国内外主要粮食作物对施用锌肥响应的研究进展

王子腾，耿元波

（1 中国科学院地理科学与资源研究所，北京 100101；2 中国科学院大学，北京 100049）

锌 (Zn) 是人体必需的微量营养元素，对人体健康至关重要，是仅次于铁的第二大微量元素[1]。研究表明，缺Zn严重危害人体健康，会影响人体正常发育[2–3]；使人体更易受到致病菌的入侵，更易患病[4]；降低人体耐受氧化胁迫的能力[5]。例如在中东地区，由于缺Zn而导致的侏儒症患者都于25岁之前死于并发的感染[6]。研究发现，成年人每天需要通过饮食摄入15～25 mg的Zn，儿童需要5～7 mg，粮食作物可食部分的Zn含量要达到40～50 mg/kg才能满足人体正常生命活动的需求[7–8]。据此，世界上约一半人口饮食中Zn的摄入不足[9]。在发展中国家，粮食作物是主要的食物来源，但是粮食作物的可食部分Zn含量普遍比较低，尤其是种植在缺Zn土壤中[10]。据统计，全球至少60%的耕地土壤Zn等微量元素含量不足，50%的人口健康受到影响[11]。目前，农业生产上主要通过施用Zn肥的方式来提高粮食作物可食部分的Zn含量，但是施用的Zn肥其表观利用率都不高，尤其是施加到土壤中的无机Zn肥受到土壤理化性质 (如pH、有机质含量等) 的影响，有效性普遍比较低[12–13]。此外，施Zn肥增加了农户的成本，如果没有产量优势或者不能降低成本将很难大面积推广[14]。本文拟探讨主要粮食作物的产量、籽粒部分的Zn含量、Zn分配对Zn肥施用的响应，发现问题并提出切实可行的改善措施，展望研究前景，为今后的相关研究提供理论依据。

1 主要粮食作物籽粒锌含量现状

粮食作物主要是指小麦、水稻、玉米等农作物。小麦大约占粮食总产量的30%[15]，小麦籽粒中的Zn含量在20～30 mg/kg之间，美国、北欧等发达国家小麦籽粒的平均Zn含量为28.7 mg/kg左右[16]，中国的在24～33 mg/kg之间[17]，在发展中国家由于土壤缺Zn，加上农户不注重Zn肥的施用，小麦籽粒的Zn含量会低至 7～11 mg/kg之间[18]；水稻供给了全球人口21%的能量与蛋白质，90%的水稻种植在东亚、南亚、东南亚等发展中国家[19]，水稻籽粒的Zn含量在20 mg/kg左右[20–21]；玉米是继小麦、水稻之后人类最主要的食物，在非洲的一些国家，如埃及和南非等，玉米是主要的食物来源，即使在发达国家，玉米也是日常食物中不可或缺的一部分[20]，玉米籽粒的Zn含量约为20 mg/kg左右[22]，在缺Zn土壤中，会低至13 mg/kg左右[23]，不同国家主要粮食作物籽粒Zn含量详细数据见表1。通过分析可以看出，主要粮食作物籽粒部分的Zn含量普遍低于40～50 mg/kg，达不到人体对Zn元素的需求。

造成粮食作物Zn含量不足的原因主要有两方面：一方面是粮食作物对于土壤Zn含量的变化非常敏感，其产量与品质易受到土壤缺Zn的影响[24]；另一方面是用于种植粮食作物的耕地，微量营养元素Zn普遍缺乏[25]。据估计目前占全球50%的用于种植粮食作物的耕地缺Zn[26–27]，Zn的有效性也比较低[28]，从而导致粮食作物可食部分的Zn含量普遍不足，并且这种情况在发展中国家呈恶化趋势[29]。此外，粮食作物中植酸的含量比较高，植酸可以与Zn在胃肠道形成络合物或者沉淀，从而影响人体对于Zn的吸收[30–31]。研究发现，如果饮食中P∶Zn ＜12，则认为基本上不会存在Zn摄入不足的情况；如果饮食中P∶Zn ＞ 18，则认为人体Zn摄入不足[32]。简言之，以粮食作物为主食的人较易出现缺Zn状况，目前主要利用补施Zn肥这一农艺措施来提高粮食作物的Zn含量，如土施Zn肥、叶面喷施Zn肥等。

表 1 不同国家主要粮食作物籽粒Zn含量 (mg/kg, DW)Table 1 Zn contents of main food crops in different countries

