Effect of Electrical Conductivity [ EC ] of the Nutrient Solution on Nutrient Uptake , Growth and Yield of Leaf Lettuce ( Lactuca sativa L . ) in Stationary Culture
Effect of Electrical Conductivity [ EC ] of the Nutrient Solution on Nutrient Uptake , Growth and Yield of Leaf Lettuce ( Lactuca sativa L . ) in Stationary Culture
复制标题
固定培养中营养液电导率[EC]对叶用生菜(Lactuca sativa L.)养分吸收、生长和产量的影响
DOI：
--
复制
发表时间：
2006
期刊：
影响因子：
--
通讯作者：
W. Weerakkody
中科院分区：
文献类型：
--
作者：
U. Samarakoon;P. Weerasinghe;W. Weerakkody
本研究在斯里兰卡高温（38.5℃）温室条件下，通过优化固定栽培的电导率（EC），以节约水培莴苣生产。四株植物在50 L槽中生长，其中较低的剂量（0.5和1 g/ L）与艾伯特溶液的标准剂量（2 g/ L）进行比较。0.5、1.0和2.0 g/l处理的EC分别为1.4、2.0、3.0 dS/m。每天调整溶液的pH值，并在两周后（早期营养生长结束时）更换新溶液，并在移栽后4周收获植株。随着营养液EC的增加，植株鲜重和干重均显著降低。1.4 dS/m的叶片形成（叶数）高于2.0和3.0 dS/m，导致鲜重和干重增加。茎高、叶面积等其他形态特征也呈现出相同的变化趋势，但差异无统计学意义。相反，氮、磷、钾和钙的吸收随EC的增加而显著增加。2.0和3.0 dS/m之间的差异最为显著。除磷外，其余3种离子的吸收率在营养后期（最后2周）均较高或相当。其余溶液中所有四种营养物质的高浓度表明，即使在营养早期和晚期结束时最低EC下，营养物质的可利用性也很高。植物生长和产量与养分吸收速率呈负相关关系，可能是由于植物养分的过量吸收对生长生理产生了毒性、不平衡或防御反应等负面影响。在斯里兰卡干旱地区热带温室中，选用1.4 dS/m （0.5 g/l）的Albert’s溶液，两周后完全更换，可作为炎热气候条件下种植叶莴苣（Lactuca sativa l .）的最佳营养浓度。叶莴苣（lacuca sativa L.）主要种植在斯里兰卡北部的露天田地和温室条件下。简单的水培技术如固定式栽培（槽式栽培）在叶菜种植上是成功的。生菜的最佳品质是在短时间内种植到收获成熟期。充足的施肥、稳定的供水和凉爽的温度保证了这一点（Anon, 1999）。1 Peradeniya大学农业学院作物科学系，斯里兰卡Peradeniya；目前在斯里兰卡，营养液用于水培，没有确定单个物种的最佳营养需求或环境条件。因此，确定养分需要量以避免因过度施肥而可能产生的毒性，并监测炎热气候条件下的生长和产量是很重要的。在Maha季节（平均白天温度），在标准肥料用量为35℃的聚隧道中，生菜在水培下成功种植（Samarakoon et al., 2006）。电导率（EC）使用电导率计测量是营养液强度的间接指示。水培的理想电导率范围在1.5至2.5 dS/m之间，由于渗透压的增加，较高的电导率会阻碍养分吸收，而较低的电导率可能严重影响植物的健康和产量（Anon, 2002）。本研究的目的是研究最佳EC作为水培溶液中养分浓度的指标对生菜生长的影响，并研究斯里兰卡干旱地区Yala季节（炎热条件）温室条件下种植生菜的可行性。材料和方法莴苣在半遮荫条件下种植在斯里兰卡干旱地区的一个10‘x 15’的多聚隧道中（斯里兰卡拉贾拉塔大学农学院）。温室（多通道）白天中午的平均气温约为38.5摄氏度。采用海绵苗圃技术对泰国品种大快莴苣种子进行发芽（Anon, 2002）。它们在播种3周后被转移到固定（槽）培养系统（板1），这是一种非循环和低成本的水培技术。科伦坡化学工业有限公司（CIC）的艾伯特溶液被用作肥料的主要来源。三种浓度的阿尔伯特溶液；0.5 g/l （T1）、1 g/l （T2）和2 g/l (T3)（表1），EC分别为1.4、2.0和3.0 dS/m，在替换两周后进行测试。在营养早期（转移后2周）和营养后期（转移后4周）末，通过在槽内添加0.1M NH4OH和0.1M磷酸溶液，调节pH值维持在5.56.5之间。根据van Ranst等人（1998）在Peradeniya大学农业学院作物科学实验室指定的程序对NH4-N、NO3-N、P、K和Ca进行了分析。同样，也对上述浓度的Albert’s溶液的水和新鲜溶液进行了植物营养成分分析。利用营养液中营养物的初始浓度和终浓度以及植物的蒸散量，分别计算营养早期和营养晚期植物每天的养分吸收率。养分的初始浓度是根据肥料样品中个别元素的CIC实验室分析报告和实验室新鲜营养液的分析结果计算的。通过添加酸和碱来调节pH值和水中存在的营养量。每个处理4个重复，每槽4株为一个小区。试验3采用完全随机区组设计（CRBD），以推荐剂量（2 g/l）阿尔伯特氏液为对照，以水培莴苣营养管理为对照。
This study was conducted to economize the hydroponics lettuce production by optimizing the Electrical Conductivity (EC) in stationary culture under hot (38.5C) greenhouse conditions in Sri Lanka. Four plants were grown in 50 L troughs, where lower dosages (0.5 and 1 g/l) were compared with the standard dosage (2 g/l) of Albert’s solution. The EC of the 0.5, 1.0 and 2.0 g/l treatments were 1.4, 2.0, 3.0 dS/m, respectively. The solutions were adjusted for pH daily and replaced with new solutions after two weeks (at the end of early vegetative growth) and plants were harvested at 4 weeks after transplanting. With increasing EC of the nutrient solution, both fresh and dry weights of plants decreased significantly. Higher leaf formation (leaf number) in 1.4 dS/m than 2.0 and 3.0 dS/m lead to increased fresh and dry weights. Other morphological features such as stem height and leaf area also appeared to be in the same trend, but were not statistically significant. In contrast, uptake of N, P, K and Ca significantly increased with increasing EC. The difference between 2.0 and 3.0 dS/m were the most dominant. Except P, uptake rates of other three ions were higher or equal in the late vegetative phase (last 2 weeks). High concentrations of all four nutrients in the remaining solutions indicated the nutrient availability even under the lowest EC at the end of both early and late vegetative stages. The inverse relationship of plant growth and yield with nutrient uptake rates could be due to negative impacts of excessive uptake of plant nutrients, on the growth physiology in the forms of toxicities, imbalances or defensive responses. Albert’s solution at EC of 1.4 dS/m (0.5 g/l) with complete replacement after two weeks could be selected as the best nutrient concentration to be used for growing leaf lettuce (Lactuca sativa L.) under hot weather conditions in tropical green houses of dry zone in Sri Lanka. INTRODUCTION Leaf lettuce (Lactuca sativa L.) is cultivated mainly in up country of Sri Lanka in open fields as well as under greenhouse conditions. It has been found that simple hydroponics techniques such as the stationary culture (trough culture) is successful in growing leafy vegetables. The best quality lettuce is obtained when it is grown to the harvesting maturity in a short period. This is assured by adequate fertilizing, steady supply of water and cool temperature (Anon, 1999). 