應用穩定同位素技術研析氮營養鹽於韭菜田中的分佈與遷移途徑

Abstract

氮素作為植物生長不可或缺的營養元素，其在農業生產中廣泛施用。然而，隨著全球糧食需求上升與化學肥料與有機肥料大量使用，氮營養鹽於農業系統中的動態與宿命日益受到關注。過量施肥造成氮素利用效率低，進而導致地表水與地下水污染、溫室氣體排放及生態失衡，對環境與人類健康皆構成潛在威脅。儘管如此，氮素在農田中經由作物吸收、土壤吸附轉化、水體流失與氣體逸散等複雜過程，迄今仍缺乏一套系統性和可量化的分析工具以整體評估農業系統中氮的移動和累積。 本研究旨在應用穩定同位素追蹤技術（15N）和營養鹽質量平衡模式，深入解析不同施肥策略下氮素於農業系統中土壤-水體-作物-氣體介面間的流布與累積行為。田間試驗在地點選於臺灣桃園市大溪區一處面積600平方公尺的露天韭菜（Allium tuberosum）農田，進行系統性田間試驗。種植韭菜的常規施肥做法遵循臺灣良好農業規範(TGAP)中的建議，試驗設計涵蓋四類肥料（化學肥料（CF）、有機肥料（OF）、緩效性肥料（SF）與雞糞粒肥(CM)）與三種施用量（過量施肥150%、全量施肥100%、半量施肥50%），並探討生物炭添加對氮素流布之調節效果。 研究結果顯示，作物吸收為氮素主要去向，約佔總施肥量之50 ~ 60%，其中以施用緩效性肥料與雞糞粒肥結合生物炭的組別表現最佳。在氮素損失方面，施用化學肥料組別之氮流失量最高，其後依序為施用有機肥組別、施用雞糞粒肥組別與施用緩效性肥料組別。氮素流失形式以地表逕流與垂直入滲為主，而緩效性肥料與有機肥料組別具顯著減緩氮素向水體遷移，提升氮肥利用效率。氣體通量分析結果亦指出，相較於施用化學肥料，施用有機與雞糞粒肥的組別，其N2O與NH3排放量較低，具有潛在減碳效益。 穩定同位素δ15N值分析進一步驗證氮源辨識與累積特性，雞糞粒肥處理組別於作物、土壤與水體中δ15N值（平均約10.3‰）明顯高於化學肥料組別（約4.6‰）與有機肥（約7.2‰），展現15N追蹤技術於肥料來源鑑別與氮素累積判釋之高效性。透過營養鹽質量收支平衡模式，本研究定量評估氮素流向比例，結果顯示緩效性肥料超過65%的氮被有效保留於作物與土壤中，而化學肥料則有近40%的氮以水體與氣體形式逸失。生物炭施用則有助於減少土壤中總氮流失。 本研究應用多層次農業氮素動態分析方法，整合15N穩定同位素示蹤、氮源辨識、流布量化與損失評估之成果，未來可作為農業施肥管理、水質保育與農業碳足跡核算之科學工具。研究成果對精準施肥策略的制定、農田氮素利用效率提升、環境污染降低與永續農業發展具高度參考價值，並有助於推動臺灣農業邁向科學化管理與環境友善之目標。

Nitrogen is an essential nutrient for plant growth and is widely applied in agricultural production. However, with the rising global demand for food and the extensive use of chemical and organic fertilizers, increasing attention has been paid to the dynamics and fate of nitrogen nutrients within agricultural systems. Excessive fertilization leads to low nitrogen use efficiency, resulting in surface and groundwater pollution, greenhouse gas emissions, and ecological imbalances, all posing potential threats to the environment and human health. Despite this, the complex processes involving crop uptake, transformation and adsorption in soil, loss through water pathways, and gaseous emissions still lack a systematic and quantifiable analytical framework to assess nitrogen mobility and accumulation in agricultural systems comprehensively. This study aimed to apply stable isotope tracing technology (15N) and nutrient mass balance modeling to investigate nitrogen distribution and accumulation behavior at the soil–water–crop–gas interface under different fertilization strategies. Field experiments were conducted in an open leek (Allium tuberosum) field covering 600 square meters in Daxi District, Taoyuan City, Taiwan. The fertilization practices followed the guidelines of the Taiwan Good Agricultural Practice (TGAP). The experimental framework was designed to include four distinct fertilizer types of chemical fertilizer (CF), organic fertilizer (OF), slow-release fertilizer (SF), and pelletized chicken manure (CM). Each fertilizer was applied at three different rates of 150% (excessive), 100% (recommended), and 50% (reduced) to assess dosage effects. Additionally, the study systematically investigated the regulatory role of biochar amendment in influencing nitrogen dynamics, including its distribution, transformation, and retention within the soil–plant–water continuum. The results indicated that crop uptake was the primary nitrogen sink, accounting for approximately 50 ~ 60% of the total nitrogen applied, with the best performance observed in treatments combining slow-release fertilizer or chicken manure with biochar. Regarding nitrogen losses, the chemical fertilizer treatments showed the highest loss rates, followed by organic fertilizer, chicken manure, and slow-release fertilizer treatments. Nitrogen losses occurred mainly via surface runoff and vertical leaching. Using slow-release and organic fertilizers significantly reduced nitrogen transport to water bodies and improved nitrogen use efficiency. Gas flux analysis revealed that treatments using organic and chicken manure fertilizers emitted less N2O and NH3 compared to chemical fertilizers, indicating potential benefits for carbon reduction. The δ15N stable isotope analysis further confirmed nitrogen source identification and accumulation characteristics. The δ15N values in crops, soil, and water for the chicken manure treatments averaged around 10.3‰, significantly higher than those for chemical fertilizers (4.6‰) and organic fertilizers (7.2‰), demonstrating the effectiveness of 15N tracing in fertilizer source identification and nitrogen accumulation interpretation. This study quantitatively assessed nitrogen flow proportions using a nutrient mass balance model. Results showed that over 65% of nitrogen from slow-release fertilizers was effectively retained in crops and soil. In comparison, nearly 40% of nitrogen from chemical fertilizers was lost via water and gas pathways. Biochar application was found to reduce total nitrogen losses from soil. This study presents a multilayered approach to analyzing agricultural nitrogen dynamics by integrating 15N stable isotope tracing, nitrogen source identification, distribution quantification, and loss evaluation. The findings provide a scientific basis for guiding fertilizer management, protecting water quality, and calculating the agricultural carbon footprint. The results offer high reference value for developing precision fertilization strategies, improving nitrogen use efficiency, mitigating environmental pollution, and promoting sustainable agriculture, supporting the advancement of Taiwan's agricultural practices toward scientific management and ecological sustainability.