosols, where drought stress is generally of limited concern (Alvarez et al., 1982) due to normally uniform rainfall with respect to crop water use and the superior water-holding capacity of these organic soils. The relation of sugarcane growth to air temperature and solar radiation has been extensively studied. In Florida, Shih and Gascho (1971) used a regression model to predict sugarcane biomass using degree days and solar radiation, and Allen (1977) found a significant relationship between TCH and a combination of solar radiation and growing degree days, as did Alvarez et al. (1982). Legendre (1975) reported a close negative association between ripening (KST) and temperature for one of five cultivars in Louisiana. Ripening was most closely associated with solar radiation. Liu et al. (1998) reported genotypic variation in base temperatures at different sugarcane development stages in Australia. Campbell et al. (1998) also reported a genotypic difference in base temperatures for node appearance between sugarcane cultivars Q117 and Q138 in Australia. Ebrahim et al. (1998) found that the ratio of leaf area per shoot biomass for different cultivars changed with air temperature in Australia, while Sinclair et al. (2004) reported a significant difference among CP cultivars in phyllocron and leaf area development in relationship to air temperatures in Florida. The genotypic variability in developmental response to meteorological conditions may lead to significant cultivar x year interactions on TCH and TSH. The effect of year on harvest traits (KST, TCH and TSH) of commercially-released CP germplasm in the EAA has not been reported. These CP cultivars are grown on >78 % of the EAA acreage (Glaz and Vonderwell, 2003). Also, the significance and magnitude of year x time of harvest interactions have not been reported in the scientific literature. The objectives of this experiment were to determine the effect of year, cultivar, time of harvest and their interactions on sugarcane yields in the EAA. While agronomic studies usually report the results of a single experiment, the magnitude of data collected in this project allowed for the analysis of a total of six separate experimental data sets (termed case studies ). Each data set was non-confounded with respect to year (different years within any given case study employ the same location, crop age, cultivars, and biweekly harvest periods). We chose to use all available data (six data sets rather than one) to strengthen the inference base for the analysis. This approach allowed us to determine if the 166

3 Journal American Society Sugar Cane Technologists, Vol. 24, 2004 year effect on sugarcane growth and its interaction with time of harvest and cultivar were consistent across different experimental conditions. MATERIALS AND METHODS The sugarcane yield trials were conducted at four locations repeated in different years through four different cropping seasons in the Everglades Agricultural Area (EAA) in Florida (Table 1). The data analyzed for this experiment was part of a larger cultivar x time of harvest sucrose accumulation trial (Gilbert et al., 2004). From the larger data set, it was possible to construct a total of six unique data sets (case studies) to examine the unconfounded effect of year in each case study (different years within any given case study employ the same location, crop age, cultivars, and biweekly harvest periods). The data sets used in this analysis were collected from sugarcane yield trials planted beginning in the fall of 1997 and harvested from the through the harvest seasons. Case studies 1 and 2 (Table 1) were located at the Everglades Research and Education Center (26 o 39' N, o 38' W), with a Lauderhill muck [euic, hyperthermic Lithic Haplosaprist] soil type (EREC). Case studies 3 and 4 were located at Lakeview Farms, Inc. (26 o 48' N, o 41' W), with a Torry muck [euic, hyperthermic, Typic Haplosaprist] soil type (Lakeview). This location is regarded as warmland muck due to its proximity to Lake Okeechobee. The lake effect reduces the risk of freezes at this site (none of the data sets included in this study included a freeze event). Case study 5 was located at Sugar Cane Growers Cooperative of Florida Hillsboro Farm (26 o 31' N, o 28' W) also with a Lauderhill muck soil (Hillsboro). Case study 6 was located at Hundley Farms, Inc. Pioneer #2 Farm(26 o 41' N, o 27' W), with a Lauderhill muck soil (Hundley). All sugarcane yield trials were planted in a randomized complete block design with either three or four replications. Cultivar was the main treatment. Each plot was four rows wide by 10.7 m long with 1.5 m row spacing. Plant populations were determined by stalk counts taken from the central two rows in each plot performed in July or August of each season. To determine the effect of time of harvest, five-stalk samples were harvested at biweekly intervals each season beginning mid- October and ending in mid-march. The term biweek corresponds to the number of biweekly periods commencing on October 14 of each year. The corresponding dates for the biweekly periods are presented in Table 2. Each five-stalk sample was topped in the field, and the millable fresh stalk weight, Brix, and pol was measured in the University of Florida EREC sugar laboratory. The fresh weight, Brix, and pol measurements were used to calculate kilograms of sugar per ton of sugarcane (KST) (Miller and James, 1977). Tons of sugarcane per hectare (TCH) was estimated using plant population and mean stalk weights. Tons of sugar per hectare (TSH) was calculated as the product of KST and TCH (divided by 0 to convert kg sucrose to tons). Repeated measures analysis of variance using SAS (Littell et al., 2002) was performed to determine the significance of the main effects of year, cultivar, and time of harvest, and the interaction of year x time of harvest and year x cultivar for each case study. All statistical comparisons were done within an individual case study, not among case studies. The interaction of cultivar x time of harvest was analyzed separately (Gilbert et al., 2004) and is not included here. Paired t-tests were performed using LSMEA estimates in SAS (Littell et al., 2002) to contrast each pair of treatment means individually for all effects. 167

