胡宏亮， 韓之剛， 張國平

(浙江大學(xué)農(nóng)業(yè)與生物技術(shù)學(xué)院，杭州 310058)

生物降解地膜對(duì)玉米的生物學(xué)效應(yīng)及其降解特性

胡宏亮， 韓之剛， 張國平*

(浙江大學(xué)農(nóng)業(yè)與生物技術(shù)學(xué)院，杭州 310058)

通過大田試驗(yàn)，從土壤保溫性、作物生長(zhǎng)發(fā)育與產(chǎn)量、田間降解等方面對(duì)5種可降解地膜進(jìn)行分析比較。結(jié)果顯示：可降解地膜覆蓋能顯著提高土壤不同深度的溫度，其中M2和M52種地膜的整體保溫效果最為突出，達(dá)到了接近普通地膜的水平；地膜覆蓋可顯著加快玉米生育進(jìn)程和增加玉米產(chǎn)量，且部分可降解地膜的促進(jìn)效果優(yōu)于普通地膜。在地膜降解方面，5種可降解地膜破裂啟動(dòng)期較為一致，發(fā)生于覆膜后約20 d，可基本滿足玉米苗期對(duì)溫度、水分的需要；覆膜90～100 d后可降解地膜從土壤表面基本消失。以上結(jié)果顯示，供試的5種可降解地膜不僅具有顯著的生物學(xué)效應(yīng)和經(jīng)濟(jì)學(xué)效果，其降解特性也基本符合玉米生長(zhǎng)對(duì)環(huán)境條件的要求，完全可以替代傳統(tǒng)地膜。

地膜； 降解； 玉米； 生物學(xué)效應(yīng)； 產(chǎn)量

Summary Over the past few decades, the use of traditional mulch film made of poly-ethylene enhanced agriculture production worldwide, and meanwhile raised a range of agricultural and ecological concern associated with degradation of soil fertility due to residue accumulation. It has become an increasingly challenging issue for agricultural sustainability. As a consequence, biodegradable films are proposed as an effective solution to alleviate this issue. Among them, poly (butyleneadipate-co-terephthalate) (PBAT), a biodegradable aliphatic-aromatic polyester, possesses similar mechanical properties to polyethylene and therefore is generally considered an ideal substitute for conventional films. This study aimed at making a comprehensive evaluation of several recently developed biodegradable films by comparing their biological effects and field degradation properties.

Five biodegradable films with a main component of PBAT were applied to cover the beds of maize in an experimental field, and then the soil temperature, plant growth indices and yield components of maize were investigated. Meanwhile, the field degradation of both biodegradable and conventional films was assessed by a standard of degradation degree.

The results showed that the biodegradable films, compared to bare plot, markedly raised soil temperatures at three observation depths (5 cm, 10 cm and 15 cm) and this heat capturing effect was as pronounced as the conventional polyethylene film. The temperature boosting effect varied with soil depth and time,i.e., the biggest diurnal fluctuation of temperature occurred at the depth of 5 cm in each treatment, while the least was at the depth of 15 cm. The growth of maize was significantly stimulated in all mulched plots, with the occurrence of seedling emergence and silking stage being 3-5 days and 10-13 days earlier than bare plots, respectively. A minor advantage of biodegradable film over conventional film was also observed. The highest chlorophyll content (indicated by SPAD) was found in the bare plot, followed by M2, and M1was the lowest, yet there were no significant differences among mulching treatments. By contrast, leaf area indices (LAI) of the biodegradable films were significantly higher than non-mulched plot, with the highest in M2. At the jointing stage, the plant height under all mulched plots were greater than that under the bare plot. While at the maturity stage, plants in the bare plot had the highest height, and there were no significant differences among the five biodegradable films. The largest accumulation of nitrogen, phosphate and potassium in plants occurred in the bare plot, being significantly higher than in the mulched plots. The fresh yield, kernels per ear and 100-kernel mass were significantly larger in all mulched plots than in the bare plot. The yield per plot of the biodegradable films was higher than that of the conventional film, yet no difference existed between the biodegradable films and the conventional film in terms of kernels per ear and 100-kernel mass. Field observation revealed that the biodegradable films started losing integrity at approximately 20 days after application in the field. The earliest clear disappearance of film started at 90 days after application for M2. While the relatively slow degradation was found in M1and M5, which were torn into separate subunits with roughly 10 cm cracks after 100 days of field exposure, reaching the 4th period of degradation.

