节水灌溉对宁夏干旱区枸杞园土壤活性有机碳库及碳排放的影响机制

As one of the most active parts in global terrestrial ecosystem C pool, agricultural carbon (C) pool is very sensitive to change in management measures. The water-saving irrigation is the trend of modernized agriculture and the important management measure of dry land farming. The transformation of irrigation patterns certainly will have a significant impact on the organic C pool and its atmospheric greenhouse effect, but the relative data and corresponding mechanism analysis are rarely known. Because of this, in this study, the typical economic forest (medlar-soil) system of Ningxia arid area was chosen for this field experiment. The drip and flooding irrigation method and different irrigation regimes were selected respectively to conduct the research on effects of different water management on soil organic carbon storage, labile organic carbon fractions and physical protection of aggregates; meanwhile, the static chamber method and the gas chromatography were employed to study the change features of soil greenhouse gas emission under different irrigation methods and some parameters, such as soil environment factors, microorganism, etc., were simultaneously monitored and measured under moisture regulation to reveal the internal relations between labile organic carbon fractions and carbon emissions; and based on the field monitoring, the DNDC model analysis was also employed to predict the short and long effects of different water management on soil carbon balance of medlar orchard. The research result can provide a scientific evidence for sustainable water management practices to ensure the soil productivity balance and improvement, efficient use of nutrient resources and C sequestration and mitigation in dry land regions.

农田碳库作为全球碳库最活跃的部分，对管理措施变化的响应十分敏感。节水灌溉是现代农业的发展趋势，也是旱地农业的重要管理措施。随着灌溉方式的转变势必会对土壤有机碳库及农田温室效应贡献产生重要影响，但相关机理研究迄今比较缺乏。本项目结合区域特色，以宁夏旱区典型经济林（枸杞—土壤）系统为研究对象，通过田间定位试验，设置不同灌溉方式(滴灌和漫灌)及灌溉制度，重点探究不同水分管理对土壤有机碳储量、活性有机碳组分特征及团聚体物理保护的影响机制，采用静态箱－气相色谱法定量研究不同灌溉方式下土壤温室气体排放通量的变化特征；结合水分调控下土壤环境因子、微生物等重要参数的同步监测与测定，揭示土壤活性有机碳组分变化与土壤碳排放的内在关系；基于田间定位监测，利用DNDC模型分析预测不同水分管理对枸杞园土壤碳平衡的短期和长期影响。研究结果将为寻求平衡稳产、高效、固碳减排综合效应的旱区水分可持续管理措施提供科学依据。

为探明宁夏旱区典型经济林（枸杞—土壤）种植体系节水灌溉方式对土壤有机碳（SOC）和碳排放特征的影响，综合评价其固碳减排、高效节水和可持续生产的协同效应，2018-2021年在宁夏银川市开展田间定位试验。试验采用裂区设计，主区设置了传统漫灌（对照，F）、节水滴灌（D）2种水分管理模式，副区分别设置了不同灌溉水平（D1、D2、D3）和（F1、F2、F3）。结果表明：（1）与F处理相比，D处理促进土壤剖面SOC增加，其中0-10 cm、10-20 cm土壤易氧化有机碳（POXC）含量分别显著提高了12.99%和18.67%。D处理土壤剖面碳库管理指数（CPMI）均高于漫灌处理，变化范围在105.60-141.55之间。（2）滴灌模式下随着灌水量的增加，SOC呈现显著下降趋势，浅层土壤下降趋势更明显，40-60 cm土层，D1土壤有机碳含量显著高于F1； 0-100 cm土层D1、D2、D3处理土壤POXC均显著高于F1、F2和F3。（3）枸杞生育期内，滴灌和漫灌均使土壤CO2和N2O排放速率在灌后第2~3天明显提高，其中F处理土壤CO2和N2O排放速率提高幅度分别为2~23%和1.7~22.3%，D处理达13~15%和7.0~13.7%。到达峰值后土壤CO2排放速率逐渐降低，且D处理降低速度较快。（4）枸杞园土壤CO2排放速率与土壤表层温度变化呈显著正相关，其影响因素主要是温度和水分。土壤N2O排放速率受施肥间隔时长影响最为显著，其次是土壤水分和温度。（5）利用DNDC模型通过对日最高、最低气温、日平均气温和水分进行矫正，可较客观准确地模拟该区域土壤CO2和N2O排放特征。（6）节灌模式增加了土壤细菌群落的多样性和稳定性，对土壤真菌群落结构的丰富度和均匀度也起到积极促进作用。（7）在高频率、短周期节灌模式基础上对枸杞园水肥一体化技术进行优化，筛选出了典型叶用枸杞水肥一体化养分最佳组合：N、P、K分别为60 mg/L，30 mg/L和40 mg/L，产量最高达13890 kg/hm2。（8）节灌模式改变了土壤理化性状导致土壤养分活性和利用效率得到明显改善，有利于枸杞园土壤实现提质增效和可持续生产。在宁夏旱区D1模式能够协同实现节水、固碳减排、平衡稳产，是一种可持续的节水灌溉模式。