Thesis Abstract of AGS Students

Effect of genotype, nitrogen fertilizer rate and time of drainage on yield, milling quality and economic returns of rice production

Somchit Opastrakul (1996)

This study was designed to investigate factors affecting grain yield, milling quality and economic returns of rice production. Two field experiments were conducted at Multiple Cropping Center Experiment Station, Chiang Mai University to study the relationship between plant growth and milling quality of 36 rice varieties and to determine effect of field drainage and nitrogen respond of rice genotype on yield and milling quality. The later experiment consisted of three factors arranged in split-split plot design with two drainage timing as a main plot and four levels of nitrogen fertilizer application (i.e. 0, 30, 60 and 90 kgN ha-1) as a sub plots and three rice varieties (i.e. KDML 105, Dor Nang Nual, and RD1) as a sub-sub plot. Field survey including on-farm survey and miller survey was undertaken in four selected districts namely Saraphi, Doi Saket, San Pa Tong and Hang Dong in Chiang Mai Province. Eighty paddy samples were collected from interviewed farmers in order to determine the relationship between farmer's practices and milling quality.

Using cluster analysis to analyze data obtained from the first experiment, analysis results show that rice varieties can be grouped into four maturity groups namely very early maturity group, early maturity group, medium maturity group and late maturity group. Average number of days to heading of very early maturity group, early maturity group, medium maturity group and late maturity group were 59, 67, 76, and 88 days respectively. Results from the study also revealed that most of improved varieties were better than local varieties in terms of yield components, grain yield, dry matter and milling quality. The positive relationship between plant growth duration and grain yield and milling quality was found in early and late maturity groups.

Analysis results of the second field experiment demonstrated that nitrogen had significant effect on yield components, grain yield, dry matter and head rice for all three varieties. The maximum

grain yield of KDML105, Dor Nang Nual, and RD1 was attained at 80, 70 and 130 kgN ha-1 in which they produced an average grain yield of 4.06, 3.27 and 5.57 t ha-1, respectively. Maximum percent head rice of KDML105 and RD1 was obtained at 70 kgN ha-1 which were 46.63 and 46.45% while the highest percent head rice of Dor Nang Nual was 37.07% which was obtained at 60 kgN ha-1. The effect of time of field drainage (i.e. at soft dough and hard dough stages) on yield and percentage of head rice was not clearly shown. However, there was a tendency that late drainage tend to decrease head rice recovery.

Economic analysis results of field survey indicated that total income and return over variable cost of non-glutinous rice were significantly higher than those of glutinous rice. The total income and

return over variable cost of non-glutinous rice were 19,438 and 10,750 baht ha-1 and those of glutinous rice were 14,638 and 4,719 baht ha-1. The variable cost of non-glutinous rice and glutinous rice were 8,688 and 9,919 baht ha-1, respectively.

Analysis results from field survey suggested that farmer's practice in terms of nitrogen application and time of field drainage did not affect percent head rice. There was also found that there was no significant interaction between nitrogen application and time of field drainage on percent head rice. However, the positive relationship was found between grain yield and nitrogen application.

In summary, since producing high rice yields with good milling quality are needed to fulfill the growing demand of high quality rice in domestic and international markets, cultural practice in terms of nitrogen application and time of field dainage as well as genetic improvement were necessary concerned to improve rice production.

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