摘要:土壤盐分胁迫下有机氮组成及氮有效性对黄河三角洲盐渍土壤肥力的形成和生产力的提高具有重要作用。本研究采集黄河三角洲盐渍土壤区小麦-玉米轮作的3种盐渍土壤，分别为轻度盐渍土（含盐量2.28 g·kg-1，S1）、中度盐渍土（含盐量3.73 g·kg-1，S2）和重度盐渍土（含盐量6.69 g·kg-1，S3），分析不同盐分含量土壤的作物产量和土壤有机氮组分含量、无机氮含量、微生物生物量氮含量及相关酶活性等指标的变异特征，明确盐分含量对土壤有机氮组成及氮有效性的影响。结果表明：3种土壤中有机氮的酸解总氮含量是有机氮的主要组分，S1、S2和S3处理下分别占土壤总有机氮68.79%、61.60%和52.30%；不同处理下各形态含量酸解总氮为酸解铵态氮>酸解未知氮>酸解氨基酸氮>酸解氨基糖氮，且各形态含量均以S1处理显著高于S2和S3处理（P < 0.05）。非酸解氮含量在3种处理间差异不显著，且均低于酸解总氮含量，其占全氮比例随土壤含盐量增加而提高。S1处理土壤硝态氮含量（22.08 mg·kg-1）和微生物生物量氮含量（20.71 mg·kg-1）最高，显著高于其他两种处理的土壤（P < 0.05）；铵态氮含量在各处理下差异不显著。S1处理的小麦、玉米总产量分别是S2和S3的1.74倍和5.85倍。回归分析发现土壤可溶性全盐含量分别与土壤无机氮、微生物生物量氮含量呈显著的负指数关系，与小麦、玉米总产量、氨基酸态氮含量之间存在显著的负线性关系。土壤无机氮含量与土壤酸解总氮含量之间呈显著的正指数关系。土壤中较高含量的可溶性全盐抑制土壤酸解有机氮的形成及氮素有效性的提高。
关键词:盐渍土壤/
小麦-玉米轮作/
土壤无机氮/
土壤有机氮/
土壤微生物生物量氮/
土壤可溶性全盐
Abstract:The soil organic nitrogen composition and nitrogen availability play important roles in the soil fertility and agricultural production of saline soils. This study investigated the effects of soil salinity on soil organic nitrogen fractionation and nitrogen availability in saline soils of the Yellow River Delta (YRD). Soil samples were taken from three wheat-maize rotation fields with low (2.28 g·kg-1, S1), moderate (3.73 g·kg-1, S2), and high (6.69 g·kg-1, S3) salinities on the Huibang Bohai Farm in the YRD. The crop yields were recorded, and the soil organic nitrogen fractions, including ammonia nitrogen (AN), amino acid nitrogen (AAN), amino sugar nitrogen (ASN), hydrolyzable unknown nitrogen (HUN), non-hydrolyzable nitrogen (NHN), soil inorganic nitrogen, and microbial biomass nitrogen were quantified. The activities of the nitrogen transformation-related enzymes (i.e., urease, protease, and nitrate reductase) were determined, and the relationships between the soil organic nitrogen fractions, inorganic nitrogen, crop yield, and soil salinity were analyzed. The results showed that total acid hydrolyzable nitrogen (TAHN), which is the sum of AN, AAN, ASN, and HUN, was the main fractions of soil organic nitrogen, taking up 68.79%, 61.60%, and 52.30% of the total organic nitrogen in S1, S2, and S3 soils, respectively. The contents of the four TAHN fractions (AN, AAN, ASN, and HUN) were all significantly higher in S1 than in S2 and S3 (P < 0.05), and the contents of AN, AAN, and HUN were all significantly higher in S2 than in S3 (P < 0.05). The contents of these fractions were AN > HUN > AAN > ASN in S1, and AN > AAN > HUN > ASN in S2 and S3. Conversely, the NHN content was in the order of S1 > S2 > S3, but the differences were not significant (P>0.05). For the same soil, the NHN content was lower than the TAHN content. The highest soil nitrate nitrogen content (22.08 mg·kg-1) and microbial biomass nitrogen (20.71 mg·kg-1) were found in S1, which was significantly higher than those in S2 and S3 (P < 0.05). The ammonium nitrogen content did not differ among the three soils. The activities of urease and nitrate reductase were in the order of S1 > S2 > S3, and the differences were significant (P < 0.05). Protease activity was significantly higher in S1 than in S2 and S3 (P < 0.05). The total yield of wheat and maize in S1 was 1.74 times of that in S2 and 5.85 times of that in S3. Correlation analyses showed that the inorganic nitrogen, microbial biomass nitrogen, AN, and HUN contents had negative exponential relationships with the soil total soluble salt content, whereas the total yield of wheat and maize and the AAN content had significant negative linear relationships with the soil total soluble salt content. The soil inorganic nitrogen content was significantly and positively correlated with the soil TAHN content. The high total soluble salt content in the soils inhibited the formation of acid hydrolyzable organic nitrogen and improved the soil nitrogen availability. These results provide theoretical support for the regulation of soil nitrogen availability in saline soils in the YRD.
Key words:Saline soil/
Wheat-maize rotation/
Soil inorganic nitrogen/
Soil organic nitrogen/
Soil microbial biomass nitrogen/
Total soluble salt in soil
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