The effect of temperature on denitrification rate was studied with nine soils differing widely in organic matter content and chemical and physical characteristics. In the range of 15 to 35C, the temperature coefficient of denitrification, Q10, was approximately 2. Denitrification rates at 35 and 45C were similar. Between 10 and 5C, denitrification rate declined abruptly. The lower limit of the temperature range conforming to a Q10 of 2 was estimated to be 11C. In this study of water‐logged soils sealed from the atmosphere, denitrification appeared to obey first‐order kinetics.

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Little is known about the relative effectiveness of granular (UG) or prilled urea (UP), urea‐ammonium nitrate solutions (UAN), and ammonium nitrate (AN) when top dressed for no‐till corn. In most of the field studies reported, the N‐fertilizer used with no‐tillage has been ammonium nitrate, ammonium sulfate, or ammonium‐based mixed fertilizers. We conducted field experiments for 3 years on three moderately well‐drained Mattapex, Bertie, and Delanco silt loam soils (all Aquic Hapludults), comparing topdressed UG, UP, UAN solution (30% N), and AN at four N rates (45, 90, 135, and 180 kg/ha) on yields of continuous corn (Zea mays L.). A zero N plot was included in each of the four replicates. Yields were significantly higher from AN than from other N sources in 1978 at Forage Farm and in 1976 and 1978 at Wye Institute. Average yield from UAN exceeded that from UP and UG at Wye Institute. In 1978, when rainfall was above normal, even at the highest rate of N (180 kg/ha) total N uptake was barely sufficient to obtain maximum yields at Forage Farm and Poplar Hill and was clearly inadequate at Wye Institute. With 180 kg/ha of N applied, N%TDM when grain had reached the dough stage was about 0.9 at Wye Institute and 1.1 at the other sites. Values associated with estimated maximum yields generally exceed 1.2%. In 1978, estimated recoveries of applied N were higher from AN than from the other N sources at Wye Institute and Forage Farm.

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