オガクズ牛ふんたい肥の長期施用がホウレンソウの生育および窒素吸収に及ぼす影響(土壌管理・施肥・灌水)  [in Japanese] Effect of Continuous Application of Compost Made from Cattle Waste and Sawdust on the Growth and Nitrogen Uptake of Spinach (Spinacia oleracea L.)(Soil Management, Fertilization & Irrigation)  [in Japanese]

岩手県の主要品目であるホウレンソウを対象に1998年から2001年まで,県内で産出するオガクズ牛ふんたい肥の連用試験を行い,年間2〜4作のホウレンソウを作付けして,生育,窒素吸収反応に及ぼす影響について調査した.化学肥料区には,年間で窒素を硝安で16-20g・m^<-2>,リン酸を重過石で20-24g・m^<-2>,カリを塩加カリで16-20g・m^<-2>施肥した.たい肥区では,1作目播種の2週間前にオガクズ牛ふんたい肥を45gN・m^<-2>施用し,2作目以降は無施用とした.その結果,たい肥区の草丈,葉幅,葉数は化学肥料区のそれを上回った.また,乾物収量,窒素吸収量もたい肥区が化学肥料区より多かった.各作付後の跡地土壌の無機態窒素含量はたい肥区が化学肥料区より低かった.さらに,ホウレンソウ中の全窒素に占める硝酸態窒素の比率は,化学肥料区に比べてたい肥区は極めて低い値を示した.これらの結果は,たい肥を施用した場合,ホウレンソウの生育および窒素吸収量が栽培期間中の土壌中の無機態窒素の存在量に対応していないことを示唆するものであった.一方,中性リン酸緩衝液によって抽出される土壌中の易分解性有機態窒素は,化学肥料区で実験開始前よりも減少し,たい肥区では増加した.

Spinach (Spinacia oleracea L.) is one of the major agricultural products in Iwate prefecture, Japan. To evaluate the effect of compost made from cattle waste and saw dust, the growth and nitrogen (N) uptake of spinach were examined between 1998 and 2001, compared to those with standard fertilization using a chemical fertilizer. The compost was applied annually at a rate of 45g N・m^<-2> before sowing, then spinach was cultivated 2-4 times per year without supplemental N application. In the standard fertilization using ammonium nitrate, super phosphate and potassium chloride, N, P_2O_5 and K_2O were applied to the soil at rates of 16-20g・m^<-2>, 20-24g・m^<-2> and 16-20g・m^<-2>, respectively. Morphological index, i.e. leaf length, leaf width and number of spinach leaves in plants receiving compost were comparable to those of plants treated with chemical fertilizer. Dry matter production and N uptake in spinach applied with the compost was higher than that applied with chemical fertilizer, while the concentration of inorganic N in soil treated with compost was much lower than that treated with chemical fertilizer after every cultivation. Furthermore, the proportion of nitrate to total N in spinach receiving compost was much lower than that in spinach treated with chemical fertilizer, a though N uptake was higher in spinach treated with compost than that treated with chemical fertilizer. These findings suggest that N uptake in spinach would not be fully explained by the concentration of inorganic N in soil. However, concentration of phosphate buffer extractable organic N, which is considered an easily decomposable organic N, increased in soil treated with compost compared to that in soil treated with chemical fertilizer.