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  土壤学报  2021, Vol. 58 Issue (6): 1496-1506  DOI: 10.11766/trxb202003150119
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黄婷苗, 王朝辉, 黄倩楠, 等. 黄淮麦区小麦籽粒锌含量差异原因与调控. 土壤学报, 2021, 58(6): 1496-1506.
HUANG Tingmiao, WANG Zhaohui, HUANG Qiannan, et al. Causes and Regulation of Variation of Zinc Concentration in Wheat Grains Produced in Huanghuai Wheat Production Region of China. Acta Pedologica Sinica, 2021, 58(6): 1496-1506.

基金项目

国家现代农业产业技术体系建设专项（CARS-3）和国家重点研发计划项目（2018YFD0200400）资助

通讯作者Corresponding author

王朝辉, E-mail: w-zhaohui@263.net

作者简介

黄婷苗(1990-), 女, 山西运城人, 博士研究生, 主要从事小麦锌营养研究。E-mail: huangtingmiao@126.com
Contents              Abstract              Full text              Figures/Tables              PDF
黄淮麦区小麦籽粒锌含量差异原因与调控
黄婷苗1,3, 王朝辉1,2, 黄倩楠1,2, 侯赛宾1,2    
1. 西北农林科技大学资源环境学院, 陕西杨凌 712100;
2. 西北农林科技大学旱区作物逆境生物学国家重点实验室, 陕西杨凌 712100;
3. 山西农业大学农学院, 山西太谷 030800
收稿日期：2020-03-15；收到修改日期：2020-06-13；优先数字出版日期(www.cnki.net)：2020-08-26
基金项目：国家现代农业产业技术体系建设专项（CARS-3）和国家重点研发计划项目（2018YFD0200400）资助
作者简介：黄婷苗(1990-), 女, 山西运城人, 博士研究生, 主要从事小麦锌营养研究。E-mail: huangtingmiao@126.com.
通讯作者Corresponding author：王朝辉, E-mail: w-zhaohui@263.net.
摘要：小麦高产优质生产对保障我国粮食安全和人们营养健康有重要意义。通过实地调研和取样分析，研究了黄淮麦区276个田块的小麦籽粒锌含量与产量和产量构成、施肥和土壤养分、作物锌吸收利用等参数的关系。结果表明，黄淮麦区缺锌和非缺锌土壤的比例分别为42%和58%，两种土壤上的小麦籽粒锌含量分别介于16~52和17~58 mg·kg-1，分别有7%和9%样本的籽粒锌达到推荐值40 mg·kg-1。缺锌田块，籽粒锌含量与磷肥用量（r=-0.273，P < 0.01）、0~20 cm土壤有效磷（r=-0.283，P < 0.01）显著负相关，高低籽粒锌组的磷肥用量分别为73和137 kg·hm-2，土壤有效磷分别为13和20 mg·kg-1，有效锌分别为0.8和0.7 mg·kg-1，但籽粒产量低于非缺锌土壤（7 204和7 857 kg·hm-2）。非缺锌田块，籽粒锌含量与磷肥用量显著负相关（r=-0.181，P < 0.05），与0~20 cm（r=0.236，P < 0.01）和20~40 cm（r=0.183，P < 0.05）土壤有效锌显著正相关，高低锌组的磷肥用量分别为112和145 kg·hm-2，0~20 cm的土壤有效磷分别为29和30 mg·kg-1，有效锌分别为3.3和2.2 mg·kg-1。因此，在缺锌土壤上，应首先解决土壤缺锌问题，将有效锌提升至临界值1.0 mg·kg-1以上，非缺锌土壤有效锌保持在3.0 mg·kg-1以上，同时适当减少磷肥用量和降低土壤有效磷水平，以减少磷对小麦锌吸收的负面影响，维持黄淮麦区小麦高产并改善籽粒锌营养。
关键词：籽粒锌含量    产量    肥料用量    土壤养分    调控措施    
Causes and Regulation of Variation of Zinc Concentration in Wheat Grains Produced in Huanghuai Wheat Production Region of China
HUANG Tingmiao1,3, WANG Zhaohui1,2, HUANG Qiannan1,2, HOU Saibin1,2    
1. College of Natural Resources and Environment, Northwest A&F university, Yangling, Shaanxi 712100, China;
2. State Key Laboratory of Crop Stress Biology in Arid Area, Northwest A&F University, Yangling, Shaanxi 712100, China;
3. College of Agronomy, Shanxi Agricultural University, Taigu, Shanxi 030800, China
Foundation item: Supported by the Modern Agricultural Research System of China (No. CARS-3) and the National Key Research and Development Program of China (No. 2018YFD0200400)
Abstract: 【Objective】China nowadays has approximately 100 million people suffering from zinc (Zn) deficiency, mainly because they live on cereal crops as their staple food and hence fail to take in adequate Zn, especially in the rural areas. As one of the major wheat-producing areas, the Huanghuai Plain contributes to about 70% of the wheat (Triticum aestivum L.) grain yield of China. So it is of great significance to understand causes of the variation of Zn concentration in wheat grains to guaranteeing high-yield and high-quality wheat production in the region, so as to ensure food security and human health.