田國成， 孫 路， 施明新， 吳發(fā)啟*

(1 西北農(nóng)林科技大學(xué)資源環(huán)境學(xué)院，陜西楊凌 712100；2 西北農(nóng)林科技大學(xué)水土保持研究所，陜西楊凌 712100)

小麥秸稈焚燒對(duì)土壤有機(jī)質(zhì)積累和微生物活性的影響

田國成1， 孫 路1， 施明新2， 吳發(fā)啟1*

(1 西北農(nóng)林科技大學(xué)資源環(huán)境學(xué)院，陜西楊凌 712100；2 西北農(nóng)林科技大學(xué)水土保持研究所，陜西楊凌 712100)

秸稈焚燒； 有機(jī)質(zhì)含量； 含水量； 微生物數(shù)量； 土壤酶活性

目前針對(duì)農(nóng)田秸稈焚燒的報(bào)道較多，但多集中在大氣環(huán)境變化方面，秸稈焚燒影響土壤環(huán)境的研究較少。本研究通過設(shè)置焚燒不同量的小麥秸稈試驗(yàn)，探究秸稈焚燒對(duì)耕層土壤有機(jī)質(zhì)積累和微生物活性的影響，以期揭示秸稈焚燒對(duì)土壤環(huán)境產(chǎn)生的具體影響，為研究和客觀評(píng)價(jià)農(nóng)田秸稈焚燒提供一定參考。

1 材料與方法

1.1 試驗(yàn)地概況

1.2 試驗(yàn)設(shè)計(jì)

小麥?zhǔn)崭盍舨?0 cm，焚燒秸稈前樣地未進(jìn)行翻耕，土地平整。將小麥秸稈均勻覆蓋在土壤表面，然后進(jìn)行焚燒。并對(duì)殘留較多的部分進(jìn)行補(bǔ)充焚燒，以保證不同焚燒處理的秸稈焚燒完全。試驗(yàn)設(shè)4個(gè)不同秸稈焚燒量處理：1)秸稈不焚燒，移出小區(qū)(CK)；2)減量焚燒，秸稈焚燒量為平均秸稈產(chǎn)量的50%(0.24 kg/m2，A1)；3)全量焚燒，秸稈焚燒量為平均秸稈產(chǎn)量(0.48 kg/m2，A2)；4)增量焚燒，秸稈焚燒量為平均秸稈產(chǎn)量的150%(0.72 kg/m2，A3)。每處理3次重復(fù)，小區(qū)面積25 m2，隨機(jī)區(qū)組排列，小區(qū)之間用田埂隔開。

1.3 樣品采集與處理

1.3.2 測(cè)定項(xiàng)目和方法 土壤有機(jī)質(zhì)采用重鉻酸鉀容量法(外加熱法)[8]；土壤含水量采用烘干法測(cè)定；土壤微生物數(shù)量采用稀釋平板法測(cè)定[9]，細(xì)菌用牛肉膏蛋白胨培養(yǎng)基，真菌用馬鈴薯葡萄糖瓊脂培養(yǎng)基(PDA)，放線菌用改良的高氏一號(hào)培養(yǎng)基。土壤蔗糖酶和過氧化氫酶活性參照關(guān)松蔭的測(cè)定方法[10]。土壤蔗糖酶活性采用 3,5-二硝基水楊酸比色法測(cè)定，以37℃恒溫培養(yǎng) 24 h 后1 g 土生成的葡萄糖的質(zhì)量(mg)數(shù)表示；過氧化氫酶的活性采用高錳酸鉀滴定法測(cè)定，以 1 g 土消耗的0.1 mol/L的高錳酸鉀的毫升(mL)數(shù)表示；脲酶活性用苯酚—次氯酸鈉比色法[11]，以經(jīng)37℃恒溫培養(yǎng)24 h后1 g土中產(chǎn)生的NH3-N的毫克數(shù)(mg)表示，磷酸酶活性測(cè)定參照經(jīng)過趙蘭坡等[12]改進(jìn)的磷酸苯二鈉法，以在37℃恒溫條件下培養(yǎng)24 h后1 g土中酚的質(zhì)量(mg)表示。

