环境科学  2022, Vol. 43 Issue (11): 5140-5148   PDF    
硝化抑制剂对我国蔬菜生产产量、氮肥利用率和氧化亚氮减排效应的影响: Meta分析
刘发波1,2, 马笑1,2, 张芬1,2, 梁涛3, 黎亮武4, 王军杰1,2, 陈新平1,2, 王孝忠1,2     
1. 西南大学资源环境学院, 长江经济带农业绿色发展中心, 重庆 400715;
2. 西南大学农业科学研究院, 重庆 400715;
3. 重庆市农业科学院, 重庆 401329;
4. 广西大学农学院, 南宁 530004
摘要: 我国蔬菜生产系统由于长期过量施肥导致氮肥利用率低和环境问题严重, 氮肥配施硝化抑制剂是降低活性氮损失、增加蔬菜产量和提高氮肥利用率的有效策略, 然而缺乏系统研究.基于数据整合分析的方法, 系统分析了氮肥配施硝化抑制剂[双氰胺(DCD)、3, 4-二甲基吡唑磷酸盐(DMPP)和2-氯-6-三氯甲基吡啶(NP)]对我国蔬菜生产的产量、植株氮吸收、氮肥利用率和氧化亚氮减排效应的影响, 进一步揭示不同田间管理措施对其效果的影响.结果表明, 氮肥配施硝化抑制剂能够显著提高蔬菜产量(9.2%)、植株氮吸收(10.4%)和氮肥利用效率(11.2%), 同时减少氧化亚氮排放(28.4%).不同硝化抑制剂类型中, NP对增产效应和氧化亚氮减排效应的影响幅度最高, 分别为16.1%和32.0%, 其次是DMPP和DCD.硝化抑制剂在不同氮肥用量中能提高蔬菜产量(6.7% ~14.7%)和减少氧化亚氮排放(14.6% ~36.8%).在中性和碱性菜地土壤中, 硝化抑制剂的增产效应和氧化亚氮减排效应的影响幅度较酸性土大.硝化抑制剂在露地栽培、根菜类和叶菜类的条件下对产量的增加和氧化亚氮的减排效果较好.主成分分析表明, 土壤总氮含量和土壤pH是影响硝化抑制剂对蔬菜产量形成和驱动氧化亚氮排放的主要因素.综上, 硝化抑制剂是实现蔬菜系统提质增效、节肥减排的重要举措.同时, 农户应根据土壤和田间管理措施选择适宜硝化抑制剂类型, 以最大限度提高其有效性.
关键词: 蔬菜      硝化抑制剂      产量      氮肥利用率      田间管理      氧化亚氮排放     
Impact of Nitrification Inhibitors on Vegetable Production Yield, Nitrogen Fertilizer Use Efficiency and Nitrous Oxide Emission Reduction in China: Meta Analysis
LIU Fa-bo1,2 , MA Xiao1,2 , ZHANG Fen1,2 , LIANG Tao3 , LI Liang-wu4 , WANG Jun-jie1,2 , CHEN Xin-ping1,2 , WANG Xiao-zhongn1,2     
1. Interdisciplinary Research Center for Agriculture Green Development in Yangtze River Basin, College of Resources and Environment, Southwest University, Chongqing 400715, China;
2. Academy of Agricultural Sciences, Southwest University, Chongqing 400715, China;
3. Chongqing Academy of Agricultural Sciences, Chongqing 401329, China;
4. College of Agriculture, Guangxi University, Nanning 530004, China
Abstract: Due to the long-term excessive fertilization in the vegetable system in China, nitrogen use efficiency (NUE) is low, and the environmental problem is serious. Nitrogen fertilizer combined with nitrification inhibitor is an effective strategy to alleviate the loss of active nitrogen and increase vegetable yield. However, systematic research on the above is lacking. Meta-analysis was used to systematically analyze the effects of nitrogen fertilizer combined with nitrification inhibitors [dicyandiamide (DCD), 3, 4-dimethylpyrazole phosphate (DMPP), and 2-chloro-6-(trichloromethyl)pyridine (NP)] on the yield, plant nitrogen uptake, nitrogen fertilizer use efficiency, and nitrous oxide emission reduction effects in vegetable production in China. This study further revealed the impacts of different field management measures on their effects. The results showed that the combination of nitrogen fertilizer and nitrification inhibitor could significantly increase vegetable yield (9.2%), plant nitrogen uptake (10.4%), and nitrogen fertilizer use efficiency (11.2%) but reduce nitrous oxide emissions (28.4%). Among the different types of nitrification inhibitors, NP had the highest impact on the yield-increasing effect and the nitrous oxide emission reduction effect, which were 16.1% and 32.0%, respectively, followed by that of DMPP and DCD. Nitrification inhibitors could significantly increase vegetable yield (6.7%-14.7%) and reduce N2O emissions (14.6%-36.8%) in different nitrogen fertilizer rates. In neutral and alkaline vegetable soil, the yield-increasing effect and the reduction effect of nitrous oxide were higher than those in acidic soil. Nitrification inhibitors had significant effects on yield increase and nitrous oxide reduction under the conditions of greenhouse or open-field cultivation, root vegetables, and leafy vegetables. Principal component analysis (PCA) showed that soil total nitrogen content and soil pH were the main factors that promoted the increase in vegetable yields and drove nitrous oxide emissions under the application of nitrification inhibitors. In summary, nitrification inhibitors were an important measure to achieve the goal of improving quality and fertilizer use efficiency, while saving fertilizer and reducing emissions in vegetable production. Farmers should choose suitable types of nitrification inhibitors according to soil and field management measures to maximize their effectiveness.
Key words: vegetables      nitrification inhibitor      yield      nitrogen use efficiency      field management      nitrous oxide emission     

