杜少平 唐超男 馬忠明 薛亮 班明輝
摘? ? 要:【目的】研究營養(yǎng)液EC值與滴灌頻率對溫室西瓜植株生長及果實產(chǎn)量、品質(zhì)的影響,以期尋求營養(yǎng)液最優(yōu)供給方式,為實現(xiàn)設(shè)施西瓜椰糠基質(zhì)栽培過程中營養(yǎng)液的高效供給及標(biāo)準(zhǔn)化管理提供理論依據(jù)?!痉椒ā吭囼炓砸窞樵耘嗷|(zhì),設(shè)置了4個EC值水平(E1:0.15 mS·cm-1,E2:0.25 mS·cm-1,E3:0.35 mS·cm-1, E4:0.45 mS·cm-1)和2個灌溉頻率(R1:2次·d-1,R2:4次·d-1),采用兩因素完全隨機設(shè)計方法,共8組處理?!窘Y(jié)果】西瓜不同生育期植株、根系形態(tài)指標(biāo)及生物量隨著營養(yǎng)液EC值的升高先增加后降低,團棵期(15 d)和坐果期(30 d)均以E2處理為優(yōu),膨果中期(45 d)莖粗和葉面積分別以E3和E2處理為優(yōu);成熟期(65 d)果實質(zhì)量隨EC值的增大持續(xù)下降,而可溶性固形物、可溶性糖含量及糖酸比等品質(zhì)指標(biāo)持續(xù)上升。低灌水頻率(2次·d-1)顯著提高了西瓜苗期(15 d)植株的莖粗、葉面積和根系形態(tài)參數(shù),促進了根冠比的提高,有利于強苗的培養(yǎng)。高灌水頻率(4次·d-1)顯著提高了西瓜坐果期(30 d)莖粗、根總表面積、根體積和生物量,以及膨果中期(45 d)的莖粗;成熟期(65 d)單果質(zhì)量以高灌溉頻率為優(yōu),品質(zhì)以低灌溉頻率為優(yōu)。此外,試驗因素的交互作用對團棵期徑粗、根系總長、根系表面積、根系鮮質(zhì)量影響極顯著(p<0.01),以E2R1組合最好;對坐果期株高和根系鮮質(zhì)量影響顯著(p<0.05),對莖葉生物量影響極顯著,均以E2R2組合最好;成熟期果實品質(zhì)以E4R1組合為優(yōu)。【結(jié)論】團棵期EC值為0.25 mS·cm-1、灌溉頻率為2次·d-1,伸蔓至坐果期EC值為0.25 mS·cm-1、灌溉頻率為4次·d-1,果實膨大期EC值為0.15~0.25 mS·cm-1、灌溉頻率為4次·d-1,成熟期EC值為0.45 mS·cm-1、灌溉頻率為2次·d-1的營養(yǎng)液分段灌溉方式能兼顧西瓜植株發(fā)育和果實品質(zhì)良好。
關(guān)鍵詞:西瓜;電導(dǎo)率;滴灌頻率;椰糠;基質(zhì)
中圖分類號:S651 文獻標(biāo)志碼:A 文章編號:1009-9980(2023)09-1932-11
收稿日期:2023-01-30 接受日期:2023-04-28
基金項目:國家西甜瓜產(chǎn)業(yè)技術(shù)體系土壤與養(yǎng)分管理崗位(CARS-25);甘肅省現(xiàn)代農(nóng)業(yè)科技支撐體系區(qū)域創(chuàng)新中心重點科技項目(2020GAAS02);中國和以色列創(chuàng)新合作示范項目
作者簡介:杜少平,男,研究員,研究方向為瓜菜作物水肥高效利用技術(shù)。Tel:13893482056,E-mail:dushaoping2007@163.com
*通信作者 Author for correspondence. Tel:0931-7617566,E-mail:mazhming@163.com
Effects of nutrient solution electrical conductivity (EC) and drip irrigation frequency on growth and quality of watermelon grown in coco coir substrate in solar greenhouse
DU Shaoping1, TANG Chaonan1, MA Zhongming2*, XUE Liang3, BAN Minghui2
(1Institute of Vegetables, Gansu Academy of Agricultural Sciences, Lanzhou 730070, China; 2Gansu Academy of Agricultural Sciences, Lanzhou 730070, China; 3 Institute of Soil, Fertilizer and Water-saving Agricultural, Gansu Academy of Agricultural Sciences, Lanzhou 730070, China)
Abstract: 【Objective】 The study aimed to explore a kind of optimal supply mode of nutrient solution and provide a guidance basis for high efficiency and standardized management of the nutrient supplement for watermelon plants grown in coconut-coir substrate through investigating the effects of nutrient solution electrical conductivity (EC) and drip irrigation frequency on plant growth and fruit weight and quality. 【Methods】 The experiments were designed with 4 EC levels (E1, E2, E3, and E4 representing the EC of nutrient solution at 0.15, 0.25, 0.35 and 0.45 mS·cm-1, respectively) and 2 irrigation rate levels (R1 and R2 representing the irrigation rate of nutrient solution at 2 times·d-1 and 4 times·d-1, respectively), complete stochastic region design of two factors was applied with 8 groups of treatment. The regulation of EC values of each treatment level was realized by diluting the A and B mother liquor. Because of the difference of the plant growth and the weather, average daily irrigation volume for each plant was controlled within 0.8-1.5 L, which was divided into several equal parts according to the irrigation rates. And the nutrient solution was applied at the following times: R1 at 8:30 and 14:30, R2 at 8:30, 11:30, 14:30 and 17:30. 