Measurement of gaseous emissions from denitrification of applied N-15 .3. Field-measurements

Abstract

Field experiments were conducted during autumn and winter (April-July) at four locations on Vertisol or Alfisol soils on the Darling Downs of Queensland in 1988 and 1989 to determine 15N losses when soil was saturated after applications of 15N labelled nitrate-N prior to sowing winter cereal crops. Losses of applied 15N were quantified by either gas emission or mass balance measurements on microplots (0.043 m2) confined laterally to a depth of 110 or 260 mm. At each field location, two experiments were established, one on a soil containing little visible crop residue where winter cereal had been harvested the previous November and another site containing residues of a recently harvested sorghum crop. Because shallow (110 mm) confinement was found to be unsatisfactory for both gas emission and mass balance measurement of 15N losses, comparison of the two methods was not applicable at one of the four field locations. Loss estimates for the six field sites by accumulating daily gas emissions averaged 80.7 � 33.4% (range 43-132%) of that estimated by mass balance. Loss estimates from peak emission measurements were generally closer to that estimated by mass balance 100.8� 39.9% (range 56-169%). Loss of applied 15N (40 kg N ha-1) when soils were saturated in April was several-fold more (19-29 kg N ha-1)) than that lost when soils were saturated in July (3.9-6.4 kg N ha-1)). Loss of 15N following saturation during July 1988 was similar in magnitude to the quantity of 15N apparently immobilized into soil organic forms (5.8-6.0 kg N ha-1)). Sorghum residues returned in March, or wheat straw added in December prior to a long period of dry weather, promoted loss of 15N applied prior to soil saturation in April or July. Alternatively, where residues of a previous winter cereal had decomposed considerably, loss of applied 15N was much lower than where sorghum residues had been added prior to saturations in April (15.3 cf. 28.6 kg N ha-1)) or July (3.9 cf. 6.4 kg N ha-1)).

Modifications of Soil Nitrogen Pools in Response to Alfalfa Root Systems and Shoot Mulch

“…Denitrification rates, measured on 16 June 1996, were always higher when alfalfa shoots were applied to either bare or alfalfa plots (Table 7) and were consistent with a previous report of higher denitrification rates following fresh residue applications (Avalakki et al, 1995). Average denitrification rates doubled from the BF treatment (76 g N ha d-1 ) to the A treatment (159 g N ha d-1 ).…”

Influence of temperature and soil water content on bacterial, archaeal and denitrifying microbial communities in drained fen grassland soil microcosms

“…Biological processes respond positively to temperature upshift and several studies have confirmed that this is also true for the denitrification process. In experiments addressing both N 2 O production and reduction to N 2 , the product ratio (N 2 O/N 2) has been found to increase with decreasing temperature (Bailey & Beauchamp, 1973;Keeney et al, 1979;Avalakki et al, 1995). One possible explanation might be that N 2 O reduction has higher activation energy than N 2 O production.…”

Legume and opportunity cropping systems in central Queensland. 2. Effect of legumes on following crops

“…2c). Other studies on cracking clay soils in Queensland (Littler and Whitehouse 1987) have also suggested that N derived from pasture was more efficient than fertiliser N for wheat growing in a Darling Downs cracking clay due to better profile distribution of the pasture N. Furthermore, denitrification may be responsible for significant losses of mineral N in these soils (Avalakki et al 1995;Armstrong et al 1996a); nitrate deeper in the profile is less liable to be lost.…”