1 Department of Crop Science, Faculty of Agriculture, University of Peradeniya, Peradeniya, Sri Lanka. Samarakoon, Weerasinghe & Weerakkody At present in Sri Lanka, nutrient solutions are used in hydroponics without determining the optimal nutrient requirement or environmental conditions for individual species. Thus, it is important to determine the nutrient requirements to avoid probable toxicities due to over fertilization and also to monitor the growth and the productivity under hot climatic conditions. Lettuce has shown to be cultivated successfully under hydroponics in the Maha season (average day time temperature) in poly tunnel is 35C with standard dosage of fertilizers (Samarakoon et al., 2006). The electrical conductivity (EC) measured using the EC meter is an indirect indication of the strength of nutrient solution. The ideal EC range for hydroponics is between 1.5 to 2.5 dS/m and higher EC hinders nutrient absorption due to increase in osmotic pressure whereas lower EC may severely affects plant health and yield (Anon, 2002). The objective of this study was to investigate the effect of optimum EC as an indicator for nutrient concentration in the hydroponics solution on the growth of lettuce and to examine the feasibility of growing lettuce under greenhouse conditions in the Yala season (hot condition) of the dry zone in Sri Lanka. METERIALS AND METHODS Lettuce was cultivated under semi-shade conditions in a 10'x 15' poly tunnel located in the dry zone of Sri Lanka (Faculty of Agriculture, Rajarata University of Sri Lanka). Average daytime temperature inside the greenhouse (poly-tunnel) at noon was around 38.5C. Lettuce seeds of variety Grand Rapid of Thailand origin were germinated using sponge nursery technique (Anon, 2002). They were transferred 3 weeks after seeding to a stationary (trough) culture system (Plate 1) which is a non-circulating and low cost hydroponic technique. Albert’s solution of the Chemical Industries Colombo Ltd. (CIC) was used as the main source of fertilizer. Three concentrations of Albert’s solution; 0.5 g/l (T1), 1 g/l (T2) and 2 g/l (T3) (Table 1) with an EC of 1.4, 2.0 and 3.0 dS/m, respectively, were tested at two week replacements. The pH was adjusted to be maintained between 5.56.5 during the period by adding, 0.1M NH4OH and 0.1M phosphoric acid solutions in the troughs at the end of the early vegetative phase (2 week after transferring) and late vegetative phase (4 week after transferring). Analyses for NH4-N, NO3-N, P, K and Ca were carried out according to procedures specified by van Ranst et al. (1998) at the Crop Science Laboratory, Faculty of Agriculture, University of Peradeniya. Similarly, water and fresh solutions of Albert’s solution of above concentrations were also analyzed for plant nutrients. Nutrient uptake rate of plants per day was calculated for early vegetative phase and late vegetative phase separately using initial and final concentrations of nutrients in the solutions and the evapotranspiration. Initial concentration of nutrients was calculated by using the CIC laboratory analysis report of individual elements present in the fertilizer samples and using the results of analysis of fresh solutions for nutrients at the laboratory. Relative adjustments were done by addition of acids and bases for pH and nutrient quantities present in water. Each treatment comprises of 4 replicates and 4 plants per trough were considered as a plot. The treatment 3, having the recommended dosage of Albert's solution, (2 g/l) was Nutrient Management of Hydroponics Lettuce used as the control and the experiment was conducted as a complete randomized block design (CRBD).