【Method】Combined with a two-year in situ farm survey, samples of wheat shoot (the aboveground part) and soil in the 0~100 cm layer were collected from 276 randomly selected farmers' fields during the wheat harvesting season in the Huanghuai wheat production region for analysis of Zn concentration. Comparison was made between wheat grains produced in Zn-deficient (DTPA-Zn < 1.0 mg·kg-1) and non-Zn-deficient (DTPA-Zn ≥ 1.0 mg·kg-1) soils in grain Zn concentration and correlation analysis performed of grain Zn concentration with grain yield, yield components, fertilization rates, soil nutrients in the 0-100 cm layer, and Zn uptake and utilization of the crop, separately.【Result】Results show that 42% and 58% of the wheat fields in the region were of Zn-deficient (DTPA-Zn < 1.0 mg·kg-1) and non-Zn-deficient (DTPA-Zn ≥ 1.0 mg·kg-1) soils, and produced grains with Zn concentration ranging from 16 to 52 mg·kg-1 and from 17 to 58 mg·kg-1, respectively. About 7% and 9% of the grain samples from the two types of wheat fields met the recommended criterion (≥ 40 mg·kg-1) for grain Zn concentration. Generally, the farmers in the region prefer to grow local specific elite cultivars of wheat, however, it was difficult to identify high-Zn or potentially high-Zn traits of the cultivars due to the limited sample size at a regional scale. In this survey, the selected wheat fields did not receive any Zn fertilizer or other Zn-containing fertilizers, and only 10% and 18% of the fields of Zn-deficient soil and non-Zn-deficient soil were applied with organic manure. In the fields of Zn-deficient soils, grain Zn concentration had nothing to do with nitrogen (N) and potassium (K) fertilization rates, but did negatively, with phosphorus (P) fertilization rate (r=-0.273, P < 0.01) and available P in the 0-20 cm soil layer (r=-0.283, P < 0.01). In the two groups of wheat fields, high and low in grain Zn concentration, with soil available P being 13 and 20 mg·kg-1, and available Zn being 0.8 and 0.7 mg·kg-1 in 0-20 cm soil, P2O5 fertilizer was applied at 65.8 and 68.4 kg·hm-2to achieve targeted grain yield. Also, the grain yield and shoot Zn uptake were observed to be lower in the fields of Zn-deficient soils(7 204 kg·hm-2 and 279 g·hm-2) than in the fields of non-Zn-deficient soils (7 857 kg·hm-2 and 318 g·hm-2). In the fields of non-Zn-deficient soils, grain Zn concentration had nothing to do with N and K fertilization rates, either, but was negatively related to P fertilization rate (r=-0.181, P < 0.05) and positively to soil available Zn in the 0-20 cm (r=0.236, P < 0.01) and 20-40 cm (r=0.183, P < 0.05) soil layers. In the two groups of wheat fields of Zn-deficient and non-Zn-deficient soils, with available P being 29 and 30 mg·kg-1, and available Zn being 3.3 and 2.2 mg·kg-1 in the 0-20 cm soil layer, P fertilizer was applied at a rate of 112 and 145 kg P2O5·hm-2, respectively, and P2O5 requirement for targeted average grain yield reached 69.2 and 70.8 kg·hm-2, respectively.【Conclusion】Therefore, it could be considered that it is advisable to address the problem of lack of available soil Zn first, by increasing the content of soil available Zn up to the critical values of 1.0 and 3.0 mg·kg-1 in the fields of Zn-deficient and non-Zn-deficient soils, respectively, and then to reduce P fertilizer application rate and hence available soil P content, so as to alleviate the negative effect of excessive P on crop Zn uptake and accumulation, for the purpose of maintaining high grain yield and improving grain Zn nutrition simultaneously in winter wheat grown in the Huanghuai wheat production region of China.
Key words: Grain Zn concentration    Grain yield    Fertilizer rates    Soil nutrients    Regulation measures    