1.3.3 數(shù)據(jù)處理 采用SPSS 18.0對(duì)數(shù)據(jù)進(jìn)行方差分析和相關(guān)性分析，Excel 2010軟件繪制圖表。

2 結(jié)果與分析

2.1 秸稈焚燒對(duì)土壤有機(jī)質(zhì)的影響

土壤有機(jī)質(zhì)是土壤的重要組成部分[13]，有機(jī)質(zhì)經(jīng)礦化產(chǎn)生的氮、磷等元素是作物吸收速效養(yǎng)分的主要來源[14]。一般認(rèn)為有機(jī)質(zhì)含量的減少將造成土壤質(zhì)量的下降。表1結(jié)果表明， 在0—5 cm土層中有機(jī)質(zhì)含量處理間表現(xiàn)出CK>A1>A2>A3的趨勢(shì)，與CK相比， A1、A2和A3的有機(jī)質(zhì)含量分別減少了6.37%、11.05%和19.47%，且差異顯著(P﹤0.05)。A1、A2、A3處理之間相比較，A3處理與A1處理之間差異顯著(P﹤0.05)。在5—10 cm和10—20 cm土層中，各焚燒處理的土壤有機(jī)質(zhì)含量與CK之間均無顯著差異。

表1 不同秸稈焚燒處理對(duì)土壤有機(jī)質(zhì)的影響(g/kg)Table 1 Effects of different crops straw burning on soil organic matter

注(Note): 同列數(shù)據(jù)后不同字母表示處理間差異達(dá)5%顯著水平 Values followed by different letters in a column are significant among treatments at the 5% level.

2.2 秸稈焚燒對(duì)土壤含水量的影響

土壤水分是土壤肥力中最活躍的因素之一[15]，是植物吸收水分最重要的供給源，也是土壤中進(jìn)行物理、化學(xué)及生物過程不可缺少的條件[16]。從表2可以看出， 0—5 cm土層的土壤含水量表現(xiàn)出CK>A1>A2>A3的趨勢(shì)。A1、A2、A3處理分別比CK減少了22.15%、27.12%、39.19%，且均差異顯著(P<0.05)。焚燒處理之間相比較，A3處理分別與A1、A2處理有顯著差異(P<0.05)。5—10 cm和10—20 cm土層的土壤含水量各處理之間均無顯著差異。

2.3 秸稈焚燒對(duì)土壤微生物的影響

土壤微生物與土壤肥力關(guān)系密切，經(jīng)土壤微生物轉(zhuǎn)化產(chǎn)生的營養(yǎng)是植物生長(zhǎng)所需養(yǎng)分的重要來源[17]。土壤微生物對(duì)土壤質(zhì)量變化的反應(yīng)較靈敏[18]，可以將土壤微生物數(shù)量作為研究土壤質(zhì)量的

表2 不同秸稈焚燒處理對(duì)土壤含水量的影響(%)Table 2 Effects of different crops straw burning on soil moisture

注(Note): 同列數(shù)據(jù)后不同字母表示處理間差異達(dá)5%顯著水平 Values followed by different letters in a column are significant among treatments at the 5% level.

一個(gè)重要指標(biāo)。 表3顯示，秸稈焚燒后0—5 cm土層的微生物數(shù)量均表現(xiàn)出CK>A1>A2>A3。與CK相比，A1、A2、A3處理的微生物數(shù)量均顯著減少(P﹤0.05)。其中細(xì)菌數(shù)量依次減少52.26%、63.41%、75.25%，真菌數(shù)量依次減少45.21%、57.98%、 63.29%，放線菌數(shù)量依次減少46.87%、56.27%、 68.26%。在5—10 cm土層中，土壤微生物數(shù)量出現(xiàn)一定程度的減少，但未達(dá)顯著水平(P>0.05)。10—20 cm，各處理的土壤微生物數(shù)量均無顯著變化。總體上，在0—5 cm土層中的3大類微生物數(shù)量在3個(gè)焚燒處理之間有顯著差異(P﹤0.05)，而在5—10 cm和10—20 cm土層中3個(gè)焚燒處理之間無顯著差異。

