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  农业环境科学学报  2020, Vol. 39 Issue (7): 1558-1567  DOI: 10.11654/jaes.2019-1364
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引用本文  

秦雪超, 潘君廷, 郭树芳, 等. 化肥减量替代对华北平原小麦-玉米轮作产量及氮流失影响[J]. 农业环境科学学报, 2020, 39(7): 1558-1567.
QIN Xue-chao, PAN Jun-ting, GUO Shu-fang, et al. Effects of chemical fertilizer reduction combined with biogas fertilizer on crop yield of wheat-maize rotation and soil nitrogen loss in North China Plain[J]. Journal of Agro-Environment Science, 2020, 39(7): 1558-1567.

基金项目

中央级公益性科研院所基本科研业务费专项(1610132019037)

Project supported

Fundamental Research Funds for Central Non-profit Scientific Institution(1610132019037)

通信作者

翟丽梅, E-mail:zhailimei@caas.cn

作者简介

秦雪超(1995-), 男, 河南鹿邑人, 硕士研究生, 主要从事农业面源污染研究。E-mail:atqinxuechao@163.com

文章历史

收稿日期: 2019-12-11
录用日期: 2020-03-30
化肥减量替代对华北平原小麦-玉米轮作产量及氮流失影响
秦雪超1 , 潘君廷1 , 郭树芳2 , 翟丽梅1 , 王洪媛1 , 武淑霞1 , 刘宏斌1     
1. 中国农业科学院农业资源与农业区划研究所/农业农村部面源污染控制重点实验室, 北京 100081;
2. 云南省农业科学院农业环境资源研究所, 昆明 650201
摘要:为降低氮素流失风险,提高肥料利用效率,在华北平原采用田间定位试验研究了不同施肥措施对小麦-玉米产量、周年氮素淋溶和径流损失的影响。结果表明,相比当地常规施肥处理(CON),减施氮肥150 kg·hm-2的条件下,单施化肥(RF)和10%比例沼液替代(RFM)不会降低小麦和玉米产量。相较于CON处理的氮素年均盈余量218.1 kg·hm-2,RF和RFM处理氮盈余量分别显著降低了66.7%和55.9%。CON处理总氮平均淋失浓度和年均淋失量分别为33.70 mg·L-1和22.01 kg·hm-2,与之相比,RF处理总氮平均淋失浓度和年均淋失量分别降低了31.45%和30.58%,而RFM处理分别降低了40.65%和43.39%。试验期间径流产流只发生2次,氮素淋溶发生次数和氮损失量远高于径流损失,因此淋溶是氮素流失的主要途径。CON处理总氮平均径流浓度和年均径流流失量分别为23.0 mg·L-1和0.095 kg·hm-2,与之相比,RF处理总氮平均径流浓度和年均径流流失量分别降低了32.9%和30.5%,而RFM处理分别降低了45.5%和50.5%。由于施肥量较高,CON处理氮淋溶表观流失率为4.19%,而RF和RFM处理氮淋溶表观流失率分别降低了2.86%和20.76%。NO3--N是氮素流失的主要形态,分别占淋溶和径流总氮流失量的66.3%和73.3%,其与总氮流失变化趋势一致。综上,化肥减量配施沼液在保证作物产量的情况下,是降低氮素流失的有效措施。
关键词面源污染        减量施肥    小麦    玉米    
Effects of chemical fertilizer reduction combined with biogas fertilizer on crop yield of wheat-maize rotation and soil nitrogen loss in North China Plain
QIN Xue-chao1 , PAN Jun-ting1 , GUO Shu-fang2 , ZHAI Li-mei1 , WANG Hong-yuan1 , WU Shu-xia1 , LIU Hong-bin1     
1. Key Laboratory of Nonpoint Source Pollution Control, Ministry of Agriculture and Rural Affairs/Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China;
2. Institute of Agricultural Environment and Resources, Yunnan Academy of Agricultural Sciences, Kunming 650201, China
Abstract: To reduce the risk of nitrogen loss and improve the efficiency of fertilizer use, field experiments were conducted in the North China Plain to study the effects of different fertilizer treatments on the crop yield of wheat and maize, annual nitrogen leaching, and runoff loss. The results showed that the yield of wheat and maize was not reduced by applying chemical fertilizer alone or 10% biogas fertilizer substitution with nitrogen fertilizer reduction of 150 kg·hm-2. Compared with the annual average nitrogen surplus of 218.1 kg·hm-2 under the CON treatment, the nitrogen surplus of the RF and RFM treatments decreased by 66.7% and 55.9%, respectively. The average leaching concentration and annual leaching amount of nitrogen in the CON treatment were 33.70 mg·L-1 and 22.01 kg·hm-2, respectively. Compared with conventional fertilization, the average nitrogen leaching concentration and annual leaching loss in the RF treatment decreased by 31.45% and 30.58%, respectively, whereas that in the RFM treatment decreased by 40.65% and 43.39%, respectively. Runoff occurred only twice during the study. The occurrence of nitrogen leaching and the amount of nitrogen loss in the study area were much higher than that of runoff loss. Leaching was the main pathway of nitrogen loss. The average nitrogen runoff concentration and annual runoff loss in the CON treatment were 23.0 mg·L-1 and 0.095 kg·hm-2, respectively. Compared with conventional fertilization, the average nitrogen runoff concentration and annual runoff loss in the RF treatment decreased by 32.9% and 30.5%, whereas that in the RFM treatment decreased by 45.5% and 50.5%, respectively. Due to the higher fertilization rate, the apparent nitrogen leaching rate of the conventional fertilization treatment was 4.19%, whereas that in the RF and RFM treatments decreased by 2.86% and 20.76%, respectively. NO3--N was the main form of nitrogen loss, accounting for 66.3% and 73.3% of the total nitrogen loss in leaching and runoff, respectively, which was consistent with the trend in total nitrogen loss. In conclusion, chemical fertilizer reduction combined with biogas fertilizer was an effective measure for reducing nitrogen loss concentration and amount while ensuring crop yield.
Keywords: non-point source pollution    nitrogen    chemical fertilizer reduction    wheat    maize    