黄淮麦区是我国粮食主产区，小麦种植面积约1 100万hm2，占我国小麦总面积的44%[1]。长期以来受“施肥越多，产量越高”观念影响，过量施用化学肥料不仅造成了土壤养分残留，施肥的增产效应下降，还导致作物营养品质降低[2-3]。锌是人体必需的微量营养元素，全球10%~32%人口遭受锌营养失调威胁，以发展中国家和农村人口更为严重[4]。我国以谷物为主食的人群锌摄取量不足，约1亿人口锌营养不良[5]。满足人体正常营养需求的小麦籽粒锌含量应达到40~60 mg·kg-1[6]，而2009—2011年对我国小麦主产区调研表明，黄淮麦区的小麦籽粒锌含量平均为30 mg·kg-1[7]，亟待改善和提高。

一般认为，籽粒锌不足应归于较低的土壤供锌水平[8]。有效锌缺乏时，作物减产、锌吸收降低，富锌品种小麦锌积累也会受阻[9-10]。根据土壤有效锌分级标准，有效锌含量低于1.0 mg·kg-1为缺锌或潜在性缺锌土壤，高于1.0 mg·kg-1为非缺锌土壤[11]。在黄淮麦区，北京的田间试验发现，有效锌为2.2 mg·kg-1的石灰性冲积土上，氮肥用量从0增加至130 kg·hm-2时，小麦籽粒锌含量由17 mg·kg-1增至27 mg·kg-1，施氮量为300 kg·hm-2时，籽粒锌含量不再增加，为29 mg·kg-1[12]。山东有效锌为1.5 mg·kg-1砂壤土的田间试验中，不同氮肥用量的小麦籽粒锌含量介于47.5~52.2 mg·kg-1[13]。河北石灰性冲积土有效锌为0.4 mg·kg-1时，低施磷处理的小麦籽粒锌含量也会达40 mg·kg-1[14]。河南安阳265个小麦品种的试验表明，籽粒锌含量存在较大变异，介于21.4~58.2 mg·kg-1[15]。说明除了土壤有效锌，其他因素也可能对籽粒锌含量的变异起决定作用，而其他因素的作用是否会因土壤有效锌水平而异尚不明确。

本研究依托分布于黄淮麦区的28个国家小麦产业技术体系综合试验站，开展了农户小麦锌含量与栽培施肥和土壤养分关系研究，以期明确在缺锌和非缺锌土壤上小麦籽粒锌含量变异及原因，探讨不同土壤上小麦籽粒锌含量的调控措施，为区域小麦高效优质生产提供依据和参考。