In sum, all the biodegradable films are capable of enhancing maize growth by improving soil temperature and even contribute a larger economic yield than the conventional film; moreover, the biodegradable films maintain stability for approximately 20 days after application in the field and disappear after 90-100 days, demonstrating the applicable effectiveness for mulching as a substitute of the conventional film.

地膜覆蓋是一項(xiàng)應(yīng)用廣泛而又十分重要的農(nóng)業(yè)生產(chǎn)輔助措施。塑料地膜通過改變土壤能量平衡從而改善作物生長(zhǎng)小氣候[1-2]。這一田間小氣候的改變可引起土壤溫度變化，并影響作物生長(zhǎng)與產(chǎn)量[3-6]。塑料地膜除了具有增溫保墑、抑制雜草、減少病蟲害和提高水分利用率等作用外，更因?yàn)槠洳僮骱?jiǎn)易性、化學(xué)穩(wěn)定性、持久性、靈活性和無毒性，在過去的數(shù)十年間全球用量快速增加[7]。我國從1979年開始從日本引進(jìn)地膜栽培技術(shù)，發(fā)展迅速，已經(jīng)成為一項(xiàng)常用的農(nóng)業(yè)增產(chǎn)措施。據(jù)統(tǒng)計(jì)，我國農(nóng)作物地膜覆蓋面積1981年為15萬hm2，而至2005年已達(dá)1 350萬hm2[8]。覆蓋作物從最初的經(jīng)濟(jì)蔬菜擴(kuò)大到包括玉米、水稻、小麥在內(nèi)的大宗糧食作物。我國現(xiàn)有的1.217億hm2土地中，使用塑料地膜覆蓋栽培的面積超過0.17億hm2，年增產(chǎn)糧食和經(jīng)濟(jì)作物收益達(dá)500億元。2011年，我國農(nóng)用塑料薄膜使用量為229.5萬t，其中地膜使用量124.5萬t，地膜覆蓋面積1 979萬hm2[9]，是世界上塑料地膜使用最多的國家。

然而，大部分塑料地膜在使用后直接殘留在土壤中或被隨意燃燒，釋放出有害物質(zhì)，對(duì)環(huán)境造成負(fù)面影響。目前，生產(chǎn)塑料地膜的材料主要從石油中獲得，地膜成分通常為聚乙烯(polyethylene, PE)，使用后造成了極大的處理困難[10]。聚乙烯在自然條件下極難降解，降解周期一般為200年。同時(shí)，我國多年來大量使用8 μm或6 μm的PE膜，因厚度薄而在田間極易破碎，不僅造成地膜二次利用率低，也因難以回收而使殘膜在土壤中不斷積累。土壤中的大量殘膜導(dǎo)致了土壤物理結(jié)構(gòu)層次的改變，使土壤水分和養(yǎng)分向下運(yùn)輸受到阻礙，土壤孔隙度、通透性降低，造成耕地質(zhì)量下降[11-13]。據(jù)統(tǒng)計(jì)，截至2003年全世界每年的農(nóng)用及相關(guān)領(lǐng)域的塑料使用量達(dá)248萬t[14]。田間殘膜的大量積累已成為農(nóng)村白色污染的主要來源之一。嚴(yán)昌榮等[15]對(duì)我國5個(gè)典型省長(zhǎng)期覆膜農(nóng)區(qū)的調(diào)查結(jié)果顯示，農(nóng)田地膜殘留量從71.9 kg/hm2(湖北)到259.1 kg/hm2(新疆)不等。顯然，有效處理大量塑料地膜已成為當(dāng)今世界的一項(xiàng)重大課題和挑戰(zhàn)。

