Journal of Microbiology and Biotechnology Research Scholars Research Library J. Microbiol. Biotech. Res., 2011, 1 (2): 113-118 (http://scholarsresearchlibrary.com/archive.html) ISSN : 2231 3168 CODEN (USA) : JMBRB4 Determination of optimum harvesting age for sugarcane ratoon crop at the Kenyan Coast E. Ongin jo and C. O. Olweny Kenya Sugar Research Foundation, P. O. Box 44-40100, Kisumu, Kenya ABSTRACT Evaluating sugarcane (Saccharum hybrids) genotypes for physiological maturity was done by monitoring sugar yield and other agronomic parameters in order to determine the optimum harvesting age of ratoon crop at the Kenyan Coast. Seven clones bred in the year 2001 and one check variety were planted during long rains of 2007 in a randomized complete block design replicated three times. The clones were evaluated in two ratoon cycles. Agronomic data was collected from seventh month up to eleventh month. The results show significant difference among the agronomic parameters and sugar yield parameters over duration of data collection. The clones registered peak sucrose accumulation at nine months. This demonstrate that sucrose accumulation is time influenced variable and hence it is economical to harvest ratoon crop at the age of nine months in Kenya coastal region. Keywords: Sugarcane, Ratoon, Kenya coast, maturity, clones INTRODUCTION Screening sugarcane varieties (Saccharum hybrids) for earliness and selection for early maturity (i.e., high sucrose content at early age) is a major objective in breeding programmes, as demanded by sugar industries [1, 2,3,4]. Traditionally, this is determined by monitoring sugar yield parameters such as, Pol % cane, Brix % cane, commercial cane sugar (CCS), and ton cane per hectare (TCH) e.t.c. [5,4]. Nonetheless, several standard analytical methods are available to determine the peak maturity or quality so that the cane is harvested at right time. Without such analysis several farmers take-up cane harvesting based on crop age and appearance. Farmers who grow a particular variety are usually conversant with the harvesting time. Even most sugar factories give cutting orders to farmers based on crop age. This is not a scientific method since 113
planting time, crop management practices and weather conditions influences maturity. Yellowing and drying of leaves, metallic sound of mature canes when topped appearance of sugar crystal, glistening when a mature cane is cut in a slanting way and held against the sun are some of the visual indices of assessing maturity of cane. Important sugarcane quality parameters for assessing cane maturity are the juice Brix, pol or sucrose percentage and purity. However, most researchers focus their evaluation on Pol % cane [5,6,4], and reported values ranged from 10.49-17.86. In milling operations, the preferred varieties are those with Pol % cane and Brix % cane values nearly equal at maturity, and a Pol value 16 or greater and purity of 80 % or greater are commercially acceptable [7]. Fibre was found positively correlated with strength of sugarcane stalk, showing the importance of fibre content in the erectness of growth habit, [8, 9,10,11]. However, low fibre content contributed to good milling quality [12] and there was lack of correlation between percent fibre and erectness with r= 0.088 to 0.195 in plant cane [13]. Maturity age is relatively specific to industrial needs. For example, early maturing varieties are those ripening at 8-10 months in India [4, 5], 10-11 months in Indonesia [14], 12-14 months in Columbia [11] and [11].9-10 months in Mauritius [15]. During the initial stages, the portion of sugar, that is stored as sucrose, is small and increases as growth continues [16, 5]. Towards maturity, vegetative growth is reduced and internode elongation rate is decreased while the sugar and fibre contents greatly increase [10,5,17] until sucrose reaches a peak and then decreases as the season progress due to respiratory loss [18,19]. Early maturing varieties have numerous benefits to both the growers and sugar industries. They provide an efficient and reliable means of achieving increased sugar yields at the beginning of the season [6, 20]., save the raw material required for a given crop cycle and allow earlier commencement of the harvesting and the processing season, and ensure profitability [21,22,23,24,11]. High correlations were reported by many workers between.juice and yield parameters. Correlation values was 0.57 between yield and fibre, and -0.76 between sucrose and fibre [10], from r = 0.62 to 0.74 between fibre and Brix, from r = 0.79 to 0.87 between Pol and purity, from r = 0.73 to 0.92 between Pol and Brix, and from r = 0.56 to 0.89 between purity and Brix [24, 10,6,22]. OBJECTIVES To evaluate 7 promising clones and one commercial variety of sugarcane for maturity and earliness through monitoring sucrose accumulation and other quality parameters, To provide background information for the economic age of harvesting ratoon sugarcane at the Kenyan coast. MATERIALS AND METHODS Plant materials and experimental location 7 promising clones and one commercial variety were selected based on their relative performance and history during preliminary trial stages. Selected clones included; MS 2001-24, MS 2001-432, MS 2001-1046, MS 2001-1237, MS 2001-1243, MS 2001-1252, MS 2001-1407 and KEN 83-737. These materials were planted during the wet season in early May 2007, at the experimental farm of the Sugarcane Breeding Centre Mtwapa at the Kenyan Coast. 114
The experimental site is located at an altitude of about 25 m.a.s.1, and latitude of 3 o 45' S and longitude 39 o ~44 E. The rainfall pattern is bimodal with annual average amount of 1000mm, and relative humidity of between 60 68 %. Mtwapa soils are predominately sandy with low organic matter and PH levels of 6.0 7.0. The test materials were established on randomized complete block design replicated three times. Plot size was 4 rows of 8m-long with an inter-row spacing of 1.2 m. Sampling procedure and yield estimate Sampling was carried out at monthly interval up to eleven months, started when cane (plant crop) was seven (7) months old in April 2008 and ended in January 2010 when cane (ratoon two) was 11 months old. Measurements for agronomic parameters were taken from the two middle rows. At harvest, the two inner rows were cut and weighed for cane yield determination. Ton cane per hectare was calculated as the product of 19.2 m 2 fresh cane to the one hectare of area. Twelve of the harvested cane stalks in each plot were taken for juice quality analysis in the laboratory. In the laboratory brix % juice, Pol % juice and purity % juice were determined using method suggested by Schneider [25].. The data for various agronomic traits were subjected to analysis of variance following the procedures of Steel and Torrie [26], and were computed using GENSTAT program 10 th edition. RESULTS AND DISCUSSION The means of agronomic parameters measured are presented in tables 1and 2. Sucrose content is estimated by both brix % juice and Pol % juice while cane yield is expressed in terms of yield per hectares. The table shows significant difference amongst the test clones in term of agronomic parameters. As shown in Table 1clone 432 produced higher number of mill able stalk at harvest followed by 24 while clone 1243 had the lowest. Three clones namely; 24, 1243 and 1252 had shown superiority for both stalk diameter and height. In terms of juice quality clone 1243 outperformed the rest including check variety KEN 83 737; however, it registered low cane yield. The reverse trend is true for clone 24.This confirms the negative correlations between quality and quantity as reported by Balasundaram N and B Bhagyalakshmi[27]. The yield of 107.7 tons per hectare gives clone 24 more acceptability. The levels of purity % were good has can be seen in both the tables1 and 2, and this showed that clones were physiologically mature and ready for harvesting and milling. All clones recorded juice purity percent of more than 80 hence suitable for crushing as has been reported by [7] Since Kenya Government policy is geared towards payment to farmers on the basis of sucrose attempt was made in analyzing monthly sucrose accumulation as shown in figure one and annex one. Sucrose accumulation was rapidly active during the first nine months where it reaches peak then declined. This could probably be attributed to normal growth habit of sugarcane as it is known that the initial stages of sugarcane growth are associated with starch accumulation in chloroplasts, and in later growth stages, the starch converts to sucrose that increases as the growth continues [16,5], until it reaches a peak and then decreases as the season progresses due to respiratory loss [18, 19]..The gradient of sugar concentrations down the stem is more pronounced during periods of rapid growth and is reduced during periods of restricted growth [16]..Stems (stalks) of high sucrose accumulating clones are generally high in moisture and low in fiber [28]. 115
Such stalks generally have a thick girth and high fresh weight as can be seen in clone 24. Stalks of low sucrose storing clones are generally thin and fibrous and have a low fresh weight. Therefore, part of the difference in sucrose storage potential among clones might be based on limits set by morphological characters. It is therefore evidenced that sugarcane ratoon crop at the Kenyan cost should be harvested at nine months in for profit maximization. Table 1: Mean agronomic performance of the test clones at 11 months at ratoon 1 cycle BRIX [ HEIGHT [ Population GIRTH [ Pol% Purity % YIELD [ CLONE % juice] cm ] Per plot cm ] juice T/Ha ] 24 18.6 246.0 253 2.07 16.8 90.3 107.7 432 18.4 229.2 260 1.84 16.4 90.1 89.5 1046 19.5 212.9 221 1.88 17.2 88.5 76.8 1237 18.4 231.3 190 2.13 16.4 89.2 94.6 1243 21.1 234.5 142 2.21 19.3 91.4 59.4 1252 17.6 265.3 236 1.88 15.7 89.2 97.9 1407 19.3 233.8 213 1.95 17.0 88.0 82.8 KEN 83-737 19.2 242.6 203 2.10 17.1 89.0 93.0 L.s.d 1.2 34.7 62 0.26 1.4 1.2 34.4 CV% 3.7 8.3 16.4 7.4 4.7 1.9 22.4 Grand Total 19.9 237.0 215 2.01 17.0 89.5 87.7 Table 2: Agronomic performance of the test clones at 11 months at ratoon 2 cycle BRIX (%) juice] Pol% juice Purity % YIELD [ T/Ha ] HEIGHT GIRTH CLONE [ cm ] POP [ cm ] 24 16.3 198.5 197 1.9 13.7 83.1 74.7 432 15.8 200.5 181 1.8 13.2 83.3 67.0 1046 17.5 183.4 182 1.9 15.3 86.9 51.4 1237 17.5 215.0 188 2.1 15.3 87.4 99.8 1243 19.2 198.5 131 2.1 17.0 88.2 49.3 1252 15.7 216.0 174 1.8 12.5 82.3 66.2 1407 18.2 188.2 191 1.9 15.5 84.8 75.6 KEN 83-737(Check) 17.8 195.5 152 2.0 15.4 86.2 61.3 L.s.d 0.94 36.3 24.9 0.18 1.4 1.2 34.4 CV% 5.3 19.3 15.2 10.2 4.7 1.9 22.4 Grand Total 19.9 237.0 215 2.01 17.0 89.5 87.7 Table 3: Agronomic performance of the 7 test clones at various months in ratoon 2 crop. Clones/ months BRIX ( % ) HEIGHT (cm) POPULATI ON GIRTH ( cm ) TCH 24 18.8 198.5 196.8 1.9 74.7 7 18.8 151.5 161.3 1.9 9 20.1 202.3 209.7 2.0 11 17.5 241.8 219.3 1.9 74.7 432 18.2 200.5 181.0 1.8 67.0 7 18.6 160.5 154.7 1.6 116
9 18.6 204.2 187.7 1.7 11 17.4 236.8 200.7 2.2 67.0 1046 18.5 183.4 182.2 1.9 51.4 7 18.1 153.0 160.3 1.8 9 19.2 183.0 184.0 1.8 11 18.2 214.1 202.3 1.9 51.4 1237 18.7 215.0 187.8 2.1 99.8 7 18.3 167.2 180.0 2.0 9 19.4 223.1 186.7 2.1 11 18.4 254.6 196.7 2.1 99.8 1243 22.2 198.5 130.9 2.1 49.3 7 22.3 158.0 126.7 2.1 9 22.5 201.1 134.7 2.1 11 21.8 236.4 131.3 2.1 49.3 1252 16.7 216.0 174.0 1.8 66.2 7 16.0 178.7 156.7 1.8 9 17.3 220.0 180.7 1.8 11 16.6 249.4 184.7 1.9 66.2 1407 19.6 188.2 191.4 1.8 75.6 7 18.7 143.4 160.7 1.7 9 19.8 188.5 198.0 1.8 11 20.2 232.8 215.7 1.9 75.6 KEN 83-737 18.8 195.5 151.8 2.0 61.3 7 17.5 159.8 127.3 2.0 9 19.2 198.7 159.0 2.0 11 19.6 228.0 169.0 2.0 61.3 Grand Total 18.9 199.5 174.5 1.9 68.2 % b r i x 20.0 19.5 19.0 18.5 18.0 17.5 17.0 Brix versus months 7 9 11 months Figure 1. Showing means brix performance of clones over months at ratoon 1 cycle 117
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