中国北方地区小麦覆盖栽培增产效应的荟萃(Meta)分析

2022-05-16 08:49秦羽青程宏波柴雨葳马建涛李瑞李亚伟常磊柴守玺
中国农业科学 2022年6期
关键词:增产率穗数覆膜

秦羽青,程宏波,柴雨葳,马建涛,李瑞,李亚伟,常磊,柴守玺*

中国北方地区小麦覆盖栽培增产效应的荟萃(Meta)分析

秦羽青,程宏波,柴雨葳,马建涛,李瑞,李亚伟,常磊,柴守玺*

甘肃省干旱生境作物学重点实验室/甘肃农业大学农学院,兰州 730070

【目的】明确中国北方地区秸秆覆盖和地膜覆盖技术对小麦生产的影响,探索两种覆盖体系的适宜推广区域。【方法】在近40年的时间跨度中检索并筛选出165篇相关文献,将其置于荟萃分析(Meta-analysis)的框架下,通过效应分析的不同展现形式(如变化率及反应比)开展理论研究。整体采用随机效应模型,分析对比不同覆盖模式下小麦农艺指标和农田水分状况的变化情况。进而以亚组分析的形式,重点揭示覆盖增产效应对不同环境条件(海拔、降水量、气温、日照)及田间管理措施(覆盖周期、种植密度、耕作、施肥)的响应规律,对其进行函数拟合、权重分析及统计检验。并且通过皮尔逊相关性分析量化本研究涉及的各个变量之间的相关性。【结果】相较于露地栽培,秸秆和地膜覆盖分别使小麦产量显著提高了19.53%(95%= 0.55%—38.52%)和24.91%(95%= 3.18%—46.64%),并且抑制了农田蒸散。不同覆盖模式下产量构成因素对增产的贡献率亦存在一定差异,分别为有效穗数>穗粒数>千粒重(秸秆覆盖);有效穗数>千粒重>穗粒数(地膜覆盖)。其中秸秆覆盖下的穗粒数增幅较高,达5.7%(95%= -4.10%—15.50%);而覆膜的有效穗数和千粒重增长更显著,分别为25.2%(95%= 14.11%—36.29%)和6.4%(95%= 1.50%—11.30%)。除了具有促产优势,覆膜的生物量和水分利用效率同样比覆秸秆高出18.17%和14.39%。具体表现为在大部分气象亚区中地膜覆盖的增产率相较于秸秆覆盖高出0.89%—23.34%。同时,随着地势的下降,覆膜的增产效应相对于非覆盖呈现出增长趋势,在低海拔地区(<800 m)增产率可达34.26%。然而,塑料薄膜相对于秸秆的增产优势会随着覆盖年限的增加而逐渐缩小,在超过8年的试验中,覆盖秸秆的整体增产率反而更高。秸秆覆盖产量还受到施肥和耕作措施的影响,尤其是在免耕,不施肥以及单施磷肥这3种处理中,增产率分别达到32.68%,25.94%和21.71%。由统计学检验可知,在海拔、年均日照时数和种植密度3个亚组中,组间异质Q的检验量整体较大,说明该组内各效应量的变异程度更高。秸秆和地膜覆盖条件下,同产量相关度最高的因子分别为有效穗数(= 0.808)和水分利用效率(= 0.718),而影响两种覆盖体系中土壤含水量的首要因子分别为蒸散量(= -0.859)以及水分利用效率(= 0.856)。【结论】两种覆盖模式皆具有明显的增产效应,且地膜覆盖在低海拔、偏旱、偏寒地区更具优势;而秸秆覆盖更适合融入长期的保护性耕作体系,从而实现生产和生态的多元协调式发展。因此,因地制宜、因时制宜选择科学的覆盖方法是我国北方小麦覆盖技术取得成功的关键。