【Results】 The different EC values of nutrient solution and drip irrigation frequency significantly affected the growth of watermelon plants and the formation of fruit yield and quality in the greenhouse. With the increase of EC value of nutrient solution, the shoot growth performance (including plant height, stem diameter, leaf area), and root morphology (including total length, surface area, volume and diameter of root), and the plant biomass of the watermelon during vegetative growth period increased first and then decreased. The low irrigation frequency (2 times·d-1) significantly increased the stem diameter, leaf area and root morphological parameters of watermelon plants at the rosette stage, promoting the improvement of root-shoot ratio, 26.52% higher than that of the high irrigation frequency (4 times·d-1), which was conducive to the cultivation of strong seedlings. In addition, compared with the low irrigation frequency, the high irrigation frequency significantly increased the plant height of watermelon in vine elongating stage by 6.75%, and obviously increased the stem diameter, total root surface area and root volume and biomass of watermelon in fruit setting stage by 5.29%, 13.33%, 10.90%, 7.71%, 11.26%, and 7.19%, respectively. At the same time, the interaction of the nutrient solution EC value and drip irrigation frequency on watermelon plant height reached a significant level (p<0.05), and the comprehensive effect of the E2R1 combination was the highest, which was 2.94 cm 24.53 cm and 154.86 cm at the rosette stage, vine elongating stage and fruit setting stage, respectively. Furthermore, at rosette stage and/or fruit setting stage, this interaction on stem diameter, total root length, root surface area, root-shoot ratio and biomassreached extremely significant level (p<0.01), and the E2R1 was the optimum combination. In the formation stage of fruit yield and quality, with the increase of EC value, the fruit weight and organic acid of watermelon respectively decreased from 2.49 kg and 0.67% to 1.96 kg and 0.58%, while the soluble solids, soluble sugar and sugar/ acid ratio respectively increased from 10.07%, 5.89% and 8.87 to 10.39%, 6.47% and 11.19%. Meanwhile, compared with the high irrigation frequency, the low irrigation frequency significantly reduced the fruit weight and organic acid by 6.41% and 11.94, and significantly increased the soluble solids, soluble sugar and sugar/ acid ratio by 2.08%, 6.20% and 11.94%, respectively. Therefore, the low irrigation frequency was beneficial to improving the fruit quality, and the high irrigation frequency was beneficial to increasing the fruit yield. In addition, the interaction of experimental factors only had an extremely significant effect on the fruit weight (p<0.01), and the treatment of E1R2 and E2R2 had the largest fruit weight, which were 2.52 kg and 2.65 kg, respectively. In the different combinations, the fruit quality of E4R1 treatment was optimum, including the lowest organic acid content, which was 0.55%, and the highest soluble solids, soluble sugar and sugar/acid ratio, which were 10.62%, 6.73% and 12.18%, respectively. 【Conclusion】 In the condition of greenhouse cultivation, the combinations of 0.25 mS·cm-1 EC and 2 times·d-1 irrigation rate during rosette stage, 0.25 mS·cm-1 EC and 4 times·d-1 irrigation rate during vine stage, 0.15-0.25 mS·cm-1 EC and 4 times·d-1 irrigation rate during fruit swelling stage, and 0.45 mS·cm-1 EC and 2 times·d-1 irrigation rate during maturation stage, would ensure the watermelon plants grown in coconut-coir substrate to grow well and produce quality fruits with high yield.