2 主要粮食作物产量对锌肥的响应

主要粮食作物小麦、水稻和玉米的产量会因为土壤缺Zn而显著下降，补施Zn肥后其产量会明显提升[83–84]。因为Zn不仅是叶绿体的组成成分[85]，而且会对碳酸酐酶 (催化光合作用过程中可逆的CO2水合反应) 的活性产生影响[86]，所以缺Zn会导致叶绿体合成受阻，碳酸酐酶活性降低，光合速率下降，最终使农作物减产。对于小麦来讲，不同的Zn肥施用方式均可以增加小麦产量 (图1)。如Yilmaz等[87]研究发现，在缺Zn土壤中，小麦产量很低，不同的补施Zn肥措施均可以显著提高其产量，在土施Zn肥措施下，小麦的产量最高，达到了2042 kg/hm2，与不施Zn肥相比产量提高了262%，与叶喷Zn肥相比提高了约63%。叶喷Zn肥的增产效果显著低于土施Zn肥，一方面是由于在本研究中土施Zn肥的施Zn量为23 kg/hm2，而叶喷Zn肥为440 g/hm2，施用量差异极大；另一方面是由于根系Zn的吸收对于小麦的增产效果要优于叶喷Zn肥[88]。然而也有研究发现，补施Zn肥后小麦的产量与不施Zn肥相比没有显著差异[89]。这种结果可能是由土壤Zn含量所决定的，例如Yilmaz等的研究区域，农田土壤有效Zn含量为0.12 mg/kg，显著低于农田土壤缺Zn临界值0.5 mg/kg[90]，属于极度缺Zn土壤，已经对小麦产量造成了显著的减产效应，补施Zn肥后，小麦产量显著提高，这与郝明德等[91]18年长期施用Zn肥的研究一致，补施Zn肥后小麦有明显的增产效应；然而也有一些研究区域，农田土壤有效Zn含量虽然不高，但是并没有达到使小麦减产的水平，因而补施Zn肥后并没有明显的增产效果[92]。与小麦一样，有研究表明补施Zn肥对于水稻有明显的增产作用 (图2)，从图2中可以看出，水稻产量随着施Zn量的增加先上升后下降。产量下降是由于过量的

Zn会对水稻产生毒害作用[93–94]，例如Kumar等[95]研究发现，过量的Zn会降低水稻Fe和Ca等元素的吸收量，并降低产量。然而，也有研究表明施用Zn肥后，水稻产量变化不显著[40]，造成这种现象的原因与小麦类似，所选取的试验地农田土壤有效Zn的背景值比较高，Zn不是作物生长的限制因子。此外，冯绪猛等[96]研究发现，与小麦一样，土施Zn肥的水稻籽粒产量明显高于叶喷Zn肥，说明土施Zn肥的增产效果要优于叶喷Zn肥。对于玉米来讲，补施Zn肥也会显著增加其产量，尤其是在缺Zn土壤中[41,79]。Liu等[48]研究发现，玉米产量会随着施Zn量的增加先上升，后趋于平稳，说明在施Zn超过一定量之后，Zn将不再是玉米生长的限制因子，增加施Zn量对于玉米就没有显著的增产作用 (图3)。与小麦、水稻不同的是，以往的研究[41,48,78–79,97]都表明玉米产量会随着施Zn量的增加而增加，一方面是因为玉米对于Zn肥的响应很高，产量潜力很大[98]，另一方面可能是由于被研究的用于种植玉米的农田土壤严重缺Zn，Zn已成为玉米产量的主要限制因子之一。

图 1 不同施Zn肥处理对小麦产量的影响Fig. 1 Effects of different Zn application methods on wheat yields

图 2 不同施锌量对水稻产量的影响Fig. 2 Effects of Zn application rates on rice yields

图 3 不同施锌量对玉米产量的影响[48]Fig. 3 Effects of different Zn application rates on maize yields[48]

