毛安然^,1, 赵护兵^,1, 杨慧敏¹, 王涛¹, 陈秀文¹, 梁文娟²¹西北农林科技大学资源环境学院,陕西杨凌 712100
²乾县果树技术服务站,陕西乾县 713300

Effects of Different Mulching Periods and Mulching Practices on Economic Return and Environment

MAO AnRan^,1, ZHAO HuBing^,1, YANG HuiMin¹, WANG Tao¹, CHEN XiuWen¹, LIANG WenJuan^{2 1}College of Natural Resources and Environment, Northwest A & F University, Yangling 712100, Shaanxi
²Fruit Tree Technical Service Station in Qianxian, Qianxian 713300, Shaanxi

通讯作者: 赵护兵,Tel:18991295902;E-mail: zhaohubing@hotmail.com

责任编辑: 李云霞
收稿日期:2020-05-14接受日期:2020-07-13网络出版日期:2021-02-01

基金资助:

国家重点研发计划项目.2018YFD0200403 国家自然科学基金项目.31272250

Received:2020-05-14Accepted:2020-07-13Online:2021-02-01
作者简介 About authors
毛安然,Tel:18437958575;E-mail: 1553453329@qq.com。








摘要
【目的】明确不同覆盖时期（夏闲期和周年覆盖）以及不同覆盖方式（垄沟覆盖、全膜覆盖和秸秆覆盖）对旱地冬小麦产量、经济效益和温室气体排放的影响,为选择适合当地小麦生产的高产、高效和环境友好型覆盖措施提供科学依据。【方法】于2017—2019年2个小麦生长季在黄土高原典型旱作区陕西省永寿县开展大田试验,试验设6个处理,采用裂区设计。不同覆盖时期为主区,设置夏闲期覆盖和周年覆盖（生育期覆盖+夏闲期覆盖）2个处理,不同覆盖方式为副区,分别为垄膜沟秸秆全地面覆盖、全膜覆盖以及秸秆全地面覆盖3个处理。研究分析小麦产量、土壤蓄水量、生育期耗水量、水分利用效率、经济利润以及温室气体排放强度。【结果】与夏闲期覆盖相比,周年覆盖2季平均增产9.5%,周年秸秆覆盖平均产量较周年垄覆沟播处理高出622 kg·hm^-2,而与全膜穴播处理没有显著差异;周年覆盖生育期耗水量和水分利用效率较夏闲期覆盖分别提高5.6%和4.0%;周年覆盖可显著提高冬小麦经济效益,较夏闲期覆盖年平均净利润提高17.8%,周年覆盖中秸秆覆盖平均净利润>全膜穴播>垄覆沟播;同时,周年覆盖2季平均温室气体排放强度较夏闲期覆盖降低11.0%,差异达显著水平。其中,以周年秸秆覆盖的温室气体排放强度最低。【结论】与夏闲期覆盖相比,周年覆盖措施能够提高水分利用效率和生育期耗水量从而提高冬小麦产量和经济效益,同时减少温室气体排放强度。其中,周年秸秆覆盖措施具有较好的经济效益和最低的温室气体排放强度,适宜在黄土旱塬区冬小麦生产中推广应用。
关键词： 夏闲期覆盖;周年覆盖;旱地冬小麦;产量;经济效益;温室气体排放强度

Abstract
【Objective】 The objective of this study was to clarify the effects of different mulching periods (mulching during the summer fallow and the year-round mulching) and different mulching practices (ridge-furrow plastic mulching, whole field plastic mulching and straw mulching) on winter wheat yield, economic return and greenhouse gas emissions in dryland. 【Method】 The experiment was carried out from 2017 to 2019 in Yongshou Country, Shaanxi Province, which was a typical rainfed farming area of the Loess Plateau. The split plot design was employed with main plot of different mulching periods (mulching during the summer fallow and mulching over the year), and sub-plot of different mulching practices (ridge-furrow plastic mulching, whole field plastic mulching and straw mulching). Wheat yield, soil water storage and evapotranspiration during the winter wheat growing season and water use efficiency, economic profit and greenhouse gas emission intensity were analyzed. 【Result】 Compare to mulching practices during the summer fallow, the average yield of year-round mulching practices was increased by 9.5%. The average yield of annual straw mulching was 622 kg·hm^-2 higher than that of annual ridge-furrow plastic mulching, but there was no significant difference between the year-round straw mulching and year-round plastic film mulching. Compare to mulching practices during the summer fallow, the year-round mulching practices increased the evapotranspiration during the winter wheat growing season and water use efficiency by 5.6% and 4.0%, respectively. Compared to mulching practices during the summer fallow, the year-round mulching practices significantly increased the economic return of winter wheat by 17.8%, and the average net economic return was straw mulching>plastic film mulching>ridge-furrow plastic mulching among the year-round mulching practices. Moreover, compared to mulching practices during the summer fallow, the average greenhouse gas emission intensity of year-round mulching practices decreased of 11.0%, and the difference was significant. The lowest greenhouse gas emission intensity was in annual straw mulching. 【Conclusion】 Compared to mulching practices during the summer fallow, the year-round mulching practices could improve water use efficiency and evapotranspiration during the winter wheat growing season, thus improving the yield and economic returns of winter wheat, while reducing the intensity of greenhouse gas emissions. In all practices, the annual straw mulching had the best economic return and the lowest intensity of greenhouse gas emissions, which was suitable for popularization and application in dryland winter wheat production areas.
Keywords：mulching during the summer fallow;the year-round mulching;dryland winter wheat;yield;economic return;the intensity of greenhouse gas emissions


