摘要
The contents, affecting factors, seasonal changes and availability of fixed ammonium in major types ofpaddy soils derived from different parent materials in Hunan Province, China, were studied using the Silva-Bremner method by laboratory and pot experiments. Results showed that the content of fixed ammoniumin the plough horizons ranged from 88.3 mg kg-1 to 388.1 mg kg-1, with 273.2 ± 77.7 mg kg-1 on average,accounting for 11.2% of total soil N on average. Content of fixed ammonium decreased in the order of newlylacustrine clayey paddy soil ＞ alluvial sandy paddy soil ＞ purple clayey paddy soil ＞ newly alluvial sandypaddy soil ＞ yellow clayey paddy soil ＞ reddish-yellow clayey paddy soil ＞ granitic sandy paddy soil. Therewere four distribution patterns of fixed ammonium in the profiles to 1-m depth, i.e., increase with the depth,decrease with increasing depth, no distinct change with the depth, and abrupt increase or decrease in somehorizon. Percentage of fixed ammonium in total N increased with the depth in most of the soils. Fixationof NH4+ by soil was higher at 30 ℃ than at 20 ℃ and 40 ℃, and continuous submergence benefited thefixation of NH4+ in newly alluvial sandy paddy soil, purple clayey paddy soil and alluvial sandy paddy soil,while alternating wetting and drying contributed to the fixation of NH4+ in yellow clayey paddy soil mostly.Fixed ammonium content in the test paddy soils was significantly correlated with ＜ 0.01 mm clay content(P ＜ 0.05), but not with ＜ 0.001 mm clay content, total N, organic N and organic matter. Fixed ammoniumcontent varied with rice growth stages. Application of N fertilizer promoted fixation of NH4+ by soil, and Nuptake by rice plant promoted release of fixed ammonium from the soil. Recently fixed ammonium in paddysoil after N fertilizer application was nearly 100% available to rice plant, while native fixed ammonium wasonly partly available, varying with the soil type and rice type.
The contents, affecting factors, seasonal changes and availability of fixedammonium in major types of paddy soils derived from different parent materials in Hunan Province,China, were studied using the Silva-Bremner method by laboratory and pot experiments. Results showedthat the content of fixed ammonium in the plough horizons ranged from 88.3 mg kg^(-1) to 388.1 mgkg^(-1), with 273.2 +- 77.7 mg kg^(-1) on average, accounting for 11.2% of total soil N on average.Content of fixed ammonium decreased in the order of newly lacustrine clayey paddy soil > alluvialsandy paddy soil > purple clayey paddy soil > newly alluvial sandy paddy soil > yellow clayey paddysoil > reddish-yellow clayey paddy soil > granitic sandy paddy soil. There were four distributionpatterns of fixed ammonium in the profiles to 1-m depth, i.e., increase with the depth, decreasewith increasing depth, no distinct change with the depth, and abrupt increase or decrease in somehorizon. Percentage of fixed ammonium in total N increased with the depth in most of the soils.Fixation of NH_4^+ by soil was higher at 30℃ than at 20℃ and 40℃, and continuous submergencebenefited the fixation of NH_4^+ in newly alluvial sandy paddy soil, purple clayey paddy soil andalluvial sandy paddy soil, while alternating wetting and drying contributed to the fixation ofNH_4^+ in yellow clayey paddy soil mostly. Fixed ammonium content in the test paddy soils wassignificantly correlated with < 0.01 mm clay content (P < 0.05), but not with < 0.001 mm claycontent, total N, organic N and organic matter. Fixed ammonium content varied with rice growthstages. Application of N fertilizer promoted fixation of NH_4^+ by soil, and N uptake by rice plantpromoted release of fixed ammonium from the soil. Recently fixed ammonium in paddy soil after Nfertilizer application was nearly 100% available to rice plant, while native fixed ammonium was onlypartly available, varying with the soil type and rice type.
基金
Froject supported by the Scientific Research Foundation of Hunan Province(No.20012-2000C168).
