C.P.M. Sweet and M.R. Boast

Transcription

1 YELD PATTERNS AS AN AD TO EVALUATE PERFORMANCE ON A COMMERCAL SUGARCANE ESTATE N SWAZLAND C.P.M. Sweet and M.R. Boast Simunye Sugar Estate P.O. Box 1, Simunye, Swaziland ABSTRACT Agronomy n Southern Africa, irrigated cane and sucrose yields show a decline through the harvest season, April to December. This decline is attributed to the change in climatic yield potential. Four season's results from Simunye in Swaziland are discussed and presented graphically, and with the eight years of data from an adjoining estate, provide a basis for performance assessment of the estates' yields. The effects of various stress factors markedly reduced early season yields, but late season yields showed little reduction. The method of graphic presentation of monthly yields can also be used to evaluate varieties, crop stages and is a method of determining optimum season length. However, in assessing individual field performance, correction of age and date of harvest is desirable. NTRODUCTON Cane and sucrose yields from irrigated fields vary markedly through the April to December harvest season in Southern Africa'~~,~. This occurs in a pattern which varies with such growth factors as age, irrigation efficiency, soil type and variety. The date of harvest is the overriding factor insofar as it reflects the progressively changing climatic yield potential. However, in the context of a reasonably well grown crop of one variety harvested at close to 12 months old, the pattern is both distinctive and predictable. Sweet and Pate16 have defined this cane yield pattern for irrigated NCo376 in Swaziland as illustrated in Figure 1. Although individual estate potentials differed slightly, the patterns were very similar. The sucrose yield patterns were more variable and difficult to define since two factors, tonnage and quality, were being interpreted and some of the historical quality data were suspect (Figure 2). These patterns provide a yardstick for performance evaluation, and this paper outlines how they are being used to understand, interpret and evaluate field performance at Simunye, an estate with 9200 ha of irrigated cane. This relatively new estate is situated in a semi-arid part of Swaziland and 1982 was its first year of Keywords: Yield pattern

2 26 AGRONOMY full production. Harvesting extends from April/May to November/December when cane of about 12 months of age is harvested at a rate of about two fields (50 ha) a day. NCo376 is the principle variety comprising about 80% of the crop. The whole area is irrigated, 80% overhead and 20% furrow. Umbuluzi x M J J A S 0 N D Month of Harvest FGURE 1. Average seasonal cane yield patterns of NCo 376 at Simunye & Umbuluzi Estates. METHOD The approach was to first establish the yield pattern and potentials that might reasonably be attained at Simunye, by reference to neighbouring estates. This could then be modified according to actual experience. Actual cane and sucrose yield patterns for three seasons, , are presented and discussed as are several other uses to which graphic presentation of yield data may be put. Likely yield pattern of NCo376 at Simunye

3 c.p.m. SWEET AND M.R. BOAST 27 \ FGURE 2. Average seasonal sucrose yield patterns of NCo 376 at Simunye and Umbuluzi Estates. of soil types, management practices and varietal composition. Data were therefore selected specifically for NCo376 from Umbuluzi, an adjoining estate, known to have good soils and a history of high yields. The cane and suer-ose yield patterns are shown in Figures 1 and 2. These patterns are not necessarily definitive, and the May sucrose yield is surprisingly low and should possibly be treated with caution, but they at least provide a basis for performance assessment. They are specific to NCo376, but may provide a basis for varietal comparisons. Seasonal yield patterns for NCo376 at Simunye Records of bqth cane and sucrose yields are shown in Figures 3 and 4. Season The 1982 milling season was the first with the estate at full production. n the rush of development insufficient attention had been given to the growing crop and this is reflected in the relatively poor cane and sucrose yields.