秸秆覆盖;地膜覆盖;小麦;产量;Meta分析

0 引言

【研究意义】表土覆盖栽培技术是缓解我国北方地区作物生产同水资源短缺之间尖锐矛盾的有效措施[1-4]。当前我国北部各省区最重要的覆盖方式包括地膜覆盖和秸秆覆盖,在当地的农业生产实践中均有着良好的表现[5-6]。而小麦(L.)作为世界上播种面积最广、同时也是北方农作区十分重要的谷类作物,亦成为覆盖栽培研究的重点方向之一[7-9]。研究两种覆盖模式下小麦生产的优势和劣势,可以为该技术的区域性精准推广奠定理论基础。【前人研究进展】Gan等[10]的研究发现,地膜覆盖相较无覆盖土壤含水量增加25%—50%,贮水量增加20%—40%,水分亏缺程度下降5%—70%,这种良好的节水保墒特性使得覆膜技术在我国干旱少雨的小麦产区得到了广泛的应用[11-13]。同时地膜可以显著提升表土温度[14-16],为小麦生长发育提供足够的热量条件并减缓前期的冷害和冻害[17]。因此,塑料薄膜覆盖在西北、华北、东北等秦岭-淮河以北的干旱半干旱农区得到大范围的推广,并且发展出一系列衍生技术,包括全膜平铺穴播、全膜平铺沟播、全膜双垄沟播、垄膜覆盖沟播、垄膜覆盖膜侧沟植、液态地膜等[18]。另一方面,推行秸秆覆盖可以减少秸秆焚烧所引发的大气污染,将原本被弃置的秸秆资源重新加以利用,已成为当下农业可持续发展的关键技术之一[19],并同少免耕技术和轮作制一起构成了保护性耕作体系的三大支柱[20]。同时,秸秆覆盖还优化了土壤的耕层结构[21]、肥力[22-23]以及微生物活性[24]。当覆盖层破损以后,其残余部分的分解将会促进土壤养分循环,使得这些营养元素更易于被小麦吸收利用[25-26]。相对而言,地膜覆盖处理下小麦产量和水分利用效率的提升幅度较大[27],0—200 cm土层中的平均储水量比秸秆覆盖高31.52%[28]。而秸秆覆盖能够提升土壤真菌群落的丰度和稳定性[29],土壤有机碳和全氮含量相对地膜覆盖分别提高l16.21%和13.24%[30],这些农田土壤生态的外源性改善同样对作物生产有促进效应。【本研究切入点】在我国相关的Meta分析领域,往往只涉及两种覆盖模式之一,且多以变化率(change ratio)为计量单位,罕有效应量分析。这就使得研究结果缺乏横向的覆盖模式对比或者纵向的统计尺度对比,难以综合性地揭示覆盖增产效应的变化规律,致使该技术的科学推广缺乏规范化标准。况且各种试验结果表明,中国北方地区秸秆和地膜覆盖都具有特定的优缺点,需要在复杂的时空动态下进行逐区分析。【拟解决的关键问题】本研究旨在通过荟萃分析(meta- analysis)的相关理论和方法[31],探讨不同的环境条件及栽培管理措施下两种覆盖模式对于小麦生产的影响及其相互之间的比较优势,为本地区覆盖技术的精准运用提供理论支撑。

1 材料与方法

1.1 数据收集和提取

利用中国知网(CNKI),万方数据知识服务平台和ScienceDirect进行文献检索,并选取“中国北方”“小麦”“产量”“覆盖”“秸秆”“地膜”为中英文检索关键词。选取的文献需要同时符合以下标准:(1)文献中的数据来源于中国北方地区的田间试验;(2)每组试验至少包括秸秆覆盖或者地膜覆盖其中的一种;(3)排除设置灌溉梯度处理的试验;(4)文献中应包含明确的试验地基本信息和试验年限。最终筛选出符合要求的104篇中文文献和61篇英文文献,并且优先从文本和表格中搜集数据,其次使用图形数字化软件GetData2.3.1以及PicPick5.1.2从图中提取。本论文搜集到的各项研究所实施的具体时间为1982—2021年,地点位于秦岭-淮河以北的中国北方地区。

1.2 数据归纳

将搜集到的各项研究中相对应的试验地信息以及田间管理措施进行分类汇总,从而探究小麦产量受这些因素影响所表现出的变化规律。本研究归纳出的解释变量有8项,分别为试验地海拔、年均降水量、年均气温、日照时数、覆盖年限、种植密度、耕作方式、施肥方式。最终将这些因素划分为不同梯度的亚区,并将两种覆盖处理同时纳入各个亚区中进行比较。

1.3 效应量分析

选取效应比的自然对数ln作为Meta分析中评价效应量大小(effect size)的数据标度。

式中,ln为反应比,和表示观察组(覆盖栽培)和对照组(露地栽培)数据的算术平均值。每项独立研究的ln的方差由下式计算:

式中,和分别为观察组和对照组的数据标准差;和分别为观察组和对照组的样本容量。

式中,和代表拥有个研究的亚组中观察组和对照组的样本容量。求得的效应值还需要进行量化处理,使其转化为变化率(change ratio,,%)以

便于亚组和处理之间的直接比较:

1.4 异质性检验

利用异质性检验统计量Q,研判本文选取的165篇文献中独立试验结果间的差异性。Q值同效应量的变异程度成正相关关系。当异质性检验结果显著时,应该选取随机效应模型(REM);否则,选取固定效应模型(FEM)[32]。由于两种覆盖处理的统计量Q的显著性均小于0.05(表1),所以运用REM模型进行效应量分析。

表1 秸秆覆盖和地膜覆盖下小麦产量的效应值分析和统计检验

Z 为效应量检验的统计量;P 为效应量的显著性水平;Q 为异质性检验统计量;PQ为Q 统计量的显著性;n 为效应量个数

Z is the statistic of effect size test; P is significant level of effect size; Q is the statistic of heterogeneity test; PQis the significant level of Q statistic; N is the number of effectors

2 结果

2.1 秸秆覆盖和地膜覆盖对小麦生产的影响

本文共搜集到8组具有特定样本容量的小麦栽培学农艺指标,分别为产量(421)、生物量(193)、有效穗数(183)、穗粒数(167)、千粒重(182)、蒸散(331)、水分利用效率(315)和土壤含水量(259)(图1)。其中千粒重及水分利用效率数据的置信区间较小,这两组数据的分析结果可信度较高。整体而言,在中国北方地区,两种覆盖模式均能显著提升小麦产量(表1)。地膜覆盖的增产率为24.91%(95%= 3.18%—46.64%,=5.51),平均比秸秆覆盖(95%=0.55%—38.52%,=7.05)高5.38%。本文中秸秆和地膜覆盖的产量效应量数目分别为185和236。其中覆膜的效应量检验统计量(Z)为6.43,比秸秆高出8.25%,说明膜下整体增产幅度更高。而秸秆覆盖样本的异质性检验统计量(Q)为956,比地膜高17.44%,说明小麦产量数据在秸秆覆盖条件下变异程度更高。具体而言,秸秆覆盖下试验数据的组间异质性在海拔、种植密度及施肥方式3个亚组当中超过了地膜覆盖(表2—3)。

通过研究覆盖处理的效应量及其分布规律,发现这些效应量整体上呈正态分布(图2)。只有在地膜覆盖下,有效穗数的ln数据在0.2—0.8的范围内出现了先降后升的趋势,故而导致其拟合曲线呈弧形分布(图2-c)。在产量指标中,覆秸秆样本的反应比在0.2—0.4区间内的分布最广(32.35%),而覆膜样本的效应量数据相对集中于0.4<ln<0.6的区间内(28.85%);同时在地膜覆盖的反应比拟合曲线中,其峰值点对应的ln相对更大,说明地膜覆盖的增产效应要优于秸秆覆盖(图2-a)。进一步发现在覆膜条件下,大多数农艺指标的加权反应比更高。然而,秸秆覆盖的穗粒数样本在ln>0的区间内占比为73.82%,比地膜高9.4%(图2-d),该趋势亦符合图1两种覆盖模式下穗粒数指标的相关变化(秸秆5.7%,地膜4.2%)。

小麦的有效穗数以及水分利用效率均受两种覆盖模式的显著影响(图1)。相较于露地栽培,地膜和秸秆覆盖使得生物量分别增加34.48%(95%= 0.36%—68.60%,= 11.92)和16.30%(95%= -14.28%—46.88%,= 9.25),覆膜在增长率更高的同时波动性亦更强。综合来看,地膜覆盖的生物产量增加率比籽粒产量的增加率高9.57%,而在覆盖秸秆时籽粒产量的增加率则更高。说明秸秆覆盖小麦虽然整体产量不及地膜覆盖,但是收获指数更高,这在自然资源相对匮乏的北方地区具有重要意义。整体上看,秸秆和地膜处理对于产量三要素的影响分别为有效穗数(18.5%±12.68%,= 4.19)>穗粒数(5.7%±9.80%,=0.44)>千粒重(4.8%± 11.20%,= 4.34);以及有效穗数(25.2%±11.09%,= 1.25)>千粒重(6.4%±4.90%,=2.86)>穗粒数(4.2%± 23.24%,= 5.41)。其中,两种覆盖因素主要通过提高单位面积有效穗数来促进增产,此外秸秆覆盖对穗粒数的影响高于地膜,而后者对千粒重的影响则更明显。