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本文引用格式
毛安然, 赵护兵, 杨慧敏, 王涛, 陈秀文, 梁文娟. 不同覆盖时期和覆盖方式对旱地冬小麦经济和环境效应的影响[J]. 中国农业科学, 2021, 54(3): 608-618 doi:10.3864/j.issn.0578-1752.2021.03.014
MAO AnRan, ZHAO HuBing, YANG HuiMin, WANG Tao, CHEN XiuWen, LIANG WenJuan. Effects of Different Mulching Periods and Mulching Practices on Economic Return and Environment[J]. Scientia Acricultura Sinica, 2021, 54(3): 608-618 doi:10.3864/j.issn.0578-1752.2021.03.014


开放科学（资源服务）标识码（OSID）:

0 引言

【研究意义】旱地养活着约40%的世界人口,而小麦作为人类食物的主要来源之一,约75%产自于旱作农业区^[1,2]。人口的持续增长使得粮食需求量不断提高,实现旱地小麦可持续生产对缓解食品需求压力、保证粮食安全具有十分重要的意义。然而,高的粮食需求量使得人们往往集中注意力于能够提高产量的农业管理措施而忽略了由此引发的环境问题,例如温室气体排放^[3,4]。粮食增产不能以牺牲环境为代价,因此,寻求有效措施促进旱地小麦增产的同时减少环境危害,协调产量和温室气体排放之间的矛盾是当前农业可持续发展进程中亟待解决的问题。【前人研究进展】水资源短缺是限制旱地农业可持续发展的首要因素。地表覆盖技术被认为是蓄积自然降水,提高水分利用效率进而提高产量的可行方法。已有的研究多集中于周年覆盖,主要覆盖方式包括垄覆沟播、全膜穴播和秸秆覆盖^[5,6]。研究表明,周年覆盖能够有效利用夏闲期降水和充分利用生育期降水,是实现小麦高产的重要途经^[7]。但是经周年覆盖后的残膜往往难以捡拾回收,其长期存留于土壤中阻碍土壤导水孔隙,影响作物生长,进而产生“白色污染”^[8,9]。由于黄土高原地区年降水较少且分布严重不均,超过2/3的降水集中在7—9月份^[10],因此,夏闲期覆盖技术逐渐成为研究热点。研究表明,夏闲期覆盖可显著提高小麦播前底墒,改善生育期土壤水分条件,促进小麦增产^[11,12]。陈玉章等在西北旱作雨养区进行覆盖试验,研究表明夏闲期全膜覆盖可使小麦增产29.0%^[13]。与周年覆盖相比,夏闲期覆盖无需考虑小麦播种以及出苗的问题,更容易操作,残膜以及残留秸秆的回收也相对容易,但是无法保蓄生育期降水可能会对产量造成影响。此外,采用农业管理措施提高作物生产力的同时也增加了环境成本,温室气体排放是小麦生产过程中产生的典型的环境危害之一^[14,15]。例如,覆膜增产的同时也增加了一部分额外的投入,包括地膜、机械以及人力投入等,而这些措施都会产生温室气体排放^[16];覆盖秸秆以及移除秸秆的人力投入等也会增加温室气体的排放。由此可见,不同覆盖模式由于其农业投入不同,其温室气体排放也存在很大的差异。【本研究切入点】目前旱地小麦保水覆盖措施研究多集中于单一覆盖时期下不同覆盖方式对冬小麦产量、水分利用效率的影响,而对不同覆盖时期经济效益和环境影响以及综合效益比较研究报道较少。因此,夏闲期覆盖在产量、经济环境效益方面是否优于周年覆盖目前鲜有报道。【拟解决的关键问题】本研究于2017—2019年连续2个小麦生长季在陕西省永寿县御驾宫村布置旱地小麦不同覆盖时期和方式保水增产试验,比较夏闲期和周年覆盖2种覆盖时期以及2种覆盖时期下垄沟覆盖、全膜覆盖和秸秆覆盖3种覆盖方式对冬小麦产量、经济效益和环境效益影响,旨在筛选出适应当地小麦生产的最优覆盖模式,为旱地冬小麦可持续生产和环境友好型覆盖种植技术提供科学依据。

