Thesis Abstract of AGS Students

Pradya Nasuriwong (1997)

A study of sugarcane response to plant density by using a fan design was conducted in Mae Hia Research and Training Station of the Faculty of Agriculture, Chiang Mai University, Mae Hia Sub-district, Muang District, Chiang Mai Province. The objectives of this study were to establish the relationship between plant densities and growth and development processes of sugarcane, and to determine the optimum plant density for optimal growth and development as well as yield of sugarcane. The experimental design was a split-plot design, arranged in a Randomized Complete Block Design (RCBD) and three replications. Two sugarcane varieties were the main plot and 12 different plant densities were the sub plots. Two selected sugarcane varieties namely, K84-200 and U-Thong 2 were planted in a systematic design, with 12 plant densities ranging from 0.32 to 3.23 plant m^-2, or 3.33 to 0.33 m² plant^-1, respectively. The sugarcane was planted on January 25, 1996.

The investigation revealed that during the early growth stage (1-120 days after planting), biological yields of both sugarcane varieties responded to plant densities similarly. However after that stage, U-Thong 2 had significantly higher biological yields than K84-200 (p<0.05), especially during the vegetative growth stage (150-229 days after planting). Plant density was a dominant factor influencing biological yields. After 120 days after planting, plant densities exhibited a strong influence on stalk fresh weight, and total dried weight which include stem dried weight, leaf blade dried weight, leaf sheath dried weight in both sugarcane varieties. These biological yields increased with plant density increased (p<0.01), due to increase in stalk number per unit area. The biological yields reached their maximum weight in the high plant density treatments (2.13 to 3.23 plant m^-2) in both varieties. The response of these state variables to plant densities can be captured in a series of quadratic growth curves.

The investigation also revealed that in both varieties, plant densities had influenced on growth components include crop growth rate, leaf area index, tiller number per square meter, plant height and stem diameter, especially during the later growth stages. During 180-229 days after planting, U-Thong 2 had significantly higher leaf area index than K84-200 (p<0.05), and had significantly higher tiller number per square meter than K84-200 (p<0.01). At all growth stages, plant height responded similarly to plant densities for both sugarcane varieties. At harvest, U-Thong 2 had smaller stem diameter than K84-200 (p<0.01).

Plant density was a dominant factor influencing sugarcane growth components. However, during the early growth stage (1-120 days after planting), plant densities did not affect growth components, but significantly influenced these components thereafter, especially in the high plant density treatments. Crop growth rate in both varieties increased with plant density. Leaf area index in both varieties was found to be increased with increasing plant density (p<0.01). Tiller number per square meter in both varieties were also increased with plant density (p<0.01). The maximum crop growth rate, leaf area index, and tiller number per square meter were also observed at the high plant density treatments (2.13 to 3.23 plant m^-2) in both varieties. During the vegetative growth stage (194-229 days after planting), plant height in both varieties increased with plant density (p<0.01), due to their competition for sunlight. At harvest, stem diameter decreased as plant density increased (p<0.01). The response of these growth components to plant densities can be captured in a series of quadratic growth curves.

The results shown that plant densities had minor effects on juice quality (commercial cane sugar (CCS), %Brix, %Polarity, and %Fiber) of both cane varieties. These values had high variation during the early stages (194 days after planting). After both varieties reached the stable stalk population stage (more than 229 days after planting), CCS values and its components had a tendency to decrease when plant density increased. Juice purity in both varieties were increased with cane age but decreased slightly when plant density increased. In term of sugar yields, it was found that reducing sugars in both varieties decreased with cane age and did not showed obvious response to plant density. Sugar yield per unit area was increased with time and plant density. The maximum sugar yield per unit area was observed at the high plant density treatments (2.13 to 3.23 plant m^-2) in both varieties. Therefore, it can be concluded that the high plant density treatments provide the highest biological yields and sugar yield in both varieties. The optimal plant density for sugarcane production ranged from 2.13 to 3.23 plant m^-2.

This research findings may benefit cane growers and sugar industry in Thailand in a number of ways. It offers an alternative to growers to improve their sugarcane production, by adjusting sugarcane plant density and row spacing, especially where the average sugarcane yield was poor and growing area was limited. Increase plant density may be the best option to improve sugarcane yields, over 40%. However, changing plant density or reducing row spacing posts another potential problem to mechanized-sugarcane farming. Growers should consider additional costs of cane sett, cultural practices, and labor for harvesting, each deserves further investigation.

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