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首页> 外文期刊>Plant and Soil >Changes in the soil organic N fractions of a tropical Alfisol fertilized with 15N-urea and cropped to maize or pasture.
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Changes in the soil organic N fractions of a tropical Alfisol fertilized with 15N-urea and cropped to maize or pasture.

机译：施以15N尿素并种植到玉米或牧场的热带金属铝土的土壤有机氮组分的变化。

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Qualitative and quantitative changes in soil and fertilizer-derived organic N fractions were assessed during one growing season in an intertropical Alfisol at Barinas, Venezuela, under maize cv. PB8 or Digitaria decumbens pasture, fertilized with 15N-urea. Before sowing, after fertilizer application and after harvesting, the organic N of top soil samples was fractionated by a two-step acid hydrolysis under reflux (H1 = 1 M HCl for 3 h; H2 = 3 M HCl for 3 h). The total hydrolysable N (HN) from H1 decreased significantly during the growing season in both maize and pasture soils. In contrast, the content of HN from H2 and that of non-hydrolysable N did not vary significantly during the growing season. The easily hydrolysable fractions, especially amino acid N, amino sugar N and amide N, were the most active N pools and the major source of N potentially available for plants. The urea-derived N that remained in the soil was mainly in organic forms at both 7 and 108 days after fertilizer application (70-82% and 93-98%, respectively), higher figures being found in pasture than in maize soil. The total amount of urea-derived HN decreased significantly during the growing season in both maize and pasture soils. This decrease was largely due to the declinein HN from H1. The amount of non-hydrolysable urea-derived N was significantly higher in pasture than in maize soil and it decreased in the former and increased in the latter during the growing season. During the growing season, the decrease of urea-derived organic N was 4.6 to 9.1 times higher than that of native organic N. Shortly after fertilizer application, the proportion of urea-derived N in the easily hydrolysable (H1) organic fractions was higher than that of soil N, whereas the reverse was true for the slowly hydrolysable (H2) or insoluble fractions. These differences were less marked, but still significant, at the end of the growing season. The easily hydrolysable organic N fractions were more sensitive than total N to the impact of land useintensification and are, therefore, a more useful index for early detection of soil biological degradation.
机译：在委内瑞拉巴里纳斯市的一个热带玉米下，在一个生长季节内，评估了土壤和肥料衍生的有机氮组分的质和量变化。用15N尿素施肥的PB8或Digitaria decumbens牧场。播种前，施肥后和收获后，通过回流两步酸水解（H1 = 1 M HCl 3 h; H2 = 3 M HCl 3 h）对表层土壤样品的有机氮进行分馏。在生长季节，玉米和牧草土壤中H1的总可水解氮（HN）均显着下降。相反，在生长季节，来自H2的HN含量和不可水解N的含量变化不大。易于水解的馏分，尤其是氨基酸N，氨基糖N和酰胺N，是最活跃的N库，也是植物潜在的主要N来源。施肥后第7天和第108天，残留在土壤中的尿素来源的氮主要以有机形式存在（分别为70-82％和93-98％），在牧场中发现的数字高于玉米土壤。玉米和牧草土壤中，尿素衍生的HN总量在生长季节明显减少。该下降主要是由于HN比H1下降。牧草中非水解性尿素来源的氮含量明显高于玉米土壤，在生长季节中，前者减少，而后者增加。在生长季节，源自尿素的有机氮的减少量比天然有机氮的减少量高4.6至9.1倍。施肥后不久，易于水解的（H1）有机馏分中源自尿素的氮的比例高于土壤氮的含量则相反，而慢速水解（H2）或不溶性组分则相反。在生长季节结束时，这些差异没有那么明显，但仍然很明显。易水解的有机氮组分对土地利用集约化的影响比总氮敏感，因此，它是早期检测土壤生物降解的更有用的指标。

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