Key words: Watermelon; Electrical conductivity; Drip irrigation frequency; Coconut-coir; Substrates
我國是世界重要的西瓜種植國和消費國,面積、產(chǎn)量均位居全球第一。2019年我國西瓜播種面積為153.9萬hm2,總產(chǎn)量為6 324.1萬t,收獲面積、產(chǎn)量分別占全球的46.3%和60.6%[1-2]。由于設(shè)施西瓜栽培能夠增加反季節(jié)供應(yīng)量,滿足人們不同季節(jié)對西瓜的消費需求,單位面積經(jīng)濟效益約是露地栽培的3倍[3]。因此,近年來設(shè)施栽培已成為西瓜的重要栽培模式。但由于設(shè)施栽培土壤長期處于高集約化、高復(fù)種指數(shù)狀態(tài),西瓜多年重茬種植后土壤連作障礙嚴(yán)重,導(dǎo)致西瓜的產(chǎn)量和品質(zhì)下降,嚴(yán)重制約著設(shè)施西瓜生產(chǎn)的可持續(xù)發(fā)展[4]。
采用無土栽培方式可有效克服土壤次生鹽漬化、土傳病蟲害等連作障礙問題,目前已成為有效克服設(shè)施西瓜地土壤連作障礙的主要栽培措施之一[5]。椰糠作為瓜菜栽培基質(zhì)具有良好的保水性和透氣性,有利于植物吸收養(yǎng)分和水分,并且其天然環(huán)保、性質(zhì)穩(wěn)定、重復(fù)利用率高等優(yōu)點,已在果蔬生產(chǎn)中得到了廣泛應(yīng)用。以往研究結(jié)果表明,椰糠基質(zhì)栽培較傳統(tǒng)泥炭基質(zhì)栽培可在一定程度上提高西甜瓜的果實品質(zhì)[6],較巖棉基質(zhì)栽培能夠促進黃瓜植株生長,獲得較高的果實品質(zhì)[7]。
營養(yǎng)液是無土基質(zhì)栽培的核心,是植物獲取營養(yǎng)的最主要途徑,營養(yǎng)液的合理供給不僅可以提高作物的產(chǎn)量和品質(zhì),而且還是降低生產(chǎn)成本的關(guān)鍵因素[8]。EC值能在一定程度上反映營養(yǎng)液的養(yǎng)分離子濃度,為營養(yǎng)液管理提供數(shù)據(jù)支持[9]。在茄果類蔬菜方面,研究提出兼顧番茄植株發(fā)育和果實品質(zhì)良好的營養(yǎng)液EC值為0.4 mS·cm-1,灌溉頻率為5次·d-1[10];黃瓜椰糠栽培適宜的流出液EC值控制區(qū)間為2.2~2.6 mS·cm-1,流出率控制在15%[11-12]。壓砂西瓜采用中低頻補灌(2~3次補灌)處理,補灌量控制在16.46~21.46 m3·666.7 m-2,能促進其營養(yǎng)物質(zhì)積累,提高水分利用效率,改善西瓜品質(zhì)[13]。葉菜方面,研究提出水培生菜的最佳營養(yǎng)液EC值為1.0~1.2 mS·cm-1[14];水培蕹菜的最佳營養(yǎng)液EC值為1.5 mS·cm-1[15]。在瓜類方面,綜合甜瓜植株生長、坐果、裂果和產(chǎn)量、品質(zhì)等因素,研究提出設(shè)施網(wǎng)紋甜瓜椰糠基質(zhì)栽培適宜的營養(yǎng)液EC值為:苗期1.8~2.3 mS·cm-1、伸蔓期2.7~3.0 mS·cm-1、開花結(jié)果期3.3~3.7 mS·cm-1[16]。