4 Gilbert: The Effect of Yield, Cultivar, and Time of Harvest on Sugarcane Yields in Florida RESULTS AND DISCUSSION Year Year had a significant effect on KST (case studies 1 and 3), TCH (case studies 4 and 6) and TSH (case studies 4 and 6) (Table 3). The three-way interaction of year x cultivar x time of harvest was not significant in 15 of 18 analyses and is not discussed. The F-statistic was of lower magnitude than similar data cases investigating the primary effects of cultivar (Gilbert et al., 2004) and location. This indicates that the year effect may be less important than cultivar and location effects in determining sugarcane KST, TCH and TSH. These findings concur with the results of Jackson and Hogarth (1992) and Jones et al. (1993) in Australia. KST was significantly higher in (134 kg sucrose ton -1 ) than (125 kg sucrose ton -1 ) in case study 1 (Table 4). KST was also significantly lower in (134 kg sucrose ton -1 ) than (138 kg sucrose ton -1 ) in case study 3. Both of these cases involved plant cane crops established in 1998 (Table 1). Case study 2, involving comparisons with first ratoon sugarcane in , did not show significant differences in KST between years. Case studies 4 and 6 both involved comparisons of first ratoon sugarcane in 1999 and 2001 (Table 1), and both reflect significant differences in TCH and TSH between years (Table 4). In both case studies, TCH and TSH were significantly lower in 1999 than Numerically, TCH and TSH were also lower in for case studies 2 and 5. Compared to recent years, industrywide sugarcane yields in the EAA were lowest for the crop harvest year. Industry-wide, TCH was 91.5 tons ha -1 in 1999 compared to 98.2 tons ha -1 in 2001 (Sugarcane Growers Cooperative of Florida, unpublished data). The growing season in the EAA was characterized by low early-season solar radiation and high early-season rainfall (Table 5). The University of Florida EREC weather station in Belle Glade, FL recorded precipitation in 24 of 30 days in June, It is surmised that low total solar irradiance in the spring would limit photosynthate assimilation and would delay sugarcane canopy closure by slowing leaf emergence rate and total stalk height, contributing factors underlying low TCH recorded in 1999 across the experimental case studies and the sugarcane industry. Recent crop modeling approaches (Sinclair et al., 2004) have assumed that temperature and solar radiation early in the growing season are limiting factors for sugarcane production in the EAA. The significant yield reduction documented for supports this assumption. Time of Harvest Time of harvest (biweek) significantly affected KST in all six case studies (Table 3). Samples collected before biweek 5 (mid-december) had significantly lower KST than later harvest dates in 139 of 146 pairwise contrasts across all the case studies. Average KST prior to mid- December was significantly lower than subsequent dates in all cases (Table 6). These results concur with previous findings indicating that early-season sugarcane is harvested prior to maximal sucrose accumulation in the EAA (Miller and James, 1977; Gilbert et al., 2004). Growers normally apply ripeners to counter this effect in early-harvested sugarcane. The effect of time on TCH was significant in five of the six case studies (Table 3). Unlike KST, TCH did not follow a clear trend across harvest dates (data not shown). The overall pattern of TCH over time thus was not as straightforward as KST. One reason for this complexity is that fresh weights, not dry weights, are customarily measured for sugarcane. Crop 168