雖然回收利用是一種可能的方法，但是從田間拾取殘膜十分費(fèi)時(shí)(16 h/hm2)，即使采用機(jī)械回收，也需要人工勞作[16]；并且在很多蔬菜栽培中，地膜受泥污和殘?jiān)廴緡?yán)重，難以直接從田間回收[17]。解決這一問題的有效途徑之一就是改變材料基質(zhì)，研制生物降解塑料地膜。如果地膜能在覆蓋一段時(shí)間后自行降解且無有害物質(zhì)殘留，將從根源上解決目前普遍的“白色污染”問題。生物降解材料在其使用末期能整合到土壤中，被微生物轉(zhuǎn)化為二氧化碳或甲烷、水分和生物質(zhì)[18-21]。根據(jù)美國材料與試驗(yàn)協(xié)會(huì)標(biāo)準(zhǔn)(American Society for Testing and Materials, ASTM)的定義，生物降解塑料是指因受自然界微生物(細(xì)菌、真菌)和藻類等的活動(dòng)影響而發(fā)生降解的可降解塑料[22-24]。聚酯由于含有一個(gè)可水解酯鍵，是一類重要的生物降解塑料，且其材料特性與傳統(tǒng)塑料相似[25-26]?？缮锝到饩埘サ啬ひ蚰茉谧匀唤鐥l件下完全降解為二氧化碳和水，近年來受到高度關(guān)注。目前已研制出多種商業(yè)用途的生物降解聚酯材料，品種包括聚乳酸、脂肪-芳香族共聚酯、聚羥基烷酸酯等。聚己二酸對(duì)苯二甲酸丁二酯[poly (butyleneadipate-co-terephthalate), PBAT]是一種脂肪芳香族聚酯，不僅具有生物降解性能，還具有與聚乙烯相似的機(jī)械性能[27]。而其他聚酯，如聚乳酸(poly lactic acid， PLA)和聚羥基丁酸酯(polyhydroxybutyrate, PHB)，難以實(shí)現(xiàn)以低成本達(dá)到覆膜所需的機(jī)械性能[28]。本研究選用新研制的幾種以PBAT為主要成分、不同配方的可控生物降解地膜(即可以通過配方改良調(diào)控降解速率的生物降解地膜)，對(duì)其在田間覆蓋期間的保溫、增產(chǎn)效果和田間降解情況進(jìn)行觀測(cè)分析，綜合評(píng)價(jià)不同生物降解地膜的生物學(xué)效應(yīng)和降解特性，從而為該類新型可控生物降解地膜的研制及應(yīng)用提供理論依據(jù)與技術(shù)支撐。

1 材料與方法

1.1 預(yù)備試驗(yàn)

試驗(yàn)在杭州市浙江大學(xué)紫金港校區(qū)實(shí)驗(yàn)農(nóng)場(chǎng)進(jìn)行。材料選用杭州鑫富藥業(yè)股份有限公司研制的5種降解地膜，主要成分為PBAT，另加少量生物降解材料及助劑；以普通膜為對(duì)照，市售，主要成分為聚乙烯；另設(shè)不覆膜(露地)處理。所用作物為蠶豆，2012年11月20日播種。根據(jù)地膜的土壤保溫性、田間機(jī)械穩(wěn)定性以及蠶豆的生長(zhǎng)發(fā)育表現(xiàn)，確定綜合效果最佳的類型，并將結(jié)果返回公司，進(jìn)一步優(yōu)化地膜配方，形成5種改良地膜，分別編號(hào)為M1～M5。

1.2 驗(yàn)證試驗(yàn)

本試驗(yàn)旨在進(jìn)一步測(cè)試所研發(fā)的5種改良地膜的生物學(xué)效應(yīng)及其大田降解特性。試驗(yàn)設(shè)7個(gè)處理，包括不覆膜(M0)、分別覆蓋5種可降解地膜(M1～M5)和覆蓋普通聚乙烯膜(M6)。供試作物為玉米，品種為浙大甜玉米7號(hào)。于2013年3月28日直播并覆膜，畦寬0.9 m，穴播，每穴2粒種子，于三葉期定苗為每穴1苗，行距40 cm，株距30 cm。各處理重復(fù)3次，小區(qū)面積12 m2。

