Ethephon in Sugarcane Cultivation

Transcription

1 Ethephon in Sugarcane Cultivation by M. Edmond Lewis Sugar Industry Research Institute ABSTRACT Sugarcane remains an important commercial crop in Jamaica, and in spite of improved technology in production, cane and sugar yields remain low. Low plant population densities, adverse weather during the maturation period, and the tendency of some cultivars to flower with the onset of long nights, remain hurdles to be overcome. The current remedial trend is the use of agro chemical technology at various stages of crop growth. While the effects of flowering and climate have gained attention over the years, early, germination and growth have not been adequately addressed. Studies with growth regulators indicate that ethephon, an ethylene-releasing chemical may offer a solution. Studies done across the Industry show variable results. In St. Thomas, sections of a field treated with 500, 750, and 1000 ml/ha of ethephon showed a tendency to increase #tiller/m, and at the same time reduce mean plant height and leaf length. In some cases when #tiller/m increases, tiller attrition rates also increase. In a sense, the increase in population achieved by early tillering is negated by competition at stalk formation. It may be concluded that ethephon treatment is only advantageous when plant population density is suboptimal. INTRODUCTION As in many economies, sugarcane remains an important commercial crop in Jamaica. In spite of the introduction of improved sugarcane varieties and better agro-management practices, sugar productivity remains fairly low. The major factors that impact on sugar productivity include, but are not limited to, poor germination of cane sett or sprouting, and consequently low tillering; adverse weather during the maturation phase (which leads to low sugar recovery during harvest); and flowering of some varieties with the onset of longer nights. The cumulative effects of these constraints show up as low cane and sugar yields at the end of the cropping period. These effects are not unique to the Jamaican Industry, but are spread throughout the cane growing world. Current trends to minimise these constraints and reap inherent benefits include the use of agro chemicals at various stages of crop growth. Various classes of agrochemicals and manipulative techniques have been tested to alleviate constraints -- sucrose enhancers at maturity; improved irrigation systems; higher planting densities; and the use of growth regulators to improve germination, tillering, and tissue differentiation during stalk elongation phase. One constraint not satisfactorily investigated in Jamaica is the use of agro chemicals to enhance germination, tillering and stalk elongation.

2 The application of ethephon is a technology used throughout the cane growing world to regulate growth in many ways: flowering, tillering, germination, and stalk maturation. In Jamaica a few farms have used it in sugarcane fields, where the main observed effects include: < Shorter leaves emerge after an ethephon application < On stalks, ethephon produces one or two shortened internodes in the active elongation zone < In some varieties ethephon promotes swelling of buds on maturing stalks < 500 ml/ha showed improved germination of sugarcane setts with relatively better tillering potential. < Slight yellowing on leaves of some varieties As a cultivation technique, the characteristics of ethephon that can have significant impact on sugarcane relate to its ability to improve germination rate and tillering. Both processes seem to have a high positive correlation. In India, the application of ethephon was found to promote seed cane sprouting (13-17%), and improved tillering and millable cane formation (12-16%). Similar observations in Jamaica indicate increases in tillering in plots treated with 500, and 750 ml/ha. In Hawaii, ethephon caused an increase in the number of tillers in the media containing 50 ppm and 100 ppm. Application technique may also influence response. In Texas, application of ethephon in the furrow on seed pieces before covering tends to be the most effective at increasing shoot counts and heights. Since shoot numbers in sugarcane tend to increase rapidly during early growth, then decline to an equilibrium level later in the season when the most rapid growth rates occur, the beneficial effects of the early season increase of shoot counts tend to disappear. One benefit of increased early season shoot counts and stalk heights would be to cause quicker canopy cover and provide better competition over weeds. This potential benefit to fields in Jamaica should also be explored. MATERIALS & METHODS Experiment I A field experiment was set up to test the effects of ethephon on germination and tillering when applied to seed pieces (setts) in the furrow before covering. Within a newly prepared field at St. Thomas Sugar Co. in the Wet East, 10 rows with BJ78100 seed pieces were treated with 500 ml/ha ethephon, then covered. At the same time, 10 rows were covered without treatment of the seed pieces. The field was then subjected to the standard cultivation practices to facilitate field establishment. Six 5 m growth stations taken from three rows in the treated section, and three rows from the untreated sections of the field were cordoned off for observations. At 60 d after covering, the first observations were taken on population and stalk heights. To determine population, all tillers within each 5 m station were checked and averaged to give the number of tillers per metre (#/m). Stalk heights were recorded from five stalks within each station, measured from soil level to top