3 主要粮食作物籽粒锌含量对锌肥的响应

3.1 小麦籽粒锌含量对施用锌肥的响应

补施Zn肥对于提高小麦籽粒的Zn含量有明显的效果[104]，产量与品质得到明显改善。Maqsood等[105]研究发现，土施Zn肥后，小麦籽粒的Zn含量由34.9 mg/kg增加到69.93 mg/kg，这与陆新春等[106]、曹玉贤等[107]、Yilmaz等[87]的研究结果基本一致，土施Zn肥可明显提高小麦籽粒的Zn含量。Wojtkowiak等[108]研究发现，土壤有效Zn含量与小麦籽粒Zn含量之间的决定系数达到了0.9105，存在极显著的相关关系。但是直接向土壤中施用Zn肥会受到土壤理化性质的影响[109–110]，Zn的利用效率比较低，例如土壤中磷酸盐含量会显著影响Zn的有效性，研究发现土壤中磷酸盐含量越高，被土壤吸附固定的Zn就越多[111]。叶喷Zn肥可以显著提高Zn的表观利用率，并且叶喷Zn肥处理下的小麦Zn含量也明显高于土施Zn肥[112]。Zheng等[39]在7个国家的23个试验点进行了相关研究，发现叶喷Zn肥均显著提高了Zn在小麦籽粒中的含量，平均增幅为84%，而土施Zn肥仅为12%，Kutman等[113]和Cakmak等[100]也有类似的研究结果。Zheng等[39]在研究中还发现，不同的小麦品种对于Zn肥的响应存在差别，小麦籽粒中Zn含量在30～60 mg/kg之间不等，因此在品种的选择上要优先考虑对于Zn肥响应较高的类型，提高Zn肥利用率。此外，元素之间存在竞争或者协同的作用，例如，Stepien等[67]研究发现，与只施Zn肥相比，同时用含有Cu、Zn、Mn的微肥叶喷小麦能够最大幅度的提高小麦籽粒的Zn含量，说明其他微量元素的补充促进了小麦对于Zn的吸收与富集。Zhang等[114]研究发现，施肥过程中P与Zn会有拮抗作用，在一定量之后，Zn在小麦籽粒中的含量会随着P的增加而逐渐降低。买文选等[115]通过研究发现，补施Zn肥会降低小麦籽粒的植酸含量，提高小麦籽粒中Zn的生物有效性。虽然叶喷Zn肥可以显著提高小麦籽粒中的Zn含量，但是叶喷Zn肥增加了小麦种植的成本，增产效益也不如土施Zn肥，所以需要去降低施肥成本，增加收益。研究发现小麦种植为防治病虫灾害 (如蚜虫)，需要喷洒农药[116]，Ram等[38]通过田间试验发现，将Zn肥和农药一起叶喷与只喷Zn肥相比，小麦籽粒中的Zn含量无显著差异。研究还发现，将农药与Zn肥一次性叶喷到小麦上与分两次相比，每公顷小麦的净收入增加了118美元，例如中国作为主要的小麦种植国家，种植面积达到了2400万公顷，则每年农民的净收入可以增加接近29亿美元[117]。

3.2 水稻籽粒锌含量对施用锌肥的响应

通过土施Zn肥，稻田施Zn量在2.5、5.5、7.5 kg/hm2的情况下与不施Zn肥相比，水稻籽粒Zn含量分别提高了0.9%、8.5%、16.4%[27]。Zn在水稻中的富集量明显提高，但是要使水稻中的Zn含量达到要求，至少施用Zn肥 (以ZnSO4·7H2O计)25 kg/hm2，这对于农户来讲，生产成本很高，很难实现[118]。Shivay 等[44]将包膜尿素 (含 ZnSO4·7H2O) 土施到土壤中，在低施用量 (0.5% ZnSO4·7H2O) 的情况下，可以显著提高Zn肥的表观利用率，达到了17.6%，但是产量不高，水稻籽粒中的Zn含量也比较低；如果要使Zn的富集量达到要求，就要增加Zn的投入量(2.0% ZnSO4·7H2O)，但是Zn的表观利用效率下降到12%。Shivay等[119]通过另一研究发现，随着施Zn量的增加 (施Zn量在1.3～9.1 kg/hm2之间)，第一年其表观利用率从16.4%下降到8.3%，第二年从17%下降到10.6%。因此土施Zn肥虽然可以提高水稻籽粒中的Zn含量，但是施用的Zn肥量太大，Zn的表观利用效率太低，约为10%[44]，这主要是因为施加到土壤中的Zn肥受到了土壤理化性质的影响，其有效性显著降低，研究发现叶喷Zn肥是克服这一缺点的有效途径[120–121]。与土施Zn肥相比，叶喷Zn肥的农学效益是其10倍，即用0.2% ZnSO4·7H2O的Zn肥叶喷水稻就可以达到用2% ZnSO4·7H2O的Zn肥土施到土壤中水稻籽粒Zn含量的水平，明显提高了Zn的表观利用率[43]。Phattarakul等[40]研究发现，在排除了土壤理化性质、管理措施等对Zn在水稻中含量的影响，叶喷Zn肥对于水稻籽粒中Zn含量的提高效果比土施Zn肥增加了66%。Wissuwa等[77]通过研究也发现，无论哪一种水稻类型，叶喷Zn肥与土施Zn肥相比都能够显著增加水稻籽粒中的Zn含量。但是与小麦一样，叶喷Zn肥的增产效益不如土施Zn肥，增加了农户的成本，一方面可以通过土施Zn肥与叶喷Zn肥的耦合进行互补，另一方面可以通过与其它农艺措施相结合来降低成本，以增加收益[38]。土施Zn肥与叶喷Zn肥的耦合与只叶喷Zn肥相比，水稻籽粒产量平均提高了约2.1%，Zn含量平均提高了约4.0%，增加了农户净收益[40]。此外，不同的水稻类型对于Zn肥的响应是不同的，Saha等[122]研究了不同水稻品种在富Zn方面的差异，不同的水稻品种即使在同一施肥模式下，其产量与Zn含量也不同，并发现‘GB1’(品种来自于印度的阿萨姆) 水稻品种在一次基肥、两次追肥的模式下，其Zn含量与产量均优于其它品种。因此针对不同的水稻类型，在兼顾产量的前提下要优先选用高富Zn的品种。

