Korea, rice cultivars have been changing to 'quality' rice rather than high yielding cultivars. However, more than 10% of paddy field has been changed to greenhouse in winter season for cropping of water-melon, oriental-melon, straw berry and et cetra. This experiment has been made to identify the usefulness of critical N and Si fertilization(SF) level to obtain high grain quality rice with reduced insect pest damage by N and SF combination. Before the experiment, watermelon-rice cropping system was maintained for three seasons by farmer from 1998 to 2001. The experiment of N and Si (silicate) fertilization levels was evaluated with Hwayoung-byeo (Oryza sativa L., medium-maturing variety) in 2002 and 2003 in Uiryeong, Korea. Nitrogen fertilization (NF) levels were three and five in 2002 and 2003, respectively, and three SF levels were compared for getting the valuable N/SF level in both years. TOYO-value was positively affected by Si application in N100% plot but it was negatively related with NF level. Normal grain percentage was positively related with TOYO-value and it was highest in 0N plot and Si plots in N100%. Other appearance qualities like powdered, damaged, and cracked grain, were decreased with increasing N fertilization level. SF improved appearance quality in N100% plots but no effects in other treatments. Leaf sheath related diseases were significantly decreased by SF but it was negatively related with NF. In conclusion, SF could be improve grain quality at the same yield levels of conventional fertilization and it also could be reduce the diseases damages of rice plant in all N treatments. NF treatment reduced grain quality and improved grain yield at N50% level, however NF above N50% could not get any kind of benefits. So, compared with conventional fertilizer, reduced NF level is recommended for high grain quality with reduced insect pest damage.

• Ramachandran Muthukumarasamy
• Ui-Gum Kang
• Ki-Do Park
• Chang-Young Park
• Soon-Do Bae
• Weon-Tae Jeon
• Young-Son Cho