表3 不同秸稈焚燒處理對(duì)土壤微生物數(shù)量的影響Table 3 Effects of different crops straw burning on soil microbial quantity

注(Note): 同列數(shù)據(jù)后不同字母表示處理間差異達(dá)5%顯著水平 Values followed by different letters in a column are significant among treatments at the 5% level.

2.4 秸稈焚燒對(duì)土壤酶活性的影響

土壤酶活性可以代表土壤養(yǎng)分轉(zhuǎn)化和運(yùn)移能力的強(qiáng)弱[19]，較靈敏地指示有關(guān)土壤質(zhì)量，是評(píng)價(jià)土壤肥力的重要指標(biāo)。由表4可以看出，在0—5 cm土層中，土壤酶活性均表現(xiàn)為CK>A1>A2>A3的趨勢(shì)。A1、A2、A3處理與CK相比土壤酶活性出現(xiàn)不同程度的降低，且大多差異顯著(P<0.05)。蔗糖酶活性依次降低了14.19%、18.74%、30.75%，脲酶活性依次降低了7.81%、16.38%、25.48%，過氧化氫酶活性依次降低9.63%、20.80%、39.53%，磷酸酶活性依次降低11.36%、26.42%、40.44%。5—10 cm和10—20 cm土層中，各焚燒處理4種土壤酶與CK相比均無顯著變化。在0—5 cm土層中，蔗糖酶和過氧化氫酶活性A3與A1、A2處理間差異顯著(P﹤0.05)；脲酶和磷酸酶活性各焚燒處理間均有顯著差異(P<0.05)。5—10 cm和10—20 cm土層中，各處理間的差異不顯著。

表4 不同秸稈焚燒處理對(duì)土壤酶活性的影響Table 4 Effects of different crops straw burning on soil enzyme activity

注(Note): 同列數(shù)據(jù)后不同字母表示處理間差異達(dá)5%顯著水平 Values followed by different letters in a column are significant among treatments at the 5% level.

3 討論

本研究結(jié)果表明，小麥秸稈焚燒造成表層(0—5 cm)土壤有機(jī)質(zhì)含量減少，隨著焚燒秸稈量的增多，有機(jī)質(zhì)減少逐漸增多。主要是因?yàn)榉贌龝?huì)使表層土壤有機(jī)質(zhì)含量在短時(shí)間內(nèi)迅速減少，影響其在土壤中的分布[20-21]。在被加熱條件下土壤有機(jī)質(zhì)會(huì)經(jīng)歷氧化分解等過程，最終轉(zhuǎn)化為H2O和CO2揮發(fā)到大氣中[22]，從而損耗土壤中的有機(jī)質(zhì)。而有機(jī)質(zhì)氧化分解的程度與加熱溫度間呈正相關(guān)關(guān)系，研究發(fā)現(xiàn)，將土壤加熱溫度由220℃升高到350℃，有機(jī)質(zhì)損失量由37%升高到90%[23]，這表明火燒強(qiáng)度變大將引起有機(jī)質(zhì)損失的增多。在本研究中，焚燒處理的土壤有機(jī)質(zhì)含量平均減少16.18%，其中增量焚燒處理的減少量是減量焚燒處理的兩倍，該結(jié)果與上述結(jié)論基本一致。盡管小麥秸稈焚燒會(huì)使部分有機(jī)質(zhì)補(bǔ)充到土壤中，但該部分含量小于土壤中被分解掉的有機(jī)質(zhì)總量[24]，因此有機(jī)質(zhì)含量表現(xiàn)出減少的趨勢(shì)。同時(shí)，由于土壤是熱的不良導(dǎo)體，尤其在土壤水分(具有較高的熱容量)存在的情況下，焚燒產(chǎn)生的熱量在土壤中傳遞深度較淺，劇烈而短暫的燃燒過程中熱傳遞僅達(dá)幾厘米[22]。本研究中，焚燒處理對(duì)土壤有機(jī)質(zhì)的影響集中在0—5 cm表層土壤中。這與Trabaud等[25]的研究結(jié)論基本一致。土壤水分的變化從另一方面也印證了這一規(guī)律。小麥秸稈焚燒后，0—5 cm土層中的含水量平均減少了29.52%，由減量焚燒到增量焚燒，水分損失從22.15%升高到39.19%； 5 cm以下土層中土壤含水量無顯著變化。這是由于火燒的熱作用使土壤溫度迅速升高，土壤水分受熱而蒸發(fā)散失，并且溫度越高蒸發(fā)量越大。綜上所述，通過增加秸稈焚燒量可使火燒產(chǎn)生的熱輻射對(duì)土壤有機(jī)質(zhì)和水分的影響加強(qiáng)，但只在表層土中的影響顯著。