1 材料与方法

1.1 试验区概况

试验于2017—2019年在黄土高原冬小麦种植区陕西省永寿县御驾宫村（35.7°N,108.2°E）进行,包含2个小麦生长季。该地区海拔995 m,年平均降水量500 mm,年平均气温10.8℃,潜在蒸发量807.4 mm,地下水位较深不能为植物吸收利用,降水是维持作物生长的唯一水源。该地区冬小麦种植模式为一年一季,上季小麦通常于6月份收获,下季小麦于同年9月份种植,这使得2季作物之间有3个月的休闲期（7—9月）,而休闲期集中了全年2/3的降水。试验期间降水情况如图1所示,2017—2018和2018—2019年降水量分别为479.4和422.9 mm,夏闲期降水量分别为177.3和277.0 mm,根据GUO等的降水分类方法^[17],2年均为欠水年。试验开始时,该区0—20 cm耕层土壤pH为8.18,有机质13.98 g·kg^-1,总氮含量为0.87 g·kg^-1,硝态氮14.89 mg·kg^-1,铵态氮2.43 mg·kg^-1,有效磷7.13 mg·kg^-1,速效钾124.38 mg·kg^-1。

图1

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图1永寿2017年6月至2019年6月各月降水量

Fig. 1Precipitation from June in 2017 to June in 2019 in Yongshou

1.2 田间试验设计

试验采用裂区设计（表1）,主处理为不同覆盖时期（周年和夏闲期）、副处理为不同覆盖方式,分别为垄沟覆盖（RM+FS）、全膜覆盖（PM）和秸秆覆盖（SM）,共6个处理,4次重复,小区面积为12 m×4 m=48 m²。夏闲期覆盖即从小麦收获后覆盖至下季小麦播前移除覆盖物,生育期进行常规播种,不覆盖;周年覆盖即小麦生育期和夏闲期覆盖,是从小麦播前进行覆盖直至夏闲期结束移除覆盖物,周年覆盖就此完成。本试验为定位试验,第2年重新进行覆盖,覆盖处理与第1年完全相同。覆盖所使用地膜均为0.008 mm厚度的普通白色农用地膜。供试小麦品种为洛旱6号,各处理播种量均为150 kg·hm^-2。在小麦生育期间喷施除草剂。各处理播前均施氮肥150 kg·hm^-2,磷肥127.5 kg·hm^-2,供试氮肥为尿素（含N 46%）,磷肥为过磷酸钙（含P₂O₅ 12%）。