化肥对促进作物生长,保证作物高产、稳产具有重要作用[1]。中国是世界上最大的化肥生产和消费国,在2013年,我国农用化肥消耗量达到了5 911.9万t,超过世界化肥消耗总量的1/3。2014年,我国耕地化肥施用量为447.2 kg·hm-2,远超过仅为125.5 kg·hm-2的世界平均化肥施用量[2]。我国每年氮肥施用量为3 360万t,占全球的33%,导致农田氮盈余量已达到175 kg·hm-2[3]。大量化肥投入造成土壤氮盈余,这不仅污染大气和水体,也造成资源浪费。

在我国华北平原小麦-玉米轮作体系中,每年氮肥投入量为588 kg·hm-2,远高于其他国家氮肥施用量[4]。有研究指出,对高化肥投入量的农田,适量的减施化肥不会影响作物产量[5],且能显著减少土壤氮盈余[6]。赵亚南等[6]研究指出,在氮肥用量从180 kg·hm-2减为96 kg·hm-2时,小麦产量并未减产,且提高了肥料利用率。另外,畜禽粪便中含有丰富的氮资源。据统计,我国2015年畜禽粪尿中氮产生量为1 229万t[7]。与单施化肥相比,有机肥能提高土壤微生物多样性,提高微生物和酶活性,降低土壤容重,改善土壤结构,活化土壤养分等[8-9]。畜禽粪便经厌氧发酵后产生的沼气可作为能源物质,沼液可作为一种液体有机肥还田再利用。有研究表明单施化肥与50%的沼液替代相比对玉米产量并无显著差异[10],而王桂良等[11]研究指出小麦产量在50%的沼液替代时产量最高。沼液和化肥合理配施能提高作物产量,增加土壤有机质和土壤氮、磷、钾等速效养分含量[11-13]。目前的研究大多只是单独研究化肥减量或者有机无机配施,而化肥减量与沼液配施相结合对于大田作物生长和环境影响特征的研究相对较少。

华北平原属于暖温带季风气候,冬季干燥寒冷,夏季高温多雨,年降水量为500~900 mm,但区域间差异大,如在河北省中南部降雨量<500 mm。施肥和降水是影响农田氮流失的主要因素。农田地下淋溶和地表径流是氮素进入水体的主要方式。在旱地作物中,氮淋溶流失量要高于径流流失量。段然等[5]研究指出,土壤氮素径流流失量低于0.70 kg∙hm-2,而氮素淋失量却远高于此[14-15]。有研究表明大量施用氮肥必将导致土壤中硝态氮大量淋失[16]。与单施化肥相比,有机无机配施能降低农田总氮、硝态氮和铵态氮淋失量[17-18]。有机肥能够改善土壤理化性质,增加土壤孔隙度,增强渗透性,提高土壤容纳雨水能力,减少氮素流失[19]