土壤酶活性的發(fā)揮是以土體和土壤有機(jī)物質(zhì)為基礎(chǔ)的，焚燒對(duì)土壤有機(jī)物質(zhì)和微生物群落的影響可通過分析土壤酶活性的變化來間接表達(dá)[29]。在本研究中，秸稈焚燒后0—5 cm土層中的蔗糖酶、脲酶、堿性磷酸酶和過氧化氫酶活性平均依次降低了21.13%、16.93%、23.21%、28.20%。溫度高于70℃時(shí)，土壤酶作為蛋白質(zhì)因熱變性而活性降低。此外，溫度升高引起的蛋白質(zhì)降解作用(如脫酰胺和肽鍵斷裂等)也是土壤酶活性降低的重要原因。這與Hernandez等[30]認(rèn)為火后許多土壤酶的活性迅速降低的結(jié)論是一致的。

相關(guān)性分析表明，秸稈焚燒量與各指標(biāo)間呈顯著負(fù)相關(guān)關(guān)系(表5)。說明秸稈焚燒強(qiáng)度與其對(duì)土壤的影響程度間呈正比。而這種相關(guān)性是在熱輻射對(duì)有機(jī)質(zhì)和水分影響以及對(duì)微生物活性的抑制的基礎(chǔ)上產(chǎn)生的。趙彬等[27]的研究未發(fā)現(xiàn)這種趨勢(shì)，其原因是火燒后數(shù)月乃至數(shù)年時(shí)間土壤成分的差異和養(yǎng)分的損失得到了部分恢復(fù)。

4 結(jié)論

小麥秸稈焚燒短期內(nèi)顯著降低了0—5 cm表層土壤中有機(jī)質(zhì)含量、含水量和細(xì)菌、真菌、放線菌數(shù)量以及蔗糖酶、脲酶、過氧化氫酶、磷酸酶活性，而對(duì)5—20 cm土層的影響不顯著。小麥秸稈焚燒對(duì)土壤環(huán)境的影響強(qiáng)度隨秸稈量的增多而加大。秸稈焚燒量與有機(jī)質(zhì)含量、含水量、微生物數(shù)量及土壤酶活性之間呈顯著負(fù)相關(guān)關(guān)系。鑒于秸稈焚燒對(duì)土壤肥力的長(zhǎng)期效應(yīng)以及對(duì)土壤環(huán)境理化性狀影響的復(fù)雜性，焚燒對(duì)土壤有機(jī)質(zhì)積累和微生物群落的影響還需長(zhǎng)期定位試驗(yàn)來探討。

表5 秸稈焚燒量與有機(jī)質(zhì)含量、含水量、 微生物數(shù)量和土壤酶活性之間的相關(guān)性Table 5 Correlative coefficients between straw burning amount and soil organic matter content, moisture content, microbial quantity and enzyme activities

注(Note): *—P<0.05.