5 Journal American Society Sugar Cane Technologists, Vol. 24, 2004 fresh weight may vary both over the season as plant relative water content changes, and diurnally due to plant stomatal activity (Liu and Helyar, 2003). Thus both time of season and time of day affect fresh weight at harvest. In addition, there is a direct relation in repeated measures experiments between size of individual samples and total plot size required. The five-stalk samples used had higher variability in TCH than KST, which may have been ameliorated by increased number of stalks per sample. However increasing sample size would have greatly increased the resources required for land and labor to implement these experiments. The effect of time of harvest on TSH was significant in all six case studies (Table 3). Harvest samples taken on or before biweek 3 (mid-november) had significantly lower TSH than subsequent sampling dates in 81 of 96 pairwise comparisons across all the case studies. Average TSH was significantly lower in biweeks 1-3 (October to mid-november) than subsequent dates in most cases (Table 6). Lower TSH was due primarily to lower KST rather than reduced TCH. These case studies confirm previous research that KST and TSH yields averaged across cultivars and years are likely to be significantly lower the first 6 weeks of the harvest season (Gilbert et al., 2004). Cultivars The effect of cultivar was highly significant on KST for all case studies (Table 3). No significant disease problems were observed on the cultivars in this study. CP was notable for its high KST, averaging greater than kg sucrose ton -1 in every case study in which it was included (Table 7). CP and CP KST levels significantly exceeded all other cultivars in case study 1. CP also had significantly greater KST than nine of 11 cultivars in case study 2 (CP was not planted in this case study). CP KST (144 kg sucrose ton -1 ) was 8-10 kg sucrose ton -1 higher than all other cultivars in case study 6. CP had significantly greater KST in 23 of 25 of the pairwise comparisons with other cultivars in the four case studies in which it was present. CP acreage in the EAA has dramatically increased in recent years (Glaz and Vonderwell, 2003), and it is now used as a standard in the CP breeding program primarily due to its superior sucrose content. In contrast, CP and CP were inferior in the majority of KST comparisons with other CP cultivars. These cultivars are not presently grown commercially in the EAA. Cultivar significantly affected TCH in all six case studies (Table 3). CP was notable for its low TCH (Table 7). Across the four case studies that included CP , TCH recorded for this cultivar averaged 54 tons ha -1 less than the highest-ranked cultivar. In contrast, CP and CP TCH were either ranked highest or not significantly different from the highest-ranked cultivar in all case studies including these cultivars. In contrast to cultivars with superior KST, superior TCH performance has not led to perceptible adoption of CP or CP by Florida sugarcane growers. Cultivar significantly affected TSH in all six case studies (Table 3). In case study 1, CP (13.7 tons sucrose ha -1 ) and CP (10.9 tons sucrose ha -1 ) recorded significantly lower TSH than other cultivars (Table 7). With the exception of case study 3, CP had the lowest TSH among all sugarcane cultivars, due primarily to low TCH. CP , CP and CP were either ranked highest for TSH or did not differ significantly from the highest-ranked cultivar across all case studies where they were included. Superior TSH was primarily due to either elevated TCH (CP ) or high KST (CP and CP ). While CP and 169

