Loading...
Please wait, while we are loading the content...
Similar Documents
Four Years Experience with Maturity Testing on Mhlume Sugar Estate
| Content Provider | Semantic Scholar |
|---|---|
| Copyright Year | 2009 |
| Abstract | Pre-harvest sampling has proved to be a useful tool at Mhlume. Graphs are presented showing the improvement in the sucrose content of Mhlume's cane at the mill compared with that of the outgrowers over a 5-year period. The method of sampling and analysis is discussed in detail. The data from the 2 seasons when the 8-10 internode sample was used are presented and the different correlations between the various cane analyses and the tons cane: tons sucrose ratio are discussed. It is concluded that the 8 10 internode sample and the whole stalk sample taken together give the most satisfactory guide to harvest scheduling at Mhlume. Introduction The sucrose content of the cane stalk at harvest time is influenced by many factors. The main factor is the rate of growth in the preceding months. When the cane plant is growing rapidly the carbohydrates produced by photosynthesis are largely utilized for vegetative growth and only a portion is stored as sucrose. As the plant growth rate slows down more carbohydrates are available for storage. When rapid growth is resumed after a period of restricted growth the stored sucrose is inverted and metabolised, causing a drop in the sucrose content of the stalk. With this in mind sugarcane farm managers aim at vigorous growth in the early and middle part of the growing cycle, with restricted growth in the latter part to ripen the cane. Therefore fertilizer must be adequate in the early stages but not enough to keep the plants growing vigorously as harvest time approaches. Similarly, irrigation should be restricted to reduce growth before harvest. A slightly different approach is to ensure that cane cut early in the harvest season, when the climate still favours growth, is cane carried over from the previous season. The age of this cane then ensures greater maturity than is possible with younger cane. The best method under Swaziland conditions is to delay harvest until the winter months, when the cane is ripened naturally by temperature effects. Unfortunately this is not feasible for the entire crop because the winter is not long enough to harvest and grind the tonnages produced. A ripening programme is usually based on a harvest programme drawn up in advance and influenced by practical considerations such as replanting requirements, age of cane at harvest, variety, yield and local experience. Many farmers never go further than this and the preliminary harvest plan is used unchanged throughout the season. It is obvious that a knowledge of the relative maturities of the fields available for harvest must improve the effectiveness of the harvest programme and therefore the yield of sucrose. Many of the factors affecting maturity cannot be controlled. It is thus extremely useful to have some form of testing for maturity in routine operation. Methods When Mhlume started its central cane maturity testing service in 1968, the cane samples collected consisted of whole stalks taken from positions marked on a sampling map. Analyses were carried out on juice expressed by a 3 -roller Barron laboratory mill and the sucrose content of the cane was estimated by the Java ratio method. The stalks were cut in half before crushing and top and bottom halves were crushed separately. Thus comparisons could be made between the results for the two halves in addition to obtaining information about the whole stalk. At the end of the 1969 season ~t was decided that both the sampling method and the analytical method should be changed. The original sampling method, whilst adequate, was prone to occasional errors because there was no allowance for suckers. The percentage by weight of suckers in carry-over cane can be quite high (nearly 34% measured at Mhlume) and in view of the great difference in sucrose content between the suckers and the first season growth (4 6% just before harvest date) it is important that the analysis should reflect the presence of the suckers. An attempt was made to find a method which gave this information as well as an increase in accuracy. A suitable method seemed to be that used by Humbert et al-l in Mexico. This offered a logical answer to the sampling problem in that the sample consisted of the whole stool. The 8 10 internode samples were processed for moisture, nitrogen, sucrose and reducing sugar content, while the rest of the sample was processed for "pol ratio" analysis. However, this method meant that a large number of stalks had to be collected and sub-sampled. It was felt that this could be avoided by taking only the 8 10 internodes from the sample stool in situ. It was considered desirable to have a whole stalk sample also, so whole stalk samples were taken from surrounding stools. The areas of sampling blocks were as much as 40 hectares, but were more usually about 20 hectares. A map was drawn of the area on a 1:5000 scale, and the proposed sampling points were marked so that good coverage of the area was obtained. There was a minimum of one sampling point