　　水稲‘ヒノヒカリ’に対して，速効性肥料を配合せずに被覆尿素のみで慣行施肥量を大幅に削減した全量基肥栽培を行い，環境に配慮した減化学肥料栽培の可能性について検証した。その結果，作況不良の異常年を除くと50％窒素施肥量を削減した場合，4～18％程度の減収となった一方で，玄米窒素含有率は低く抑えられ，食味は向上する傾向にあった。用いる被覆尿素の種類は，リニア型30日タイプとシグモイド型80日タイプを1：1で配合した場合が，リニア型100日タイプ単品よりもわずかに収量が上回る傾向にあった。なお，施肥後から移植直前までの田面水中窒素濃度は被覆尿素を用いることで，著しく低く抑えられ，窒素を全く施用しない場合と同水準で推移したことから，施肥窒素が水田外に表面流去するリスクが低減されることが明らかとなった。　

　Effect of Coated Urea for Low Chemical Fertilizing Cultivation of Rice Plants to Prevent Pollution Irrigation Water. ARAKI Masato, Kohei TANAKA, Tomizou YAMAMOTO and Yukie MIZUDA (Fukuoka Agricultural Research Center, Chikushino, Fukuoka 818-8549, Japan) Bull. Fukuoka Agric. Res. Cent., 23: 1 6 (2004)

　The influences of the single basal application of coated urea, without the use of readily available fertilizer on the yield and palatability of 'HINOHIKARI' rice and the quality of water in a paddy were examined to determine whether this fertilizing would be applicable to farming. The research revealed that the application of nitrogen at a rate reduced by 50% resulted in a yield of 82~96% compare to conventional fertilizer application. On the other hand, the palatability score of the former was superior to that of the latter because there was a difference in the nitrogen contents in brown rice. With regard to the choice of coated urea, in once case, mixture with a 1:1 ratio of　linear 30-day type and sigmoid 80-day type was administrated; and in another case, linear 100-day type alone was administrated, resulting in a better yield. At the same time, the concentration of nitrogen in the paddy water remained at a remarkably low level, once the coated urea was applied to immediately before planting, and the risk of applied nitrogen run-off from the paddy was reduced.