1 材料与方法 1.1 研究区域概况

黄淮冬麦区主要包括山东全部、河南中北部、河北中南部、江苏和安徽淮北地区以及陕西、山西、甘肃三省部分地区。该区夏季降水集中，雨热同期，为温带湿润半湿润季风气候，年均温11~14℃、降水570~1 000 mm。冬小麦-夏玉米轮作是主要的粮食作物种植制度，一年两熟。小麦、玉米秸秆均还田。小麦季一般灌水1~4次，农户种植的小麦品种为当地推荐的主栽品系。土壤类型以黄潮土为主，部分为黄土和棕壤，壤土和砂壤土质地为主。0~20 cm土层土壤的基本理化性状如表 1。

表 1 黄淮麦区0~20 cm土层土壤的基本理化性状（n = 276） Table 1 Basic soil physicochemical properties in the 0-20 cm soil layer in the Huanghuai wheat production region of China(n = 276)
1.2 样品采集与处理

在2014—2015年和2015—2016年两个小麦生长季，分别选择代表性农户地块128和148个，包括126个小麦品种。采用问卷调查获得所选地块的肥料用量、小麦品种、种植模式等信息。其中，施有机肥的田块均折合成氮、磷、钾纯养分计入肥料用量。小麦收获时，每个田块选择10 m × 5 m长势均匀的区域作为采样区。在样区内随机选择三个有代表性的1 m2样方，测定穗数，并随机采集包含100个穗的小麦全株[16]，剪除根系，地上部秸秆和穗作为考种和化学分析样品，风干后脱粒。分取籽粒、秸秆和颖壳样品30~40 g，快速用自来水和去离子水冲洗三次，于65℃烘干至恒重，计算风干样品含水量。测定小麦千粒重，计算穗粒数和收获指数。烘干的植物样品用碳化钨研磨罐的球磨仪（MM400，德国）研细混匀，密封待测。籽粒、秸秆（包括茎叶、颖壳和穗轴）生物量和千粒重均以烘干质量表示。

在采样区的小麦行间，随机选择三个样点，20 cm为一层，用不锈钢土钻采0~100 cm的土壤样品，同层的土样捏碎混匀，取500 g作为分析样品。风干后，研磨过1 mm尼龙筛，用于测定土壤pH、硝态氮和铵态氮、有效磷、速效钾和有效铁、有效锰、有效铜、有效锌含量；研磨过0.15 mm尼龙筛，用于分析土壤有机质和全氮。

1.3 样品测定

植株样品用浓HNO3-H2O2微波消解，电感耦合等离子体质谱仪ICP-MS（iCAP Qc，美国）测定锌含量。以小麦粉国家标准物质（GWB10011，GSB-2）监控消解、测定过程质量。

土壤pH采用2.5：1水土比、pH计（PHS-3C，雷磁，上海）测定；1 mol·L-1 KCl浸提、高分辨连续流动分析仪（AA3，SEAL，德国）测定硝态氮、铵态氮含量；0.5 mol·L-1的NaHCO3浸提、连续流动分析仪测定有效磷；1 mol·L-1的NH4OAc浸提、火焰光度计（Model 410，Sherwood，英国）测定速效钾；有效铁、有效锰、有效铜、有效锌用pH 7.30的二乙三胺五乙酸-氯化钙-三乙醇胺（DTPA- CaCl2-TEA）浸提、原子吸收分光光度计（Z-2000，Hitachi，日本）测定；有机质用K2Cr2O7-H2SO4氧化法测定；全氮用浓H2SO4加混合催化剂消煮、连续流动分析仪测定。

1.4 数据计算与分析

籽粒产量以三要素的乘积表示，锌吸收量和锌收获指数计算公式如下：

籽粒（秸秆）锌吸收量/（g·hm–2） = 籽粒（秸秆）生物量/（kg·hm–2）×籽粒（秸秆）锌含量/（mg·kg–1） /1 000

锌收获指数/%= 籽粒锌吸收量 /（籽粒锌吸收量+秸秆锌吸收量）×100

为了便于土壤锌营养调控与管理，根据0~20 cm土层的有效锌含量将调研田块划分为缺锌土壤（DTPA-Zn < 1.0 mg·kg-1）和非缺锌土壤（DTPA-Zn≥1.0 mg·kg-1）两类[11]。两类土壤间的差异用独立样本成组数据t检验分析；缺锌、非缺锌土壤，不同指标与籽粒锌含量的关系用皮尔森（Pearson）相关系数表示，显著性水平设为0.05。所有分析均用统计软件SPSS 21.0完成。