本研究为了保证华北平原小麦、玉米产量的可持续性,探讨了在减施化肥条件下,单施化肥和部分有机替代对于作物产量和氮流失的影响,以期为化肥合理减施提供科学依据。

1 材料与方法 1.1 试验地概况

本试验地位于河北省正定县新安镇(38°14.29′ N,114°34.52′ E),土壤类型为黄褐土,质地为中壤。平均海拔为78 m,年平均气温为13.1 ℃,年平均降雨量为489 mm,属于黄淮海半湿润平原,种植模式为冬小麦-夏玉米轮作。冬小麦生育期为每年10月初到次年6月初,夏玉米生育期为每年6月中旬到10月初。试验开始时土壤(0~20 cm)基础理化性质为:土壤容重1.24 g·cm-3,pH 7.5,有机质21.5 g·kg-1,总氮0.91 g·kg-1,总磷0.75 g·kg-1,有效磷24.1 mg·kg-1,硝态氮12.9 mg·kg-1,铵态氮0.74 mg·kg-1

1.2 试验设计

试验始于2014年,设置3个处理:(1)CON,常规施肥;(2)RF,化肥减量;(3)RFM,化肥减量替代(10%沼液+90%化肥减量)。沼液取自试验田附近养殖场,年投入量为22.5 t·hm-2。各处理具体施肥量见表 1。氮肥50%作基肥,50%作追肥施入农田,磷、钾肥和沼液于每年的10月初玉米收获后和小麦种植前一次性施入土壤。每个处理设3个重复,小区面积为36 m2(8 m×4.5 m)。根据小麦和玉米生长状况进行灌溉,2015年和2016年小麦生育期灌溉2次,分别在返青拔节期和灌浆乳熟期;玉米生长期灌溉1次,在出苗时期。2017年小麦生育期灌溉3次,分别在苗期、返青拔节期和灌浆乳熟期;玉米生长期灌溉2次,分别在出苗期和乳熟期。灌溉方式为沟灌,每次灌溉量均为125 mm。小麦、玉米品种分别为衡4399和星硕F1。在小区地下90 cm处安装淋溶液收集桶,用于收集每次降雨或灌溉产流后的渗滤液。田间径流水收集池长4.5 m、宽1.0 m、深1.5 m,用于收集每次径流产流水样(图 1)。

表 1 不同处理具体施肥量 Table 1 Amount of fertilizer application under different treatments

图 1 田间淋溶水(a)和径流水(b)收集装置 Figure 1 The collection devices of leaching(a)and runoff (b)in cropland
1.3 样品采集与测定

每年在玉米收获后,用直径5 cm的土钻在每个小区多点随机采集0~100 cm土样,每20 cm为一层,混匀并装在密封的塑料袋中,用于进一步分析。每年6月和10月小麦、玉米收获时采集一定面积植株样,风干、脱粒,计算籽粒和秸秆干物质量。在每次灌溉或降雨产流后测量渗滤液和径流水体积,并取100 mL水样放置于-20 ℃冰箱中冷冻保存,用于进一步分析。及时清空剩余的渗滤液和径流水,避免干扰下一次采样。

水样中的总氮用紫外分光光度计测定,可溶性总氮、硝态氮和铵态氮浓度用连续流动分析仪(AA3)分析。土壤含水率采用烘干法,土壤有机质采用重铬酸钾容量法,土壤全氮采用凯氏定氮法,土壤全磷采用H2SO4-HClO4消煮,有效磷采用0.5 mol·L-1 NaHCO3溶液浸提-钼锑抗比色法,硝态氮采用0.01 mol·L-1 CaCl2溶液浸提,连续流动分析仪(AA3)测定。作物收获后,用H2SO4-H2O2消煮,凯氏定氮法测定小麦、玉米籽粒和秸秆中全氮含量[20]

氮盈余(kg·hm-2)=施氮量+降雨氮输入量+灌溉氮输入量-(作物吸氮量+氮淋溶淋失量+氮径流流失量)

氮表观流失率(%)=氮淋失量(径流流失量)/施氮量×100%

水体氮损失排放强度(kg N·Mg-1)=(氮淋失量+氮径流流失量)/作物产量

氮淋失量计算公式:

式中:NL为总氮、可溶性总氮、硝态氮或铵态氮淋失总量,kg·hm-2n为淋溶发生次数;NLCi为总氮、可溶性总氮、硝态氮或铵态氮淋失浓度,mg·L-1Vi为每次淋溶发生时淋溶水体积,L;1.2为淋溶收集面积,m2