6 Gilbert: The Effect of Yield, Cultivar, and Time of Harvest on Sugarcane Yields in Florida CP are among the most widely-grown clones in the EAA, CP does not appear in the Florida sugarcane variety census (Glaz and Vonderwell, 2003). Given the choice, growers are more likely to adopt high KST clones over those with high TCH and low KST characteristics (like CP ) since high TCH is associated with increased harvest, transport, and milling costs. Our results justify the recent decision to use CP as a breeding program check and parent to raise the bar for KST levels in the CP breeding program. However as the use of high-kst clones continues to increase, there is concern that lower fiber levels of harvested cane will reduce bagasse production below what is needed to generate power for Florida mills. This is a reversal of previous preferences for the mills of high-kst low-fiber cultivars. Year x Time of Harvest The interaction of year x time of harvest was significant for KST in five of the six case studies (Table 3). The year x time of harvest KST means are shown in Figure 1. In case study 1, KST levels in exceeded by 8-10 kg sucrose ton -1 throughout the growing season (Fig 1A). The year x time of harvest interaction was not significant due to the relatively consistent difference between years in KST across sampling events. For the remaining five case studies, KST differences between years varied throughout the harvest season, leading to significant year x time interaction terms. In case study 2, biweek 3 (the first sampling period) was the only date where significant KST differences between and were recorded (Fig 1B). The magnitude of the difference in KST between years declined as the harvest season progressed. In case study 3 (Fig 1C), early-season KST values in exceeded those in by 9 kg sucrose ton -1, but by Dec (biweek 4) significantly greater KST was recorded in across most harvest dates. Comparisons of and also had significantly different KST primarily early in the harvest season (Fig 1D, E, F). These results indicate that differences in KST among years are likely to be most pronounced early in the season. However, differences in KST among years measured early in the season were not necessarily maintained throughout the season. For example, in case study 3, early-season KST was 9 kg sucrose ton -1 greater in than , whereas late-season KST was 8 kg sucrose ton -1 greater in 2000 than Similar shifts were seen in other cases (Figs. 1B, C, D, E and F). Crossing of KST response lines (averaged across all cultivars) between years implies that good early-season KST will not necessarily be indicative of high sugar content throughout the year. Year x time of harvest interactions were significant for TCH in two of six case studies and for TSH in three of six case studies (Table 3). Among-year TCH and TSH differences measured early in the season generally persisted across later sampling dates. In case studies 1 and 2, TCH and TSH were statistically similar among years across all sampling dates, whereas in case study 4, among-year TCH and TSH differences were highly significant (data not shown). Case study 5 was the only data set where the year x time of harvest interaction was highly significant on TSH. While KST differences among years fluctuated up to 25 kg sucrose ton -1 (19 % of the yearly mean) between early and late harvest, differences in TSH among years were generally maintained throughout the season, fluctuating an average of 0.4 tons sucrose ha -1 (3 % of the yearly mean) between early and late harvest. It appears that differences among years are more stable for TSH than KST. Year x Cultivar The year x cultivar interaction term was significant for KST in three of six cases (Table 3). In case study 2, only CP-1743 and CP had significantly different KST between

7 Journal American Society Sugar Cane Technologists, Vol. 24, and (Fig 2A). In case study 5, 1999 KST values for CP-1743 and CP exceeded those in (Fig 2B), and this among-year KST difference was also recorded for CP-1743 in case study 6 (Fig 2C). For these three case studies, between-year KST differences were not significant for 20 of 25 comparisons. Spearman s rank correlation coefficients averaged 0.75 across the case studies, indicating a strong correlation of cultivar KST among years. It appears that cultivar KST, averaged across all harvest dates, is relatively stable between years, with the notable exception of CP While growers should use maturity curve information to determine optimum harvest time for a given cultivar within a season (Gilbert et al., 2004), our results suggest that growers should expect consistent KST performance for these CP cultivars across different harvest seasons. The interaction of year x cultivar was significant on TCH in four cases (Table 3). In case study 1 (Fig 3A), CP was the only cultivar that recorded significant TCH differences among years (Fig 3A). In case study 3 (Fig. 3B), CP and CP showed an opposite response in TCH among years. CP had significantly greater TCH in than in both case study 5 (Fig. 3C) and case study 6 (Fig 3D). However, the majority of year x cultivar comparisons (22 of 29) were not significant among years, indicating cultivar TCH was generally more stable across years. The interaction of year x cultivar was significant on TSH in two of six cases (Table 3). In case study 3 (Fig. 4A), among-year TSH differences for CP and CP described opposite responses. Both CP and CP had significantly greater TSH in than in case study 6 (Fig. 4B). Nine of 13 cultivar x year TSH comparisons were not significantly different among years. CONCLUSIO Year had a significant effect on KST, TCH and TSH in only two of six case studies, indicating that the year effect was not as significant a determinant of sugarcane yield as cultivar or time of harvest in the EAA. The 1999 growing season had unusually low solar irradiance which was associated with low TCH in the two case studies that recorded significant among-year TCH differences. In all six case studies, KST and TSH were significantly lower prior to mid-december and mid-november, respectively, when compared to subsequent harvest dates. There were significant interactions of year x time of harvest on KST, with KST differences among years most pronounced early in the harvest season. CP was superior to other cultivars in 92% of pairwise KST comparisons. CP , CP and CP collectively recorded superior TSH, but low KST values for CP make it an economically less attractive option for growers. While CP-1743 had significantly different KST between years, most of the CP cultivars tested were stable for KST, TCH and TSH across years. These results indicate that the year effect on sugarcane KST, TCH and TSH or yields of a specific cultivar in the EAA is likely to be small. ACKNOWLEDGEMENTS The authors gratefully acknowledge the assistance of Mr. Robert Taylor, Mr. Matthew Duchrow, Mr. Vincent Sampson and Mr. Henry Westcarth in sample collection and processing and the cooperation of Lakeview Farms, Inc. and Hundley Farms, Inc. This research was supported by the Florida Agricultural Experiment Station and a grant from the Sugar Cane Growers Cooperative 171

