Effects of different types of fertilizers and methods on dry matter production, yield and nitrogen use efficiency of rice cultivars under field conditions

　To examine the effects of different types of fertilizers and application methods on dry matter production, yield, nitrogen accumulation and use efficiency in rice cultivars, we used two rice cultivars (Nipponbare and Takanari) and five fertilizer methods, i.e. Control (0N), Conventional method, Deep fertilizer method, Standard fertilizer method and High fertilizer method in 2009. Dry matter production was more markedly increased with nitrogen fertilizer application than in control, and it was higher with deep fertilizer application in Takanari and standard fertilizer application in Nipponbare, respectively. The differences in dry matter production resulted from CGR and mean LAI in rice cultivars. Greater dry matter production was accompanied with the nitrogen accumulation at harvesting. Rice cultivars accumulated the largest amount of nitrogen at deep fertilizer application. Higher fertilizer application increased the number of panicle and total spikelets m–2. The higher grain yield in Takanari resulted from the larger sink capacity. The grain yield of rice cultivars tended to be higher with deep fertilizer application due to the increase in sink capacity. Both deep fertilizer application and basal application of slow-release fertilizer increased the recovery efficiency and partial factor productivity of applied N, however, using slow-release fertilizer is recommended in terms of labor saving and lower cost.

　水稲の乾物生産，収量，窒素利用効率に及ぼす肥料と施肥法の影響を試験するため，水稲品種日本晴とタカナリを供試し，対照区（無施肥），慣行施肥区（分割追肥），深層追肥区，標準緩効性肥料基肥施肥区，倍量緩効性肥料基肥施肥区の５試験区を用いて栽培を行った．窒素施肥とともに，乾物生産が増大し，最終乾物重はタカナリでは深層追肥区，日本晴では標準緩効性肥料基肥施肥区で最も高くなった．乾物重の相違には個体群成長速度と葉面積指数が主として影響していた．収穫期の乾物重が大きいほど，窒素蓄積が多くなった．窒素蓄積量は両品種ともに深層追肥区で多くなった．施肥量の増加は穂数と㎡当たり穎花数を増加させた．タカナリの収量が高いことには，シンク容量が大きいことが関係した．両品種ともに慣行施肥区に比べ深層追肥区の収量が高くなったが，これにはシンク容量の拡大が関係していた．深層追肥区，標準緩効性肥料基肥施肥区ともに慣行施肥区に比べ窒素回収効率，部分要因生産性ともに向上したが，省力・低コストの観点からは施肥効率の高い緩効性肥料の利用が推奨された．

原著論文 (Original paper)