我国蔬菜产业快速发展, 截至2019年我国蔬菜种植面积是1980年的6.6倍, 占我国农作物种植面积12.6%[1].然而, 我国蔬菜产业一直处于小农户主导、高肥料投入和高环境代价的生产模式[2].大幅增加化肥的施用并没有带来蔬菜产量的增加, 反而导致较低的氮肥利用效率[3, 4].氮肥的大量损失极大地干扰了N的生物地球化学循环, 对水、空气和土壤造成了严重的环境问题[5~7].蔬菜生产系统是氧化亚氮(N2O)排放的热点系统, 排放量平均值为3.91 kg·hm-2, 较其他作物系统高1.2~4.2倍[8].因此, 寻求减少N2O排放、提高氮肥利用率的有效措施以实现蔬菜稳产增产和降低环境代价, 对实现我国蔬菜绿色发展至关重要.

硝化抑制剂(NIs)能够延缓土壤中铵态氮(NH4+-N)向硝态氮(NO3--N)转化, 延长NH4+-N在土壤中存留的时间, 增加土壤基质对NH4+-N生物吸收和吸附, 减少活性氮损失[9, 10], 因而被认为是提高氮肥利用率、促进作物生产和降低环境污染的有效措施之一.先前国内外学者通过Meta分析对硝化抑制剂的农学效应以及环境代价等方面进行了研究[11~13], 结果表明, 硝化抑制剂能够提高作物产量5.0%~20.0%和氮肥利用效率4.0%~18.0%, 提高作物品质, 增加农民收益, 同时减少37.0%~48.0%氮淋洗损失, 减少38.0%~57.0%的N2O和NO排放.以上研究主要集中于粮食系统或整个农作物系统[12, 14], 而针对蔬菜作物较为系统和较为具体评价硝化抑制剂的田间应用效果的研究目前还较少.近年来硝化抑制剂在蔬菜生产的应用效果受到越来越多的关注, 有研究重点关注其对区域蔬菜产量、土壤氮转化特征和单一途径活性氮损失的影响[15, 16].如Min等[17]的田间试验结果表明, 减氮配施硝化抑制剂2-氯-6-三氯甲基吡啶(NP)使番茄产量增加23.0%~36.0%, 同时降低37.0%的N2O排放.然而, 受田间管理、区域土壤特性、作物种类和硝化抑制剂类型等多种因素的影响, 硝化抑制剂的田间应用效果有很大的差异.Fan等[18]的研究表明, 硝化抑制剂在低pH土壤上增加蔬菜产量和减少N2O排放的趋势均不明显. Zhang[19]的研究表明过量氮肥的施用导致土壤大量的氮盈余会掩盖硝化抑制剂的增产效果, 削弱N2O的减排潜力.有研究指出[20], 添加双氰胺(DCD)并不影响集约化蔬菜轮作系统N2O排放, 而NP有显著缓解N2O排放的效果.而设施栽培较大的灌溉水量和持续较高的土壤温度, 加速硝化抑制剂的下层迁移, 缩短其半衰期从而有效性降低[21].我国蔬菜种植区域广泛, 与其他作物相比蔬菜生产条件较为复杂, 由于蔬菜生育期较短, 复种指数高, 同时具有设施和露地不同的栽培方式, 因此, 系统评价硝化抑制剂在我国蔬菜不同田间生产条件下的应用效果对硝化抑制剂在我国蔬菜生产中全面推广具有更为重要的指导意义.