两种覆盖模式下小麦田的蒸散量显著下降(秸秆:-6.61%,95%= -29.56%—16.33%,=6.31;地膜:-14.71%,95%= -50.74%—21.32%,=4.02),地膜对于田间蒸散的总体抑制能力更优。与之相对应的是,覆膜处理下土壤含水量平均增加17.22%(95%=6.22%—28.22%,= 2.34),比覆秸秆高7.48个百分点。这些抗旱节水效应的最终结果是覆膜水分利用效率的平均增长率(45.44%±9.08%,=5.52)同样高于秸秆(31.05%±13.71%,=1.71),且离散程度更低。

黑点和白点所在的线段代表秸秆和地膜处理的变化率,无括号和有括号的SD分别对应秸秆和地膜处理

2.2 环境因素对于小麦覆盖栽培的影响

试验地海拔高度直接影响了覆盖条件下的小麦产量,随着平均海拔的升高,其产量增长率相对露地处理逐渐减少(图3-a)。在海拔超过1 250 m的地区,地膜带来了10.95%(95%=-10.95%—32.86%)的增产效应,而在地势最低的亚组中(海拔<800 m),该增长率可达34.26%(95%= 21.16%—47.35%)。覆秸秆小麦的增长率表现为:海拔>1 250 m,6.25%(95%=-8.32%—20.82%);海拔800—1 150 m,18.80%(95%= 4.08%—33.52%);海拔<800 m,18.92%(95%= 2.01%—35.84%);海拔1 150—1 250 m,24.17%(95%= 4.58%—43.77%)。

随着年均降水量的增多,覆盖小麦的产量呈正增长趋势(图3-b)。本研究中,地膜覆盖的增产率在不同的降水梯度中均高于秸秆覆盖,但是两者的差距在干旱半干旱区(年均降水量<550 mm)比相对湿润的地区更为明显。当降水量高于650 mm,秸秆覆盖样本的增产率最高,达到了29.84%;而地膜覆盖在450—550 mm降水量的地区具有最显著的增产效应(36.57%±2.29%)。覆膜产量的效应量为0.273,比覆秸秆处理高出55.15%(图4-a,b)。

RCS为Reduced Chi-Sqr的缩写,代表残差均方 RCS is the abbreviation of Reduced Chi-Sqr, representing mean square of residual

黑点和白点所在的线段代表秸秆和地膜处理的变化率。图5同

温度的升高同样促进了覆盖体系的生产力(图3-c)。相对而言,当平均气温超过12.5℃时,秸秆覆盖的增产率(35.25%±16.52%)高过地膜约5.03%。而在9—10.5℃的亚区中,虽然地膜处理的增产率(18.14%)要高于秸秆(17.25%),但是差距是微弱的。整体而言,覆膜的增产幅度在平均气温10.5—12.5℃的地区最为明显,达到了39.01%(95%=27.82%—50.21%)。全体覆膜样本的平均效应(0.207)比秸秆覆盖高28.76%。不同覆盖模式下小麦产量同气温的拟合曲线有着明显差异(图4-c,d)。虽然两者均表现出上升趋势,但是秸秆覆盖曲线的节点导数值(即该点的曲线斜率)随气温增加有逐渐升高的趋势,而在覆膜处理下其二次曲线的斜率则有下降趋势。这说明随着试验地温度条件的改善,覆膜的优势逐渐下降,而覆秸秆的优势则相对凸显。同时,秸秆覆盖曲线的决定系数2为0.67,比地膜覆盖高40个百分点,说明前者的拟合关系可以更准确地解释小麦产量的变异。

秸秆或地膜处理中,年日照时数显著影响了小麦产量(图3-d)。覆盖秸秆的增产率依次为日照时数>2 500 h,25.71%(95%= 11.89%—39.52%);日照时数<2 200 h,19.94%(95%= 14.43%—25.44%);日照时数2 200—2 500 h,15.96%(95%= 12.43%—19.49%)。而地膜试验的产量则随日照时数的增加逐渐提高。当日照时数高于2 500 h时,增产率为30.08%(95%= 11.76%—48.40%),分别比(0,2 200 h)和(2 200,2 500 h)这两个日照区间高13.54%(95%=1.54%—31.54%)和8.05%(95%= 1.49%—42.56%)。

