Paper presented at the 52nd CFCS Annual Meeting, Guadeloupe, July 10-16, 2016
FERTIGATING LETTUCE (LACTUCA SATIVA L.) USING COMPOST TEA Gaius Eudoxie, Marshagaye Beckford, Kris Grogan and Micah Martin Department of Food Production, University of the West Indies, St. Augustine, Trinidad and Tobago Keywords: Compost Tea, Lettuce, Application Rate, Root Architecture, Nutrient Partitioning
Abstract Crop nutrient management is a critical component of productivity and quality. Commercial horticulture has relied almost exclusively on inorganic nutrient sources to satisfy plant nutritional requirements. Compost tea represents a sustainable alternative technology but its use has not been extensively researched. A factorial experiment was conducted subjecting lettuce plants to four increasing concentrations of compost tea; 0, 5, 10 and 20 % (m/v) applied at either 100 or 200 cm3 plant-1 day-1, for 30 days. At the end of the trial, measurements were made of leaf area (LA), yield, shoot and root dry mass (DM), root to shoot ratio, and nitrogen (N) and phosphorus (P) contents of shoots and roots. Compost tea concentration significantly (P < 0.05) affected all growth indices showing a similar pattern. Increasing concentration up to 10 % (m/v), positively improved growth and yield above the control. Increasing further to 20 % (m/v) reduced LA, yield and dry mass. For these variables, applying compost tea at 200 cm3 plant-1 day-1 resulted in a better response. Increasing concentration of compost tea showed a directly proportional relationship to shoot and root N content. However, the effect was nonsignificant for P. Yield and shoot DM were affected by the combination of compost tea concentration and application rate. Similar patterns of increasing yield were seen for increasing concentration within both rates however, the differences were significant for all concentrations at the higher application rate. Application of 200 cm3, 5 % compost tea resulted in the greatest yield, shoot and root DM. In addition to root DM, root surface area was significantly correlated with yield and shoot DM. Compost tea used at appropriate concentrations improved root growth and lettuce productivity. Materials and methods Repeated trials were conducted in an open ventilated greenhouse located at the UWI St. Augustine campus, Trinidad and Tobago (10.644276 °N, -61.401714 °W) over two months. Mean maximum and minimum temperature were 33 and 24 °C respectively, at a corresponding relative humidity of 65 and 95 %. Lettuce was grown in Promix (Sunshine Professional Growing Mix #15/LC15®, Sun Gro Horticulture, British Columbia, Canada) and fertigated with compost tea. Compost tea was made from cattle manure and corn straw composted using a rotary drum in-vessel system for two months. Three concentrations were tested consisting 5, 10 and 20 % m/v, with corresponding compost to water ratios of 1:20, 1:10 and 1:5 respectively. A control treatment was included where water substituted for the compost tea. Aerated extracts were prepared as described by Pant et al. (2009) and used as the only source of nutrients. Selected properties of the compost teas are displayed in Table 1. pH and EC were measured using an Eijkelkamp pH/mV/EC meter (Agriearch Equipment 2G Giesbeck, the Netherlands). NH4+ and NO3- were determined via steam distillation (Bremner, 1996) and P by the ascorbic acid method (Kuo, 1996). Compost teas were applied at 100 or 200 cm3 plant-1 day-1. Compost tea concentration and rate were combined in a factorial design with each treatment replicated five times. Treatments were arranged in a completely randomised layout. Compost teas were applied as a drench treatment to ’Trinity Iceberg’ lettuce using a 0.001 m3 hand held spray can calibrated to deliver 100 cm3 after 20 seconds, using a fine spray nozzle. In addition to the compost teas plants also received 100 cm3 of water daily to minimise water stress. Plants were harvested whole including roots, after four weeks. Prior to harvesting, LA was measured using image analysis (Xiao, 2005). Adhering root media was removed by washing under running water and final rinsing with distilled water. Roots were separated from shoots and fresh weights recorded. Dry weights were determined after oven drying at 65 °C for 48 hrs. Subsequently, lettuce shoots and roots were ground to pass a 0.5 mm sieve using a Wiley mill (Glen Creston Ltd., Middlesex, UK). Milled samples were digested with H2SO4Salicylic acid-H2O2 formulation (Temminghoff and Houba, 2004), followed by N determination using steam distillation (Bremner, 1996) and P determination by the ascorbic acid method (Kuo, 1996). The trial was immediately repeated. At the end of the second growth period plants were harvested and treated in a similar manner to that explained for trial 1. Data were analysed statistically by GLM ANOVA, examining main and interactive factor effects, using Minitab 17 Statistical Software (Minitab Inc. PA, USA). Means of all plant parameters for significant treatment effects were statistically separated using Tukey’s multiple range test. Significance was defined at P<0.05. Data is presented for trial 1 only.
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