　花崗岩質土壌の露地野菜畑におけるおがくず入り牛ふん堆肥連用が夏作における土壌窒素無機化および窒素収支に及ぼす影響を検討した。一年間に6t/10aの牛ふん堆肥を7年間連用することによって，可分解性有機態窒素量Ｎ₀は10mg/100g程度蓄積した。夏作期間における土壌窒素無機化量は，牛ふん堆肥連用区が化学肥料単用区に比べて6.5～10.5kg/10a多かった。堆肥の窒素肥効率相当分の減肥を行っても，堆肥連用による作物の増収効果は維持されたが，堆肥連用区の潜在的な窒素負荷量は化学肥料単用区に比べて6.3～9.5kg/10a多かった。以上の結果から，花崗岩質土壌の露地野菜畑における堆肥の連年施用量は毎作3t/10a程度とし，夏作では堆肥の肥効率だけでなく土壌窒素供給量を考慮してさらに減肥する必要がある。

　Effects of Continuous Manure Application on Soil Nitrogen Mineralization and Nitrogen Balance of Granitic Soil Vegetable Fields　FUJITOMI Shin-ichi, Takayuki SUEYOSHI, Toshihiko HIRANO(Fukuoka Agricultural Research Center, Chikushino, Fukuoka 818-8549, Japan)Bull. Fukuoka Agric. Res. Cent.24: - (2004)

　We examined the effects of continuous cattle manure application on soil nitrogen mineralization and nitrogen balance of summer cropping of granitic soil pumpkin fields. The continuous sawdust-cattle manure application of 60 t ha^－１ a year for sevev years running resulted in an increase in the nitrogen mineralization potential　by 100 mg N kg^－１. In terms of the estimated amount of mineralized soil nitrogen,　there was from 69 to 107 kg ha^－１ more of it in the field with continuously applied manure than in the field with applied chemical fertilizer only. In terms of the potential amount of nitrogen load in the field where manure was continuously, it was larger by　67 to 97 kg ha^－１ than in the field where only chemical fertilizer was applied. Also even when reducing the amount of chemical fertilizer containing the fertilizer efficiency ratio in manure, the effect of increased yield was maintained by the continuous manure application. From these results, 30 t ha^－１ of continuous cattle manure application in a cropping season was an appropriate amount for vegetable fields of granitic soil. It seems that reducing amount of nitrogen fertilizer in consideration of the nitrogen supplied by the soil.