生育期間觀察各處理玉米生育進(jìn)程；播種后每隔10 d測(cè)定土表下5 cm、10 cm和15 cm 3個(gè)深度的溫度。拔節(jié)期測(cè)定株高、葉面積指數(shù)和功能葉葉綠素含量。成熟后測(cè)定株高、地上部干質(zhì)量、每穗粒數(shù)、百粒質(zhì)量及小區(qū)產(chǎn)量，并分析莖稈和葉片的氮、磷、鉀含量。氮含量采用凱氏定氮法，在FOSS Tecator Digestor Auto消煮儀上360 ℃消煮后用定氮儀(Kjeltec 8400)測(cè)定；磷、鉀含量采用ICP測(cè)定，用微波(Multiwave 3000，Anton Paar)消煮后在ICP儀(Optima 8000)上測(cè)定。所有數(shù)據(jù)均采用Microsoft Excel 2013和SAS 9.1.3軟件進(jìn)行統(tǒng)計(jì)分析。

同時(shí)，試驗(yàn)期間每隔10 d對(duì)地膜降解情況進(jìn)行田間調(diào)查和統(tǒng)計(jì)。以0～5級(jí)評(píng)估地膜降解程度：0級(jí)，地膜外觀形態(tài)完整，未出現(xiàn)裂紋；1級(jí)，開始出現(xiàn)10 cm以下裂紋；2級(jí)，出現(xiàn)約20 cm較大裂紋；3級(jí)，出現(xiàn)約50 cm大塊裂紋；4級(jí)，地膜分裂成多塊較大的獨(dú)立部分，并且內(nèi)部出現(xiàn)10 cm裂紋；5級(jí)，土壤表面地膜基本消失，僅少量殘留。

2 結(jié)果與分析

2.1 不同覆膜處理對(duì)土壤溫度的影響

2013年4月11日和4月21日不同覆膜處理的土壤溫度變化見圖1。從中可以看出：可降解地膜和普通地膜均可顯著提高不同深度土壤的溫度，且整體上不同降解地膜和普通膜之間差異不大，5種可降解地膜之間無顯著差異。地膜的增溫作用因土壤深度和測(cè)量時(shí)間而異。在淺土層(5 cm)下，土壤溫度日變化最大，以4月11日為例，露地處理在觀察期間在15 ℃至22 ℃之間變動(dòng)，而地膜處理在17 ℃至27 ℃之間；而在15 cm深土壤下，露地處理在14 ℃至18 ℃之間變動(dòng)，地膜處理則在16.5 ℃至21.5 ℃之間。另外，10 cm和15 cm深土壤的日最高溫度出現(xiàn)在17:00時(shí)，而5 cm深土壤的日最高溫出現(xiàn)較早。4月21日的觀察結(jié)果顯示，可降解地膜和普通地膜均顯著提高了3個(gè)不同土壤深度的溫度，且與露地處理的溫度差異隨日照時(shí)間而增大；同時(shí)，與4月11日相比，可降解地膜與普通地膜在3個(gè)土壤層的溫度差異減小，說明可降解地膜由于發(fā)生了一定的田間破損或降解而失去了完整性，保溫性能已呈下降趨勢(shì)。

A：2013年4月11日;B：2013年4月21日。M0：不覆膜；(M1～M5)：覆蓋5種不同配方的可降解地膜；M6：覆蓋普通聚乙烯地膜。柱狀圖上的不同小寫字母表示在該時(shí)刻和該土壤深度下不同地膜處理之間在P<0.05水平差異有統(tǒng)計(jì)學(xué)意義。A: April 11, 2013; B: April 21, 2013. M0: Bare plot without film mulching; (M1-M5): Plots mulched with five biodegradable films of different compositions; M6: Plot mulched with conventional polyethylene film. Different lowercase letters above the columns represent statistically significant differences among the different mulch film treatments at the same soil depth during the same time (P<0.05).

