| Nitrification was one of the most important steps in nitrogen cycling. Nitrification could provide nitrogen which was directly absorbed by plants and also generate N03--N which was apt to leach. And this would decrease the nitrogen use efficiency and cause under-water pollution. There were a lot of factors affecting nitrification, such as temperature, moisture and nitrogen addition. In this paper, we chose soils of three different land-use types(forest, arid land and paddy soil) in rainy area of west China as object and studied the effect of temperature and moisture, nitrogen addition and nitrogen deposition on soil nitrification by using laboratory incubation and outdoor cultivation methods. The main results were as follows:(1) Temperature and moisture significantly affected the soil nitrification. Without considering the influence of temperature, soil nitrification rate of three land-use types (forest, arid land and paddy soil) firstly increased and then decreased with the soil moisture increasing from 20%FWC to 80%FWC. The maximum value of nitrification rate was in 65.1%FWC(forest),62.8%FWC(arid land) and 71.8%FWC(paddy soil),respectively. Temperature had the same effect on nitrification with soil moisture. Soil nitrification rate of three land-use types (forest, arid land and paddy soil) firstly increased and then decreased with the soil temperature increasing from 5℃ to 35℃ and the maximum value of nitrification rate was in 25.7℃ (forest),26.3℃ (arid land) and 27.8℃ (paddy soil),respectively. Temperature and moisture had a significant interaction effect on soil nitrification. Soil nitrification rate of three land-use types were highest under 25℃ +60%FWC treatment which indicated soil rapid nitrification was happened under 25℃ +60%FWC treatment.25℃+60%FWC treatment was the optimal temperature and moisture combination for nitrification in this area.(2) Nitrogen addition showed a promotion effect on soil nitrification in all three land-use types, and with the increase of nitrogen concentrations, nitrification intensity increased. The one-way analysis of variance of nitrification rate under different nitrogen concentrations showed the increase of nitrogen concentration had a weak promotion effect on forest soil nitrification, while significantly promoted soil nitrification in arid land and paddy soil. With the increase of incubation time, nitrification rate of forest soil showed a tendency of decreasing, and in paddy soil it was firstly increased and then decreased, while in arid land, nitrification rate showed two kinds of change trend which were decreased with the increasing of incubation time(N0 and N5) and firstly increased and then decreased with the increasing of incubation(N10, N20 and N30). During all 30-days incubation, nitrification rate of forest soil was only significantly among first 7-days incubation(P< 0.05, n=15), and in paddy soil there were significant differences of nitrification rate in 1-day,21-day and 30-day incubation(P<0.05, n=15), while nitrification rate of arid land was significantly different in all incubation days(P<0.05, n=15). In all three land-use types, there were no significant differences among different nitrogen addition types.(3) In all three land-use types(forest, arid land and paddy soil), soil net accumulated nitrate-N firstly increased and then decreased with increase of the nitrogen deposition amount. Soil net accumulated nitrate-N in all three land-use types were highest in june indicating a rapid nitrification. With the increase of nitrogen deposition amount, soil nte accumulated nitrate- N decreased. In all three land-use types, soil net accumulated nitrate-N in different deposition concentration ranked as N30>N20>N10>N5>N0 when soil net accumulated nitrate-N>0, while the order was total different when soil net accumulated nitrate-N<0.(4) Land-use types significantly affect soil nitrification. The comparison of nitrification rate in three land-use types showed that arid land had the highest nitrification rate, and paddy soil took the second place, and forest soil had the lowest nitrification rate which indicated arid land had a rapid nitrification, and paddy soil took the second place, and forest soil had a weak nitrification. |
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