Table 1
表1
表1田间试验设计
Table 1Field experimental design

主处理 Main plot	副处理 Subplot	收获后地表处理 Surface treatment after the harvest	播前 Before seeding	播种 Sowing
夏闲期 Summer fallow period	垄沟覆盖RM+FS	上季小麦收获后翻地起垄,垄上覆膜,沟内覆盖当季收获的秸秆,垄宽35 cm,沟宽30 cm The plot was plowed after the last wheat harvest, 35 cm-wide ridges and 30 cm-wide furrows were created, plastic mulch was placed on top of the ridge and wheat straw from the harvest crop was placed in the furrow	下季小麦播前移走覆盖物,施肥旋耕 The plastic film and wheat straw was manually removed from the plot before the next wheat seeding, after which the plot was applied basal fertilizer and plowed	常规平作,行宽20 cm Conventional flatten culture with 20 cm spacing between rows
	全膜覆盖 PM	上季小麦收获后翻地,地膜全地面覆盖,膜上覆土1 cm The plot was plowed after the last wheat harvest, the whole soil surface was mulched with plastic film and evenly covered with 1 cm of soil	下季小麦播前移走覆盖物,施肥旋耕 The plastic film was manually removed from the plot before the next wheat seeding, after which the plot was applied basal fertilizer and plowed	常规平作,行宽20 cm Conventional flatten culture with 20 cm spacing between rows
	秸秆覆盖 SM	麦秆全地面覆盖,覆盖量10 t·hm-2 Wheat straw (10 t·hm-2) was applied over the whole soil surface during the summer fallow	下季小麦播前移走覆盖物,施肥旋耕 The wheat straw was manually removed from the plot before the next wheat seeding, after which the plot was applied basal fertilizer and plowed	常规平作,行宽20 cm Conventional flatten culture with 20 cm spacing between rows
周年 Year- round	垄覆沟播 RM+FS	上季小麦收获后,沟内覆盖当季收获的秸秆,保留覆盖处理至夏闲期结束 Wheat straw from the harvest crop was placed in the furrow after the last wheat harvest and mulching treatment was retained until the end of the summer fallow	下季小麦播前移走覆盖物,施肥旋耕后起垄覆盖,垄宽35 cm,沟宽30 cm The plastic film and wheat straw was manually removed from the plot before seeding, after which the plot was applied basal fertilizer and plowed, 35 cm-wide ridges and 30 cm-wide furrows were created before the next wheat seeding. Plastic mulch is placed on top of the ridge	沟内种2行小麦,小麦行距20 cm,小麦行和地膜相距5 cm The wheat was manually planted in each furrow in two rows 20 cm spacing, ensuring that the wheat was 5 cm away from each ridge
	全膜穴播 PM	上季小麦收获后,保留覆盖处理至夏闲期结束 Mulching treatment was retained after the last wheat harvest until the end of the summer fallow	下季小麦播前移走覆盖物,施肥旋耕后地膜全地面覆盖,膜上覆土1 cm The plastic film was manually removed from the plot before the next wheat seeding, after which the plot was applied basal fertilizer and plowed, The whole soil surface was mulched with plastic film and evenly covered with 1 cm of soil	小麦行距20 cm,株距12 cm,每穴播10粒左右 The wheat was manually sown in shallow holes with 20 cm spacing between rows and 12 cm spacing within rows
	秸秆覆盖 SM	上季小麦收获后,保留覆盖处理至夏闲期结束 Mulching treatment was retained after the last wheat harvest until the end of the summer fallow	下季小麦播前移走覆盖物,施肥旋耕 The wheat straw was manually removed from the plot before the next wheat seeding, after which the plot was applied basal fertilizer and plowed	常规平作,行宽20 cm,播后麦草全地面覆盖,覆盖量10 t·hm-2 Conventional flatten culture with 20 cm spacing between rows. Wheat straw (10 t·hm-2) was applied after seeding

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1.3 测定项目与方法

（1）土壤蓄水量的测定及计算

以20 cm为一层,在每个小区分别采集小麦播前和收获后0—200 cm土层的土壤样品用烘干法进行土壤含水量的测定。

小麦播前（收获后）土壤蓄水量计算公式为:

（1）W= h × ρ × ω% ×10
式中,W为土壤蓄水量（mm）;h为土层深度（cm）;ρ为土壤容重（g·cm^-3）;ω%为土壤含水量。

由于本试验无灌溉条件,生育期无地表径流且地下水位较深,生育期耗水量可通过以下方式计算:

（2）ET=（W1-W2）+P
式中,ET为小麦生育期耗水量（mm）;P为小麦生育期≥5 mm有效降雨量;W1、W2分别为小麦播前和收获时的土壤贮水量（mm）。

水分利用效率及休闲效率计算公式:

（3）WUE = Y/ET
式中,WUE为水分利用效率（kg·hm^-2·mm^-1）,Y为籽粒产量（kg·hm^-2）,ET为小麦生育期总耗水量（mm）。

（2）经济效益计算

产量效益=籽粒产量×市场价格;

净利润=小麦产量效益-经济投入。

小麦平均市场价格按2.4 元/kg计算;经济投入指小麦生产过程中机械、材料、劳动等总消耗,以当地机械翻耕（675 元/hm²）、覆膜（450 元/hm²） 、播种 （225 元/hm²）、收获（600 元/hm²）以及其他农资（如种子、化肥、农药、地膜）消耗的市场价格计算投入。生产过程中的人力投入（包括覆盖以及移除秸秆、移除残膜等）以每人60元/d计算。

