@article{oai:repository.naro.go.jp:00001610,
 author = {建部, 雅子 and TAKEBE, Masako and 唐澤, 敏彦 and KARASAWA, Toshihiko and 駒田, 充生 and KOMADA, Michio and 佐藤, 文生 and SATOa, Fumio and 西村, 誠一 and NISHIMURA, Seiichi and 高橋, 茂 and TAKAHASHI, Shigeru and 加藤, 直人 and KATO, Naoto},
 journal = {中央農業総合研究センター研究報告, Bulletin of the National Agricultural Research Center},
 month = {Mar},
 note = {Some farmers are known to have difficulties in beginning organic farming, and hence the ratio of the area of organic farms to the whole farmland area and the ratio of organic production to total agricultural production remains low in Japan. It is necessary to get stable yields to motivate farmers and expand the organic farming area. A field experiment investigating organic farming was begun in 2008, and the yield and soil inorganic nitrogen levels in organically-and conventionally-cultivated carrot and lettuce fields were compared for 3 years, in a Hapludands field in NARO Agricultural Research Center (36°02'N, 140°10'E) located in Tsukuba, Japan. In the study, the target yield of the organic crops was over 80 % of the conventional crop yield. Soil inorganic nitrogen concentrations (0-15 cm layer) were measured during the growing period of carrot and lettuce at 2 or 3 weekly intervals, and the effect on the productivity of organic crops was studied by comparison with conventional crops.  1. Nitrogen mineralization of applied marketed organic fertilizer was rapid under the field cultivation of carrots in summer and the mulch and tunnel cultivation of lettuces in winter. The nitrogen efficiency was almost the same as that of applied chemical fertilizer. The fermented chicken manure gave equal soil inorganic nitrogen levels to the marketed organic fertilizer when it was supplied at a modified amount according to the nitrogen efficiency rate.  2. The abundant inorganic nitrogen at the sowing time was not useful for the field cultivation of carrot as much precipitation caused nitrogen leaching. Carrot yields increased with an increase in the soil inorganic nitrogen concentration at 2 or 3 weeks after top dressing in the case of both organic and conventional cultivation. Therefore it was advisable to raise the proportion of the top dressing for both the organic and conventional cultivation of carrots.  3. Lettuce yield increased with an increase in the average soil inorganic nitrogen concentration during the growing period up to about 280 mg kg^－1 dry soil, and then decreased. The application of excess nitrogen resulted in low yields for both organic and conventional cultivation.  4. The application of cattle manure compost was effective for winter lettuce production in both organic and conventional cultivation. Lettuce dry weights and phosphorus concentrations in the early growth stage were higher in plots with applied compost than in plots without compost, and the phosphorus concentration of lettuce was highly correlated with the dry weight at 1 or 2 week before harvest. A positive effect of the cattle manure compost was the phosphorus supply from the compost which accelerated the early growth of the lettuce.  5. In the 3 years during the transition period to organic farming, yields of carrot and lettuce cultivated organically, which received nutrients from the organic fertilizers, was on average 96 and 127 %, respectively, of that of crops grown conventionally. The released inorganic nitrogen from the organic fertilizers explained the productivity of organic cultivation as well as conventional cultivation.},
 pages = {25--51},
 title = {有機栽培転換期における土壌無機態窒素の推移と堆肥施用がニンジン、レタス収量に及ぼす影響},
 volume = {21},
 year = {2014},
 yomi = {タケベ, マサコ and カラサワ, トシヒコ and コマダ, ミチオ and サトウ, フミオ and ニシムラ, セイイチ and タカハシ, シゲル and カトウ, ナオト}
}