벼 담수직파재배에서 입모수가 적정입모수(120개/m2 )보다 적은 과소구를 60개/m2 , 적정입모수보다 많은 과다구를 200개/m2 로 설정하여, 과소구의 경우 3엽기에 4 kg/10a의 질소를 추가 시비하여 분얼발생을 촉진시키고 과다구에서는 5엽기에 시용하는 분얼비 3.3 kg/10a의 질소시비를 생략하여 분얼을 억제한 결과는 아래와 같다. 1. 개체별 최고분얼수는 적정구가 9.8개인데 비하여 과소구는 15.2개, 과다구는 8.6개이었으며, 개체별 유효분얼수는 적정구가 3.7개, 과소구가 6.5개, 그리고 과다구가 2.4개로 입모가 과다할수록 개체당 분얼수가 줄어들고 유효경비율이 낮아졌다. 2. 분얼발생 양상은 입모밀도에 관계없이 주간 3절위에서 첫 번째 1차 분얼이 발생하였으며, 유효분얼은 과소구, 적정구, 과다구에서 각각 6.5개/plant, 3.7개/plant, 2.4개/plant 발생하였다. 3. 입모과소구의 벼 개체내에서 분얼의 발생 순서와 간장, 수장, 무효분얼수, 수당립수, 임실율은 부의상관관계가 있었으나, 적정 입모밀도에서는 유의한 상관이 없었다. 입모과다구에서는 분얼발생순서와 수장, 무효분얼, 완전미율이 유의한 상관관계를 나타내었다. 4. 현미외관 특성은 입모 과소구가 적정구나 과다구 보다 청미발생이 적어서 완전미율이 가장 높게 나타났으며, 과다구와 적정구의 경우에는 1차 분얼에서 청미발생이 과소구보다 15-20%정도 높게 나타났다. 5. 쌀 수량은 적정구가 494 kg/10a인데 비하여 과소구는 적정구의 99%, 과다구는 적정구의 97%의 수량이 확보되었다.

This research was carried out to determine the effect of controlling nitrogen application on tiller development, yield, and quality of rice under scanty or excess seedling stands in direct-seeded rice on flooded soil surface. Seedling stand was set to 3 levels: scanty (60/m2) , optimum (120/m2) , and excess (200/m2) . In the scanty plot, additional 4 kg/10a nitrogen was applied at the 3rd leaf stage to promote tiller development. On the other hand, applying 3.3 kg/10a nitrogen at 5th leaf stage in the excess plot was omitted to suppress tillering. Maximum numbers of tillers per plant were 15.2 and 8.6 in scanty and excess plots, respectively, as compared with 9.8 in optimum plot. Productive tiller rate decreased with the increase in number of seedling stands. Regardless of seedling density, the first tiller developed on the 3rd node of rice stem from the bottom. The primary tillers developed at 3, 4, 5, 6, 7 nodes in scanty plot, 3, 4, 5 nodes in optimum plot, and 3, 4 nodes in excess plot. The secondary tillers developed only in some portion of plants in scanty and optimum plots. The order of tiller emergence was negatively correlated to stem length, panicle length, non-productive tiller number, grain number per panicle, and fertility in scanty plot, and to perfect grain ratio in excess plot. In the optimum plot, however, the order of tiller emergence was not correlated to any of the mentioned characteristics. The perfect grain ratio of scanty plot was the highest because green-kerneled rice was a very small portion in the primary tillers as compared with those of optimum and excess plots. Yield indexes of scanty and excess plots were 99%, and 97%, respectively, of the yield (494 kg/10a) in optimum plot. In conclusion, when seedling stands are not at optimum level, rice yield and quality similar to optimum planting density level can be obtained by means of controlling nitrogen application.

• 정남진(농촌진흥청)
• 김정일(작물과학원)
• 박정화(작물과학원)
• 김제규(농촌진흥청)