per 4 hectares. When the sampler reached his -sampling point he was required to judge whether or not the cane at the sampling point was representative of the 182 Proceedings o f The South African Sugar Technologists ' AssociationJune 19 72 area. If it was not, he was required to move his sampling position to more representative cane. He did not mark this particular area as the sampling point for all future sampling, but was merely required to sample within the same general area on subsequent occasions. On arrival at his sampling point the sampler chose a representative stool of not less than ten stalks (this was to prevent a natural tendency to select the smallest stool possible). He then counted the stalks in the stool and entered this information in his sampling book. A note was also made of how many suckers and immature stalks were present. The 8 10 internode sample was then taken from all the stalks that would go to the mill at the time of harvest. Finally he selected two representative stalks, one each from stools on either side of the 'one from which he had taken the 8 10 internode samples. All the 8 10 internode samples from the different sampling points within a block were composited, and the same was done with the whole stalks.The two bulk samples were then analysed separately. The analytical method adopted was the cold extraction method of direct cane analysis (Buchanan, 1966)'. On arrival in the laboratory the cane samples were chopped into pieces approximately 30 cm long and these were then disintegrated using a Jeffco cutter-grinder. Care was taken to ensure that the sub-samples taken for analysis were representative. The blender used for cold extraction was the "Ultra-Turrax" and not the SMRl blender. This necessitated a change in the cane to water ratio from a 1:2 to a 1:3 mixture. Brix was determined using a precision refractometer and a Dietert Moisture Teller dried the sample for moisture determination. Reducing sugar analysis was done using Soxhlet's modification of Fehling's method on the filtered juice from the blender. The calculations necessary for the method are somewhat tedious but these were automated to an extent by the use of a calculator with programming facilities. Results and Discussion The seasonal sucrose graphs in Figure 1 show the mean weekly sucrose results from Mhlume mill for the Mhlume estate cane and the "outgrowers' " cane. The results in 1967 showed no tendency for Mhlume's sucrose percentage to be better or worse than the outgrowers.' 1968 was the first year the central cane maturity testing service operated and as can be seen from the graph there was little impact except at the beginning of the season. From 1969 there was a distinct improvement in performance and the sucrose content of Mhlume cane stayed higher than that of the outgrowers cane for the early ,and late parts of the season. The sudden improvement in sucrose levels in the outgrowers' cane in midseason was mainly due to cutting a preponderance of NCo 310 at that stage. The best example of this was in 1969 when the sucrose percentage of the outgrowers' went up by more than 2% in one week as they moved into NCo 310 fields. The very marked difference between data for Mhlume and the outgrowers' in 1971 was thought to be due to some extent to the better drying off control achieved following recommendations published in the Rhodesian Sugar Association news bulletin (Gosnell, 1971)2. The drying off philosophy has changed over the last 5 years at Mhlume. During the first 4 years irrigation was discontinued some time before harvest, the period being longer in summer than in winter (6 to 8 weeks vs 3 t o4 weeks). The intention was to ripen the field as well as to facilitate vehicle movement. Irrigation was based on Class A pan evaporation and a factor of 100% of pan was used for fully canopied cane. Accuracy of control was made more difficult by the surface irrigation system used over much of the estate. Similar drying off programmes were used by the outgrowers' though some preferred a fairly short drying off period and one favoured a long drying off period with a final irrigation shortly before harvest. In 1971 Mhlume changed over to an extended drying off system as mentioned earlier. This system involved a 50% pan factor for cane harvested from April to September and a 67% pan factor for the October to January harvest period. The duration of drying off varied from 4 months in fields with deep top-soil to 2 months in fields with shallow top-soil. In Figure 2 the average seasonal sucrose percentages for the 5 year period 1967 to 1971 are compared using the 1967 value as 100%. In these histograms the steady improvement in Mhlume's sucrose percentages over the last 5 years is apparent. In 1971 Mhlume's yield in tons Sucrose per hectare per month was the second highest ever obtained, showing that it is possible to increase sucrose percentages without sacrificing yield. The histograms for the outgrowers' data show a much more va |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.sasta.co.za/wp-content/uploads/Proceedings/1970s/1972_Truen_Four%20Years%20Experience%20With.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