由此可見,EC值是設(shè)施農(nóng)業(yè)無土栽培營養(yǎng)液管理的重要技術(shù)參數(shù),然而目前針對設(shè)施西瓜椰糠基質(zhì)栽培模式下營養(yǎng)液灌溉技術(shù)的研究未見報道。為此,筆者在本文中通過設(shè)施西瓜椰糠基質(zhì)栽培模式下,不同營養(yǎng)液EC值與灌溉頻率對西瓜植株、根系生長和果實產(chǎn)量、品質(zhì)的影響研究,以期為營養(yǎng)液高效利用及西瓜的優(yōu)質(zhì)高產(chǎn)提供科學(xué)依據(jù)。
1 材料和方法
1.1 試驗材料
試驗地點:試驗在甘肅省農(nóng)業(yè)科學(xué)院張掖節(jié)水試驗站塑料大棚中進行,地處典型的綠洲荒漠交錯帶,地理位置為100°22′51 E,38°50′49 N,屬溫帶大陸性荒漠氣候區(qū),海拔1555 m,年均氣溫6 ℃,無霜期165 d,年均降水量128 mm、蒸發(fā)量約2341 mm,年日照時數(shù)約3300 h。
西瓜品種為中早熟品種美麗(武威安泰達種業(yè)有限責(zé)任公司),果實圓形,皮色濃綠,瓜瓤大紅,質(zhì)地脆沙、汁多纖維細,中心可溶性固形物含量12.0%左右,單果質(zhì)量6~8 kg。椰糠條(100 cm × 20 cm × 15 cm)采用冉美椰糠(由青島冉美商貿(mào)有限公司提供),母液營養(yǎng)液配方見表1[15],試劑為無土栽培專用(由北京艾格拉農(nóng)業(yè)科技有限公司提供)。
1.2 試驗處理
本試驗為椰糠基質(zhì)開放式栽培,采用營養(yǎng)液EC值與灌溉頻率兩因素完全隨機設(shè)計。依據(jù)實際生產(chǎn)經(jīng)驗設(shè)4個EC值水平(E1:0.15 mS·cm-1,E2:0.25 mS·cm-1,E3:0.35 mS·cm-1, E4:0.45 mS·cm-1)和2個灌溉頻率水平(R1:2次·d-1,R2:4次·d-1),共8個處理組(E1R1,E1R2,E2R1,E2R2,E3R1,E3R2,E4R1,E4R2),3次重復(fù),隨機區(qū)組排列。
A、B母液等體積混合按不同比例稀釋,利用電導(dǎo)率儀(精度0.01 mS·cm-1,DDS-307實驗室電導(dǎo)率儀)調(diào)節(jié)各水平工作液至目標(biāo)EC值范圍±0.05 mS·cm-1內(nèi),然后用磷酸調(diào)節(jié)各營養(yǎng)液pH值在6.5~6.8之間。各水平營養(yǎng)液灌溉頻率實施時間:R1為08:30和14:30,R2為08:30、11:30、14:30和17:30。各處理每日每株灌溉量一致,且按照灌溉頻率進行平均分配,根據(jù)西瓜生長發(fā)育和天氣變化控制在0.8~1.5 L。按照營養(yǎng)液EC值水平,首部安裝了4個儲液罐和4條獨立的輸水主管道,并通過主管水表和支管球閥控制灌溉量和滴灌頻率。
西瓜于2021年3月6日育苗,4月10日定植(三葉一心),6月27日收獲。移栽前2 d將所有營養(yǎng)液EC值調(diào)至約0.05 mS·cm-1沖洗浸泡椰糠栽培條至流出液與供給液EC值基本一致,選擇長勢一致且無病蟲害的健康苗定植,每條椰糠袋定植3株,株距35 cm,行距80 cm。緩苗5 d后開始試驗處理,采用吊蔓栽培和單蔓整枝方式,人工授粉,每株在12~15節(jié)位只留1個正常發(fā)育果實。