2 结果 2.1 黄淮麦区小麦籽粒锌含量

黄淮麦区土壤缺锌和非缺锌的田块比例分别为42%和58%。分析表明（图 1），缺锌田块籽粒锌含量介于16~52 mg·kg-1，平均为29 mg·kg-1，7%的样本籽粒锌达到满足人体锌营养需求的40~60 mg·kg-1推荐值。非缺锌田块，籽粒锌含量介于17~58 mg·kg-1，平均为30 mg·kg-1，9%的样本超过40 mg·kg-1。黄淮麦区小麦籽粒锌含量平均为30 mg·kg-1。

图 1 黄淮麦区缺锌（a））和非缺锌（b））土壤的小麦籽粒锌含量频率分布 Fig. 1 Frequency distributions of wheat grain Zn concentration in wheat fields of Zn-deficient soils(a))and non-Zn-deficient soils(b))investigated in the Huanghuai wheat production region of China
2.2 小麦产量和锌吸收利用与籽粒锌关系

分析表明，土壤缺锌与否影响小麦籽粒产量和地上部锌吸收（表 2）。与非缺锌田块相比，缺锌田块的籽粒产量和收获指数分别降低9%和3%，籽粒和秸秆锌吸收分别降低13%和10%。相关分析表明，无论缺锌还是非缺锌田块，小麦籽粒锌含量与籽粒、秸秆锌吸收量均呈极显著正相关关系（P < 0.01），与产量、秸秆生物量、产量构成及锌收获指数无显著相关。

表 2 黄淮麦区缺锌和非缺锌土壤的小麦产量、产量构成、锌吸收利用及其与籽粒锌含量的关系（n = 276） Table 2 Grain yield, yield composition, and Zn uptake and utilization of the wheat crop and their relationships with grain Zn concentration relative to soil Zn levels(deficient and non-deficient)in the Huanghuai wheat production region of China(n = 276)
2.3 肥料用量与籽粒锌关系

调研区域均未施用锌肥，缺锌、非缺锌田块，分别有10%和18%的农户施用了有机肥。回归分析表明，两类土壤的籽粒锌含量均随磷肥用量增加明显下降，而与氮钾肥用量无关（图 2）。缺锌田块，平均氮、磷、钾肥用量分别为241、128和78 kg·hm-2，磷肥用量为69~203 kg·hm-2时，籽粒锌含量介于（27.6±13.0）~（30.3±13.0）mg·kg-1。非缺锌田块，平均氮、磷、钾肥用量分别为224、135和80 kg·hm-2，磷肥用量为80~214 kg·hm-2时，籽粒锌含量介于（28.2±14.0）~（30.9±14.0）mg·kg-1。

注：NS，不显著，下同。  Note: 'NS' means no significant. The same below. 图 2 黄淮麦区缺锌（a）~ c））和非缺锌（d）~ f））土壤小麦籽粒锌含量与氮、磷、钾肥用量的关系 Fig. 2 Relationships of grain Zn concentration with N, P and K fertilization rates in fields of Zn-deficient soils(a)-c))and non-Zn-deficient soils(d)-f))investigated in the Huanghuai wheat production region of China
2.4 土壤养分与籽粒锌关系

分析表明（图 3），决定小麦籽粒锌含量变异的主要土壤养分因土壤锌情况而异。相关分析发现，缺锌田块，籽粒锌含量与0~20 cm有效磷极显著负相关，与60~80 cm铵态氮显著正相关；回归分析表明，0~20 cm土壤有效磷为5.5~34 mg·kg-1时，籽粒锌含量介于（26.1±11.8）~（30.6±11.8）mg·kg-1（图 4a））。非缺锌田块，籽粒锌含量与0~40 cm有效锌和0~20 cm有效铁均呈显著正相关关系；回归分析表明，0~20 cm土壤有效锌为1.1~4.9 mg·kg-1时，籽粒锌含量介于（28.9±13.8）~（32.7±13.8）mg·kg-1（图 4b））。

