実規模の圃場と乳牛を用いた重窒素標識牛ふん尿堆肥製造過程における窒素収支  [in Japanese] Nitrogen Balance during Production of ^<15>N-Labeled Dairy Cow Composted Manure on a Practical Scale  [in Japanese]

420m^2の草地と乳牛5頭を供試して,重窒素標識牛ふん尿堆肥を作成し,その過程における重窒素のフローを明らかにした.標識サイレージを給与した牛の排泄ふんの重窒素濃度は,6.2atom%の1番草給与開始後2日目から急激に上昇し,8日目にはほぼ定常状態となったが,4.0atom%の2番草給与を開始すると緩やかに減少し,非標識乾草給与によって急激に減少した.排泄尿の重窒素濃度の推移は,排泄ふんのそれと同様の傾向を示したが,排泄尿の重窒素濃度は,給与開始後数日間をのぞき排泄ふんのそれと比べると著しく低かった.製造堆肥の重窒素濃度を高めるために,排泄ふんの重窒素濃度が3.0atom%以上の期間に回収されたふんと尿のみを堆肥製造に供した.ふんと尿は,80℃の通風乾燥機中で個別に乾燥後,混合し,吸引通気式堆肥製造装置を用いて堆肥化した.製造された重窒素標識堆肥の重窒素濃度は,3.95atom%であった.製造堆肥中窒素を塩酸濃度と環流時間を変えることにより逐次分画し,重窒素標識の均一性を調べたところ,いずれの画分もほぼ同様に標識されており,本報で得られた堆肥は,施用堆肥由来窒素の動態を調査するトレーサーとして適当であると考えられた.以上の結果,施用重窒素量を100とした場合,ふん尿堆肥製造の各過程における重窒素の損失率は,標識牧草栽培過程58.9%,圃場からの搬出過程8.9%,サイレージ調製過程0.3%,ふん尿回収過程8.3%,ふん尿選別過程2.0%,乾燥処理・堆肥化過程11.1%となり,最終的に堆肥中に残った重窒素量は,施用重窒素量の10.6%となった.

^<15>N-labeled composted manure was produced using five adult dairy cows and 420 m^2 of grassland and the flow of ^<15>N during the process was analyzed. Cows were fed ^<15>N-labeled Dactylis gromerata 1st cut silage containing 6.2 atom% ^<15>N. After 2 days, ^<15>N concentration in their feces increased significantly, reaching 4.95 atom% ^<15>N at the 10th day, and ^<15>N concentration was almost stable after 8 days. Cows were subsequently fed 2nd cut silage containing 4.0 atom% ^<15>N, resulting in a slight decrease in ^<15>N concentration. However, ^<15>N concentration remained high at approx. 3 atom% ^<15>N, and decreased immediately after non ^<15>N-labeled hay was fed upon completion of the 17-day procedure. Results of ^<15>N concentration in urine were almost parallel with those for feces, although ^<15>N concentration was significantly lower. In order to increase ^<15>N concentration, feces and urine excreted when ^<15>N concentration in the feces exceeded 3 atom% ^<15>N were used for production of the compost. After dehydrating the feces to 68 kg kg^<-1> water content and concentrating the urine in a heating oven at 80℃, the dried feces and concentrated urine were mixed and composted in an air sucking composter for 4 weeks. One hundred and forty seven kilograms of composted manure was obtained, containing 3.95 atom% ^<15>N and 50 kg kg^<-1> water. Uniformity of labeled ^<15>N was determined by fraction separation through acid hydrolysis differing by acid concentration, and almost uniform homogeneity was confirmed. Satisfactory compost manure labeled ^<15>N was obtained using this procedure. Relative N recovery ratio compared to the amount of N contained in the applied ^<15>N labeled fertilizer was 23.6% in excreta, with the loss of 11.1% during drying and composting, and 10.6% N remained in the final composted manure.