4 28 AGRONOMY Yields reached the Umbuluzi levels only in May, and there was obviously considerable room for improvement. Season The second year of full production was a good growing season. This was reflected in both cane and sucrose curves which show a marked improvement over However, low water reserves necessitated a 50% reduction in irrigation from June to September which restricted late season yields. The evidence at the stage suggested that Simunye should be able to match Umbuluzi's performance in a favourable season, and that the yield patterns were very similar, apart from Umbuluzi's suspect May sucrose figure. t also indicated that November is a low yield potential month, and that the milling season should start and finish earlier. Season Growth measurements predicted a record crop until cyclone Demoina damaged the irrigation system at the end of January. rrigation could not be resumed for six weeks and severe stress was evident in the hot, dry period that followed. M J J A S 0 N D FGURE 3. Seasonal cane yield patterns of NCo 376 at Simunye

5 C.P.M. SWEET AND M.R. BOAST 29 The curves not only reflect the marked reduction in yield, but also show that the effect was greatest in May with a 14% depression relative to The relative status of 1984 yields improved and by November 1984 was ahead of The cane most affected was the oldest cane, cut first in the season, while the severe water stress had very little effect on cane only two to three months old. This highlights the sensitivity of early season cane to stress in the summer months, and shows that, in the event of water shortages, distribution should favour older cane. This agrees with the other workers who found that young cane is more tolerant to stress (Elli~~,~), but also serves as a warning against excessive drying off of early harvested cane. Season Growth measurements again predicted high yields, but about four weeks before harvesting commenced on 25th April, a violent storm severely lodged the early crop. Yields were affected for the first three months of harvesting, with considerable losses being sustained. Whereas the 1984 loss was only in terms 0,90 e M J J A S 0 N D FGURE 4. Seasonal sucrose yield3,katterns of NCo 376 at Simunye \

6 AGRONOMY 1 FGURE 5. Varietal performance at Simunye : 1984 seasop A cane' N ha ' M J J A S 0 N FGURE 6. Varietal performance at Simunye : 1985 season

7 of cane yield, in 1985 both cane and quality were affected and sucrose yields were Again the oldest cane was the hardest hit, and from August on sucrose yields were as good as in previous years. The high sucrose yields late in the season were achieved despite heavy flowering, / which indicated that the attainable norm for November approaches 1.1 tons sucrose/ ha/rnonth, 10% better than Umbuluzi level, After four crops, a much clearer picture is emerging of what performance levels can be expected throughout the milling season, as well as the range of potential loss in unfavourable circumstances. Where these losses cannot be attributed to factors such as climatic conditions, then poor management is likely to be the cause, highlighting the need for remedial action. Varietal performance Discussion has centred so far on NCo376, but with 20% of the estate under other varieties, it is important to assess their relative performances. This used to be done by comparing the mean seasonal yield for each variety, but this can be misleading as one variety may have been harvested in a high potential period and another in a low potential period. Plotting each variety on the graph according to harvest date provides a truer picture which is easily evaluated visually. The varietal pictures of sucrose yield for 1984 and 1985 are presented as examples (Figures 5 and 6). Each point lists hectares as a measure of reliability, since individual field results will fluctuate more widely than the mean of several fields. Season t was immediately obvious from Figure 5 that N was responsible for the poor early performance, while J59-3 and NCo334 were also markedly inferior to NCo376. The September and October cut N14 yielded very well but represented only four fields, while the large area cut in November performed similarly to NCo376. N14 therefore appears to be a promising variety. The pressing need was to replace N and and this was duly programmed over the next two years to avoid excessive plough-out in any year. Season Only a little N remained and the area under J59-3 was reduced. The benefit is apparent in Figure 6, where yields of NCo376 and the estate as a whole are seen to be similar however did considerably better than in previous years. Much of the replacement was with N14 which' has performed as well as or better than NCo376. ts particularly high yield in August occurred on a block of good soils, and is indicative of a high potential in favourable conditions. Relative performance of plant and ratoon cane As with varieties, yields of ratoon crops at different stages are often averaged for the season without regard to time of harvest. Again, this may be misleading and graphs can provide a better picture, sometimes highlighting unsuspected differences, Figure 7 shows the 1985 performance of plant and ratoon NCo376 and N14. The ratoon yields.are better than the plant crop yields in both varieties, but the difference is considerably greater with N14, with the ratoon yields being 20% greater il