1.3 測試指標(biāo)與方法
1.3.1 植株形態(tài)指標(biāo) 從定植后的第15天(團棵期)開始,每處理選擇5株長勢一致的植株掛牌標(biāo)記,每間隔15 d采集一次植株形態(tài)指標(biāo),一直到第45天即膨果中期。用卷尺測定株高,游標(biāo)卡尺測定距椰糠塊上表面約5 cm處莖粗,用便攜式葉面積儀(LI-3000C,美國)測定莖基部以上第5~7枚葉片的葉面積,取其平均值。
1.3.2 根部形態(tài)指標(biāo) 分別在西瓜團棵期(定植后15 d)和開花坐果期(定植后30 d),每處理選擇3株長勢一致的植株采集其根系,用根系掃描儀(WinRHIZO,加拿大)測定其根系形態(tài)指標(biāo),包括總根長、表面積、根體積和直徑。
1.3.3 植株生物量指標(biāo) 分別在西瓜團棵期和開花坐果期,結(jié)合根系形態(tài)指標(biāo)的測定取樣,根、莖分離后,分別測定根系和莖葉鮮質(zhì)量,計算根冠比。
1.3.4? ? 單果質(zhì)量和品質(zhì)指標(biāo)? ? 西瓜成熟期(定植后65 d),每處理選擇10個具有代表性的果實先測定單瓜質(zhì)量,再將果實沿縱徑切開后利用手持測糖儀(精度0.1%,日本愛拓PAL-1型)測定可溶性固形物含量,然后沿果實縱徑方向取等量果肉樣品于組織搗碎機中研磨成漿,采用蒽酮比色法[17]測定可溶性糖含量,滴定法[17]測定有機酸含量,并計算糖酸比。
1.4 數(shù)據(jù)處理
采用Excel 2010和SPSS 19.0統(tǒng)計軟件進行試驗數(shù)據(jù)分析。
2 結(jié)果與分析
2.1 營養(yǎng)液EC值與灌溉頻率對植株形態(tài)的影響
株高、徑粗和葉面積能反映植物的健康情況,是生殖生長的基礎(chǔ)。由表2可知,西瓜定植后的15 d即團棵期,營養(yǎng)液EC值對西瓜株高、徑粗、葉面積的影響均達到極顯著水平(p<0.01),其中株高和徑粗均以E1和E2水平的最高,葉面積則以E2和E3水平的最高;滴灌頻率對徑粗和葉面積影響達到極顯著水平,R1水平顯著高于R2水平;兩因素的交互作用對株高和徑粗影響顯著,其中株高以E1R2和E2R2處理的最高,徑粗以E1R2和E2R1處理的最高,葉面積則以E2R1、E3R1處理的最高。西瓜定植后的30 d即坐果期,營養(yǎng)液EC值對株高、徑粗、葉面積的影響均達到極顯著水平(p<0.01),其中株高以E2水平最高,徑粗和葉面積均以E1和E2水平最高,滴灌頻率對株高影響顯著,以R2水平顯著高于R1水平,而對徑粗和葉面積影響不顯著,兩因素的交互作用僅對株高影響顯著,其中株高以E2R2和E3R2處理的最高,徑粗以E1R2和E2R1處理的最高,葉面積則以E1R2、E2R2處理的最高。西瓜定植后的45 d即膨果中期,營養(yǎng)液EC值對徑粗和葉面積的影響均達到極顯著水平(p<0.01),其中株高和葉面積以E2水平較高,而徑粗以E3水平最高;滴灌頻率僅對徑粗影響顯著,R2水平顯著高于R1水平;兩因素的交互作用僅對株高影響顯著,其中株高以E1R2和E2R1處理的最高,徑粗以E3R2處理的最高,葉面積則以E2R1處理的最高。
