Modeling approach for nitrogen use efficiency and cycling in beef cow-calf production systems integrated with forage rice production

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  • 飼料イネ生産と結びついた肉用繁殖生産システムの窒素の利用性と循環性に関するモデル分析
  • シリョウ イネ セイサン ト ムスビツイタ ニクヨウ ハンショク セイサン システム ノ チッソ ノ リヨウセイ ト ジュンカンセイ ニ カンスル モデル ブンセキ

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Abstract

In recent, surplus paddy rice fields have been increasing in Japan due to decreased rice consumption. The surplus fields can be utilized for forage rice production and animal excretion can be applied to the fields as manure. In such systems, forage rice is supplied to cattle as whole crop rice silage (WCRS). The objectives of this study were to (1) develop a simulation model for beef cow-calf production systems integrated with forage rice production, (2) apply the model to quantify the nitrogen (N) flows in the systems and (3) examine the effects of alternative scenarios for forage rice production and nutrient values of WCRS on N flows, N use efficiency and cycling index in the systems. The life cycle energy requirements of a cow and her calves were determined based on Japanese Feeding Standard for beef cattle published in 2000 and diets involving WCRS were formulated according to the technical manual for WCRS production and feeding in 2006. The WCRS intake, N intake and N excretion were calculated in daily basis and then N flows and N balances in the system were calculated in annual basis. The three alternative scenarios (increases in harvestable forage rice yield and CP and TDN contents of WCRS) were evaluated by simulation. The result showed that increases in harvestable forage rice yield and CP content of WCRS lead to decreases in N use efficiency and cycling index in the systems. In particular, since improvement of harvestable forage rice yield appears to be supported from economic point of view, this result may indicate the discrepancy between economic optimization and N management optimization.

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