8 Gilbert: The Effect of Yield, Cultivar, and Time of Harvest on Sugarcane Yields in Florida of Florida and approved for publication as Journal Series No. R-81. REFERENCES 1. Allen, R.J A five-year comparison of solar radiation and sugarcane production in the Everglades Agricultural Area. Proc. Soil Crop Sci. Soc. Fl. 36: Alvarez, J., D.R. Crane, T.H. Spreen, and G. Kidder A yield prediction model for Florida sugarcane. Agric. Syst. 9: Arceneaux, G., and L.P. Hebert A statistical analysis of varietal yields of sugarcane obtained over a period of years. Agron. J. 35: Campbell, J.A., M.J. Robertson, and C.P.L. Grof Temperature effects on node appearance in sugarcane. Aust. J. Plant Physiol. 25: Ebrahim, M.K., O. Zingsheim, M.N. El-Shourbagy, P.H. Moore, and E. Komor Growth and sugar storage in sugarcane grown at temperatures below and above optimum. Plant Physiol. 153: Ellis, T.O., and G. Arceneaux The effect of rainfall and time-related trends on production of sugarcane under extensive cultivation. Proc. Int. Soc. Sugar Cane Technol. 11: Gilbert, R.A., J.M. Shine, Jr., J.D. Miller, and R.W. Rice Sucrose accumulation and harvest schedule recommendations for CP sugarcane cultivars. Crop Management. Online. doi: /cm rs. 8. Glaz, B., and J. Vonderwell Sugarcane variety census: Florida Sugar Journal 66(2): Jackson, P.A., and D.M. Hogarth Genotype x environment interactions in sugarcane. I. Patterns of response across sites and crop-years in northern Queensland. Aust. J. Agric. Res. 43: Jones, P.N., R. Ferraris, and L.S. Chapman A technique for minimizing confounding genotype x year and genotype x crop type effects in sugarcane. Euphytica 67: Legendre, B.L Ripening of sugarcane: effects of sunlight, temperature, and rainfall. Crop Sci. 15: Legendre, B.L Changes in juice quality of nine commercial sugarcane varieties grown in Louisiana. J. Am. Soc. Sugar Cane Technol. 4: Littell, R.C., W.W. Stroup, and R.J. Freund SAS for linear models. Fourth Edition. Cary, NC. SAS Institute Inc. 466 pp. 172