8 M J J A S 0 N FGURE 7. Ratoon performance of NCo 376 and N14 at Simunye : 1985 season than plant crop yields, except in October. t appears that either the planting procedure for N14 needs improving or that it is a poor yielder at plant, or a combination of the two, something that requires further investigation. Whereas Figure 6 showed both varieties N14 and NCo376 yielding similarly in most months, when only the ratoon yields are considered then N14 is distinctly superior. The same system could be used to evaluate individual ratoon stages as well. Prediction of yields and trends By plotting yields as the season progresses and using past yield patterns, realistic yield predictions can be made by extrapolation, in the context of current growing conditions. For example, the 1983 curves (Figures 3 and 4) show yield levels that may be expected with late season water restrictions, and these may be used as a guide in the event of future water restrictions. Similarly, the early season yield depression depicts the effect of severe lodging a month before harvesting commences. Optimum milling season The length of season is usually determined by mill capacity, but timing can

9 C.P.M. SWEET AND M.R. BOAST 3 3 be hotly debated between millers and growers, with millers favouring the high quality fate season while growers often prefer the high yielding early period. Seasonal performance graphs allow rational evaluation of the options which can then be considered in relation to practical factors. At Simunye the indication is that once all poor varieties have been replaced, milling should commence mid- April or earlier, and end by mid -November, weather permitting. Field performance graphs As a result of the marked seasonal change in yield potential, ratoon performance is accurately reflected in yield differences only if the harvest date is constant. As this is frequently not the case, Sweet and pate16 developed correction factors for irrigated NCo376 in Swaziland and Zimbabwe which express cane yield as the Mayharvested equivalent, i.e. what the yield would have been had the crop been in a May harvest cycle. This effectively counteracts the seasonal yield decline, and has been termed the corrected tons cane/ha/month (COTCHM). t is a useful measure of performance, and when plotted against crop stage provides a simple visual aid to performance assessment. This is illustrated in Figure 8, which shows how misleading yield in tons cane/ha/month (TCHM) can be. Similar graphs have been drawn for each individual field on Simunye which will not bnly aid field performance evaluation, but will also help establish each individual field's performance potential. The yield of cane, rather than sucrose, is generally more convenient for assessing x / /\ \ / / x x\ Performance \-;- -p;&; ; --- L P 1 R 2R 3R 4R 5R 6R Crop stage FGURE 8. Field performance graph : corrected TCHM (COTCHM)

10 34 AGRONOMY field performance, and is considered quite acceptable since sucrose yield is proportional to cane yield in the context of any given variety, and the grower has much more control over cane yield than over cane quality. CONCLUSON These yield patterns have proved a valuable aid to field performance assessment and are particularly useful at estate level whereas the COTCHM concept, which compensates for season yield decline, is of value at individual field level. They have helped to identify, explain and understand growth fluctuations as well as quantify losses and define yield potentials. The early part of the season is obviously very sensitive to adverse growth conditions in the summer, and even as late as March. Early season yields will therefore fluctuate more widely than late season yields. This identifies the early crop as requiring particular management. The relatively low May and November sucrose yields recorded by the neighbouring estate of Umbuluzi can presumably be avoided under favourable conditions of growth. Otherwise the two estates exhibit very similar production patterns. The use of such patterns could be extended to define patterns for other varieties, or evaluate different ratoon stages. Seasonal yield patterns of cane and sucrose yields are proving a useful aid to performance evaluation on Simunye estate and may well have application elsewhere. REFERENCES 1. Cackett, K.k., and Rampf. J.J. (1981). Sugarcane for ethanol - should field management practices be modified? Proc. S. Afr. Sug, technol. Ass. 58: Ellis, R.D. (1983). rrigation control to conserve water. Zimbabwe Sug. Ass. Exp. Stn. Bull 1/ Ellis, R.D., Wilson, J.H. and Spies, P.M. (1985). Development of an irrigation policy to optimise sugar production during seasons of water shortage. Proc. S. Afr. Sug. Technol. ASS. 59: Gosnell, J.M. and Koenig, M.J.P. (1972). Some effects of varieties on seasonal fluctuation in cane quality. Proc. S. Afr. Sug. Tecnol. Ass. 46: Lonsdale, J.E. and Gosneil, J.M. (1975). Effects of age and harvest season on the yield and quality of sugarcane. Proc. S. Afr. Sug. Technol. Ass. 49: Sweet, C.P.M. and Patel, R. (1985). Chan,ges in cane yield of irrigated variety NCo376 due to seasonal and their implications when evaluating field performance. Proc. S. Afr. Sug. Technol. Ass. 59: