Goat and Rabbit Research Centre, SonTay, Hatay, Vietnam
* Finca Ecologica, University of Agriculture and Forestry, Thu Duc, Ho Chi Minh City, Vietnam
**Swedish University of Agricultural Science, Department of Crop Production Science, Uppsala, Sweden
The experiment was carried out in 1994 and 1995 at the Goat and Rabbit Research Centre in Bavi district, which is a hilly area in North Vietnam. The treatments were arranged in a Latin square split-plot design, and included four varieties: Hoanam, POJ 3016, F 156, My 55-14 and two planting distances: 90cm or 150 cm between rows. Treatments with dead leaves included mulching and no-mulching. Sugar cane was harvested at 10 and 12 months after planting.
After two years the results showed that: varieties F156, Hoanam and My 55-14 produced significantly more edible biomass than the traditional variety POJ 30-16, which has been planted for a long time in Bavi district. There were no advantages in yield nor in feed value when sugar cane was harvested at 10 compared with 12 months. Returning the dead leaves to the soil increased yields of edible biomass, the amount of carbon sequestered in soil, and the growth rates of maize planted in soil samples from the experimental plots after harvest. Narrowing the row distance from 150 to 90 cm led to increases in biomass yield without affecting brix or extraction rate of the juice.
Returning the dead leaves to the soil, decreasing the row distance and selection of
newly introduced sugar cane varieties are management practices which can be recommended to
farmers in the Bavi area.
Key words: Sugar cane, row distance, animal feed, harvest time, dead leaves, mulching
The impact on the sugar cane industry of introducing new varieties and clones during the last four decades has been reviewed by Heinz (1991). The increase in sugar production has largely come about as a result of breeding for higher stalk yield and sugar content and for improved disease resistance. At the present time there are 12 varieties of sugar cane being planted widely in different ecological areas of Vietnam (Tran 1988). Eight of these varieties were released prior to 1992 (FAO 1992). Since 1967, research has concentrated on developing new varieties by crossing existing strains and importing new ones that adapt well to the different ecological zones in Vietnam. The outcome has been an increase in stalk yield from 35 tonnes/ha in 1980 to 43 tonnes/ha in 1993 (Handbook of General Information of Sugar cane Industry in Vietnam 1994).
The traditional variety planted in the Bavi area since some forty years is POJ 3016 (crossbreed between POJ 2878 and POJ 2940). It came originally from Java, Indonesia and was imported into Vietnam in 1935. POJ 3016 can give high stalk yield (90-100 tonnes/ha) and good quality. It was classified in the early ripe variety group, but less resistant ability to diseases than F156 and My 55-14. Among the new varieties introduced recently is F 156, which was imported from Taiwan in 1970, and by 1981 was being grown throughout the country. It is resistant to many diseases and is tolerant of dry conditions. It matures at between 13 and 15 months and can yield 80-100 tonnes/ha of cane stalk (FAO 1992). Planted at 90-100 cm spacing between rows (National Centre of Plant Variety Testing 1992) it has a reported sucrose (Pol) content of 13.5%. My 55-14 was imported from Cuba in 1974. It adapts to a wide range of conditions, is quick growing and can yield 80-100 tonnes stalk/ha with good sugar content (Nguyen Huu Uoc 1987, 1989). This is a variety with early germination, good tillering and late flowering (FAO 1992) and has adapted well to the hilly lands of Hoabinh, Thanhhoa and the Eastern provinces of South Vietnam. In 1991 the Hoanam variety was brought into Vietnam from China for testing. It was found to be high yielding and of good quality for chewing due to the soft peel and because the fibre bundle is not tough ( Nguyen Thi Dao, 1994 pers. comm.). It was decided to compare these three new varieties with the traditional POJ 3016, when grown at reduced row spacing and with and without mulching. These factors were included in the design of this experiment as it had been shown previously that they had a marked impact on sugar cane yield and on soil fertility when the traditional POJ 3016 was used (Nguyen Thi Mui et al 1996a).
The experiment was carried out in January 1994 and 1995 at the Goat and Rabbit Research Centre in Bavi district, which is a hilly area. The soil composition at the experimental site was as follows: pH 4.5, K2O 0.045%, P205 0.08%, N 0.11%. In general, the soil is of low fertility, in particular with low levels of organic matter and moisture.
The design of the experiment was a Latin square split-plot design, including four varieties and two planting distances, mulching with dead leaves or not and with four replications. The treatments were :
Variety was the main plot, mulching or no mulching treatments were the sub-plots and row spacings were split-plots. The size of the experimental plot was 90 and 72 m2 and the recorded area was 60 and 54 m2 for 150 cm and 90cm row spacing, respectively. The total number of plots was 64 giving a total experimental area of 5,080 m. The treatments were randomized and the soil in the experimental area was also quite uniform. Stem cuttings of the four varieties were used as planting material, requiring 8 and 10 tonnes/ha for 150 and 90 cm row spacing, respectively. At harvest the experimental plots were divided into 2 equal parts for harvesting. One half was harvested at 10 months after planting and the other half at 12 months.
The whole plant was cut at ground level. The stalk was separated from the whole plant by cutting immediately below the second node measured from the top. The growing points (tops) were then separated from the leaf blades (green leaf). Each component was weighed and sampled for chemical analysis.
Samples of the stalk from each plot (about 10 kg) were crushed by passing them three times through a 2-roll mill driven by a buffalo. On the second and third pass the partially pressed stalks were doubled to maximise extraction of the juice. Extraction rate was expressed as weight of juice as a percentage of the weight of cane stalks. The total soluble solids in the juice (Brix) were determined using a hand refractometer.
Soil samples at 0-20cm depth were taken from each experimental plot immediately after each harvest. Equal amounts (3 kg) were put into clay pots (about 5 litre capacity) for a biological test of overall soil fertility. Three seeds of maize were planted. After 5 weeks the maize plants were removed from the soil, washed to remove soil from the roots and allowed to dry for 1 hour. The total fresh biomass and the roots were weighed.
Samples of soil at 0-20 cm depth were taken from each plot after the 12 month harvest. The 64 samples were bulked into 8 sub-samples corresponding to mulching and not mulching treatments for each variety. The sub-samples were analysed for pH, N, P, K and carbon by standard methods (AOAC 1985). Estimates were made of the populations of fungi, bacteria and actinomycetes according to "Standard methods of analysis for Soil, Plant tissue, Water and Fertilizer" (Philippine, Los Baņos, Laguna, 1980) with asparagine-manitol agar media for bacteria, glycerol agar for actinomycetes and peptone-dextrosugar plus rose bengal and streptomycin for fungi.
Other management practices and measurements such as fertilizer application, cultural practices and pesticide control were carried out according to the traditional practices of the farmers.
The data were analysed by Analysis of Variance using the General Linear Model of the statistical software by Minitab (1993, Release 9.2). The differences between mean values of variety treatment in each of the two years were tested using Tukey 's pairwise comparisons.
The mean numbers of plants/m for the different treatments are shown in Table 1. The
number of plants obtained was highest for F 156 in the first harvest year. In the second
year the number of plants was lowest for POJ 3016. The number of plants in year 1 was not
affected when dead leaves were left on the soil surface, although there was a slight
tendency (P=0.22) for the mulching treatment to support a higher population in year 2. As
was to be expected, the plant density increased as the distance between rows decreased,
with the effect slightly reduced in year 2 (differences of 55 and 40% respectively in
years 1 and 2).
The number of plants was not much reduced in the second year in this experiment but cane yield declined compared with the first year. It was noticed that the canes in the second year were of smaller diameter and shorter, thus yield was probably constrained by factors other than plant density such as fertilizer and moisture.
The yield of edible biomass (stalks, tops and green leaves) which can be used as animal feed (Tables 2 and 3) varied among varieties, all the introduced varieties out-yielding the traditional POJ 3016, especially in the second harvest year. F 156 and My 55-14 maintained relatively higher yields in the second year than the Hoanam variety.
Mulching increased cane stalk yield by 4.2% in the first year (86.8 vs. 83.3 tonnes/ha). The difference was more marked in the second year, the increase being 20.8% compared with no-mulching (70.3 vs. 58.2 tonnes/ha). Mulching also increased total biomass yield in both years but much more in the second year (21%) than in the first year (4.3%). In the second year the main components of the biomass (stalk and tops) were increased by mulching (P=0.001) but the effect was less noticeable (P=0.25) for the green leaf component. It was very interesting to note that the increase of sugar cane yield due to mulching confirmed the findings of an earlier experiment (Mui et al 1996a), where mulching resulted in 6.3% and 20% of increase for the first and second year, respectively. These effects are similar to those observed by Arzeno (1992), Phan Gia Tan (1995), Sinha et al (1991), Singh and Singh (1984) and Ball Coelho et al (1993).
When the row spacing was reduced, the sugar cane yield responses were significantly higher and similar for all cultivars. These results were in agreement with Richard et al (1991), Devi et al (1990), Phodat et al (1989), Yadav (1992) and Mandloi et al (1989). Yields of biomass were increased by narrow row spacing more in year two (63%) than in year one (38%). This trend was also observed for all the components of the biomass, and similar results were reported by Arvind et al (1990), Irvine et al (1984), Sharma (1982) and Singh and Singh (1992).
There were no important differences due to treatment in juice extraction rate and Brix value (Table 4). The 90cm row spacing resulted in a lower extraction rate in the first year and a higher Brix value in the second year compared with the 150cm distance. The Brix values were similar to those reported by Nguyen Thi Dao (pers. comm, 1993), and Tran Van Soi (1988) for the same varieties. Studies in India by Singh and Singh (1992) showed that sugar content was not influenced by row spacing in the plant crop, but was increased significantly by narrower row spacing in the ratoon crop, being maximum at 75 cm row spacing because of less fibre in the canes planted with the narrow spacing. Less fibre and more sugar would be an advantage in sugar cane destined for animal feed.
Advancing the harvest time to 10 rather than 12 months resulted in increased extraction rate of juice (Table 5) but decreased yields of stalk and total biomass and the Brix content. Earlier harvesting led to a lower content of dry matter, a higher content of fibre in the dry matter and had little effect on the protein content (Table 6). These data can be interpreted to indicate that there is no advantage in harvesting the sugar cane early when it is destined for animal feed. Similar conclusions were reached by Alvarez and Preston (1976).
The amounts of dead leaves collected monthly from 6 months after planting to the time of harvest are shown in Table 7. The highest values were recorded for the F 156 variety in both years. In contrast with the yield of edible biomass, that of the dead leaves increased in the second year. There were more dead leaves at the narrower distance (P=0.001 and 0.014 in years 1 and 2) and an slight indication that they were higher due to mulching (P=0.03 and 0.25 in years 1 and 2).
The results of the biological test of soil fertility (Table 8) show highly significant increases in the weights of maize plants grown in soil taken from the mulching treatments, but no effects due to variety or plant spacing. Chemical and microbiological analysis (Table 9) showed that mulching led to a higher content of soil carbon (P=0.014) and an indication of greater fungal biomass (P=0.25) but there were very small effects on other parameters.
This paper was submitted in 1996 to the Swedish University of Agricultural Sciences in
partial fullfillment of the requirements for the Master of Science degree in
"Livestock-based Systems for Sustainable Use of Natural Renewable Resources".
Financial support from SAREC to participate in the Master's course is gratefully
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Received 1 June 1997
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