3 visible dewlap (TVD). Four sets of observations were taken at ~ 20 d intervals. After that, the canes became tall for accurate measurements without destruction of tillers. Experiment II The second experiment was set up to test the hypothesis that ethephon can be used to increase plant population density within a field, thus eliminating the need to supply. Three levels of ethephon: 500, 750, and 1000 ml/ha were applied in five replicates within a field at ~ 120 d after planting. Stations were established similar to that done in Experiment I. Observations taken were population density per metre, stalk height, and leaf length. The first observations were taken at setup, then at ~ 20 d intervals thereafter. Again, only four other observations could be taken before height became a limiting factor. Data from Experiment I were subjected to t-tests to determine if statistical differences existed for rates of germination, and subsequent plant population densities between the two sections of the field. The general analysis of variance (ANOVA) was used for Experiment II to analyse data on population density, stalk height, and leaf length to determine which rate, if any, influenced growth characteristics significantly. The data from the ethephon treatments were then combined and a t-test used to do comparisons with the untreated control. RESULTS Experiment I Owing to lack of moisture in the field to facilitate germination, no measurements were taken 30 days post application (dpa). At 60 dpa, readings for both height, and number of tillers/m were greater in the untreated section. By the second, and subsequent intervals, the mean heights for canes in the section treated with ethephon remained lower than those in the untreated section, Table I, but the number of tillers/m in the section treated with ethephon increased significantly (p < 0.018), Table II.

4 Table I. Mean stalk heights of BJ78100 at 60 d, then at 20 d intervals, after ethephon treatment on seed pieces before covering, St. Thomas Sugar Co Interval Treated Untreated SED Prob Table II. Mean tiller counts (#/m) of BJ78100 at 60 d, then at 20 d intervals, after ethephon treatment on seed pieces before covering, St. Thomas Sugar Co Interval Treated Untreated SED Prob Experiment II The ANOVA done on the data recorded for stalk heights and population densities taken at setup indicates that there were no statistical differences (p < 0.103) between the means of observations recorded from any treatment plot. Stalk Height With time, the higher rates of ethephon (750, 1000 ml/ha) reduced growth significantly (p < 0.001), Figure I & Table I. Mild rates of the growth regulator tended to increase growth above the control, but higher rates tended to induce stunting. Mild yellowing was also observed in plots treated with the chemical. This may have been an indication of a breakdown of chlorophyll. Cane stalk heights in the plots treated with 750 and 1000 ml/ha were significantly shorter than those treated with 500

5 ml/ha. Also of note is that the confidence interval widens between the 1000ml/ha rate and the control. While it may be argued that rates of 750 and 1000 ml/ha may be high, the the lowest rate of 500 ml/ha seemed no better than the control. There may be a need to fine-tune the rates between 500, and 1000 ml/ha. Table III. Mean stalk heights, tiller counts and leaf length of BJ8252 at each 21d interval, St. Thomas Sugar Co. Interval Treated Untreated Height #Tillers/m Leaf Length Height #Tillers/ m Leaf Length Figure I. Mean stalk heights of canes treated with three rates of ethephon at St. Thomas Sugar Co. Individual 95% Confidence Intervals for means Treat Mean (----*-----) (----*----) (----*-----) (----*----)