9 Journal American Society Sugar Cane Technologists, Vol. 24, Liu, D.L., and K.R. Helyar Simulation of seasonal stalk water content and fresh weight yield of sugarcane. Field Crops Res. 82: Liu, D.L., G. Kingston, and T.A. Bull A new technique for determining the thermal parameters of phenological development in sugarcane, including suboptimum and supraoptimum temperature regimes. Agric. For. Meteorol. 90: Lumsden, T.G., R.E. Schulz, N.L. Lechler, and E.J. Schmidt Assessing the potential for improved sugarcane yield forecasting using seasonal rainfall forecasts and crop yield models. Proc. S. Afr. Sug. Technol. Assoc. 74: Miller, J.D., and N.I. James Maturity of six sugarcane varieties in Florida. Proc. Am. Soc. Sugar Cane Technol. 7: Milligan, S.B., K.A. Gravois, K.P. Bischoff, and F.A. Martin Crop effects on broadsense heritabilities and genetic variances of sugarcane yield components. Crop Sci. 30: Shih, S.F., and G.J. Gascho Sugarcane biomass production and nutrient content as related to climate in Florida. Proc. Am. Soc. Sugar Cane Technol. 8: Sinclair, T.R., R.A. Gilbert, R.E. Perdomo, J.M. Shine, Jr., G. Powell, and G. Montes Sugarcane leaf area development under field conditions in Florida, USA. Field Crops Res. 88:

10 Gilbert: The Effect of Yield, Cultivar, and Time of Harvest on Sugarcane Yields in Florida Table 1. The six data cases used in this study. Within a given case study, location, crop age, cultivar, and sampling date were consistent across different harvest years. Case study Harvest years Location Crop age CP cultivars Biweekly harvest periods EREC Plant , , -1743, , , , , ,5,6,7,8,9, EREC 1 st ratoon , , , , -1743, -1827, , , , , , Lakeview Plant , -1743, , , , , , ,5,6,7,8,9,10,11 1,2,4,6,7,8,9,10, Lakeview Hillsboro st ratoon , -1743, , , , , , Plant , , -1743, , , , , ,2,3,4,5,6,7,8,9,10,11 2,3,4,6,7,8,9,10, Hundley 1 st ratoon , , -1743, 1,2,3,4,5,6,7,8,9,10, , EREC = University of Florida Everglades Research and Education Center, Belle Glade, FL; Lakeview, Hillsboro and Hundley are private commercial sugarcane farms. Biweekly harvest periods: The first 2-week sampling period was defined as October

11 Journal American Society Sugar Cane Technologists, Vol. 24, 2004 Table 2. Biweekly harvest periods and corresponding dates. Biweek Dates 1 October 14 October 27 2 October 28 November 10 3 November 11 November 24 4 November 25 December 8 5 December 9 December 22 6 December 23 January 6 7 January 7 January 20 8 January 21 February 3 9 February 4 February February 18 March 3 11 March 4 March

12 Gilbert: The Effect of Yield, Cultivar, and Time of Harvest on Sugarcane Yields in Florida Table 3. F statistics from repeated measures ANOVA for KST, TCH, and TSH for the six case studies. DF F- test DF F- test DF F- test DF F- test DF F- test DF F- test Case 1 Case 2 Case 3 Case 4 Case 5 Case KST Year (Y) * Time (T) Cultivar (C) Y x T Y x C * T x C * Y x C x T TCH Year (Y) * Time (T) * Cultivar (C) Y x T * Y x C * * T x C Y x C x T TSH Year (Y) * Time (T) * Cultivar (C) Y x T * Y x C * T x C * Y x C x T * and indicate F-test significance at the P < 0.05 and P < 0.01 levels, respectively. 176

13 Journal American Society Sugar Cane Technologists, Vol. 24, 2004 Table 4. KST, TCH and TSH for the six case studies averaged by year. Year KST TCH TSH kg sucrose ton -1 tons cane ha -1 tons sucrose ha -1 Case * Case Case Case Case Case * 18.6 * * and indicate significantly greater year mean within a case study at the P < 0.05 and P < 0.01 levels, respectively. 177

14 Gilbert: The Effect of Yield, Cultivar, and Time of Harvest on Sugarcane Yields in Florida Table 5. Solar radiation (daily average) and rainfall (total) data from the EAA. Solar radiation Precipitation Year January - June July - December January - June July December MJ m -2 d cm Everglades Research and Education Center weather station. Table 6. Time of harvest effects on KST (kilograms sucrose ton -1 ) and TSH (tons sucrose ha -1 ) for the six case studies. Biweek: Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 KST TSH KST TSH KST TSH KST TSH KST TSH KST TSH LSD Least Significant Difference at P <