硝化抑制剂是增加蔬菜产量、提高氮肥利用率和降低活性氮损失的重要举措, 双氰胺(DCD)、3, 4-二甲基吡唑磷酸盐(DMPP)和2-氯-6-三氯甲基吡啶(NP)这3种硝化抑制剂在农业生产中应用最为普遍, 然而缺乏系统研究其在农业生产中的作用效果.尽管当前基于Meta分析的方法探究硝化抑制剂在蔬菜生产影响受到越来越多的关注, 然而先前的研究重点关注于对N2O排放或产量单一指标的影响, 缺乏对产量、氮肥利用率、植株氮吸收和活性氮损失的综合影响, 同时缺乏探究硝化抑制剂作用效果的驱动因子分析.本研究收集整理了国内外学者发表的资料, 运用整合分析的方法, 系统量化了DCD、NP和DMPP这3种硝化抑制剂对我国蔬菜产量、植株氮吸收、氮肥利用率和N2O排放等方面综合影响, 同时, 阐明了区域土壤特性、管理措施和蔬菜类型等因素对3种硝化抑制剂应用效果的影响, 进而明确影响硝化抑制剂对蔬菜生产田间应用效果的关键驱动因子, 对指导我国蔬菜绿色生产中优化施肥策略的制定有重要的借鉴意义.

1 材料与方法 1.1 数据收集及筛选

本研究数据来源于2021年6月之前发表于中国知网、Web of science和Google Scholar这3个文献数据库, 以“蔬菜(vegetable)”、“硝化抑制剂(nitrification inhibitor)”、“N2O排放(N2O emission)”、“蔬菜产量(vegetable yield)”和“氮肥利用效率(nitrogen use efficiency, NUE)”等作为关键词进行文献的搜索, 并进行筛选.筛选的标准为:①试验研究必须来自大田试验, 而非盆栽或土柱试验; ②同一试验必须包括至少一对配对的对照组和处理组, 对照组为不施用硝化抑制剂, 处理组为施用硝化抑制剂, 且对照组和处理组氮肥用量一致; ③至少完成一季蔬菜全生育期的研究, 所测定的指标至少包含N2O排放量、蔬菜产量、NUE和植株氮吸收等其中一项.硝化抑制剂类型包括双氰胺(DCD)、3, 4-二甲基吡唑磷酸盐(DMPP)和2-氯-6-三氯甲基吡啶(NP).数据收集过程中, 如果数据是以图的形式展示, 利用GetData Graph Digitizer 2.24软件来获得.基于以上筛选标准, 获取有效文献22篇, 采集了117组数据.收集的内容包括:作者、标题、试验时间、采样点、土壤类型、土壤pH值、有机质含量、土壤总氮含量、硝化抑制剂种类、氮肥用量、植株氮吸收量、氮肥利用效率、N2O累积排放量和所涉及指标的标准差等.

