Denitrification and nitrous oxide emission in thawing soil

The research was to identify the time of denitrification loss, and specifically, {dollar}rm Nsb2O{dollar} emission in relation to soil thawing. The hypothesis was that thawing soil emitted {dollar}rm Nsb2O{dollar} in the field or in the laboratory, and further, that denitrification (as measured by the {dollar}rmsp{lcub}15{rcub}N{dollar} mass balance technique) occurs at soil thaw.; Denitrification and {dollar}rm Nsb2O{dollar} flux were monitored in the field during two springs and one summer, followed by two laboratory experiments. Cylinders were placed in the field in the fall of 1988 and 57 kg N {dollar}rm hasp{lcub}-1{rcub}{dollar} of {dollar}rmsp{lcub}15{rcub}N{dollar} labeled {dollar}rm KNOsb3{dollar} added to the soil. Soil {dollar}rmsp{lcub}15{rcub}N{dollar} mass balance technique showed 23 kg N {dollar}rm hasp{lcub}-1{rcub}{dollar} of the added N had been lost by April 29, 1989. Daily gas trapping showed 3.5 kg {dollar}rm Nsb2O{dollar}-N {dollar}rm hasp{lcub}-1{rcub}{dollar} was emitted in April, mostly during an 11-day period of soil thaw. The {dollar}rm Nsb2O{dollar} flux was monitored throughout the growing season, but the April flux was greater than the accumulated flux in the summer. In 1990, {dollar}rmsp{lcub}15{rcub}N{dollar} labeled {dollar}rm KNOsb3{dollar} was applied at the outset of the thaw at a rate of 100 kg N {dollar}rm hasp{lcub}-1{rcub}.{dollar} The {dollar}rmsp{lcub}15{rcub}N{dollar} mass balance technique showed 32.7 kg N {dollar}rm hasp{lcub}-1{rcub}{dollar} was lost by May while there was a flux of 16.3 kg {dollar}rm Nsb2O{dollar}-N {dollar}rm hasp{lcub}-1{rcub}{dollar} from added-N during a 10-day thawing period in April.; The first laboratory experiment included three soils. Treatments were N-added {dollar}(rmsp{lcub}15{rcub}N{dollar}-{dollar}rm KNOsb3{dollar} at 80 kg {dollar}rm hasp{lcub}-1{rcub}),{dollar} gamma irradiation, and frozen and non-frozen soil. The incubation was carried out for 88 h with gas sampling every 8 h to analyze for {dollar}rm Nsb2O{dollar} and {dollar}rm COsb2.{dollar} Denitrification occurred during the thawing of frozen soils with 14 to 23% of added {dollar}rmsp{lcub}15{rcub}N{dollar} denitrified. {dollar}rm Nsb2O{dollar}-N constituted less than 3% of the total gaseous N produced. Denitrification and {dollar}rm Nsb2O{dollar} flux from irradiated soils were not different from non-irradiated soils, suggesting the activity of radiation-resistant enzymes or the loss of sterility. Little difference was found between the denitrification rates of non-frozen and frozen soils, suggesting that freezing neither enhances nor inhibits denitrification at cool temperatures.; In a second laboratory experiment, denitrification and {dollar}rm Nsb2O{dollar} flux were measured during thaw of frozen, manure amended soil samples. During a 66 h thaw period, treatments with manure emitted 0.97 kg {dollar}rm Nsb2O{dollar}-N {dollar}rm hasp{lcub}-1{rcub}{dollar} and non-manure treatments emitted 0.25 kg {dollar}rm Nsb2O{dollar}-N {dollar}rm hasp{lcub}-1{rcub}.{dollar} Soil {dollar}rmsp{lcub}15{rcub}N{dollar} mass balance indicated that 39% of added {dollar}rm KNOsb3{dollar}-N (80 kg {dollar}rm hasp{lcub}-1{rcub}){dollar} was denitrified in manure treated soil and 20% was lost from the non-manure treatments. The addition of manure significantly increased denitrification of added {dollar}rm NOsb3sp-{dollar} but appeared to decrease the proportion of {dollar}rm Nsb2O{dollar} emitted from the thawing soil.; In all, this work indicates that denitrification and {dollar}rm Nsb2O{dollar} emission occur during the soil thaw in north central Alberta.