水稲に対する日照不足条件下におけるケイ酸の効果  [in Japanese] Effects of silicate fertilizer application on the yield of rice plants grown under insufficient light condition  [in Japanese]

日照不足条件下で水稲の吸収する窒素・ケイ酸の視点で解析し,収量向上に対する検討を行った.1)稲作期間中の平均日照時間が平年よりも多い年次の場合は収量に対するケイ酸の効果を示す収量比(ケイ酸施用区収量/ケイ酸無施用区収量)は稲わら施用系列で101に対して,平均日照時間が平年よりも少ない年次のそれは稲わら施用系列で113,平均日照時間が平均的な年次のそれは稲わら施用系列で106と向上した.このことから,収量向上に対するケイ酸施用の効果は稲作期間中の平均日照時間が少ない年次および平均的な年次で高い傾向であった.2)水稲による成熟期におけるケイ酸吸収量は土壌のケイ酸供給量の高低にかかわらず日照時間の多い1996年が1995年より高く,いずれも5%水準で有意であった.同様に,収量および成熟期における窒素吸収量についても日照時間の多い1996年が1995年より高い傾向であった.3)水稲による穂肥窒素の利用率は,日射量545MJで57.9%,325MJで40%,208MJで34.8%,146MJで31.4%で幼穂形成期〜出穂期の日射量に対応して低下した.4)各光量子量における止葉のみかけの光合成速度はシリカ200区>シリカ25区>無施用区であり,無施用区とシリカ施用区のみかけの光合成速度は5%水準で有意であった.収量はシリカ200区で656gm^<-2>,シリカ25区で6.17gm^<-2>,無施用区で606gm^<-2>で,出穂期〜成熟期の乾物生産増加量もシリカ200区914gm^<-2>,シリカ25区で836gm^<-2>,無施用区で802gm^<-2>でケイ酸施用によって高くなる傾向であった.

Field experiments were conducted to evaluate the effects of nitrogen and silica on the yields of rice plants under insufficient light condition. Results obtained were as follows: 1. A linear negative relationship was observed between sunshine irradiation periods and the rice yield ratios of Si-application plot to no Si-application plot in rice straw application experiment. The rice yield ratios were 113, 106, and 101 for the year of shorter, average, and longer sunshine irradiation periods (average irradiation time; 5.5, 7.0, and 8.1h d^<-1>), respectively. This result indicates that Si application is more effective for the rice yield in relatively shorter sunshine irradiation than in longer irradiation. 2. The amounts of SiO_2 and N uptake by rice plants and the rice yields were higher in the year of longer sunshine irradiation (1996) than in the shorter year (1995), regardless of soil type (significant at 5% level). 3. The recoveries of topdressed N by rice plants in the panicle formation stage were 57.9, 40.0, 34.8, and 31.4% under irradiation conditions of 545, 325, 208, and 146 MJ, respectively. 4. Apparent photosynthetic rate of flag leaf was significantly higher in Si application plot than in no Si application plot. In addition, brown rice and dry matter productions in the heading to maturity stages of rice were higher in Si application plot than in no Si application plot.