2.2 營養(yǎng)液EC值與灌溉頻率對根系形態(tài)的影響
西瓜根系的發(fā)育主要在營養(yǎng)生長期,從表3可以看出,西瓜團棵期,營養(yǎng)液EC值和滴灌頻率對根系形態(tài)指標(biāo)的影響均達到極顯著水平(p<0.01),根系形態(tài)指標(biāo)均隨著EC值的升高呈先增加后降低的變化趨勢,整體在E2水平時最高,且R1水平顯著高于R2水平,兩因素的交互作用對總根長和表面積影響達到極顯著水平,其中總根長以E2R1處理最高,而表面積、根體積和根直徑均以E2R1和E3R1處理最高。西瓜開花坐果期,營養(yǎng)液EC值和滴灌頻率對根系形態(tài)指標(biāo)的影響也達到顯著水平,與團棵期相似,根系形態(tài)指標(biāo)均隨著EC值的升高呈先增加后降低的變化趨勢,總根長和表面積在E2水平時最高,根體積和根直徑在E2和E3水平時最高,R2水平的總根長、表面積和根體積顯著高于R1水平,而根直徑則相反。兩因素的交互作用僅對根直徑影響達到顯著水平,其中總根長、表面積和根體積均以E2R2處理最高,而根直徑則以E2R1處理最高。
2.3 營養(yǎng)液EC值與灌溉頻率對西瓜地上、地下部生物量的影響
從表4營養(yǎng)液EC值與灌溉頻率對西瓜營養(yǎng)生長期地上、地下部的生物量影響來看,團棵期EC值對西瓜地上、地下部生物量及根冠比的影響均達到極顯著水平,其中地上部莖葉生物量以E2水平最高,地下部根系生物量以E2和E3水平最高,根冠比則以E1處理最高。滴灌頻率及兩因素的交互作用對根系生物量及根冠比影響極顯著,R1水平顯著高于R2水平,在不同組合處理中,E2R1和E2R2處理的莖葉生物量最高,E1R1、E2R1和E3R1處理的根系生物量最高,E1R1處理的西瓜根冠比顯著高于其他處理。在西瓜開花坐果期,EC值、滴灌頻率及兩因素交互作用對莖葉、根系生物量的影響均達到顯著水平,其中莖葉和根系生物量均以E2水平和R2水平最高,E1R2、E2R1和E2R2處理顯著高于其他處理。
2.4 營養(yǎng)液EC值與灌溉頻率對西瓜單果質(zhì)量和品質(zhì)的影響
EC值、滴灌頻率及兩因素交互作用對西瓜單果質(zhì)量的影響均達到極顯著水平(表5),其中西瓜單果質(zhì)量隨EC值的升高而降低,E1和E2水平顯著高于E3和E4水平,且R2水平顯著高于R1水平,E1R2和E2R2處理顯著高于其他處理。EC值和滴灌頻率對西瓜品質(zhì)指標(biāo)的影響均達到極顯著水平,其中西瓜果實可溶性固形物含量、可溶性總糖含量及糖酸比均隨著EC值的升高而增加,且R1水平顯著高于R2水平,而果實有機酸含量則表現(xiàn)出相反趨勢。從不同處理組合對西瓜品質(zhì)的影響來看,以E4R1處理的果實可溶性固形物、可溶性總糖含量及糖酸比最高。
3 討 論