为明确影响硝化抑制剂应用效果的主要驱动因素, 本研究将这些驱动因子划分为:土壤特性、蔬菜类型和田间管理措施(硝化抑制剂类型、栽培类型、氮肥用量), 具体分类见表 1.其中蔬菜类型主要分成叶菜类、果菜类和根菜类这3类.叶菜类蔬菜主要包括空心菜、苋菜和白菜等, 果菜类蔬菜主要包括黄瓜、辣椒和茄子等, 根菜类蔬菜主要是萝卜.

表 1 数据分类 Table 1 Data classification

1.2 数据分析

单位产量N2O排放量计算公式为:

(1)

本研究采用Meta分析的方法研究了氮肥配施硝化抑制剂的条件下对蔬菜产量、植株氮吸收、NUE和N2O排放量的影响.计算过程采用Hedges等[22]的计算方法, 计算每一组数据的效应值(RR), 通过自然对数的转化以量化氮肥配施硝化抑制剂(NIs)条件下对各变量的响应程度, 计算公式如下:

(2)

式中, Xt表示添加硝化抑制剂处理(处理组)的平均值, Xc表示只施用化肥处理(对照组)的平均值.

另外, 权重(w)、权重响应比(mean RR)、mean RR的标准误、95%的置信区间(CI)和由硝化抑制剂的添加引起既定变量的变化率(C)可通过下式计算:

(3)
(4)
(5)
(6)
(7)
(8)

式中, StSc分别表示处理组的标准差和对照组的标准差; ntnc分别表示处理组和对照组的样本量; 如果一些研究中没有给出相应的标准差, 则以公式(4)计算权重[23].采用卡方检验(K-S test)对每一项变量的效应值进行正态分布检验, 发现并非所有都符合正态分布(图 1).对不符合正态分布的变量的效应值进行非参数bootstrap分析(重取样过程, n=10 000次迭代).运用OpenMEE软件采用随机效应模型最大似然法进行每一类别变量的效应值、权重效应比及其95% CI的计算[24], 并运用Origin作随机森林图.如果95% CI包含零值表明该变量中处理组与对照组没有显著差异(P>0.05).同时, 采用SPSS V20.0 (IBM, Chicago, USA) 对处理组和对照组、以及不同NIs类型的产量、植株氮吸收、NUE以及N2O排放量进行单因素方差分析, 采用LSD检验计算显著性(P<0.05).利用主成分分析(PCA), 采用Origin软件分析了土壤理化性质与N2O排放量和产量的关系.

图 1 氮肥配施硝化抑制剂条件下N2O排放的样本分布频率 Fig. 1 Sample distribution frequency of nitrous oxide emissions under the condition of nitrogen fertilizer combined with nitrification inhibitor

2 结果与分析 2.1 硝化抑制剂对蔬菜生产和N2O排放的影响

图 2可知, 相比于施用氮肥(未添加硝化抑制剂), 氮肥配施硝化抑制剂增加了9.2%(95%置信区间:7.8%~10.7%)的蔬菜产量, 植株氮吸收和氮肥利用率分别提高了10.4%(95%置信区间:5.4%~5.7%)和11.2%(95%置信区间:8.0%~14.6%), 同时, 单位面积和单位产量N2O排放分别减少了28.4%(95%置信区间:-27.3%~-29.5%)和42.1%(95%置信区间:-32.7%~-50.2%).