6 Leaf blade length At time of setup leaf lengths were not measured, but were taken at subsequent 20 d intervals. Again the control (no chemical) had statistically longer leaf blades (p<0.001) than the ethephon treated at all time intervals, Table III. This observation is similar to that reported by the South African Sugar Association, and the Indian Sugarcane Breeding Institute. Significant interactions Significant leaf blade length x time interactions were observed for ethephon in sugarcane. Where the chemical caused reduced length of leaf blade and stalk height, there were compensations through increased tillering in treatment plots. Leaf length also co-vary with stalk height (p < 0.025) indicating that a reduced capability of leaves to photosynthesise affected the general growth rate of the plant. This relationship was not observed with leaf length and number of tillers, or stalk height with number of tillers. The implication here could be that ethephon applied to foliage influenced the leaf source, stem sink relationship more than the leaf source, root sink relationship. to the extent that more tillers. Time seemed to be the over-riding factor determining the extent of the relationships. All parameters - tiller density, stalk height, and leaf blade length came under the influence of the chemical (p < 0.001) during one or more of the time periods. Stand Density The resultant plant population density of plots treated with the various rates of ethephon showed no advantage from the treatments. The means ranged from a low of 9.9/m to a high of 14.4/m even when the effects were combined for a mean of 12.6/m, it was not statistically different from the mean of the control, 11.0/m. Where germination is good there tended to be increased tiller dieback at stalk formation stage, giving the impression that gains from ethephon could become a liability where good quality setts give optimal establishment. Leaf colour In many of the plots given ethephon treatments across the Industry, plants showed slight yellowing in addition to reduced stalk height, and leaf blade length. In instances where stalk height of the control significantly exceeded that of the ethephon treatments it may be theorised that tillering is a compensatory effect for reduced height. However, the yellowing effect indicates loss of chlorophyll, and in the long run will translate to lowered agronomic performance in susceptible cultivars. This may be a varietal effect, and not the general case for cultivars, in all locations. While the general principle of improved tillering may be an acceptable outcome, prolonged yellowing of leaves on juvenile stalks suggests reduced capacity of plant to resume normal functioning after an ethephon treatment, and should not be accepted.

7 Summary of Experiment II - ethephon treatment on foliage after germination, St. Thomas Sugar Co Parameter Cont rol Etheph on SED Plant height Leaf length P Tiller density (#/m) Summary of Experiment I - ethephon treatment on setts in furrow before covering, St. Thomas Sugar Co Parameter Cont rol Etheph on SED P Plant height Tiller density (#/m) Conclusion The studies with ethephon indicate a distinct possibility that the chemical may be used to improve field stand especially where germination is less than ideal. The evidence however, is not as pronounced as that reported from Texas and India. Its potential to improve germination when applied to the furrow could not be verified and needs more intensive investigation. Retarded early growth is not an outcome farmers would like, especially with the challenges of weed pressures and moisture stress. Tiller attrition at stalk formation stage as observed in treatment plots diminished early gains, and may only be important where germination is less than ideal, and field stand suboptimal.

8 References 1. Adams, Ashley Nailwal, T.K., V.K. Gupta, N.K. Sand, and R.C. Pant Role of ethylene in tillering of sugarcane. 3. Rao, Manjunatha S., M. Krishnamurthi, and Pipat Weerathaworn. Effect of ethephon on yield and sugar content of different sugarcane cultivars in Thailand. 4. Solomon, S., Ishwar Singh and V.K Madan. Effect of 2-chloroethyl phosphonic acid on early growth and advancement of maturity in sugarcane. 5. South Africa Sugar Association, Flowering in sugarcane. SASA Information Sheet. 6. Sugarcane Breeding Institute (India), Control of flowering in sugarcane. SBI Quarterly Newsletter Vol. 23, No. 4, pp Wiedenfeld, Bob Enhanced sugarcane establishment using plant growth regulators. Journal American Society of Sugarcane Technologists 23:48-61.