2.2 不同覆膜處理對(duì)玉米生育進(jìn)程的影響

在露地栽培條件下，玉米的全生育期為97.3 d，可降解地膜和普通地膜均顯著縮短了玉米達(dá)到各生育時(shí)期需要的時(shí)間，為85.0～87.3 d(表1)。地膜覆蓋加速玉米生長(zhǎng)發(fā)育的效果在苗期就開始體現(xiàn)，地膜覆蓋玉米12～14.3 d即出苗，而露地玉米需要17.3 d，提前了3～5 d；到拔節(jié)期、抽雄期和吐絲期，露地和覆膜處理之間的差異進(jìn)一步拉大，至吐絲期，地膜覆蓋比露地處理早10～13 d。顯然，地膜覆蓋處理加快玉米生育進(jìn)程對(duì)于鮮食玉米提早上市、增加收益具有積極意義。

可降解地膜與普通地膜相比具有一定的微弱優(yōu)勢(shì)。苗期至吐絲期及成熟期，均以5種可降解地膜處理的較早，其中以M2和M5的作用最為明顯，玉米成熟比普通地膜(M6)早2 d以上。

表1 不同覆膜處理對(duì)玉米主要生育期出現(xiàn)時(shí)間的影響

Table 1 Effect of different mulch film treatments on growth stages of maize d

生育期GrowthstageM0M1M2M3M4M5M6出苗Seedlingemergence17.3a(0)12.3c(5.0)12.3c(5.0)12.0c(5.3)12.6c(4.7)13.3bc(4.0)14.3b(3.0)拔節(jié)Jointing31.0a(0)25.3d(5.7)25.7d(5.3)25.0d(6.0)26.0cd(5.0)26.7c(5.3)27.0b(4.0)抽雄Tasseling70.3a(0)62.8b(7.7)62.3b(8.0)62.0b(8.3)63.7b(6.7)62.0b(8.3)63.0b(7.3)吐絲Silking81.7a(0)70.0b(11.7)69.3b(12.3)70.7b(11.0)70.3b(11.3)68.7b(13.0)71.3b(10.3)成熟Maturity97.3a(0)86.0cd(11.3)85.3d(12.0)86.6bc(10.7)86.0cd(11.3)85.0d(12.3)87.3b(10.0)

M0：不覆膜；(M1～M5)：覆蓋5種不同配方的可降解地膜；M6：覆蓋普通聚乙烯地膜。括號(hào)內(nèi)的數(shù)字表示該處理比露地處理提前的天數(shù)；同行數(shù)據(jù)后的不同小寫字母表示在P<0.05水平差異有統(tǒng)計(jì)學(xué)意義。

M0: Bare plot without film mulching; (M1-M5): Plots mulched with five biodegradable films of different compositions; M6: Plot mulched with conventional polyethylene film. Numbers in brackets represent days earlier than the treatment of bare plot. Values within a row followed by different lowercase letters represent statistically significant difference at the 0.05 probability level.

2.3 不同覆膜處理對(duì)玉米生長(zhǎng)與養(yǎng)分吸收的影響

拔節(jié)期葉片葉綠素含量以露地處理的最高，M2次之，M1最低，各處理間在統(tǒng)計(jì)學(xué)上差異不顯著(表2)。拔節(jié)期的玉米葉面積指數(shù)以可降解地膜最高且顯著高于普通地膜，露地處理最小，僅1.87。拔節(jié)期株高以露地處理的最低，僅140.8 cm，顯著低于可降解地膜處理(160.2～178.5 cm)和普通地膜(171.8 cm)；可降解地膜以M1最低，M2、M4和M5表現(xiàn)相近。在成熟期，露地處理株高為207.1 cm，明顯高于可降解地膜(199.4～205.3 cm)和普通膜(196.1 cm)?？梢?，在拔節(jié)期前露地玉米因地溫較低，生長(zhǎng)相對(duì)緩慢；拔節(jié)后，由于溫度上升，露地玉米發(fā)育加快，同時(shí)地膜保溫優(yōu)勢(shì)對(duì)玉米生長(zhǎng)的影響已較小。以上結(jié)果與趙愛琴等[29]的報(bào)道不同，其原因可能是本試驗(yàn)中5月以后氣溫較高，地膜的保溫作用相對(duì)較小。在氮、磷、鉀積累方面以不覆膜的積累量最高，顯著高于部分地膜覆蓋處理。在覆膜處理中，氮、磷、鉀積累量均以M2最高，M6最低。露地處理的養(yǎng)分積累量最高，其原因可能是取樣時(shí)M0處理的玉米植株生育期相對(duì)滯后，莖、葉等營養(yǎng)器官仍保留有較多的養(yǎng)分；而覆膜處理植株均已完熟，莖、葉中的養(yǎng)分已較多轉(zhuǎn)移至籽?；虮涣苁?。

