土壤微生物体氮测定方法的研究

STUDY ON THE METHODS FOR MEASURING MICROBIAL BIOMASS NITROGEN IN SOILS

用熏蒸 0 5mol/LK2 SO4 直接浸取NH+ 4 N法 (简称薰蒸 铵态氮法 ) ,熏蒸 淹水培养法和熏蒸 通气培养法测定了有机质、全氮和C/N比差异较大的 15种土壤的铵态氮增量 (FN)。结果表明 ,它们之间有极显著的正相关 ,在反映土壤微生物体氮上有相同趋势。两种培养方法测定的FN 近乎一致 ,由此而计算的微生物体氮也几乎相同。对红油土铵态氮法测定值仅为两种培养法的 1/ 10。把铵态氮法中的FN 校正后 ,其结果与 2种培养法测定的微生物体氮同样近乎一致。用 3种方法测定的微生物体氮均与土壤有机碳存在显著正相关性。淹水培养和铵态氮法水分条件易控制 ,又无NH3的挥发损失 ,比通气培养法更加优越。对培养试验和长期肥料定位试验的土样测定结果表明 ,土壤中易矿化新鲜有机物料也会使熏蒸 淹水培养法测定的FN 显著下降 ,由此而计算的微生物体氮也显著减少 ,但熏蒸 铵态氮法测定的FN 不受新鲜有机物质的影响。与土壤微生物数目进行比较后发现 ,土壤中含易分解有机物质少或微生物体氮含量低时 ,选用熏蒸 淹水培养法测定误差小 ;当土壤中富含新鲜有机物质时 ,熏蒸 铵态氮法测定的结果更加可靠。用这两种方法在同类土壤上测定的FN 的比值相对稳定 ,微生物体氮 (BN)的平均比值为 0 98～ 1 0 1。

Fumigaton-0.5mol/L K 2SO 4 extracting NH + 4?N directly (named briefly as NH + 4?N method), fumigation?waterlogged incubation and fumigation?aerobic incubation methods were used to measure the NH + 4?N flush( F N ) in 15 soils with a wide range of the organic matter, total nitrogen and C/N ratio. Results showed that there existed significant positive correlation and similar tendency in reflecting soil microbial biomass nitrogen among three methods. The nitrogen flush( F N ) measured by 2 incubation methods was almost the same, and microbial biomass nitrogen calculated from their F N was also the same. To the manual loessial soils, the nitrogen flush measured by NH + 4?N method was only one?tenth of that of 2 incubation methods. NH + 4?N methods was almost equal to these measured by 2 incubation methods. The significant positive correlation existed between the soil microbial biomass nitrogen measured by three methods and soil organic carbon. The moisture condition was easily controlled and there was no ammonia volatilization loss in waterlogged incubatuon, and NH + 4?N method had such advatages as simple and rapid, so both of the two methods were superior to the aerobic incubation method. Incubation experiment and results obtained by analysising soils collected from long?term experiments showed that nitrogen flush( F N ) and microbial biomass nitrogen calculated from F N obtained from waterlogged incubatin decreased significantly when easily decomposable organic material being contained in the soil. However, the F N measured with NH + 4?N method was not affected by easily decomposable organic material. By comparing with microorganism numbers, the results indicated that the waterlogged incubation method was more suitable for soils with little easily decomposable organic material or with small microbial biomass nitrogen amount as the measurement error was smaller and the results were more reliable; vice versa, the NH + 4?N method was more reliable for soils with rich easily decomposable organic material. The ratios of nitrogen flush in the same soils determined by the two methods is relatively stable and the ratios of microbial biomass nitrogen measured by two methods was 0 98～1 01, and the average ratio was 1 0, and was not affected by fertilization.