Measurement of gaseous emissions from denitrification of applied N-15 .2. Effects of temperature and added straw

Abstract

Gas emissions of applied 1 5~ were measured beneath a soil cover daily following saturation of Vertisol and Alfisol soils repacked in pots to the original field bulk density and held at three temperatures (5, 15 or 30°C) with or without addition of wheat straw. Collective gas emissions over 57, 43 and 15 days at 5, 15 and 30°C respectively were compared with the 1 5~ loss determined by mass balance.Loss measured by gas emissions (15N2 and 15Nz0) ranged from 36% to 152% of the denitrification loss as determined by 1 5~ mass balance. In the absence of added straw, measurement by gas emissions was consistently less than loss by 15N balance. Where straw was added, 15N loss by gas emissions was overestimated, probably because of a smaller headspace (0.3 L) than considered desirable (1-1.5 L) for emission measurements.Potential denitrification rates, in the presence of added straw, were similar for the Vertisol and Alfisol. Decreasing temperature slowed potential rates of denitrification from -2.5 kg ha-' day-' at 30°C to 0 . 8 kg ha-' day-' at 15'C and 0.4-0.5 kg ha-' day-' at 5OC. Decreasing temperature prolonged the period of waterlogging following a saturating event. Thus, collective loss of 15N was considerable even at the lower rates of denitrification at 5OC (52-76% over 57 days) or 15OC (87-92% over 43 days).Straw addition (10.5 t ha-') to the Vertisol, which contained no visible plant residues from previous crops, more than doubled the losses of applied 15N. In the absence of straw, rates of denitrification and immobilization were similar in magnitude, 0.97, 0.26 and 0.16 kg ha-' day-' for 30, 15 and 5OC respectively. Very rapid loss of applied 1 5~ in the presence of added straw led to decreases in immobilization of applied 15N, highlighting the potential effects of the much higher maximum rates for denitrification than for immobilization.The N20 emissions generally represented the smaller fraction (<25%) of denitrification emissions, becoming smaller as temperature was increased. As a proportion of emissions due to denitrification, N2O emissions were very low (<0.5% Vertisol, <3% Alfisol) in the presence of added straw.

Site selective real-time measurements of atmospheric N&lt;sub&gt;2&lt;/sub&gt;O isotopomers by laser spectroscopy

“…6) can, thus, be interpreted as a decreasing share of N 2 O reduction versus N 2 O production. The N 2 O versus (N 2 O + N 2 ) ratio increase correlates with a night-time air temperature decrease from 13 • C to 6 • C at the nearby NABEL station (data not shown), which is consistent with the temperature dependence observed in laboratory studies on soil samples (Avalakki et al, 1995;Bailey and Beauchamp, 1973).…”

N2O emissions and source processes in snow-covered soils in the Swiss Alps

“…The SP values found here for the forest soil (SPs = −1.6 ± 1.0 ‰) indicate that N 2 O reduction is of minor importance, as this process was found to result in SP above zero [42,45,52]. This interpretation is plausible as elevated nitrate availability, low pH Isotopes in Environmental and Health Studies 529 (0-5 cm: 4.0 ± 0.9) and shallow snow cover/low soil temperatures have previously been found to result in high N 2 O/N 2 product ratios [54][55][56]. In contrast the elevated SP values (16.4 ± 5.7 ‰) for the grassland indicate a significant contribution of N 2 O to N 2 reduction.…”

Concepts in modelling N2O emissions from land use

“…As well as affecting nitrification and denitrification process rates, temperature can alter the ratio of the products of denitrification, with declining N 2 :N 2 O ratios as temperature decreases (Avalakki et al 1995). Defining temperature optima and accounting for adaptation will require improved understanding of the microbial ecology (Avrahami et al 2003).…”