（3）温室气体排放计算

与小麦生产有关的温室气体排放主要来自于:（1）肥料、除草剂、种子和地膜的生产、运输和使用;（2）农业机械应用中所消耗柴油的生产和运输;（3）人力投入。N₂O排放依据前人研究结果^[18,19,20]。虽然土壤CO₂是导致全球变暖的重要因素之一,但是据统计,在全球范围内,土壤CO₂净通量对农业温室气体排放的贡献极小,占农业温室气体排放比例不足1%^[21];CONANT等^[22]表示,土壤有机碳含量在短时间内很难检测到微小的变化,因此在我们的研究中均没有考虑。温室气体（GHG）排放通过以下方式计算:

GHG 排放 = $\sum_{i=1}^{n} A I_{i}$×EF_i + E_N2O

式中,AI_i为作物生长期间的农业投入（包括肥料、除草剂、种子、柴油、人力和地膜等）;EF_i为生命周期中每一个农业投入的GHG排放系数;n为农业投入量;E_N2O田间氮肥投入引起的土壤中N₂O排放。

温室气体排放强度（GHGI）是指单位产量范围内的GHG排放^[19]。计算如下:

GHGI（kg CO₂ eq·Mg^-1）= GHG排放（kg CO₂ eq·hm^-2）/产量（kg·hm^-2）×1000。

1.4 统计分析

采用Excel 2010进行数据处理,用SPSS 24.0进行方差分析,LSD法进行处理间差异显著性检验,显著性水平α=0.05。

2 结果

2.1 不同覆盖时期和覆盖方式对产量影响

不同覆盖时期和覆盖方式对冬小麦产量的影响不同。对不同覆盖时期而言,周年覆盖2季平均产量达到5 558 kg·hm^-2,较夏闲期覆盖平均增产9.5%,且差异达显著水平（图2）。其中,周年垄覆沟播处理较夏闲期垄沟覆盖平均增产5.9%,周年全膜穴播处理较夏闲期全膜覆盖平均增产17.4%,周年秸秆覆盖处理较夏闲期秸秆覆盖处理平均增产5.5%。相同覆盖时期条件下,夏闲期覆盖中秸秆覆盖处理2季平均产量显著高于垄沟覆盖和全膜覆盖处理,而夏闲期垄沟覆盖和全膜覆盖处理之间差异未达显著水平;周年覆盖中秸秆覆盖和全膜穴播处理平均产量没有显著差异,但较周年垄覆沟播处理分别显著高出622和666 kg·hm^-2。

图2

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图2不同覆盖时期以及覆盖方式下的冬小麦产量

SFM:夏闲期覆盖;YM:周年覆盖;RM+FS:垄覆沟播;PM:全膜穴播;SM:秸秆覆盖
图中误差线表示标准差。不同大写字母表示不同覆盖时期间差异显著（P<0.05）;小写字母表示同一覆盖时期不同覆盖方式之间的差异显著（P<0.05）。下同
Fig. 2Winter wheat yield under different mulching periods and mulching practices

SFM: Mulching during the summer fallow; YM: The year-round mulching; RM+FS: Ridge-furrow plastic mulching; PM: Whole field plastic mulching; SM: straw mulching
Error bars indicate standard error. Different capital letters mean significant differences between different mulching periods (P<0.05); different lowercase letters mean significant differences between different mulching practices in the same mulching period (P<0.05). The same as below

2.2 不同覆盖时期和覆盖方式的水分利用差异

2017—2019年不同处理下旱地麦田水分利用差异如表所示（表2）。就不同覆盖时期2季平均蓄水量结果来看,夏闲期覆盖与周年覆盖播前和收获时土壤蓄水量均没有显著差异。但是同一时期不同覆盖方式下土壤播前蓄水量存在明显的不同,夏闲期和周年3种覆盖方式下2季平均播前土壤蓄水量均表现为SM>PM>RM+FS。

Table 2
表2
表2不同覆盖时期以及覆盖方式下对冬小麦水分利用的影响
Table 2Effect of different mulching periods and mulching practices on water use of winter wheat