3.3 玉米籽粒锌含量对施用锌肥的响应

与小麦、水稻一样，土施Zn肥与叶喷Zn肥不仅都可以提高玉米籽粒中的Zn含量[123]，还可以提高玉米的产量[98]。Harris等[66]通过研究发现，与不施Zn肥相比，在施Zn量为2.75 kg/hm2情况下，Zn在玉米籽粒中的富集量提高了18.0%；在施Zn量5.5 kg/hm2的情况下，富集量提高了39.8%。通过土施Zn肥，玉米籽粒中的Zn含量明显提高，但是施加的Zn肥量太大，Zn肥的有效性偏低。在发展中国家补施Zn肥增加了农户的生产成本，降低了农户施Zn肥的积极性，例如在巴基斯坦，不超过5%的农户施用Zn肥[124]。Manzeke等[78]依据津巴布韦当地的实际情况，将秸秆 (实际施Zn量430 g/hm2)、畜禽粪便 (实际施Zn量113 g/hm2) 等作为含Zn有机肥与NPK肥一起施入到土壤中，与只施用NPK肥相比，玉米籽粒中的Zn含量分别提高了64.3%和50%，同时也提高了玉米的产量。这是因为畜禽粪便中含有丰富的有机Zn，不仅提供了农作物生长所必需的微量营养元素Zn，而且提升了土壤肥力[110]。

4 施用锌肥对主要粮食作物中锌分配的影响

大量研究表明，施Zn肥可以显著提高主要粮食作物Zn含量，缓解农作物缺Zn情况，并能够增加产量[125–126]。但是农作物有特定的吸收分配机制，Zn元素正常情况下由根部吸收，经过木质部和韧皮部的运输，才能够在农作物的可食部位进行富集[127]。例如，Jiang等[128]通过同位素示踪的方法发现，水稻可食部分的Zn元素主要来自于根部的吸收，叶喷Zn肥大约50%的Zn元素留在了叶子里，另外的50%的分配到了其他有机体中，很少一部分被分配到谷粒当中。与水稻不同的是，小麦籽粒中的Zn还可以由叶子里的Zn重新分配进行补充[129]。通过施肥途径施加的Zn元素是否能够更多的在粮食作物可食部位分配，也是科学研究关注的热点。

对于小麦，Maqsood等[105]研究了巴基斯坦的12个小麦品种后发现，向土壤中施用Zn肥对于小麦籽粒及秸秆的Zn含量均有显著的提升作用，在秸秆中Zn的平均含量为41.54 mg/kg，在小麦籽粒中Zn的平均含量为58.92 mg/kg，与不施Zn肥相比分别提高了17.7%，22.1%。Li等[130]研究了叶喷Zn肥对小麦籽粒、白面粉、麸皮中Zn含量的影响，发现施用Zn肥后，Zn含量与不施Zn肥相比分别提高了92.5%、64.8%、77%，并且麸皮中的Zn含量最高为74.0 mg/kg，其次是小麦籽粒，为42.2 mg/kg，最低为白面粉，Zn含量为13.3 mg/kg。这与Zhang等[131]的研究结果一致，Zn在麦麸、小麦籽粒、白面粉中的含量是逐渐递减的 (图4)。在中国，小麦主要吃的是白面粉，所占的比重超过了85%[132]，补施Zn肥虽能显著增加小麦籽粒的Zn含量，但是作为主要消耗品的白面粉，其Zn含量仍然比较低。对于水稻来讲，Phattarakul等[40]研究发现，通过土施Zn肥，Zn在精米中的含量为16.2 mg/kg，与稻谷、糙米相比Zn含量分别下降了15.3%、22.1%；通过叶喷Zn肥，Zn在精米中的含量为17.7 mg/kg，分别下降了45.2%、27.5%；通过土施Zn肥与叶喷Zn肥结合的方式，Zn在精米中的含量为18.4 mg/kg，分别下降了47.0%、27.8% (图5)。这与相关研究的结果基本一致，发现补施Zn肥后稻谷中含Zn总量占水稻总Zn吸收量的比值为18.22%[44]，Zn在精米中的富集量与稻谷相比下降明显，约为12%[20]。综上所述，白面、精米等细粮的Zn含量与麦麸、糙米等粗粮相比具有很大的差异，因此在日常的饮食中应该增加粗粮的摄入量，弥补细粮Zn含量不足的状况。何宇纳等[133]研究中国成年人粗杂粮摄入水平时也发现，高粗粮摄入水平的群体其每日的摄Zn量显著高于低粗粮摄入水平的群体。