图 2 氮肥配施硝化抑制剂对蔬菜产量、植株N吸收、NUE和N2O排放的影响 Fig. 2 Effect of nitrogen fertilizer combined with nitrification inhibitor on vegetable yield, plant N uptake, NUE, and nitrous oxide emission

2.2 不同生产条件下硝化抑制剂对产量、植株氮吸收和NUE的影响

相比于施用氮肥(未添加硝化抑制剂), 3种类型硝化抑制剂均能显著增加蔬菜产量[图 3(a)], DCD、DMPP和NP增产幅度分别为4.6%、7.7%和16.1%.不同施氮量下硝化抑制剂对蔬菜产量有显著影响, 施氮量<200、200~400和>400 kg·hm-2时增产幅度分别为14.7%、9.8%和6.7%.在不同pH条件下, 土壤6.5≤pH≤7.5时增产幅度最高(14.2%).硝化抑制剂的添加对露地蔬菜的增产幅度(11.4%)高于设施蔬菜(5.9%).在所有蔬菜类型中, 对根菜类和叶菜类蔬菜增产效果显著, 分别为13.8%和9.3%.

图 3 氮肥配施硝化抑制剂在不同生产条件下对蔬菜产量、植株N吸收和NUE的影响 Fig. 3 Effect of nitrogen fertilizer combined with nitrification inhibitor on vegetable yield, plant N uptake, and NUE under different production conditions

相比于施用氮肥(未添加硝化抑制剂), 硝化抑制剂NP对植株氮吸收显著提高了12.4%, 而DCD(4.2%)和DMPP(5.3%)均无显著影响[图 3(b)].从氮肥用量看, 随着氮肥用量和土壤pH增加, 硝化抑制剂对蔬菜氮吸收的提高效果逐渐降低; 氮肥配施硝化抑制剂显著提高了叶菜类蔬菜的植株氮吸收, 为11.4%, 且高于果菜类(5.1%).不同栽培类型间植株氮吸收对氮肥配施硝化抑制的响应差异不显著.NP和DMPP对氮肥利用率增加效果高于DCD, 硝化抑制剂在露地蔬菜、施氮量 < 200 kg·hm-2、中性或碱性土壤、根菜类和果菜类的条件下对提升氮肥利用率效果显著[图 3(c)].

2.3 不同生产条件下N2O减排效应对硝化抑制剂的响应

在单位面积上[图 4(a)]:氮肥配施不同硝化抑制剂类型DCD、DMPP和NP分别减少N2O排放23.6%、22.4%和32.0%; 当氮肥施用量为<200、200~400和>400 kg·hm-2时N2O的减排幅度分别为14.6%、27.3%和36.8%.在6.5≤pH≤7.5的土壤中减少N2O排放的幅度最大(43.2%), 其次是pH>7.5(34.2%)和pH<6.5(27.4%)的土壤; 氮肥配施硝化抑制剂对露地栽培N2O减排幅度较设施栽培高13.0%; 叶菜类、果菜类和根菜类蔬菜N2O减排幅度分别为28.3%、27.4%和34.2%.

图 4 氮肥配施硝化抑制剂在不同生产条件下对蔬菜生产单位面积和单位产量N2O排放的影响 Fig. 4 Effect of nitrogen fertilizer combined with nitrification inhibitor on nitrous oxide emissions per unit area and per unit yield under different vegetable production conditions

在单位产量上[图 4(b)]:NP的N2O减排效果最高(46.2%), 较DCD和DMPP分别高7.8%和10.7%; 当氮肥施用量为<200、200~400和>400 kg·hm-2时N2O的减排幅度分别为44.2%、42.9%和37.3%; 硝化抑制剂在pH<6.5、6.5≤pH≤7.5和pH>7.5的菜地土壤上分别减少N2O排放40.1%、52.2%和44.1%; 露地栽培和设施栽培分别减少N2O排放41.4%和43.2%; 叶菜类、果菜类和根菜类蔬菜N2O减排幅度分别为42.3%、47.3%和37.8%.