表2 不同覆膜處理對(duì)玉米生長(zhǎng)和養(yǎng)分吸收的影響

Table 2 Effects of different mulch film treatments on maize growth and nutrient uptake

生長(zhǎng)指標(biāo)GrowthindicesM0M1M2M3M4M5M6葉綠素含量(SPAD值)Chlorophyllcontent(SPADvalue)50.85a48.72a50.50a49.17a49.99a49.42a49.20a葉面積指數(shù)Leafareaindex1.87c2.71ab2.89a2.70ab2.70ab2.81ab2.57b株高Plantheight/cm拔節(jié)期Jointingstage140.8c160.2b178.4a166.5ab174.0a178.5a171.8ab成熟期Maturitystage207.1a199.4ab204.9a203.9a204.1a205.3a196.1b氮素積累量Naccumulation/(g/plant)1.153a0.956b1.156a0.957b0.821c0.966b0.815c磷素積累量Paccumulation/(g/plant)0.223a0.183b0.231a0.192b0.155c0.193b0.155c鉀素積累量Kaccumulation/(g/plant)1.787a1.529b1.763a1.551b1.183c1.411b1.163c

M0：不覆膜；(M1～M5)：覆蓋5種不同配方的可降解地膜；M6：覆蓋普通聚乙烯地膜。同行數(shù)據(jù)后的不同小寫字母表示在P<0.05水平差異有統(tǒng)計(jì)學(xué)意義。

M0: Bare plot without film mulching; (M1-M5): Plots mulched with five biodegradable films of different compositions; M6: Plot mulched with conventional polyethylene film. Values within a row followed by different lowercase letters represent statistically significant difference at the 0.05 probability level.

2.4 不同覆膜處理對(duì)玉米產(chǎn)量及構(gòu)成因子的影響

5種可降解地膜和普通地膜覆蓋處理的小區(qū)鮮玉米產(chǎn)量均顯著高于露地處理，其中以可降解地膜M2和M5的產(chǎn)量最高，且顯著高于普通地膜；5種可降解地膜處理在統(tǒng)計(jì)學(xué)上無顯著差異(表3)。每穗粒數(shù)和百粒質(zhì)量均為覆膜處理高于露地處理，但5種降解地膜處理之間以及它們與普通地膜之間在統(tǒng)計(jì)學(xué)上無顯著差異。顯然，M2和M5的小區(qū)產(chǎn)量高于普通地膜是由于幾個(gè)產(chǎn)量構(gòu)成因子綜合改善的結(jié)果，抑或由于每株穗(棒)數(shù)較多所致。

表3 在不同覆膜處理下玉米每穗粒數(shù)、百粒質(zhì)量與小區(qū)產(chǎn)量

M0：不覆膜；(M1～M5)：覆蓋5種不同配方的可降解地膜；M6：覆蓋普通聚乙烯地膜。同行數(shù)據(jù)后的不同小寫字母表示在P<0.05水平差異有統(tǒng)計(jì)學(xué)意義。

M0: Bare plot without film mulching; (M1-M5): Plots mulched with five biodegradable films of different compositions; M6: Plot mulched with conventional polyethylene film. Values within a row followed by different lowercase letters represent statistically significant difference at the 0.05 probability level.

2.5 地膜降解速率

可降解地膜的降解程度隨覆蓋時(shí)間增加而逐漸加深，而普通地膜的變化較小，只出現(xiàn)少量細(xì)小的裂紋，屬于正常破損(圖2)。

不同可降解地膜的降解啟動(dòng)期基本相同，但降解速率存在著一定的差異。覆蓋后約20 d，地膜形態(tài)完整性開始變差，出現(xiàn)細(xì)小的裂縫；不同地膜的啟動(dòng)期長(zhǎng)度各異，M1和M3啟動(dòng)期最長(zhǎng)，1級(jí)程度降解持續(xù)約30 d，其他可降解地膜則約為20 d。此后，可降解地膜M2、M3和M4降解速率較快，覆蓋后90 d，M2基本從土壤表面消失；M3和M4在覆蓋后100 d基本消失；M1和M5降解相對(duì)較慢，但在生育期末降解也達(dá)到4級(jí)(表4)。

M0：不覆膜；(M1～M5)：覆蓋5種不同配方的可降解地膜；M6：覆蓋普通聚乙烯地膜。M0: Bare plot without film mulching; (M1-M5): Plots mulched with five biodegradable films of different compositions; M6: Plot mulched with conventional polyethylene film.