图 3 黄淮麦区缺锌（a））、非缺锌（b））土壤的小麦籽粒锌含量与0~100 cm土壤养分的简单相关关系 Fig. 3 Pearson correlations between grain Zn concentration and soil nutrients in the 0-100 cm soil layers in the fields of Zn-deficient soils(a))and non-Zn-deficient soils(b))investigated in the Huanghuai wheat production region of China

图 4 黄淮麦区缺锌土壤0~20 cm有效磷与籽粒锌含量（a））及非缺锌土壤0~20 cm有效锌与籽粒锌含量（b））的关系 Fig. 4 Relationships of grain Zn concentration with soil available P(a))and Zn(b))in the 0-20 cm soil layer of the fields of Zn-deficient and non-Zn-deficient soils investigated in the Huanghuai wheat production region of China, respectively
3 讨论 3.1 黄淮麦区小麦籽粒锌含量变异

在黄淮麦区，无论是缺锌还是非缺锌土壤，小麦籽粒锌含量均存在较大变异（图 1），与伊朗、塞尔维亚和我国黄土高原等地的结果类似[17-19]，两种土壤上，分别有7%和9%的样本籽粒锌达到满足人体锌营养需求的40 mg·kg-1。调研中，农户小麦种植并不施用锌肥，说明通过合理的农艺措施调控，即使不施锌肥，也可使小麦籽粒锌含量提高至目标需求值。两种土壤上的小麦籽粒锌含量均与产量无关（表 2），可见“产量稀释”效应或者不存在，或者被其他因素的作用削弱，在实际生产中它并不是改善农户小麦籽粒锌营养的限制因素。品种也可能是籽粒锌含量变异的一个因素。虽然调研区域农户种植的品种繁多，且多为当地主栽品种，但相同品种出现频次有限，如种植最广泛的济麦22，在缺锌、非缺锌田块出现的次数分别为11和20，多数品种不足三次，较少的样本量限制了品种对籽粒锌贡献的分析，同时也从另一方面说明田间管理、土壤条件等对改善区域小麦籽粒锌营养的重要性。因此，施肥和土壤养分引起的作物锌吸收利用差异应得到重视。

3.2 缺锌土壤的籽粒锌含量变异原因及调控

缺锌田块，籽粒锌含量与磷肥用量、0~20 cm的土壤有效磷显著负相关。说明较高的磷肥投入和表层土壤有效磷是该地区小麦籽粒锌含量低的主要原因。大量研究表明，磷肥施用会降低根系锌吸收、锌由根系向地上部转移以及菌根侵染，进而诱导作物缺锌，降低籽粒锌含量[20-21]。在河北曲周有效锌为0.4 mg·kg-1的石灰性冲积土上，纯磷施用量由0增加至100 kg·hm-2时，小麦籽粒锌含量由46 mg·kg-1降低至23 mg·kg-1[22]，相应的表层土壤有效磷从4 mg·kg-1增加至31 mg·kg-1[14]。本研究中，缺锌田块0~20 cm土壤有效磷平均为18 mg·kg-1（图 4），高于优化作物生长所需的适宜范围11~15 mg·kg-1[23-24]，平均磷肥用量128 kg·hm-2，也高于当地定位试验推荐的最佳磷肥用量114 kg·hm-2[25]。因此，在保障小麦不减产的前提下，应适当减少磷肥投入，降低土壤有效磷，改善小麦锌营养。