2.4 施用硝化抑制剂条件下氮肥用量和N2O排放的关系

本研究将施用氮肥(未添加硝化抑制剂)和氮肥配施硝化抑制剂条件下N2O排放量和氮肥用量进行曲线拟合(图 5), 结果表明, 不论是只施用氮肥还是氮肥配施硝化抑制剂条件下, N2O排放量随施氮量的增加呈指数函数形式增长.然而, 氮肥配施硝化抑制剂条件下, 氮肥用量与N2O排放量的响应曲线较施用氮肥(未添加硝化抑制剂)的响应曲线平缓, 即氮肥用量越大, 氮肥配施硝化抑制剂比施用氮肥(未添加硝化抑制剂)的N2O排放量增长缓慢, 这进一步说明硝化抑制剂的应用能有效地减少菜地土壤N2O的排放.

ONF表示施用氮肥(未添加硝化抑制剂); NIs表示氮肥配施硝化抑制剂 图 5 氮肥配施硝化抑制剂条件下氮肥用量和N2O排放的关系 Fig. 5 Relationship between the amount of nitrogen fertilizer and nitrous oxide emission under the condition of combined application of nitrogen fertilizer and nitrification inhibitor

2.5 施用硝化抑制剂条件下影响蔬菜产量和N2O排放的因素分析

利用主成分(PCA)分析了在氮肥配施硝化抑制剂的前提下, 土壤pH值、土壤总氮含量(TN)、有机碳含量(SOC)、碳氮比(C/N)和氮肥用量与N2O排放量和蔬菜产量的关系(图 6).主成分分析筛选出前两个主成分, 累积方差分别为61.7%、59.8%.通过主成分分析发现, 土壤中的总氮含量是影响蔬菜生产N2O排放和蔬菜产量的主要因素, 并且总氮含量与蔬菜N2O排放和产量呈正相关性.然而, 在氮肥配施硝化抑制剂的条件下氮肥用量和N2O排放、蔬菜产量的关系正相关性较弱.土壤中的C/N与蔬菜N2O排放和产量都呈负相关关系.

图 6 氮肥配施硝化抑制剂条件下土壤理化性质和氮肥用量与N2O排放和蔬菜产量的主成分分析 Fig. 6 Principal component analysis of soil physical and chemical properties, nitrogen fertilizer rate, and N2O emission and vegetable yield under combined application of nitrogen fertilizer and nitrification inhibitor

3 讨论 3.1 硝化抑制剂对蔬菜产量和N2O排放的影响

硝化抑制剂可抑制土壤硝化作用中的氨氧化细菌(AOB)和氨氧化古菌(AOA)或相关酶活性[25], 延缓铵态氮向硝态氮的转换, 有效地延长氮肥的肥效和阻止氮素流失[26], 同时土壤中的盐基离子如K+、Ca2+和Mg2+的淋溶损失相应降低[27], 增加作物对氮素、盐基离子的吸收量, 进而增加作物产量提高氮肥利用率.另一方面, 能保持长时间高含量的铵态氮, 有效缓解硝态氮的累积, 减少土壤反硝化底物浓度[28, 29], 从而减少土壤中的N2O排放.本研究结果表明, 与施用氮肥(未添加硝化抑制剂)相比, 氮肥配施硝化抑制剂显著增加蔬菜产量9.2%, 提高植株氮吸收10.4%和氮肥利用率11.2%, 同时, 显著减少N2O排放28.4%(图 2).硝化抑制剂对蔬菜系统的增产效应稍高于粮食作物系统(7.0%)[30], 但是对N2O减排效果低于粮食作物系统(50.0%)[12, 14].Yang等[12]对DCD和DMPP的田间应用效果进行整合分析发现, DCD和DMPP对蔬菜作物的增产效果均高于粮食作物.Gao等[31]的研究发现硝化抑制剂对蔬菜系统N2O减排效果(26.0%)显著低于小麦(47.0%)和水稻系统(49.0%).由于蔬菜作物特殊的生物学特性(根系浅, 养分吸收能力弱; 生育期短, 复种指数高; 养分需求量大)和社会经济学特性[32](肥料投入成本高, 单位产量施肥成本低, 误导农民大量施肥), 造成大量水分和肥料的投入, 尤其是氮肥.两个系统的水肥投入的巨大差异造成土壤理化性质(土壤pH和有机质含量等)和土壤含水量的不同[33], 导致硝化抑制剂在两种作物系统具有明显差异.硝化抑制剂在蔬菜和粮食系统中对N2O减排效果差异较大, 主要因为两个系统间土壤本底、氮肥施用量和作物类型的不一致, 共同导致土壤硝化或反硝化的反应底物浓度出现差异, 最终影响硝化抑制剂的N2O减排效果.例如, 过量施用氮肥导致菜地土壤酸化严重, 土壤pH值和碳氮比较粮食作物农田土壤低, 硝化-反硝化过程相关微生物活性弱, 降低N2O排放强度[33, 34], 是导致硝化抑制剂在蔬菜系统中对N2O的减排效果低于粮食作物系统的原因之一.

