Leaching of nitrate causes several serious environment problems. It is better to understand the
nitrification process in different soil types, so that it could be managed, especially in proper fertilization way to reduce nitrate leaching. Nitrification research has not been paid more attention to this area. Purpose of this paper is to study nitrification in three types of managed soils from three ecological regions of Shaanxi Province, China. They were Loess soils from north,
Cumulic cinnamon soils from middle and paddy soils from south of the province, the soil pH was 8 18, 8 22 and 6 52, and the physical clay contents were 23 10 % , 40 00 %, and 55 12 %, respectively. The changes of NO 3 N accumulation with time were determined during the process of nitrification under various moisture, temperature regimes and four nitrogen fertilizers in the laboratory incubation. The equation, d N /d t = bN(B-N) , was used to express the accumulation of nitrate (NO - 3) with time.
The maximal rate of nitrification ( K max ) and the
delay period ( t d ) were derived from the equation and used to characterize quantitatively the nitrification process in different soil conditions.
Soil moisture content obviously affected the nitrification. Particularly significant differences existed among the maximal rates of three soils at the same water content; but the delay period had no remarkable differences. While soil moisture content maintained 40 % of field holding capacity ( FHC ), K max of loess soils, cumulic cinnamon soils and paddy soils were 11 4, 4 72 and 2 61 mg/kg -1 ·d -1 , respectively. At 60 % of FHC , K max were 15 12, 14 04 and 8 55, and K max were 14 10, 10 12 and 3 77 mgkg -1 d -1 at 80% of FHC , respectively. K max of cumulic cinnamon soils and paddy soils changed significantly with soil moisture, but not loess soils. This is related to clay content of soils. Comparison 80 % to 40 % of FHC , the latter largely reduced nitrification of loess soils and cumulic cinnamon soils, but not on paddy soil. 60 % of FHC was proper for carrying on nitrification. Nitrification was fairly sensitive to soil temperature, K max and t d changed largely under low or high soil temperature. When soil temperature was 20 ℃ and 30 ℃, K max and t d were 6 98, 15 12 mgkg -1 d -1 and 2 9, 1 46 d for loess soils, 11 28, 14 04 mgkg -1 d -1 and 6 4, 1 44 d for cumulic cinnamon soils, 3 84, 8 55 mgkg -1 d -1 and 4 46, 3 45 d for paddy soils, respectively. Temperature of 20 ℃ not only decreased K max but also prolonged t d, and 40 ℃ seriously restrained nitrification in all soil samples. Nitrifying bacteria are more response to soil temperature than to soil moisture. 30℃ was suitable for conducting nitrification under experimental soil samples. It was no any certain regulation that different nitrogen fertilizers influenced on K max and t d in all soil samples. After adding
ammonium sulfate, ammonium chloride, ammonium bicarbonate and urea, K max and t d were 15 12, 15 39, 16 28, 18 00 mgkg -1 d -1 and 1 46, 1 63, 1 41, 1 56 d for loess soils, 14 04, 12 58, 14 40, 9 68 mgkg -1 d -1 and 1 44, 3 05, 3 32, 2 70 d for cumulic cinnamon soils, 8 55, 4 61, 4 39, 5 36 mgkg -1 d -1 and 3 45, 3 44, 2 19, 2 54 d for paddy soils, respectively. On loess soils urea had the highest K max , ammonium bicarbonate on cumulic cinnamon soils and ammonium sulfate on paddy soils. t d had no big difference in each soil sample. However, the maximal NO - 3N accumulation rate of these fertilizers in three soil samples was in a descending order of ammonium sulfate > urea > ammonium bicarbonate > ammonium chloride. The effects on nitrification for the different
n fertilizers depended on their anion containing, SO
More abstracts about the Effect of Soil Moisture,Temperature and Different Nitrogen Fertilizers on Nitrification