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Effect of wheat straw burning on soil organic matter accumulation and microbial activity

TIAN Guo-cheng1, SUN Lu1, SHI Ming-xin2, WU Fa-qi1*

(1CollegeofResourcesandEnvironment,NorthwestA&FUniversity,Yangling,Shaanxi712100,China;2InstituteofSoilandWaterConservation,NorthwestA&FUniversity,Yangling,Shaanxi712100,China)

【Objectives】Open burning of agricultural waste is practiced to clear the surface biomass from land, to control pests and diseases, and to return some nutrients. Emissions from field burning activities deteriorate local air quality and seriously impede agricultural development. Recently many studies had been conducted to assess air pollution caused by straw burning. However, data are relatively limited in change of soil physical and organic subsequent to straw burning. Topsoil of different straw burning quantity was collected to study the immediate effect of straw burning on content of soil organic matter and soil microbial activity. 【Methods】 A field experiment was established in June 2012. The experimental treatments included 4 levels of amount of burned wheat straw: no burning (CK), decrement group (0.24 kg/m2, A1), normal group (0.48 kg/m2, A2) and increment group (0.72 kg/m2, A3). The wheat straw was put evenly over soil surface and then was burned, and the remained wheat straws were additionally burned in order to make straw burnt completely. After five hours, when soil temperature had returned to normal, soil samples were collected from 0-5, 5-10 and 10-20 cm depth of soil in each treatment and analyzed through laboratory experiment. To elucidate the specific effect of burning wheat straw on soil environment, change of indicators, soil organic matter content, moisture content, microorganism quantity and enzyme activities in each layer of soil, were analyzed. 【Results】 Burning wheat straw had significant influence on topsoil. The indicators of soil constituents were reduced with different degrees in different treatments. In the layer of 0-5 cm, the content of soil organic matter and moisture was reduced by 6.37%-19.47% and 22.15%-39.19% respectively. The quantities of bacteria, fungi and actinomyces were respectively decreased by 52.26%-75.25%, 45.21%-63.29%, 46.87%-68.26%. Activities of sucrase, urease, catalase and phosphatase were decreased by 14.19%-30.75%, 7.81%-25.48%, 9.63%-39.53% and 11.36%-40.44% respectively. There were significant differences between most combustion treatments and the control, while there was no significant difference in the 5-20 cm soil layer. The content of each indicator was decreased in the order of A3>A2>A1. The combustion treatments with different amount of straw mostly had significant difference between each other. The correlation analysis indicated that amount of straw burning had significantly negative correlations with soil organic matter content, moisture, soil microbial quantity and soil enzyme activity. 【Conclusions】 The results indicated that wheat straw burning significantly reduced soil organic matter content and soil microbial activity in topsoil (0-5 cm) in a short time, and the impact strength was proportional to the amount of burned straw. In the layer of 5-20 cm, the effect of the straw burning was small. The correlation analysis indicated that straw burning amount had significantly negative correlations with soil organic matter content, moisture, soil microbial quantity and soil enzyme activity. Due to long-term effect of straw burning on soil fertility and the complexity of the effect on the physical and chemical properties in soil environment of straw burning, long-term in-situ study should be carried out to better assess effect of wheat straw burning in field.

straw burning；soil organic matter content；soil moisture；soil enzyme activity； microbial quantity

2014-04-03 接受日期： 2014-06-30 網(wǎng)絡(luò)出版日期： 2015-05-07

“十二五”國家科技支撐項(xiàng)目(2012BAD14B11)資助。

田國成(1987—)，男，河北興隆人，碩士研究生，主要從事土地資源利用與管理方面的研究。 E-mail: 905098882@qq.com * 通信作者 E-mail: wufaqi@263.net

S153.6+2； S154.3

A

1008-505X(2015)04-1081-07