年份 Year	覆盖时期 Mulching period	覆盖方式 Mulching practice	播前蓄水量 Soil water storage before seeding (mm)	收获后蓄水量 Soil water storage after the harvest (mm)	生育期总耗水 Evapotranspiration,ET (mm)	水分利用效率 Water use efficiency (kg·hm-2·mm-1)
2017—2018	夏闲期 Summer fallow period	RM+FS	388.45a	297.43a	395.22b	12.64a
		PM	438.28a	310.00a	432.47ab	12.04a
		SM	464.58a	310.78a	458.00a	13.25a
		均值Mean	430.44A	306.07A	428.56A	12.64A
	周年 Year-round	RM+FS	388.45a	316.96a	601.11a	12.87a
		PM	438.28a	301.31a	441.16b	10.66a
		SM	464.58a	295.17a	473.61b	10.74a
		均值Mean	430.44A	304.48A	505.30A	11.42A
2018—2019	夏闲期 Summer fallow period	RM+FS	483.92b	335.00a	294.82b	15.94a
		PM	497.87ab	335.86a	307.92ab	15.45a
		SM	521.52a	341.09a	326.33a	15.42a
		均值Mean	501.10A	337.31A	309.69A	15.60A
	周年 Year-round	RM+FS	497.37a	306.56a	336.71a	16.13a
		PM	504.38a	287.46a	362.82a	19.07a
		SM	527.82a	325.85a	347.87a	18.67a
		均值Mean	509.86A	306.62A	349.13A	17.96A
两年平均 Average	夏闲期 Summer fallow period	RM+FS	436.18b	316.21a	345.02b	14.29a
		PM	468.07ab	322.93a	370.19ab	13.75a
		SM	493.05a	325.94a	392.16a	14.34a
		均值Mean	465.77A	321.69A	369.13B	14.12B
	周年 Year-round	RM+FS	442.91b	311.76a	356.20b	14.50a
		PM	471.33ab	294.39a	401.99a	14.87a
		SM	496.20a	310.51a	410.74a	14.71a
		均值Mean	470.15A	305.55A	389.65A	14.69A

均值间比较是指不同覆盖时期间的比较,不同大写字母表示夏闲期覆盖和周年覆盖处理差异显著（P<0.05）;小写字母表示同一覆盖时期不同覆盖方式之间的差异显著（P<0.05）
Mean comparison refers to the comparison between different mulching periods, different capital letters mean significant differences between different mulching periods (P<0.05); different lowercase letters mean significant differences between different mulching practices in the same mulching period (P<0.05)

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与夏闲期覆盖相比,周年覆盖显著提高生育期耗水量和水分利用效率。就2年平均结果来看,周年覆盖生育期总耗水量和水分利用效率较夏闲期覆盖分别提高5.6%和4.0%,差异均达显著水平。针对同一覆盖时期,夏闲期秸秆覆盖处理2季平均生育期耗水量显著高于夏闲期垄沟覆盖处理,而与同时期全膜覆盖处理差异未达显著水平。周年覆盖3种覆盖方式2季平均生育期耗水量与夏闲期3种覆盖方式表现出一致的规律。

2.3 不同覆盖时期和覆盖方式的经济效益分析

与夏闲期覆盖相比,周年覆盖可显著提高冬小麦经济效益,2季平均净利润总体上提高17.8%（图3）。夏闲期覆盖中秸秆覆盖处理2季平均净利润为8 007元/hm²,显著高于垄沟覆盖和全膜覆盖处理,而夏闲期垄沟覆盖和全膜覆盖处理经济效益没有显著差异;周年覆盖下3种覆盖方式2季平均净利润依次为SM>PM>RM+FS,其中周年秸秆覆盖处理其2季平均净利润较周年周年全膜穴播显著提高30.6%,周年全膜穴播处理2季平均净利润较周年垄覆沟播显著高出21.7%。

图3

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图3不同覆盖时期以及覆盖方式下冬小麦经济效益

Fig. 3Winter wheat economic return under different mulching periods and mulching practices

2.4 不同覆盖时期和覆盖方式温室气体排放强度（GHGI）差异

基于不同覆盖处理的温室气体排放量和小麦产量,可以计算出夏闲期和周年3种覆盖方式下温室气体排放强度（图4）。2季平均结果表明:周年覆盖较夏闲期覆盖可以显著降低温室气体排放强度。夏闲期3种覆盖方式中秸秆覆盖处理2季平均温室气体排放强度显著低于垄沟覆盖和全膜覆盖处理,夏闲期地膜覆盖处理中垄沟覆盖2季平均温室气体排放强度显著低于全膜覆盖处理;周年覆盖各处理中以周年秸秆覆盖2季平均温室气体排放强度最低,较周年垄覆沟播和全膜穴播处理分别显著降低44.7%和50.1%,而周年垄覆沟播和全膜穴播处理间差异未达显著水平。