無土栽培學(xué)中,電導(dǎo)率(electrical conductivity,EC)是營養(yǎng)液管理中最重要的參數(shù)之一,EC值的大小反映營養(yǎng)液中鹽類化合物的含量高低,也直接決定養(yǎng)分供應(yīng)量的多少[18]。本研究結(jié)果表明,營養(yǎng)液EC值對西瓜營養(yǎng)生長和果實產(chǎn)量、品質(zhì)形成的影響不盡相同。在西瓜營養(yǎng)生長階段,除苗期株高、徑粗隨營養(yǎng)液EC值的升高表現(xiàn)出降低的趨勢外,其他植株、根系生長指標(biāo)均隨著營養(yǎng)液EC值的升高表現(xiàn)出先增加后降低的變化趨勢,且整體表現(xiàn)為在EC值0.25 mS·cm-1時最高。前人在生菜[14]、蕹菜[15]、黃瓜[19]和網(wǎng)紋甜瓜[20]上的研究也表明,營養(yǎng)液EC值過高或過低均不利于植株的生長發(fā)育。其原因可能有以下三方面:首先,根系是最易受到逆境脅迫的器官,根際可溶性鹽含量過高會造成離子脅迫和滲透脅迫,阻礙根系吸收運輸水分及養(yǎng)分[21-23],過低則滿足不了植物生長需要。在較高的營養(yǎng)液環(huán)境下,番茄的根系活力[24]、西瓜根系形態(tài)指標(biāo)[25]均會受到顯著抑制。其次,高濃度營養(yǎng)液可以改變植株內(nèi)源激素的動態(tài)平衡,通過影響細胞壁的可塑性和細胞微管排列方向,從而調(diào)控細胞生長[26]。高曉旭等[27]的研究表明在栽培基質(zhì)電導(dǎo)率EC值為8.08 dS·cm-1營養(yǎng)液處理下黃瓜和番茄幼苗下胚軸皮層薄壁細胞較對照分別縮短49%和48%。另外,營養(yǎng)液濃度過高會導(dǎo)致植株光合能力減弱。高博文等[21]的研究發(fā)現(xiàn)隨著鹽濃度的增加,所有品種的西瓜幼苗凈光合速率呈持續(xù)降低的趨勢。林多等[20]的研究表明,過高或過低濃度的營養(yǎng)液對網(wǎng)紋甜瓜葉片凈光合速率的影響主要是由與葉肉細胞光合活性下降有關(guān)的非氣孔限制因素造成的。在西瓜果實生長發(fā)育階段,西瓜單果質(zhì)量隨營養(yǎng)液EC值增加表現(xiàn)出降低的趨勢,而可溶性固形物含量、總糖含量及糖酸比等品質(zhì)指標(biāo)則相反。王中原等[28]的研究也表明,網(wǎng)紋甜瓜在EC值2.0 mS·cm-1時平均單果質(zhì)量最大,但可溶性固形物和總糖含量最低,EC值3.0 mS·cm-1時,單果質(zhì)量較小,但果實總糖含量最高。同樣的研究結(jié)果也表現(xiàn)在番茄上[29-32]。營養(yǎng)液EC值升高導(dǎo)致單果質(zhì)量降低的主要原因可能是鹽脅迫下,植株生長減緩、碳同化量減少,滲透調(diào)節(jié)能耗和維持生長能耗增加,生物量分配格局發(fā)生改變[33]。而果實可溶性糖含量增加的主要原因可能是鹽脅迫后,光合運轉(zhuǎn)糖-蔗糖在果實內(nèi)的快速分解,提高了蔗糖向果實內(nèi)的運輸,從而增加了果實的可溶性糖含量[34]。果實可溶性糖是植株適應(yīng)高鹽環(huán)境的產(chǎn)物之一,其含量的增加有利于保持植株的吸水能力[35]。