15 Journal American Society Sugar Cane Technologists, Vol. 24, 2004 Table 7. Cultivar effects on KST (kilograms sucrose ton -1 ), TCH (tons cane ha -1 ) and TSH (tons sucrose ha -1 ) for the six case studies. CP Cultivar Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 KST TCH TSH KST TCH TSH KST TCH TSH KST TCH TSH KST TCH TSH KST TCH TSH LSD Least Significant Difference at P <

16 Gilbert: The Effect of Yield, Cultivar, and Time of Harvest on Sugarcane Yields in Florida A) Case 1: Year x Time of Harvest KST B) Case 2: Year x Time of Harvest KST KST (kg sucrose ton -1 ) * * * KST (kg sucrose ton -1 ) Biweek Biweek C) Case 3: Year x Time of Harvest KST D) Case 4: Year x Time of Harvest KST KST (kg sucrose ton -1 ) * * KST (kg sucrose ton -1 ) * * Biweek Biweek Figure 1. Year x time of harvest kilograms of sucrose per ton (KST) means for (A) Case Study 1, (B) Case Study 2, (C) Case Study 3, (D) Case Study 4, (E) Case Study 5 and (F) Case Study 6 data sets. Indicates significant difference between years at a given biweekly sampling time at P < 0.05 (*) or 0.01 () levels. 1

17 Journal American Society Sugar Cane Technologists, Vol. 24, 2004 E) Case 5: Year x Time of Harvest KST F) Case 6: Year x Time of Harvest KST KST (kg sucrose ton -1 ) * * KST (kg sucrose ton -1 ) Biweek Biweek Figure 1, Continued. Year x time of harvest kilograms of sucrose per ton (KST) means for (A) Case Study 1, (B) Case Study 2, (C) Case Study 3, (D) Case Study 4, (E) Case Study 5 and (F) Case Study 6 data sets. Indicates significant difference between years at a given biweekly sampling time at P < 0.05 (*) or 0.01 () levels. 181

18 Gilbert: The Effect of Yield, Cultivar, and Time of Harvest on Sugarcane Yields in Florida A) Case Study 2: Year x Cultivar KST * * B) Case Study 5: Year x Cultivar KST 1999 * * 2001 KST (kg sucrose ton -1 ) C) Case Study 6: Year x Cultivar KST * KST (kg sucrose ton -1 ) KST (kg sucrose ton -1 ) Figure 2. Year x cultivar kilograms of sucrose per ton (KST) means for (A) Case Study 2, (B) Case Study 3, and (C) Case Study 6 data sets. Indicates significant difference between years at a given biweekly sampling time at P < 0.05 (*) or 0.01 () levels. 182

19 Journal American Society Sugar Cane Technologists, Vol. 24, 2004 A) Case Study 1: Year x Cultivar TCH B) Case Study 3: Year x Cultivar TCH TCH (tons cane ha -1 ) * TCH (tons cane ha -1 ) C) Case Study 5: Year x Cultivar TCH D) Case Study 6: Year x Cultivar TCH TCH (tons cane ha -1 ) * TCH (tons cane ha -1 ) Figure 3. Year x cultivar tons of cane per hectare (TCH) means for (A) Case Study 1, (B) Case Study 3, (C) Case Study 5 and (D) Case Study 6 data sets. Indicates significant difference between years for a given cultivar at P < 0.05 (*) or 0.01 () levels. 183

20 Gilbert: The Effect of Yield, Cultivar, and Time of Harvest on Sugarcane Yields in Florida A) Case Study 3: Year x Cultivar TSH B) Case Study 6: Year x Cultivar TSH TSH (tons sucrose ha -1 ) TSH (tons sucrose ha -1 ) Figure 4. Year x cultivar tons of sucrose per hectare (TSH) means for (A) Case Study 3, and (B) Case Study 6 data sets. Indicates significant difference between years for a given cultivar at P<0.05 (*) or 0.01 () levels. 184