需注意的是，本研究中小麦籽粒锌含量与土壤有效锌无关，而与地上部锌吸收呈显著正相关（表 2）。小麦籽粒锌来源于土壤锌，但即使在土壤锌缺乏的情况下，还会有其他因素促使小麦吸收了更多的锌，以提高其籽粒锌含量。除了品种外，氮肥的投入可能是另外一个重要原因。黄土高原缺锌土壤上，氮肥用量由0增加至320 kg·hm-2时，小麦籽粒锌含量从22 mg·kg-1增加至35 mg·kg-1，地上部锌吸收由127 g·hm-2增至243 g·hm-2[26]。华北平原石灰性缺锌土壤的研究也表明，氮肥用量由0增至300 kg·hm-2时，小麦根系和地上部锌吸收分别增加了108%和304%，籽粒锌含量由26 mg·kg-1增加至36 mg·kg-1[27]。黄淮麦区，农户施氮量普遍较高，平均241 kg·hm-2。充足的氮营养可增强小麦锌吸收和锌在韧皮部的移动，进而增加籽粒锌的累积[28-29]。

可见，对于缺锌田块，降低磷肥投入和土壤有效磷是提高籽粒锌含量的主要措施。为调控籽粒锌至目标值，将籽粒锌含量高于40 mg·kg-1的样本定为高锌组，低于平均值（29 mg·kg-1）的定为低锌组（图 5）。低、高锌组的小麦平均籽粒锌含量分别为24和45 mg·kg-1，籽粒产量为7 267和7 669 kg·hm-2，施磷量137和73 kg·hm-2，土壤有效磷20和13 mg·kg-1，有效锌0.7和0.8 mg·kg-1。可见，改善缺锌土壤的小麦籽粒锌营养，不会以牺牲产量为代价，且两组平均产量对应的需磷（P2O5）量分别为65.8和68.4 kg·hm-2[30]，与高锌组的施磷量73 kg·hm-2接近。因此，应减少当前较高的磷肥投入，使与作物从土壤带走的磷量保持一致。黄淮麦区约有42%的田块为缺锌土壤，土壤有效锌的差异虽然不能解释籽粒锌变异（图 3），但与非缺锌土壤相比，缺锌土壤的小麦产量确实降低（表 2）。说明减施磷肥的同时，也应解决土壤缺锌问题，补施锌肥或有机无机配施等[31-32]，使缺锌田块的有效锌至少先提升至临界值1.0 mg·kg-1以上，以实现小麦增产提锌。

注：L-Zn，低锌组为籽粒锌含量低于平均值的样本，H-Zn，高锌组为籽粒锌含量高于40 mg·kg-1的样本。误差线为均数标准误；*表示低高锌组的差异达5%显著水平，NS代表两组间差异不显著，下同。  Note: 'L-Zn' means grain samples lower than the mean value in Zn concentration in the group of fields of Zn-deficient soils, and 'H-Zn', those higher than 40 mg·kg-1 in Zn concentration in the group of fields of non-Zn-deficient soils. Error bars are standard deviations of the means. The symbols of * and NS represents significant difference and insignificant difference between the low and high Zn groups by t-test at 0.05 level, respectively. The same below. 图 5 缺锌田块低高锌组的籽粒锌含量（a））、籽粒产量（b））、磷用量（c））、土壤有效磷（d））和有效锌（e）） Fig. 5 Grain Zn concentration(a)), grain yield(b)), P fertilization rate(c)), and soil available P(d))and Zn(e))in the fields relative to soil Zn levels
3.3 非缺锌土壤的籽粒锌含量变异原因及调控