氮径流流失量计算公式:

式中:NR为总氮、可溶性总氮、硝态氮或铵态氮径流流失总量,kg·hm-2n为径流发生次数;NRCi为总氮、可溶性总氮、硝态氮或铵态氮流失浓度,mg·L-1Vi为每次径流发生时径流水体积,L;4.5为径流池面积,m2

1.4 数据处理与分析

运用Microsoft Excel 2016进行数据分析、处理和绘图,运用SPSS 22单因素方差分析进行显著性检验,LSD法进行均值比较。

2 结果与分析 2.1 作物产量

根据3 a的试验结果,CON与RF、RFM处理相比,小麦和玉米产量差异均不显著(P>0.05)(图 2),CON、RF、RFM 3个处理小麦年均产量分别为9 234、9 068、9022 kg·hm-2,玉米年均产量为9 701、9 555、9 822 kg·hm-2。适当减施化肥不会显著降低作物产量,且配施沼液能提高玉米产量。

图中小写字母的异同分别表示处理间在0.05水平是否存在显著差异。下同 The same or different lowercase letters in the figure indicate whether there is significant difference among treatments(P < 0.05). The same below 图 2 不同年份各施肥处理小麦和玉米籽粒产量 Figure 2 Grain yield of wheat and maize under different treatments in different years
2.2 农田氮素淋失浓度和淋失量变化

研究区域灌溉和降雨多发生在4—10月,该时段是淋溶发生的主要时期。在此期间,CON、RF和RFM处理的氮素流失浓度随月份增长而先增加后降低,其中7月和8月是最高时期。CON、RF和RFM处理的总氮浓度变化范围为2.00~109.64、3.35~70.55 mg·L-1和4.30~53.10 mg·L-1,平均值为33.70、23.10 mg·L-1和20.00 mg·L-1图 3)。与CON处理相比,RF和RFM处理平均总氮淋失浓度分别降低了31.45%和40.65%。总氮淋溶浓度峰值出现在施肥后发生灌溉或连续降雨的时期。CON处理淋溶水中总氮淋失浓度显著高于RF和RFM处理(P<0.05),其中,RFM处理降低氮淋溶效果最佳。

图 3 不同月份淋溶水总氮、可溶性总氮和硝态氮浓度变化 Figure 3 Dynamics of total nitrogen(TN), total dissolved nitrogen (TDN)and NO3--N concentration in leachate water during the different months

不同处理总氮、可溶性总氮和NO3--N淋失浓度变化趋向一致(图 3)。全年间淋溶水总氮、可溶性总氮和NO3--N呈现先增加后降低的趋势。7月和8月是氮素淋溶浓度最高的时期,且氮素浓度波动较大。7月,CON处理总氮、可溶性总氮和NO3--N平均浓度分别为68.47、60.12 mg·L-1和52.37 mg·L-1,均显著高于RF和RFM处理(P<0.05)。根据地下水质量标准(GB/T 14848—2017),仅有CON处理7月淋溶水NO3--N平均浓度超过30.00 mg·L-1,达到了Ⅴ类水标准,由此可见,化肥减量和化肥减量替代能够有效降低土壤NO3--N淋失风险。

CON处理总氮淋失量为22.01 kg·hm-2,显著高于RF和RFM处理(P<0.05)(图 4),和CON相比,RF和RFM处理总氮淋失量减少了30.58%和43.39%。CON处理的可溶性总氮和NO3--N淋失量均显著高于RF和RFM处理,而RF和RFM处理间无显著差异。和CON处理相比,RF和RFM处理可溶性总氮淋失量分别降低了30.70%和42.46%,NO3--N淋失量分别降低了34.46%和45.95%。各处理NH4+-N淋失量一直维持在一个较低的水平,且无显著差异。常规施肥极大增加了氮素淋失量,相较于化肥减量,化肥减量替代能更有效地降低氮素淋失量。

图 4 总氮、可溶性总氮、硝态氮和铵态氮年均淋失量 Figure 4 Average annual leaching of total nitrogen(TN), total dissolved nitrogen (TDN), NO3--N and NH4+-N

淋溶水中可溶性总氮占总氮淋失量的78.56%,NO3--N占总氮淋失量的66.31%,NH4+-N占总氮淋失量的0.83%(图 4)。淋溶水总氮主要为可溶态,NO3--N是总氮的主要淋失形态。