表4 不同地膜的田間降解程度

M0：不覆膜；(M1～M5)：覆蓋5種不同配方的可降解地膜；M6：覆蓋普通聚乙烯地膜。(0～5)表示地膜降解程度指標(biāo)。0級(jí)：地膜外觀形態(tài)完整，未出現(xiàn)裂紋；1級(jí)：開始出現(xiàn)10 cm以下裂紋；2級(jí)：出現(xiàn)約20 cm較大裂紋；3級(jí)：出現(xiàn)約50 cm大塊裂紋；4級(jí)：地膜分裂成多塊較大的獨(dú)立部分，并且內(nèi)部出現(xiàn)10 cm裂紋；5級(jí)：土壤表面地膜基本消失，僅少量殘留。

M0: Bare plot without film mulching; (M1-M5): Plots mulched with five biodegradable films of different compositions; M6: Plot mulched with conventional polyethylene film. Numbers 0-5 indicate different degradation degrees of mulch films. 0: Films remaining intact; 1: Films losing integrity and developing minor cracks within 10 cm in length; 2: Larger cracks with length of approximately 20 cm; 3: Cracks developing into bigger ones sized 50 cm in length; 4: Films torn into separate subunits with roughly 10 cm cracks in each; 5: Disappearance of films with tiny fragments allowed.

3 討論

隨著傳統(tǒng)聚乙烯地膜使用量的不斷增加，其負(fù)面影響也不斷顯現(xiàn)。由于自然界尚不存在對(duì)聚乙烯快速降解的微生物，普通地膜需要長(zhǎng)達(dá)200年以上的周期才能完全消失。作為對(duì)傳統(tǒng)非降解地膜的一種環(huán)保型替代產(chǎn)品，生物降解地膜需要滿足幾個(gè)基本條件：1)具有接近或同等的生物學(xué)效應(yīng)。增溫保墑、改善田間小氣候，達(dá)到促進(jìn)作物生長(zhǎng)，貢獻(xiàn)與傳統(tǒng)地膜相近的經(jīng)濟(jì)產(chǎn)出；2)具有適宜于覆蓋作物的降解特性。在作物苗期或低溫時(shí)期保持穩(wěn)定、完整的田間形態(tài)，以保證適宜的土壤溫度和濕度；在作物生長(zhǎng)后期或收獲之后，及時(shí)啟動(dòng)降解，并在后茬種植之前基本分解為細(xì)小的碎片，避免對(duì)下季作物根系水分和礦物質(zhì)元素吸收造成影響；3)具有足夠的力學(xué)性能和拉伸強(qiáng)度，達(dá)到田間鋪蓋的強(qiáng)度要求，能抑制雜草生長(zhǎng)。傳統(tǒng)厚度較大的聚乙烯地膜由于機(jī)械性能較好，且在自然界中不易分解，因此可以較好地滿足這一要求，但可降解地膜使用了新型材料(主要為PBAT)，其田間實(shí)際抗雜草情況尚有待驗(yàn)證。這也是評(píng)價(jià)可降解地膜實(shí)際應(yīng)用價(jià)值的重要標(biāo)準(zhǔn)。

本試驗(yàn)選用的5種可降解地膜在提高土壤溫度、加快和促進(jìn)玉米生長(zhǎng)發(fā)育方面具有顯著的效果，且得到了比普通地膜更高的玉米鮮穗產(chǎn)量，表明可降解地膜具備更強(qiáng)的生物學(xué)效應(yīng)。在地膜田間降解方面，5種可降解地膜均在覆膜后20 d開始出現(xiàn)裂縫，在覆膜60～80 d后開始達(dá)到3級(jí)降解程度，在該時(shí)期地膜的完整性受到較大的影響，可以推測(cè)對(duì)土壤的增溫作用開始減弱，同時(shí)雜草生長(zhǎng)開始加快。結(jié)合玉米生育進(jìn)程，可降解地膜的啟動(dòng)降解期稍早，尚不能有效抑制前期雜草生長(zhǎng)，地膜在自身受到損壞的同時(shí)，其受雜草生長(zhǎng)導(dǎo)致的機(jī)械力影響而破裂更加明顯。到覆膜后100 d，可降解地膜基本從田間表面消失，在生物學(xué)效應(yīng)上基本不影響作物后期的生長(zhǎng)。

