紫云英持续回田后亚热带水田土壤可溶性有机氮迁移特征及其生态风险

Soil soluble organic nitrogen (SON) is main component of N cycling in terrestrial ecosystems, and its behavior process and environmental effect in ecosystems have been greatly concerned in the world. However, people are not aware of leaching characteristics and ecological risk of soil SON components in cropland after Chinese milk vetch application successively. Taking subtropical paddy soils with different fertility level as research objects, the dynamics, rate, model, main impact factors and mechanism of SON and its components leaching in the subtropical paddy soils with various fertility level after different quantities of Chinese milk vetch application successively were studied by continuous field plot experiments combined with analysis technologies of TOC, CFI, NMR, FTIR and AAA, the relationships between soluble N concerntrations and compositons in both surface and percolating water and SON leaching characteristics in the subtropical paddy soils after different quantities of Chinese milk vetch application continuously were discussed, and SON leaching ecological risk and its dynamics in the subtropical paddy soils applied continuously with different amounts of Chinese milk vetch were estimated. The results will provide theoretical basis to better understand the environment risk of SON leaching, control N non-point pollution of farmland and promote the rational implementation of applying green manure and reducing application of chemical fertilizer in subtropical ecosystem of paddy soil.

土壤可溶性有机氮（SON）是陆地生态系统氮素循环的主要成分，其行为过程和环境效应已为国内外所关注，但至今人们对紫云英回田后水田土壤SON成分迁移特征及其生态风险却知之甚少。本研究以亚热带不同肥力水平水稻土为对象，采用野外定位试验方法，利用总有机碳分析（TOC）、连续流动注射(CFI)、核磁共振（NMR）、傅里叶变换红外光谱（FTIR）和氨基酸自动分析（AAA）等技术，深入研究亚热带不同肥力水平水稻土持续施用不同数量紫云英后SON及其成分的迁移特征（动态、速率和模型等）与主控因素，揭示SON及其成分迁移机理；探讨亚热带水稻土持续施用不同数量紫云英后表层水和渗漏水中可溶性氮数量及其组成与SON迁移特征的关系；评估紫云英持续回田后亚热带水稻土SON迁移的生态风险及其动态，为深入揭示亚热带水田生态系统土壤SON迁移的生态风险、防控农田氮素面源污染、促进绿肥还田及化肥减施计划的合理实施提供科学依据。

本研究以亚热带三种不同肥力水平水稻土为研究对象，采用野外定位试验方法，深入研究水稻土持续施用不同数量紫云英后可溶性有机氮（SON）及其成分的动态、迁移特征及其生态风险。结果表明：（1）持续翻压紫云英可不同程度提高供试水稻土耕层土壤SON含量，其动态变化主要受土壤初始有机质、微生物量、谷酰胺酶、蛋白酶和pH的影响；（2）紫云英翻压后5-10天供试水稻土SON和DON含量达峰值，水稻移栽期耕层土壤SON变化速率最高，主要受耕层土壤细菌群落多样性和丰富度的影响；（3）紫云英翻压处理较单施化肥处理能够丰富耕层土壤游离氨基酸氮（FAA-N)种类并增加各氨基酸组分的含量，显著提高水田耕层土壤蛋白质氮含量、水稻生育中后期耕层土壤酰胺氮(A-N)含量以及耕层土壤大分子量SON含量；（4）翻压紫云英可以促进SON向下部土层迁移，其中对FAA-N和A-N向下迁移的促进作用较为显著，易迁移的成分主要包括丝氨酸、甘氨酸、脯氨酸等氨基酸和小分子酰胺类物质；（5）土壤溶解性有机氮（DON）具有向下迁移积累趋势，随紫云英的分解和水稻生长发育，DON向下迁移的深度和数量逐渐增加；（6）DON是稻田土壤氮素损失的重要形态之一，供试土壤DON最高可占土壤溶解性总氮的79%，DON的淋失量可达9.44-18.18 kg N ha-1 茬-1，意味着氮肥施用量的4.14%-7.97%可能通过土壤DON淋失，较施用等氮量尿素而言，施用紫云英能够降低供试稻田DON的损失；（7）紫云英配施化肥可以显著提高土壤中的DOC含量，高肥力的灰泥田中DOC淋溶损失风险最大，而DON则在低肥力的黄泥田中淋溶损失风险最大。供试水稻土20~60 cm层次中DON淋失总量早于DOC达到峰值。总之，本研究结果发现紫云英翻压后7-10内要特别注意田间水分管理，以防止DOC、DON因农田排水流失而导致面源污染；翻压紫云英并不会增加黏质水稻土SON、DON的损失，但砂质水稻土持续翻压紫云英后SON、DON的迁移特征是否相同有待于进一步研究。