图 4 喷施不同锌肥小麦籽粒不同组分的Zn含量[35]Fig. 4 Zn contents in different grain parts of wheat sprayed with different Zn fertilizers[35]

图 5 不同施锌方式下水稻籽粒不同组分的Zn含量[40]Fig. 5 Zn contents in different grain parts of rice affected by Zn fertilization mode [40]

5 问题与讨论

补施Zn肥可以提高粮食作物可食部分的Zn含量，增加作物的产量，但是两种施肥措施都存在缺陷：Zn在人们主要消费的白面粉和精米中的含量很少；施用较高量的Zn肥虽提高了主要粮食作物的的Zn含量，但是在土壤有效Zn含量处于中等偏下水平的土壤上，主要粮食作物的产量对Zn肥的响应不明显，甚至过高的施Zn量会使农作物减产，加上Zn肥的价格比较高，让农户难以接受；Zn肥的利用率很低，尤其是盲目的大量施用Zn肥会造成浪费，并使土壤遭受潜在的Zn污染[134]；肥料中的各营养元素之间存在交互作用，Zn与其它营养元素之间存在竞争或者协同作用，影响Zn肥的吸收；不同的农作物品种对于Zn肥的响应具有较大差异，富Zn量较高的品种，其产量偏低，产量较高的品种，其富Zn量达不到要求，产量与Zn含量难以同时达标。

针对国内外研究现状及存在的一系列问题，今后的研究可重点关注：1) 深入开展与Zn元素在肥–土–作物系统中吸收分配机制相关的研究，清楚掌握Zn元素在肥–土–作物系统中的富集与分配规律，同时建立全国范围内主要农田土壤的Zn数据库，构建产量、富Zn量与Zn肥之间的响应模型，为通过施肥途径改善粮食作物缺Zn状况提供有力的理论依据，避免不必要的浪费与污染或者施Zn肥不足，实现精准施肥。2) 加大新型廉价肥料技术的研发力度，降低肥料制作成本，寻找其他廉价替代品，例如畜禽粪便、污泥堆肥等，降低补施Zn肥的成本，与其它农艺措施相结合，提高产量，增加农户的净收益。3) 进一步探索改善土壤理化性质的有效措施，例如，pH、土壤有机质和离子强度等，降低土壤对Zn的固定能力，提高Zn肥对于农作物的有效性及其肥效的持久性，也可以通过添加其它物质，如生物质炭等。研究表明生物质炭不仅含有一定量的微量元素[135]，能够增加土壤保水保肥的能力[136]，而且还可以促进作物根系的生长，提高作物的养分吸收能力[137]，今后可进行生物质炭与Zn的耦合研究。4) 加强系统研究，综合考虑多种营养元素对粮食作物产量与品质的影响，探明微量元素、常量元素之间的交互作用，找到最佳投入量与最佳配比，整体提升粮食作物的营养价值。5) 对小麦、水稻、玉米等主要粮食作物的品种进行筛选，在兼顾产量优势的前提下，选出对施Zn肥高响应的品种或通过杂交与基因工程育种技术来获得对Zn肥高产量与高富

Zn量响应的品种类型。6) 加强主要粮食作物富Zn的分子生物学机制研究，例如研究[138–140]发现ZIP转运蛋白起到了将Zn转入到根细胞的转运子作用，增加了粮食作物对Zn的吸收富集能力，今后可在分子水平上对与Zn的吸收、富集及转运相关的基因进行鉴定和筛选，并可通过基因工程育种技术和杂交技术等进行品种改良。

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