2.3 农田氮素径流浓度和流失量变化

3年研究期间地表径流产流次数仅为2次。在产流前两周内分别有3次和4次降雨,多次的降雨导致土壤水处于饱和状态,促使径流产生。在第一次产流时,CON处理总氮浓度显著高于RF和RFM处理(P<0.05)。而在第二次产流时,由于降雨量较小,且远离施肥期,各处理径流水中总氮浓度无显著差异。

全年仅有7月产生了径流,且氮素浓度波动较大(图 5)。7月,CON处理总氮、可溶性总氮和NO3--N平均浓度分别为23.03、19.99 mg·L-1和17.60 mg·L-1,均高于RF和RFM处理。与CON处理相比,RF和RFM处理总氮、可溶性总氮和NO3--N平均浓度分别降低了32.90%和45.50%、30.10%和44.80%、30.50%和47.00%。

图 5 不同月份径流水中总氮、可溶性总氮、硝态氮浓度变化 Figure 5 Dynamics of total nitrogen(TN), total dissolved nitrogen (TDN)and NO3--N concentration in runoff water during the different months

CON、RF和RFM处理总氮径流损失量分别为0.10、0.07 kg·hm-2和0.05 kg·hm-2图 6),化肥减量替代降低了总氮流失量。其中可溶性总氮、NO3--N和NH4+-N分别占总氮流失量的86.60%、73.30%和5.01%。NO3--N是径流水中氮素流失的主要形态。

图 6 土壤总氮、可溶性总氮、硝态氮和铵态氮年均径流损失量 Figure 6 Average annual runoff loss of total nitrogen(TN), total dissolved nitrogen (TDN), NO3--N and NO4+-N in soil
2.4 农田不同施氮处理淋溶、径流氮损失的比例和氮素平衡

CON、RF和RFM处理氮淋溶表观流失率分别为4.19%、4.07%和3.32%(图 7),氮径流表观流失率分别为0.02%、0.02%和0.01%,化肥减量替代降低了氮素流失。氮淋溶和径流表观流失率分别为3.86%和0.02%,与径流相比,淋溶是氮素流失的主要途径。CON、RF和RFM处理水体氮排放强度分别为1.17、0.82 kg N·Mg-1和0.66 kg N·Mg-1图 7)。化肥减量和化肥减量替代显著降低了水体氮排放强度,其中以化肥减量替代效果最为显著,降低了43.59%。

图 7 不同处理淋溶、径流氮表观流失率和水体氮排放强度 Figure 7 Apparent nitrogen loss ratio of leaching and runoff, and nitrogen emission intensity via (leaching and runoff)water of different treatments

化肥是农田氮素输入的主要来源,灌溉和降雨分别占农田氮输入的5.69%~12.74%和0.65%~7.46%(图 8)。作物吸氮量为296~396 kg·hm-2,是农田氮素输出的主要形式,占总氮输入的54.95%~83.63%。氮淋溶占总氮输出的1.21%~9.88%,而氮径流流失最高占比仅为0.04%。作物携出是农田氮素主要输出方式,但各处理间并无显著差异。CON、RF和RFM处理年平均氮盈余量分别为218.06、72.56 kg·hm-2和96.20 kg·hm-2,CON处理显著增加了土壤氮盈余量。与CON处理相比,RF和RFM处理土壤氮盈余分别降低了66.72%和55.88%(P<0.05)(图 8)。相较于RF和RFM,CON处理呈现出更高的氮淋溶和径流流失风险。

图 8 不同年份农田氮素输入和输出量变化 Figure 8 Changes of nitrogen input and output in cropland in different years
3 讨论 3.1 化肥减量配施沼液对作物产量的影响

本研究中常规施肥处理与减量施肥处理相比,小麦和玉米产量并没有显著变化,但前者盈余量远高于后者。这一结果表明,区域施肥不合理条件下,适当降低肥料投入可以保证作物产量,降低氮盈余量[6, 21]。化肥的施用量远超作物需求量,不仅对作物产量增加无益处,还会大幅增加土壤中氮的盈余,造成氮资源浪费[22]。本研究发现,与单施化肥相比,沼液与化肥配施增加了玉米产量,但效果并不显著,这与有机肥的替代比例有关[23]。王桂良等[11]研究指出,用沼液替代30%的化肥氮未能显著提高小麦产量,且随着沼液替代量的增加,小麦产量呈现先增加后降低的趋势。也有研究表明[24]沼液替代50%化肥并未显著增加作物产量。合适的有机肥替代量应取决于土壤肥力,肥力较贫瘠的土壤,应采用较低的有机替代比例,以满足作物对养分的即时需求,减少微生物生长繁殖所消耗的养分;肥力较高的土壤,可采用较高的有机肥替代比例,以提高土壤微生物活性,活化土壤养分,同步提高作物产量和土壤肥力[25]