2.3 田间管理对于小麦覆盖栽培的影响

随着时间推移,地膜覆盖的优势显著下降,在覆盖年限1—2年、3—4年、5—8年以及大于8年的分组中其增产率分别为39.50%(95%= 22.87%—56.13%)、24.27%(95%= 1.06%—47.48%)、19.65%(95%=2.93%—36.37%)、21.86%(95%=16.97%—26.75%);相反,秸秆覆盖的增产效应则通过时间的积累而逐渐显现,对应的增产率分别为3.37%(95%= -14.29%—21.03%)、11.24%(95%= -7.06%—29.54%)、9.81%(95%= -9.35%—28.98%)、46.53%(95%= 30.20%—62.87%)(图5-a)。拟合分析的结果显示,覆膜的产量效应量在时间尺度上先增后减(图6-b)。在超过5年的秸秆覆盖试验中,产量效应量为0.198,比1—2年的处理高出25.53%;而5年以上覆膜试验的效应量为0.238,尽管依然优于同期的秸秆处理,但是相对于1—2年的覆膜小麦却显著降低了6.36%(图6-a,b)。

各曲线和公式反映了产量同降水量或气温的二次拟合。a,c和b,d分别代表秸秆和地膜处理

种植密度对两种覆盖小麦的影响基本上是相反的。在密度最低的亚组(<300万株/hm2)中,地膜覆盖的增产优势最明显,为42.93%(95%= 28.07%—57.78%)。相对而言秸秆覆盖的增产效应在低密度栽培条件下最弱,仅为1.31%(95%= -6.05%—8.66%)(图5-b)。而在密植小麦亚组(>400万株/hm2)中情况则正好相反,秸秆覆盖下小麦产量的变化率增至18.89%(95%= -1.59%—39.37%),而地膜处理则降为28.79%(95%= 6.21%—51.37%)。两种覆盖模式下产量的效应量均随种植密度增加而表现出先升后降的趋势(图6-c,d)。通过分类运算,发现在密度超过400万株/hm2的亚组中,地膜覆盖的效应值(0.264)相对秸秆覆盖增加了51.21%,为各个亚组之最。而图5-b的结果显示,该亚组间两种覆盖体系的增产率比较接近。研究中出现这种矛盾的现象说明效应值和增产率是两种独立的分析尺度,通过两者的同步使用可以更完整地揭示覆盖对小麦产量的动态影响。

免耕技术和秸秆覆盖相结合可以使得产量的相对增长量得以显著提高(32.68%±27.78%),之后依次是旋耕(19.55%±26.58%),传统耕作(17.39%±9.35%)及深松耕(16.53%±11.34%)(图5-c)。在传统耕作处理中,两种覆盖方式的增产率差异最大,其中地膜处理(95%= 25.27%—51.84%)要高出21.16个百分点。而在旋耕以及深松耕条件下,覆盖间的增产效应差距不大,地膜处理仅高出4.24%(95%= 6.21%—41.37%)和4.72%(95%=1.36%—41.14%)。

表2 环境因素对产量影响的亚组分析

Qtra为组内异质Q检验量,P-Qtra为组内异质性检验的显著程度,Qter为组间异质Q检验量,P-Qter为组间异质性检验的显著程度,CV为变异系数,Weight为效应量权重。每组数据中左边为秸秆覆盖,右边括号中的为地膜覆盖。下同

Qtra is test statistic of intra group heterogeneity Q, P-Qtra is the significance of intra group heterogeneity test, Qter is test statistic of inter group heterogeneity Q, P-Qter is the significance of inter group heterogeneity test, CV is coefficient of variation, and weight is the effect weight.In each group of data, the left is straw mulching, and the right in bracket is plastic film mulching.The same as below

图5 田间管理措施对于覆盖栽培模式下小麦产量的影响

各曲线和公式反映了产量同覆盖年限或者种植密度的二次拟合。a,c和b,d分别代表秸秆和地膜处理

在肥料梯度处理中,不施肥条件下的秸秆覆盖使小麦产量显著提高25.94%(95%= -0.07%—51.94%),其优势相对最为明显(高出地膜覆盖11.40个百分点)(图5-d)。接着依次是单施磷肥,21.71%(95%= 2.89%—40.52%);单施氮肥,19.96%(95%= 13.43%—26.49%);单施有机肥,18.25%(95%= 6.72%—29.77%);单施无机肥,15.50%(95%= 12.89%—18.11%)以及有机无机配施,13.36%(95%= -8.99%—35.71%)。而在覆膜条件下,小麦增产率在单施磷肥、单施无机肥、有机无机配施的处理中高于秸秆覆盖,其中当化肥结合有机肥施用时,其产量相较于覆盖秸秆增幅最大,为22.57%(95%= 17.80%—27.34%)。在单施有机肥的处理中,两种覆盖方式的增产率最为接近,其中覆秸秆处理(95%= 6.72%—29.77%)高出1.03%。