图4

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图4不同覆盖时期以及覆盖方式下产生的温室气体排放强度

Fig. 4The intensity of greenhouse gas emissions under different mulching period and mulching practices

3 讨论

3.1 覆盖方式对旱地冬小麦产量的影响

覆盖是提高旱地小麦产量的重要措施之一。旱地小麦试验表明,在夏季休闲期采用地膜或秸秆覆盖均有利于提高土壤播前底墒,改善土壤养分状况,增加籽粒产量^[23]。刘党校等^[24]的研究表明,生育期地膜覆盖对温度和墒情的调控能够促进冬小麦分蘖,提高穗数和千粒重。李廷亮等^[25]在黄土旱塬进行周年覆盖试验,结果表明,周年垄膜沟播种植较传统无覆盖模式增产8.6%,周年全膜覆土穴播加监控施肥模式使得籽粒产量提高40%。本研究对夏闲期覆盖和周年覆盖下各处理籽粒产量进行比较,结果显示,周年覆盖较夏闲期覆盖2季平均增产9.5%,且差异达显著水平。赵红梅等^[26]的研究表明,在夏闲期覆盖确保小麦底墒的基础上,在小麦生育期间地膜能够减少土壤蒸发的同时增加作物蒸腾耗水,提高水分利用效率,进而增加籽粒产量。而在我们的研究中,周年覆盖2季生育期平均耗水量和水分利用效率均显著高于夏闲期覆盖,这为旱地小麦高产奠定了基础,进而使得周年覆盖小麦籽粒产量显著高于夏闲期覆盖。由于试验地两年均为欠水年,所以小麦生长处于干旱胁迫状态,尽管生育期降水较少,但对小麦生长发育仍起着至关重要的作用。因此,周年覆盖较夏闲期覆盖表现出了明显的增产优势。

针对同一时期不同覆盖方式,有研究表明,穗数与小麦产量呈显著正相关关系,垄覆沟播由于覆膜占据大量无效种植面积,使得小麦穗数减少,从而影响产量形成^[27]。因此本研究中无论夏闲期覆盖或是周年覆盖,垄覆沟播处理2季平均籽粒产量均显著低于秸秆覆盖和全膜穴播处理。同时,我们的研究还发现,秸秆覆盖处理表现出了明显的增产优势,夏闲期秸秆覆盖处理较垄沟覆盖和全膜覆盖处理2季平均籽粒产量显著提高,这与李富翠等秸秆覆盖能够促使小麦增产的研究结果一致^[28,29],而周年秸秆覆盖2季平均籽粒产量与全膜穴播处理基本持平,这可能和周年秸秆覆盖造成小麦早春生长期土壤温度降低有关^[30]。

3.2 覆盖方式对旱地麦田水分利用的影响

水分是制约旱地小麦产量的关键因素之一。由于黄土高原地区地下水位较深且无灌溉水源,作物生长主要依靠降水^[31]。GUO等^[17]研究表明,在黄土高原地区,作物产量与夏闲期降雨量呈显著正相关,因此,夏闲期降雨的保蓄将直接影响籽粒产量的形成。高艳梅等^[32]研究表明,休闲期渗水地膜覆盖条件下,土壤播前蓄水量每增加1 mm,小麦可增产13 kg·hm^-2以上。充足的底墒能够诱导植物根系下扎至土壤深层,使得深层土壤水分得以吸收利用,从而为丰产奠定基础^[33]。在地表覆盖秸秆或地膜等均能够阻止水分垂直蒸发,使得降水能入渗至2 m以下土层,显著增加土壤含水量,提高播前底墒^[30,34]。我们的研究结果表明,无论夏闲期覆盖或是周年覆盖,秸秆覆盖处理的蓄水能力均显著高于垄沟覆盖处理,与全膜覆盖处理播前蓄水量基本持平。秸秆覆盖在夏闲期能够保蓄更多水分的这一优势可能与本研究采用10 t·hm^-2的覆盖量有关。有研究表明,在一定范围内,土壤含水量与秸秆覆盖量呈线性正相关^[35]。另外,与地膜覆盖相比,秸秆覆盖的渗水能力较强,有利于降雨入渗。

除了播前底墒,生育期降水也是保证旱地小麦稳产和高产的重要因素。廖允成等^[34]研究表明,夏闲期覆盖和生育期覆盖相结合能够最大限度保蓄全年降水,为旱地小麦生长提供良好的水分条件。但是在本研究中,周年覆盖和夏闲期覆盖各处理收获期蓄水量却没有显著差异,这是因为高产建立在高耗水的基础上^[5]。周年覆盖后期促进水分消耗由棵间蒸发向作物蒸腾转化,增加蒸腾耗水比例,使得其生育期耗水量和水分利用效率显著高于夏闲期,进而显著提高产量^[25,34,36]。