灌溉頻率是科學(xué)合理灌溉的重要內(nèi)容之一,灌溉頻率能夠影響作物地下及地上的生長環(huán)境,尤其對作物地下生長環(huán)境的影響更為明顯,作物在不同的生長發(fā)育期,由于根系吸水能力以及在介質(zhì)中的分布不同,對灌溉頻率也有不同的響應(yīng)。水分敏感指數(shù)表明,西瓜苗期和果實成熟期的水分敏感程度較低,開花坐果期和果實膨大期的水分敏感程度較高[36]。本研究結(jié)果表明,西瓜團棵期,2次·d-1的灌溉頻率有利于壯苗;伸蔓期至膨果期,4次·d-1的灌溉頻率有利于促進植株營養(yǎng)生長和提高單果質(zhì)量,而2次·d-1的灌溉頻率則顯著提高了果實品質(zhì)。這主要是由于西瓜苗期外界氣溫較低、地上部分生長緩慢,蒸發(fā)蒸騰量較少,另外,苗期根系生長迅速,適度虧水能夠刺激根系生長,有利于開花坐果期復(fù)水后植株的加速生長[37]。從團棵期至膨果期,外界氣溫持續(xù)上升,地上部莖葉和果實開始旺盛生長,蒸發(fā)蒸騰量增加,逐步健全的根系群需吸收大量水分和養(yǎng)分供給地上部生長發(fā)育。研究表明,灌水量相同條件下,增加灌水頻率,可以增加土壤蓄水、減少滲漏和蒸發(fā)[38],既保證了根際的水分充分供應(yīng),又降低了養(yǎng)分濃度,擴大了根接觸面,促進了根系對水分和養(yǎng)分的吸收利用[10]。果實成熟期,由于植株的營養(yǎng)生長和生殖生長都進入末期,植株的需水量較果實膨大期有所降低。研究表明,在果實成熟期采用中低水量有利于獲得理想的植株葉片光和色素含量[37],低頻率灌溉有利于改善果實的品質(zhì)和口感[39-42]。
合理營養(yǎng)液灌溉管理是無土栽培作物高產(chǎn)優(yōu)質(zhì)的基礎(chǔ),不同營養(yǎng)液EC值與灌溉頻率的處理通過對基質(zhì)條EC值、含水量以及含氧量等根際生長環(huán)境因素的影響,進而影響植株的生長發(fā)育以及果實產(chǎn)量和品質(zhì)[10,43]。本研究結(jié)果表明,營養(yǎng)液EC值與滴灌頻率的交互作用對西瓜地上、地下部生物量的影響均達到顯著水平,表明營養(yǎng)液EC值與灌溉頻率是相互作用的,EC值通過影響根系活性從而調(diào)控作物對水分的吸收運輸[23],而灌溉頻率則可以通過調(diào)控基質(zhì)中的含水量和EC值水平,從而調(diào)節(jié)植株的生長發(fā)育[44]。作物全生育期單一的營養(yǎng)液管理模式難以同時保證產(chǎn)量最高和品質(zhì)最佳,如本研究中,E1R2組合處理的單果質(zhì)量最高,而E4R1組合處理的果實含糖量及糖酸比最高,這與Magán等[45]的研究結(jié)果一致。因此,為改善品質(zhì)、提高產(chǎn)量,基質(zhì)栽培應(yīng)根據(jù)作物不同生育時期生長情況合理調(diào)整營養(yǎng)液灌溉方式,進行分段管理,以滿足實際生產(chǎn)需求。
4 結(jié) 論
兼顧西瓜植株發(fā)育和果實品質(zhì)的營養(yǎng)液分段管理方式為:團棵期營養(yǎng)液以EC值0.25 mS·cm-1,灌溉頻率2次·d-1為宜;伸蔓期營養(yǎng)液以EC值0.25 mS·cm-1,灌溉頻率4次·d-1為宜;果實膨大期營養(yǎng)液以EC值0.15~0.25 mS·cm-1,灌溉頻率4次·d-1為宜;成熟期營養(yǎng)液以EC值0.45 mS·cm-1,灌溉頻率2次·d-1為宜。
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