2.4 覆盖条件下小麦主要农艺指标及耗水指标的相关性分析

通过皮尔逊相关性分析可知,覆秸秆小麦的产量同生物产量、有效穗数、穗粒数、千粒重、土壤含水量之间存在显著的相关关系;而在覆盖地膜的处理中,与产量显著相关的指标有生物产量、有效穗数、千粒重、水分利用效率、土壤含水量(表4)。从产量构成要素的角度分析,秸秆及地膜覆盖下与产量的关联性密切程度分别表现为有效穗数(0.808)>穗粒数(0.796)>千粒重(0.549);有效穗数(0.677)>千粒重(0.586)>穗粒数(0.364),整体而言有效穗数对产量的贡献率最高。秸秆覆盖下的产量三要素之间皆存在显著的负相关关系,由于变化率(图1)和相关性(表4)分析的结果都反映出这三者之间有效穗数对产量形成的意义最为重要,建议实际生产中主攻穗数。而在覆膜条件下,有效穗数对穗粒数、千粒重分别表现出极显著负相关(-0.887)及显著正相关(0.760),因此可以在适当牺牲穗粒数的前提下,全力保证小麦的穗数和千粒重。

表3 田间管理因素对产量影响的亚组分析

CT、NT、RT、ST、NF、AN、AP、AO、AI、OIF分别代表传统耕作、免耕、旋耕、深松耕、不施肥、单施氮肥、单施磷肥、单施有机肥、单施无机肥、有机无机配施

CT, NT, RT, ST, NF, AN, AP, AO, AI and OIF respectively represent conventional tillage, no tillage, rotary tillage, subsoiling tillage, no fertilization, single application of nitrogen fertilizer, single application of phosphorus fertilizer, single application of organic fertilizer, single application of inorganic fertilizer and combined application of organic and inorganic fertilizer

表4 覆盖模式下小麦主要农艺指标及农田水分状况的相关性分析

每组数据的上排和下排分别为秸秆覆盖以及地膜覆盖处理

The top and bottom rows of every group data are straw mulching and plastic film mulching treatments, respectively

从农田水分动态的层面分析,土壤含水量同覆盖产量呈显著正相关,其中覆膜处理的相关系数为0.492,比秸秆处理高0.019;而覆膜水分利用效率同产量极显著相关(0.718)。此外,虽然蒸散量同产量之间并无统计学意义,但是却与水分利用效率呈显著的负相关(秸秆-0.561,地膜 -0.913)。因此覆盖材料抑制生产性耗水(尤其是棵间蒸发)的效应和作物水生产力的提高有直接关系。同时,覆盖对土壤温度的影响也决定着土壤水分的运行和蒸散强度。最终这种水温耦合效应促成了小麦水分利用效率的提高。

3 讨论

3.1 覆盖对小麦生产的影响

在相对干旱的地区,覆盖技术被证实对产量[33-34]、水分生产力[35-37]、耗水状况[38]、经济效益[39]及整个农田生态系统[40]有着广泛的影响。本文基于Meta分析的方法检索到165篇有效文献,从中筛选出2 051组试验数据进行研究。结果表明秸秆覆盖和地膜覆盖都可以显著地提高小麦产量,但是覆膜措施的增产率和增产的效应量分别比秸秆覆盖高5.38%和13.85%。影响秸秆和地膜覆盖产量的主要因素分别为有效穗数、穗粒数、生物产量以及水分利用效率、有效穗数、千粒重。前人在研究覆秸秆小麦的增产规律时,发现有效穗数、穗粒数、千粒重对产量的贡献度依次降低[41],该结论同本研究一致。然而在地膜覆盖试验中,3种因素对于产量的影响按相关系数划分依次为有效穗数(0.677)>千粒重(0.586)>穗粒数(0.364),说明两种覆盖措施不仅在增产效应方面存在差距,而且对各产量构成要素的影响也是不同的。同时,覆盖技术显著抑制了农田蒸散,但是秸秆覆盖处理的降幅为6.61%(95%= -29.56%—16.33%),尚不及地膜覆盖的一半(14.71%,95%= -50.74%—21.32%)。利用反应比ln的加权分析,发现覆膜水分利用效率和土壤含水量比秸秆覆盖显著高出26.44%和17.47%。另一方面,就秸秆覆盖而言,在年均降水量、年均气温、覆盖周期这3个亚组中组间异质性较低(表2—3),说明对应覆盖效应的组间合并结果较为可靠;具体而言,当年均降水550—650 mm(Qtra =4.34)、年均气温>12.5℃(Qtra =1.25)、覆盖周期5—8年(Qtra =1.89)时,组内合并结果较为可靠。而在年均降水<450 mm(Qtra =4.09)、气温9—10.5℃(Qtra =1.12)、不施肥(Qtra =2.16)这3个小组中,地膜覆盖的组内异质性较低,故而具有良好的覆盖效应检验效果。整体上讲,地膜覆盖技术为中国北方地区小麦的生产带来了更可观的正向效应。然而,残存的农用地膜难以分解将会导致逐渐累积的土壤退化[42-43]。与之相比,秸秆覆盖则改善了农田生态系统,有利于作物生产力的可持续发展[44]。为了更好地发挥覆盖技术的特定优势,也有许多学者正在开展秸秆地膜双覆盖的研究[29, 45-46]。