3.3 覆盖方式对旱地冬小麦经济效益的影响

由于农民承担经济风险的能力有限,一种农业管理措施是否被采用往往取决于它所带来的经济效益而不仅仅依靠产量^[37]。经济效益由籽粒产量和农业投入两个因素决定^[38],因此,提高籽粒产量的同时降低生产成本才能实现资源最大化利用,进而取得高收益。本研究中,夏闲期进行覆盖之前需进行深翻,至小麦播前揭膜再深翻一次然后开始播种,而周年覆盖只在小麦播前深翻一次,因此周年覆盖的生产成本要低于夏闲期覆盖,再则周年覆盖2季小麦籽粒平均产量显著高于夏闲期覆盖,由此解释了我们研究中周年覆盖的经济效益高于夏闲期覆盖的原因。

研究还表明,周年覆盖和夏闲期覆盖中均以秸秆覆盖处理2季平均经济利润最高,这是因为夏闲期垄沟覆盖和全膜覆盖与周年覆盖地膜用量相同,花费分别为500和813元/hm²,且覆膜需要增加额外的机械和人工投入,提高了生产总投入。而我国秸秆资源丰富,尤其是目前禁止燃烧秸秆以后,大量的秸秆废弃并堆积于路边,因此利用废弃秸秆覆盖能够大大缩减生产成本,同时显著提高产量,因而提高了经济效益。CHEN等^[18]的研究表明,秸秆覆盖和地膜覆盖均能维持较高的生产力,但是,由覆盖地膜带来的产量的增加无法抵消覆膜产生的额外花费,这与本研究结果一致。

3.4 覆盖方式对旱地冬小麦温室气体排放强度的影响

据统计,全球温室气体排放呈上升趋势,而农业温室气体排放占总体的10%—12%^[21],IPCC报告显示,如果到2050年全球变暖的问题能够被阻止的话,那么全球温室气体排放较2000年需减少到50%—85%^[39]。不断增长的食物需求压力和全球气候变化都需要农业生产能够在不降低作物生产力的同时减少温室气体的排放,这就需要我们能够最大化利用固定资源（土地、光照、良好的生长条件等）和优化农业投入^[40]。地表覆盖技术能够充分利用光照、水分等资源促进旱地作物产量大幅度增加,但是同时也带来了不同程度的环境危害。温室气体排放强度（GHGI）的计算则量化了农业温室气体排放和籽粒产量的关系,是我们判断农业管理措施是否符合可持续发展理念的重要指标之一^[19]。

最近的研究显示,增加作物产量可以有效降低温室气体排放强度^[41,42],在我们的研究中,周年覆盖使得旱地冬小麦产量大幅度增加,因此与夏闲期覆盖相比,周年覆盖各处理均降低了温室气体排放强度,这与前人研究结果一致。并且,相比较夏闲期覆盖,周年覆盖处理只需对土壤进行一次深翻,降低了柴油等消耗,从而减少单位面积温室气体排放,这也是周年覆盖处理下温室气体排放强度显著降低的重要原因之一。而对同一时期不同覆盖方式而言,HE等^[43]研究表明,与农户模式相比,尽管地膜覆盖通过大幅度提高产量降低了温室气体排放强度,但是并没有减少温室气体排放,地膜覆盖产生的额外的农业投入带来了更高的温室气体排放。此外,经周年覆盖后的地膜大都光解风化,难以回收利用,对环境造成了严重污染^[13]。幸运的是,本研究结果表明,秸秆覆盖相比较地膜覆盖在维持较高产量的同时也减少了由农业投入引起的温室气体排放,缓和了农业生产和环境危害的矛盾,其中以周年秸秆覆盖效果最好。

4 结论

与夏闲期覆盖相比,周年覆盖能够有效蓄积夏闲期降水和高效利用生育期降水,提高了冬小麦籽粒产量和经济效益,同时减少了温室气体排放强度。考虑到地膜覆盖经济投入大,且对环境造成了严重污染,所以周年秸秆覆盖是协调旱地冬小麦籽粒产量和经济效益与温室气体排放之间矛盾的有效途径,适合在旱地冬小麦种植区域干旱年份推广应用。

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