3.2 化肥减量配施沼液对土壤氮素流失和氮平衡的影响

地表径流和地下淋溶是农田氮素流失的两个主要途径。灌溉和降雨是促使土壤产生淋溶和径流的主要驱动力,连续强降雨更易增加淋溶水中氮素浓度,加大氮素流失[26-28]。肥料氮是氮素流失的物质基础,施肥量的高低是造成氮素流失量大小的重要因素[29-32]。例如,王立刚等[33]在山东桓台的研究结果指出,当氮肥投入量高于300 kg·hm-2时作物产量不再增加,但氮淋失量却急剧升高。高施肥量引起氮素流失量增加主要是由于氮肥大量投入到农田后,未被植物吸收利用的氮素残留在土壤中,在干旱地区经过硝化作用,使得残留在土壤中的无机氮多以NO3--N的形式存在,极易随土壤水向下迁移[16]。本研究在目前华北平原常规施氮量基础上,小麦和玉米季氮肥分别减施75 kg·hm-2下,实现了总氮淋失量降低30.58%,淋溶液和径流水中的总氮浓度也分别显著降低了31.45%和32.92%。本研究各处理间淋溶水量并无显著差异,进一步表明合理的施肥管理措施是降低氮淋失的主要途径。

虽然地下淋溶和地表径流是氮随水流失的两个主要途径,但是由于本研究所处华北平原,研究区内仅有2017年作物生育期年降雨量超过了450 mm,且单次降雨强度较弱,因此区域内地表径流发生几率较低[34-35]。研究期间,试验区3年仅产生了2次径流,与径流相比,淋溶是该地区氮素流失的主要途径。常规施肥处理氮年均淋失量为22.01 kg·hm-2,表观淋失率为4.19%,显著高于径流损失。Ju等[36]的研究也得出了相似的结论,其指出华北平原小麦季氮素在1 m土层中的淋失率约为2.7%,玉米季约为12.1%。

相较于化肥减量,化肥减量替代能进一步有效降低总氮流失量[37-40]。已有研究表明,商品有机肥配施能显著降低土壤总氮和硝态氮的淋失,且随着有机肥配施比例的增加,土壤氮淋失量明显下降[40]。这可能是由于有机肥中含有的微生物等在作物生长初期可以固定施入土壤中的盈余氮素,并在作物生长中后期通过矿化作用再将氮释放,从而减少了硝态氮向深层土壤的淋失[41]。本研究使用的是沼肥,替代比例为10%,在此替代比例下,沼肥替代处理仍较等量化肥处理总氮淋失量减少了18.49%,表观流失率降低了18.43%。沼肥施入土壤后,其所带入的水分、铵态氮和总氮主要集中于0~5 cm表层土壤,在深层土壤中并无显著差异[42],且沼肥施入提高了生育期土壤固氮菌的数量,有助于减少氮流失[43]。Du等[15]研究表明,沼液中含有大量的铵态氮和可以矿化为铵态氮的有机氮复合化合物,因此沼液替代化肥可减少土壤氮素淋失率,但不同的替代比例效果不同。由于沼液中氮的形态主要是铵态氮,沼液替代化肥施入农田后,在降低氮淋溶的同时可能会提高农田氨挥发的排放量[10],且沼液配施增加了土壤水分含量,可能对氮的反硝化有促进作用[44]。如黄红英等[45]研究指出,沼液全量替代提高了农田N2O排放量。此外还需注意沼液大量还田所带入的抗生素以及重金属污染等问题[46]

4 结论

(1)淋溶是华北平原氮素流失的主要途径。氮素流失的主要形态是硝态氮,分别占淋溶和径流总氮流失量的66.31%和73.33%。

(2)根据作物氮素需求适当降低化肥氮投入可以在保证作物产量的同时显著降低氮素流失的环境风险。

(3)在一些养殖集中区域,在减施化肥的基础上适当进行化肥替代,可进一步降低氮素流失造成的环境风险。而合理的沼液替代比例是保证作物产量和管控环境风险的关键,也是未来进一步探究的重点。

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