研究表明，黄淮麦区58%的田块属于非缺锌土壤。非缺锌田块，籽粒锌含量与磷肥用量显著负相关、而与土壤有效磷无关。土壤有效锌为2.3~2.4 mg·kg-1的盆栽试验中，磷供应从20 μmol·L-1增加至500 μmol·L-1时，小麦籽粒产量增加了113%，锌含量降低了38%[33]。华北平原农户施磷肥常过高[34]，本调研中磷肥用量介于0~518 kg·hm-2，平均为135 kg·hm-2，籽粒产量7 857 kg·hm-2，土壤有效磷高达29 mg·kg-1，已是小麦生长最佳土壤有效磷范围的近2倍[23-24]。说明过高的磷供应已成为抑制小麦锌吸收的根本原因。多数关于磷锌互作的田间研究主要集中于缺锌土壤[21，35-36]，对非缺锌土壤的磷锌作用机理有待进一步探索。再者，本研究中，小麦籽粒锌含量与土壤有效锌、地上部锌吸收均呈显著正相关（图 3b，表 2），证明在施磷过高、土壤有效磷也过高的非缺锌土壤，较高的土壤有效锌对小麦籽粒锌含量提高亦重要。河北小麦-玉米轮作体系连续三年施用锌肥的试验表明，小麦籽粒锌含量与土壤有效锌呈线性-平台的关系，当有效锌高于7.57 mg·kg-1时，籽粒锌含量不再增加，保持在53.6 mg·kg-1[37]。本研究中，非缺锌田块0~20 cm土壤的有效锌介于1.0~9.8 mg·kg-1，多数农田有效锌仍低于7.57 mg·kg-1（图 4b）。墨西哥黏壤土的有效锌高达9.55 mg·kg-1时，不会出现作物生长受阻和环境风险[38]，同样，河北石灰性土壤连续8年施锌的研究也表明，合理锌肥用量（5.7 kg·hm-2）明显改善籽粒锌营养的同时，不会引起其他重金属元素（如Cu、Cd、Pb、Cr、As）积累带来的健康风险[39]。因此，在黄淮麦区，降低磷肥用量和土壤有效磷含量，提高土壤有效锌，对改善小麦籽粒锌营养非常重要。

同样，将籽粒锌含量高于40 mg·kg-1的样本定为高锌组，低于平均值30 mg·kg-1的定为低锌组（图 6）。在非缺锌土壤上，低、高锌组的小麦籽粒锌含量分别为25和46 mg·kg-1，籽粒产量为7 840和7 189 kg·hm-2，磷肥用量145和112 kg·hm-2，土壤有效磷30和29 mg·kg-1，有效锌2.2和3.3 mg·kg-1（图 6），说明可在不减产的前提下，提高非缺锌田块的小麦籽粒锌含量。两组平均产量对应的需磷（P2O5）量分别为69.2和70.8 kg·hm-2[30]，低于农户施磷量。因此，在非缺锌土壤上，更需减少磷肥用量，因有效磷过高，有效锌成了决定小麦籽粒锌的主要因素（图 3），降低磷肥用量的同时，也应注重土壤有效锌的提高，如提倡施用锌肥或配施有机肥等[40-41]，保持有效锌在3.0 mg·kg-1以上。

图 6 非缺锌田块低高锌组的籽粒锌含量（a））、籽粒产量（b））、磷用量（c））、土壤有效磷（d））和有效锌（e）） Fig. 6 Grain Zn concentration(a)), grain yield(b)), P fertilization rate(c)), and soil available P(d))and soil available Zn(e))in the fields relative to soil Zn levels
4 结论

黄淮麦区农田土壤缺锌和非缺锌的比例为42%和58%，两种土壤的小麦籽粒锌含量均存在较大变异，分别有7%和9%的样本籽粒锌达到40 mg·kg-1推荐标准。无论土壤是否缺锌，籽粒锌含量不受“产量稀释”效应影响，但缺锌田块的籽粒产量、地上部锌吸收明显低于非缺锌田块。较高的磷肥用量和土壤有效磷及较低的有效锌是实现小麦高产增锌的主要障碍因子。缺锌土壤，首先应解决土壤缺锌问题，至少先将有效锌提高至临界值1.0 mg·kg-1以上，非缺锌土壤的有效锌保持在3.0 mg·kg-1以上，同时减少磷肥用量、降低土壤有效磷，以减轻磷-锌拮抗作用，维持小麦高产并改善籽粒锌营养。

致谢 感谢国家小麦产业技术体系综合试验站科研人员、技术推广工作者和当地农户在样品采集方面的给予的协作和支持。

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