3.2 覆盖模式下小麦产量对环境因素的响应

覆盖栽培的成功与否很大程度上取决于外界的环境因素[47-48]。本研究中,日照时数显著改变了不同覆盖模式下小麦的产量(图3-d),其中覆膜增产效应受到年均降水和气温的影响(图3-b,c)。在大多数的环境梯度里,地膜覆盖的表现要优于秸秆覆盖,其增产率相对高出0.89%—23.34%。但是当试验地年均气温高于12.5℃时,秸秆覆盖的增产幅度(35.25%,95%= 18.72%—51.77%)反超地膜(30.22%,95%= 18.06%—42.38%),该现象符合当地的大田覆盖研究结果[49]。究其原因,秸秆覆盖在某种程度上抑制了土壤温度的升高[50],在小麦的早期生长阶段,这种影响危及了植株的出苗和幼根发育,致使其后期穗分化不充分,小穗数减少,旗叶尖部枯黄。在气温偏低的亚组中(<9℃),该连锁生理反应最终导致秸秆覆盖的产量增幅较覆膜处理下降了4.35%。整体而言,在中国北方地区的小麦栽培实践中,当气温偏高时秸秆覆盖的增产潜力相对较大,而地膜覆盖则更适合于低海拔(<1 150 m)以及半干旱偏湿润(降水量450—550 mm)区推广。

3.3 覆盖模式下小麦产量对田间管理的响应

田间管理措施同样广泛地影响了覆盖小麦的生产状况[51-52]。随着覆盖周期的延长,秸秆覆盖的增产率显著提高,当连续使用该技术超过8年以上,其增产率及效应值分别较地膜处理显著提高24.67%和14.80%(图5-a,图6-a,b)。相应地,一旦覆膜时限超过2年,其增产率基本维持稳定,而反应比则呈现出先增后减的趋势。长期使用塑料薄膜会影响土壤微生物群落的正常发展,加速有机质竭耗,并且提高土壤的斥水性[53],从而为整个地区农业生产的可持续性带来隐患。另一方面,相较于露地栽培,秸秆覆盖同免耕、不施肥以及单施磷肥这3种农艺措施相结合可以显著增产32.68%,25.94%以及21.71%。通过减量施肥、保护性耕作及秸秆覆盖的协调配合,可以在确保高产的同时明显改善土壤质量[54],这就为当下覆盖技术的突破提供了有益思路。在实践生产中,需要统筹考量各项田间管理措施的适用条件,如是方能将其与不同的覆盖模式进行科学组合,从而建立起立体、高效、绿色的作物栽培体系。

4 结论

在中国北方地区,表土覆盖是不可替代的小麦节水增产技术。笔者希望利用Meta分析的理论框架对两种覆盖模式的优劣进行分类探讨。本研究中,覆秸秆和地膜分别显著增产19.53%和24.91%,其中小麦的穗粒数在覆秸秆条件下增幅较大(5.7%),而有效穗数和千粒重在覆膜处理中增长更明显(25.2%和6.4%)。同时,秸秆和地膜覆盖可以促使土壤含水量增加9.74%和17.22%。而最终的覆盖效应又会随着不同的环境条件和田间管理措施产生相应的变化。在北方复杂的时空动态条件下,构建符合地区特点的覆盖栽培体系需要把握精准的生态尺度和农艺尺度。以精准覆盖为基点,将短期收益和长期效益相平衡,将经济产出和生态保护相结合,将应用价值和技术潜力相统筹,才能促进小麦栽培学科的良性发展。本文希望通过对相关文献的整合分析为覆盖技术的区域性推广提供初步的理论参考。