3.2 不同生产条件下硝化抑制剂添对蔬菜产量和N2O排放的影响

土壤pH是调控硝化抑制剂应用效果的主要因素之一(图 6).本研究表明, 硝化抑制剂能够显著提高中性和碱性土壤上的蔬菜产量, 但对酸性土壤增产效果不明显[图 3(a)], 这与先前研究结果一致[35].导致这一差异的原因在于, 氮肥的施入极大激发中性和碱性土壤的硝化作用[36], 而低pH条件下土壤硝化作用微弱[37]; 高强度的硝化作用保证作物苗期充足的氮素营养供应, 且硝化抑制剂的添加有效地延长氮肥肥效, 满足作物后期的生长对氮素营养的需求[26], 有助于作物产量的增加, 进而提高氮肥利用率.N2O主要由微生物的硝化和反硝化作用产生, 硝化作用为反硝化过程提供底物来源[38].硝化作用是一个以氨氧化菌(AOB)和氨氧化古菌(AOA)为主导的生化过程.有研究证实[39], 土壤pH主导着氨氧化微生物的生态位, 在中性和碱性土壤的硝化作用AOB(氨氧化细菌)发挥主要作用, AOA(氨氧化古菌)主导着酸性土壤的硝化作用.Beeckman等[25]基于文献综述发现, DCD、DMPP和NP这3种硝化抑制剂对AOB的抑制效果显著高于AOA.因此, 硝化抑制剂降低反硝化底物的供应强度在碱性和中性土中大于酸性土[12], 进而解释了本研究中硝化抑制剂对N2O的减排幅度在中性和碱性菜地土壤要高于酸性土的原因.

在不同氮肥用量下, 硝化抑制剂对蔬菜的增产效应和N2O减排效应有所差异.本研究结果显示, 氮肥配施硝化抑制剂的条件下, 氮肥用量与产量呈负相关性[图 6(b)], 即随着氮肥用量增加, 硝化抑制剂的增产效应呈降低的趋势[图 4(a)]. Min等[17]通过田间试验表明, 氮肥用量相对较低时配施硝化抑制剂能更有效地促进蔬菜的增产, 提高氮肥利用率, 并且这一趋势在其他作物上也得到了证实[40, 41].本研究中, N2O排放量随氮肥用量的增加以指数函数形式响应(图 5), 这与李巧玲[42]和邱炜红等[43]的研究得出不同蔬菜季土壤N2O排放量因氮肥用量增多以指数增加的结果相一致.此外, 本研究中添加硝化抑制剂的N2O排放与氮肥用量的响应曲线在只施用氮肥曲线之下, 且随着氮肥用量的增加, 差距逐渐增大(图 5), 从而解释了本研究中随着氮肥用量的增加, 硝化抑制剂减少N2O排放的作用效果随之增加的原因.

