利用根箱法解析水稻根际土壤中氮的行为

为研究水田土壤中氮的行为,施给15NH4 或15NO3-标记的硝胺(NH415NO3或15NH4NO3)的沙壤土(Shirasu soil)添充在根箱里,对Japonica水稻(品种Hinohikari)进行温室栽培6周.收割后,水稻植株分地上部和根部,对各自的全氮,15N atom％进行测定.根箱各区域的土壤按着鲜土形态进行采取后,对此全氮,NO3-N,水溶性NH4-N,KCl抽出NH4-N和其各自的15N atom％进行测定.研究结果表明,土壤全氮含量与栽培前相比,在非根际明显降低,但在根际比非根际要高,保持了与栽培前相同的水平.土壤NO3-N浓度从非根际到根际递增,但与其栽培前相比显著地降低,在整个根箱里,施给NO3-N的79％为因脱氮而损失.土壤中NO3-N的大部分来自于土壤氮化合物,来自施肥的比例却较低,尤其是在根际.反而,施给NO3-N的残存率约仅为16％左右,但其中有机态氮所占的比率在非根际里55％～86％,在根际却达到了93％.土壤水溶性NH4-N和KCl抽出NH4-N浓度靠近根际逐渐降低,而且在非根际两者匀由1∶10的比例存在,但在根际里水溶性NH4-N没被检索到.在非根际里,土壤KCl抽出NH4-N的35％～66％为来自施肥,但其比例在根际里却降到15％左右.在土壤中残存的来自施给NH4-N的氮化合物之中,有机态氮所占的比例在非根际里约为11％～65％,但在根际却达到了92％.以上结果表明,在水稻根际,氮的无机化和有机化的活性比非根际显著.

The Behavior of Nitrogen in the Rhizosphere of Rice Plant Using the Rhizobox System

Behavior of N in the rhizosphere of rice (Oryza sativa L.) plant was investigated using a rhizobox system filled with a shirasu soil applied with NH415NO3 or 15NH4NO3. The rhizobox consisted of one 2-mm width center compartment(CC), five 1-mm width compartments, and one bulk compartment(BC) on both sides of CC．Rice was sowed and grown in CC. After 6th weeks after clutivation,the soil from each compartment were collected and analyzed for contents and 15N excess％ of the soil total-N,water-soluble NO3-N,NH4-N and KCl-extractable NH4-N. The obtained results were summarized as follows: 1) The total-N content of soil decreased in all the compartments except CC compared with that before cultivation,but that of CC did not change. 2) The water-soluble NO3-N content of soil decreased remarkably in all the compartments compared with that before cultivation,and about 79% of applied NO3-N was lost from soil due to denitrification. The NO3-N content of soil slightly increased from BC toward CC. The most of NO3-N were derived from the soil N especially in the CC. 3) The contents of water-soluble NH4-N and KCl-extractable NH4-N decreased from BC toward CC and the ratio of water-soluble NH4-N to KCl-extractable NH4-N are 1:10 in all the compartments except CC which water-soluble NH4-N was not detected. 4) Mineralization of soil-N and immobilizaition of fertilizer-N were more actively at CC than in the other compartments.