INFLUENCE OF FLUCTUATING TEMPERATURES AND CONSTANT SOIL MOISTURES ON NITROGEN CHANGES IN AMENDED AND UNAMENDED LOAM

Abstract

Wood Mountain loam was wetted with water, (NH₄)₂SO₄, and peptone solutions to provide 22, 14, and 10% moisture while adding 0 and 50 ppm N. These treatments were incubated for 14 days at T13/2 (i.e., 13 C day, and 2 C night), T18/7, T24/13, and T27/16 to simulate soil conditions in the top 15 cm in May, June, July, and August. Progressive seasonal temperature change was simulated by transferring other replicates from T13/2 to T18/7; from T18/7 to T24/13; from T24/13 to T27/16; and from T27/16 to T18/7 for another 14 days. Field measurements were used to test the validity of the simulation. In the unamended soil there was no nitrification at T13/2, but there was where peptone or (NH₄)₂SO₄ was added. Generally, nitrification and mineralization were directly proportional to temperature and to moisture content. In the first 14 days nitrification (ppm) = 6 + 1.4 temperature (C); the Q₁₀ coefficient was 1.7. Mineralization at T18/7 following T27/16 (September) was much greater than at T18/7 following T13/2 (May). Addition of (NH₄)₂SO₄ caused priming of indigenous organic-N. The simulation study indicated that fallow soil at 22, 14, and 10% moisture would produce 90, 60, and 50 ppm nitrate-N between the beginning of May and mid-September. Field sites with average moisture contents of 24.5 and 15.5% were found to produce at least 104 and 41 ppm during the same period.