DMPP、DCD和NP是当前施用最为广泛的3种硝化抑制剂, 不同类型硝化抑制剂对蔬菜的增产效应和N2O减排效应存在差异[31, 44].本研究中NP和DMPP对蔬菜的增产幅度、提高氮肥利用率和N2O减排幅度均优于DCD.Gao等[31]通过Meta分析评估了常用的3种硝化抑制剂对作物和环境的效益发现, 添加硝化抑制剂能够使作物增产5.8%~12.0%, 减少30.4%~60.1% N2O排放, 同时DMPP和NP提高氮肥利用率的效果高于DCD.不同硝化抑制剂增加作物产量和抑制N2O排放的能力取决于其本身的特性[45]、用量[46]和土壤生态条件[47]等, 而这些因素的叠加效应增大了不同类型硝化抑制剂田间应用效果的差异性.

从不同栽培类型来看, 硝化抑制剂在露地栽培中的增产效应和N2O减排的能力要高于设施栽培[图 3(a)图 4(a)].可能原因在于, 一方面设施蔬菜以果菜类为主, 露地蔬菜以叶菜类和根菜类为主, 本研究结果显示硝化抑制剂对果菜类的增产作用和N2O减排幅度均低于叶菜类和根菜类蔬菜; 另一方面, 设施栽培氮肥用量远高于露地菜地[48], 这种过量氮肥的投入可能掩盖硝化抑制剂促进设施菜地增产的效果.由于长期过量氮肥的施用, 设施菜地土壤pH随种植年限增加而显著降低[49, 50], 较露地菜地而言, 设施菜地土壤酸化和盐渍化严重[51]; 此外, 设施蔬菜灌水频繁, 增加表层土壤硝酸盐向下层的迁移, 硝酸盐淋洗量增加[52], 减少N2O的排放, 这些因素可能会降低硝化抑制剂对设施蔬菜的增产效应和N2O减排效果.

3.3 不确定分析

本研究基于Meta分析的研究方法, 综合量化了氮肥配施硝化抑制剂在不同生产条件下对蔬菜产量、植株氮吸收、NUE和N2O排放的影响程度.然而, 本研究也存在一些不确定性.首先, 由于缺乏足够的数据样本, 在数据分类时土壤因素只考虑土壤pH值的影响, 因而不能全面评估不同土壤理化性质下添加硝化抑制剂的影响; 其次, 3种类型硝化抑制剂应用于蔬菜生产样本量并不均匀并且有关硝化抑制剂对根菜和果菜类蔬菜田间应用效果的研究相对较少, 导致在比较不同类型硝化抑制剂、硝化抑制剂对不同类型蔬菜的田间应用效果的差异时准确性降低.因此, 为了更准确的评价硝化抑制剂对我国蔬菜增产效应和N2O减排效应的影响, 未来需要在多个地点进行多种蔬菜品种多年持续的田间研究.

4 结论

(1) 在我国蔬菜生产系统中, 氮肥配施硝化抑制剂能够显著提高蔬菜产量(9.2%)、植株氮吸收(10.4%)和氮肥利用效率(11.2%), 同时减少N2O排放(28.4%).

(2) 不同硝化抑制剂类型中, NP和DMPP对增产效应、提高氮肥利用率和N2O减排效应的影响幅度强于DCD.硝化抑制剂在不同氮肥用量中能提高蔬菜产量(6.7%~14.7%)和减少N2O排放(14.6%~36.8%).硝化抑制剂在酸性或是碱性菜地、设施或是露地栽培、根菜类和叶菜类的条件下对产量的增加和N2O的减排效果较好.

(3) 土壤总氮含量和土壤pH是硝化抑制剂施用条件下促进蔬菜产量形成和驱动N2O排放的主要因素.

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