【作者】 杨绒；

【导师】 周建斌；

【作者基本信息】 西北农林科技大学 ， 植物营养学， 2006， 硕士

【摘要】 土壤中能够被水或盐溶液浸提出的有机氮素被称为可溶性有机氮（Soluble organic nitrogen,SON）。土壤中的SON既不同于无机氮亦不同于土壤中的不溶性氮素,它是土壤溶液中有机氮（Dissolved organic nitrogen,DON）的潜在来源。土壤溶液中的有机氮被认为是林地生态系统氮素流失的主要形态,并且微生物和植物均可以直接或间接吸收利用SON,因此,SON在林地生态系统氮素循环中具有重要作用。已有研究表明,土壤中SON和无机氮库的大小相近。长期以来,很多研究者把目光主要集中于对土壤中无机氮的研究,而在很大程度上忽视了土壤中SON这一组分的作用。本研究采用1 mol/L KCl浸提,过流酸钾氧化法测定了土壤中SON的含量。通过大田试验和室内培养试验研究了黄土区土壤中可溶性有机氮的含量及栽培模式、施肥、土壤类型、植被等因素对其含量的影响,获得以下主要结论:1.采用过硫酸钾氧化法测定溶液中全氮,不同厂家生产的过硫酸钾产品氧化后在220 nm和275 nm波长处的吸收峰存在极显著差异,空白矫正吸光值(A₂₂₀-2A₂₇₅)高达2.5左右,严重影响测定结果的准确性。采用蒸馏水和去离子水对测定结果无明显影响,均可满足实验要求。用高压锅（120～124℃）氧化30 min空白吸收值低,并可定量回收溶液中的尿素态氮和铵态氮,是较为适宜的氧化方式。采用0.15 mol/L NaOH和30 g/L过硫酸钾氧化剂配比,且样品和氧化剂的加入体积比为1:1时,可氧化尿素态氮的最大范围为20 mg/L。2.杨陵区农田和日光温室土壤中SON的含量平均分别为44.60 mg/kg和320.16 mg/kg,分别占可溶性总氮（ TSN ）的79%和73%,说明SON是土壤氮素中不可忽视的氮素组分。不同栽培模式对土壤中SON的含量及其占TSN的比例的影响因生育时期的不同而异。覆草显著增加了小麦拔节期0～5 cm土层土壤中SON的含量,覆膜各土层SON含量均较常规模式有所提高;开花期覆草和覆膜模式土壤中TSN和SON含量较拔节期的显著下降。施用无机氮肥对土壤中SON的含量无显著影响。相关分析结果表明,Nmin和SON之间无显著相关性。3.黄土区所采集3种类型土壤--黑垆土、红油土和淋溶褐土（分别采自永寿、杨凌和周至）中SON的平均含量分别为24.75、39.10和41.80 mg/kg,占可溶性总氮（ TSN ）的51.25%、68.28%和68.57%,分别为土壤全氮的2.54%、3.75%和4.00%;土壤游离氨基酸的含量分别为7.18、7.42和7.41mgN/kg,分别占SON的30.53%、19.23%和17.50%,占全氮的0.74%、0.71%和0.71%.方差分析结果表明,土壤类型对土壤SON含量及其在TSN中的比例、游离氨基酸在SON中所占的比例有显著影响,而对游离氨基酸的含量及更多还原

【Abstract】 The soluble organic nitrogen in soil （SON） is defined as the organic nitrogen in soil that could be extracted by water or other salt solutions. The behavior of SON in soil is different from that of mineral nitrogen and insoluble organic nitrogen. The SON is the potential source of dissolved organic nitrogen （DON）, and DON is considered as the main N forms losing from forest ecosystems. SON is also one of the labile forms of N available to microorganisms and plants. Therefore, SON plays a vital role in N cycling in forest ecosystems. Recently, researchers found that the content of SON in arable soils in England was as high as mineral N in the soils, and considered it as an important N pool in N cycles. However, more attention has often been focused on the behavior of mineral nitrogen in agricultural soils and overlooked the roles of SON in soil nitrogen cycles; and little is known about the content and characteristics of SON in the soils on the Loess Plateau in China.In this study, persulphate oxidation method was used to determine SON content in different soils. The incubation and field experiments were carried out to study the concentration of SON in soils on the Loess Plateau, and the effects of cultivating types, fertilizer, soil types, and vegetation on SON were also evaluated. The main results showed as follows:1. Effects of the potassium persulfate products from two different companies, oxidizing methods （boiled water and autoclave） and the types of pure water used in the experiment on the accuracy of total nitrogen in solution determined by persulfate oxidation method were studied. The results showed that there were significantly differences in absorbance （at 220 nm and 275 nm） after autoclaving between the different potassium persulfate products produced by different companies; the blank absorbance of a product was as high as 2.5, and had a significant effect on the determination of the method. The types of water, i.e., distilled water or deionized water, had no significant effects on the N recovery of urea. Autoclaving oxidation method （30 min at 120℃） was considered as the optimum oxidizing method, which had a lower blank absorbance, and the urea-nitrogen and ammonium-nitrogen could be recovered completely. When the volume ratio of oxidizing reagent （0.15 mol/LNaOH and 30 g/LK₂S₂O₈） to sample was 1:1, the maximum oxidation concentration of urea-nitrogen was更多还原