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increasing Effects of wheat yield under mulching cultivation in Northern of China: A Meta-analysis

Qin Yuqing, CHENG HongBo, Chai Yuwei, Ma Jiantao, Li Rui, Li Yawei, CHANG Lei, Chai Shouxi*

Key Laboratory of Crop Science in Arid Environment of Gansu Province/College of Agriculture, Gansu Agricultural University, Lanzhou 730070

【Objective】The aim of this study was to identify the impact of straw mulching and plastic film mulching on wheat production in Northern China, so as to explore the suitable promotion areas of two mulching systems.【Method】In this study, a total of 165 literature was retrieved and screened in recent 40 years, which were put into the framework of Meta-analysis, and were carried out through different forms of overall effect analysis (such as change rate and response ratio) for theoretical research.Generally, by adopting random effect model, the changes of wheat agronomic indexes and farmland moisture conditions under different mulching patterns were analyzed.Then, the response rules of mulching yield increasing effect to various environmental conditions (altitude, precipitation, temperature, and sunshine) and field management measures (mulching period, planting density, tillage, and fertilization) were revealed by subgroup analysis, while the function fitting, weight analysis and statistical test were carried out.The correlation between the variables involved in this study was quantitatively analyzed by Pearson correlation coefficient method.【Result】Compared with the open field cultivation, the straw and plastic film mulching significantly increased wheat yield by 19.53% (95%=0.55%-38.52%) and 24.91% (95%=3.18%-46.64%), which also inhibited field evapotranspiration.Furthermore, it was found that there were some differences in contribution rate of yield components to yield under different mulching patterns, which were: effective spike number > grain number per spike > 1000 grain weight (straw mulching); effective spike number > 1 000 grain weight > grain number per spike (plastic film mulching).The increase of grain number per spike under straw mulching was higher, that about 5.7% (95%= -4.10%-15.50%); while increase of effective spike number and 1000 grain weight under film mulching was more significant, which were 25.2% (95%= 14.11%-36.29%) and 6.4% (95%= 1.50%-11.30%), respectively.In addition to the advantages of promoting production, the biomass and water use efficiency of film mulching were also 18.17% and 14.39% higher than that of straw mulching, respectively.Specifically, the yield increase rate of plastic film mulching was 0.89%-23.34% higher than that of straw mulching in most meteorological subregions.Meanwhile, with the declined of terrain height, the yield increasing effect of plastic film showed the growth trend, compared with non-mulching treatments, and the yield increase rate could reach 34.26% in low altitude area (< 800m).However, the yield increasing advantage of plastic film mulching over straw mulching was declined gradually with the increase of mulching years.In the more than 8 years of mulching experiments, the overall yield increasing rate of straw mulching was higher.The yield of straw mulching was also affected by fertilization and tillage measures, especially in the three treatments of no tillage, no fertilization and applying phosphate fertilizer, the yield increase rates were 32.68%, 25.94% and 21.71%, respectively.According to statistical test, among the three subgroups of altitude, average annual sunshine hours and planting density, their inter group heterogeneity Q test statistics were larger, indicated that the variation degree of each effect quantity in these groups was higher.Finally, it was found that under the conditions of straw and plastic film mulching, the factors with the highest correlation to yield were effective spike number (= 0.808) and water use efficiency (= 0.718), while the most primary factors affecting the soil water content in two mulching systems were evapotranspiration (= -0.859) and water use efficiency (= 0.856), respectively.【Conclusion】In conclusion, these two mulching patterns possessed obvious effect on yield increase, while plastic film mulching had more advantages in low altitude, relative drought and cold regions; The straw mulching was more suitable for long-term conservation tillage system, so as to achieve the coordinated development of production and ecology.Therefore, the key to the success of wheat mulching technology in northern China is to choose scientific mulching methods according to local and time conditions.

straw mulching; plastic film mulching; wheat; yield; meta-analysis

2021-06-02;

2021-11-05

国家现代农业产业技术体系(CARS-3-2-47)、国家自然科学基金(31760362)

秦羽青,E-mail:3279533406@qq.com。通信作者柴守玺,E-mail:sxchai@126.com

(责任编辑 杨鑫浩)

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