但與普通地膜相比，可降解地膜也有明顯的不足之處。首先是材料成本上，目前可降解地膜使用成本是市售聚乙烯地膜的近3倍，因此難以在生產(chǎn)上大面積推廣。降低可降解地膜的價(jià)格將是該產(chǎn)品推廣應(yīng)用的主要措施?？梢韵嘈牛S著生產(chǎn)工藝的改進(jìn)、規(guī)模生產(chǎn)的推進(jìn)以及政府對(duì)新產(chǎn)品支持力度的加大，會(huì)逐漸降低可降解地膜的生產(chǎn)成本，從而被廣大農(nóng)民所接受。除了以高分子為材料的可降解膜，目前以苧麻纖維為主要成分的環(huán)保型麻地膜是一種成本低、發(fā)展前景好的可降解地膜。我國由于麻類原料生產(chǎn)和人力資源方面的優(yōu)勢(shì)，麻地膜產(chǎn)品成本較低[30]。中國麻類研究所以苧麻落麻、黃麻等為主要材料研制出了可降解麻地膜[30]，并在白菜、早稻育秧、辣椒等試驗(yàn)或示范中取得了優(yōu)異效果[31-33]。麻地膜還具有獨(dú)特的土肥優(yōu)勢(shì)，降解后的麻類纖維無污染，并能改善土壤物理形狀；麻地膜降解物還能提高土壤有機(jī)質(zhì)含量和微生物數(shù)量，提高土壤肥力[31]。有報(bào)道指出，可降解材料的降解特性通常與其化學(xué)組分[34-35]、工藝參數(shù)、貯藏與使用環(huán)境[36-37]有關(guān)。在地膜開發(fā)與生產(chǎn)過程中，還需要根據(jù)地理區(qū)域、種植栽培方式和季節(jié)性添加特殊的降解助劑，以調(diào)整地膜的物理特性[38]。目前已有類似的研究證明可以通過良好的配方控制，使可降解地膜達(dá)到與高密度聚乙烯相近甚至更好的機(jī)械性能[39]。喬海軍等[40]選用以淀粉、聚己內(nèi)酯和石蠟等為主要成分的生物降解地膜，在甘肅省進(jìn)行玉米覆膜試驗(yàn)，發(fā)現(xiàn)可降解地膜在播種后30 d部分破損，出現(xiàn)少量破孔，在覆膜170 d后大量破碎為小塊地膜，部分變得很薄很脆。Kijchavengkul等[41]研究表明，降解地膜的生物學(xué)效果及降解速率與自然光強(qiáng)弱有關(guān)。因此，在實(shí)際使用時(shí)，需要考慮當(dāng)?shù)鼗蛟耘嗉竟?jié)的自然因素而選擇適宜的降解地膜種類。

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Biological effect of biodegradable mulch films on maize and their degradation properties. Journal of Zhejiang University (Agric. & Life Sci.), 2015,41(2):179-188

Hu Hongliang, Han Zhigang, Zhang Guoping*

(CollegeofAgricultureandBiotechnology,ZhejiangUniversity,Hangzhou310058,China)

mulch film; degradation; maize; biological effect; yield

國家科技支撐計(jì)劃項(xiàng)目(2012BAD11B03).

聯(lián)系方式：胡宏亮，E-mail:hlhu@zju.edu.cn

2014-09-19；接受日期(Accepted)：2014-11-24；網(wǎng)絡(luò)出版日期(Published online)：2015-03-20

S 31; X 705

A

*通信作者(Corresponding author)：張國平，Tel:+86-571-88982115;E-mail:zhanggp@zju.edu.cn

URL:http://www.cnki.net/kcms/detail/33.1247.S.20150320.2106.011.html